Image processing device, image processing method, and program

Abstract

To provide a technique capable of suppressing the occurrence of unevenness due to variations in recording characteristics including variations in discharge characteristics between a plurality of nozzles in a recording head regardless of the structure of the recording head.SOLUTION: An image processing device updates a first set correction target value in accordance with the difference between a first set correction target value set in a correction target value generation region including a unit region corresponding to one or a plurality of nozzles and the recording density by the unit region corresponding to the correction target value generation region, and updates a second set correction target value in accordance with the difference between a second set correction target value set in the correction target value generation region which is adjacent to an update region being the correction target value generation region that updates the correction target value and which has not updated the correction target value yet and the correction target value of the update region.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an image processing apparatus, an image processing method, and a program that use a plurality of nozzles to generate print data for printing an image on a print medium that moves relatively to the plurality of nozzles. [Background technology]

[0002] Head shading technology and color shading technology are known as technologies for correcting uneven density and color caused by the ink ejection characteristics of each nozzle of a recording head capable of ejecting ink from multiple nozzles by an inkjet method. These technologies increase or decrease the number of recording dots in an area where the ejection amount based on the ejection characteristics is outside a predetermined range, thereby correcting density differences and color differences between that area and an area where the ejection amount is within the predetermined range.

[0003] In addition, in an area where the discharge amount based on the discharge characteristics is outside the predetermined range, if the discharge amount is significantly outside the predetermined range, the fluctuation in the number of dots recorded by the head shading technology will be large. As a result, the dot patterns recorded between the area where the discharge amount is outside the predetermined range and the area where the discharge amount is within the predetermined range will be significantly different, and such a difference in the dot patterns may be visually recognized as unevenness in spatial frequency. As a technology for solving such a problem, for example, Patent Document 1 discloses a technology for suppressing the occurrence of unevenness in spatial frequency by using small dots and dots made of low-density ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-168000 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology disclosed in Patent Document 1 requires the print head to be equipped with nozzles capable of ejecting small-sized dots and capable of ejecting low-concentration ink, and the above technology cannot be applied to print heads that do not have such configuration.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology that can suppress the occurrence of unevenness caused by variations in printing characteristics, including variations in ejection characteristics among multiple nozzles in a printing head, regardless of the configuration of the printing head. [Means for solving the problem]

[0007] In order to achieve the above object, one embodiment of the present invention is an image processing apparatus comprising: an acquisition means for acquiring a recording density according to recording characteristics in a unit area corresponding to one or more nozzles that eject ink; and a correction target value generation means for generating a correction target value that is a target density value when generating a correction value used in head shading processing according to the recording density acquired by the acquisition means, wherein the correction target value generation means performs a first update to update the first set correction target value according to a difference between a first set correction target value set in a correction target value generation area including the unit area and a recording density by the unit area corresponding to the correction target value generation area, and updates the correction target value in the correction target value generation area. a second update is performed to update the second set correction target value according to a difference between a second set correction target value set in the correction target value generation area adjacent to the update area and in which the correction target value has not yet been updated, and a first updated correction target value which is the updated correction target value in the update area; and in the first update, when a difference in the number of dots during recording between the first set correction target value and a recording density by the unit area corresponding to the correction target value generation area in which the first set correction target value is set exceeds a first threshold value, the first set correction target value is updated to a first updated correction target value on the recording density side where the difference in the number of dots from the recording density is equal to or less than the first threshold value. Effect of the Invention

[0008] According to the present invention, it is possible to suppress the occurrence of unevenness caused by variations in printing characteristics, including variations in ejection characteristics among a plurality of nozzles in a print head, regardless of the configuration of the print head. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a printing system including an image processing apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the arrangement of nozzles in a print head. [Diagram 3] FIG. 2 is a block diagram of the control system of the recording device and the host PC. [Figure 4] FIG. 2 is a block diagram of a functional configuration for image processing in the printing system. [Diagram 5] 4 is a flowchart showing a processing routine of image processing. [Figure 6] 10 is a flowchart showing a processing routine of a generation process for generating a correction value. [Figure 7] 11 is a relationship diagram used when estimating gradation characteristics from read values. [Figure 8] 11 is a flowchart showing a processing routine of a correction target value generation process. [Figure 9] FIG. 4 is a diagram showing print densities in a correction target value generation area. [Figure 10] 13 is a flowchart showing a processing routine of an update process. [Figure 11] 6A and 6B are diagrams illustrating updating of correction target values ​​of an attention area. [Figure 12] 6A and 6B are diagrams for explaining update of correction target values ​​of a target area. [Figure 13] 11 is a diagram showing the range of tolerance and the degree of color difference according to the tolerance of color difference; [Figure 14] 5A and 5B are diagrams for explaining a method of obtaining a correction value. [Figure 15]FIG. 13 is a diagram showing a modified example of a correction target value generation area. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an example of an embodiment of an image processing device, an image processing method, and a program will be described in detail with reference to the attached drawings. Note that the following embodiment does not limit the present invention, and not all of the combinations of features described in the present embodiment are necessarily essential to the solution of the present invention. Furthermore, the relative positions and shapes of the components described in the embodiment are merely examples, and are not intended to limit the scope of the present invention to only those.

[0011] Fig. 1 is a schematic diagram of a recording system including an image processing device according to an embodiment. The recording system 10 in Fig. 1 includes a recording device 100 that ejects ink onto a recording medium to record, and a personal computer (PC) 200 that serves as a host device for the recording device 100. In this embodiment, the host PC 200 functions as the image processing device.

[0012] <Recording device> The recording device 100 is a full-line type inkjet recording device. The recording device 100 includes a recording head 102 that ejects ink onto a recording medium M to perform recording, a transport roller 104 that transports the recording medium M, and a scanner 106 that can read an image recorded on the recording medium M.

[0013] The four recording heads 102, recording heads 102K, 102C, 102M, and 102Y, are arranged side by side along the Y direction. Recording head 102K is located on the most upstream side in the +Y direction and ejects black ink (K ink). Recording head 102C is located downstream of recording head 102K in the +Y direction and ejects cyan ink (C ink). Recording head 102M is located downstream of recording head 102C in the +Y direction and ejects magenta ink (M ink). Recording head 102Y is located downstream of recording head 102M in the +Y direction and ejects yellow ink (Y ink).

[0014] The print head 102 extends in the X direction intersecting (orthogonal in this embodiment) the Y direction, and is provided with a nozzle row in which a plurality of nozzles are arranged in the X direction at a pitch of 1200 dpi corresponding to a printing area in the width direction of the printing medium M transported in the Y direction. The nozzles in the print head 102 are configured to eject corresponding inks. The printing apparatus 100 is provided with a supply mechanism that supplies the corresponding inks to the print head 102.

[0015] The transport roller 104 rotates by the driving force of a transport motor (not shown) and transports the recording medium M in the Y direction. In addition to the transport roller 104, the recording device 100 is provided with a roller driven by the transport motor, and the recording medium M is transported by this roller and the transport roller 104. The transport mechanism for the recording medium M in the recording device 100 is not limited to rollers such as the transport roller 104, and various known techniques can be applied.

[0016] While the recording medium M is being transported by the transport roller 104 or the like, ink is ejected from the nozzles of the recording heads 102K, 102C, 102M, and 102Y based on the recording data at a frequency according to the transport speed of the recording medium M. As a result, ink dots of each color are applied to the recording medium M in accordance with the recording data, and an image is formed on the recording medium M.

[0017] The scanner 106 is provided downstream of the recording head 102 in the +Y direction, and its reading area has a length covering the recording area of ​​the recording medium M in the X direction. Specifically, the scanner 106 has reading elements (not shown) arranged at a predetermined pitch along the X direction on the surface facing the recording medium M. The scanner 106 can read an image recorded on the recording medium M conveyed by the conveying roller 104, such as an image recorded by the recording head 102, and output it as RGB multi-value data. In this embodiment, the scanner 106 is used to read a test pattern recorded when performing head shading processing (HS processing). The reading mechanism in the recording device 100 is not limited to the scanner 106. In other words, the reading mechanism may be provided separately from the recording device 100, or may be configured to read an image recorded on the recording medium M while moving in the X direction.

[0018] <Recording head> Figure 2 shows examples of the arrangement of chips, each of which has nozzles that eject ink, in a recording head. (a) is an example of rectangular chips arranged in a staggered pattern, and (b) is an example of parallelogram chips arranged along a specific direction.

[0019] In the recording head 102, a nozzle row is formed by arranging a plurality of nozzles 210 that eject ink in the X direction on the surface facing the recording medium M. The length of this nozzle row is formed in the X direction to correspond to the width of the recording area of ​​the recording medium M.

[0020] More specifically, the print head 102 has a plurality of chips 202 each having a nozzle row formed thereon, which are arranged so that adjacent chips are adjacent to each other in the Y direction and are shifted so that they overlap in the X direction (see FIG. 2(a)). Specifically, the chips 202 are rectangular. Then, for the chip 202-1 located at the most upstream side in the +X direction and the chip 202-2 adjacent to the chip 202-1, the chip 202-2 is arranged downstream in the +Y direction of the chip 202-1 so that they overlap in part in the X direction. Also, for the chip 202-2 and the chip 202-3 adjacent to the chip 202-2, the chip 202-3 is arranged upstream in the +Y direction of the chip 202-2 so that they overlap in part in the X direction. Then, for the chip adjacent to the chip 202-3 and subsequent chips, the above arrangement is repeated. That is, the chips 202 are arranged in a staggered arrangement so as to extend in the X direction as a whole. Each chip 202 has four nozzle rows formed in the Y direction, each of which has a plurality of nozzles 210 arranged in the X direction. The four nozzle rows are shifted in the +X direction by a predetermined amount as they move downstream in the +Y direction. The nozzle rows formed by each chip 202 are configured to be able to record dots at a pitch of 1200 dpi in the recording area 212 by selectively performing a discharge operation. The length of the recording area 212 in the X direction corresponds to the range that can be recorded in the X direction by the recording head 102, that is, the range in which the nozzles are formed in the X direction.

[0021] The chip configuration of the recording head 102 is not limited to the above-mentioned form, and may be a chip configuration as shown in FIG. 2(b). In FIG. 2(b), the recording head 102 has a plurality of chips 204 with nozzle rows formed thereon arranged in a line along the X direction. Specifically, the chips 204 are parallelograms. The plurality of chips 204 are arranged along the X direction without being shifted in the Y direction so that the short sides of adjacent chips are parallel to each other. Each chip 204 has three nozzle rows formed in the Y direction, each of which is formed by arranging a plurality of nozzles 210 in the X direction. The three nozzle rows are shifted in the −X direction by a predetermined amount as they move toward the downstream side in the +Y direction. The nozzle rows formed by each chip 204 are configured to be able to record dots at a pitch of 1200 dpi on the recording area 212 by selectively executing an ejection operation.

[0022] 2(a) and (b) show an area 220 formed to divide the recording area 212. This area 220 is an area for generating a correction target value used when acquiring a correction value used in HS processing, and details thereof including the correction target value will be described later. Hereinafter, the area 220 is referred to as a correction target value generation area 220.

[0023] The recording device 100 is not limited to a full-line type inkjet recording device, and may be a so-called serial scan type inkjet recording device in which recording and reading are performed by scanning a recording head or a scanner in the X direction. The recording device 100 is also not limited to a type in which ink is directly applied from the recording head 102 to the recording medium M. That is, the recording device 100 may be a type in which an ink layer is once formed on an intermediate transfer body, and then the ink layer is transferred to the recording medium M. In the recording device 100, the ink that can be recorded by the recording head 102 is four different colors of ink, but the present invention is not limited to this, and one to three, or five or more colors of ink may be used.

[0024] <Control system configuration of the recording device> Fig. 3 is a block diagram of the control system of the recording device and image processing device that constitute the recording system. Note that Fig. 3 shows the main components, and the recording device 100 and the host PC 200 as the image processing device may have components other than those shown in Fig. 3.

[0025] The recording device 100 includes a main control unit 302 that controls the entire recording device 100. The main control unit 302 is composed of, for example, a central processing unit (CPU), a ROM, and a RAM. The recording device 100 also includes a print buffer 304 in which print data before being output to the print head 102 is stored as raster data, and a head driver 306 that controls the print head 102. The head driver 306 ejects ink from each nozzle according to the print data stored in the print buffer 304. The recording device 100 also includes a transport motor driver 308 that controls the transport motor, and a communication interface (I / F) 310 for transmitting and receiving data signals to and from the host PC 200. The recording device 100 also includes a data buffer 312 that temporarily stores image data received from the host PC 200. Each of the above-mentioned components is connected to each other via a system bus 314.

[0026] <Control system configuration of image processing device> The host PC 200, which functions as an image processing device, is equipped with a main control unit 322 capable of executing the creation of image data, various processes on the created image data, and the generation of information used in executing the processes. The main control unit 322 is composed of, for example, a CPU, a ROM, a RAM, etc. The host PC 200 also has a communication I / F 324 for transmitting and receiving data signals to and from the recording device 100. The communication I / F 324 is connected to the communication I / F 310 of the recording device 100 by a signal line 332.

[0027] Furthermore, the host PC 200 includes a display I / F 326 connected to a display (not shown) as a display unit, and a keyboard / mouse I / F 328 connected to a keyboard (not shown) and a mouse (not shown) as an operation unit. The main control unit 322 controls the display via the display I / F 326. The main control unit 322 also receives operation contents of a user using a keyboard and mouse via the keyboard / mouse I / F 328. The main control unit 322 then executes various processes based on the operation contents that have been input. Each of the above-mentioned components is connected via a system bus 330.

[0028] <Functional configuration of the recording system> Next, a functional configuration of the recording system 10 will be described. In the following description, a configuration related to image processing for obtaining recording data, which is binary data representing whether or not ink is ejected for each pixel on a recording medium, will be described, and a description of various well-known components included in the recording system 10 will be omitted. Figure 4 is a block diagram showing the functional configuration of the recording system.

[0029] The recording system 10 includes an input unit 402 to which image data is input, and an input color conversion processing unit 404 that converts the image data output from the input unit 402 into image data corresponding to the color reproduction gamut of the recording device 100. The main control unit 322 also includes an ink color separation processing unit 406 that converts the color signal values ​​of the image data converted by the input color conversion processing unit 404 into color signal values ​​corresponding to the inks used in the recording device 100. The main control unit 322 also includes an HS processing unit 408 that performs correction on the image data having the ink color signal values ​​converted by the ink color separation processing unit 406 in accordance with the ejection characteristics of each nozzle in the recording head 102.

[0030] The main control unit 322 further includes an output tone correction processing unit 410 that performs correction to adjust the number of ink dots recorded by an output unit 414 (described later) for each ink color on image data having color signal values ​​obtained by the HS processing unit 408. The main control unit 322 also includes a quantization processing unit 412 that performs quantization processing on image data having color signal values ​​obtained by the output tone correction processing unit 410, and an output unit 414 that outputs binary data (dot data) obtained by the quantization processing to the recording device 100.

[0031] The above-described configuration may be provided in the main control unit 302 or the main control unit 322, or a part of the configuration may be provided in the main control unit 302 and the remaining configuration may be provided in the main control unit 322. In the following explanation, for ease of understanding, the above-described configuration will be described as being provided in the main control unit 322.

[0032] <Image processing> In the recording system 10 described above, recording is performed on a recording medium M. In this recording system 10, the host PC 200 performs image processing to convert image data into recording data recordable by the recording device 100, and based on the image processing result obtained, recording is performed on a recording medium by the recording device 100. In the recording system 10, image processing is started, for example, in response to an instruction from a user via the host PC 200.

[0033] Fig. 5 is a flowchart showing a detailed processing routine of image processing. The series of processes shown in the flowchart in Fig. 5 are performed by the CPU in the main control unit 322 expanding program code stored in the ROM into the RAM and executing it. Alternatively, some or all of the functions of the steps in Fig. 5 may be performed by hardware such as an ASIC or an electric circuit. Furthermore, the symbol S in the description of each process in this specification means a step in a flowchart showing the contents of each process. The same applies to the following flowcharts.

[0034] When image processing is started, first, the input unit 402 acquires image data (S502). In the host PC 200, image data created in the host PC 200 or other computers is stored in a storage area. Therefore, the input unit 402 acquires the image data stored in the storage area. This image data is 8-bit luminance data represented by R (red), G (green), and B (blue).

[0035] Next, the input color conversion processing unit 404 performs color conversion processing (S504) to convert the RGB input signal values ​​of the input image data into device color signal values ​​of R', G', and B' that correspond to the color reproduction gamut of the recording device 100. For this conversion, known techniques using matrix calculation processing and a three-dimensional lookup table (LUT) can be used.

[0036] Thereafter, the ink color separation processing unit 406 performs color separation processing to convert the device color signal values ​​converted by the input color conversion processing unit 404 into color signal values ​​corresponding to the ink colors used in the printing device 100 (S506). Specifically, since the printing device 100 uses inks of K (black), C (cyan), magenta (M), and Y (yellow), in S506, the device color signal values ​​(R', G', B') are converted into ink color signal values ​​(K, C, M, Y). The values ​​of K, C, M, and Y are each represented by 8 bits, similar to the values ​​of R, G, and B. In this conversion, similar to S504, a known technique such as a three-dimensional LUT can be used.

[0037] Once the ink color signal values ​​have been acquired, the HS processor 408 then performs HS processing to correct the ink color signal values ​​to accommodate unevenness resulting from variations in the ejection characteristics of the nozzles that make up the print head 102 (S508). In S508, the ink color signal values ​​(K, C, M, Y) are converted using a one-dimensional LUT to acquire HS color signal values ​​(K', C', M', Y'). Once the HS signal values ​​have been acquired, the output tone correction processor 410 then performs correction on the image data having the HS processed HS color signal values ​​to adjust the number of ink dots to be printed for each ink color (S510).

[0038] Thereafter, the quantization processing unit 412 performs quantization processing on the image data having the color signal value corrected by the output tone correction processing unit 410 (S512), and the main control unit 322 ends the image processing as the print data generation processing. The quantization processing can use known techniques such as error diffusion and dithering. The quantization level can be binary or multi-value, i.e., ternary or more. If it is binary, it is converted to ON (eject) / OFF (not eject) of ink ejection at each pixel. If it is multi-value, i.e., ternary or more, it is further expanded by index expansion into binary data of ON / OFF of ink ejection at each pixel. The index expansion can use known techniques. For example, a dot arrangement according to the quantization level is held in advance as a table, and the dot arrangement (binary value of ON / OFF of ink ejection) is determined based on the quantization level.

[0039] The binary data thus obtained by image processing, that is, the recording data, is output by the output unit 414 to the recording device 100 via the communication I / F 324. When a user instructs the recording device 100 to start recording, a recording process is executed in which recording is performed on the recording medium based on the input binary data.

[0040] The above-described image processing may be modified as follows. The image data held by the input unit 402 is expressed in RGB format, but is not limited to this. The expression format of each pixel may be CMYK format. Alternatively, it may be a color number format associated with colors expressed in an input-independent color space, for example, Lab, according to an existing standard. In addition, the number of bits for each process in the image processing is 8 bits, but is not limited to this, and may be high gradation such as 16 bits. Furthermore, although not specifically described in the above image processing, in the process after conversion to ink color signal values ​​in the color separation process in S506, processing is performed for each ink color.

[0041] In the color conversion process of S504, a method may be used to convert data from a device-dependent color space data format such as RGB or CMYK of the input image data to a device-independent color space such as Lab or XYZ, and then convert it back to a device-dependent color space. In the color separation process of S506, although the conversion to the four colors of CMYK is shown as an example, the colors to be converted are not limited to these four colors. For example, for the purpose of reducing graininess, if the recording device 100 has other types of inks, such as light-colored inks with the same hue as CMYK and low density, conversion to the corresponding ink colors is performed. Also, the recording device 100 may have special colors different in hue from the primary colors (CMYK), such as orange, green, violet, and blue, as ink colors.

[0042] <Generation of correction values used in HS processing> Next, the generation of correction values used in HS processing will be described. Specifically, a one-dimensional lookup table, which is a conversion table for converting gradation values, is generated as the correction value. FIG. 6 is a flowchart showing a detailed processing routine of the generation process for generating the correction values used in HS processing. The series of processes shown in the flowchart of FIG. 6 is performed by the main control unit 322 when the CPU expands and executes the program code stored in the ROM into the RAM. Alternatively, part or all of the functions of the steps in FIG. 6 may be executed by hardware such as an ASIC or an electric circuit.

[0043] In the generation process of FIG. 6, first, the main control unit 322 records a predetermined test pattern on the recording medium M in the recording device 100 (S602). The predetermined test pattern is a known pattern for obtaining the ejection characteristics of the nozzles in a unit area (described later) for obtaining correction values, and is recorded over the entire recording area 212 in the X direction. Next, the main control unit 322 reads the recorded test pattern by the scanner 106 (S604). That is, the main control unit 322 controls the recording device 100 to record a predetermined test pattern and read the recorded predetermined test pattern.

[0044] Thereafter, the main control unit 322 analyzes the read value for each unit area in the printing area 212 and estimates the amount of ink ejected in that unit area (S606). Then, based on the estimated ejection amount, the main control unit 322 estimates the gradation characteristic, which is the relationship between the input gradation and the printing density in the unit area (S608). A unit area is an area for acquiring a correction value, and corresponds to one or multiple nozzles that are continuous in the X direction. Note that this unit area is smaller in the X direction than a correction target value generation area, which will be described later.

[0045] The host PC 200 holds, in a storage area or the like, the correspondence between the signal value (read value) read by the scanner 106 and the density (recording density) to be recorded. Therefore, by recording and reading a specific gradation pattern, that is, a predetermined test pattern, it is possible to estimate the gradation characteristic, which is the correspondence between the input gradation and the recording density.

[0046] FIG. 7(a) is a graph showing the relationship between the read value by the scanner and the recording density. The storage area of ​​the host PC 200 stores information showing the correspondence between the read value by the scanner 106 and the recording density as shown in FIG. 7(a). In FIG. 7(a), the horizontal axis shows the read value by the scanner 106, and takes values ​​from 0 to 255. The signal value when the brightest color assumed by the scanner 106 is "255", and the signal value when the darkest color assumed by the scanner 106 is "0". The vertical axis shows the recording density. In FIG. 7(a), for example, when the read value is P1 in a unit area, the recording density is P2. After the recording density in the unit area is obtained in this way, the ink ejection amount (hereinafter also simply referred to as "ejection amount") in the unit area is estimated from the obtained recording density.

[0047] Therefore, in S606, the recording density is obtained for each unit area from the read value by the scanner 106, and the ink ejection amount corresponding to the unit area is estimated based on this recording density. FIG. 7(b) is a graph showing the relationship between recording density and ejection amount. Information showing the correspondence between recording density and ejection amount is also stored in the memory area of ​​the host PC 200. In FIG. 7(b), the horizontal axis shows recording density, and the vertical axis shows the estimated ink ejection amount. In FIG. 7(b), when the recording density is P2, the estimated ink ejection amount is P3. That is, in S606, when the read value by the scanner 106 is P1, P3 is obtained as the estimated ink ejection amount.

[0048] 7B, the estimated ink ejection amount on the vertical axis may be a specific ejection amount value or may be a number of ranks determined according to a set criterion. For example, the ranks may be three ranks, large, medium and small, or four or more ranks from large to small, and each rank is associated with the estimated ink ejection amount.

[0049] Once the ink ejection volume has been estimated, in S608, gradation characteristics are estimated based on the ejection volume. FIG. 7(c) is a graph showing an example of gradation characteristics corresponding to ejection volume ranks. The gradation characteristics corresponding to these ejection volume ranks are also stored in the storage area of ​​the host PC 200. In FIG. 7(c), the horizontal axis indicates the signal value input for printing, that is, the input gradation value, and the vertical axis indicates the printing density. The horizontal axis is an 8-bit gradation value ranging from 0 to 255. In the gradation characteristics of FIG. 7(c), the larger the gradation value, the greater the number of dots printed, that is, the greater the printing density.

[0050] The three gradation characteristics 702, 704, and 706 in Fig. 7(c) show gradation characteristics for different ejection amount ranks. The gradation characteristic 702 shows the relationship between the input gradation value and the print density when printing with a large ejection amount. In the gradation characteristic 702, the print density is higher on the low gradation value side compared to the gradation characteristics 704 and 706, and the print density is saturated on the low gradation value side below the maximum input gradation value, that is, the upper limit of the print density is reached. Therefore, if the ejection amount or ejection amount rank estimated in S606 is large, the gradation characteristic 702 is selected as the estimated gradation characteristic in S608.

[0051] Gradation characteristic 704 shows the relationship between input gradation value and print density when printing with a medium ejection amount. Gradation characteristic 704 has a lower print density at each gradation value compared to gradation characteristic 702. On the other hand, compared to gradation characteristic 706, the print density is higher on the low gradation value side. Gradation characteristic 704 reaches the upper limit of print density at the maximum input gradation value. Therefore, if the ejection amount or ejection amount rank estimated in S606 is medium, gradation characteristic 704 is selected as the estimated gradation characteristic in S608.

[0052] Gradation characteristic 706 shows the relationship between input gradation value and print density when printing with a small ejection amount. Gradation characteristic 706 has a lower print density at each gradation value compared to gradation characteristics 702 and 704. With gradation characteristic 706, the upper limit of print density is not reached even at the maximum input gradation value. Therefore, if the ejection amount or ejection amount rank estimated in S606 is small, gradation characteristic 706 is selected as the estimated gradation characteristic in S608.

[0053] In this embodiment, a test pattern of one gradation is recorded and then read to estimate the ejection amount and estimate the gradation characteristics, but this is not limited to this. In other words, multiple test patterns of different gradations may be recorded and read, and the gradation characteristics may be generated from the read values. In this case, the gradation characteristics, which are the relationship between the input gradation value and the recording density shown in FIG. 7(c), can be generated from the relationship between the read value and the recording density shown in FIG. 7(a).

[0054] Returning to Fig. 6, after estimating the gradation characteristics, the main control unit 322 next performs a correction target value generation process for generating a correction target value that becomes a target density value for correction for each correction target value generation region (S610). Fig. 8 is a flowchart showing the processing routine of the correction target value generation process, which is a subroutine of the generation process.

[0055] When the correction target value generation process is started, first, the main control unit 322 sets a correction target value generation area for generating a correction target value (S802). In S802, the recording area 212 is divided into a plurality of areas, and a correction target value generation area 220 (see FIG. 2) is set. The correction target value generation area 220 is, for example, an area corresponding to a plurality of nozzles arranged in a regular sequence in the X direction in a chip in which nozzles are generated. Specifically, when the chips 202 are arranged in the recording head 102 as shown in FIG. 2(a), for example, an area including four nozzles 210 arranged at different positions in the Y direction and continuous in the X direction is set as the correction target value generation area 220. Also, when the chips 204 are arranged in the recording head 102 as shown in FIG. 2(b), for example, an area including all the nozzles 210 formed in one chip 204 is set as the correction target value generation area 220.

[0056] Moreover, the correction target value generation area 220 is larger than the unit area where the print density is detected by reading by the scanner 106, that is, the area where the correction value used in the HS process is generated, and is, for example, an integer multiple of the unit area. The reason why the correction target value generation area 220 is larger than the unit area is that the nozzle variations in the chips 202 and 204 have high frequency components. The detection of the print density and the calculation of the correction value used in the HS process are performed to correct the nozzle variations in the chip, and therefore need to be performed in a small area of ​​several nozzles. In contrast, the calculation of the correction target value is performed because it corresponds to low frequency variations such as variations between chips.

[0057] The corrected target value generation area 220 and the unit area are each set to a size suitable for the configuration of the recording system 10. The corrected target value generation area 220 is, for example, about several mm to a dozen mm. The unit area is, for example, about 0.1 mm, which corresponds to the size of several nozzles. The size of these areas may be set larger or smaller depending on the calculation speed of the host PC 200, etc.

[0058] Next, the main control unit 322 sets a predetermined correction target value for each correction target value generation area 220 (S804). Then, in each correction target value generation area 220, the correction amount (see FIG. 9) when HS processing is performed using the predetermined correction target value is calculated (S806). The predetermined correction target value is a value stored in a storage area of ​​the host PC 200. In S804, the same predetermined correction target value is set for all of the correction target value generation areas 220. Note that in S804, the predetermined correction target value may be set individually for each correction target value generation area 220. In addition, in S806, the correction amount when HS processing is performed using the predetermined correction target value is calculated. That is, in S806, the difference between the recording density in each correction target value generation area 220 and the predetermined correction target value is calculated. The recording density in each correction target value generation area 220 is the recording density obtained from the read value by the scanner 106 of the recorded test pattern. In other words, it is the recording density obtained from the value read in S604.

[0059] After that, the main control unit 322 acquires the amount of change in recording density due to the HS process for each correction target value generation region 220 (S808). Then, the acquired amount of change is compared with a preset threshold value F, and it is determined whether the amount of change is equal to or less than the threshold value F in each correction target value generation region 220 (S810). In S808, the amount of change is set to the correction amount calculated in S806, that is, the number of dots according to the difference in density value before and after the HS process. The threshold value F as the first threshold value is set to a value that is a predetermined amount smaller than the lower limit of the difference in the number of dots at which the difference in the dot pattern is visually recognized as unevenness. In other words, the threshold value F is the upper limit of the amount of change in the number of dots at which the difference in the dot pattern is not visually recognized as unevenness. The predetermined amount can be appropriately changed according to, for example, the type of ink, the type of recording medium, etc.

[0060] In S810, if it is determined that the amount of change is equal to or less than the threshold F in each correction target value generation area 220, the process proceeds to S612 while leaving the predetermined correction target value as the correction target value for generating the correction value. Also, in S810, if it is determined that the amount of change is not equal to or less than the threshold F in each correction target value generation area, that is, if there is a correction target value generation area in which the amount of change is greater than the threshold F, the main control unit 322 performs an update process to update the correction target value (S812). Then, when the update process ends, the process proceeds to S612. That is, in the determination process of S810, if the amount of change is equal to or less than the threshold F in all correction target value generation areas 220, the process proceeds to S612 without going through S812. On the other hand, in the determination process of S810, if there is even one correction target value generation area 220 in which the amount of change is greater than the threshold F, the process proceeds to S812.

[0061] Here, a case where there is a correction target value generation area 220 in which the amount of change is equal to or greater than the threshold value F will be described. FIG. 9 is a diagram showing an area in the vicinity of the correction target value generation area in which the amount of change is greater than the threshold value F. In FIG. 9, areas 1 to 5 indicate the correction target value generation areas 220 arranged in the X direction, and the thick solid lines parallel to the X direction indicate the recording density recorded by the nozzles 210 corresponding to the correction target value generation areas 220. The recording density is calculated from the read value by the scanner 106 in S402. Also, although only area 1 is shown in FIG. 9, multiple nozzles correspond to each area, and there is variation in the ejection amount for each nozzle. The illustrated recording density is the average of the variation in the ejection amount for each nozzle in the area. The dashed lines extending in the X direction indicate a predetermined correction target value.

[0062] In FIG. 9, the ejection amount from the corresponding nozzles 210 in the regions 1, 2, 4, and 5 is almost equal, and the print densities are almost the same. On the other hand, in the region 3, the ejection amount from the corresponding nozzles 210 is large, and the print densities are higher than those in the other regions. The print densities in the regions 1, 2, 4, and 5 are almost equal to the predetermined correction target value, and the correction amount during the HS process, that is, the increase or decrease in the number of dots, is small. On the other hand, the print density in the region 3 is much larger than the predetermined correction target value, and if it is to be adjusted to the predetermined correction target value, the number of dots needs to be significantly reduced. In this case, the difference in the dot pattern exceeds the threshold F, which is the upper limit of the change in the number of dots that is not visually recognized as unevenness. Therefore, when the region 3 is corrected to match the predetermined correction target value, the difference in the number of dots between the region 3 and the regions 2 and 4 adjacent to the region 3 becomes large, and unevenness in the spatial frequency occurs in these regions. On the other hand, if the correction amount for the region 3 is set to be equal to or less than the threshold F, the density difference between the region 3 and the regions 2 and 4 is not eliminated, and unevenness in density occurs in these regions.

[0063] Therefore, in this embodiment, when there is a correction target value generation region in which the change amount exceeds the threshold F, the correction target value is updated for a plurality of regions centered on the correction target value generation region so that the change amount between adjacent regions is equal to or less than the threshold F. That is, in this embodiment, in the update process of S812, the update of the correction target value is considered for a plurality of regions including the correction target value generation region in which the correction target value needs to be changed, and the correction target value is updated according to the result. The update process of S812 will be described in detail below with reference to FIG. 10. FIG. 10 is a flowchart showing the processing routine of the update process, which is a subroutine of the correction target value generation process.

[0064] When the update process is started, first, the main control unit 322 determines an attention area in the correction target value generation area 220 in which the correction target value is to be updated (S1002). In S1002, the correction target value generation area 220 in which it is determined that the amount of change has exceeded the threshold value F in the comparison in S810 is determined as the attention area. For example, in FIG. 9, area 3 is determined as the attention area. In the following description, for ease of understanding, a case in which one correction target value generation area is determined as the attention area will be described. Note that, when there are multiple correction target value generation areas 220 in which it is determined that the amount of change has exceeded the threshold value F, all of the correction target value generation areas 220 are set as attention areas and the following process is executed.

[0065] Next, the main control unit 322 updates the correction target value of the attention area from the predetermined correction target value to a new correction target value (S1004). That is, in S1004, a first update is performed to update the first set correction target value, which is the predetermined correction target value set in the attention area. In S1004, the predetermined correction target value is the recording density side, and a density value at which the difference in the number of dots when recording with the recording density is equal to or less than a threshold F is set as a first updated correction target value, which is a new correction target value. The amount of change from the recording density to the new correction target value (first updated correction target value) may be a value that varies according to the difference between the recording density and the number of dots when recording with the new correction target value and is equal to or less than the threshold F, and may be, for example, a fixed value that is set in advance. Note that the amount of change may be a variable value that varies according to the difference from the predetermined correction target value of the recording density of the attention area.

[0066] Here, the recording density values ​​and the correction target values ​​of the areas near the attention area will be described. FIG. 11(a) is a diagram showing the recording densities in areas 1 to 5, which are the correction target value generation area 220, as in FIG. 9. FIG. 11(b) is a diagram showing the correction target values ​​updated in S1004. In FIG. 11(a), only the area 3 has a high recording density, and the difference in the number of dots when adjusted to a predetermined correction target value exceeds the threshold value F, so the area 3 is set as the attention area in S1002. Then, in S1004, the correction target value of the area 3 is updated from the predetermined correction target value to a new correction target value 1102, as shown in FIG. 11(b). The correction target value 1102 is a correction target value used when acquiring a correction value used in the HS process for the recording density 1104 in the area 3. Therefore, the area 3 is printed at the recording density of the correction target value 1102 by the HS process. Because HS processing changes the print density from 1104 to the print density of the corrected target value 1102, the print density of the corrected target value 1102 is a density value obtained by reducing the number of dots from the print density 1104 by a predetermined number that is equal to or less than the threshold value F.

[0067] Meanwhile, in the area 2 adjacent to the area 3 which is the area of ​​interest, the print density is equivalent to the predetermined correction target value. Note that the amount of change in the area 2 is determined to be equal to or less than the threshold value F in S810, so the area 2 is not set as the area of ​​interest in S1002, and the correction target value is not updated in S1004. However, if there is a density difference between the predetermined correction target value in the area 2 and the correction target value 1102 in the area 3, in which the difference in the number of dots exceeds the threshold value F, and the color difference exceeds the allowable color difference threshold value Fc, dot pattern difference unevenness, density unevenness, and color unevenness will occur in the print after the HS process. The allowable color difference threshold value Fc will be described later. Note that the same applies to the area 4 adjacent to the area 3.

[0068] In order to suppress the occurrence of such unevenness, in this embodiment, it is considered whether or not to update the correction target value of the area adjacent to the area where the correction target value has been updated. That is, after updating the correction target value of the attention area in S1004, the main control unit 322 next determines the area adjacent to the update area where the correction target value has been updated and where the correction target value has not yet been updated as the target area (S1006). After that, the main control unit 322 compares the correction target value of the update area with the correction target value of the target area (S1008). Then, the main control unit 322 determines whether the difference in the number of dots between the correction target value of the update area and the correction target value of the target area is equal to or less than the threshold F and the color difference is equal to or less than the allowable color difference threshold Fc (S1010).

[0069] When the update region is the region of interest (see FIG. 11(b)), in S1006, regions 2 and 4, which are adjacent to region 3 as the update region and for which the correction target value has not yet been updated, are determined as the target regions. Then, in S1008, the correction target value 1102 of region 3 is compared with a predetermined correction target value in region 2 as the target region and a predetermined correction target value in region 4 as the target region. The case where the update region is not the region of interest, i.e. region 3, will be described later. Note that in S1006, the region whose correction target value has been most recently updated is determined as the update region.

[0070] In S1010, if it is determined that the difference in the number of dots between the correction target value of the update area and the correction target value of the target area is equal to or less than the threshold F and the color difference is equal to or less than the allowable color difference threshold Fc, the update process ends and the correction target value generation process ends. Also, if it is determined in S1010 that the difference in the number of dots between the correction target value of the update process and the correction target value of the target area is not equal to or less than the threshold F and the color difference is not equal to or less than the allowable color difference threshold Fc, the process proceeds to S1012.

[0071] In S1012, the main control unit 322 updates the correction target value of the target area to a new correction target value. That is, in S1012, a second update is performed to update the second set correction target value, which is a predetermined correction target value set in the target area. The second updated correction target value, which is the new correction target value of the target area, is located on the predetermined correction target value side (second set correction target value side) than the correction target value of the updated area. Then, a density value is set such that the difference in the number of dots when printed is equal to or less than the threshold value F and the color difference is equal to or less than the allowable color difference threshold value Fc, relative to the correction target value of the updated area.

[0072] For example, in the case of FIG. 11B, in S1012, the correction target values ​​of the region 2 and the region 4 are updated. FIG. 12A is a diagram showing new correction target values ​​of the target region. In this case, in S1012, a density value on the predetermined correction target value side in the region 2, where the difference in the number of dots with respect to the correction target value 1102 is equal to or less than the threshold F and the color difference is equal to or less than the allowable color difference threshold Fc, is set as a new correction target value 1202. Then, the correction target value of the region 2 is updated from the predetermined correction target value to the correction target value 1202. Also, in the region 4, a density value on the predetermined correction target value side, where the difference in the number of dots with respect to the correction target value 1102 is equal to or less than the threshold F and the color difference is equal to or less than the allowable color difference threshold Fc, is set as a new correction target value 1204. Then, the correction target value of the region 4 is updated from the predetermined correction target value to the correction target value 1204.

[0073] In S1010, if it is determined that the difference between the correction target value of all the target regions and the correction target value of the update region is equal to or less than the threshold F in dot count and the color difference is equal to or less than the allowable color difference threshold Fc, the update process ends. On the other hand, if it is determined that the difference between the correction target value of any one of the target regions and the correction target value of the update region is not equal to or less than the threshold F in dot count and the color difference is not equal to or less than the allowable color difference threshold Fc, the process proceeds to S1012.

[0074] Then, the process proceeds to S1006 and the subsequent processes are performed. Specifically, as shown in FIG. 12(a), immediately after updating the correction target values ​​of regions 2 and 4, regions 2 and 4 become update regions in S1006, and regions 1 and 5, which are adjacent to regions 2 and 4 and have not yet updated their correction target values, are determined as target regions. In other words, region 3, whose correction target value has already been updated, is excluded from the target region. Then, in S1008, the correction target value 1202 of region 2 is compared with a predetermined correction target value in region 1, which is the target region, and the correction target value 1204 of region 4 is compared with a predetermined correction target value in region 5, which is the target region. Then, the processes from S1010 onwards are performed.

[0075] Fig. 12(b) corresponds to Fig. 12(a) and shows the distribution of correction target values ​​updated by update processing for each region. In Fig. 12(b), the correction target values ​​have been updated for regions 2, 3, and 4. The difference between the updated correction target value and the correction target value in the adjacent region is such that the difference in dot count is equal to or less than the threshold value F, and the color difference is equal to or less than the allowable color difference threshold value Fc. Therefore, by performing HS processing using the correction value calculated according to the updated correction target value, the occurrence of density unevenness, color unevenness, and spatial frequency unevenness due to dot pattern differences in the recording result is suppressed.

[0076] The allowable color difference threshold Fc as the second threshold will now be described. The human eye is more likely to detect color differences between adjacent regions, but less likely to detect color differences between regions that are far apart. Generally, the allowable color difference is ranked as shown in FIG. 13. FIG. 13 is a table showing the range of color difference ΔE and the degree of perceived color difference according to the rank of the allowable color difference. Color difference ΔE is expressed as the CIE-L * a * b * It is calculated according to a well-known formula.

[0077] According to the ranks in Fig. 13, at AA tolerance, slight color difference is perceived in adjacent comparison, and at the next higher rank, AAA tolerance, stricter allowable color difference standards can be set. Therefore, for a color difference to be equal to or less than the allowable color difference threshold Fc, it is preferable that the color difference ΔE is equal to or less than 0.8, which is the upper limit of the AAA tolerance. In other words, by setting the color difference due to the correction target value to 0.8 or less between areas 1 and 2, between areas 2 and 3, between areas 3 and 4, and between areas 4 and 5, the color difference between adjacent areas will not be noticeable, and color unevenness will not be noticeable.

[0078] In the update process, new correction target values ​​are obtained for adjacent regions based on conditions including the allowable color difference threshold Fc, but the present invention is not limited to this. For example, allowable color difference thresholds may also be set for correction target values ​​of regions separated from each other, such as region 1 and region 3. For example, in the rank of FIG. 13, the A-class tolerance is a level that is almost unnoticeable in a distance comparison. Therefore, when updating the correction target value of the target region, the correction target value is updated to a correction target value that takes into account the correction target value of the separated region and has a color difference with the correction target value that is equal to or less than the third threshold. For example, the color difference equal to or less than the third threshold is set to a color difference ΔE of 3.2 or less, which is the A-class tolerance, from the table of FIG. 13.

[0079] Returning to FIG. 6, after generating the correction target values ​​in each correction target value generation area in S610, the main control unit 322 then generates a correction value to be used in HS processing for each unit area according to the correction target value (S612), and ends the generation process as the correction value generation process. In S612, for the correction target value of the unit area, the correction target value set in the correction target value generation area 220 including the unit area is used. The generated correction value becomes a correction value for correcting the ink color signal value in order to obtain an HS color signal value that matches the correction target value in the HS process in S508. In other words, this correction value is a value for matching the color and density when printed based on the print data obtained by image processing to the correction target value.

[0080] FIG. 14(a) is a diagram showing a gradation characteristic 704. FIG. 14(b) is a diagram showing an example of a one-dimensional LUT which is a correction value used in HS processing. Here, it is assumed that a correction target value to be recorded at an input gradation value P4 is P6. Then, it is assumed that a gradation characteristic 704 is estimated in S608 as a gradation characteristic of a unit area for determining a correction value. In this gradation characteristic 704, since the recording density recorded at the input gradation value P4 is P5, it is necessary to convert it so that it is recorded at the recording density P6. Specifically, a correction value is generated which determines the relationship of an output gradation value to an input gradation value such that the input gradation value P4 is converted to an input gradation value P7 which gives the recording density P6 which is a correction target value. That is, in this case, in S612, a one-dimensional LUT which is a conversion table which converts the input gradation value P4 to the output gradation value P7 is generated as a correction value as shown in FIG. 14(b).

[0081] As described above, in the host PC 200, when the difference in the number of dots during printing between the printing density based on the read value of the test pattern and the set correction target value exceeds the threshold value F, the host PC 200 updates the correction target value. The new correction target value to be updated is compared with the correction target value before the update so that the difference in the number of dots is equal to or less than the threshold value F.

[0082] Moreover, the correction target values ​​of the update area, which is adjacent to the update area where the correction target value has been updated, and which has not yet been updated, are treated as target areas, and the correction target values ​​of the update area and the target area are compared. Then, when either one of the conditions that the difference in the number of dots between the compared correction target values ​​exceeds a threshold F or the color difference exceeds an allowable color difference threshold Fc is satisfied, the correction target value of the target area is updated. The difference in the number of dots between the correction target value of the updated update area and the correction target value of the updated target area is equal to or smaller than the threshold, and the color difference is equal to or smaller than the allowable color difference threshold.

[0083] In conventional HS correction technology, the amount of correction for each correction region does not depend on the density value of other regions, and the amount of correction for regions that have density values ​​close to the correction target value before correction is small, and in some cases, no correction is performed at all. In the present invention, the amount of correction for a region of interest is determined depending on the density value of the region of interest and the density value of another region different from the region of interest. Therefore, even regions that have density values ​​that do not require much correction are subject to correction.

[0084] As a result, in the print results printed based on the print data generated in the image processing, it is possible to suppress the occurrence of uneven density and color caused by the nozzle ejection characteristics, as well as uneven spatial frequency caused by HS processing. Also, by updating the correction target value as described above, the occurrence of unevenness is suppressed, and the above unevenness can be suppressed regardless of the configuration of the print head.

[0085] (Other embodiments) The above embodiment may be modified as shown in (1) to (6) below.

[0086] (1) Although not specifically described in the above embodiment, in S1002 of the update process, if there are multiple correction target value generation areas 220 in which it is determined that the change amount has exceeded the threshold value F, for example, the area whose print density is the furthest from the correction target value is set as the attention area. Then, after the update of the correction target value in the attention area and the target area corresponding to the attention area is completed, the area whose print density is the next furthest from the correction target value and whose correction target value has not yet been updated is set as the attention area. This makes it possible to efficiently update the correction target value in the correction target value generation area. Note that the method of determining the attention area is not limited to this, and a method of processing and optimizing many combinations based on the print density, threshold value F, and allowable color difference threshold value Fc in all areas may also be used.

[0087] (2) Although not specifically mentioned in the above embodiment, the threshold value F and the allowable color difference threshold value Fc may be changed depending on conditions such as ink color and input tone value, or may be constant regardless of the above conditions. For example, even if the color difference is the same when measured, there are colors whose color difference is easily detected by the human eye and colors whose color difference is difficult to detect. Therefore, the threshold value F and the allowable color difference threshold value Fc may be changed depending on the ink color and input tone value based on the ease of detection by the human eye.

[0088] In general, the human eye has difficulty perceiving color differences in colors with high brightness and saturation. For this reason, the allowable color difference threshold Fc can be increased for colors with high brightness and saturation. Examples of colors for which the allowable color difference threshold Fc can be increased include light gradations close to white and bright colors such as yellow. Alternatively, in the case of cyan or magenta, the high gradation areas where a large amount of ink is applied have higher saturation than the low gradation areas, making it difficult for the human eye to perceive color differences, so the allowable color difference threshold Fc can be increased.

[0089] The threshold value F also differs depending on the recording conditions and ink color, depending on whether the density unevenness is easily detected by the human eye. Therefore, the threshold value F may be set to be different depending on the recording conditions and ink color. For example, in the case of low gradation where there are almost no dots, even if the number of dots changes slightly, the pattern difference cannot be detected. In addition, in the case of high gradation where there are many dots, since there is no non-printed area where the dot pattern is visible, even if the number of dots changes slightly, the dot pattern difference cannot be detected. In addition, when a recording medium with large bleeding such as plain paper is used, the dot pattern is less noticeable than when a recording medium with small bleeding such as glossy paper is used. Therefore, the threshold value F may be set to be large for the characteristics, gradation, and color of the recording medium where the dot pattern is less noticeable.

[0090] (3) In the above embodiment, the correction target value is determined in each of the correction target value generation regions 220 based on the ejection characteristics of the nozzles 210 constituting the recording head 102, but this is not limited to the above. The unevenness may be caused by the transport characteristics of the recording medium, that is, the operational variations of the transport roller and the transport motor, and the characteristics of the recording medium, that is, the waviness of the recording medium M caused by the application of ink, so-called cockling, etc. In other words, in the image formed on the recording medium, not only the density unevenness caused by the variation in the ejection characteristics of the nozzles, but also the density unevenness caused by the operational variations due to the eccentricity of the transport roller generated in the Y direction, for example, occurs. In addition, the density unevenness occurs due to the cockling caused by the recording medium absorbing moisture and the shrinkage of paper fibers. Therefore, the correction target value may be determined according to the above-mentioned operational variations and cockling.

[0091] In this case, the entire recording area 1502 is divided in the X direction and the Y direction to create a correction target value generation area 1504 (see FIG. 15). FIG. 15 is a diagram showing a modified example of the correction target value generation area. Then, the generation process is performed in the same manner as in the above embodiment, but in the update process, an area adjacent to the update area in the X direction and an area adjacent to the update area in the Y direction are set as target areas.

[0092] (4) In the above embodiment, the host PC 200 as an image processing device performs image processing including HS processing on image data to generate print data, and generates correction values ​​to be used in the HS processing according to variations in print characteristics including ink ejection characteristics. However, the functions of such an image processing device may be configured by a plurality of devices including the host PC 200. For example, the image processing device according to this embodiment only needs to have a function to generate correction target values ​​for acquiring correction values ​​to be used in the HS processing, and all or part of the other components may be realized by other devices. In addition, the recording device 100 and the host PC 200 are provided separately, but this is not limited thereto, and the recording device 100 may have various functions as an image processing device of the host PC 200.

[0093] (5) In the above embodiment, the correction target value generation area 220 is an integer multiple of the unit area, but this is not limiting, and the correction target value generation area 220 does not have to be an integer multiple of the unit area. In this case, a unit area is generated that is located at a boundary position where two correction target value generation areas 220 overlap. For this unit area, a correction target value is set based on the correction target values ​​set in the two correction target value generation areas and the ratio of each correction target value generation area in the unit area.

[0094] (6) The above embodiment and the various forms shown in (1) to (5) may be combined as appropriate. The present invention can also be realized by supplying a program that realizes one or more functions of the above embodiment to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0095] 200 host PCs 322 Main control unit

Claims

1. an acquisition means for acquiring a recording density according to recording characteristics in a unit area corresponding to one or more nozzles that eject ink; a correction target value generating means for generating a correction target value, which is a target density value when generating a correction value used in a head shading process, in accordance with the recording density acquired by the acquiring means, The correction target value generating means performing a first update for updating the first set correction target value in accordance with a difference between a first set correction target value set in a correction target value generation area including the unit area and a recording density by the unit area corresponding to the correction target value generation area; performing a second update to update the second set correction target value according to a difference between a second set correction target value that is set in the correction target value generation region that is adjacent to an update region that is the correction target value generation region in which the correction target value has been updated and that has not yet updated the correction target value, and a first updated correction target value that is the updated correction target value in the update region; In the first update, when a difference in the number of dots during printing between the first set correction target value and a printing density by the unit area corresponding to the correction target value generation area in which the first set correction target value is set exceeds a first threshold value, the first set correction target value is updated to a first updated correction target value on the printing density side, the difference in the number of dots from the printing density being equal to or less than the first threshold value.

2. 2. The image processing device according to claim 1, wherein when there are a plurality of correction target value generation areas in which the difference between the number of dots based on the first set correction target value and the number of dots based on the recording density by the unit area corresponding to the correction target value generation area in which the first set correction target value is set exceeds the first threshold value, the correction target value generation means updates the correction target value starting from the correction target value generation area in which the difference is largest.

3. 3. The image processing device according to claim 1, wherein, in the second update, when at least one of a condition that a difference in the number of dots at the time of recording between the first update correction target value and the second set correction target value exceeds the first threshold and a condition that a color difference exceeds a second threshold is satisfied, the second set correction target value is updated to a second update correction target value that is on the second set correction target value side of the first update correction target value, the difference in the number of dots from the first update correction target value is equal to or less than the first threshold, and the color difference from the first update correction target value is equal to or less than the second threshold.

4. 4. The image processing apparatus according to claim 3, wherein the second threshold value is a color difference ΔE of 0.

8.

5. 5 . The image processing apparatus according to claim 3 , wherein the correction target value generation means acquires the second updated correction target value so that a color difference between the correction target value generation regions spaced apart from each other is equal to or smaller than a third threshold value.

6. 6. The image processing apparatus according to claim 5, wherein the third threshold value is a color difference ΔE of 3.

2.

7. 7. The image processing apparatus according to claim 1, wherein the first threshold value varies depending on a tone value, an ink color, and characteristics of a recording medium.

8. 7. The image processing apparatus according to claim 3, wherein the second threshold value varies depending on the lightness, saturation, and tone value of the ink.

9. 9. The image processing apparatus according to claim 1, wherein the printing characteristics include ink ejection characteristics of each nozzle, transport characteristics of the printing medium, and characteristics of the printing medium.

10. 10. The image processing apparatus according to claim 1, wherein the correction target value generation area is divided in a direction in which nozzle rows are arranged, or in the direction and a direction intersecting the direction.

11. 11. The image processing device according to claim 1, wherein the correction target value generation area is larger than the unit area and corresponds to a plurality of nozzles arranged consecutively with regularity in a predetermined direction.

12. 12. The image processing apparatus according to claim 1, further comprising a correction value generating unit configured to generate the correction value for each unit area based on the correction target value in the correction target value generating area.

13. The method further includes a print data generating unit that generates print data representing whether or not to eject ink from the nozzles onto the pixels based on the image data, 13. The image processing device according to claim 1, wherein, when generating the recording data, the recording data generating means performs head shading processing using the correction value generated based on the correction target value generated by the correction target value generating means.

14. 14. The image processing apparatus according to claim 1, further comprising a recording unit that performs recording by ejecting ink from a nozzle.

15. 15. The image processing apparatus according to claim 14, further comprising a reading means capable of reading the image recorded by the recording means.

16. An image processing method for generating a correction target value, which is a target density value when generating a correction value used in head shading processing, based on a recording density in accordance with a recording characteristic in a unit area corresponding to one or more nozzles that eject ink, comprising: a first step of updating the first set correction target value in accordance with a difference between a first set correction target value set in a correction target value generation area including the unit area and a recording density by the unit area corresponding to the correction target value generation area; a second step of updating the second set correction target value in accordance with a difference between a second set correction target value set in the correction target value generation region adjacent to an update region that is the correction target value generation region in which the correction target value has been updated and in which the correction target value has not yet been updated, and a first updated correction target value that is the correction target value updated in the update region, an image processing method characterized in that, in the first step, when a difference in the number of dots during printing between the first set correction target value and a printing density by the unit area corresponding to the correction target value generation area in which the first set correction target value is set exceeds a first threshold value, the first set correction target value is updated to a first updated correction target value which is on the printing density side and in which the difference in the number of dots from the printing density is equal to or less than the first threshold value.

17. A program for causing a computer to function as the image processing device according to any one of claims 1 to 13.

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