Image processing apparatus, printing apparatus, image processing method, and program

Abstract

To properly correct density variations in printed images. [Solution] The image processing apparatus is used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, and has a generation processing unit that generates a first halftone image data for ejecting the first ink whose ejection amount has been corrected using ejection amount correction data for correcting the ejection amount of the first ink, and a second halftone image data for ejecting the second ink whose ejection amount has been corrected using ejection amount correspondence data and ejection amount correction data that show the ejection amount of the second ink relative to the ejection amount of the first ink.

Description

Technical Field

[0001] The present disclosure relates to an image processing apparatus, a printing apparatus, an image processing method, and a program.

Background Art

[0002] An inkjet printing apparatus prints an image on a print medium using ink generated by dissolving a dye or a pigment in a solvent. Hereinafter, the ink generated by dissolving a dye or a pigment in a solvent, that is, the first ink containing a coloring material such as a dye or a pigment, is referred to as a coloring material ink. In recent years, in an inkjet printing apparatus, printing characteristics are improved by using an ink that does not contain a coloring material such as a dye or a pigment and has a specific function. Hereinafter, the second ink that does not contain a coloring material such as a dye or a pigment and has a specific function is referred to as a functional ink.

[0003] Examples of the functional ink include a clear ink that does not contain a coloring material, a primer ink also referred to as a treatment liquid, and the like. For example, by ejecting the clear ink toward a portion where the density of the coloring material ink on the print medium is low, the amount of ink on the print medium is made uniform to reduce gloss unevenness. Also, before or after ejecting the coloring material ink, by ejecting a primer ink that has an effect of fixing the coloring material ink, bleeding of the ink is prevented and deterioration of the image quality is suppressed.

[0004] In order to print an image using such a functional ink, it is necessary to generate image data for the functional ink in addition to the image data for the coloring material ink. For example, Patent Document 1 discloses generating image data for the coloring material ink from CMYK color space image data obtained by converting RGB color space image data, and directly generating image data for the functional ink from the RGB color space image data.

[0005] Incidentally, inkjet printers are equipped with a print head that can eject ink from nozzles. Due to manufacturing errors and other reasons, there may be variations in the amount of ink ejected from multiple nozzles in the print head. When there are variations in the amount of ink ejected from multiple nozzles in the print head, density unevenness may occur in the printed image printed on the printing medium. Head Shading (HS) correction processing is known as a process to reduce density unevenness in printed images. In HS correction processing, the number or size of ink dots ejected onto the printing medium is changed by processing the image data according to the density variation for each nozzle position of the print head. This reduces density unevenness in the printed image. As a method for obtaining density variation for each nozzle position of the print head, for example, a method is used in which patch images (for example, multiple patch images with different tonal values) are printed on the printing medium, and the patch images on the printing medium are read and analyzed using a scanner. Note that the density variation for each nozzle position of the print head indicates the characteristics of density unevenness in the print head. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-310355 [Overview of the project] [Problems that the invention aims to solve]

[0007] The density of a printed image on a printing medium is not determined solely by the amount of colorant ink ejected, but is also affected by the amount of functional ink ejected. The influence of the functional ink ejection amount is based on the interaction between the colorant ink and the functional ink on the printing medium. Therefore, in order to properly correct density variations in a printed image, it is necessary to appropriately correct the amount of functional ink ejected in relation to the amount of colorant ink ejected.

[0008] This disclosure aims to appropriately correct density variations in printed images. [Means for solving the problem]

[0009] An image processing apparatus according to one aspect of the present disclosure is an image processing apparatus used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, and includes a generation processing unit that generates a first halftone image data for ejecting the first ink whose ejection amount has been corrected using ejection amount correction data for correcting the ejection amount of the first ink, and a second halftone image data for ejecting the second ink whose ejection amount has been corrected using ejection amount correspondence data indicating the ejection amount of the second ink relative to the ejection amount of the first ink and the ejection amount correction data. [Effects of the Invention]

[0010] According to this disclosure, density variations in printed images can be appropriately corrected. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram showing the hardware configuration of a printing system. [Figure 2] This is a schematic diagram of the image printing unit and the image acquisition unit. [Figure 3] This is a block diagram showing the functional configuration of the image processing unit in the first embodiment. [Figure 4] This is an explanatory diagram showing an example of a discharge volume correction table in the first embodiment. [Figure 5] This is an explanatory diagram showing an example of a discharge volume correspondence table in the first embodiment. [Figure 6] This is an explanatory diagram showing an example of a primer ink correction table. [Figure 7] This is a schematic diagram showing an example of a concentration fluctuation acquisition chart. [Figure 8] This is a flowchart showing the concentration fluctuation correction process in the first embodiment. [Figure 9] This is a block diagram showing the functional configuration of the image processing unit in the second embodiment. [Figure 10]It is an explanatory diagram showing an example of a discharge amount correction table in the second embodiment. [Figure 11] It is an explanatory diagram showing an example of a discharge amount correspondence table in the second embodiment. [Figure 12] It is a flowchart showing the density variation correction process in the second embodiment. [Figure 13] It is a block diagram showing the functional configuration of the image processing unit in the third embodiment. [Figure 14] It is an explanatory diagram showing an example of a discharge amount correspondence table in the third embodiment. [Figure 15] It is a flowchart showing the density variation correction process in the third embodiment. [Figure 16] It is a flowchart showing the image generation process. [Figure 17] It is an explanatory diagram explaining the flow of the image generation process.

Mode for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the matters disclosed, and not all combinations of the features described in the following embodiments are essential for the solution means of the present disclosure. The same reference numerals are used for the same configurations for explanation.

[0013] <<First Embodiment>> <Hardware Configuration of the Printing System> First, a printing system 1 (printing device) including an image processing unit 106 which is an example of an image processing apparatus according to the present embodiment will be described. FIG. 1 is a block diagram showing the hardware configuration of the printing system 1. In the present embodiment, a configuration capable of appropriately correcting density unevenness of a printed image will be described. As shown in FIG. 1, the printing system 1 includes a CPU 100, a RAM 101, a ROM 102, an operation unit 103, a display unit 104, a storage device 105, an image processing unit 106, an image printing unit 107, an image acquisition unit 108, an I / F unit 109, and a bus 110.

[0014] The CPU (Central Processing Unit) 100 controls the overall operation of the printing system 1 using the input data and the computer program stored in RAM 101 or ROM 102. In this embodiment, the CPU 100 controls the entire printing system 1, but this is not the only way. For example, the entire printing system 1 may be controlled by multiple hardware components sharing the processing.

[0015] The RAM (Random Access Memory) 101 has a storage area for temporarily storing computer programs or data read from the storage device 105, data received from the outside via the I / F unit 109, etc. The RAM 101 is also used as a storage area by the CPU 100 when it performs various processes. Furthermore, the RAM 101 is used as a storage area by the image processing unit 106 when it performs image processing.

[0016] The ROM (Read Only Memory) 102 has a storage area for storing setting parameters for each part of the printing system 1, a boot program, and the like.

[0017] The control unit 103 is an input device such as a keyboard or mouse, and accepts operations (instructions) from the operator. By operating the control unit 103, the operator can input various instructions to the CPU 100.

[0018] The display unit 104 is a display device such as a CRT (Cathode Ray Tube) display or a liquid crystal display. The display unit 104 can display the processing results of the CPU 100 as images, characters, etc. If the display unit 104 is a touch panel capable of detecting touch operations, the display unit 104 may function as part of the operation unit 103.

[0019] The storage device 105 is a large-capacity information storage device, such as a hard disk drive. The storage device 105 stores computer programs and data that allow the OS (operating system) or CPU 100 to execute various processes. The storage device 105 also holds image data used for processing each part. Examples of image data used for processing each part include multi-level image data for acquiring characteristics of each nozzle position, and image data for each nozzle for detecting the position of non-discharging nozzles. The computer programs and data stored in the storage device 105 are read as appropriate according to the control of the CPU 100 and stored in the RAM 101, and are then processed by the CPU 100.

[0020] The image processing unit 106 is implemented as a processor capable of executing computer programs or as a dedicated image processing circuit. The image processing unit 106 performs various image processing operations to convert the image data input as the target for printing into image data that can be output by the image printing unit 107, which will be described later. Alternatively, instead of providing a dedicated processor for the image processing unit 106, the CPU 100 may be configured to perform various image processing operations as the image processing unit 106.

[0021] The image printing unit 107 prints an image by ejecting ink onto a printing medium based on image data received directly from the image processing unit 106, or image data received from the image processing unit 106 via the RAM 101 or storage device 105. The printing medium can be any medium on which an image can be printed by depositing ink droplets. Examples of printing mediums include printing paper, label paper, and envelope paper.

[0022] The image acquisition unit 108 includes an image sensor (line sensor or area sensor) that captures a printed image on a printing medium printed by the image printing unit 107. The image acquisition unit 108 can acquire density unevenness characteristics as density fluctuations for each nozzle position of the print head from the printed image captured by the image sensor. As the image sensor constituting the image acquisition unit 108, an in-line scanner mounted on an inkjet printing device, an offline scanner of an external device, etc., may be used.

[0023] The I / F (interface) unit 109 functions as an interface for connecting the printing system 1 with external devices. The I / F unit 109 also functions as an interface for exchanging data with communication devices using infrared communication, wireless LAN (Local Area Network), etc. The I / F unit 109 also functions as an interface for connecting to the internet. This allows the I / F unit 109 to exchange data with external devices, such as input images.

[0024] The CPU 100, RAM 101, ROM 102, operation unit 103, display unit 104, storage device 105, image processing unit 106, image printing unit 107, image acquisition unit 108, and I / F unit 109 are all connected to the bus 110. The CPU 100, RAM 101, ROM 102, operation unit 103, display unit 104, storage device 105, image processing unit 106, image printing unit 107, image acquisition unit 108, and I / F unit 109 can exchange data via the bus 110. In addition, some of the parts of the printing system 1 described above, such as the image printing unit 107 and the image acquisition unit 108, may be connected via the I / F unit 109.

[0025] <Hardware configuration of the image printing unit and image acquisition unit> Next, the image printing unit 107 and the image acquisition unit 108 will be described. Figure 2 is a schematic diagram of the image printing unit 107 and the image acquisition unit 108. The image printing unit 107 is an inkjet printing unit that forms an image by ejecting ink from the nozzles of the print head onto the printing medium. In Figure 2, the Z direction represents the vertical direction and intersects (orthogonal in this embodiment) with the XY plane defined by the X and Y directions. In this embodiment, the width direction of the printing medium MD is the X direction, and the transport direction of the printing medium MD is the Y direction.

[0026] As shown in Figure 2, the image printing unit 107 includes first to fourth print heads 201 to 204 corresponding to the first colorant ink, and a fifth print head 205 corresponding to the second primer ink. As mentioned above, the colorant ink is an ink containing a colorant such as a dye or pigment. The primer ink is a functional ink that does not contain a colorant and has the effect of fixing the colorant ink well. The first to fourth print heads 201 to 204 corresponding to four inks, black (K), cyan (C), magenta (M), and yellow (Y), are arranged downstream of the fifth print head 205 in the transport direction (+Y direction). The first to fifth print heads 201 to 205 are so-called full-line type print heads in which a plurality of nozzles (not shown) for ejecting ink are arranged along a predetermined direction in a range corresponding to the width of the printing medium MD. The first print head 201 ejects black ink (K ink) toward the printing medium MD. The second print head 202 ejects cyan ink (C ink) towards the print medium MD. The third print head 203 ejects magenta ink (M ink) towards the print medium MD. The fourth print head 204 ejects yellow ink (Y ink) towards the print medium MD. The fifth print head 205 ejects primer ink (P ink) towards the print medium MD.

[0027] The print medium MD is transported in the transport direction (+Y direction) indicated by arrow 208 in Figure 2 by the rotation of transport rollers 206 (and other rollers not shown) driven by a motor (not shown). Ink is ejected from multiple nozzles (not shown) of the first to fifth print heads 201 to 205 onto the transported print medium MD according to the print data, thereby printing one raster image corresponding to the nozzle row of each print head. By repeating the ejection operation of each print head onto the transported print medium MD, for example, one page of image is printed on the print medium MD.

[0028] The image acquisition unit 108 is positioned downstream (towards the +Y direction) of the transport direction from the first to fifth print heads 201 to 205. After an image is formed by the first to fifth print heads 201 to 205, the print medium MD is transported to the image acquisition unit 108 by transport rollers 206, etc. The image acquisition unit 108 sequentially captures the printed image on the print medium MD transported by the transport rollers 206, etc., and acquires it as two-dimensional RGB image data. The image acquisition unit 108 stores the acquired RGB image data in the storage device 105. At this time, the resolution of the image acquired by the image acquisition unit 108 is 1200 dpi. However, the resolution is not limited to this and can be arbitrary, and may differ between the X direction and the Y direction. For example, the resolution in the X direction may be 1200 dpi and the resolution in the Y direction may be 600 dpi.

[0029] <Functional Configuration of Image Processing Unit> Next, the image processing unit 106 in the first embodiment will be described. Figure 3 is a block diagram showing the functional configuration of the image processing unit 106 in the first embodiment. As shown in Figure 3, the image processing unit 106 includes a color conversion processing unit 301, a correction processing unit 302, a data holding unit 305, and a halftone processing unit 306.

[0030] The color conversion processing unit 301 converts the input image data received via the I / F unit 109 into image data with a color gamut that can be reproduced by the image printing unit 107. The input image data is data representing color coordinates (R, G, B) in a color space such as sRGB, which is the color gamut that can be represented by the display unit 104 (display). The color conversion processing unit 301 converts the 8-bit input image data representing the color coordinates (R, G, B) of the color gamut that can be represented by the display unit 104 into RGB signal image data representing the color coordinates (R', G', B') of the color gamut that can be reproduced by the image printing unit 107. The conversion of the input image data by the color conversion processing unit 301 is performed using known methods such as matrix arithmetic processing and processing using a 3D lookup table.

[0031] Furthermore, the color conversion processing unit 301 performs color conversion processing on the converted RGB signal image data. When performing color conversion processing, the color conversion processing unit 301 converts the RGB signal image data into image data of color signals corresponding to the inks used in the image printing unit 107. In this embodiment, the inks used in the image printing unit 107 are black ink (K ink), cyan ink (C ink), magenta ink (M ink), yellow ink (Y ink), and primer ink (P ink). In this case, the RGB signal image data is converted into image data (C_img, M_img, Y_img, K_img, P_img) consisting of 8-bit color signals (CMYKP signals) for each of C, M, Y, K, and P. The color conversion processing by the color conversion processing unit 301 is performed using a combination of processing with a 3D lookup table and interpolation processing.

[0032] The color conversion processing by the color conversion processing unit 301 may be performed using known methods such as matrix operations. The color conversion processing unit 301 may convert the RGB signal image data to CMYK signal image data (C_img, M_img, Y_img, K_img), and then generate image data corresponding to the primer ink (P_img) based on the CMYK signal image data. The image data generated by the color conversion processing may be temporarily stored in a memory (not shown) so that the same image data can be printed on multiple printing media. In addition, the CMYKP signal image data, the CMYK signal image data, and the image data corresponding to the primer ink are bitmap data.

[0033] The correction processing unit 302 refers to the ejection amount correction table 303 held in the data holding unit 305 and performs density variation correction processing on the CMYK signal image data (C_img, M_img, Y_img, K_img) of the CMYKP signal image data. Density variation correction processing is a process that corrects density variations for each nozzle position of each print head in order to correct density unevenness that occurs in the image on the printing medium due to the printing characteristics of the first to fourth print heads 201 to 204. The ejection amount correction table is also called a density variation correction table. The data holding unit 305 holds four types of ejection amount correction tables corresponding to each color: black (K), cyan (C), magenta (M), and yellow (Y). The correction processing unit 302 refers to the ejection amount correction table and performs density variation correction processing for each image data corresponding to each color to obtain CMYK signal image data (C_img', M_img', Y_img', K_img') that has been corrected for density variations due to the characteristics of each print head.

[0034] Figure 4 is an explanatory diagram showing an example of an ejection rate correction table in the first embodiment. In the example shown in Figure 4, the leftmost column of the ejection rate correction table shows the input signal value. The input signal value in the ejection rate correction table is an 8-bit signal value corresponding to any one of the signal values ​​of the CMYK signal image data. The rightmost column of the ejection rate correction table shows the correction value for each nozzle number relative to the input signal value. The nozzle number is the number associated with each nozzle of the print head corresponding to the colorant ink.

[0035] As shown in Figure 4, the ejection volume correction table is a table that stores correction values ​​for each nozzle number relative to the input signal value. The correction processing unit 302 corrects the signal values ​​of each color in the CMYK signal image data by referring to the input signal value and nozzle number corresponding to the signal value of each color in the CMYK signal image data and obtains a correction value. For example, in the example shown in Figure 4, if the input signal value is 16 and the nozzle number is 0, the correction value obtained by referring to the ejection volume correction table will be 28. Note that the larger the signal value of the image data, the larger the ink ejection volume. As a result, a correction value is obtained that is corrected so that the ejection volume is larger (the density is higher) compared to the input signal value before correction. Furthermore, the ejection volume correction table for correcting the ejection volume of the colorant ink (first ink) is ejection volume correction data that shows the correction value for the signal value of the CMYK signal image data corresponding to the colorant ink.

[0036] Furthermore, the correction processing unit 302 performs linear interpolation when referring to the discharge volume correction table. For example, in the example shown in Figure 4, when the input signal value is 8 and the nozzle number is 0, linear interpolation is performed based on the correction value (0) for when the input signal value is 0 and the nozzle number is 0, and the correction value (28) for when the input signal value is 16 and the nozzle number is 0. As a result, when the input signal value is 8 and the nozzle number is 0, the correction value obtained by referring to the discharge volume correction table becomes 14.

[0037] Furthermore, the correction processing unit 302 refers to the ejection amount correction table 303 held in the data holding unit 305 and the ejection amount correspondence table 304 pre-stored in the storage device 105 to generate a correction table for the primer ink. The ejection amount correspondence table is used to generate image data (P_img) corresponding to the primer ink based on the image data of the CMYK signal.

[0038] Figure 5 is an explanatory diagram showing an example of a discharge volume correspondence table in the first embodiment. Figure 5(a) is a table showing an example of a discharge volume correspondence table in the first embodiment. In the example shown in Figure 5(a), the left column of the discharge volume correspondence table shows the input signal value. The input signal value of the discharge volume correspondence table is an 8-bit signal value corresponding to the discharge volume of the colorant ink. The right column of the discharge volume correspondence table shows the output signal value. The output signal value of the discharge volume correspondence table is an 8-bit signal value corresponding to the discharge volume of the primer ink. Figure 5(b) is a graph corresponding to the discharge volume correspondence table in Figure 5(a). The graph shown in Figure 5(b) is a graph of the discharge volume correspondence table in Figure 5(a). The horizontal axis of the graph shown in Figure 5(b) shows the input signal value of the discharge volume correspondence table. The vertical axis of the graph shown in Figure 5(b) shows the output signal value of the discharge volume correspondence table. As shown in Figure 5(a), the ejection volume correspondence table is a table that maintains the relationship between the signal value corresponding to the ejection volume of the colorant ink and the signal value corresponding to the ejection volume of the primer ink. The ejection volume correspondence table is also ejection volume correspondence data that shows the signal value corresponding to the ejection volume of the primer ink (second ink) in relation to the signal value corresponding to the ejection volume of the colorant ink (first ink).

[0039] The correction processing unit 302 generates an average value correction table by averaging four types of ejection rate correction tables corresponding to each color: black (K), cyan (C), magenta (M), and yellow (Y). The correction processing unit 302 generates a primer ink correction table by referencing the ejection rate correspondence table and using the signal values ​​of the generated average value correction table as input signal values. The input signal values ​​for the primer ink correction table are obtained by referencing the output signal values ​​of the ejection rate correspondence table and using the input signal values ​​of the average value correction table as input signal values. The correction values ​​for the primer ink correction table are obtained by referencing the output signal values ​​of the ejection rate correspondence table and using the correction values ​​of the average value correction table as input signal values.

[0040] Furthermore, when generating the average value correction table, the correction processing unit 302 may perform a weighted average according to the visibility of density unevenness for each color: black (K), cyan (C), magenta (M), and yellow (Y). The correction processing unit 302 may also use only the discharge volume correction table corresponding to black (K), which has relatively high visibility of density unevenness, as the average value correction table.

[0041] Figure 6 is an explanatory diagram showing an example of a primer ink correction table in the first embodiment. Figure 6 shows an example in which the primer ink correction table is generated from the ejection amount correspondence table shown in Figure 5(a), using the ejection amount correction table shown in Figure 4 as the average value correction table. In the example shown in Figure 6, the leftmost column of the primer ink correction table shows the input signal value. The input signal value of the primer ink correction table is an 8-bit signal value corresponding to the signal value of the image data of the color signal corresponding to the primer ink. The rightmost column of the primer ink correction table shows the correction value for each nozzle number relative to the input signal value. The nozzle number is the number associated with each nozzle of the print head corresponding to the primer ink.

[0042] The input signal value for the primer ink correction table is obtained by using the input signal value of the discharge rate correction table (average value correction table) shown in Figure 4 as the input signal value and referring to the output signal value of the discharge rate correspondence table shown in Figure 5(a). The correction value for each nozzle number in the primer ink correction table is obtained by using the correction value for each nozzle number in the discharge rate correction table (average value correction table) shown in Figure 4 as the input signal value and referring to the output signal value of the discharge rate correspondence table shown in Figure 5(a). Note that 255 is added to the input signal value of the primer ink correction table as the maximum value of the input signal value. The correction value corresponding to the maximum value of the input signal value is the same value as the correction value corresponding to the second largest input signal value (100). This is because extrapolation is used to avoid the correction value being determined when referring to the primer ink correction table.

[0043] By referring to the primer ink correction table, corrected image data (P_img') corresponding to the primer ink is obtained from the CMYK signal image data, correcting for density fluctuations due to the characteristics of the print head corresponding to the colorant ink. The corrected image data (P_img') corresponding to the primer ink corresponds to image data in which the amount of primer ink ejected has been corrected compared to the image data (P_img) corresponding to the primer ink generated by the color conversion processing unit 301.

[0044] Returning to Figure 3, the halftone processing unit 306 performs halftone processing (quantization processing) on ​​the image data that has undergone density variation correction processing to generate halftone image data. The halftone processing unit 306 converts the image data of each 8-bit CMYKP signal (C_img', M_img', Y_img', K_img', P_img') into halftone image data of each 1-bit CMYKP signal. The halftone image data (C_ht, M_ht, Y_ht, K_ht, P_ht) generated by the halftone processing unit 306 is transmitted to the image printing unit 107. In this embodiment, for example, a known dithering method is used for halftone processing. Note that the halftone processing is not limited to the dithering method; any method such as error diffusion can be used.

[0045] The data storage unit 305 generates an output volume correction table based on the image data of the density fluctuation acquisition chart acquired by the image acquisition unit 108. The data storage unit 305 stores the generated output volume correction table. By updating the output volume correction table as needed, the data storage unit 305 can also respond to changes in density unevenness over time. The data storage unit 305 may also acquire and store an output volume correction table generated by an external processing device.

[0046] Furthermore, when the image printing unit 107 receives halftone image data of the density variation acquisition chart from the halftone processing unit 306, it prints the image of the density variation acquisition chart onto the printing medium by ejecting ink from the first to fifth print heads 201 to 205. The image acquisition unit 108 captures an image of the density variation acquisition chart on the printing medium printed by the image printing unit 107. The image data of the density variation acquisition chart acquired by the image acquisition unit 108 is transmitted to the data holding unit 305.

[0047] Figure 7 is a schematic diagram showing an example of a density variation acquisition chart. As shown in Figure 7, the density variation acquisition chart image is provided with a density acquisition area 350. The density acquisition area 350 is a measurement image for acquiring density variations for each nozzle position of the print head. Nine types of uniform patch images with different gradations are arranged in the density acquisition area 350. The nine types of patch images, in order from highest to lowest gradation, include the first patch image 351, the second patch image 352, the third patch image 353, the fourth patch image 354, and the fifth patch image 355. Furthermore, in addition to the first to fifth patch images 351 to 355, the nine types of patch images also include the sixth patch image 356, the seventh patch image 357, the eighth patch image 358, and the ninth patch image 359, in order from highest to lowest gradation. The first to ninth patch images 351 to 359 are formed on the printing medium so as to extend in the width direction (X direction) of the printing medium. Furthermore, the first to ninth patch images 351 to 359 are arranged on the printing medium so as to be aligned along the transport direction (Y direction) of the printing medium. The image data of the density variation acquisition chart acquired by the image acquisition unit 108 is two-dimensional RGB image data. The image data of the density variation acquisition chart acquired by the image acquisition unit 108 is converted into one-channel scan image data using a pre-prepared color conversion table that matches the color characteristics of the scanner, and stored in the storage device 105. The resolution of the scan image is 1200 dpi, the same as the resolution of the image formed by the ink droplets ejected from each nozzle of the print head.

[0048] The color space of the scanned image data is arbitrary. The color conversion table is a table that converts to a value linear to density, such as Y in the "CIE XYZ color space" or L* in "CIE L*a*b*". When the density acquisition area 350 (measurement image) of the density variation acquisition chart is printed using color inks such as cyan (C), magenta (M), and yellow (Y), the density of the scanned image may be not limited to a value corresponding to brightness, but may also be a value corresponding to saturation. For example, the values ​​of the R channel, G channel, and B channel may be used as values ​​corresponding to the complementary colors of cyan (C), magenta (M), and yellow (Y), respectively. If the resolution of the scanned image differs from the resolution of the image formed by the ink droplets ejected from each nozzle of the print head, the ejection amount correction table can be generated by converting to the same resolution through arbitrary interpolation processing.

[0049] <Concentration fluctuation correction processing> Next, we will describe the density variation correction process as an image processing (image processing method) performed by the image processing unit 106 in the first embodiment. Figure 8 is a flowchart of the density variation correction process in the first embodiment.

[0050] First, in step S101, the color conversion processing unit 301 of the image processing unit 106 performs color conversion processing based on the input image data and obtains CMYKP signal image data. At this time, the color conversion processing unit 301 converts the input image data input via the I / F unit 109 into image data with a color gamut that can be reproduced by the image printing unit 107. Then, the color conversion processing unit 301 performs color conversion processing on the converted RGB signal image data and obtains CMYKP signal image data.

[0051] Next, in step S102, the correction processing unit 302 acquires the CMYK ink ejection amount correction table 303 held in the data holding unit 305. As mentioned above, the ejection amount correction table 303 is generated and held by the data holding unit 305. Alternatively, the image processing unit 106 may not have a data holding unit 305, and the correction processing unit 302 may acquire the ejection amount correction table generated by an external processing unit.

[0052] Next, in step S103, the correction processing unit 302 obtains the discharge amount correspondence table 304 which has been previously stored in the storage device 105.

[0053] Next, in step S104, the correction processing unit 302 generates a correction table for the primer ink (P ink) from the ejection volume correction table and the ejection volume correspondence table. At this time, the correction processing unit 302 generates an average value correction table by averaging the four types of ejection volume correction tables corresponding to each color: black (K), cyan (C), magenta (M), and yellow (Y). Then, the correction processing unit 302 generates a correction table for the primer ink by referring to the ejection volume correspondence table using the signal values ​​of the generated average value correction table as input signal values.

[0054] Next, in step S105, the correction processing unit 302 corrects the CMYKP signal image data using the acquired CMYK ink ejection amount correction table and the generated primer ink correction table. At this time, the correction processing unit 302 performs density variation correction processing on the CMYK signal image data. The correction processing unit 302 refers to the ejection amount correction table and generates corrected CMYK signal image data that corrects for density variations due to the characteristics of each print head. The correction processing unit 302 also refers to the primer ink correction table and generates image data corresponding to the corrected primer ink that corrects for density variations due to the characteristics of each print head.

[0055] After the density variation correction processing is performed by the correction processing unit 302, in the next step S106, the halftone processing unit 306 performs halftone processing. Here, the image data of the corrected CMYK signal and the image data corresponding to the primer ink are collectively referred to as the image data of the corrected CMYKP signal. At this time, the halftone processing unit 306 performs halftone processing on each 8-bit image data of the corrected CMYKP signal to generate halftone image data of each 1-bit CMYKP signal. The halftone image data generated by the halftone processing unit 306 is transmitted to the image printing unit 107.

[0056] Then, in step S107, the image printing unit 107 prints the input image onto the printing medium based on the halftone image data transmitted from the halftone processing unit 306. At this time, when the image printing unit 107 receives the halftone image data from the halftone processing unit 306, it prints the input image onto the printing medium by ejecting CMYK ink and primer ink from the first to fifth print heads 201 to 205.

[0057] By performing the processing control described above, it is possible to generate CMYK signal image data and image data corresponding to the primer ink, which are appropriately corrected based on the CMYK ink (colorant ink) ejection amount correction table. As a result, the ejection amount of the colorant ink is corrected based on the halftone image data of the CMYK signal after halftone processing, and the ejection amount of the primer ink is corrected based on the halftone image data corresponding to the primer ink after halftone processing. Therefore, the ejection amount of the primer ink can be appropriately corrected according to the ejection amount of the colorant ink corrected based on the colorant ink ejection amount correction table. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image.

[0058] As described above, according to the first embodiment, density unevenness in printed images can be appropriately corrected. That is, in this embodiment, the correction processing unit 302 uses a CMYK ink (colorant ink) ejection amount correction table to generate corrected CMYK signal image data in which the ejection amount of the colorant ink has been corrected. The correction processing unit 302 uses an ejection amount correspondence table and an ejection amount correction table to generate corrected image data corresponding to the primer ink in which the ejection amount of the primer ink has been corrected. The halftone processing unit 306 performs halftone processing on the corrected CMYK signal image data and the image data corresponding to the corrected primer ink to generate halftone image data of the CMYKP signal. Of the halftone image data of the CMYKP signal, the halftone image data of the CMYK signal is the first halftone image data for ejecting colorant ink whose ejection amount has been corrected using the ejection amount correction table. Of the halftone image data of the CMYKP signal, the halftone image data corresponding to the primer ink is the second halftone image data for ejecting primer ink whose ejection amount has been corrected using the ejection amount correspondence table and the ejection amount correction table. The correction processing unit 302 and the halftone processing unit 306 constitute a generation processing unit that generates a first halftone image data and a second halftone image data. As a result, the ejection amount of colorant ink is corrected based on the first halftone image data, and the ejection amount of primer ink is corrected based on the second halftone image data. Therefore, the ejection amount of primer ink can be appropriately corrected according to the ejection amount of colorant ink corrected based on the ejection amount correction table of colorant ink. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image. In this way, density unevenness in the printed image can be appropriately corrected.

[0059] The first embodiment described above illustrates an example of correcting density variations for each nozzle position of the print head, but it is not limited to this. For example, this embodiment can also be applied to target density correction, which corrects the average density variation of the print head. In this case, an ejection volume correction table and a primer ink correction table are used, in which the correction value for the input signal value is the same for each nozzle number.

[0060] In the first embodiment described above, the color conversion processing unit 301 converts RGB signal image data into CMYKP signal image data (C_img, M_img, Y_img, K_img, P_img), but is not limited to this. When converting RGB signal image data, the color conversion processing unit 301 may omit the process of generating image data (P_img) corresponding to the primer ink.

[0061] <<Second Embodiment>> Next, a second embodiment will be described. The individual components in the second embodiment have the same configuration as those in the first embodiment described above, except for the functional configuration of the image processing unit 106. Therefore, they will be described using the same reference numerals as those used in the first embodiment. In the first embodiment, an example of correcting input image data in accordance with density fluctuations due to the characteristics of the print head was described. In the second embodiment, an example of correcting the threshold value of the dither matrix used in the halftone processing unit in accordance with density fluctuations due to the characteristics of the print head will be described. Note that in the second embodiment, the differences from the first embodiment will be the main focus of the description, and similarities will be omitted.

[0062] <Functional Configuration of Image Processing Unit> Figure 9 is a block diagram showing the functional configuration of the image processing unit 106 in the second embodiment. As shown in Figure 9, the image processing unit 106 in the second embodiment includes a color conversion processing unit 401, a correction processing unit 402, a data holding unit 405, and a halftone processing unit 406.

[0063] In the second embodiment, the color conversion processing unit 401 performs a color conversion process to convert input image data received via the I / F unit 109 into image data of color signals corresponding to the colorant inks used in the image printing unit 107. The colorant inks used in the image printing unit 107 are black ink (K ink), cyan ink (C ink), magenta ink (M ink), and yellow ink (Y ink). In this case, the RGB signal image data is converted into image data (C_img, M_img, Y_img, K_img) consisting of 8-bit color signals (CMYK signals) for C, M, Y, and K.

[0064] In the second embodiment, the correction processing unit 402 refers to the ejection amount correction table 403 held in the data holding unit 405 and performs density variation correction processing on the threshold of the reference dither matrix for each color. The reference dither matrix is ​​a matrix with an 8-bit threshold for each 256 × 256 pixel, and has four types of reference dither matrices (C_th, M_th, Y_th, K_th) corresponding to each CMYK color. The resolution of the image corresponding to the reference dither matrix is ​​1200 dpi, the same as the resolution of the image formed by the ink droplets ejected from each nozzle of the print head. The data holding unit 405 holds four types of ejection amount correction tables corresponding to each color: black (K), cyan (C), magenta (M), and yellow (Y). The correction processing unit 402 refers to the ejection amount correction table and performs density variation correction processing for each reference dither matrix of each color to obtain corrected dither matrices (C_th', M_th', Y_th', K_th') that correct for density variations due to the characteristics of each print head.

[0065] Figure 10 is an explanatory diagram showing an example of an ejection rate correction table in the second embodiment. In the example shown in Figure 10, the leftmost column of the ejection rate correction table shows the input threshold. The input threshold of the ejection rate correction table is an 8-bit threshold corresponding to the threshold of the reference dither matrix for each CMYK color. The nozzle number is the number associated with each nozzle of the print head corresponding to the colorant ink.

[0066] As shown in Figure 10, the discharge volume correction table is a table that stores correction values ​​for each nozzle number relative to the input threshold. The correction processing unit 302 corrects the threshold of the reference dither matrix for each CMYK color by referring to the input threshold and nozzle number corresponding to the threshold of the reference dither matrix for each CMYK color and obtains a correction value. For example, in the example shown in Figure 10, if the input threshold is 16 and the nozzle number is 0, the correction value obtained by referring to the discharge volume correction table will be 8. Note that the smaller the dither matrix threshold, the greater the ink discharge volume. As a result, a correction value is obtained that is corrected so that the discharge volume after halftone processing using the dither matrix is ​​greater (the density is higher) compared to the input threshold before correction. The discharge volume correction table is discharge volume correction data that shows the correction value relative to the dither matrix threshold corresponding to the colorant ink (first ink).

[0067] Furthermore, the correction processing unit 402 performs linear interpolation when referring to the discharge volume correction table. For example, in the example shown in Figure 10, when the input threshold is 8 and the nozzle number is 0, linear interpolation is performed based on the correction value (0) for when the input threshold is 0 and the nozzle number is 0, and the correction value (8) for when the input threshold is 16 and the nozzle number is 0. As a result, when the input signal value is 8 and the nozzle number is 0, the correction value obtained by referring to the discharge volume correction table becomes 4. Furthermore, if the width of the reference dither matrix in the X direction is small compared to the number of nozzle numbers in the discharge volume correction table, the reference dither matrix is ​​repeatedly arranged in a tile-like pattern in the X direction so that the threshold column corresponds to all nozzle numbers in the discharge volume correction table.

[0068] Furthermore, the correction processing unit 402 refers to four types of reference dither matrices corresponding to each color and the ejection volume correspondence table 404 pre-stored in the storage device 105 to generate four types of dither matrices corresponding to the primer ink. After generating the four types of dither matrices corresponding to the primer ink, the correction processing unit 402 refers to the ejection volume correction table to generate four types of dither matrices corresponding to the corrected primer ink. This results in four types of dither matrices (Cp_th', Mp_th', Yp_th', Kp_th') corresponding to the corrected primer ink, which has been corrected for density variations due to the characteristics of each print head. For example, Cp_th' corresponds to the dither matrix corresponding to the corrected primer ink, which is obtained from the dither matrix corresponding to the corrected cyan ink.

[0069] Figure 11 is an explanatory diagram showing an example of an ink discharge rate correspondence table in the second embodiment. Figure 11(a) is a table showing an example of an ink discharge rate correspondence table in the second embodiment. In the example shown in Figure 11(a), the left column of the ink discharge rate correspondence table shows the input threshold. The input threshold of the ink discharge rate correspondence table is an 8-bit signal value corresponding to the discharge rate of the primer ink. The right column of the ink discharge rate correspondence table shows the output threshold. The output threshold of the ink discharge rate correspondence table is an 8-bit signal value corresponding to the discharge rate of the colorant ink. Figure 11(b) is a graph corresponding to the ink discharge rate correspondence table in Figure 11(a). The graph shown in Figure 11(b) is a graph of the ink discharge rate correspondence table in Figure 11(a). The horizontal axis of the graph shown in Figure 11(b) shows the input threshold of the ink discharge rate correspondence table. The vertical axis of the graph shown in Figure 11(b) shows the output threshold of the ink discharge rate correspondence table. As shown in Figure 11(a), the discharge volume correspondence table in the second embodiment is a table that maintains the relationship between the signal value corresponding to the discharge volume of the primer ink and the signal value corresponding to the discharge volume of the colorant ink. Furthermore, the discharge volume correspondence table in the second embodiment is discharge volume correspondence data showing the signal value corresponding to the discharge volume of the colorant ink (first ink) in relation to the signal value corresponding to the discharge volume of the primer ink (second ink). It can also be said that the discharge volume correspondence table in the second embodiment is discharge volume correspondence data showing the signal value corresponding to the discharge volume of the primer ink in relation to the signal value corresponding to the discharge volume of the colorant ink. In the second embodiment, the signal values ​​corresponding to the discharge volumes of the colorant ink and the primer ink are used as thresholds for the corrected dither matrix. When the dither matrix is ​​corrected so that the threshold increases, the ink discharge volume (number of discharged dots) decreases. The discharge volume correspondence table in the second embodiment is symmetrical with respect to the input=output axis compared to the discharge volume correspondence table in the first embodiment. By performing halftone processing using the dither matrix obtained by referring to the discharge volume correspondence table, it is possible to generate halftone image data corresponding to the primer ink.

[0070] Returning to Figure 9, the halftone processing unit 406 in the second embodiment performs halftone processing (quantization processing) using a dither matrix that has undergone density variation correction processing to generate halftone image data. In this embodiment, the dither method is used for halftone processing. When performing halftone processing, the halftone processing unit 406 performs comparison processing between the image data of each 8-bit CMYK signal and the corrected dither matrix corresponding to each color (C_th', M_th', Y_th', K_th'). As a result, the halftone processing unit 406 converts the image data of each 8-bit CMYK signal (C_img, M_img, Y_img, K_img) into halftone image data of each 1-bit CMYK signal (C_ht, M_ht, Y_ht, K_ht).

[0071] Furthermore, the halftone processing unit 406 compares the image data of each 8-bit CMYK signal with four types of dither matrices (Cp_th', Mp_th', Yp_th', Kp_th') corresponding to the corrected primer ink. This converts the image data of each 8-bit CMYK signal into 1-bit halftone image data (Cp_ht, Mp_ht, Yp_ht, Kp_ht) for each primer ink. Additionally, the halftone processing unit 406 obtains the halftone image data (P_ht) corresponding to the primer ink by performing a logical OR operation on the 1-bit halftone image data. Alternatively, the halftone processing unit 406 may convert the image data of each 8-bit CMYK signal (C_img, M_img, Y_img, K_img) into multi-bit halftone image data for each primer ink. In this case, the halftone processing unit 406 may obtain halftone image data corresponding to the primer ink by taking the maximum value for each pixel of the halftone image data for the primer ink, rather than by performing a logical OR operation. Alternatively, the halftone processing unit 406 may obtain halftone image data corresponding to the primer ink by performing a simple addition for each pixel of the halftone image data for the primer ink.

[0072] In the second embodiment, the data holding unit 405 generates a discharge volume correction table based on the image data of the density fluctuation acquisition chart acquired by the image acquisition unit 108. The data holding unit 405 holds the generated discharge volume correction table. By appropriately updating the discharge volume correction table, the data holding unit 405 can also respond to changes in density unevenness over time. The data holding unit 405 may also acquire and hold a discharge volume correction table generated by an external processing device.

[0073] Furthermore, when the image printing unit 107 receives halftone image data of the density variation acquisition chart from the halftone processing unit 406, it prints the image of the density variation acquisition chart onto the printing medium by ejecting ink from the first to fifth print heads 201 to 205. The image acquisition unit 108 captures an image of the density variation acquisition chart on the printing medium printed by the image printing unit 107. The image data of the density variation acquisition chart acquired by the image acquisition unit 108 is transmitted to the data holding unit 405 in the second embodiment.

[0074] <Concentration fluctuation correction processing> Next, we will describe the density variation correction process as an image processing (image processing method) performed by the image processing unit 106 in the second embodiment. Figure 12 is a flowchart showing the density variation correction process in the second embodiment.

[0075] First, in step S201, the color conversion processing unit 401 of the image processing unit 106 performs color conversion processing on the input image data and obtains CMYK signal image data. At this time, the color conversion processing unit 401 converts the input image data input via the I / F unit 109 into image data with a color gamut that can be reproduced by the image printing unit 107. Then, the color conversion processing unit 401 performs color conversion processing on the converted RGB signal image data and obtains CMYK signal image data.

[0076] Next, in step S202, the correction processing unit 402 acquires the CMYK ink ejection amount correction table 403 held in the data holding unit 405. As mentioned above, the ejection amount correction table 403 is generated and held by the data holding unit 405. Alternatively, the image processing unit 106 may not have a data holding unit 405, and the correction processing unit 402 may acquire the ejection amount correction table generated by an external processing unit.

[0077] Next, in step S203, the correction processing unit 402 obtains the discharge amount correspondence table 404 which has been previously stored in the storage device 105.

[0078] Next, in step S204, the correction processing unit 402 acquires a reference dither matrix 407 corresponding to each CMYK color, which is pre-stored in the storage device 105.

[0079] Next, in step S205, the correction processing unit 402 generates a corrected dither matrix corresponding to each CMYK color based on the CMYK ink ejection amount correction table and the reference dither matrix corresponding to each CMYK color. At this time, the correction processing unit 402 refers to one of the four types of ejection amount correction tables and performs density variation correction processing for each reference dither matrix of each color to generate a corrected dither matrix corresponding to each CMYK color.

[0080] Next, in step S206, the correction processing unit 402 generates a dither matrix corresponding to the corrected primer ink based on the CMYK ink ejection volume correction table, the ejection volume correspondence table, and the reference dither matrix. At this time, the correction processing unit 402 refers to the reference dither matrix and the ejection volume correspondence table to generate a dither matrix corresponding to the primer ink. Once the correction processing unit 402 has generated a dither matrix corresponding to the primer ink, it refers to the ejection volume correction table to generate a dither matrix corresponding to the corrected primer ink.

[0081] After the density variation correction processing is performed by the correction processing unit 402, in the next step S207, the halftone processing unit 406 performs halftone processing for each CMYK color. At this time, the halftone processing unit 406 uses the image data of each 8-bit CMYK signal and the dither matrix corresponding to each corrected CMYK color to perform halftone processing using the dither method and generate halftone image data of each 1-bit CMYK signal. The halftone image data of the CMYK signals generated by the halftone processing unit 406 is transmitted to the image printing unit 107.

[0082] Next, in step S208, the halftone processing unit 406 performs halftone processing on the primer ink. At this time, the halftone processing unit 406 uses the image data of each 8-bit CMYK signal and the dither matrix corresponding to the corrected primer ink to perform halftone processing by dithering and generate 1-bit halftone image data for each primer ink. Then, the halftone processing unit 406 generates halftone image data corresponding to the primer ink by taking the logical OR of the 1-bit halftone image data for each primer ink. The halftone image data corresponding to the primer ink generated by the halftone processing unit 406 is transmitted to the image printing unit 107.

[0083] Then, in step S209, the image printing unit 107 prints the input image onto the printing medium based on the halftone image data transmitted from the halftone processing unit 406. At this time, when the image printing unit 107 receives the halftone image data from the halftone processing unit 406, it prints the input image onto the printing medium by ejecting CMYK ink and primer ink from the first to fifth print heads 201 to 205.

[0084] By performing the processing control described above, it is possible to generate dither matrices corresponding to each CMYK color and a dither matrix corresponding to the primer ink, which are appropriately corrected based on the CMYK ink (colorant ink) ejection amount correction table. As a result, the ejection amount of the colorant ink is corrected based on the halftone image data of the CMYK signal after halftone processing, and the ejection amount of the primer ink is corrected based on the halftone image data corresponding to the primer ink after halftone processing. Therefore, the ejection amount of the primer ink can be appropriately corrected according to the ejection amount of the colorant ink corrected based on the colorant ink ejection amount correction table. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image.

[0085] As described above, according to the second embodiment, density unevenness in printed images can be appropriately corrected. That is, in this embodiment, the correction processing unit 402 generates a dither matrix corresponding to each color of the corrected CMYK using a CMYK ink (colorant ink) ejection amount correction table. The correction processing unit 402 generates a dither matrix corresponding to the corrected primer ink using an ejection amount correspondence table and an ejection amount correction table. The halftone processing unit 406 generates halftone image data of the CMYK signal by comparing the image data of the CMYK signal with the dither matrix corresponding to each color of the corrected CMYK. The halftone processing unit 406 generates halftone image data corresponding to the primer ink by comparing the image data of the CMYK signal with the dither matrix corresponding to the corrected primer ink. The halftone image data of the CMYK signal is a first halftone image data for ejecting colorant ink whose ejection amount has been corrected using the ejection amount correction table. The halftone image data corresponding to the primer ink is a second halftone image data for ejecting primer ink whose ejection amount has been corrected using the ejection amount correspondence table and an ejection amount correction table. The correction processing unit 402 and the halftone processing unit 406 constitute a generation processing unit that generates a first halftone image data and a second halftone image data. As a result, the ejection amount of colorant ink is corrected based on the first halftone image data, and the ejection amount of primer ink is corrected based on the second halftone image data. Therefore, the ejection amount of primer ink can be appropriately corrected according to the ejection amount of colorant ink corrected based on the ejection amount correction table of colorant ink. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image. In this way, density unevenness in the printed image can be appropriately corrected.

[0086] Furthermore, in the second embodiment, density variation correction processing is performed on the reference dither matrix. As a result, as long as the density variation characteristics in the print head do not change, the same dither matrix can be used for each corrected CMYK color and for the corrected primer ink. Therefore, the computational load on the image processing unit 106 can be reduced.

[0087] Furthermore, a dither matrix corresponding to the primer ink is generated based on a reference dither matrix corresponding to each CMYK color, an ejection volume correspondence table, and an ejection volume correction table. This generates halftone image data corresponding to the primer ink so that the dots of the colorant ink and the dots of the primer ink overlap as much as possible on the printing medium. Consequently, the primer ink is more likely to be ejected in positions where the colorant ink is easily ejected (where the dither matrix threshold is small), thereby enhancing the effect of fixing the colorant ink with the primer ink.

[0088] In the second embodiment described above, in addition to the reference dither matrices corresponding to each CMYK color, a reference dither matrix corresponding to the primer ink may be prepared in advance. In this case, a corrected dither matrix corresponding to the primer ink may be generated based on the reference dither matrix corresponding to the primer ink, the ejection volume corresponding table, and the ejection volume correction table. This eliminates the correlation between the position where the colorant ink is ejected and the position where the primer ink is ejected.

[0089] <<Third Embodiment>> Next, a third embodiment will be described. Except for the functional configuration of the image processing unit 106, the individual components in the third embodiment have the same configuration as those in the first embodiment described above, and will therefore be described using the same reference numerals as those used in the first embodiment. In the first embodiment, an example of correcting input image data according to density fluctuations due to the characteristics of the print head was described. In the third embodiment, an example of generating a halftone image corresponding to a primer ink based on a halftone image of a CMYK signal corrected for density fluctuations due to the characteristics of the print head will be described. Note that in the third embodiment, the differences from the first embodiment will be the focus of the description, and similarities will be omitted.

[0090] <Functional Configuration of Image Processing Unit> Figure 13 is a block diagram showing the functional configuration of the image processing unit 106 in the third embodiment. As shown in Figure 13, the image processing unit 106 in the third embodiment includes a color conversion processing unit 301, a correction processing unit 302, a data holding unit 305, a halftone processing unit 306, and an image generation unit 507.

[0091] The color conversion processing unit 301 performs color conversion processing based on the input image data and obtains CMYK signal image data (C_img, M_img, Y_img, K_img), which is bitmap data. The correction processing unit 302 refers to the output amount correction table and performs density fluctuation correction processing on the CMYK signal image data and obtains corrected CMYK signal image data (C_img', M_img', Y_img', K_img'). The halftone processing unit 306 performs halftone processing on the corrected CMYK signal image data and generates CMYK signal halftone image data (C_ht, M_ht, Y_ht, K_ht).

[0092] The image generation unit 507 generates halftone image data (P_ht) for primer ink based on the halftone image data (C_ht, M_ht, Y_ht, K_ht) of the CMYK signals and the ejection volume correspondence table in the third embodiment. Figure 14 is an explanatory diagram showing an example of the ejection volume correspondence table in the third embodiment. Figure 14(a) is a table showing an example of the ejection volume correspondence table in the third embodiment. In the example shown in Figure 14(a), the left column of the ejection volume correspondence table shows the number of input dots. The number of input dots in the ejection volume correspondence table is an 8-bit signal value corresponding to the number of ejected dots of the colorant ink in a predetermined area. The right column of the ejection volume correspondence table shows the number of output dots. The number of output dots in the ejection volume correspondence table is an 8-bit signal value corresponding to the number of ejected dots of the primer ink in a predetermined area. Figure 14(b) is a graph corresponding to the ejection volume correspondence table in Figure 14(a). The graph shown in Figure 14(b) is a graph of the ejection volume correspondence table in Figure 14(a). The horizontal axis of the graph shown in Figure 14(b) represents the number of input dots in the discharge volume correspondence table. The vertical axis of the graph shown in Figure 14(b) represents the number of output dots in the discharge volume correspondence table. As shown in Figure 14(a), the discharge volume correspondence table is a table that maintains the relationship between the number of discharged dots of the colorant ink and the number of discharged dots of the primer ink. The discharge volume correspondence table is discharge volume correspondence data that shows the number of discharged dots of the primer ink (second ink) in relation to the number of discharged dots of the colorant ink (first ink).

[0093] <Concentration fluctuation correction processing> Next, we will describe the density variation correction process as an image processing (image processing method) performed by the image processing unit 106 in the third embodiment. Figure 15 is a flowchart showing the density variation correction process in the third embodiment.

[0094] First, in step S301, the color conversion processing unit 301 of the image processing unit 106 performs color conversion processing based on the input image data and obtains CMYK signal image data. At this time, the color conversion processing unit 301 converts the input image data input via the I / F unit 109 into image data with a color gamut that can be reproduced by the image printing unit 107. Then, the color conversion processing unit 301 performs color conversion processing on the converted RGB signal image data and obtains CMYK signal image data.

[0095] Next, in step S302, the correction processing unit 302 acquires the CMYK ink ejection amount correction table 303 held in the data holding unit 305. As mentioned above, the ejection amount correction table 303 is generated by the data holding unit 305. Alternatively, the image processing unit 106 may not have a data holding unit 305, and the correction processing unit 302 may acquire the ejection amount correction table generated by an external processing device.

[0096] Next, in step S303, the correction processing unit 302 corrects the CMYK signal image data based on the acquired ejection amount correction table. At this time, the correction processing unit 302 refers to the ejection amount correction table and performs density variation correction processing on the CMYK signal image data, and acquires corrected CMYK signal image data that corrects for density variations due to the characteristics of each print head.

[0097] After the density variation correction processing is performed by the correction processing unit 302, in the next step S304, the halftone processing unit 306 performs halftone processing. At this time, the halftone processing unit 306 performs halftone processing on each 8-bit image data of the corrected CMYK signal and generates halftone image data of each 1-bit CMYK signal. The halftone image data of the CMYK signal generated by the halftone processing unit 306 is transmitted to the image generation unit 507 and the image printing unit 107.

[0098] In the next step S305, the image generation unit 507 acquires the ejection volume correspondence table 504 which has been previously stored in the storage device 105.

[0099] In the next step, S306, the image generation unit 507 refers to the ejection amount correspondence table and performs image generation processing on the halftone image data of the CMYK signal to generate halftone image data corresponding to the primer ink. The halftone image data corresponding to the primer ink generated by the image generation unit 507 is transmitted to the image printing unit 107. Details of the image generation process will be described later.

[0100] Then, in step S307, the image printing unit 107 prints the input image onto the printing medium based on the halftone image data transmitted from the halftone processing unit 306 and the image generation unit 507. At this time, when the image printing unit 107 receives the halftone image data from the halftone processing unit 306 and the image generation unit 507, it prints the input image onto the printing medium by ejecting CMYK ink and primer ink from the first to fifth print heads 201 to 205.

[0101] <Image generation process> Next, the image generation process by the image generation unit 507 will be described. Figure 16 is a flowchart of the image generation process. Figure 17 is an explanatory diagram illustrating the flow of the image generation process.

[0102] First, in step S401, the image generation unit 507 calculates the sum of the halftone image data for each pixel of the CMYK signal. This allows the image generation unit 507 to generate total halftone image data, which is the sum of the halftone image data for each pixel of the CMYK signal. In the example shown in Figure 17, each pixel of the total halftone image data 610 can take an integer value (pixel value) between 0 and 4.

[0103] Next, in step S402, the image generation unit 507 acquires the pixel values ​​of multiple pixels included in the unit area to be processed in the total halftone image data. Hereinafter, the unit area to be processed in the total halftone image data will be referred to as the processing area. In the example shown in Figure 17, the 4x4 pixel area indicated by the thick frame in the total halftone image data 610 is defined as the processing area. The total halftone image data 610 is provided with a first processing area 601, a second processing area 602, a third processing area 603, and a fourth processing area 604. In this embodiment, processing is performed in the order of the first processing area 601, the second processing area 602, the third processing area 603, and the fourth processing area 604.

[0104] Next, in step S403, the image generation unit 507 calculates the total value of the total halftone image data within the processing area, in other words, the total number of CMYK inks ejected. In the example shown in Figure 17, the total number of CMYK inks ejected in the first processing area 601 is 9. Also, the total number of CMYK inks ejected in the second processing area 602 is 4, the total number of CMYK inks ejected in the third processing area 603 is 4, and the total number of CMYK inks ejected in the fourth processing area 604 is 3.

[0105] Next, in step S404, the image generation unit 507 refers to the ejection amount correspondence table and converts the total number of CMYK inks ejected in the processing area into the number of primer inks ejected in the processing area. In the example shown in Figure 17, the number of primer inks ejected in the first processing area 601 is 4. Also, the number of primer inks ejected in the second processing area 602 is 2, the number of primer inks ejected in the third processing area 603 is 2, and the number of primer inks ejected in the fourth processing area 604 is 1.

[0106] Furthermore, in step S405, the image generation unit 507 obtains the priority order for the placement of primer ink dots in the processing area based on the pixel values ​​of the total halftone image data in the processing area. The priority order for dot placement is set such that the larger the pixel value in the total halftone image data, the more preferentially the primer ink dots are placed. In the example shown in Figure 17, the pixel with the largest pixel value (2) in the total halftone image data 610 in the processing area is set to a priority order of 1. If the pixel values ​​of the total halftone image data in the processing area are the same, the priority order for dot placement may be set randomly or in a predetermined priority order. The processing in step S405 may be performed before the processing in steps S403 and S404, or it may be performed after the processing in steps S403 and S404.

[0107] Next, in step S406, the image generation unit 507 generates halftone image data corresponding to the primer ink based on the number of primer inks ejected in the processing area and the priority order of the dot arrangement in the processing area. In the example shown in Figure 17, the dot arrangement of the primer ink with an ejection number of 4 is determined in the first processing area 601 of the halftone image data 650 corresponding to the primer ink. The dot arrangement of the primer ink with an ejection number of 2 is determined in the second processing area 602 of the halftone image data 650 corresponding to the primer ink. The dot arrangement of the primer ink with an ejection number of 2 is determined in the third processing area 603 of the halftone image data 650 corresponding to the primer ink. The dot arrangement of the primer ink with an ejection number of 1 is determined in the fourth processing area 604 of the halftone image data 650 corresponding to the primer ink.

[0108] Next, in step S407, the image generation unit 507 determines whether processing in all processing areas is complete. If processing in all processing areas is not complete, i.e., if the determination in step S407 is NO, the process returns to step S402 and processing in the next processing area is performed. On the other hand, if processing in all processing areas is complete, i.e., if the determination in step S407 is YES, the image generation process ends.

[0109] By performing the processing control described above, it is possible to generate halftone image data of the CMYK signal and halftone image data corresponding to the primer ink, which are appropriately corrected based on the CMYK ink (colorant ink) ejection amount correction table. As a result, the number of colorant inks ejected (ejection amount) is corrected based on the corrected CMYK signal halftone image data, and the number of primer inks ejected (ejection amount) is corrected based on the corrected halftone image data corresponding to the primer ink. Therefore, the number of primer inks ejected can be appropriately corrected according to the number of colorant inks ejected, which has been corrected based on the colorant ink ejection amount correction table. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image.

[0110] As described above, according to the third embodiment, density unevenness in printed images can be appropriately corrected. Specifically, in this embodiment, the correction processing unit 302 corrects the image data of the corrected CMYK signal, in which the ejection amount of the colorant ink has been corrected, using a CMYK ink (colorant ink) ejection amount correction table. The halftone processing unit 306 generates halftone image data of the CMYK signal by performing halftone processing on the corrected CMYK signal image data. The image generation unit 507 generates halftone image data corresponding to the primer ink using an ejection amount correspondence table based on the halftone image data of the CMYK signal. The halftone image data of the CMYK signal is a first halftone image data for ejecting colorant ink whose ejection amount has been corrected using the ejection amount correction table. The halftone image data corresponding to the primer ink is a second halftone image data for ejecting primer ink whose ejection amount has been corrected using the ejection amount correspondence table and the ejection amount correction table. The correction processing unit 302, the halftone processing unit 306, and the image generation unit 507 constitute a generation processing unit that generates the first halftone image data and the second halftone image data. As a result, the amount of colorant ink ejected is corrected based on the first halftone image data, and the amount of primer ink ejected is corrected based on the second halftone image data. Therefore, the amount of primer ink ejected can be appropriately corrected according to the amount of colorant ink ejected, which has been corrected based on the colorant ink ejection amount correction table. This makes it possible to correct density fluctuations in the printed image according to the characteristics of the print head with high accuracy, and to appropriately correct density unevenness in the printed image. In this way, density unevenness in the printed image can be appropriately corrected.

[0111] In the third embodiment, the priority order of primer ink dot placement is obtained based on total halftone image data, which is obtained by summing the halftone image data of the CMYK signals pixel by pixel. The number of primer inks ejected is obtained based on the total halftone image data and the ejection amount correspondence table. Then, based on the priority order of primer ink dot placement and the number of primer inks ejected, halftone image data corresponding to the primer ink is generated. As a result, halftone image data corresponding to the primer ink is generated so that the dots of the colorant ink and the dots of the primer ink overlap as much as possible on the printing medium. Therefore, since the primer ink is more likely to be ejected in positions where a large amount of colorant ink is ejected, the effect of fixing the colorant ink with the primer ink can be enhanced.

[0112] In the embodiments described above, a primer ink is used as the functional ink (second ink), but the invention is not limited to this, and a clear ink may also be used.

[0113] <<Other Embodiments>> The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0114] The disclosure of this embodiment includes configurations represented by the following examples of image processing apparatus, printing apparatus, image processing method, and program.

[0115] <Configuration 1> An image processing apparatus used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, An image processing apparatus characterized by having a generation processing unit that generates a first halftone image data for ejecting a first ink whose ejection amount has been corrected using ejection amount correction data for correcting the ejection amount of a first ink, and a second halftone image data for ejecting a second ink whose ejection amount has been corrected using ejection amount corresponding data indicating the ejection amount of a second ink relative to the ejection amount of a first ink and the ejection amount correction data.

[0116] <Configuration 2> The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates image data corresponding to the corrected first ink, in which the ejection amount of the first ink has been corrected using the ejection amount correction data, and image data corresponding to the corrected second ink, in which the ejection amount of the second ink has been corrected using the ejection amount corresponding data and the ejection amount correction data. A halftone processing unit that generates the first halftone image data and the second halftone image data by performing halftone processing on the image data corresponding to the first ink after correction and the image data corresponding to the second ink after correction, An image processing apparatus as described in configuration 1, including the image processing apparatus described in configuration 1.

[0117] <Structure 3> The image processing apparatus according to configuration 2, wherein the ejection amount correction data indicates a correction value for the signal value of image data corresponding to the first ink.

[0118] <Structure 4> The image processing apparatus according to configuration 2 or 3, wherein the image data corresponding to the first ink is bitmap data.

[0119] <Composition 5> The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates a dither matrix corresponding to the corrected first ink, in which the ejection volume of the first ink has been corrected using the ejection volume correction data, and a dither matrix corresponding to the corrected second ink, in which the ejection volume of the second ink has been corrected using the ejection volume corresponding data and the ejection volume correction data. A halftone processing unit that generates the first halftone image data by comparing image data corresponding to the first ink with the corrected dither matrix corresponding to the first ink, and generates the second halftone image data by comparing image data corresponding to the first ink with the corrected dither matrix corresponding to the second ink, An image processing apparatus as described in configuration 1, including the image processing apparatus described in configuration 1.

[0120] <Composition 6> The image processing apparatus according to configuration 5, wherein the ejection volume correction data indicates a correction value for the threshold of the dither matrix corresponding to the first ink.

[0121] <Composition 7> The image processing apparatus according to configuration 5 or 6, wherein the image data corresponding to the first ink is bitmap data.

[0122] <Structure 8> The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates image data corresponding to the corrected first ink, in which the ejection amount of the first ink has been corrected using the ejection amount correction data, A halftone processing unit that generates the first halftone image data by performing halftone processing on the image data corresponding to the first ink after correction, An image generation unit that generates a second halftone image data using the discharge amount corresponding data based on the first halftone image data, An image processing apparatus as described in configuration 1, including the image processing apparatus described in configuration 1.

[0123] <Composition 9> The image processing apparatus according to configuration 8, wherein the image generation unit generates the second halftone image data based on the number of second inks ejected, which is obtained based on the first halftone image data and the ejection amount corresponding data, and the priority order of the dot arrangement of the second inks, which is obtained based on the first halftone image data.

[0124] <Composition 10> The image processing apparatus according to configuration 8 or 9, wherein the ejection amount correction data indicates a correction value for the signal value of image data corresponding to the first ink.

[0125] <Composition 11> The image processing apparatus according to any one of the configurations 8 to 10, wherein the image data corresponding to the first ink is bitmap data.

[0126] <Composition 12> A printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, A printing apparatus comprising an image processing apparatus as described in any one of items 1 to 11.

[0127] <Composition 13> The printing apparatus according to configuration 12, further comprising a recording device for storing the aforementioned discharge volume-corresponding data.

[0128] <Composition 14> An image processing method used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, A step of obtaining ejection amount correction data to correct the ejection amount of the first ink, The steps include generating a first halftone image data for ejecting a first ink whose ejection amount has been corrected using the ejection amount correction data, and a second halftone image data for ejecting a second ink whose ejection amount has been corrected using ejection amount correspondence data indicating the ejection amount of the second ink relative to the ejection amount of the first ink and the ejection amount correction data, An image processing method characterized by having the following features.

[0129] <Composition 15> A program that causes a computer to perform the image processing method described in Configuration 14. [Explanation of Symbols]

[0130] 1. Printing System 106 Image Processing Unit 305 Data storage unit 306 Halftone Processing Unit

Claims

1. An image processing apparatus used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, An image processing apparatus characterized by having a generation processing unit that generates a first halftone image data for ejecting a first ink whose ejection amount has been corrected using ejection amount correction data for correcting the ejection amount of a first ink, and a second halftone image data for ejecting a second ink whose ejection amount has been corrected using ejection amount corresponding data indicating the ejection amount of a second ink relative to the ejection amount of a first ink and the ejection amount correction data.

2. The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates image data corresponding to the corrected first ink, in which the ejection amount of the first ink has been corrected using the ejection amount correction data, and image data corresponding to the corrected second ink, in which the ejection amount of the second ink has been corrected using the ejection amount corresponding data and the ejection amount correction data. A halftone processing unit that generates the first halftone image data and the second halftone image data by performing halftone processing on the corrected image data corresponding to the first ink and the corrected image data corresponding to the second ink, The image processing apparatus according to claim 1, including the following:

3. The image processing apparatus according to claim 2, wherein the ejection amount correction data indicates a correction value for the signal value of image data corresponding to the first ink.

4. The image processing apparatus according to claim 2, wherein the image data corresponding to the first ink is bitmap data.

5. The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates a dither matrix corresponding to the corrected first ink, in which the ejection volume of the first ink has been corrected using the ejection volume correction data, and a dither matrix corresponding to the corrected second ink, in which the ejection volume of the second ink has been corrected using the ejection volume corresponding data and the ejection volume correction data. A halftone processing unit that generates the first halftone image data by comparing image data corresponding to the first ink with the corrected dither matrix corresponding to the first ink, and generates the second halftone image data by comparing image data corresponding to the first ink with the corrected dither matrix corresponding to the second ink, The image processing apparatus according to claim 1, including the following:

6. The image processing apparatus according to claim 5, wherein the ejection volume correction data indicates a correction value for the threshold of the dither matrix corresponding to the first ink.

7. The image processing apparatus according to claim 5, wherein the image data corresponding to the first ink is bitmap data.

8. The system further includes a color conversion processing unit that converts input image data into image data corresponding to a first ink. The generation processing unit is, A correction processing unit that generates image data corresponding to the corrected first ink, in which the ejection amount of the first ink has been corrected using the ejection amount correction data, A halftone processing unit that generates the first halftone image data by performing halftone processing on the image data corresponding to the first ink after correction, An image generation unit that generates the second halftone image data using the ejection amount corresponding data based on the first halftone image data, The image processing apparatus according to claim 1, including the following:

9. The image processing apparatus according to claim 8, wherein the image generation unit generates the second halftone image data based on the number of second inks ejected obtained based on the first halftone image data and the ejection amount corresponding data, and the priority order of the dot arrangement of the second inks obtained based on the first halftone image data.

10. The image processing apparatus according to claim 8, wherein the ejection amount correction data indicates a correction value for the signal value of image data corresponding to the first ink.

11. The image processing apparatus according to claim 8, wherein the image data corresponding to the first ink is bitmap data.

12. A printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, A printing apparatus comprising an image processing apparatus according to any one of claims 1 to 11.

13. The printing apparatus according to claim 12, further comprising a storage device for storing the aforementioned discharge volume-corresponding data.

14. An image processing method used in a printing apparatus that prints an image by ejecting a first ink containing a colorant and a second ink not containing a colorant, A step of obtaining ejection amount correction data to correct the ejection amount of the first ink, The steps include generating a first halftone image data for ejecting a first ink whose ejection amount has been corrected using the ejection amount correction data, and a second halftone image data for ejecting a second ink whose ejection amount has been corrected using ejection amount correspondence data indicating the ejection amount of the second ink relative to the ejection amount of the first ink and the ejection amount correction data, An image processing method characterized by having the following features.

15. A program for causing a computer to perform the image processing method described in claim 14.

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