Image processing method and image processing device

Abstract

To record a high-quality image with durability against recording misregistration.SOLUTION: An image processing device 1 generates quantization data for superimposing and recording a first dot pattern 101 and a second dot pattern 102 on a recording medium. The first dot pattern 101 and the second dot pattern 102 are lattice patterns whose combinations of two basis vectors are different from each other. There are superposition dots 104 and proximate dots 105 in which dots of the first dot pattern 101 and dots of the second dot pattern 102 are arranged with a distance smaller than a distance between lattices, in a combined dot pattern 100 in which the lattice patterns are combined. The proximate dots 105 include a plurality of proximate dots whose approaching directions are different.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image processing method and an image processing device. [Background technology]

[0002] In a printing device that prints an image by relative movement between a print head and a print medium, the print position deviation that accompanies this relative movement can cause noticeable graininess and density unevenness in the image. For example, when multi-pass printing is performed with a serial inkjet printing device, if print position deviation occurs in any print scan, the relative deviation of dot groups printed in different print scans can affect the dispersibility of the dots, which can be perceived as graininess or density unevenness.

[0003] Patent Document 1 discloses a method for suppressing density unevenness caused by misalignment between scans in multi-pass printing by controlling the frequency with which dots printed in one scan and dots printed in another scan are adjacent in the scanning direction.

[0004] Furthermore, Patent Document 2 discloses a method for creating threshold matrices for each of the first and second printing scans, which stabilizes the dot coverage on the printing medium even if a printing position shift occurs between the first and second printing scans. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-35886 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-113819 [Patent Document 3] U.S. Patent No. 6,867,884 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the configuration of Patent Document 1 is effective when the dots printed in one scan and the dots printed in the other scan are misaligned in the scanning direction of the print head, but is not effective when they are misaligned in the sub-scanning direction.Furthermore, the configuration of Patent Document 2 can suppress changes in density unevenness and graininess, but the issue of graininess that originally existed in the image remains.

[0007] The present invention is intended to solve the above problems, and its purpose is to print high-quality images without noticeable graininess or density unevenness, even when printing position deviation occurs due to relative movement between the print head and the print medium. [Means for solving the problem]

[0008] To this end, the present invention provides a method for obtaining gradation data corresponding to a predetermined gradation value, and Recorded by forward scanning of the recording means first data corresponding to a first dot pattern; Recorded by the backward scanning of the recording means, andand generating second data corresponding to a second dot pattern to be recorded on a recording medium so as to be superimposed on the first dot pattern, wherein the first dot pattern includes a first grid formed of dots repeatedly arranged at a first interval in a first direction and dots repeatedly arranged at a second interval in a second direction, and the second dot pattern includes a second grid formed of dots repeatedly arranged at a third interval in a third direction and dots repeatedly arranged at a fourth interval in a fourth direction, and the first dot pattern is recorded at a first relative position where the center of one dot included in the second dot pattern overlaps the center of one dot included in the first dot pattern. The composite dot pattern obtained by combining the first dot pattern and the second dot pattern includes (i) a first adjacent dot in which a first dot included in the first dot pattern and a second dot included in the second dot pattern are adjacent at a distance shorter than any of the first, second, third, and fourth intervals, and (ii) a second adjacent dot in which a third dot included in the first dot pattern and a fourth dot included in the second dot pattern are adjacent at a distance shorter than any of the first, second, third, and fourth intervals, and is characterized in that a first slope of a line connecting the centers of each of the first adjacent dots is different from a second slope of a line connecting the centers of each of the second adjacent dots. [Effects of the Invention]

[0009] According to the present invention, even if a recording position shift occurs due to the relative movement between the recording head and the recording medium, it is possible to record a high-quality image without making graininess or density unevenness noticeable. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a diagram showing an example of a robust pattern. [Figure 2] FIG. 10 is a diagram showing a state in which the first and second dot patterns are shifted. [Figure 3] 10A and 10B are diagrams illustrating the reproduction of a shift and translationally symmetric dot pattern. [Figure 4]10A and 10B are diagrams showing deviations within a reproduction period of a translationally symmetric dot pattern. [Figure 5] FIG. [Figure 6] 10A and 10B are diagrams showing changes in the coverage area due to separation of overlapping dots. [Figure 7] FIG. 10 is a diagram showing the separation of overlapping dots and the overlapping of adjacent dots in parallel. [Figure 8] FIG. 10 is a diagram illustrating a counterexample to the second condition for realizing a robust pattern. [Figure 9] FIG. 10 is a diagram illustrating a counterexample to the second condition for realizing a robust pattern. [Figure 10] FIG. 10 is a diagram illustrating a counterexample to the third condition for realizing a robust pattern. [Figure 11] FIG. 2 is a diagram illustrating the configuration of a recording apparatus. [Figure 12] FIG. 2 is a diagram illustrating a recording head. [Figure 13] FIG. 1 is a block diagram showing the configuration of a recording system. [Figure 14] 4 is a flowchart of image processing in the first embodiment. [Figure 15] FIG. 10 is an explanatory diagram of bidirectional multi-pass printing. [Figure 16] FIG. 1 is a functional block diagram for implementing quantization processing. [Figure 17] FIG. 10 is a diagram showing an example of a threshold matrix. [Figure 18] 10A and 10B are diagrams showing the results of quantization processing corresponding to different gradation values. [Figure 19] FIG. 10 is a diagram showing a dot pattern resulting from a quantization process. [Figure 20] FIG. 10 is a diagram showing the results of quantization processing in the second embodiment. [Figure 21] FIG. 10 is a diagram showing a dot pattern according to the result of quantization processing in the second embodiment. [Figure 22] FIG. 10 is a schematic diagram of a recording head used in a third embodiment. [Figure 23] 10 is a flowchart of image processing in the third embodiment. [Figure 24] 4A and 4B are diagrams showing dot arrangement patterns and reference index patterns. [Figure 25] FIG. 10 is a diagram for explaining a time-division driving method. [Figure 26] FIG. 10 is a diagram for explaining drive control in the third embodiment. [Figure 27] 10A and 10B are diagrams for explaining shifting of drive timing in reciprocating scanning. [Figure 28] A diagram explaining column shifting of a raster group. [Figure 29] FIG. 10 is a diagram showing a grating pattern realized in the third embodiment. [Figure 30] FIG. 1 is a diagram showing an index pattern and binary data. [Figure 31] FIG. 10 is a diagram showing a method for creating an index pattern. [Figure 32] FIG. 11 is a diagram showing a threshold matrix used in the third embodiment. [Figure 33] FIG. 10 is a diagram showing a robust pattern realized in the third embodiment. [Figure 34] FIG. 10 is a diagram showing a threshold matrix used in a low gradation region. [Figure 35] FIG. 10 is a diagram showing a dot pattern formed in a low gradation region. [Figure 36] 10 is a flowchart of image processing in the fourth embodiment. [Figure 37] 10A and 10B are diagrams showing dot arrangement patterns and index patterns according to a fourth embodiment. [Figure 38] FIG. 3 is a diagram showing a mask pattern used in mask processing. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Features of Robust Patterns> First, a robust pattern that can be commonly adopted in the embodiments of the present invention will be described. In this specification, a robust pattern is a dot pattern formed when two sets of dot patterns are printed in a predetermined pixel area, and has the characteristic that the dot coverage and graininess in the pixel area do not change significantly even if the two sets of dot patterns are misaligned relative to each other. Note that coverage refers to the ratio of the area covered by dots to the printing medium.

[0012] FIG. 1 is a diagram showing an example of a robust pattern. Here, dots with a diameter of 42 μm are selectively arranged at pixel positions arranged at 1200 dpi in the XY plane. The figure shows how a robust pattern 100 is formed by overlapping a first dot pattern 101 consisting of a group of first dots with a second dot pattern 102 consisting of a group of second dots. While only a portion of the pattern is shown here, each pattern is assumed to be repeatedly arranged in the XY directions.

[0013] <1 pixel deviation> 2 is a diagram showing a state in which the second dot pattern 102 is shifted by one pixel with respect to the first dot pattern 101. The center shows a state in which there is no shift, and is equivalent to the robust pattern 100 in Fig. 1. The surrounding patterns show a state in which the second dot pattern 202 is shifted by one pixel (21 μm) with respect to the first dot pattern 101 in each of the eight directions on the XY plane.

[0014] It can be seen that a similar repeating pattern 200 appears in each dot pattern. Furthermore, although the positions at which the repeating patterns 200 appear differ from one another, these nine patterns are essentially the same dot pattern, with the same repeating patterns 200 laid out vertically and horizontally. In such a case, even if the second dot pattern 102 is further shifted by one pixel in the same direction for each of the eight surrounding patterns, a pattern in which the repeating patterns 200 are laid out vertically and horizontally can be obtained, as described above.

[0015] Thus, the robust pattern 100 has the characteristic that even if the first dot pattern 101 and the second dot pattern 102 are misaligned relative to each other, the same dot pattern can be obtained regardless of the amount or direction of the misalignment. Hereinafter, the characteristic that a pattern in which the same repeating pattern 200 is arranged at different phases can be obtained even if the first dot pattern 101 and the second dot pattern 102 are misaligned relative to each other in the X and Y directions will be referred to as "translational symmetry." The minimum amount of misalignment at which the "translational symmetry" is reproduced will be referred to as the "translational symmetry reproduction period." In the robust pattern described with reference to FIGS. 1 to 3, one pixel (21 μm) at 1200 dpi is the "translational symmetry reproduction period."

[0016] 3(a) and (b) are diagrams for explaining the mechanism by which translational symmetry is obtained in a robust pattern.

[0017] 3(a) shows a state in which there is no misalignment between the first dot pattern 101 and the second dot pattern 102. The dot pattern in FIG. 3(a) includes overlapping dots 301, in which the first dots constituting the first dot pattern 101 and the second dots constituting the second dot pattern 102 overlap. It also includes adjacent dots 302-305, in which the first dots and second dots partially overlap, and single dots that do not overlap with other dots. In the figure, a reference line passing through the center of the overlapping dot 301 is indicated by a dashed line.

[0018] Focusing on any superimposed dot 301, it can be seen that the arrangement of the first dots and second dots around it is in a point-symmetric relationship with respect to the superimposed dot 301. For example, in the figure, adjacent dot 302, which is made up of a first dot on the left and a second dot on the right, is arranged in a position that is point-symmetric with respect to the superimposed dot 301, adjacent dot 303, which is made up of the second dot on the left and the first dot on the right. Furthermore, adjacent dot 304, which is made up of a first dot above and a second dot below, is arranged in a position that is point-symmetric with respect to the superimposed dot 301, adjacent dot 305, which is made up of the second dot above and the first dot below.

[0019] Figure 3(b) shows the state in which the second dot pattern 102 is shifted by one pixel (21 μm) in the +X direction with respect to the first dot pattern 101. In Figure 3(b), the overlapping dot 301 in Figure 3(a) changes to a nearby dot 302 made up of a first dot on the left and a second dot on the right. Also, the nearby dot 303 made up of a second dot on the left and a first dot on the right in Figure 3(a) changes to the overlapping dot 301 in Figure 3(b).

[0020] Comparing the two figures, the positions of the superimposed dots 301 in Figure 3(a) and the positions of the superimposed dots 301 in Figure 3(b) differ, but the number and period of the superimposed dots 301, i.e., the number and period of the reference lines, do not change. Furthermore, the layout of the first dots and second dots in the repeating pattern 200 surrounded by the reference lines also does not change. In other words, even if a shift of one pixel unit, i.e., a translationally symmetric reproduction period unit, occurs between the first dot pattern 101 and the second dot pattern 102, the dot coverage in the repeating pattern 200 does not increase or decrease.

[0021] <Deviation less than the translationally symmetric recurrence period> 4(a) and (b) are diagrams for explaining the influence of a misalignment of less than one pixel (21 μm) between the first dot pattern 101 and the second dot pattern 102. FIG. 4(a) is a diagram conveniently showing the unit of misalignment of less than one pixel. One pixel at 1200 dpi is further divided into 8 × 8 at 9600 dpi. At 9600 dpi, the spacing between each grid is approximately 2.6 μm.

[0022] 4(b) shows a state in which the upper left corner of the first dot pattern 101 is fixed at the origin A(0,0), while the upper left corner of the second dot pattern 102 is shifted to various positions. Five cases are shown here, where the upper left corner of the second dot pattern 102 is shifted to point A(0,0), point B(4,0), point C(8,0), point D(4,4), and point E(8,8). The pattern at point A(0,0) corresponds to the robust pattern 100 shown in the center of FIG. 2. The pattern at point C(8,0) corresponds to the pattern at the center right of FIG. 2, and the pattern at point E(8,8) corresponds to the pattern at the bottom right of FIG. 2.

[0023] 5(a) and (b) show the change in dot coverage when the displacement is less than the translationally symmetric reproduction period. Fig. 5(a) shows the variation in dot coverage when the second dot pattern 102 changes between point A(0,0) and point C(8,0) in Fig. 4, i.e., when the second dot pattern 102 is displaced in the +X direction (to the right). Fig. 5(b) shows the variation in dot coverage when the second dot pattern changes between point A(0,0) and point E(8,8), i.e., when the second dot pattern is displaced in the +X and +Y directions (toward the lower right). Here, dot coverage refers to the proportion of the paper surface covered by dots with a diameter of 42 μm, and dot coverage variation refers to the value by which the dot coverage fluctuates due to displacement.

[0024] In Figure 5(a), the pattern at point A (0,0) and the pattern at point C (8,0) are shifted by one period of the translationally symmetric reproduction period, so they have translational symmetry and the same dot coverage (40.1%). Therefore, the dot coverage variation is 0% for both. In contrast, the pattern at point B (4,0) is a pattern between point A (0,0) and point C (8,0), but it does not have translational symmetry with point A (0,0) or point C (8,0), and its dot coverage has increased to 40.5%. Therefore, the dot coverage variation is +0.4% (= 40.5 - 40.1).

[0025] In Figure 5(b), the pattern at point A(0,0) and the pattern at point E(8,8) are shifted by one period of the translationally symmetric reproduction period, so they have translational symmetry with each other and both have dot coverage of 40.1%. Therefore, the dot coverage variation is 0% for both. In contrast, the pattern at point D(4,4) is a pattern between point A(0,0) and point E(8,8), but it does not have translational symmetry with point A(0,0) or point E(8,8), and its dot coverage has also increased to 40.6%. Therefore, the dot coverage variation is +0.5% (=40.6-40.1). However, this level of variation is sufficiently small compared to the coverage of the paper surface and is difficult to detect visually.

[0026] That is, in the robust pattern, density fluctuations that occur due to shifts smaller than the translationally symmetric reproduction period are not visually perceptible, and density fluctuations do not occur due to shifts in units of the translationally symmetric reproduction period. For this reason, the robust pattern is a pattern that is less likely to produce density unevenness regardless of the direction or amount of shift.

[0027] <About nearby dots> Figure 6 is a microscopic diagram showing the change in coverage area due to the separation of overlapping dots. The horizontal axis shows the amount of deviation of the second dot from the first dot, in units of 9600 dpi pixels. One pixel corresponds to approximately 2.6 μm. The vertical axis shows the coverage area on the paper, in units of dots. In other words, "1" corresponds to the coverage area of ​​one dot with a diameter of 42 μm.

[0028] When the first dot and second dot completely overlap, the coverage area is 1. As the second dot shifts relative to the first dot, the coverage area gradually increases, and at about 16 pixels the two dots become completely separated and the coverage area becomes 2. After that, the coverage area remains 2 regardless of the amount of shift. However, when a shift occurs between the first and second dot patterns, there are places where the overlapping dots separate, as shown in Figure 6, and places where the separated dots change into overlapping dots.

[0029] 7(a) to 7(c) are diagrams showing how overlapping dots separate and how adjacent dots overlap as the first dot pattern 101 and the second dot pattern 102 shift. FIG. 7(a) shows the case where adjacent dots spaced apart by a distance of 1.5 dots (≈63 μm) overlap, while FIG. 7(b) shows the case where adjacent dots spaced apart by a distance of 1.0 dot (≈42 μm) overlap. FIG. 7(c) shows the case where adjacent dots spaced apart by a distance of 0.5 dots (≈21 μm) overlap. In each diagram, the dotted line indicates the area covered by the overlapping dots as they separate, the dashed line indicates the area covered by the overlapping adjacent dots, and the solid line indicates the sum of these two types of coverage (total coverage area). In each diagram, the horizontal axis indicates the range until the adjacent dots become completely overlapping dots.

[0030] In Figure 7(a), the initial and final values ​​of the total coverage area are 3 dots, with a maximum value of 3.8 dots at the median of 12 pixels. In Figure 7(b), the initial and final values ​​of the total coverage area are 3 dots, with a maximum value of 3.3 dots at the median of 8 pixels. In Figure 7(c), the total coverage area remains stable at 2.6 dots from the initial value to the final value.

[0031] 7(a) to 7(c), in order to suppress density changes due to deviations less than the translationally symmetric reproduction period, it is preferable to make the distance between two dots constituting adjacent dots prepared in advance as small as possible, and even more preferable to make it 0.5 dots or less. However, visually detected density is not necessarily proportional to the dot coverage. In other words, it is preferable to appropriately adjust the distance between adjacent dots that should be prepared in advance in a robust pattern depending on the printing resolution, dot diameter, dot density, etc.

[0032] <Conditions for robust patterns> The conditions for a pattern to become a robust pattern having the above-described characteristics will be described below.

[0033] The first condition is that the first dot pattern and the second dot pattern are configured as different grid patterns.

[0034] Here, the definition of a lattice pattern will be explained. In this specification, a lattice pattern refers to a pattern in which the position of any dot can be specified from the position of another dot using two basis vectors. For example, the first dot pattern 101 in FIG. 1 can be said to be a lattice pattern with a1 and b1 as basis vectors. The second dot pattern 102 can be said to be a lattice pattern with a2 and b2 as basis vectors. Two lattice patterns defined with the same basis vector can be considered to be the same lattice pattern, and two lattice patterns defined with different basis vectors can be considered to be different lattice patterns. In other words, the first dot pattern 101 with basis vectors a1 and b1 and the second dot pattern 102 with basis vectors a2 and b2 are different lattice patterns.

[0035] If the first dot pattern and the second dot pattern are the same lattice pattern, almost all dots will become overlapping dots at positions where any dot becomes an overlapping dot. In this case, if the deviation is smaller than the lattice distance defined by the basis vector, the translationally symmetric dot pattern will not be reproduced, and there is a concern that deviations smaller than the magnitude of the basis vector will result in uneven density and worsening graininess.

[0036] The second condition is that when superimposed dots are generated using any dot, superimposed dots and adjacent dots are mixed together, and the first and second dots that make up the adjacent dots are arranged at a distance smaller than the lattice distance defined by the basis vectors.

[0037] Figure 8 shows an example of a pattern that satisfies the first condition but not the second condition. The first dot pattern 801 and the second dot pattern 802 are different lattice patterns, but in the composite dot pattern 803 that is created by superimposing them, there are no adjacent dots. All dots are superimposed dots 804 or single dots 805. In this case, translational symmetry cannot be obtained between the first dot pattern 801 and the second dot pattern 802 when the offset is smaller than the inter-lattice distance, and the effect of stabilizing the coverage area as described in Figures 7(a) to (c) cannot be obtained.

[0038] FIG. 9 shows another example of a pattern that satisfies the first condition but not the second condition. In this example, a first dot pattern 901 and a second dot pattern 902 are different lattice patterns, and a composite dot pattern 903 is created by superimposing these patterns, resulting in a superimposed dot 904 and adjacent dots 905. However, the distance D2 between the two dots that make up the adjacent dot 905 is greater than the inter-lattice distance D1 defined by the basis vector of the first dot pattern 901. In this case, even if a relative shift within the inter-lattice distance occurs between the first dot pattern 901 and the second dot pattern 902, causing the superimposed dot 904 to separate, the adjacent dots 905 cannot sufficiently overlap. As a result, this pattern also fails to achieve the effect of stabilizing the coverage area described with reference to FIGS. 7(a) to 7(c).

[0039] The third condition is that some of the adjacent dots have different proximity directions, where the proximity direction refers to the slope of the line connecting the centers of the first and second dots that make up the adjacent dots.

[0040] 10 shows an example of a pattern that satisfies the first and second conditions but not the third condition. In this example, a first dot pattern 1001 and a second dot pattern 1002 are different lattice patterns, and a composite dot pattern 1003 formed by superimposing these patterns contains overlapping dots 1004 and adjacent dots 1005. The first dot and second dot that make up the adjacent dot 1005 are spaced apart by a distance D2 that is smaller than the inter-lattice distance D1 between the first dot pattern 1001 and the second dot pattern 1002.

[0041] However, in the composite dot pattern 1003, each adjacent dot 1005 is formed by a first dot and a second dot being adjacent in the X direction, and is not formed by adjacent dots in any direction other than the X direction. In this case, if the first dot pattern 1001 and the second dot pattern 1002 are shifted in the direction of proximity, i.e., the X direction, the effects described in Figures 7(a) to 7(c) can be obtained. However, if the first dot pattern 1001 and the second dot pattern 1002 are shifted in the Y direction, which is orthogonal to the X direction, even if the overlapping dot 1004 is separated in the Y direction, the two dots that make up the adjacent dots do not overlap, resulting in a change in the coverage area.

[0042] In contrast, the robust pattern 100 described in FIG. 1 satisfies all of the above-mentioned first to third conditions. That is, referring again to FIG. 1, the first dot pattern 101 and the second dot pattern 102 are configured as lattice patterns with different basis vectors (first condition). In the combined dot pattern 100 obtained by superimposing these patterns, there are overlapping dots 104 and adjacent dots 105, and the first dot and the second dot that constitute the adjacent dot 105 are arranged at a distance smaller than the inter-lattice distance defined by the basis vectors (second condition). Furthermore, in the combined dot pattern 100, there are multiple adjacent dots with different proximity directions, such as adjacent dots adjacent in the X direction, adjacent dots adjacent in the Y direction, and adjacent dots adjacent in a diagonal direction (third condition).

[0043] Therefore, composite dot pattern 100 that satisfies the above three conditions provides the effects already explained with reference to Figures 2 to 7. That is, even if a relative misalignment occurs between the first and second dot patterns, no change in graininess or density unevenness is perceived, and the image can be recognized as having high image quality.

[0044] An embodiment utilizing a robust pattern having the above characteristics will now be described in detail.

[0045] (First embodiment) In this embodiment, the robust pattern is used when performing bidirectional multi-pass printing with a serial type inkjet printing apparatus.

[0046] 11 is a perspective view showing an outline of a printing unit in a serial inkjet printing apparatus 2 (hereinafter simply referred to as a printing apparatus) applicable to this embodiment. The printing medium P fed to the printing unit is conveyed in the -Y direction (sub-scanning direction) by the nip between a conveying roller 1101 arranged on the conveying path and a pinch roller 1102 driven by the conveying roller 1101 as the conveying roller 1101 rotates.

[0047] The platen 1103 is provided at a recording position opposite the surface (nozzle surface) on which the nozzles of the inkjet recording head H are formed, and by supporting the back surface of the recording medium P from below, the distance between the surface of the recording medium P and the nozzle surface of the recording head H is maintained constant.

[0048] The recording medium P in the area where recording has been performed on the platen 1103 is nipped between the discharge roller 1105 and the driven spur 1106, and is transported in the -Y direction as the discharge roller 1105 rotates, and is discharged onto the discharge tray 1107.

[0049] The print head H is detachably mounted on a carriage 1108 with its nozzle surface facing the platen 1103 or the print medium P. The carriage 1108 is moved back and forth in the X direction, which is the main scanning direction, along two guide rails 1109 and 1110 by the driving force of a carriage motor (not shown), and during this movement the print head H performs an ejection operation in accordance with an ejection signal.

[0050] The ±X direction in which the carriage 1108 moves intersects with the -Y direction in which the recording medium is transported and is called the main scanning direction. In contrast, the -Y direction in which the recording medium is transported is called the sub-scanning direction. An image is formed on the recording medium P in stages by alternating between main scanning (movement accompanied by ejection) of the carriage 1108 and the recording head H and transport of the recording medium P (sub-scanning).

[0051] 12 is a schematic diagram of the print head H as viewed from the nozzle surface. Four nozzle arrays 1201 to 1204 are arranged in parallel on the nozzle surface, and each nozzle array has 128 nozzles that eject the same type of ink, arranged in the Y direction at a pitch of 1200 dpi. In this embodiment, nozzle array 1201 ejects cyan ink, nozzle array 1202 ejects magenta ink, nozzle array 1203 ejects yellow ink, and nozzle array 1204 ejects black ink.

[0052] Fig. 13 is a block diagram illustrating the control configuration of an inkjet recording system applicable to this embodiment. The inkjet recording system in this embodiment includes the inkjet recording apparatus 2 described in Fig. 11 and an image processing apparatus 1. The image processing apparatus 1 can be, for example, a PC.

[0053] The image processing device 1 generates image data that can be recorded by the recording device 2. In the image processing device 1, a main control unit 1308 is composed of a CPU, ROM, RAM, ASIC, etc., and performs image creation in the image processing device 1 and image processing when the created image is recorded by the recording device 2. An image processing device I / F 1309 exchanges data signals with the recording device 2. A display unit 1310 displays various information to the user and can be, for example, an LCD. An operation unit 1314 is an operation unit for user operation and can be, for example, a keyboard or mouse. A system bus 1312 connects the main control unit 1308 to each function. An I / F signal line 1313 connects the image processing device 1 and the recording device 2. The I / F signal line 1313 can be, for example, one conforming to Centronics specifications.

[0054] In the printing device 2, a controller 1301 is configured with a CPU, ROM, RAM, etc., and controls the entire printing device 2. A print buffer 1302 stores image data as raster data before transferring it to the print head H. The inkjet print head H ejects ink from each nozzle in accordance with the image data stored in the print buffer 1302.

[0055] A paper feed / discharge motor control unit 1304 drives a transport motor (not shown) to control the transport and feeding / discharging of the recording medium P. A carriage motor control unit 1300 drives a carriage motor (not shown) to control the reciprocating scanning of the carriage 1108. A data buffer 1306 temporarily stores image data received from the image processing device 1. A system bus 1307 connects the various functions of the recording device 2.

[0056] 14 is a flowchart illustrating the processing executed by the main control unit 1308 of the image processing device 1 when an arbitrary image is recorded by the recording device 2. This processing is started when the user inputs a command to record an arbitrary image.

[0057] When this process starts, the main control unit 1308 first performs color correction processing in step S1401. In this embodiment, image data generated by an application or the like is assumed to have pixels arranged at 1200 dpi, each with an 8-bit, 256-level luminance value for R (red), G (green), and B (blue). In the color correction processing, the main control unit 1308 converts this RGB data for each pixel into R'B'G' data expressed in a color space specific to the recording device 2. A specific conversion method can be, for example, by referencing a lookup table stored in advance in memory.

[0058] In step S1402, the main control unit 1308 performs color separation processing on the R'G'B' data. Specifically, by referring to a lookup table stored in advance in memory, the luminance value R'G'B' of each pixel is converted into an 8-bit, 256-level CMYK density value corresponding to the ink color used by the recording device 2.

[0059] In step S1403, the main control unit 1308 performs division processing on the 8-bit, 256-level CMYK data to generate density data C1, M1, Y1, and K1 for the forward scan and density data C2, M2, Y2, and K2 for the backward scan. At this time, the main control unit 1308 divides the density values ​​of each color indicated by the CMYK data into approximately equal parts.

[0060] After that, the same process is carried out in parallel for each ink color, so for simplicity, only the black data (K1, K2) will be explained here.

[0061] In steps S1404-1 and S1404-2, the main control unit 1308 performs tone correction processing on each of the density values ​​K1 and K2. The tone correction processing is a correction for ensuring a linear relationship between the input density value and the optical density expressed on the recording medium P. This is usually performed by referencing a one-dimensional lookup table prepared in advance. Through the tone correction processing of steps S1404-1 and S1404-2, the 8-bit, 256-level density values ​​K1 and K2 are converted into 8-bit, 256-level density values ​​K1' and K2'.

[0062] In steps S1405-1 and S1405-2, the main control unit 1308 performs a predetermined quantization process on each of the density values ​​K1' and K2' to generate a quantized value K1" for the forward scan and a quantized value K2" for the backward scan. The quantized value K1" is 1-bit binary data that indicates whether each pixel is printed (1) or not printed (0) for the forward scan. The quantized value K2" is 1-bit binary data that indicates whether each pixel is printed (1) or not printed (0) for the backward scan. This completes the process.

[0063] The binary data C1″M1″Y1″K1″ for forward scanning and the binary data C2″M2″Y2″K2″ for backward scanning generated by the image processing device are sent to the printing device 2. The controller 1301 of the printing device 2 performs predetermined multi-pass printing according to the received binary data.

[0064] In the flowchart of FIG. 14, a division process is performed between the color separation process and the tone correction process to divide the data for forward scanning and backward scanning, but the division process may also be performed after tone correction.

[0065] 15 is a schematic diagram for explaining bidirectional two-pass multi-pass printing performed under the control of the controller 1301 in the printing apparatus 2. For simplicity of explanation, the printing operation of the black nozzle row 1204 (see FIG. 12) among the multiple nozzle rows arranged in the print head H will be explained here.

[0066] When performing two-pass multi-pass printing, the 128 nozzles included in the nozzle array 1204 are divided into a first divided region and a second divided region.

[0067] In the first printing scan, the controller 1301 moves the print head H in the +X direction, which is the forward direction, and performs a discharge operation in accordance with the binary data K1" using the first divided area. Thereafter, the controller 1301 transports the print medium by 64 pixels in the -Y direction. For convenience, in FIG. 15, the relative positional relationship between each divided area and the print medium is shown by moving the nozzle array 1204 in the +Y direction.

[0068] In the second printing scan, the controller 1301 moves the print head H in the backward direction, which is the opposite direction to the first printing scan, and performs a discharge operation in accordance with the binary data K2″ using the first divided area and the second divided area.Then, the controller 1301 transports the print medium in the −Y direction by 64 pixels.

[0069] In the third printing scan, the controller 1301 moves the print head H in the forward direction and performs a discharge operation in accordance with the binary data K1″ using the first and second divided areas.Then, the controller 1301 transports the print medium in the −Y direction by 64 pixels.

[0070] Thereafter, backward scanning such as the second printing scan and forward scanning such as the third printing scan are repeated with a transport operation of 64 pixels between them. As a result, in each unit area of ​​the printing medium, a dot pattern according to the binary data K1" printed by the forward scan and a dot pattern according to the binary data K2" printed by the backward scan are printed in an overlapping manner. In this embodiment, the dot pattern according to the binary data K1" printed by the forward scan is called the first dot pattern, and the dot pattern according to the binary data K2" printed by the backward scan is called the second dot pattern.

[0071] Fig. 16 is a functional block diagram for realizing the quantization processing executed in steps S1405-1 and S1405-2 in Fig. 14. Each block shown in Fig. 16 is realized by the main control unit 1308 of the image processing device 1 described with reference to Fig. 13.

[0072] The image input unit 1601 transmits each of the 256-level gradation data C1'C2'M1'M2'Y1'Y2'K1'K2' after gradation correction processing to a separately prepared dither core 1602. While Fig. 16 shows the configuration of the dither core 1602 for K1', similar dither cores 1602 are also prepared for the other gradation data.

[0073] A plurality of threshold matrices 1604 corresponding to each of the gradation data C1'C2'M1'M2'Y1'Y2'K1'K2' are stored in advance in the memory 1603. The threshold matrix 1604 stores thresholds in association with the pixel positions of individual pixels, and can be generated by a computer and stored in the memory 1603 in advance.

[0074] The threshold acquisition unit 1605 references the threshold matrix 1604 corresponding to K1', acquires from the threshold matrix 1604 the threshold Th corresponding to the pixel position of K1' received by the dither core 1602, and provides this to the quantization processing unit 1606. The quantization processing unit 1606 compares the gradation value K1' of the processing target pixel input from the image input unit 1601 with the threshold Th provided by the threshold acquisition unit 1605, and determines whether to print (1) or not print (0) a dot for the processing target pixel. The quantization result output unit 1607 outputs the information on whether to print (1) or not print (0) determined by the quantization processing unit 1606 as quantized data K1" of the processing target pixel.

[0075] 17 is a diagram showing an example of the threshold matrix stored in the memory 1603. The threshold matrix includes a first threshold matrix 1701 for forward scanning and a second threshold matrix 1702 for backward scanning.

[0076] In the figure, each square corresponds to a pixel arranged on the XY plane, and the value shown inside the square indicates the threshold value for the corresponding pixel position. In this embodiment, K1'K2' has a value between 0 and 255, so the threshold value Th is a value between 0 and 254. If K1'>Th for a pixel to be processed, the quantized value K1" of the pixel to be processed is recorded (K1"=1). On the other hand, if K1'≦Th, the quantized value K1" of the pixel to be processed is not recorded (K1"=0). The same applies to the relationship between K2' and K2".

[0077] In this embodiment, threshold matrices 1701 and 1702 each having a 20 pixel x 20 pixel area as shown in Fig. 17 are prepared, and these threshold matrices are repeatedly used in the X and Y directions for both forward and backward scanning. However, the size of the threshold matrices is not limited to this. They may be larger or smaller.

[0078] The first threshold matrix 1701 of this embodiment is created so that, at a predetermined gradation value, the dot pattern printed according to the results of the quantization process becomes the first dot pattern 101 in Fig. 1. The second threshold matrix 1702 is created so that, at the predetermined gradation value, the dot pattern printed according to the results of the quantization process becomes the second dot pattern 102 in Fig. 1. Therefore, even if a print position shift occurs between the forward scan that prints the first dot pattern 101 and the forward scan that prints the second dot pattern 102 at the predetermined gradation value, it is possible to print a high-quality image without significant changes in dot coverage and granularity.

[0079] Figs. 18(a) to 18(c) are diagrams showing the results of quantization processing using the first threshold matrix 1701 and the second threshold matrix 1702 when the same values of K1' and K2' are input to each pixel. Fig. 18(a) shows the case where K1' = K2' = 13 is input to each pixel. Pixels in the first threshold matrix 1701 where the threshold Th satisfies Th < K1' = 13, and pixels in the second threshold matrix 1702 where the threshold Th satisfies Th < K2' = 13, that is, pixels indicating dot recording, are shown as black pixels.

[0080] Similarly, Fig. 18(b) shows the case where K1' = K2' = 26 is input to each pixel, and Fig. 18(c) shows the case where K1' = K2' = 51 is input to each pixel. In any of Figs. 18(a) to 18(c), it can be seen that the black pixel groups of the first threshold matrix 1701 and the black pixel groups of the second threshold matrix 1702 form different lattice patterns from each other.

[0081] Figs. 19(a) to 19(c) are diagrams showing dot patterns formed on a recording medium when dots are recorded according to the quantization results shown in Figs. 18(a) to 18(c). The recording resolution is 1200 dpi, and the dot diameter is 42 μm.

[0082] FIG. 19(a) shows a first dot pattern and a second dot pattern in which dots are printed according to the black pixels in FIG. 18(a), and a composite dot pattern in which these are superimposed. The first dot pattern and the second dot pattern are different lattice patterns with an inter-lattice distance Da1 (first condition). The composite dot pattern includes an overlapping dot 191 and multiple adjacent dots 192 and 193. The first and second dots constituting the adjacent dots 192 and 193 are spaced apart by distances Da2 and Da3 that are smaller than the inter-lattice distance Da1 (second condition). Furthermore, the proximity directions of the first and second dots in the adjacent dots 192 and 193 are different from each other (third condition). Specifically, the proximity direction of the first and second dots in the adjacent dot 192 is the X direction, while the proximity direction of the first and second dots in the adjacent dot 193 is the Y direction. From the above, the composite dot pattern can be considered a robust pattern.

[0083] FIG. 19(b) shows a one-dot pattern in which dots are printed according to the black pixels in FIG. 18(b), a second dot pattern, and a composite dot pattern in which they are superimposed. Furthermore, FIG. 19(c) shows a one-dot pattern in which dots are printed according to the black pixels in FIG. 18(c), a second dot pattern, and a composite dot pattern in which they are superimposed. Although the inter-lattice distances (Db1, Dc1), the distances between the first and second dots constituting adjacent dots (Db2, Db3, Dc2, Dc3), and the proximity directions are different, the first to third conditions are satisfied for each composite dot pattern. In other words, the composite dot patterns formed at any of the gradation values ​​shown in FIG. 19 can be considered robust patterns.

[0084] As explained above, by using the threshold matrix of this embodiment described in Fig. 17, a robust pattern can be formed using the first dot pattern printed during the forward scan and the second dot pattern printed during the backward scan. As a result, even if a deviation occurs in any direction within the XY plane between the forward scan and the backward scan, a translationally symmetric dot pattern is reproduced, and the dot coverage and granularity do not change significantly, making it possible to print a high-quality image.

[0085] Here, we will briefly explain a method for creating a threshold matrix that can obtain a suitable robust pattern in multiple gradations, as described above. Conventionally, a known method for creating a threshold matrix to obtain high dot dispersion involves evaluating the dot density in the pixel regions that make up the threshold matrix and setting threshold values ​​for each pixel in the threshold matrix in ascending order. In this embodiment, constraints are added to represent different grid patterns within each threshold matrix, and threshold values ​​are set for each pixel in the threshold matrix while evaluating the dot density in the composite dot pattern. In any case, if a threshold matrix that satisfies the above first to third conditions is realized for each gradation, a translationally symmetric dot pattern can be reproduced regardless of the direction of deviation that occurs between the forward scan and the backward scan, making it possible to print high-quality images.

[0086] <Application of the first embodiment> Although the above description has been given taking as an example a case where dots with a diameter of 42 μm are printed at a printing resolution of 1200 dpi, the present embodiment is not limited to such conditions.

[0087] 14 (S1403), the density values ​​of each color CMYK are divided into two almost equally, but the division process may be performed with a bias. In this case, a bias will occur in the number of dots printed in the first dot pattern and the second dot pattern formed on the print medium, but as long as the first to third conditions described above are met, the same effects as in the above embodiment can be obtained.

[0088] Furthermore, although the above description has been given using an example of two-pass bidirectional multi-pass printing, this embodiment can also be applied to four-pass or more bidirectional printing. In the case of 2N multi-pass printing, in which a unit area on a print medium is printed with N forward scans and N backward scans, a first dot pattern is formed by combining N forward scans, and a second dot pattern is formed by combining N backward scans.

[0089] Furthermore, although two-pass bidirectional multi-pass printing has been described above, in multi-pass printing, misalignment of the printing position may occur between print scans even when the print scans are in the same direction. In such cases, it is sufficient to make the dot patterns formed by the first print scan and the second print scan the first dot pattern and the second dot pattern, respectively.

[0090] Furthermore, while the above description has been given using an example in which the first dot pattern and the second dot pattern are printed with the same ink and the same dot size, they may also be printed with different inks or different dot sizes. For example, the first dot pattern may be printed in black and the second dot pattern in cyan, or the first dot pattern may be printed with large dots and the second dot pattern with small dots. Even in such cases, if the composite dot pattern is a robust pattern, it is possible to mitigate changes in hue and graininess that may accompany misalignment between the dot patterns. In this case, one-pass printing may be used in which the first dot pattern and the second dot pattern are printed in the same printing scan.

[0091] (Second embodiment) In the past, even if desirable dot dispersion was achieved with a single color, it was sometimes impaired when an image was printed using mixed colors, resulting in noticeable graininess. To address this issue, Patent Document 3 discloses a quantization method that achieves desirable dot dispersion even with mixed colors. Specifically, it discloses a quantization process in which a single dither matrix capable of achieving desirable dispersion is prepared and this same dither matrix is ​​used for multiple colors while offsetting their respective threshold values. This embodiment describes a form in which quantization is performed using the dither matrix described in FIG. 17 while offsetting their respective threshold values ​​for multiple colors. This embodiment also uses the inkjet printing system described in FIGS. 11 to 13.

[0092] The quantization process of this embodiment will be described with reference to FIG. 16 again. Here, as an example of the priority order for quantization, black is the first color and cyan is the second color. First, in the dither core 1602 for K1', which is the first color, the threshold acquisition unit 1605 references the threshold matrix 1604 and provides the threshold Thk corresponding to the pixel position of the pixel to be processed to the quantization processing unit 1606. Specifically, the first threshold matrix 1701 described in FIG. 17 is used as the dither matrix for K1'.

[0093] The quantization processing unit 1606 compares the gradation value of K1' input from the image input unit 1601 with the threshold value Thk provided by the threshold value acquisition unit 1605, and determines whether to print (1) or not print (0) a dot for the pixel to be processed. When K1´>Thk, K1″=1 When K1´≦Thk, K1″=0.

[0094] Next, in the dither core 1602 for cyan, which is the second color, the threshold acquisition unit 1605 refers to the first threshold matrix 1701 and provides the threshold Thk corresponding to the pixel position of the pixel to be processed to the quantization processing unit 1606. The quantization processing unit 1606 for cyan subtracts the value of K1' from the provided threshold Thk and sets the result as a new threshold Thc for C1'. That is, Let Thc = Thk -K1'. At this time, if Thc becomes a negative value, the maximum gradation value 255 is added to correct the threshold value Thc. Thc=255+Thc

[0095] Then, the quantization processing unit 1606 performs quantization processing of C1' input from the image input unit 1601 using the threshold value Thc obtained in this way. When C1´>Thc, C1″=1 When C1´≦Thc, C1″=0.

[0096] The same processing as above is also performed on K2'C2', which is the grayscale data for the backward scan, using the second threshold matrix 1702.

[0097] 20(a) to 20(c) are diagrams showing the results of the quantization process of this embodiment. FIG. 20(a) shows the distribution of pixels for which the quantized data K1'' and K2'' are 1 when K1'=K2'=20 is input to each pixel. For K1'K2', which is the first color, pixels for which thresholds of 0 to 19 are set in the first threshold matrix 1701 and the second threshold matrix 1702 become black pixels.

[0098] FIG. 20(b) shows the distribution of pixels for which quantized data C1" and C2" are 1 when C1' = C2' = 6 is input to each pixel. FIG. 20(b) shows the threshold matrices after the individual thresholds of the first threshold matrix 1701 and the second threshold matrix 1702 have been corrected according to the above equations. For the second color, C1'C2', pixels for which a corrected threshold value of 0 to 5 is set in the corrected first and second threshold matrices are black pixels. These black pixels correspond to pixels for which a threshold value of 20 to 25 is set in the first threshold matrix 1701 and the second threshold matrix 1702 before correction. That is, in the sum of K1" and C1", pixels for which a threshold value of 0 to 25 is set in the first threshold matrix 1701 are black pixels, and in the sum of K2" and C2", pixels for which a threshold value of 0 to 25 is set in the second threshold matrix 1702 are black pixels.

[0099] Figure 20(c) shows a dot pattern formed on a recording medium when dots are recorded according to the quantization results shown in Figures 20(a) and (b). In Figure 20(c), the recording resolution is 1200 dpi, and the dot diameter is 42 μm. The first dot pattern, which is the sum of K1" and C1", is a lattice pattern according to a first threshold matrix 1701. The second dot pattern, which is the sum of K2" and C2", is a lattice pattern according to a second threshold matrix 1702. Therefore, the composite dot pattern obtained by combining these two lattice patterns is a robust pattern.

[0100] Similar processing can be performed for magenta and yellow. That is, if magenta is the third color and yellow is the fourth color, the value obtained by subtracting the values ​​of K1' and C1' from the threshold value Thk is set as a new threshold value Thm for M1', and the value obtained by subtracting the values ​​of K1', C1', and M1' from the threshold value Thk is set as a new threshold value Thy for Y1'. If the resulting value is negative, the maximum gradation value of 255 is added to correct the threshold value.

[0101] In other words, according to this embodiment, even if a deviation occurs in any direction within the XY plane between the forward scan and the return scan, it is possible to suppress fluctuations in dot coverage while maintaining high dot dispersion in mixed colors, and to print a high-quality image in which density unevenness or hue unevenness is not detected.

[0102] Although the above description assumes that black is the first color and cyan is the second color, the priority order of the quantization process is not particularly limited. For example, cyan may be set as the first color, and the threshold value for black may be corrected according to the cyan tone value. However, in order to reduce the graininess of the entire image, it is preferable to set the priority order starting with the ink with the strongest dot power and most noticeable on the recording medium. Note that the terms "strong" and "weak" dot power refer to the relative relationship of the degree to which one dot recorded on the recording medium reduces the brightness. Therefore, when using four ink colors, black, cyan, magenta, and yellow, as in this embodiment, it is preferable to set the priority order as follows: black as the first color, cyan as the second color, magenta as the third color, and yellow as the fourth color.

[0103] Furthermore, when inks with the same hue but different brightness, such as light cyan and light magenta, are used, it is preferable to give higher priority to cyan and magenta than to light cyan and light magenta.Furthermore, even when using the same black ink, when there are nozzle rows for large dots and nozzle rows for small dots, it is preferable to set the priority of large dots higher than that of small dots.

[0104] 21 shows the dot pattern formed on a recording medium when the quantization process of this embodiment is performed after setting the first color to large dots (42 μm) and the second color to small dots (30 μm). Because the dot diameters that make up the grid pattern are not uniform, the translational symmetry of the composite dot pattern is somewhat impaired, but the effect of suppressing fluctuations in dot coverage over a wide area and suppressing uneven hue and density can be fully achieved.

[0105] (Third embodiment) In this embodiment, as in the first and second embodiments, a serial type inkjet printing apparatus and inkjet printing system such as those described with reference to Figures 11 and 13 are used. However, in this embodiment, a print head of a different form from those in the above embodiments is used, and image processing and drive control are performed according to the print head.

[0106] <Nozzle arrangement> 22(a) to 22(c) are schematic diagrams of the print head H used in this embodiment, observed from the nozzle surface. As shown in Fig. 22(a), six nozzle rows are arranged in parallel on the nozzle surface. From left to right, they are a black nozzle row 2201, a first cyan nozzle row 2202, a first magenta nozzle row 2203, a yellow nozzle row 2204, a second magenta nozzle row 2205, and a second cyan nozzle row 2206.

[0107] FIG. 22(b) is an enlarged view of the black nozzle array 2201. The black nozzle array 2201 is configured with LEv and LOd arrays, each of which has nozzles that eject 5 pl of black ink, arranged in the Y direction at a pitch of 600 dpi. The LEv and LOd arrays each have 128 nozzles, with the LEv array being offset by half a pitch in the -Y direction from the LOd array. By performing a print scan using the black nozzle array 2201 configured in this way, black dots with a dot diameter of 38 μm can be printed on the print medium at a print density of 1200 dpi. The yellow nozzle array 2204 has the same configuration as the black nozzle array 2201.

[0108] 22(c) is an enlarged view of the first cyan nozzle row 2202 and the second cyan nozzle row 2206. The first cyan nozzle row 2202 includes an LEv row that ejects 5 pL of cyan ink, an MEv row that ejects 2 pL of cyan ink, and an SOd row that ejects 1 pL of cyan ink. Meanwhile, the second cyan nozzle row 2206 includes an LOd row that ejects 5 pL of cyan ink, an MOd row that ejects 2 pL of cyan ink, and an SEv row that ejects 1 pL of cyan ink. Each nozzle row is composed of 128 nozzles arranged in the Y direction at a pitch of 600 dpi.

[0109] In the first cyan nozzle row 2202 and the second cyan nozzle row 2206, the LEv row is offset by half a pitch (1200 dpi) in the -Y direction from the LOd row, the MEv row is offset by the MOd row, and the SEv row is offset by the SOd row. The MEv and MOd rows, which eject 2 pL, and the SEv and SOd rows, which eject 1 pL, are offset by ¼ pitch (2400 dpi) in the -Y direction from the LEv and LOd rows, which eject 5 pL. The first magenta nozzle row 2203 and the second magenta nozzle row 2205 have the same configuration as the first cyan nozzle row 2202 and the second cyan nozzle row 2206.

[0110] <Image processing> 23 is a flowchart illustrating the processing executed by the main control unit 1308 of the image processing device 1 when an arbitrary image is recorded by the recording device 2 of this embodiment. The processing performed in S2501 to S2505 is the same as the processing in S1401 to S1405 of the first embodiment described in Fig. 14, and therefore a description thereof will be omitted here. However, while the resolution of the image data was 1200 dpi in the first embodiment, it is 600 dpi in this embodiment.

[0111] The same processing from step S2504-1 and step S2504-2 onwards is carried out in parallel for each ink colour. Here, the cyan data (C1', C2') will be explained.

[0112] In steps S2505-1 and S2505-2, the main control unit 1308 performs a predetermined quantization process on each of the multi-value data C1' and C2' to generate quantized data C1'' for the forward scan and quantized data C2'' for the backward scan. The quantization process is performed in the same manner as in the first embodiment.

[0113] In steps S2506-1 and S2506-2, the main control unit 1308 performs index expansion processing. In the index expansion processing of this embodiment, a prepared index pattern is used to convert 600 x 600 dpi binary data C1" and C2" into 600 x 1200 dpi binary data C1p and C2p. That is, an area of ​​1 pixel in the X direction by 1 pixel in the Y direction is divided into areas of 1 pixel in the X direction by 2 pixels in the Y direction, and a dot is set to be printed (1) or not printed (0) for each pixel.

[0114] 24(a) to (c) are diagrams showing dot arrangement patterns and reference index patterns used in the index expansion process. FIG. 24(a) is a diagram showing dot arrangement patterns. One pixel area of ​​600 × 600 dpi corresponds to two pixels of 600 × 1200 dpi. When the quantized data C1″ and C2″ of one pixel of 600 × 600 dpi is “0,” indicating that no dot is to be printed, no dot is to be placed in either pixel of 600 × 1200 dpi. On the other hand, when the quantized data C1″ and C2″ of one pixel of 600 × 600 dpi is “1,” indicating that a dot is to be printed, there are two possible positions for actually printing the dot. In this embodiment, pattern A is prepared, which places dots on the upper pixel, i.e., the pixel on the −Y side, and pattern B is prepared, which places dots on the lower pixel, i.e., the pixel on the +Y side. In the dot arrangement pattern of this embodiment, dots are printed on the upper pixels by the nozzles in the LEv column, and dots are printed on the lower pixels by the nozzles in the LOd column (see FIG. 22(b)).

[0115] 24(b) is a diagram showing reference index pattern 2500. In this embodiment, different index patterns are used in the index expansion process of step S2506-1 and the index expansion process of step S2506-2, but both are created based on reference index pattern 2500.

[0116] In the reference index pattern 2500, each square corresponds to one pixel area of ​​600 x 600 dpi. For each pixel, it is determined whether dots are to be arranged using pattern A or pattern B when the quantization value of the corresponding pixel is "1."

[0117] Figure 24(c) shows binary data of 600 dpi in the X direction and 1200 dpi in the Y direction when the quantized value of each pixel is uniformly "1" and index expansion processing is performed according to the reference index pattern 2500. Binary data such as that shown in Figure 24(c) is generated for each of forward scanning and backward scanning, and is sent to the printing device 2. The controller 1301 of the printing device 2 performs predetermined printing control according to the received binary data.

[0118] The dot arrangement pattern in FIG. 26(a) is for 5 pl ink droplets, that is, for the LEv and LOd rows, but it may also be set to output a mixture of 1 pl and 3 pl ink droplets.

[0119] <Time-division drive control> In the inkjet print head H of this embodiment, a voltage pulse is applied to an electrothermal conversion element (heater) provided in correspondence with each nozzle, causing film boiling in the ink, and the ink is ejected by the growth energy of the generated bubbles. In this case, since applying a voltage pulse to multiple heaters simultaneously would require a large-capacity power supply, a conventionally known time-division driving method is adopted.

[0120] 25(a) and (b) are diagrams for explaining the time-division driving method. In the time-division driving method of this embodiment, 128 nozzles arranged in the same nozzle row are divided into 16 blocks, and the timing of applying a voltage pulse to the heater is shifted for each block.

[0121] 25(a) is a diagram showing the block numbers and the drive order of each block. It shows that the nozzles in block 1 are driven at the first timing, the nozzles in block 2 are driven at the fifth timing, and the nozzles in block 16 are driven at the 16th timing. Each of the 16 blocks is driven at one of the 1st to 16th timings obtained by dividing the period corresponding to one pixel at 600 dpi into 16 parts.

[0122] 25(b) shows the nozzles arranged in nozzle row 2300, a drive timing chart for each nozzle, and the dot recording state. The nozzles arranged in the Y direction are divided into blocks, starting from the first nozzle on the -Y direction side: Block 1, Block 2, and so on, with the 16th nozzle being divided into Block 16. The 17th to 32nd nozzles are then divided again into Block 1, Block 2, and Block 16, respectively. That is, Block 1 includes the 1st, 17th, to 113th nozzles, Block 2 includes the 2nd, 18th, to 114th nozzles, and Block 16 includes the 16th, 32nd, to 128th nozzles.

[0123] Timing chart 2310 shows the drive timing for each nozzle according to the table in Figure 25(a). Here, only the drive timing for nozzles 1 through 16 is shown, but timing chart 2310 is repeated for nozzles 17 and beyond. In the diagram, the horizontal axis represents time and the vertical axis represents the voltage applied to the heater. As shown in the diagram, the period corresponding to one pixel at 600 dpi is divided into 16 parts, and the nozzles are driven in this order: 1st, 5th, 9th, 13th, and finally the 16th nozzle.

[0124] Under this drive control, when the carriage 1108 (see FIG. 11) is moved in the +X direction, a dot pattern 2320 is formed on the print medium. Because the dots are ejected while the carriage 1108 is moving in the X direction, the dots are arranged with a shift in the X direction according to the drive order. To explain in more detail, when one pixel area of ​​600 dpi is divided into 16 sections, the dots printed by four adjacent nozzles, such as the first to fourth nozzles, are arranged with a shift of four sections. As a result, on the print medium, diagonal lines that are inclined relative to the X direction are repeatedly arranged in the Y direction.

[0125] On the other hand, when the carriage 1108 is moved in the -X direction under the above drive control, a dot pattern 2321 is formed on the recording medium. Compared to the dot pattern 2320 of the forward scan, the inclination direction of the diagonal lines is reversed to the main scanning direction.

[0126] While the time-division driving described above reduces the number of nozzles driven simultaneously and saves power consumption, it also results in variations in the dot printing positions within a single 600 dpi pixel area, as seen in dot patterns 2320 and 2321.

[0127] <Recording control method> A control method for realizing a robust pattern on a print medium when two-pass printing is performed under the index expansion process, print head configuration, and time-division drive control described above will now be described.

[0128] 26(a) to 26(c) are diagrams for explaining drive control using the first cyan nozzle row 2302 and the second cyan nozzle row 2306 described in Fig. 22(c). Here, the state is shown in which dots with a diameter of 38 μm are printed in each pixel using the LEv row and the LOd row, which eject 5 pL of cyan ink.

[0129] Figure 26(a) shows a dot pattern obtained when dots are printed on each pixel at 600 dpi using the LEv and LOd columns without the time-division driving method described above. Figure 26(b) shows a dot pattern obtained when the printing position of the LOd column is shifted by one pixel at 1200 dpi relative to the printing position of the LEv column without the time-division driving method. By shifting the printing positions of the LOd and LEv columns by one pixel at 1200 dpi in the X direction, a grid pattern with higher dot dispersion than that shown in Figure 26(a) can be formed.

[0130] Figure 26(c) shows the dot pattern obtained when the pattern of Figure 26(b) is printed by forward scanning with time-division driving. That is, the pattern obtained reflects the shift shown in dot pattern 2320 of Figure 25(b) compared to the pattern of Figure 26(b). In this case, although it is a grid pattern, the spacing between the lines connecting the centers of the dots printed in the LOd column and the lines connecting the centers of the dots printed in the LEv column is unequal, resulting in a decrease in dot dispersion compared to Figure 26(b).

[0131] Figure 26(d) shows the dot pattern that results when dots are printed with the LOd row position further shifted in the +X direction by (600 dpi ÷ 16 × 2 ≈ 15.9 μm) from the state of Figure 26(c). By shifting the position in this way, the spacing between the dots printed in the LEv row and the dots printed in the LOd row becomes equal, achieving a desirable grid pattern.

[0132] Here, the shift amount of (600 dpi ÷ 16 × 2) is half the shift in the X direction between dots adjacent in the Y direction (600 dpi ÷ 16 × 4) in the time-division driving described in Figure 25(b), that is, it corresponds to two blocks of time-division driving. Therefore, in this embodiment, the above-mentioned time-division driving is used, and drive control is performed in the forward scan so that the drive timing of column LOd is delayed by two blocks from the reference position.

[0133] 27(a) and (b) are schematic diagrams for explaining the above-described shifting of drive timing during forward and backward print scans. Fig. 27(a) shows the drive timing for the forward scan, and Fig. 27(b) shows the drive timing for the backward scan. The print head H is provided with a first cyan nozzle row 2302 and a second cyan nozzle row 2306, as shown in Fig. 22(c).

[0134] In the forward scan, first, when the LEv column reaches the reference position, the LEv column is driven by the time-division driving method described above. After that, when the LOd column reaches the reference position, it is not driven, but when it reaches a position shifted by two blocks (600 dpi ÷ 16 × 2) from the reference position, it is driven by the time-division driving method.

[0135] In the backward scan, the LOd column is not driven when it reaches the reference position, but is driven by time-division driving when it reaches a position shifted by two blocks (600 dpi ÷ 16 × 2) from the reference position. After that, when the LEv column reaches the reference position, the LEv column is driven by time-division driving.

[0136] By performing the drive control described above, the grid pattern shown in Figure 26(d) is obtained during forward scanning, and a grid pattern that is the inverse of Figure 26(d) in the main scanning direction is obtained during backward scanning. However, if there is a limit to the offset resolution due to the circumstances of the recording device, it is sufficient to achieve an offset of at least 1200 dpi.

[0137] Note that, although the above description has been given of shifting (delaying) the drive timing of the LOd column relative to the LEv column, the dot pattern shown in Figure 26(d) can also be obtained by advancing the drive timing of the LEv column relative to the LOd column. Also, the nozzle column whose drive timing is shifted may be switched between the LEv column and the LOd column during forward scanning and backward scanning.

[0138] Incidentally, Figure 26 describes a drive method for achieving a suitable grid pattern for four nozzles adjacent in the Y direction (eight nozzles in the LOd and LEv columns). However, in the time-division drive of this embodiment, as shown in Figure 25(b), a deviation of 11 blocks occurs every four nozzles. For this reason, this embodiment provides an index pattern and threshold matrix that eliminates this deviation and enables a suitable grid pattern to be obtained across the entire nozzle array.

[0139] <About index patterns> Figures 28(a) and (b) are diagrams explaining the column shifting of raster groups. In both figures, the left side shows the binary data for the LEv column, and the right side shows the dot pattern based on that binary data. In the figures, the vertical and horizontal borders define one pixel area of ​​600 dpi, and each black square indicates that dot printing is set by the binary data. Hereinafter, a group of pixels with the same pixel position in the X direction will be called a column, and a group of pixels with the same pixel position in the Y direction will be called a raster.

[0140] Figure 28(a) shows the binary data for nozzles 1 to 16 in the LEv column when print (1) is set for the same column every three columns, and the dot pattern when dots are printed in a forward scan according to that binary data. Because time-division driving is performed, the dot pattern 2320 shown in Figure 25(b) is repeatedly arranged every three columns and every four rasters.

[0141] Figure 28(b) shows the binary data in which the nozzles in the LEv column are divided into raster groups of four nozzles each, and the recording pixels between adjacent raster groups are shifted in the +X direction by one column, and the dot pattern based on that binary data.

[0142] Comparing the dot patterns in Figure 28(a) and (b), Figure 28(b) shows that the misalignment between dots caused by time-division drive is less noticeable, resulting in an image with superior uniformity. While the illustration here is for nozzles 1 to 16, the same effect can be achieved for nozzles 17 to 128 by shifting the position of the recording pixels for each raster group according to the above rules.

[0143] Figures 29(a) and (b) are diagrams similar to Figures 28(a) and (b) that show the relationship between the binary data and the dot pattern for the LEv and LOd columns. In each grid, the black squares in the upper region indicate that printing (1) is set for the nozzles in the LEv column, and the black squares in the lower region indicate that printing (1) is set for the nozzles in the LOd column. In the dot pattern, there is a shift between the dots printed by the LEv and LOd columns due to time-division driving, and there is also a shift between the dots printed by the LEv and LOd columns due to the control described in Figures 27(a) and (b).

[0144] For this reason, with regular binary data such as that shown in Figure 29(a), a certain degree of dot dispersion is achieved, but a strict grid pattern is not obtained. In contrast, Figure 29(b) shows the result when the column shifting in units of raster groups described in Figure 28(b) is performed on the binary data of Figure 29(a). It can be seen that a suitable grid pattern is obtained with the dot pattern of Figure 29(b).

[0145] In this embodiment, as described above, an index pattern is prepared in advance that will result in a suitable grid pattern such as that shown in Figure 29(b) on the recording medium, taking into consideration the nozzle positions of the LEv and LOd columns and the characteristics of time-division driving.

[0146] 30(a) to 30(d) are diagrams showing an index pattern 3001 for forward scanning used in this embodiment and the binary data that results when this index pattern 3001 is used. The index pattern 3001 for forward scanning shown in FIG. 30(a) is obtained by reflecting the column shifting described in FIG. 28(b) to the reference index pattern 2500 described in FIG. 24(b). Specifically, the reference index pattern 2500 is repeatedly arranged in the X and Y directions, and the content of this pattern is shifted by one column in the +X direction in units of raster groups. FIG. 30(b) shows the binary data that results when the index pattern 3001 shown in FIG. 30(a) is expanded according to the dot arrangement pattern shown in FIG. 24(a).

[0147] On the other hand, Figure 30(c) shows a pattern representing the print pixels of the binary data shown in Figure 29(b) at 600 dpi. That is, when gradation data of approximately 2 / 16 (12.5%) is input, the quantization process of this embodiment generates binary data such as that shown in Figure 30(c). Figure 30(d) shows the result of expanding the binary data shown in Figure 30(c) according to the expansion pattern shown in Figure 30(b). Specifically, it shows the result of ANDing the pattern in Figure 30(b) with the pattern in Figure 30(c). By using the nozzles in the LEv and LOd columns and performing an ejection operation according to the binary data in Figure 30(c), a suitable grid pattern such as that shown in Figure 29(b) is printed on the print medium.

[0148] Figures 31(a) and (b) are diagrams illustrating a specific method for creating an index pattern 3001 for forward scanning in this embodiment from the reference index pattern 2500 described in Figure 25(b). First, as shown in Figure 31(a), a reference index pattern 2500 having an 8-pixel by 8-pixel area is prepared, and the pattern contents of the lower four pixels (on the +Y direction side) are shifted by one pixel in the +X direction. Hereinafter, the index pattern created in this way will be referred to as a first index pattern 3101. Then, for the first eight rasters, the first index pattern 3101 is repeatedly used in the X direction.

[0149] Next, as shown in Figure 31(b), second index pattern 3102 is created by shifting the contents of first index pattern 3101 overall by two pixels in the +X direction. Then, for the second eight rasters, second index pattern 3102 is repeatedly used in the X direction. Subsequently, third index pattern 3103 and fourth index pattern 3104 are created and arranged in the same manner as above, completing index patterns for a total of 32 rasters.

[0150] In this embodiment, the index pattern having a 32 pixel x 32 pixel area created in this way is used in the index expansion process for forward scanning in S2506-1 of Fig. 24. On the other hand, in the index expansion process for backward scanning in S2506-2 of Fig. 24, the index pattern used is the index pattern 3001 for forward scanning that is inverted in the main scanning direction.

[0151] <About the threshold matrix> 32(a) and (b) are diagrams showing threshold matrices used in the quantization process of this embodiment. FIG. 32(a) is the threshold matrix used in the quantization process for forward scanning, and FIG. 32(b) is the threshold matrix used in the quantization process for backward scanning. Both threshold matrices have a pixel area of ​​32 pixels x 32 pixels, similar to the index pattern described above. The diagram shows the result of quantization when gradation data of C1' = C2' = 32 is input to all 32 pixels x 32 pixels. The pixels shown in black correspond to pixels that are recorded (C1" = 1, C2" = 1). It can be seen that the distribution of black pixels in the area surrounded by a thick frame in FIG. 32(a) matches the distribution of binary data in FIG. 30(c), which shows the case when gradation data of approximately 12.5% ​​(32 / 255) is input. Here, the arrangement of black pixels in the threshold matrix for forward scanning shown in FIG. 32(a) and the threshold matrix for backward scanning shown in FIG. 32(b) has an inverted relationship in the X direction.

[0152] When creating a threshold matrix such as that used in this embodiment, as in the first embodiment, thresholds can be set while evaluating the dot density, with the constraints imposed to represent different grid patterns in forward and backward scans. In this case, in this embodiment, it is sufficient to form an optimal grid pattern, taking into account the constraints of the nozzle arrangement and time-division drive in particular.

[0153] 33 is a diagram showing the dot patterns of this embodiment formed on a recording medium when the series of controls described above are performed. Shown here are a first dot pattern 3301 recorded on the recording medium during a forward scan in accordance with gradation data C1', a second dot pattern 3302 recorded on the recording medium during a backward scan in accordance with gradation data C2', and a composite dot pattern 3300 formed by combining these.

[0154] As shown in the figure, first dot pattern 3301 and second dot pattern 3302 are different lattice patterns (first condition). Furthermore, in combined dot pattern 3300, which is formed by superimposing these patterns, there are overlapping dots 3303 and adjacent dots 3304, and the first and second dots constituting adjacent dot 3304 are spaced apart by a distance smaller than the inter-lattice distance (second condition). Furthermore, combined dot pattern 3300 includes multiple adjacent dots with different proximity directions, such as adjacent dots 3304 adjacent in the X direction, adjacent dots 3305 adjacent in the Y direction, and adjacent dots 3306 adjacent in a diagonal direction (third condition). For these reasons, combined dot pattern 3300 of this embodiment can be considered a robust pattern.

[0155] As described above, according to this embodiment, quantization processing is performed using the threshold matrix shown in Figures 32(a) and (b) under the print head shown in Figure 22 and the time-division drive control shown in Figure 25, and index expansion processing is performed using the index pattern shown in Figure 30(a). As a result, it is possible to form suitable grid patterns that are different from each other in the forward scan and the backward scan, and to print a suitable robust pattern on the print medium, without making the nozzle arrangement configuration of the print head H or print position deviation caused by time-division drive control conspicuous.

[0156] <Control in the low gradation range> When quantization processing is performed using the threshold matrices shown in Figures 32(a) and (b), a situation occurs in which only one of the LEv nozzle row or the LOd nozzle row is used in the low gradation region. This is because, when attempting to form a grid pattern using one dot pattern, only one of the LEv nozzle row or the LOd nozzle row is used, and the same nozzle row is also used in the other dot pattern that is inverted in the X direction. In this case, there is a risk that the nozzle row usage frequency will be biased, shortening the life of the print head. In consideration of the above, in this embodiment, a special threshold matrix is ​​prepared for the low gradation region.

[0157] Figures 34(a) to (d) are diagrams for explaining the threshold matrix used in the low gradation region of this embodiment. Figure 34(a) is a threshold matrix for the forward scan. The threshold matrix for the forward scan is the same as the threshold matrix shown in Figure 32(a). Here, when gradation data of C1' = 32 is uniformly input, pixels that are printed (C1" = 1) are shown as black pixels. Figure 34(b) shows the results of index expansion processing using the index pattern of Figure 30(a) based on Figure 34(a). It can be seen that all pixels for which printing (1) is set correspond to the LEv nozzle array.

[0158] On the other hand, Figure 34(c) shows a threshold matrix for the backward scan used in the low gradation region. This threshold matrix is ​​obtained by further offsetting the thresholds of the threshold matrix inverted in the X direction by an odd raster so that all pixels for which printing (1) is set correspond to the LOd nozzle row. In this way, as shown in Figure 34(d), all pixels for which printing (1) is set correspond to the LOd nozzle row, and the frequency of use of the LEv nozzle row and the LOd nozzle row can be equalized. In addition, it is possible to realize different grid patterns for the first dot pattern and the second dot pattern.

[0159] FIG. 35 shows a dot pattern formed on a print medium when gradation data C1′=C2′=8 is uniformly input. This figure shows a first dot pattern 3501 printed on the print medium during a forward scan in accordance with gradation data C1′, a second dot pattern 3502 printed on the print medium during a backward scan in accordance with gradation data C2′, and a composite dot pattern 3503 formed by combining these. In this example, the first dot pattern 3501 is printed only by the LEv nozzle array, and the second dot pattern 3502 is printed only by the LOd nozzle array, so there are no overlapping dots in the composite dot pattern. However, if the first dot pattern 3501 and the second dot pattern 3502 are shifted in the Y direction by approximately one pixel at 1200 dpi, a shifted dot pattern 3504 is obtained, which includes an overlapping dot 3505 and multiple adjacent dots 3306 and 3307. In this shifted dot pattern 3504, there are a plurality of adjacent dots 3306 and 3307 that are adjacent in different directions, forming a robust pattern.

[0160] According to the embodiment described above, the image processing device 1 can perform the main image processing at a resolution of 600 dpi, i.e., with low load. Meanwhile, the printing device 2 uses a printhead capable of achieving a printing resolution of 1200 dpi and utilizes time-division drive to achieve printing at a substantially 1200 dpi x 1200 dpi resolution. Furthermore, in the series of image processing, threshold matrices and index patterns suitable for the printhead nozzle arrangement configuration and time-division drive control are prepared for forward scanning and backward scanning, and image processing is performed based on these. This makes it possible to print suitable grid patterns that are different from each other in forward scanning and backward scanning without conspicuously shifting the print position due to the nozzle arrangement configuration of the printhead and time-division drive control. As a result, it is possible to print suitable robust patterns on the printing medium.

[0161] (Fourth embodiment) In the third embodiment, the reference index pattern 2500 shown in Fig. 25 is shifted in columns by raster groups to generate the index pattern shown in Fig. 30(a) that is actually used, and an index pattern that is the inverse of this index pattern in the X direction. The image processing device 1 then uses the index patterns generated in this way to allocate print data to the LEv column and the LOd column. In contrast, in this embodiment, this allocation of print data to the LEv column and the LOd column is performed by masking.

[0162] 36 is a flowchart illustrating the processing executed by the main control unit 1308 of the image processing device 1 when an arbitrary image is recorded by the recording device 2 of this embodiment. The processing performed in S3601 to S3605-1 and S3605-2 is the same as the processing in S2501 to S2505-1 and S2505-2 of the third embodiment described in FIG. 23, and therefore a description thereof will be omitted.

[0163] In S3606-1 and S3606-2, in this embodiment, index expansion processing is performed using an index pattern different from that in the third embodiment.

[0164] 37(a) to 37(c) are diagrams showing dot arrangement patterns and index patterns used in the index expansion process of this embodiment. Fig. 37(a) is a diagram showing dot arrangement patterns of this embodiment. In this embodiment, when the quantization value of one pixel of 600 x 600 dpi is "1", only pattern C is prepared, which arranges dots in both the upper and lower pixels.

[0165] Fig. 37(b) is a diagram showing an index pattern. In this embodiment, pattern C is set for all pixels that make up an 8x8 pixel area. Therefore, if the quantization value of each pixel is uniformly "1", the binary data of 600 dpi in the X direction and 1200 dpi in the Y direction will be as shown in Fig. 37(c) regardless of whether it is forward scanning or backward scanning.

[0166] Returning to the explanation of Figure 36, in steps S3607-1 and S3607-2, the main control unit performs masking. In masking, for each 600 dpi pixel, either the upper or lower pixel that makes up that pixel is masked. In other words, for each 600 dpi pixel, it is determined whether to record using the LEv column or the LOd column. This type of masking is performed by logical ANDing the binary data generated in the index expansion process with a mask pattern prepared in advance.

[0167] 38(a) and (b) show mask patterns used in the above mask processing. FIG. 38(a) is a mask pattern with the same content as the reference index pattern described in FIG. 25(c). FIG. 38(b) shows the state in which the mask pattern of FIG. 38(a) has been shifted by columns in units of raster groups. By performing mask processing using the mask pattern shown in FIG. 38(b), the first dot pattern of the third embodiment can be formed on the recording medium during forward scanning. Furthermore, by performing mask processing using a mask pattern obtained by inverting the mask pattern of FIG. 38(b) in the main scanning direction during backward scanning, the second dot pattern of the third embodiment can be formed. As a result, the composite dot pattern obtained by combining the first dot pattern and the second dot pattern is also a robust pattern similar to that of the third embodiment.

[0168] (Other embodiments) While the above description has been given assuming that the image processing device 1 performs each of the steps illustrated in FIGS. 14, 23, and 36, some steps may also be performed by the controller 1301 of the recording device 2. Regarding the steps illustrated in the flowcharts, there is no clear distinction between which steps are performed by the image processing device 1 and which steps are performed by the recording device 2. For example, in the third and fourth embodiments, if the image processing device 1 performs the quantization process, the image processing device 1 can perform the quantization process at a resolution of 600 dpi, which is lower than the recording resolution, thereby reducing the processing load. In this case, in the recording device 2, the controller 1301 performs index expansion using the dot arrangement pattern and index pattern stored in the data buffer 1306. In this case, the entire recording system, including the image processing device 1 and the recording device 2, constitutes the image processing device of the present invention. Depending on the performance of the recording device, the recording device 2 may directly receive multi-value RGB image data and perform all of the steps illustrated in the flowcharts. In this case, the recording device 2 constitutes the image processing device of the present invention.

[0169] Furthermore, the number of bits of the input and output data for each step is not limited to the number of bits described above, and the number of bits of the output data may be set higher than the number of bits of the input data to maintain precision. Furthermore, while the number of colors of the recording device has been described using four colors (CMYK) as an example, the recording device may also use similar colors with different densities, such as light cyan, light magenta, and gray, or spot colors such as red, green, and blue. In this case, the color separation process simply generates the type of gradation data corresponding to the number of colors, and the subsequent image processing described above can be performed for each color.

[0170] Furthermore, while the above embodiments have been described using a serial-type inkjet printing apparatus as an example, all of the above embodiments can also be applied to line-type printing apparatuses. Even with a line-type inkjet print head, when printing the same pixel area using two or more nozzle arrays, misalignment between the nozzle arrays can become an issue. In such cases, the dot pattern formed by one nozzle array can be designated as the first dot pattern, and the dot pattern formed by another nozzle array can be designated as the second dot pattern, and processing similar to that of the above embodiments can be performed.

[0171] In the third and fourth embodiments, a thermal jet print head is used, which ejects ink by applying a voltage pulse to a heater, but the ejection method is not particularly limited in any of the above embodiments. For example, the present invention can be effectively applied to various printing devices, such as a so-called piezo-type inkjet printing device that ejects ink using a piezoelectric element.

[0172] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments 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]

[0173] 1. Image processing device 100 Synthetic Dot Patterns 101 First dot pattern 102 Second dot pattern 104 Superimposed Dots 105 Proximity Dots H Recording head

Claims

1. acquiring gradation data corresponding to a predetermined gradation value; generating, based on the gradation data, first data corresponding to a first dot pattern to be recorded by a forward scan of a recording means, and second data corresponding to a second dot pattern to be recorded by a backward scan of the recording means and to be recorded on a recording medium so as to be superimposed on the first dot pattern; 1. An image processing method comprising: the first dot pattern includes a first lattice formed of dots repeatedly arranged at a first interval in a first direction and dots repeatedly arranged at a second interval in a second direction; the second dot pattern includes a second lattice formed of dots repeatedly arranged at a third interval in a third direction and dots repeatedly arranged at a fourth interval in a fourth direction, a composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a first relative position where a center of one dot included in the first dot pattern overlaps a center of one dot included in the second dot pattern, (i) a first adjacent dot in which a first dot included in the first dot pattern and a second dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals; (ii) a second adjacent dot in which a third dot included in the first dot pattern and a fourth dot included in the second dot pattern are adjacent at a distance shorter than any of the first, second, third, and fourth intervals; Including, An image processing method, wherein a first slope of a line connecting the centers of the first adjacent dots is different from a second slope of a line connecting the centers of the second adjacent dots.

2. The composite dot pattern is (iii) a fifth dot included in the first dot pattern and a sixth dot included in the second dot pattern include a third adjacent dot that is adjacent to the fifth dot and the sixth dot, the third adjacent dot being spaced apart from the fifth dot and the sixth dot, at a distance shorter than any of the first, second, third, and fourth intervals; 2. The image processing method according to claim 1, wherein a third slope of the line connecting the centers of the third adjacent dots is different from the first slope and also different from the second slope.

3. 3. The image processing method according to claim 1, wherein the composite dot pattern includes a plurality of unit areas each including the overlapping dot, the first adjacent dot, and the second adjacent dot, in a repeating arrangement.

4. a second composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a second relative position different from the first relative position, (iv) superimposed dots formed by superimposing dots included in the first dot pattern and dots included in the second dot pattern; (v) a fourth adjacent dot, in which a seventh dot included in the first dot pattern and an eighth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the seventh dot and the eighth dot is the first slope; (vi) a fifth adjacent dot in which a ninth dot included in the first dot pattern and a tenth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the ninth dot and the tenth dot is the second slope; 4. The image processing method according to claim 1, further comprising:

5. generating two sets of gradation data based on the gradation data; quantizing one of the two grayscale data using a first threshold matrix to generate first quantized data; generating second quantized data by quantizing the other of the two grayscale data using a second threshold matrix different from the first threshold matrix; 5. The image processing method according to claim 1, further comprising:

6. First gradation data and second gradation data are generated based on the gradation data of the first gradation value; third gradation data and fourth gradation data are generated based on gradation data of a second gradation value higher than the first gradation value; a recording dot pattern corresponding to a result of quantizing the third gradation data using the first threshold matrix is ​​a pattern in which recording dots are added to a recording dot pattern corresponding to a result of quantizing the first gradation data using the first threshold matrix, 6. The image processing method according to claim 5, wherein the recording dot pattern corresponding to the result of quantizing the fourth gradation data using the second threshold matrix is ​​a pattern in which recording dots are added to the recording dot pattern corresponding to the result of quantizing the second gradation data using the second threshold matrix.

7. the grayscale data corresponds to a first color; the first dot pattern and the second dot pattern are patterns for recording dots of the first color, The image processing method includes: obtaining gradation data corresponding to a second color; a step of further generating third data corresponding to a third dot pattern for recording dots of the second color based on the gradation data corresponding to the second color, and fourth data corresponding to a fourth dot pattern for recording dots of the second color, which is recorded on a recording medium so as to be superimposed on the third dot pattern; and the third dot pattern includes a third lattice formed of dots repeatedly arranged at a fifth interval in a fifth direction and dots repeatedly arranged at a sixth interval in a sixth direction, the fourth dot pattern includes a fourth lattice formed of dots repeatedly arranged at seventh intervals in a seventh direction and dots repeatedly arranged at eighth intervals in an eighth direction, A second composite dot pattern is formed by combining the third dot pattern and the fourth dot pattern at a relative position where the center of one dot included in the third dot pattern overlaps the center of one dot included in the fourth dot pattern, (iii) a third adjacent dot in which a fifth dot included in the third dot pattern and a sixth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; (iv) a fourth adjacent dot in which a seventh dot included in the third dot pattern and an eighth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; Contains, 2. The image processing method according to claim 1, wherein a third slope of the line connecting the centers of the third adjacent dots is different from a fourth slope of the line connecting the centers of the fourth adjacent dots.

8. generating first gradation data and second gradation data based on the gradation data corresponding to the first color, and generating third gradation data and fourth gradation data based on the gradation data corresponding to the second color; generating first quantized data corresponding to the first color by comparing a first threshold value in a first threshold matrix with the first grayscale data; generating third quantized data corresponding to the second color by comparing a corrected threshold value obtained by subtracting the value of the first gradation data from the first threshold value with the third gradation data; generating second quantized data corresponding to the first color by comparing a second threshold value in a second threshold matrix with the second grayscale data; generating fourth quantized data corresponding to the second color by comparing a corrected threshold value obtained by subtracting the value of the third gradation data from the second threshold value with the fourth gradation data; 8. The image processing method according to claim 7, further comprising:

9. 9. The image processing method according to claim 7, wherein the brightness of the dots of the first color is lower than the brightness of the dots of the second color.

10. 10. The image processing method according to claim 7, wherein the third dot pattern is printed by the forward scan, and the fourth dot pattern is printed by the backward scan.

11. A program for causing one or more processors in a computer to execute the image processing method according to any one of claims 1 to 10.

12. an acquisition means for acquiring gradation data corresponding to a predetermined gradation value; a generating means for generating, based on the gradation data, first data corresponding to a first dot pattern to be recorded by a forward scan of a recording means, and second data corresponding to a second dot pattern to be recorded by a backward scan of the recording means and to be recorded on the recording medium so as to be superimposed on the first dot pattern; An image processing device comprising: the first dot pattern includes a first lattice formed of dots repeatedly arranged at a first interval in a first direction and dots repeatedly arranged at a second interval in a second direction; the second dot pattern includes a second lattice formed of dots repeatedly arranged at a third interval in a third direction and dots repeatedly arranged at a fourth interval in a fourth direction, a composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a first relative position where a center of one dot included in the first dot pattern overlaps a center of one dot included in the second dot pattern, (i) a first adjacent dot in which a first dot included in the first dot pattern and a second dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals; (ii) a third dot included in the first dot pattern and a fourth dot included in the second dot pattern are second adjacent dots that are adjacent at a distance shorter than any of the first, second, third, and fourth intervals; Including, an image processing device, characterized in that a first gradient of a line connecting the centers of the first adjacent dots is different from a second gradient of a line connecting the centers of the second adjacent dots;

13. The composite dot pattern is (iii) a third adjacent dot in which a fifth dot included in the first dot pattern and a sixth dot included in the second dot pattern are adjacent at a distance shorter than any of the first, second, third, and fourth intervals; 13. The image processing device according to claim 12, wherein a third slope of the line connecting the centers of the third adjacent dots is different from the first slope and also different from the second slope.

14. 14. The image processing device according to claim 12, wherein the composite dot pattern includes a plurality of unit areas each including the overlapping dot, the first adjacent dot, and the second adjacent dot, in a repeated arrangement.

15. A second composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a second relative position different from the first relative position is (iv) superimposed dots formed by superimposing dots included in the first dot pattern and dots included in the second dot pattern; (v) a fourth adjacent dot, in which a seventh dot included in the first dot pattern and an eighth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the seventh dot and the eighth dot is the first slope; (vi) a fifth adjacent dot in which a ninth dot included in the first dot pattern and a tenth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the ninth dot and the tenth dot is the second slope; 15. The image processing device according to claim 12, further comprising:

16. The generating means generating two sets of gradation data based on the gradation data; quantizing one of the two grayscale data using a first threshold matrix to generate first quantized data; 16. The image processing device according to claim 12, wherein the second quantized data is generated by quantizing the other of the two grayscale data using a second threshold matrix different from the first threshold matrix.

17. the generating means generates first gradation data and second gradation data based on gradation data of a first gradation value, and generates third gradation data and fourth gradation data based on gradation data of a second gradation value higher than the first gradation value; a recording dot pattern corresponding to a result of quantizing the third gradation data using the first threshold matrix is ​​a pattern in which recording dots are added to a recording dot pattern corresponding to a result of quantizing the first gradation data using the first threshold matrix, 17. The image processing device according to claim 16, wherein the recording dot pattern corresponding to the result of quantizing the fourth gradation data using the second threshold matrix is ​​a pattern in which recording dots are added to the recording dot pattern corresponding to the result of quantizing the second gradation data using the second threshold matrix.

18. the gradation data corresponds to a first color; the first dot pattern and the second dot pattern are patterns for recording dots of the first color, the acquiring means further acquires gradation data corresponding to a second color; the generating means further generates, based on the gradation data corresponding to the second color, third data corresponding to a third dot pattern for recording dots of the second color, and fourth data corresponding to a fourth dot pattern for recording dots of the second color, the fourth data being recorded on the recording medium so as to be superimposed on the third dot pattern, the third dot pattern includes a third lattice formed of dots repeatedly arranged at a fifth interval in a fifth direction and dots repeatedly arranged at a sixth interval in a sixth direction, the fourth dot pattern includes a fourth lattice formed of dots repeatedly arranged at seventh intervals in a seventh direction and dots repeatedly arranged at eighth intervals in an eighth direction, A second composite dot pattern is formed by combining the third dot pattern and the fourth dot pattern at a relative position where the center of one dot included in the third dot pattern overlaps the center of one dot included in the fourth dot pattern, (iii) a third adjacent dot in which a fifth dot included in the third dot pattern and a sixth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; (iv) a fourth adjacent dot in which a seventh dot included in the third dot pattern and an eighth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; Contains, 13. The image processing device according to claim 12, wherein a third slope of a line connecting the centers of the third adjacent dots is different from a fourth slope of a line connecting the centers of the fourth adjacent dots.

19. The generating means generating first gradation data and second gradation data based on the gradation data corresponding to the first color, and generating third gradation data and fourth gradation data based on the gradation data corresponding to the second color; generating first quantized data corresponding to the first color by comparing a first threshold value in a first threshold matrix with the first grayscale data; generating third quantized data corresponding to the second color by comparing a corrected threshold value obtained by subtracting the value of the first gradation data from the first threshold value with the third gradation data; generating second quantized data corresponding to the first color by comparing a second threshold value in a second threshold matrix with the second grayscale data; 19. The image processing device according to claim 18, wherein fourth quantized data corresponding to the second color is generated by comparing a corrected threshold value obtained by subtracting the value of the third gradation data from the second threshold value with the fourth gradation data.

20. 20. An image processing apparatus according to claim 18, wherein the brightness of the dots of the first color is lower than the brightness of the dots of the second color.

21. the third dot pattern is recorded by the forward scan, the fourth dot pattern is recorded by the backward scan; 21. The image processing device according to claim 12, wherein the image processing device is a computer.

22. A step of obtaining gradation data corresponding to a predetermined gradation value; generating, based on the gradation data, first data corresponding to a first dot pattern to be recorded by a first nozzle array provided in a recording means in a predetermined scan, and second data corresponding to a second dot pattern to be recorded by a second nozzle array provided in the recording means in the predetermined scan and to be recorded on a recording medium so as to be superimposed on the first dot pattern; 1. An image processing method comprising: the first dot pattern includes a first lattice formed of dots repeatedly arranged at a first interval in a first direction and dots repeatedly arranged at a second interval in a second direction; the second dot pattern includes a second lattice formed of dots repeatedly arranged at a third interval in a third direction and dots repeatedly arranged at a fourth interval in a fourth direction, a composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a first relative position where a center of one dot included in the first dot pattern overlaps a center of one dot included in the second dot pattern, (i) a first adjacent dot in which a first dot included in the first dot pattern and a second dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals; (ii) a second adjacent dot in which a third dot included in the first dot pattern and a fourth dot included in the second dot pattern are adjacent at a distance shorter than any of the first, second, third, and fourth intervals; Including, An image processing method, wherein a first slope of a line connecting the centers of the first adjacent dots is different from a second slope of a line connecting the centers of the second adjacent dots.

23. The composite dot pattern: (iii) a fifth dot included in the first dot pattern and a sixth dot included in the second dot pattern include a third adjacent dot that is adjacent to the fifth dot and the sixth dot, the third adjacent dot being spaced apart from the fifth dot and the sixth dot, at a distance shorter than any of the first, second, third, and fourth intervals; 23. The image processing method according to claim 22, wherein a third slope of the line connecting the centers of the third adjacent dots is different from the first slope and also different from the second slope.

24. An image processing method as described in Claim 22 or 23, characterized in that the composite dot pattern includes multiple unit areas each including the overlapping dot, the first adjacent dot, and the second adjacent dot in a repeating arrangement.

25. A second composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a second relative position different from the first relative position, (iv) superimposed dots formed by superimposing dots included in the first dot pattern and dots included in the second dot pattern; (v) a fourth adjacent dot, in which a seventh dot included in the first dot pattern and an eighth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the seventh dot and the eighth dot is the first slope; (vi) a fifth adjacent dot in which a ninth dot included in the first dot pattern and a tenth dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals, and the slope connecting the centers of the ninth dot and the tenth dot is the second slope; 25. The image processing method according to claim 22, further comprising:

26. A step of generating two gradation data based on the gradation data; quantizing one of the two grayscale data using a first threshold matrix to generate first quantized data; generating second quantized data by quantizing the other of the two grayscale data using a second threshold matrix different from the first threshold matrix; 26. The image processing method according to any one of claims 22 to 25, further comprising:

27. ​​First gradation data and second gradation data are generated based on the gradation data of the first gradation value; third gradation data and fourth gradation data are generated based on gradation data of a second gradation value higher than the first gradation value; a recording dot pattern corresponding to a result of quantizing the third gradation data using the first threshold matrix is ​​a pattern in which recording dots are added to a recording dot pattern corresponding to a result of quantizing the first gradation data using the first threshold matrix, 27. The image processing method according to claim 26, wherein the recording dot pattern corresponding to the result of quantizing the fourth gradation data using the second threshold matrix is ​​a pattern in which recording dots are added to the recording dot pattern corresponding to the result of quantizing the second gradation data using the second threshold matrix.

28. The gradation data corresponds to a first color, the first dot pattern and the second dot pattern are patterns for recording dots of the first color, The image processing method includes: obtaining gradation data corresponding to a second color; a step of further generating third data corresponding to a third dot pattern for recording dots of the second color based on the gradation data corresponding to the second color, and fourth data corresponding to a fourth dot pattern for recording dots of the second color, which is recorded on a recording medium so as to be superimposed on the third dot pattern; and the third dot pattern includes a third lattice formed of dots repeatedly arranged at a fifth interval in a fifth direction and dots repeatedly arranged at a sixth interval in a sixth direction, the fourth dot pattern includes a fourth lattice formed of dots repeatedly arranged at seventh intervals in a seventh direction and dots repeatedly arranged at eighth intervals in an eighth direction, A second composite dot pattern is formed by combining the third dot pattern and the fourth dot pattern at a relative position where the center of one dot included in the third dot pattern overlaps the center of one dot included in the fourth dot pattern, (iii) a third adjacent dot in which a fifth dot included in the third dot pattern and a sixth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; (iv) a fourth adjacent dot in which a seventh dot included in the third dot pattern and an eighth dot included in the fourth dot pattern are adjacent at a distance shorter than any of the fifth, sixth, seventh, and eighth intervals; Contains, 23. The image processing method according to claim 22, wherein a third slope of a line connecting the centers of the third adjacent dots is different from a fourth slope of a line connecting the centers of the fourth adjacent dots.

29. A step of generating first gradation data and second gradation data based on the gradation data corresponding to the first color, and generating third gradation data and fourth gradation data based on the gradation data corresponding to the second color; generating first quantized data corresponding to the first color by comparing a first threshold value in a first threshold matrix with the first grayscale data; generating third quantized data corresponding to the second color by comparing a corrected threshold value obtained by subtracting the value of the first gradation data from the first threshold value with the third gradation data; generating second quantized data corresponding to the first color by comparing a second threshold value in a second threshold matrix with the second grayscale data; generating fourth quantized data corresponding to the second color by comparing a corrected threshold value obtained by subtracting the value of the third gradation data from the second threshold value with the fourth gradation data; 29. The image processing method according to claim 28, further comprising:

30. The image processing method according to claim 28 or 29, wherein the brightness of the dots of the first color is lower than the brightness of the dots of the second color.

31. An acquisition means for acquiring gradation data corresponding to a predetermined gradation value; a generating means for generating, based on the gradation data, first data corresponding to a first dot pattern to be recorded by a first nozzle array provided in a recording means in a predetermined scan, and second data corresponding to a second dot pattern to be recorded by a second nozzle array provided in the recording means in the predetermined scan and to be recorded on a recording medium so as to be superimposed on the first dot pattern; An image processing device comprising: the first dot pattern includes a first lattice formed of dots repeatedly arranged at a first interval in a first direction and dots repeatedly arranged at a second interval in a second direction; the second dot pattern includes a second lattice formed of dots repeatedly arranged at a third interval in a third direction and dots repeatedly arranged at a fourth interval in a fourth direction, a composite dot pattern obtained by combining the first dot pattern and the second dot pattern at a first relative position where a center of one dot included in the first dot pattern overlaps a center of one dot included in the second dot pattern, (i) a first adjacent dot in which a first dot included in the first dot pattern and a second dot included in the second dot pattern are adjacent to each other at a distance shorter than any of the first, second, third, and fourth intervals; (ii) a third dot included in the first dot pattern and a fourth dot included in the second dot pattern are second adjacent dots that are adjacent at a distance shorter than any of the first, second, third, and fourth intervals; Including, an image processing device, characterized in that a first gradient of a line connecting the centers of the first adjacent dots is different from a second gradient of a line connecting the centers of the second adjacent dots;

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