Image processing method, image processing device, and storage medium

Abstract

This invention relates to an image processing method, an image processing apparatus, and a storage medium. The aim is to print high-quality images resistant to printing misalignment. To this end, the image processing apparatus generates quantized data for printing a first dot pattern and a second dot pattern in an overlapping manner. The first and second dot patterns are lattice patterns that differ in the combination of two basis vectors. In the composite dot pattern obtained by synthesizing the first and second dot patterns, there exist neighboring points, in which points in the first and second dot patterns are arranged at intervals smaller than the lattice spacing. The neighboring points include a plurality of neighboring points that differ in their proximity direction.

Description

[0001] (This application is a divisional application of the application filed on July 29, 2021, with application number 202110865682.2 and titled "Image Processing Method, Image Processing Apparatus and Storage Medium".) Technical Field

[0002] This invention relates to image processing methods and image processing apparatus. Background Technology

[0003] In printing devices that print images by moving the printhead and printing medium relative to each other, the graininess or density inhomogeneity of the image caused by printing misalignment due to the aforementioned relative movement sometimes becomes apparent. For example, in serial inkjet printing devices that perform multiple print passes and where printing misalignment occurs in any print scan, the relative misalignment between groups of dots printed in different print scans affects the dot dispersion, and in some cases this is sensed as graininess or density inhomogeneity.

[0004] Japanese Patent Application Publication No. 2017-035886 discloses a method for suppressing uneven density caused by printing misalignment between scans in multi-pass printing by controlling the frequency at which points printed in one scan are adjacent to points printed in another scan in the scanning direction.

[0005] In addition, Japanese Patent Application Publication No. 2014-113819 discloses a method for creating a threshold matrix for each of the first and second print scans that can stabilize the coverage of dots on the print medium, even if a print misalignment occurs between the first and second print scans.

[0006] While the configuration described in Japanese Patent Application Publication No. 2017-035886 is effective for situations where dots printed in one scan are misaligned relative to dots printed in another scan in the scanning direction of the printhead, it does not achieve the same effect for misalignments in the sub-scanning direction. Furthermore, although the configuration in Japanese Patent Application Publication No. 2014-113819 can suppress uneven density and variations in graininess, issues regarding pre-existing graininess in the image still remain. Summary of the Invention

[0007] This invention was made to solve the aforementioned problems. Therefore, the object of this invention is to print high-quality images while minimizing unevenness in grain size or density, even in the event of printing misalignment caused by movement of the print head and printing medium relative to each other.

[0008] In a first aspect of the invention, an image processing method is provided, comprising the steps of: obtaining grayscale data, the grayscale data being used to represent a predetermined grayscale value on a printing medium by printing a first dot pattern and a second dot pattern in an overlapping manner on the printing medium; and generating data for causing a print head to print the first dot pattern and data for causing the print head to print the second dot pattern based on the grayscale data corresponding to the predetermined grayscale value, wherein the first dot pattern and the second dot pattern are each a grid pattern whose position from an arbitrary point to a point other than the arbitrary point is specified by two basis vectors, and are grid patterns that differ in the combination of the two basis vectors, by printing the first dot pattern on the printing medium by overlapping the first dot pattern on the printing medium to represent a predetermined grayscale value; and generating data for causing a print head to print the first dot pattern and data for causing the print head to print the second dot pattern based on the grayscale data corresponding to the predetermined grayscale value, wherein the first dot pattern and the second dot pattern are each grid pattern whose position from an arbitrary point to a point other than the arbitrary point is specified by two basis vectors, and are grid patterns that differ in the combination of the two basis vectors, by printing the first dot pattern on the printing medium to represent a predetermined grayscale value on the printing medium by overlapping the first dot pattern on the printing medium to represent a predetermined grayscale value on the printing medium; and generating data for causing a print head to print the first dot pattern and the second dot pattern based on the grayscale data corresponding to the predetermined grayscale value, by printing the first dot pattern on the printing medium to represent a predetermined grayscale value on the printing medium ... overlapping the first dot pattern on the printing medium to represent a predetermined grayscale value on the printing medium; and generating data for causing a print head to print the first dot pattern and the second dot pattern based on the grayscale data corresponding to the predetermined A composite point pattern formed by superimposing any point included in the first point pattern and any point included in the second point pattern one on top of the other includes superimposed points and neighboring points. The superimposed points are formed by superimposing a point included in the first point pattern and a point included in the second point pattern. Among the neighboring points, a point included in the first point pattern and a point included in the second point pattern are arranged at intervals smaller than the grid spacing defined by the basis vector. The neighboring points include a plurality of neighboring points that differ in the inclination of the straight line connecting the center of a point in the first point pattern and the center of a point in the second point pattern that forms the neighboring points.

[0009] In a second aspect of the invention, an image processing apparatus is provided, comprising: a unit configured to obtain grayscale data for representing a predetermined grayscale value on a printing medium by printing a first dot pattern and a second dot pattern in an overlapping manner; and a unit configured to generate data for causing a print head to print the first dot pattern and data for causing the print head to print the second dot pattern based on the grayscale data corresponding to the predetermined grayscale value, wherein the first dot pattern and the second dot pattern are each a lattice pattern whose position from an arbitrary point to a point other than the arbitrary point is specified by two basis vectors, and are lattice patterns different in terms of the combination of the two basis vectors, by... The composite point pattern formed by superimposing any point included in the first point pattern and any point included in the second point pattern one on top of the other includes superimposed points and neighboring points. The superimposed points are formed by superimposing a point included in the first point pattern and a point included in the second point pattern. Among the neighboring points, a point included in the first point pattern and a point included in the second point pattern are arranged at intervals smaller than the grid spacing defined by the basis vector. The neighboring points include a plurality of neighboring points that differ in the inclination of the straight line connecting the center of a point in the first point pattern and the center of a point in the second point pattern that forms the neighboring points.

[0010] In a third aspect of the invention, a non-transitory computer-readable storage medium is provided, the program being configured to cause one or more processors of a computer to perform an image processing method, the image processing method comprising the steps of: obtaining grayscale data, the grayscale data being used to represent a predetermined grayscale value on a printing medium by printing a first dot pattern and a second dot pattern in an overlapping manner on the printing medium; and generating data for causing a print head to print the first dot pattern and data for causing the print head to print the second dot pattern based on the grayscale data corresponding to the predetermined grayscale value, wherein the first dot pattern and the second dot pattern are each a lattice pattern whose position from an arbitrary point to a point other than the arbitrary point is specified by two basis vectors, and are... A composite point pattern formed by superimposing any point included in the first point pattern and any point included in the second point pattern on top of each other, comprising superimposed points and neighboring points, wherein the superimposed points are formed by superimposing a point included in the first point pattern and a point included in the second point pattern, wherein the neighboring points are arranged at intervals smaller than the grid spacing defined by the basis vectors, and the neighboring points comprise a plurality of neighboring points that differ in the inclination of the straight line connecting the center of a point in the first point pattern and the center of a point in the second point pattern.

[0011] Further features of the invention will become apparent from the following description of typical embodiments with reference to the accompanying drawings. Attached Figure Description

[0012] Figure 1 This is a diagram illustrating an example of a robust pattern;

[0013] Figure 2 It is a diagram showing the state in which the first and second point patterns are misaligned relative to each other;

[0014] Figure 3A and 3B It is a diagram used to illustrate the misalignment and reproduction of a translated symmetrical point pattern;

[0015] Figure 4A and 4B It is a diagram showing the misalignment state in the reproduction cycle of the translational symmetric point pattern;

[0016] Figure 5A and 5B It is a graph used to illustrate changes in coverage;

[0017] Figure 6 This is a diagram showing the change in coverage area that occurs as the overlapping points separate;

[0018] Figures 7A to 7C It is a diagram that shows the separation of superimposed points and the superposition of neighboring points in parallel;

[0019] Figure 8 This is a diagram used to illustrate a counterexample of the second condition for achieving robust patterns;

[0020] Figure 9 This is a diagram used to illustrate a counterexample of the second condition for achieving robust patterns;

[0021] Figure 10 This is a diagram used to illustrate a counterexample to the third condition for achieving robust patterns;

[0022] Figure 11 It is a diagram used to illustrate the structure of printing equipment;

[0023] Figure 12 This is a diagram used to illustrate the print head;

[0024] Figure 13 This is a block diagram showing the structure of the printing system;

[0025] Figure 14 This is a flowchart of the image processing in the first embodiment;

[0026] Figure 15 It is an explanatory diagram that is printed bidirectionally and multiple times;

[0027] Figure 16 This is a functional block diagram used to implement quantization processing;

[0028] Figure 17 This is a diagram showing an example of a threshold matrix;

[0029] Figures 18A to 18C This is a graph showing the results of quantization processing for different grayscale values;

[0030] Figures 19A to 19C It is a diagram showing the dot pattern based on the results of quantization.

[0031] Figures 20A to 20C This is a diagram showing the result of quantization processing in the second embodiment;

[0032] Figure 21 This is a diagram showing the dot pattern based on the result of quantization processing in the second embodiment;

[0033] Figures 22A to 22C This is a schematic diagram showing the printhead used in the third embodiment;

[0034] Figure 23 This is a flowchart of image processing in the third embodiment;

[0035] Figures 24A to 24C It is a diagram showing the point arrangement pattern and the reference index pattern;

[0036] Figure 25A and 25B This is a diagram used to illustrate the time-division driven method;

[0037] Figures 26A to 26D This is a diagram used to illustrate the drive control in the third embodiment;

[0038] Figure 27A and 27B It is a diagram used to illustrate the offset of the drive timing in forward and reverse scans;

[0039] Figure 28A and 28B It is a diagram used to illustrate the vertical offset of a grid group;

[0040] Figure 29A and 29B This is a diagram illustrating the lattice pattern implemented in the third embodiment;

[0041] Figures 30A to 30D It is a graph showing the index pattern and binary data;

[0042] Figure 31A and 31B This is a diagram illustrating a method for creating an index pattern;

[0043] Figure 32A and 32B This is a diagram illustrating the threshold matrix used in the third embodiment;

[0044] Figure 33 This is a diagram illustrating the robust pattern implemented in the third embodiment;

[0045] Figures 34A to 34D This is a diagram showing the threshold matrix used in the low grayscale value region;

[0046] Figure 35 It is a diagram showing the dot pattern formed in a low grayscale value area;

[0047] Figure 36 This is a flowchart of image processing in the fourth embodiment;

[0048] Figures 37A to 37C This is a diagram illustrating the dot arrangement pattern and index pattern in the fourth embodiment; and

[0049] Figure 38A and 38B This is a diagram showing the mask pattern used in mask processing. Detailed Implementation

[0050] <Characteristics of robust patterns>

[0051] First, a description of robust patterns generally applicable to embodiments of the present invention is given. In this specification, a robust pattern is a dot pattern formed by printing two dot patterns in an overlapping manner within a predetermined pixel area, and has the characteristic that even if the two dot patterns are misaligned relative to each other, the dot coverage and granularity in the pixel area do not change significantly. Note that coverage indicates the proportion of the dot coverage area relative to the printing medium.

[0052] Figure 1 This is a diagram illustrating an example of a robust pattern. Figure 1 This shows the state where points with a diameter of 42 μm are selectively arranged at pixel positions on the XY plane at 1200 dpi. Figure 1 The diagram shows a state where a first dot pattern 101, formed by a group of first points, and a second dot pattern 102, formed by a group of second points, are placed one on top of the other to form a robust pattern 100. Figure 1 In the image, although the patterns are partially cut out and shown, it is assumed that each pattern is arranged repeatedly in the X and Y directions.

[0053] <Misalignment in units of one pixel>

[0054] Figure 2 This shows the state where the second dot pattern 102 is offset by one pixel relative to the first dot pattern 101. The central pattern shows the state where there is no offset, and is consistent with... Figure 1 The robust pattern 100 is the same as the central pattern. The pattern around the central pattern shows the state of the second point pattern 102 being offset by one pixel (21 μm) relative to the first point pattern 101 in eight directions on the XY plane.

[0055] Similar repeating patterns 200 were found to appear in each dot pattern. Furthermore, although these nine patterns differ in the position of the repeating pattern 200, they are essentially the same dot patterns where the repeating pattern 200 is repeated in both the vertical and horizontal directions. In this case, if the second dot pattern 102 of each of the eight patterns shown around the central pattern is further offset by one pixel in the same direction, a pattern where the repeating pattern 200 is repeated in both the vertical and horizontal directions is obtained as described above.

[0056] As described above, the robust pattern 100 has the characteristic that, even when the first point pattern 101 and the second point pattern 102 are misaligned relative to each other, the same point pattern can be obtained regardless of the amount and direction of the misalignment. In the following description, the characteristic is referred to as "translational symmetry": even if the first point pattern 101 and the second point pattern 102 are misaligned relative to each other in the XY direction, the same repeating pattern 200 can be obtained arranged at different phases. Furthermore, the minimum misalignment amount required to reproduce "translational symmetry" is called the "translational symmetry reproduction period." Figure 1 and 2 In the robust pattern described, a pixel (21 μm) at 1200 dpi is a “translation-symmetric reproduction period”.

[0057] Figure 3A and 3B It is a diagram used to illustrate the mechanism by which translational symmetry can be obtained in robust patterns.

[0058] Figure 3A This shows a state where there is no misalignment between the first point pattern 101 and the second point pattern 102. Figure 3A The dot pattern includes overlapping points 301, in which a first point forming the first dot pattern 101 and a second point forming the second dot pattern 102 are superimposed one on top of the other. Furthermore, Figure 3A The dot pattern includes neighboring points 302 to 305, where the first and second points are partially superimposed on each other, and individual points not superimposed on the other points. Figure 3A In the diagram, a dashed line is used to indicate the baseline passing through the center of the superposition point 301.

[0059] In this case, if we focus on any one of the superposition points 301, we find that the arrangement of the first and second points around that superposition point 301 is point-symmetric with respect to the superposition point 301. For example, in Figure 3A In the process, the neighboring point 303 formed by the second point on the left and the first point on the right is arranged at a position symmetrical to the neighboring point 302 formed by the first point on the left and the second point on the right relative to the superposition point 301. In addition, the neighboring point 305 formed by the second point on the upper side and the first point on the lower side is arranged at a position symmetrical to the neighboring point 304 formed by the first point on the upper side and the second point on the lower side relative to the superposition point 301.

[0060] Figure 3B This shows the state where the second point pattern 102 is offset by one pixel (21 μm) relative to the first point pattern 101 in the +X direction. Figure 3A The various superposition points 301 in the middle are changed to Figure 3B The nearest point 302 is formed by the first point on the left and the second point on the right. Furthermore, Figure 3AThe neighboring point 303 formed by the second point on the left and the first point on the right is changed to Figure 3B The superposition point is 301.

[0061] By comparison Figure 3A and 3B ,although Figure 3B The position of the superposition point 301 is from Figure 3A The position of the overlay point 301 changes, but the number and period of the overlay points 301 (i.e., the number and period of the baselines) remain unchanged. Furthermore, the layout of the first and second points in the repeating pattern 200 surrounded by the baselines also remains unchanged. Specifically, even if a misalignment occurs between the first point pattern 101 and the second point pattern 102 in units of one pixel (i.e., in units of translational symmetry reproduction period), the point coverage in the repeating pattern 200 remains unchanged.

[0062] <Dislocation with a period smaller than that of translational symmetry>

[0063] Figure 4A and 4B This is a diagram used to illustrate the effect of a misalignment of less than one pixel (21 μm) between the first dot pattern 101 and the second dot pattern 102. Figure 4A The diagram is shown for simplicity, illustrating misalignment units smaller than one pixel. A pixel at 1200 dpi is shown as further subdivided into 8×8 regions at 9600 dpi. At 9600 dpi, the grid spacing is approximately 2.6 μm.

[0064] Figure 4B The following states are shown: with the upper left corner of the first point pattern 101 fixed at the origin A(0,0), the upper left corner of the second point pattern 102 is offset to various positions. Figure 4B The diagram shows five states where the upper left corner of the second point pattern 102 is offset to points A(0,0), B(4,0), C(8,0), D(4,4), and E(8,8). The pattern at point A(0,0) corresponds to... Figure 2 The central portion shows a robust pattern 100. The pattern at point C(8,0) corresponds to... Figure 2 The pattern in the center right part, and the pattern at point E(8,8) corresponds to Figure 2 The pattern in the lower right part.

[0065] Figure 5A and 5B This is a graph showing the change in point coverage in misalignments with a reproduction period smaller than that of translational symmetry. Figure 5A The position of pattern 102 at the second point is shown. Figure 4AThe change in point coverage when the points A(0,0) and C(8,0) change (specifically, when the second point pattern 102 is misaligned in the +X direction (right direction)). On the other hand, Figure 5B The diagram illustrates the change in dot coverage when the position of the second dot pattern changes between point A(0,0) and point E(8,8) (specifically, when the second dot pattern is misaligned in the +XY direction (lower right direction). In this case, dot coverage indicates the proportion of the sheet surface covered by dots with a diameter of 42 μm, and the change in dot coverage indicates the rate of change of dot coverage due to misalignment.

[0066] exist Figure 5A In the diagram, the patterns at point A(0,0) and point C(8,0) are in a relationship where these patterns are offset from each other by a translational symmetry reproduction cycle. Therefore, these patterns are translationally symmetric and have the same point coverage (40.1%). Thus, the point coverage variation in these two patterns is 0%. On the other hand, the pattern at point B(4,0) is between those at points A(0,0) and C(8,0), and is not translationally symmetric to the patterns at points A(0,0) and C(8,0), and has a larger point coverage of 40.5%. Therefore, the point coverage variation is +0.4% (=40.5-40.1).

[0067] exist Figure 5B In the diagram, the patterns at point A(0,0) and point E(8,8) are in a relationship where these patterns are offset from each other by a translational symmetry reproduction cycle. Therefore, these patterns are translationally symmetric, and both have a point coverage of 40.1%. Consequently, the point coverage variation in these two patterns is 0%. On the other hand, the pattern at point D(4,4) is between points A(0,0) and E(8,8), and is not translationally symmetric with the patterns at points A(0,0) and E(8,8), and has a larger point coverage of 40.6%. Therefore, the point coverage variation is +0.5% (=40.6-40.1). However, this degree of variation is sufficiently small to be perceived by visually as the coverage of the sheet surface is small enough to be imperceptible.

[0068] Specifically, in the robust pattern described above, concentration changes caused by misalignments smaller than the translational symmetry reproduction period are not visually perceptible, and no concentration change itself occurs within misalignments measured in units of the translational symmetry reproduction period. Therefore, the robust pattern described above is one in which concentration non-uniformity is unlikely to occur regardless of the misalignment direction or amount.

[0069] <About neighboring points>

[0070] Figure 6This is a graph showing the change in coverage area at a microscopic level as the overlapping points separate. The horizontal axis represents the misalignment of the second point relative to the first point, and the unit is 9600 dpi pixels. One pixel corresponds to approximately 2.6 μm. The vertical axis represents the coverage area relative to the sheet, and the unit is points. Specifically, "1" corresponds to the coverage area of ​​a point with a diameter of 42 μm.

[0071] When the first and second points are perfectly superimposed, one on top of the other, the coverage area is 1. The more the second point is misaligned relative to the first point, the larger the coverage area becomes. When the two points are completely separated by a misalignment of approximately 16 pixels, the coverage area becomes 2. Afterward, regardless of the misalignment, the coverage area remains at 2. Note that when a misalignment occurs between the first and second point patterns, there is a situation as follows: Figure 6 In that case, the separated parts of the superimposed points and the separated points are changed to the superimposed parts.

[0072] Figures 7A to 7C It is a diagram showing in parallel the state in which the superimposed points are separated due to the misalignment between the first point pattern 101 and the second point pattern 102, and the state in which the points of neighboring points are superimposed on top of each other due to the misalignment. Figure 7A This illustrates a case where neighboring points, spaced apart by 1.5 points (approximately 63 μm), are superimposed one on top of the other. Figure 7B This illustrates a case where neighboring points, spaced far apart by an interval corresponding to 1.0 points (approximately 42 μm), are superimposed one on top of the other. Furthermore, Figure 7C The figures illustrate the superposition of neighboring points spaced apart by 0.5 points (approximately 21 μm) one on top of the other. In each figure, the coverage area of ​​the ultimately separated superimposed points is shown by a dotted line, the coverage area of ​​the ultimately superimposed neighboring points is shown by a dashed line, and the sum of these two types of coverage areas (total coverage area) is shown by a solid line. Furthermore, in each figure, the horizontal axis represents the range until the neighboring points become completely superimposed points.

[0073] exist Figure 7A In this context, the initial and final values ​​of the total coverage area are 3 points, and the total coverage area reaches its maximum value of 3.8 points at the median of 12 pixels. Figure 7B In this context, the initial and final values ​​of the total coverage area are 3 points, and the total coverage area reaches its maximum value of 3.3 points at the median of 8 pixels. Figure 7C In the middle, the total coverage area stabilized at 2.6 points from the initial value to the final value.

[0074] In particular, through comparison Figures 7A to 7CIn order to suppress concentration changes caused by misalignments smaller than the translation symmetry reproduction period, it is preferable to make the interval between two points forming pre-prepared adjacent points as small as possible, more preferably equal to 0.5 points or less. However, the concentration detected visually is not always proportional to the coverage of the points. Specifically, it is preferable to appropriately adjust the interval between two points to be pre-prepared in a robust pattern according to the printing resolution, point diameter, and point density.

[0075] <Conditions for a Stable Pattern>

[0076] The following describes the conditions required for a pattern to become a robust pattern with the above characteristics.

[0077] The first condition is that the first dot pattern and the second dot pattern are formed by different grid patterns from each other.

[0078] This section defines a lattice pattern. In this specification, a lattice pattern is a pattern in which the position of any point from one point to another can be specified by two basis vectors. For example, Figure 1 The first point pattern 101 can be referred to as a lattice pattern with a1 and b1 as basis vectors. Furthermore, the second point pattern 102 can be referred to as a lattice pattern with a2 and b2 as basis vectors. Two lattice patterns defined by the same basis vectors can be considered as identical lattice patterns, and two lattice patterns defined by different basis vectors can be considered as different lattice patterns. Specifically, the first point pattern 101 with basis vectors a1 and b1 and the second point pattern 102 with basis vectors a2 and b2 are different point patterns.

[0079] When the first and second point patterns are the same lattice pattern, almost all points become superimposed points at any point where they become superimposed points. In this case, translating the symmetrical point pattern in a misalignment smaller than the lattice spacing defined by the basis vectors will not reproduce the pattern. Therefore, there is a risk of uneven concentration and deteriorated particle size in cases of misalignments larger than the basis vectors.

[0080] The second condition is that, when generating overlay points from arbitrary points, the overlay points and neighboring points exist in a mixed manner. Furthermore, the first and second points forming the neighboring points are arranged at an interval smaller than the grid spacing defined by the basis vectors.

[0081] Figure 8An example of a pattern that satisfies the first condition but not the second condition is shown. Although the first dot pattern 801 and the second dot pattern 802 are different dot patterns, there are no neighboring points in the composite dot pattern 803 obtained by superimposing patterns 801 and 802 one on top of the other. All points are either superimposed points 804 or individual points 805. In this case, translational symmetry cannot be achieved between the first dot pattern 801 and the second dot pattern 802 in a misalignment smaller than the grid spacing, and the desired result cannot be obtained. Figures 7A to 7C The effect of stabilizing the coverage area.

[0082] also, Figure 9 Another example of a pattern that satisfies the first condition but not the second condition is shown. In this example, the first point pattern 901 and the second point pattern 902 are different lattice patterns, and in the composite point pattern 903 obtained by superimposing patterns 901 and 902 one on top of the other, there are superimposed points 904 and adjacent points 905. However, the interval D2 between the two points forming adjacent points 905 is greater than the lattice spacing D1 defined by the basis vectors of the first point pattern 901. In this case, with the first point pattern 901 and the second point pattern 902 misaligned relative to each other at a distance equal to or less than the lattice spacing and the superimposed point 904 separated, the points of adjacent points 905 cannot be sufficiently superimposed one on top of the other. As a result, again in this pattern, it is not possible to obtain a pattern as described above. Figures 7A to 7C The effect of stabilizing the coverage area.

[0083] The third condition is that there are neighboring points with different directions of approach among multiple neighboring points. In this case, the direction of approach refers to the inclination of the straight line connecting the centers of the first and second points that form each neighboring point.

[0084] Figure 10 An example of a pattern that satisfies the first and second conditions but not the third condition is shown. In this example, the first dot pattern 1001 and the second dot pattern 1002 are different lattice patterns, and there are overlapping points 1004 and neighboring points 1005 in the composite dot pattern 1003 obtained by superimposing patterns 1001 and 1002 one on top of the other. Furthermore, the first and second points forming each neighboring point 1005 are arranged with a spacing D2 smaller than the lattice spacing D1 of the first dot pattern 1001 and the second dot pattern 1002.

[0085] However, in the composite point pattern 1003, all neighboring points 1005 are formed by the first point and the second point approaching each other in the X direction, and not by approaching each other in directions other than the X direction. In this configuration, even when the first point pattern 1001 and the second point pattern 1002 are misaligned in the approach direction (i.e., the X direction), it is possible to obtain... Figure 7A and 7C The effect described herein. However, when the first dot pattern 1001 and the second dot pattern 1002 are misaligned in the Y direction, which is perpendicular to the X direction, as the superimposed point 1004 separates in the Y direction, the two points forming each adjacent point are not superimposed in a manner where one is on top of the other, and this results in a change in the coverage area.

[0086] on the other hand, Figure 1 The robust pattern 100 satisfies all of the first to third conditions mentioned above. Specifically, refer to... Figure 1 The first point pattern 101 and the second point pattern 102 are formed by lattice patterns with different basis vectors (first condition). In the composite point pattern 100 obtained by superimposing patterns 101 and 102 one on top of the other, there are superimposed points 104 and neighboring points 105, and the first and second points forming each neighboring point 105 are arranged at intervals smaller than the lattice spacing defined by the basis vectors (second condition). Furthermore, in the composite point pattern 100, there are multiple neighboring points with different approach directions, such as neighboring points of the first and second points approaching each other in the X direction, neighboring points of the first and second points approaching each other in the Y direction, and neighboring points of the first and second points approaching each other in the diagonal direction, etc. (third condition).

[0087] Therefore, in the composite point pattern 100 that satisfies the above three conditions, a result is obtained by using... Figures 2 to 7C The effects have been described. Specifically, even if a relative misalignment occurs between the first and second dot patterns, no changes in grain size or unevenness in concentration are detected, and the obtained image can be identified as a high-quality image.

[0088] The following describes in detail an embodiment using a robust pattern with the above-described features.

[0089] (First Embodiment)

[0090] In this embodiment, the robust pattern described above is used when bidirectional multi-pass printing is performed on a serial inkjet printer.

[0091] Figure 11 This is a perspective view showing an outline of a printing unit in a serial inkjet printing apparatus 2 (hereinafter also simply referred to as the printing apparatus) applicable to this embodiment. The roller gap (which includes a transport roller 1101 arranged on the transport path and a clamping roller 1102 configured to follow the transport roller 1101) transports the printing medium P to the printing unit along the -Y direction (sub-scanning direction) as the transport roller 1101 rotates.

[0092] The platen 1103 is positioned at the printing position of the printhead H facing the nozzle surface (nozzle surface) of the inkjet printhead H, and supports the back side of the printing medium P from below to maintain a constant distance between the front side of the printing medium P and the nozzle surface of the printhead H.

[0093] The printing medium P in the area where printing is performed on the printing plate 1103 is conveyed in the -Y direction as the printing roller 1105 rotates, while being held by the discharge roller 1105 and the ratchet 1106 configured to follow the discharge roller 1105, and discharged to the discharge tray 1107.

[0094] The printhead H is detachably mounted on the carriage 1108 with its nozzle face facing the pressure plate 1103 or the printing medium P. The carriage 1108 is driven by the carriage motor (not shown) to reciprocate along two guide rails 1109 and 1110 in the X direction, which is the main scanning direction, and during this reciprocating motion, the printhead H performs an ejection operation according to the ejection signal.

[0095] The ±X direction of the carriage 1108's movement intersects with the -Y direction of the printing media transport and is referred to as the main scanning direction. On the other hand, the -Y direction of the printing media transport is referred to as the secondary scanning direction. The main scanning (involving ejection movement) of the carriage 1108 and the printhead H, along with the transport of the printing media P (secondary scanning), are alternately repeated, thereby gradually forming an image on the printing media P.

[0096] Figure 12 This is a schematic diagram showing the printhead H as viewed from the nozzle side. On the nozzle side, four nozzle rows 1201-1204 are arranged in parallel. In each nozzle row, 128 nozzles configured to eject the same type of ink are arranged along the Y direction at a spacing of 1200 dpi. In this embodiment, nozzle row 1201 ejects cyan ink, nozzle row 1202 ejects magenta ink, nozzle row 1203 ejects yellow ink, and nozzle row 1204 ejects black ink.

[0097] Figure 13 This is a block diagram illustrating the control structure of the inkjet printing system applicable to this embodiment. The inkjet printing system of this embodiment includes... Figure 11 The inkjet printing device 2 and the image processing device 1 are described above. The image processing device 1 may be, for example, a personal computer (PC).

[0098] Image processing device 1 generates image data that can be printed by printing device 2. In image processing device 1, main control unit 1308 is composed of a central processing unit, read-only memory (ROM), random access memory (RAM), or application-specific integrated circuit (ASIC), and performs image processing such as creating images in image processing device 1 and printing the created images in printing device 2. Image processing device I / F 1309 exchanges data signals with printing device 2. Display unit 1310 displays various information to the user, and, for example, a liquid crystal display (LCD) is suitable as display unit 1310. Operation unit 1314 is the operation unit used by the user to perform operations, and, for example, a keyboard and mouse are suitable as operation unit 1314. System bus 1312 connects main control unit 1308 and various functions to each other. I / F signal line 1313 connects image processing device 1 and printing device 2 to each other. For example, a line conforming to Centronics Data Computer Corporation specifications is suitable as type I / F signal line 1313.

[0099] In printing device 2, controller 1301 consists of CPU, ROM, and RAM, and controls the entire printing device 2. Print buffer 1302 stores image data as raster data before it is sent to print head H. Inkjet print head H ejects ink from nozzles according to the image data stored in print buffer 1302.

[0100] The feed-discharge motor control unit 1304 drives a transport motor (not shown) and controls the transport, feeding, and discharge of the printing medium P. The carriage motor control unit 1300 drives a carriage motor (not shown) and controls the reciprocating scan of the carriage 1108. The data buffer 1306 temporarily stores image data received from the image processing device 1. The system bus 1307 connects the functions of the printing devices 2 to each other.

[0101] Figure 14 This is a flowchart illustrating the process performed by the main control unit 1308 of the image processing device 1 when printing any image using the printing device 2. This process begins when the user inputs a print command for any image.

[0102] At the start of this process, the main control unit 1308 first performs color correction processing in step S1401. In this embodiment, it is assumed that the image data generated by the application, etc., is data in which each pixel arranged at 1200 dpi has 8-bit 256-level luminance values ​​for R (red), G (green), and B (blue). In the color correction processing, the main control unit 1308 converts such RGB data of each pixel into R'G'B' data represented in the color space specific to the printing device 2. For example, as a specific conversion method, the conversion can be performed by referring to a lookup table pre-stored in memory.

[0103] In step S1402, the main control unit 1308 performs color separation processing on the R'G'B' data. Specifically, the main control unit 1308 refers to a lookup table pre-stored in the memory and converts the brightness value R'G'B' of each pixel into an 8-bit 256-level density value CMYK corresponding to the ink color used by the printing device 2.

[0104] In step S1403, the main control unit 1308 performs segmentation processing on the 8-bit 256-level CMYK data and generates concentration data C1, M1, Y1, and K1 for forward scanning and concentration data C2, M2, Y2, and K2 for reverse scanning. In this case, the main control unit 1308 can roughly equally divide the concentration values ​​of each color indicated in the CMYK data into two parts.

[0105] The same processing is performed on each ink color in parallel below. Therefore, for simplicity, only the processing for the black data (K1, K2) will be described here.

[0106] In steps S1404-1 and S1404-2, the main control unit 1308 performs grayscale correction processing on the concentration values ​​K1 and K2 respectively. Grayscale correction is performed to achieve a linear relationship between the input concentration values ​​and the optical concentration represented on the printing medium P. Typically, grayscale correction is performed by referring to a pre-prepared one-dimensional lookup table. Through the grayscale correction processing in steps S1404-1 and S1404-2, the 8-bit 256-level concentration values ​​K1 and K2 are converted into 8-bit 256-level concentration values ​​K1' and K2'.

[0107] In steps S1405-1 and S1405-2, the main control unit 1308 performs predetermined quantization processing on each concentration value K1' and K2', and generates a quantized value K1" for forward scanning and a quantized value K2" for reverse scanning. The quantized value K1" is a 1-bit binary data indicating whether each pixel in the forward scan is printed (1) or not printed (0). The quantized value K2" is a 1-bit binary data indicating whether each pixel in the reverse scan is printed (1) or not printed (0). This process is thus completed.

[0108] Binary data C1”, M1”, Y1”, and K1” generated in the image processing device for forward scanning and binary data C2”, M2”, Y2”, and K2” for reverse scanning are sent to the printing device 2. The controller 1301 of the printing device 2 performs a predetermined multi-pass printing based on the received binary data.

[0109] Note that, although in Figure 14The flowchart shows a segmentation process between color separation and grayscale correction to divide the data into data for forward scanning and data for reverse scanning, but the segmentation process can be performed after grayscale correction.

[0110] Figure 15 This is a schematic diagram illustrating bidirectional, two-pass, multi-pass printing performed in printing device 2 under the control of controller 1301. In this case, for simplicity, the nozzle row 1204 for black ink among the multiple nozzle rows arranged in printhead H is described (see [link to diagram]). Figure 12 The printing operation.

[0111] In the case of multiple printing passes with two passes, the 128 nozzles included in nozzle column 1204 are divided into a first segmentation region and a second segmentation region.

[0112] In the first print scan, the controller 1301 moves the print head H along the +X direction (which is the positive direction) while performing an ejection operation based on binary data K1” using a first segmented region. Then, the controller 1301 delivers 64 pixels of print media along the -Y direction. Figure 15 In this process, the nozzle array 1204 is moved along the +Y direction to indicate the relative positional relationship between the segmented area and the printing medium.

[0113] In the second print scan, the controller 1301 moves the print head H in the opposite direction to that in the first print scan while performing an ejection operation based on binary data K2” using the first and second segmentation regions. Then, the controller 1301 delivers 64 pixels of print media along the -Y direction.

[0114] In the third print scan, the controller 1301 moves the print head H in the positive direction while performing an ejection operation based on binary data K1” using the first and second segmentation regions. Then, the controller 1301 delivers 64 pixels of print media along the -Y direction.

[0115] Subsequently, these scans are repeated by transferring 64 pixels between a reverse scan (such as a second print scan) and a forward scan (such as a third print scan). This results in the overlapping printing of dot patterns based on binary data K1” printed in the forward scan and dot patterns based on binary data K2” printed in the reverse scan in each unit area of ​​the print medium. In this embodiment, the dot pattern based on binary data K1” printed in the forward scan is referred to as the first dot pattern, and the dot pattern based on binary data K2” printed in the reverse scan is referred to as the second dot pattern.

[0116] Figure 16 It is used to achieve in Figure 14 Functional block diagram of the quantization processing performed in steps S1405-1 and S1405-2. Figure 16 The block in Figure 13 The main control unit 1308 of the image processing device 1 described herein is implemented.

[0117] The image input unit 1601 sends 256 levels of grayscale data C1', C2', M1', M2', Y1', Y2', K1', and K2', which have undergone grayscale correction processing, to the dithering core 1602 prepared for each grayscale data. Although Figure 16 The structure of the dithering core 1602 for K1' is shown, but a similar dithering core 1602 is also prepared for other grayscale data.

[0118] Multiple threshold matrices 1604 corresponding to the various grayscale data C1', C2', M1', M2', Y1', Y2', K1', and K2' are pre-stored in memory 1603. The threshold matrices 1604 store the thresholds in association with the pixel positions of each pixel, and can be generated by a computer and pre-stored in memory 1603.

[0119] The threshold acquisition unit 1605 refers to the threshold matrix 1604 corresponding to K1', obtains the threshold Th corresponding to the pixel position of K1' and received from the threshold matrix 1604 by the dithering kernel 1602, and provides the threshold Th to the quantization processing unit 1606. The quantization processing unit 1606 compares the gray value K1' of the pixel to be processed received from the image input unit 1601 with the threshold Th provided by the threshold acquisition unit 1605, and determines whether the point of the pixel to be processed is printed (1) or not printed (0). The quantization result output unit 1607 outputs the information of printing (1) or not printing (0) determined by the quantization processing unit 1606 as the quantization data K1 of the pixel to be processed.

[0120] Figure 17 This is a diagram showing an example of the threshold matrix stored in memory 1603. A first threshold matrix 1701 for forward scanning and a second threshold matrix 1702 for reverse scanning are prepared as threshold matrices.

[0121] exist Figure 17Among them, each square corresponds to a pixel arranged on the XY plane, and the value described in each square indicates the threshold value of the corresponding pixel position. In this embodiment, since each of K1' and K2' has a value of one of 0 to 255, each threshold Th is set to one of the values of 0 to 254. When K1' in the pixel to be processed is greater than Th, the quantization value K1” of the pixel to be processed is set to printed (K1” = 1). On the other hand, when K1' ≤ Th, the quantization value K1” of the pixel to be processed is set to non - printed (K1” = 0). The same applies to the relationship between K2' and K2”.

[0122] In this embodiment, threshold matrices 1701 and 1702 each having a region of 20 pixels × 20 pixels as shown in Figure 17 are prepared, and both are used by repeatedly arranging threshold matrices 1701 and 1702 in the X - direction and Y - direction respectively in forward scanning and backward scanning. Note that the size of the threshold matrix is not limited to this size. The size can be larger or smaller.

[0123] The first threshold matrix 1701 of this embodiment is created such that at a predetermined gray value, the dot pattern printed according to the result of the quantization process becomes Figure 1 the first dot pattern 101 in Figure 1 In addition, the second threshold matrix 1702 is created such that at a predetermined gray value, the dot pattern printed according to the result of the quantization process becomes

[0124] Figures 18A to 18C the second dot pattern 102 in Figure 18A Thus, even if a printing misalignment occurs at a predetermined gray value between the forward scanning for printing the first dot pattern 101 and the backward scanning for printing the second dot pattern 102, the dot coverage and granularity do not change significantly, and a high - quality image can be printed.

[0125] Similarly, Figure 18B shows the case where K1' = K2' = 13 is input for all pixels, and Figure 18C shows the case where K1' = K2' = 26 is input for all pixels, and Figures 18A to 18CIn the first threshold matrix 1701, the black pixel group and the black pixel group in the second threshold matrix 1702 form different grid patterns.

[0126] Figures 19A to 19C It is shown in accordance with Figures 18A to 18C The image shown is a diagram of the dot pattern formed on the printing medium in the case of quantized print dots. The printing resolution is 1200 dpi and the dot diameter is 42 μm.

[0127] Figure 19A Showing according to Figure 18A The black pixels in the graph are used to print a first dot pattern and a second dot pattern, and a composite dot pattern is obtained by superimposing these patterns one on top of the other. The first dot pattern and the second dot pattern are grid patterns with a grid spacing of Da1 and different from each other (first condition). In the composite dot pattern, a superimposed dot 191 and a plurality of neighboring dots 192 and 193 are formed. The first dot and the second dot forming the neighboring dots 192 and 193 are arranged at intervals of Da2 and Da3, which are smaller than the grid spacing Da1 (second condition). Furthermore, the neighboring dots 192 and 193 are different in their approach directions to the first dot and the second dot (third condition). Specifically, the approach direction of the first dot and the second dot in neighboring dot 192 is the X direction, while the approach direction of the first dot and the second dot in neighboring dot 193 is the Y direction. Therefore, the composite dot pattern can be considered a robust pattern.

[0128] Figure 19B Showing according to Figure 18B The black pixels in the graph are used to print the first and second dot patterns, and a composite dot pattern is obtained by superimposing these patterns one on top of the other. Furthermore, Figure 19C Showing according to Figure 18C The black pixels in the graph are used to print first and second dot patterns, and a composite dot pattern is obtained by superimposing these patterns one on top of the other. Although these composite dot patterns differ in grid spacing (Db1, Dc1), the interval between the first and second points forming each neighboring point (Db2, Db3, Dc2, and Dc3), and the direction of proximity, both composite dot patterns satisfy the first to third conditions. In other words, in Figures 19A to 19C The composite point pattern formed at all the grayscale values ​​shown can be considered a robust pattern.

[0129] As mentioned above, using Figure 17The threshold matrix of the described embodiment allows for the formation of a robust pattern using a first dot pattern printed in the forward scan and a second dot pattern printed in the reverse scan. As a result, even if misalignment occurs in any direction in the XY plane between the forward and reverse scans, the translationally symmetric dot pattern is reproduced, and the dot coverage and granularity do not change significantly. Therefore, high-quality images can be printed.

[0130] A simplified description of the method described above for creating a threshold matrix that can obtain preferred robust patterns across multiple gray levels is provided. Conventionally, methods for creating threshold matrices to obtain high dot dispersion include evaluating the density or sparsity of points in the pixel region forming the threshold matrix and setting thresholds for each pixel in the threshold matrix in ascending order. In this embodiment, thresholds can be set for each pixel of the threshold matrix by adding constraints to each threshold matrix to represent different grid patterns and by further evaluating the density-sparseness of points in the synthesized dot pattern. In any case, as long as a threshold matrix satisfying the first to third conditions described above is implemented at each gray level, even if misalignment occurs in any direction between forward and reverse scanning, translationally symmetrical dot patterns can be reproduced and high-quality images can be printed.

[0131] <Application of the First Embodiment>

[0132] Although the above example illustrates printing a 42μm diameter dot at a 1200dpi resolution, this embodiment is certainly not limited to such conditions.

[0133] Furthermore, despite Figure 14 In the segmentation process (S1403), the concentration values ​​CMYK of each color are divided into two parts approximately equally. However, the concentration values ​​can be segmented unevenly in the segmentation process. In this case, although the number of printed dots is uneven between the first dot pattern and the second dot pattern formed on the printing medium, as long as the first to third conditions described above are met, the same effect as in the above embodiment can be obtained.

[0134] Furthermore, although the above description of two-pass bidirectional multi-pass printing is given as an example, this embodiment can be applied to four-pass or more bidirectional printing. In 2N-pass multi-pass printing, which involves printing by performing N forward scans and N reverse scans in each unit area of ​​the printing medium, the printing device must only form the first dot pattern in the composite of N forward scans and the second dot pattern in the composite of N reverse scans.

[0135] Furthermore, although the above describes two-pass bidirectional multi-pass printing, misalignment between print scans can still occur in multi-pass printing, even if the print scans are in the same direction. In this case, the dot pattern formed in the first print scan and the dot pattern formed in the second print scan must be the first dot pattern and the second dot pattern, respectively.

[0136] Furthermore, although the example given is printing the first and second dot patterns with the same ink and dot size, these patterns can be printed with different inks or different dot sizes. For example, the printing could be such that the first dot pattern is printed in black and the second dot pattern in cyan. Alternatively, the printing could be such that the first dot pattern is printed with large dots and the second dot pattern with small dots. Again, in this case, as long as the composite dot pattern is robust, hue inhomogeneity and grain variation caused by printing misalignment between the dot patterns can be reduced. In this case, the printing could be a single pass of the first and second dot patterns in the same print scan.

[0137] (Second Embodiment)

[0138] Traditionally, a situation exists where, even if preferred dot dispersion is achieved for a single color, the dot dispersion decreases and granularity becomes noticeable in the printing of mixed-color images. To address this problem, U.S. Patent 6,867,884 discloses a quantization method for achieving preferred dot dispersion in color mixing. Specifically, U.S. Patent 6,867,884 discloses a quantization process that involves preparing a dithering matrix capable of achieving preferred dispersion, and applying the same dithering matrix to multiple colors while shifting a threshold among them. In this embodiment, a method is provided for shifting the threshold among multiple colors by using... Figure 17 This section describes the quantization processing mode using the dithering matrix. Note that it is assumed that this embodiment also uses... Figures 11 to 13 The inkjet printing system described above.

[0139] Refer again Figure 16 The quantization process of this embodiment will be explained. In this case, as an example of the priority of quantization, black is set as the first color and cyan is set as the second color. First, in the dithering kernel 1602 used as the first color K1', 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, it is assumed that using Figure 17 The first threshold matrix 1701 is used as the jitter matrix for K1'.

[0140] The quantization processing unit 1606 compares the gray value of K1' received from the image input unit 1601 with the threshold Thk provided by the threshold acquisition unit 1605, and determines whether to print (1) or not print (0) the point for the pixel to be processed. Specifically:

[0141] In the case that K1'>Thk, K1”=1

[0142] When K1'≤Thk, K1”=0.

[0143] Next, in the dithering kernel 1602 used for cyan as the second color, the thresholding unit 1605 refers to the first threshold matrix 1701 described above 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 used for cyan sets the value obtained by subtracting the value of K1' from the provided threshold Thk as a new threshold Thc for C1'. Specifically:

[0144] Thc = Thk - K1'.

[0145] In this case, if Thc is negative, the quantization processing unit 1606 adds the maximum gray value 255 to correct the threshold Thc.

[0146] Thc = 255 + Thc

[0147] Then, the quantization processing unit 1606 performs quantization processing on C1' received from the image input unit 1601 using the threshold Thrc obtained as described above. Specifically:

[0148] In the case where C1'>Thc, C1”=1

[0149] When C1'≤Thc, C1”=0.

[0150] Note that the same processing as described above is also performed on K2' and C2', which are grayscale data used for backward scanning, by using the second threshold matrix 1702.

[0151] Figures 20A to 20C This is a graph showing the result of the quantization process performed in this embodiment. Figure 20A The diagram shows the distribution of pixels where the quantization data K1” and K2” are 1 when each pixel input K1' = K2' = 20. For K1' and K2' as the first color, pixels with thresholds of 0 to 19 set in the first threshold matrix 1701 and the second threshold matrix 1702 are black pixels.

[0152] Figure 20BThis shows the distribution of pixels where the quantization data C1” and C2” are 1, given that C1’=C2’=6 for each pixel input. Figure 20B The diagram shows the threshold matrices obtained by correcting the individual thresholds in the first threshold matrix 1701 and the second threshold matrix 1702 according to the formula described above. For C1' and C2', which are the second colors, pixels with correction thresholds of 0 to 5 set in the corrected first and second threshold matrices are black pixels. Such black pixels correspond to pixels with thresholds of 20 to 25 set in the first threshold matrix 1701 and the second threshold matrix 1702 before correction. Specifically, in the sum of K1" and C1" the pixels with thresholds of 0 to 25 set in the first threshold matrix 1701 are black pixels, and in the sum of K2" and C2" the pixels with thresholds of 0 to 25 set in the second threshold matrix 1702 are black pixels.

[0153] Figure 20C Shown in accordance with Figure 20A and 20B The quantization results shown are the dot patterns formed on the printing medium in the case of printed dots. Figure 20C In the example, the printing 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 based on the first threshold matrix 1701. Furthermore, the second dot pattern, which is the sum of K2” and C2”, is a lattice pattern based on the second threshold matrix 1702. Therefore, the composite dot pattern obtained by synthesizing these two lattice patterns is a robust pattern.

[0154] The same processing can be applied to magenta and yellow. Specifically, when 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 Thk is set as the new threshold Thm for M1', and the value obtained by subtracting the values ​​of K1', C1', and M1' from the threshold Thk is set as the new threshold Thy for Y1'. Then, if the obtained value is negative, the threshold can be corrected by adding the maximum grayscale value of 255 to the negative value.

[0155] Specifically, in this embodiment, even if misalignment occurs in any direction on the XY plane between forward and reverse scanning, changes in dot coverage can be suppressed while maintaining a high level of dot dispersion in color mixing, and high-quality images without detected density or hue inhomogeneity can be printed.

[0156] Note that although the above describes the case where black is set as the first color and cyan as the second color, the priority order of quantization is not limited to a specific order. For example, cyan can be set as the first color, and the threshold for black can be corrected based on the grayscale value of cyan. However, to reduce the graininess of the entire image, it is preferable to set the priority in order of inks with high dot power that tend to be noticeable on the printing medium. Note that high or low dot power indicates the relative degree to which a dot printed on the printing medium reduces brightness. Therefore, when using four colors of ink—black, cyan, magenta, and yellow—as in this embodiment, it is preferable to set the priority order such that the first color is black, the second color is cyan, the third color is magenta, and the fourth color is yellow.

[0157] Furthermore, when using inks with the same hue but different brightness, such as light cyan or light magenta, it is preferable to set the priority of cyan or magenta higher than that of light cyan or light magenta. Additionally, when there are nozzle rows for large dots and nozzle rows for small dots for the same black ink, it is preferable to set the priority of large dots higher than that of small dots.

[0158] Figure 21 The diagram shows a dot pattern formed on a printing medium when the quantization process of this embodiment is performed with large dots (42 μm) set to the first color and small dots (30 μm) set to the second color. Due to the uneven diameter of the dots forming the grid pattern, the translational symmetry of the synthesized grid pattern is slightly compromised. However, variations in dot coverage can be suppressed over a wide area, and the effect of suppressing hue and density inhomogeneities is fully demonstrated.

[0159] (Third Embodiment)

[0160] Similarly, in this embodiment, it is used as in the first and second embodiments. Figure 11 and Figure 13 The serial inkjet printing device and inkjet printing system described above. However, in this embodiment, a printhead of a different mode than that in the above embodiments is used, and image processing and drive control corresponding to that printhead are performed.

[0161] <Nozzle Arrangement>

[0162] Figures 22A to 22C This is a schematic diagram showing the printhead H used in this embodiment as seen from the nozzle side. Figure 22AAs shown, six nozzle rows are arranged in parallel on the nozzle surface. From left to right, these nozzle rows are: black nozzle row 2201, first cyan nozzle row 2202, first magenta nozzle row 2203, yellow nozzle row 2204, second magenta nozzle row 2205, and second cyan nozzle row 2206.

[0163] Figure 22B This is an enlarged view of the black nozzle column 2201. The black nozzle column 2201 has LEV and LOd columns arranged on it. Each of the LEV and LOd columns is formed by nozzles arranged along the Y direction at a spacing of 600 dpi, configured to eject 5 plc of black ink. Each of the LEV and LOd columns contains 128 nozzles, and the LEV column is offset relative to the LOd column by half a spacing in the -Y direction. Using the black nozzle column 2201 with this structure for printing scanning allows for the printing of black dots with a diameter of 38 μm on the printing medium at a print density of 1200 dpi. The yellow nozzle column 2204 has the same structure as the black nozzle column 2201.

[0164] Figure 22C This is an enlarged view of the first cyan nozzle array 2202 and the second cyan nozzle array 2206. In the first cyan nozzle array 2202, there are LEV columns configured to eject 5 pl of cyan ink, MEV columns configured to eject 2 pl of cyan ink, and SOd columns configured to eject 1 pl of cyan ink. On the other hand, in the second cyan nozzle array 2206, there are LOd columns configured to eject 5 pl of cyan ink, MOd columns configured to eject 2 pl of cyan ink, and SEV columns configured to eject 1 pl of cyan ink. Each nozzle array is constructed by arranging 128 nozzles along the Y direction at a spacing of 600 dpi.

[0165] In the first cyan nozzle array 2202 and the second cyan nozzle array 2206, the LEV column relative to the LOD column, the MEV column relative to the Mod column, and the SEV column relative to the SOd column are arranged to be offset by half a pitch (1200 dpi) in the -Y direction. Furthermore, the MEV and Mod columns configured to eject 2 pl of cyan ink, and the SEV and SOd columns configured to eject 1 pl of cyan ink, are arranged to be shifted by 1 / 4 pitch (2400 dpi) in the -Y direction relative to the LEV and LOD columns configured to eject 5 pl of cyan ink. The first magenta nozzle array 2203 and the second magenta nozzle array 2205 have the same structure as the first cyan nozzle array 2202 and the second cyan nozzle array 2206.

[0166] Image Processing

[0167] Figure 23This is a flowchart illustrating the processes performed by the main control unit 1308 of the image processing device 1 when the printing device 2 prints any image in this embodiment. The processes performed in S2501 to S2505 are similar to... Figure 14 The processes S1401 to S1405 of the first embodiment are the same, so a description of these processes is omitted here. Note that although the resolution of the image data is 1200 dpi in the first embodiment, the resolution is 600 dpi in this embodiment.

[0168] In the processing following steps S2504-1 and S2504-2, the same processing is performed in parallel for each ink color. In this section, the processing for the cyan data (C1' and C2') is described.

[0169] In steps S2505-1 and S2505-2, the main control unit 1308 performs predetermined quantization processing on the multi-valued data C1' and C2' respectively, and generates quantized data C1" for forward scanning and quantized data C2" for reverse scanning. The quantization processing method is the same as that in the first embodiment.

[0170] In steps S2506-1 and S2506-2, the main control unit 1308 performs index expansion processing. In the index expansion processing of this embodiment, the main control unit 1308 converts 600×600dpi binary data C1” and C2” into 600×1200dpi binary data C1p and C2p using a pre-prepared index pattern. Specifically, a region of one pixel in the X direction × one pixel in the Y direction is divided to form a region of one pixel in the X direction × two pixels in the Y direction, and printing (1) or non-printing (0) is set for each pixel.

[0171] Figures 24A to 24C This is a diagram showing the point arrangement pattern and the reference index pattern used in the index expansion process. Figure 24AThis diagram illustrates the dot arrangement pattern. One pixel region of 600×600 dpi is associated with two pixels of 600×1200 dpi. When the quantization data C1" or C2" of one pixel at 600×600 dpi is "0" (non-printing of a specific indicator point), no dots are arranged for the two pixels at 600×1200 dpi. On the other hand, when the quantization data C1" or C2" of one pixel at 600×600 dpi is "1" (printing of a specific indicator point), two positions can be considered as locations for the actual printing dots. In this embodiment, pattern A and pattern B are prepared, wherein in pattern A, dots are arranged for the upper pixel (specifically, the pixel on the -Y direction side), and in pattern B, dots are arranged for the lower pixel (specifically, the pixel on the +Y direction side). In the dot arrangement pattern of this embodiment, for the upper pixel, the nozzle printing dots are in the LEV column, and for the lower pixel, the nozzle printing dots are in the LOD column (see...). Figure 22B ).

[0172] Figure 24B This is a diagram illustrating the base index pattern 2500. In this embodiment, different index patterns are used in the index unrolling process of step S2506-1 and the index unrolling process of step S2506-2. However, both patterns are created based on the base index pattern 2500.

[0173] In the reference index pattern 2500, each square corresponds to a pixel area of ​​600×600 dpi. For each pixel, the reference index pattern 2500 defines whether the points are arranged according to pattern A or pattern B when the quantization value of the corresponding pixel is "1".

[0174] Figure 24C This shows binary data with 600 dpi in the X direction and 1200 dpi in the Y direction, where all pixel quantization values ​​are "1" and the data is expanded according to the reference index pattern 2500. (Example) Figure 24C The binary data is generated separately for forward and reverse scanning and is sent to the printing device 2. The controller 1301 of the printing device 2 performs predetermined printing control based on the received binary data.

[0175] Note that, although Figure 24A The dot pattern is the pattern used for 5pl ink droplets (i.e., the pattern used for LEV and LOD columns), but it can be set to output 1pl and 3pl ink droplets in a mixed mode.

[0176] Time-division drive control

[0177] In the inkjet printhead H of this embodiment, voltage pulses are applied to thermoelectric conversion elements (heaters) provided for each nozzle to induce film boiling in the ink, and the ink is ejected by the growth energy of the generated bubbles. In this case, if voltage pulses are to be applied to multiple heaters simultaneously, a high-capacity power supply is required. Therefore, a conventionally known time-division driving method is employed.

[0178] Figure 25A and 25B This is a diagram used to illustrate the time-division driving method. In the time-division driving of this embodiment, 128 nozzles arranged in the same nozzle column are divided into 16 blocks, and the timing of applying voltage pulses to the heaters in each block is offset relative to the timing in other blocks.

[0179] Figure 25A This is a diagram showing the block numbers and the order of the driving blocks. Figure 25A Indication: The nozzles included in the first timing drive block 1, the nozzles included in the fifth timing drive block 2, and the nozzles included in the sixteenth timing drive block 16. The first to sixteenth timings are obtained by dividing the time period corresponding to one pixel of 600 dpi into 16 time periods, driving each of the 16 blocks.

[0180] Figure 25B This diagram illustrates the nozzles arranged in nozzle column 2300, the driving timing of each nozzle, and the dot printing state. The nozzles arranged along the Y direction are assigned to blocks such as block 1, block 2, ..., starting from the first nozzle on the -Y direction side, and the 16th nozzle is assigned to block 16. Then, the 17th to 32nd nozzles are again assigned to blocks 1, 2, ..., and 16, respectively. Specifically, block 1 includes the 1st, 17th, ..., and 113th nozzles; block 2 includes the 2nd, 18th, ..., and 114th nozzles; and block 16 includes the 16th, 32nd, ..., and 128th nozzles.

[0181] Timing diagram 2310 shows according to Figure 25A The table shows the drive timing of each nozzle. Although only the drive timing of nozzles 1 through 16 is shown in this figure, the drive timing of nozzle 17 and thereafter is a repetition of the drive timing in timing diagram 2310. In timing diagram 2310, the horizontal axis represents time, and the vertical axis represents the voltage applied to the heater. According to timing diagram 2310, in 16 time periods obtained by dividing the time period corresponding to one pixel of 600 dpi into 16 segments, the nozzles are driven in the order of nozzle 1, nozzle 5, nozzle 9, and nozzle 13, and finally nozzle 16.

[0182] Under such drive control, the carriage 1108 (see...) Figure 11 When moving along the +X direction, a dot pattern 2320 is formed on the printing medium. Since ejection occurs simultaneously with the carriage 1108 moving along the X direction, the dots are arranged in a state where they are offset from each other in the X direction according to the driving sequence. More specifically, since each region obtained by dividing a 600 dpi pixel area into 16 segments is called an interval, as in the first to fourth dots, the dots printed by the four adjacent nozzles are each arranged to be offset from the adjacent point by four intervals. Therefore, diagonal lines inclined relative to the X direction are repeatedly arranged along the Y direction on the printing medium.

[0183] On the other hand, when the carriage 1108 is moved in the -X direction under the aforementioned drive control, a dot pattern 2321 is formed on the printing medium. The tilt direction of the diagonal lines is reversed in the main scanning direction relative to the direction in the dot pattern 2320 used for forward scanning.

[0184] When performing time-division driving as described above, the number of nozzles driven simultaneously can be reduced, and the power supply capacity can be decreased. On the other hand, similar to dot patterns 2320 and 2321, the printing position of the dots varies within a single pixel area of ​​600 dpi.

[0185] <Printing Control Methods>

[0186] A description of a control method is provided for achieving robust patterns on a printing medium in the case of multiple passes of printing using the index expansion process, printhead structure, and time-division drive control described above.

[0187] Figures 26A to 26D It is used to illustrate its use. Figure 22C A diagram showing the drive control of the first cyan nozzle array 2202 and the second cyan nozzle array 2206. Figures 26A to 26D This shows the state of printing a 38μm diameter dot for each pixel by using the LEV and LOd columns configured to eject 5pl of cyan ink.

[0188] Figure 26A The diagram shows a dot pattern obtained by printing individual pixels at 600 dpi using the LEV and LOd columns without the aforementioned time-division driving. Figure 26B This shows the dot pattern obtained when the print position of the LOd column is offset by one pixel (1200 dpi) relative to the print position of the LEV column, without time-division driving. Offsetting the print position of the LOd column by one pixel (1200 dpi) relative to the print position of the LEV column in the X direction allows for the formation of a dot pattern with... Figure 26A The point dispersion in the middle is compared to the grid pattern with higher point dispersion.

[0189] Figure 26C This shows printing in forward scan while in time-division driven mode. Figure 26B The dot pattern obtained in the case of a pattern. Specifically, the dot pattern obtained will be... Figure 25B The offset shown in dot pattern 2320 is reflected in Figure 26B The pattern of the pattern. Although the pattern in this case is a grid pattern, the spacing between the lines connecting the centers of the points printed by the LOd column and the lines connecting the centers of the points printed by the LEV column is uneven, and the point dispersion is lower than Figure 26B The point dispersion in.

[0190] Figure 26D The print position in the LOD column is shown from Figure 26C The dot pattern is obtained when the state is further offset in the +X direction (600dpi÷16×2≈15.9μm). This offset makes the spacing between the dots printed by the LOD column and the dots printed by the LEV column uniform, and achieves a preferred grid pattern.

[0191] Here, the offset of (600dpi÷16×2) corresponds to... Figure 25B The offset in the X direction between adjacent points in the Y direction in the time-division drive is half of the offset in the Y direction (600dpi ÷ 16 × 4) (i.e., two blocks in the time-division drive). Therefore, in this embodiment, the drive control is performed using the time-division drive described above, and the drive timing of the LOD column is delayed in the forward scan, so that the print position is offset relative to the reference position by an amount corresponding to two blocks.

[0192] Figure 27A and 27B This is a schematic diagram illustrating how the drive timing is offset as described above during forward and reverse printing scans. Figure 27A The drive timing during forward scanning is shown, and Figure 27B The drive timing during reverse scanning is shown. In printhead H, the first cyan nozzle column 2202 and the second cyan nozzle column 2206 are as follows: Figure 22C The configuration shown.

[0193] In the forward scan, firstly, the LEV column is driven using time-division driving when it reaches the reference position. Then, the LOd column is not driven when it reaches the reference position. Instead, the LOd column is driven using time-division driving when it reaches a position offset from the reference position by a distance corresponding to two blocks (600 dpi ÷ 16 × 2).

[0194] In reverse scan, firstly, the LOd column is not driven when it reaches the reference position. Instead, it is driven in time-division mode when it reaches a position offset from the reference position by a distance corresponding to two blocks (600 dpi ÷ 16 × 2). Then, the LEV column is driven in time-division mode when it reaches the reference position.

[0195] The drive control described above enables the acquisition of [data / properties] during forward scanning. Figure 26D The grid pattern shown is obtained in the reverse scan from the main scan direction. Figure 26D The grid pattern is an inverted grid pattern. However, if there are limitations on the resolution of the offset due to limitations of the printing equipment, only an offset of at least 1200 dpi needs to be achieved.

[0196] Although the above explains the offset (delay) of the driving timing of the LOD column relative to the driving timing of the LEV column, it can also be obtained by advancing the driving timing of the LEV column relative to the driving timing of the LOD column. Figure 26D The dot pattern is shown. Furthermore, the nozzle column whose driving timing offset occurs can be switched between the LEV and LOD columns during forward and reverse scans.

[0197] exist Figures 26A to 26D The document describes a driving method for achieving a preferred lattice pattern for four nozzles (eight nozzles in the LOd and LEV columns) that are adjacent to each other in the Y direction. However, in the time-division driving of this embodiment, as... Figure 25B As shown, an offset of 11 blocks occurs for every four nozzles. Therefore, in this embodiment, an index pattern and threshold matrix are prepared that can eliminate such offset and enable a preferred grid pattern to be obtained throughout the nozzle column area.

[0198] <About Index Patterns>

[0199] Figure 28A and 28B This is a diagram used to illustrate the vertical offset of a grid group. In Figure 28A and 28B Each, the left side shows the binary data for the LEV column, and the right side shows the dot pattern based on that binary data. Figure 28A and 28B In the diagram, vertical and horizontal borders define a pixel region of 600 dpi, and individual black squares indicate the points set for printing by binary data. In the following description, groups of pixels at the same pixel position in the X direction are called columns, and groups of pixels at the same pixel position in the Y direction are called raster.

[0200] Figure 28A The diagram shows binary data in a state where printing (1) is set for nozzles 1 to 16 in column LEV in a column arranged at intervals of three columns, and a dot pattern when dots are printed in forward scanning based on this binary data. Since time-division driving is performed, Figure 25B The dot pattern 2320 shown is arranged in a repeating pattern of four grids with intervals of three vertical columns.

[0201] Figure 28B The binary data and the dot pattern based on the binary data are shown in the following state: the nozzles in the LEV column are divided into grid groups, each consisting of four nozzles, and the printed pixels are offset by one column in the +X direction between every two adjacent grid groups.

[0202] exist Figure 28A dot patterns and Figure 28B When comparing point patterns, the point offset due to time-division driving occurs... Figure 28B It's not very obvious in the middle, and Figure 28B It is an image with good uniformity. Although 1 to 16 nozzles are shown here, the same effect can be achieved by offsetting the position of the printed pixels in grid groups for 17 to 128 nozzles according to the rules above.

[0203] and Figure 28A and 28B Same, Figure 29A and 29B Each is a graph illustrating the relationship between binary data and dot patterns for columns LEV and LOd. In each cell, the black square in the upper region indicates the printing setting for the corresponding nozzle in column LEV (1), while the black square in the lower region indicates the printing setting for the corresponding nozzle in column LOd (1). In the dot pattern, the dots printed by column LEV and column LOd are offset from each other due to time-division driving, and also due to… Figure 27A and 27B The controls described herein are offset from each other.

[0204] Therefore, for such Figure 29A The binary data shown exhibits a certain degree of point dispersion, but does not achieve a strictly defined lattice pattern. On the other hand, Figure 29B Showing the Figure 29A binary data Figure 28A and 28B The aforementioned case of vertical offset in units of grid groups. It was found that... Figure 29B The preferred dot pattern was obtained from the dot pattern.

[0205] In this embodiment, as described above, an index pattern is prepared in advance that allows for consideration of the nozzle positions in the LEV and LOD columns and the characteristics of time-division driving. Figure 29B That way, a preferred grid pattern can be obtained on the printing medium.

[0206] Figures 30A to 30D This is a diagram showing the index pattern 3001 used for forward scanning in this embodiment and the binary data obtained when using the index pattern 3001. Figure 30A The index pattern 3001 used for the forward scan shown is... Figure 28B The aforementioned longitudinal offset is reflected in Figure 24B The reference index pattern 2500 is described above. Specifically, the index pattern 3001 is a pattern in which the reference index pattern 2500 is repeated in the X and Y directions, and the content of the pattern is offset by one column in the +X direction for each grid group. Figure 30B Shown in accordance with Figure 24A The dotted pattern shown unfolds Figure 30A The binary data in the case of index pattern 3001.

[0207] on the other hand, Figure 30C yes Figure 29B The printed pixels in the binary data shown are a 600 dpi pattern. Specifically, with approximately 2 / 16 (12.5%) of grayscale data as input, the quantization process in this embodiment generates a pattern as shown. Figure 30C The binary data shown. Figure 30D Showing according to Figure 30B The unfolded pattern shown Figure 30C The results of the binary data are shown. Specifically, Figure 30D yes Figure 30B patterns and Figure 30C The result of a logical AND operation on the pattern. This is determined by using the nozzles in the LEV and LOD columns based on... Figure 30C The binary data is ejected, which allows printing on the printing medium to be performed as... Figure 29B The preferred grid pattern is shown.

[0208] Figure 31A and 31B It is used to explain the basis Figure 24B A diagram illustrating a specific method for creating the index pattern 3001 used for forward scanning in this embodiment using the reference index pattern 2500. First, as... Figure 31AAs shown, a reference index pattern 2500 with an area of ​​8 pixels × 8 pixels is prepared, and the pattern content of the bottom four pixels (+Y direction side) in each column is offset by one pixel in the +X direction. Hereinafter, the index pattern thus created is referred to as the first index pattern 3101. Then, for the initial eight grids, the first index pattern 3101 is repeated in the X direction.

[0209] Next, as Figure 31B As shown, a second index pattern 3102 is created by offsetting the entire content of the first index pattern 3101 by two pixels in the +X direction. Then, for the next eight grid cells, the second index pattern 3102 is repeated in the X direction. The third index pattern 3103 and the fourth index pattern 3104 are created and arranged similarly, thus completing an index pattern of a total of 32 grid cells.

[0210] In this embodiment, Figure 23 The forward scanning process in S2506-1 uses an index pattern with a region of 32 pixels × 32 pixels, created in this way. On the other hand, in... Figure 23 In the index expansion process used for reverse scanning in S2506-2, the pattern obtained by reversing the index pattern 3001 used for forward scanning in the main scanning direction is used.

[0211] <About the threshold matrix>

[0212] Figure 32A and 32B This is a diagram showing the threshold matrix used in the quantization process of this embodiment. Figure 32A It is the threshold matrix used in the quantization process for forward scanning, and Figure 32B These are the threshold matrices used in the quantization process during reverse scanning. Like the index matrices described above, these two threshold matrices have pixel regions of 32 pixels × 32 pixels. Figure 32A and 32B This shows the quantization result when grayscale data of C1' = C2' = 32 is input into all 32 pixels × 32 pixels. Pixels shown in black correspond to the printed pixels (C1” = 1, C2” = 1). It can be observed that... Figure 32A The distribution of black pixels in the area enclosed by the thick frame illustrates the case where approximately 12.5% ​​(32 / 255) of grayscale data was input. Figure 30C The distribution is consistent in binary data. In this case, Figure 32A The threshold matrix used for the forward scan shown is Figure 32B The threshold matrix used for the reverse scan shown is arranged in the opposite relationship of the black pixels in the X direction.

[0213] Furthermore, when creating the threshold matrix used in this embodiment, as in the first embodiment, the image processing device 1 only needs to add constraints for representing different grid patterns in forward and reverse scanning, and then set the threshold while performing point density-sparseness evaluation. In this case, in this embodiment, the image processing device 1 only needs to form the preferred grid pattern while taking into account the constraints of the nozzle arrangement structure and time-division driving.

[0214] Figure 33 This is a diagram showing the dot pattern formed on the printing medium in this embodiment under the above-described series of control operations. Figure 33 The diagram shows a first dot pattern 3301 printed on a printing medium in a forward scan based on grayscale data C1', a second dot pattern 3302 printed on a printing medium in a reverse scan based on grayscale data C2', and a composite dot pattern 3300 of patterns 3301 and 3302.

[0215] according to Figure 33 First, the first dot pattern 3301 and the second dot pattern 3302 are different grid patterns (first condition). Furthermore, in the composite dot pattern 3300 obtained by superimposing patterns 3301 and 3302 in a manner where one is superimposed on the other, there are superimposed points 3303 and neighboring points 3304, and the first and second points forming the neighboring points 3304 are arranged at intervals smaller than the grid spacing (second condition). Furthermore, in the composite dot pattern 3300, there are multiple neighboring points with different approach directions, such as neighboring points 3304 approaching in the X direction, neighboring points 3305 approaching in the Y direction, and neighboring points 3306 approaching in an oblique direction, etc. (third condition). Therefore, the composite dot pattern 3300 of this embodiment can be considered a robust pattern.

[0216] As described above, according to this embodiment, in Figure 25A and 25B Under the time-division drive control shown, by utilizing Figures 22A to 22C The printhead shown uses Figure 32A and 32B The threshold matrix shown is used for quantization, and quantization is performed by using... Figure 30A The index pattern shown is used for index expansion processing. This allows for the formation of different preferred grid patterns for forward and reverse scanning while minimizing print position shifts caused by the nozzle arrangement structure and time-division drive control in the print head H, and enables the printing of preferred robust patterns on the printing medium.

[0217] <Control in low grayscale areas>

[0218] In use Figure 32A and32B When using the threshold matrix shown for quantization, a situation arises where only one of the LEV and LOd nozzle columns is used in the low grayscale region. This is because, when a grid pattern is formed within a dot pattern, it is inevitable that only one of the LEV and LOd nozzle columns will be used, and the same nozzle column will also be used in another dot pattern obtained by reversing that dot pattern along the X direction. In this case, there is a risk that the frequency of nozzle column usage becomes uneven and the printhead lifespan becomes shorter. In view of this, in this embodiment, a special threshold matrix is ​​prepared for the low grayscale region.

[0219] Figures 34A to 34D This is a diagram illustrating the threshold matrix used in the low grayscale region of this embodiment. Figure 34A This is the threshold matrix used for forward scanning. Assume the threshold matrix used for forward scanning is... Figure 32A The threshold matrices shown are the same. Figure 34A In the case of uniformly inputting grayscale data of C1'=32, the pixels of the print (C1”=1) are shown as black pixels. Figure 34B Shown by using Figure 30A The index pattern is based on Figure 34A The result of the index expansion process. It can be seen that all pixels set to print (1) correspond to the LEV nozzle column.

[0220] on the other hand, Figure 34C This is the threshold matrix used for reverse scanning in the low grayscale value region. The threshold matrix is ​​as follows: the threshold of the threshold matrix inverted in the X direction is further offset by an odd number of grid cells, such that all pixels set for printing (1) correspond to the LOd nozzle column. For example... Figure 34D As shown, this makes all pixels set for printing (1) correspond to the LOd nozzle column, and allows the usage frequency of the LOd nozzle column to be equal to the usage frequency of the LEV nozzle column. Furthermore, different dot patterns can be achieved in the first dot pattern and the second dot pattern.

[0221] Figure 35 This is a diagram showing the dot pattern formed on the printing medium when grayscale data of C1'=C2'=8 is uniformly input. Figure 35The diagram illustrates a first dot pattern 3501 printed on a printing medium in a forward scan based on grayscale data C1', a second dot pattern 3502 printed on a printing medium in a reverse scan based on grayscale data C2', and a composite dot pattern 3503 of patterns 3501 and 3502. In this example, since the first dot pattern 3501 is printed only by the LEV nozzle column and the second dot pattern 3502 is printed only by the LOd nozzle column, there are no overlapping dots in the composite dot pattern. However, when the first dot pattern 3501 and the second dot pattern 3502 are offset from each other by one pixel (1200 dpi) in the Y direction, an offset dot pattern 3504 is obtained, including an overlapping dot 3305 and multiple neighboring dots 3306 and 3307. In this offset dot pattern 3504, there are neighboring dots 3306 and 3307 with different approximate directions, thus forming a robust pattern.

[0222] According to the above embodiment, image processing device 1 can perform primary image processing at a resolution of 600 dpi (in other words, at a low load). On the other hand, printing device 2, by using a printhead capable of achieving a print resolution of 1200 dpi and by using time-division driving, can achieve printing at essentially 1200 dpi × 1200 dpi. Furthermore, in a series of image processing steps, threshold matrices and index patterns suitable for the nozzle arrangement structure and time-division drive control of the printhead are prepared for forward and reverse scanning, and image processing based on these matrices and patterns is performed. This allows different preferred grid patterns to be printed in forward and reverse scanning while minimizing print position shifts caused by the nozzle arrangement structure and time-division drive control in the printhead. As a result, preferred robust patterns can be printed on the printing medium.

[0223] (Fourth Embodiment)

[0224] In the third embodiment, for Figure 24B The reference index pattern 2500 shown is shifted vertically in units of grid groups to generate the actual data for use. Figure 30A The index pattern shown is an index pattern obtained by reversing the index pattern in the X direction. Then, the image processing device 1 assigns each image data to the LEV column or LOD column using the index pattern generated as described above. On the other hand, in this embodiment, this assignment of print data to the LEV column or LOD column is performed by mask processing.

[0225] Figure 36 This is a flowchart illustrating the processes performed by the main control unit 1308 of the image processing device 1 when the printing device 2 prints any image in this embodiment. The processes performed in S3601 to S3605-1 and S3605-2 are similar to... Figure 23The processes S2501 to S2505-1 and S2505-2 in the third embodiment are the same, so the description of these processes is omitted.

[0226] In this embodiment, in S3606-1 and S3606-2, the main control unit 1308 uses an index pattern different from the index pattern in the third embodiment to perform index expansion processing.

[0227] Figures 37A to 37C This is a diagram illustrating the point arrangement pattern and index pattern used in the index expansion process of this embodiment. Figure 37A This is a diagram illustrating the dot arrangement pattern of this embodiment. In this embodiment, when the quantization value of a pixel at 600dpi×600dpi is "1", pattern C, which arranges dots in both the upper and lower pixels, is used only.

[0228] Figure 37B This is a diagram illustrating the index pattern. In this embodiment, pattern C is set for all pixels forming an 8×8 pixel area. Therefore, with the quantization value of each pixel consistently set to "1", the binary data for 600 dpi in the X direction and 1200 dpi in the Y direction are identical regardless of whether the scan is forward or reverse. Figure 37C As shown.

[0229] Return to Figure 36 The description states that in steps S3607-1 and S3607-2, the main control unit performs masking processing. In this masking processing, for each 600 dpi pixel, one of the pixels above or below that pixel is masked. Specifically, for each 600 dpi pixel, it is determined whether to print in the LEV column or the LOD column. This masking processing is performed by calculating a logical AND between the binary data generated in the index expansion process and the pre-prepared mask pattern.

[0230] Figure 38A and 38B The mask pattern used in the masking process described above is shown. Figure 38A It has the same Figure 24B A mask pattern containing the same content as the aforementioned baseline index pattern. Furthermore, Figure 38B Showing the Figure 38A The mask pattern is shifted vertically in units of grid groups. Using... Figure 38B The mask pattern shown is used for masking, which enables the formation of the first dot pattern in the third embodiment on the printing medium during forward scanning. Furthermore, by using a method that reverses the main scanning direction... Figure 38BThe mask pattern obtained from the mask pattern is used for masking, which enables the formation of the second dot pattern in the third embodiment during reverse scanning. Therefore, the synthesized dot pattern obtained by synthesizing the first dot pattern and the second dot pattern is the same robust pattern as the robust pattern in the third embodiment.

[0231] (Other embodiments)

[0232] Although the above explains that image processing device 1 performs... Figure 14 , Figure 23 and Figure 36 The steps described in the flowchart above are not explicitly defined, but the controller 1301 of the printing device 2 can perform only a portion of these steps. In the steps shown in the flowchart above, there is no clear boundary between the steps performed by the image processing device 1 and the steps performed by the printing device 2. For example, in the third and fourth embodiments, if the image processing device 1 performs the steps up to quantization, it can do so at a resolution 600 dpi lower than the printing resolution, thus reducing the processing load. In this case, in the printing device 2, the controller 1301 performs indexing using the dot arrangement pattern and index pattern stored in the data buffer 1306. In this case, the entire printing system including the image processing device 1 and the printing device 2 is the image processing device of the present invention. Furthermore, depending on the performance of the printing device, the printing device 2 can directly receive multi-valued RGB image data and perform all the steps described in the flowchart above. In this case, the printing device 2 is the image processing device of the present invention.

[0233] Furthermore, the number of bits in the input-output data at each step is not limited to the aforementioned number of bits. The number of bits in the output data can be set higher than the number of bits in the input data to maintain accuracy. Additionally, although the four colors CMYK are described as an example of the number of colors in a printing device, the printing device can be configured to use colors of the same type but different intensities, such as light cyan, light magenta, and gray, as well as specific colors such as red, green, and blue. In this case, the image processing device can generate grayscale data of the same type as the number of colors in the color separation process, and perform the aforementioned image processing on each color in the processing following the color separation process.

[0234] Furthermore, although a serial inkjet printing device was described as an example in the above embodiments, all of the above embodiments can also be applied to line printing devices. Similarly, in line inkjet printheads, misalignment between nozzle columns can sometimes become a problem when two or more nozzle columns are printing on the same pixel area. In this case, the image processing device only needs to perform processing similar to that in the above embodiments when the dot pattern formed by any one nozzle column is the first dot pattern and the dot pattern formed by another nozzle column is the second dot pattern.

[0235] Furthermore, although thermal jet printheads that eject ink by applying voltage pulses to a heater are used in the third and fourth embodiments, the ejection method is not limited to a specific method in any of the above embodiments. For example, these embodiments can be effectively applied to various printing devices, such as so-called piezoelectric inkjet recording devices that eject ink using piezoelectric elements.

[0236] Other embodiments

[0237] The embodiments of the present invention can also be implemented by providing software (programs) that perform the functions of the above embodiments to a system or device via a network or various storage media, and the computer or central processing unit (CPU) or microprocessor unit (MPU) of the system or device reads out and executes the program.

[0238] Although the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims is to be interpreted in the broadest sense to include all such modifications, equivalent structures, and functions.

Claims

1. An image processing method, comprising the following steps: Obtain grayscale data corresponding to the predetermined grayscale value; as well as Based on the grayscale data, first data for printing a first dot pattern and second data for printing a second dot pattern are generated. The second dot pattern will be printed on the printing medium in a manner that overlaps with the first dot pattern. The first dot pattern includes a first grid formed by dots arranged repeatedly at a first interval in a first direction and dots arranged repeatedly at a second interval in a second direction, and The second dot pattern comprises a second grid formed by dots arranged at a third interval in a third direction and dots arranged at a fourth interval in a fourth direction. The composite dot pattern formed by combining the first dot pattern and the second dot pattern in a first relative position includes the following (i) and (ii), in which the center of a dot in the second dot pattern is superimposed on the center of a dot in the first dot pattern: (i) A first neighboring point, wherein a first point included in the first point pattern and a second point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval; and (ii) A second neighboring point, wherein the third point included in the first point pattern and the fourth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval. The first inclination of the straight line connecting the centers of the first neighboring points is different from the second inclination of the straight line connecting the centers of the second neighboring points.

2. The image processing method according to claim 1, wherein, The composite dot pattern includes the following (iii): (iii) A third neighboring point, wherein the fifth point included in the first point pattern and the sixth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval. The third inclination of the straight line connecting the centers of the third neighboring points is different from the first inclination and the second inclination.

3. The image processing method according to claim 1, wherein, In the composite point pattern, multiple unit regions are arranged in a repeating manner, and each unit region includes an overlay point, a first neighboring point, and a second neighboring point.

4. The image processing method according to claim 1, wherein, The second composite dot pattern formed by combining the first dot pattern and the second dot pattern at a second relative position different from the first relative position includes the following (iv) to (vi): (iv) Overlapping points, which are formed by overlapping the points included in the first point pattern and the points included in the second point pattern. (v) A fourth neighboring point, wherein the seventh point included in the first point pattern and the eighth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval, and the inclination of the straight line connecting the centers of the seventh and eighth points is the first inclination, and (vi) The fifth neighboring point, wherein the ninth point included in the first point pattern and the tenth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval, and the inclination of the straight line connecting the centers of the ninth point and the tenth point is the second inclination.

5. The image processing method according to claim 1 further includes the following steps: Two grayscale data are generated based on the grayscale data; First quantized data is generated by quantizing one of the two grayscale data using a first threshold matrix; as well as The second quantized data is generated by quantizing another grayscale data of the two grayscale data using a second threshold matrix that is different from the first threshold matrix.

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

7. The image processing method according to claim 1, wherein, The grayscale data corresponds to a first color, and the first dot pattern and the second dot pattern are patterns used to print dots of the first color. The image processing method further includes the following steps: Obtain the grayscale data corresponding to the second color; and Based on the grayscale data corresponding to the second color, third data corresponding to a third dot pattern for printing dots of the second color and fourth data corresponding to a fourth dot pattern for printing dots of the second color are generated. The fourth dot pattern will be printed on the printing medium in a manner that overlaps with the third dot pattern. The third dot pattern comprises a third grid formed by dots repeated at a fifth interval in the fifth direction and dots repeated at a sixth interval in the sixth direction, and... The fourth dot pattern comprises a fourth grid formed by dots arranged at a seventh interval in the seventh direction and dots arranged at an eighth interval in the eighth direction. The second composite dot pattern formed by combining the third dot pattern and the fourth dot pattern in the following relative positions includes (iii) and (iv), in which the center of a dot in the fourth dot pattern is superimposed on the center of a dot in the third dot pattern: (iii) A third neighboring point, wherein the fifth point included in the third point pattern and the sixth point included in the fourth point pattern are located at a distance relative to each other that is less than any one of the fifth interval, the sixth interval, the seventh interval, and the eighth interval, and (iv) A fourth neighboring point, wherein the seventh point included in the third point pattern and the eighth point included in the fourth point pattern are located at a distance relative to each other that is less than any one of the fifth interval, the sixth interval, the seventh interval, and the eighth interval. The third inclination of the straight line connecting the centers of the third neighboring points is different from the fourth inclination of the straight line connecting the centers of the fourth neighboring points.

8. The image processing method according to claim 7 further includes the following steps: First grayscale data and second grayscale data are generated based on the grayscale data corresponding to the first color; The third and fourth grayscale data are generated based on the grayscale data corresponding to the second color; First quantized data corresponding to the first color is generated by comparing a first threshold in a first threshold matrix with the first grayscale data. A third quantized data corresponding to the second color is generated by comparing a correction threshold obtained by subtracting the value of the first grayscale data from the first threshold with the third grayscale data. A second quantized data corresponding to the first color is generated by comparing a second threshold in a second threshold matrix with the second grayscale data. as well as A fourth quantized data corresponding to the second color is generated by comparing a correction threshold obtained by subtracting the value of the third grayscale data from the second threshold with the fourth grayscale data.

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. The image processing method according to claim 1, wherein, The first dot pattern is printed in the forward scan of the printing unit, and the second dot pattern is printed in the reverse scan of the printing unit.

11. The image processing method according to claim 1, wherein, The first dot pattern is printed using a first row of nozzles arranged in the printing unit during a predetermined scan, and the second dot pattern is printed using a second row of nozzles arranged in the printing unit during the predetermined scan.

12. A computer-readable storage medium storing a computer program that, when executed by a computer, causes the computer to implement the image processing method according to any one of claims 1 to 11.

13. An image processing apparatus, comprising: The obtaining unit is configured to obtain grayscale data corresponding to a predetermined grayscale value; as well as A generation unit is configured to generate first data for printing a first dot pattern and second data for printing a second dot pattern based on the grayscale data, the second dot pattern being printed on a printing medium in a manner that overlaps with the first dot pattern. The first dot pattern includes a first grid formed by dots arranged repeatedly at a first interval in a first direction and dots arranged repeatedly at a second interval in a second direction, and The second dot pattern comprises a second grid formed by dots arranged at a third interval in a third direction and dots arranged at a fourth interval in a fourth direction. The composite dot pattern formed by combining the first dot pattern and the second dot pattern in a first relative position includes the following (i) and (ii), in which the center of a dot in the second dot pattern is superimposed on the center of a dot in the first dot pattern: (i) A first neighboring point, wherein a first point included in the first point pattern and a second point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval; and (ii) A second neighboring point, wherein the third point included in the first point pattern and the fourth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval. The first inclination of the straight line connecting the centers of the first neighboring points is different from the second inclination of the straight line connecting the centers of the second neighboring points.

14. The image processing apparatus according to claim 13, wherein, The composite dot pattern includes the following (iii): (iii) A third neighboring point, wherein the fifth point included in the first point pattern and the sixth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval. The third inclination of the straight line connecting the centers of the third neighboring points is different from the first inclination and the second inclination.

15. The image processing apparatus according to claim 13, wherein, In the composite point pattern, multiple unit regions are arranged in a repeating manner, and each unit region includes an overlay point, a first neighboring point, and a second neighboring point.

16. The image processing apparatus according to claim 13, wherein, The second composite dot pattern formed by combining the first dot pattern and the second dot pattern at a second relative position different from the first relative position includes the following (iv) to (vi): (iv) Overlapping points, which are formed by overlapping the points included in the first point pattern and the points included in the second point pattern. (v) A fourth neighboring point, wherein the seventh point included in the first point pattern and the eighth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval, and the inclination of the straight line connecting the centers of the seventh and eighth points is the first inclination, and (vi) The fifth neighboring point, wherein the ninth point included in the first point pattern and the tenth point included in the second point pattern are located at a distance relative to each other that is less than any one of the first interval, the second interval, the third interval, and the fourth interval, and the inclination of the straight line connecting the centers of the ninth point and the tenth point is the second inclination.

17. The image processing apparatus according to claim 13, wherein, The generation unit performs the following operations: Two grayscale data are generated based on the grayscale data; First quantized data is generated by quantizing one of the two grayscale data using a first threshold matrix; as well as The second quantized data is generated by quantizing another grayscale data of the two grayscale data using a second threshold matrix that is different from the first threshold matrix.

18. The image processing apparatus according to claim 17, wherein, The generation unit generates first grayscale data and second grayscale data based on grayscale data with a first grayscale value, and generates third grayscale data and fourth grayscale data based on grayscale data with a second grayscale value that is higher than the first grayscale value. The print dot pattern corresponding to the result of quantization of the third grayscale data using the first threshold matrix is ​​a pattern in which print dots are added to the print dot pattern corresponding to the result of quantization of the first grayscale data using the first threshold matrix, and The print dot pattern corresponding to the result of quantization of the fourth grayscale data using the second threshold matrix is ​​a pattern in which print dots are added to the print dot pattern corresponding to the result of quantization of the second grayscale data using the second threshold matrix.

19. The image processing apparatus according to claim 13, wherein, The grayscale data corresponds to the first color. The first dot pattern and the second dot pattern are patterns used to print dots of the first color. The obtaining unit also obtains grayscale data corresponding to the second color. The generation unit further generates, based on grayscale data corresponding to the second color, third data corresponding to a third dot pattern for printing dots of the second color and fourth data corresponding to a fourth dot pattern for printing dots of the second color. The fourth dot pattern will be printed on the printing medium in a manner that overlaps with the third dot pattern. The third dot pattern comprises a third grid formed by dots repeated at a fifth interval in the fifth direction and dots repeated at a sixth interval in the sixth direction, and... The fourth dot pattern comprises a fourth grid formed by dots arranged at a seventh interval in the seventh direction and dots arranged at an eighth interval in the eighth direction. The second composite dot pattern formed by combining the third dot pattern and the fourth dot pattern in the following relative positions includes (iii) and (iv), in which the center of a dot in the fourth dot pattern is superimposed on the center of a dot in the third dot pattern: (iii) A third neighboring point, wherein the fifth point included in the third point pattern and the sixth point included in the fourth point pattern are located at a distance relative to each other that is less than any one of the fifth interval, the sixth interval, the seventh interval, and the eighth interval, and (iv) A fourth neighboring point, wherein the seventh point included in the third point pattern and the eighth point included in the fourth point pattern are located at a distance relative to each other that is less than any one of the fifth interval, the sixth interval, the seventh interval, and the eighth interval. The third inclination of the straight line connecting the centers of the third neighboring points is different from the fourth inclination of the straight line connecting the centers of the fourth neighboring points.

20. The image processing apparatus according to claim 19, wherein, The generation unit performs the following operations: First grayscale data and second grayscale data are generated based on the grayscale data corresponding to the first color; The third and fourth grayscale data are generated based on the grayscale data corresponding to the second color; First quantized data corresponding to the first color is generated by comparing a first threshold in a first threshold matrix with the first grayscale data. A third quantized data corresponding to the second color is generated by comparing a correction threshold obtained by subtracting the value of the first grayscale data from the first threshold with the third grayscale data. A second quantized data corresponding to the first color is generated by comparing a second threshold in a second threshold matrix with the second grayscale data. as well as A fourth quantized data corresponding to the second color is generated by comparing a correction threshold obtained by subtracting the value of the third grayscale data from the second threshold with the fourth grayscale data.

21. The image processing apparatus according to claim 19, wherein, The brightness of the dots of the first color is lower than the brightness of the dots of the second color.

22. The image processing apparatus according to claim 13, wherein, The first dot pattern is printed in the forward scan of the printing unit, and the second dot pattern is printed in the reverse scan of the printing unit.

23. The image processing apparatus according to claim 13, wherein, The first dot pattern is printed using a first row of nozzles arranged in the printing unit during a predetermined scan, and the second dot pattern is printed using a second row of nozzles arranged in the printing unit during the predetermined scan.

24. A computer program product comprising a computer program that, when executed by a computer, causes the computer to implement the image processing method according to any one of claims 1 to 11.

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