JP2006256259A - Dot arrangement determining method, method and apparatus for preparing threshold value matrix, program, image processing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dot arrangement determining method which can suppress deterioration of the quality of an image caused by droplet interference between dots and can realize a half-toning processing, a method and apparatus for preparing a threshold value matrix, a program, an image processing apparatus and an image forming apparatus. <P>SOLUTION: While a condition that the droplet interference between the dots is generated (depending relation between the dots) is grasped, the amount of dot displacement generated by the depending relation (the amount of dot displacement) is quantitatively grasped. The dot arrangement determining method for determining the dot arrangement (dot forming position, on-off of the dot, when dot size modulation is possible, dot size or combinations thereof) under a condition that an estimated amount of the dot displacement is taken into consideration based on these information, is provided. In addition, based on an optimum dot arrangement determined by estimating the dot displacement by the depending relation, a method for preparing the threshold value matrix for preparing the threshold value matrix, is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dot arrangement determination method, a threshold matrix creation method and apparatus using the same, and a program for realizing the function thereof by a computer, an image processing apparatus and an image forming apparatus using the threshold matrix, In particular, the present invention relates to a digital halftoning technique suitable for an ink jet recording apparatus.

  An ink jet recording apparatus causes ink to adhere to a recording medium such as recording paper by ejecting ink droplets from the nozzles of a recording head (also referred to as a print head). Comprehensive “image”) is recorded. When dots are formed with high density and high speed with this type of apparatus, the droplet ejection interval between adjacent dots becomes very short, and before the ink droplets that have landed on the recording medium finish fixing, the following Ink droplets (inks for forming adjacent dots) are ejected.

  Immediately after landing, ink droplets coalesce on the surface of the recording medium, so that the original droplet shape deforms and the dot shape collapses. Droplet interference (or landing interference) This is one of the causes of image quality degradation. Between different color inks, interference occurs between ink colors even in areas where dots do not overlap, and color mixing occurs. Further, the same color inks do not have a desired (for example, ideal circular) dot shape, and image degradation occurs.

In Patent Document 1, in order to correct the droplet ejection interference between different color inks in a so-called shuttle type (serial scan type) ink jet recording apparatus, the dot distribution of each scan in multipass printing is adaptively controlled according to the density level. Propose to do.
JP 2004-209943 A

  As described above, there occurs a phenomenon in which the formation position, dot size, and dot shape of dots ejected later in time change depending on the surrounding dot distribution (this change is referred to as “dot displacement” in this specification). I will decide). In the conventional halftoning process, since dot displacement is not taken into consideration, there is a problem that image quality is degraded due to dot displacement. The method disclosed in Patent Document 1 is a technique aimed at eliminating droplet interference between different colors. In a situation where droplet interference occurs between inks of the same color, droplet interference occurs. A technique for determining the dot arrangement so as to avoid the above is not disclosed.

  The present invention has been made in view of such circumstances, and a dot arrangement determination method, a threshold matrix creation method and apparatus, a program, and image processing that can realize a halftoning process for solving the problem of dot displacement due to droplet interference. An object is to provide an image forming apparatus and an image forming apparatus.

  In order to achieve the above object, a dot arrangement determining method according to claim 1 is a dependency information acquisition step for obtaining information for specifying a dependency relationship between dots in which droplet interference occurs, and the dependency Dot placement using the dot displacement amount specifying step for specifying the amount of dot displacement expected at the position of interest based on the information acquired in the relationship information acquiring step, and the dot displacement amount information specified in the dot displacement amount specifying step And a dot arrangement calculation step for performing a calculation for determining.

  According to the present invention, while grasping the condition for causing droplet interference between dots (dependence between dots), the amount of dot displacement (dot displacement) caused by the dependence is quantitatively grasped. Based on this information, the dot arrangement (dot formation position, dot on / off, dot size when dot size modulation is possible, or a combination thereof) in consideration of the expected dot displacement amount decide. Thereby, even if droplet interference occurs, an optimal dot arrangement can be determined and a high-quality image can be obtained.

  The “dot arrangement” referred to in claim 1 is not limited to the dot arrangement form calculated based on actual image data (dot pattern as a result of the halftoning process), and is added when creating a threshold matrix. A virtual dot arrangement as in determining the dot position is also included.

  In the dependency relationship information acquisition step and the dot displacement amount specifying step, information on the dependency relationship and the dot displacement amount may be stored in a storage unit such as a memory in advance, and information may be acquired by reading out necessary information. It is also possible to actually print a test pattern or the like, read the print result, perform analysis processing, and acquire information on the dependency relationship or the dot displacement amount.

  According to a second aspect of the present invention, there is provided a dot arrangement determination method, a dependency relationship information acquisition step for obtaining information for specifying a dependency relationship between dots in which droplet interference occurs, and information acquired in the dependency relationship information acquisition step. A repetition unit determination step for determining a repetition unit of the dependency in the image, a threshold matrix size determination step for determining a threshold matrix size by an integer multiple of the repetition unit determined in the repetition unit determination step, and the dependency relationship information A dot displacement amount specifying step for specifying a dot displacement amount expected at the target position based on the information acquired in the acquiring step, and a dot arrangement candidate corresponding to the threshold matrix threshold value of the size determined in the threshold matrix size determining step Including a change in dot displacement due to the dependency specified in the dot displacement specifying step Evaluates the dot arrangement in the state, characterized in that it comprises a threshold value determining step of inputting a threshold value, the undecided position of the threshold value in the matrix of the determined group dot arrangement was based on the evaluation result.

  According to the present invention, an optimal dot arrangement is determined in anticipation of dot displacement based on mutual dependency between dots, and a threshold matrix is created based on the determined dot displacement. It is possible to realize a halftoning process that improves the problem of deterioration.

  The invention according to claim 3 relates to an aspect of the threshold value matrix creating method according to claim 2, wherein the threshold value determining step is dot arrangement corresponding to the threshold value of the threshold value matrix determined in the threshold value matrix size step. A candidate selection step for selecting a candidate for the dot placement, and dot placement selected in the candidate selection step, evaluation of dot placement including a change in dot displacement due to the dependency specified in the dot displacement amount specifying step And a dot arrangement evaluation step for performing the above.

  As dot placement candidates corresponding to a certain threshold value, all possible combinations may be listed and evaluation of each dot placement may be performed, or after narrowing down dot placement candidates with high possibility, the narrowed candidates You may evaluate dot arrangement in the inside. As an evaluation index of dot arrangement, an embodiment using a value that evaluates at least one of granularity and anisotropy is preferable, and it is more preferable in consideration of both a value indicating granularity and a value indicating anisotropy. Evaluation can be made.

  According to a fourth aspect of the present invention, there is provided a program for causing a computer to execute each step in the threshold matrix creating method according to the second or third aspect.

  The threshold matrix creation program according to the present invention can be applied as an operation program for a central processing unit (CPU) incorporated in a printer or the like, and can also be applied to a computer system such as a personal computer.

  Further, the program according to the present invention may be configured as a single application software, or may be incorporated as a part of another application such as an image editing software. The program according to the present invention is recorded on a CD-ROM, magnetic disk or other information storage medium (external storage device), and the program is provided to a third party through the information storage medium, or the program is recorded through a communication line such as the Internet. It is also possible to provide a download service.

  The invention according to claim 5 provides an apparatus for creating a threshold matrix that achieves the object. That is, the threshold value matrix creating apparatus according to claim 5 is a dependency relationship information acquisition unit that obtains information for specifying a dependency relationship between dots in which droplet interference occurs, and information acquired by the dependency relationship information acquisition unit. Repetitive unit determining means for determining the repetitive unit of the dependency in the image, threshold matrix size determining means for determining a threshold matrix size by an integral multiple of the repetitive unit determined by the repetitive unit determining means, and the dependency relationship information Dot displacement amount specifying means for specifying the amount of dot displacement expected at the target position based on the information acquired by the acquiring means, and dot arrangement candidates corresponding to the threshold value matrix threshold value determined by the threshold matrix size determining means The change in the dot displacement amount due to the dependency specified in the dot displacement amount specifying step And a threshold value determination unit that evaluates the dot arrangement in the included state and inputs a threshold value to an undetermined position in the threshold value matrix based on the dot arrangement determined based on the evaluation result. .

  The invention according to claim 6 provides an image processing apparatus that achieves the object. That is, an image processing apparatus according to claim 6 inputs threshold matrix storage means for storing threshold matrix data created by the threshold matrix creation method according to claim 2 or 3, and multi-tone digital image data. And a halftoning processing unit that generates dot data by area gradation by applying the threshold matrix to the digital image data input from the image input unit.

  According to the present invention, an optimum dot arrangement can be determined in anticipation of dot displacement due to droplet interference, so that a high-quality pseudo gradation image can be obtained.

  The invention according to claim 7 provides an image forming apparatus that achieves the object. That is, an image forming apparatus according to claim 7 inputs threshold matrix storage means for storing threshold matrix data created by the threshold matrix creation method according to claim 2 or 3, and multi-tone digital image data. Generated by the halftoning processing unit, the halftoning processing unit that applies the threshold matrix to the digital image data input from the image input unit to generate dot data by area gradation, and the halftoning processing unit A recording head having a droplet discharge element array in which a plurality of droplet discharge elements that are driven based on dot data are arranged, and at least one of the recording head and the recording medium is conveyed, and the recording head and the recording medium And a conveying means for relatively moving the two.

  As a configuration example of the recording head in the image forming apparatus of the present invention, a plurality of droplet discharge elements (recording elements that discharge ink droplets for forming dots) are arranged over a length corresponding to the entire width of the recording medium. A full-line head having a droplet discharge element array can be used. In this case, a combination of a plurality of relatively short recording head modules having droplet ejection element arrays that are less than the length corresponding to the entire width of the recording medium, and connecting them together, the length corresponding to the entire width of the recording medium as a whole. There is an aspect that constitutes a droplet discharge element array.

  A full-line type head is usually arranged along a direction perpendicular to the relative feeding direction (relative conveyance direction) of the recording medium, but has a certain angle with respect to the direction perpendicular to the conveyance direction. There may be a mode in which the ejection head is arranged along the oblique direction.

  “Recording medium” refers to a medium that receives an image recorded by the action of a recording head (an image forming medium, a recording medium, a printing medium, an image receiving medium, an ejection medium in the case of an inkjet recording apparatus, an ejection medium, etc. ), Resin sheets such as continuous paper, cut paper, sticker paper, OHP sheet, film, cloth, intermediate transfer medium, printed circuit board on which a wiring pattern is printed by an ink jet recording apparatus, and other various materials and shapes Media.

  “Conveyance means” means a mode in which the recording medium is transported to a stopped (fixed) recording head, a mode in which the recording head is moved relative to the stopped recording medium, or a movement of both the recording head and the recording medium Any of the embodiments are included. In the case of forming a color image, a recording head may be arranged for each color of a plurality of inks (recording liquids), or a configuration in which a plurality of colors of ink can be ejected from one recording head may be employed.

  According to an eighth aspect of the present invention, there is provided an image forming apparatus according to a fifth aspect of the present invention, a threshold value matrix creating apparatus according to the fifth aspect, a threshold value matrix storing means for storing threshold value matrix data created by the threshold value matrix creating apparatus, Image input means for inputting tone digital image data, halftoning processing means for generating dot data by area gradation by applying the threshold matrix to the digital image data input from the image input means, and the half A recording head having a droplet discharge element array in which a plurality of droplet discharge elements driven based on dot data generated by the toning processing means are arranged, and at least one of the recording head and the recording medium is conveyed. The recording head and the recording medium are provided with conveying means for relatively moving the recording head and the recording medium.

  An aspect in which the image forming apparatus itself has a threshold matrix creation function is also possible. According to such an aspect, the dependency relationship and the dot displacement amount that change in accordance with changes in various conditions such as the type of ink and the type of recording medium. In response to this, an optimum threshold value matrix can be adaptively created, and good image formation becomes possible.

  A ninth aspect of the present invention relates to an aspect of the image forming apparatus according to the seventh or eighth aspect, wherein the test of controlling the driving of the liquid droplet ejection element so as to eject a test pattern for examining the dependency relationship. A pattern formation control means is provided.

  The reading means for reading the test pattern print result, and the information processing means for generating the information indicating the dependency and the information indicating the amount of dot displacement from the information read by the reading means, these means: An image forming apparatus may be provided, or a dedicated device (such as a dot measuring device) may be used separately.

  According to the present invention, since the dot arrangement is determined in consideration of the dot displacement based on the dependency relationship between the dots, the optimum dot arrangement can be determined even if droplet interference occurs. In addition, since the threshold value matrix is created based on the dot arrangement, halftoning processing that solves the problem of image quality degradation due to dot displacement can be realized by using the threshold value matrix.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment: Example Using Threshold Matrix Method]
[Procedure for creating threshold matrix]
FIG. 1 is a flowchart showing a schematic procedure of a threshold matrix creating method according to an embodiment of the present invention. As shown in the figure, first, the interdependence of dots such as which dots influence each other to cause droplet interference is determined (step S10), and based on this, the repetition unit of the dependency is determined (step S20). ). Then, a visually effective unit (final threshold matrix size) is determined from the obtained repeating unit (step S30), and how the concentration of the target position changes under what conditions and depending on the dependency ( The knowledge of the amount of dot displacement as to whether it changes quantitatively) is obtained (step S40). When knowledge about the size of the threshold matrix and the amount of dot displacement is thus determined, thresholds (that is, dot arrangement) are sequentially determined based on these knowledges, and the threshold matrix is determined (step S50).

  Although detailed description will be given later, since the phenomenon of droplet interference is determined by the dot formation position and the droplet ejection order, the information on the dot formation position and the droplet ejection order is necessary for determining the dependency (processing in step S10). It becomes. Further, even if the dots are close to each other, droplet interference does not occur if the dots are sufficiently separated in time, so that information on the droplet ejection time (interval) is also required. In the above process, when the premise of the single pass method is added, the droplet ejection order information and the droplet ejection interval information are determined from the nozzle arrangement structure in the recording head (ink ejection head).

  Since the threshold matrix is used repeatedly (spatially) with respect to the image plane, its size is relatively small (for example, 128 × 128 pixels, 256 × 256 pixels, 512 × 512 pixels, etc.). It must be an integer multiple of the size (repetition unit) that makes the dependency repetitive structure after adding droplet ejection interval information.

  Hereinafter, the contents of steps S10 to S50 will be described in detail.

[Determining dependencies]
The dot displacement has a dependency relationship with surrounding dots (the dots that have been ejected later are affected by the previously ejected dots). Step S10 in FIG. 1 is a step of performing a process of determining the dot formation position having such a dependency relationship (which becomes a constraint condition when determining the dot arrangement).

  That is, in step S10, a condition for causing droplet interference is determined in association with the dot formation position from the dot formation position of the image and the droplet ejection order (droplet ejection time difference) information.

  At this time, information on the time difference (interval) at which droplet interference occurs and the spatial distance are required in advance. When there is dot size modulation, the strictest condition (generally the maximum size dot) is used. By using the strictest conditions, it is possible to include a case where there is no dependency among the combinations of dot sizes, and the same result can be obtained without obtaining the dependency for each dot size.

  FIG. 2 is a flowchart showing a procedure of processing for determining the dependency relationship. In this processing, an array V (i, j) corresponding to each dot formation position, an array DI (i, j) for storing the result of the dependency relationship, and a temporary array N are used. In order to simplify the explanation, a head model having a nozzle arrangement as shown in FIG. 3 is assumed. In FIG. 3, reference numeral 30 denotes a head, and reference numeral 32 denotes a nozzle. A recording medium such as recording paper (not shown in the drawing) is conveyed from the top to the bottom of FIG. FIG. 4 is a chart showing an example of array V (i, j), and FIG. 5 is a chart of an example of array DI (i, j). 4 and 5 exemplify only 4 × 4 elements (16 pixels), the array V (i, j) and the array DI (i, j) are elements corresponding to the number of pixels of the entire screen. (In terms of a printer, it has an element of the number of pixels of the maximum size image that can be created by the printer).

  As shown in FIG. 2, when the dependency determination routine is started, first, the array V (i, j) and the array DI (i, j) are initialized (step S110). Next, the dot formation time is written in all the cells of the array V (i, j) (step S112). For example, it may be a relative time when the first droplet ejection time is set to time “0”. In the table of FIG. 4, the time is written in a relative time based on the droplet ejection time t0 at the position (i0, j0).

  Next, the process proceeds to step S114 of FIG. 2, and the array V (i, j) is rearranged in ascending order of dot formation time, and the sorting result (order) is stored in the array T (k). This process is performed in order of decreasing droplet ejection time in the array V (i, j) (in order of droplet ejection time), and after processing at a certain position, a loop is performed while changing the position (steps S118 to S126). The calculation order is determined.

  First, “0” is set (initialized) to the variable k representing the order (step S116), and the loop is started. Here, the case where the array V (i0, j0) (that is, the position (i0, j0) shown in FIG. 4) is processed will be described.

  In step S118 of FIG. 2, it is determined whether or not the value of the variable k is smaller than the number of pixels. Here, the “number of pixels” means the number of elements of the array V (i, j) (that is, the number of elements of the array T (k)), and it is determined whether or not the processing has been completed for all pixel positions. Is for. If the inequality “k <number of pixels” is satisfied in step S118, the process proceeds to step S120, and the array N is initialized.

  Next, droplet interference occurs from the spatial positional relationship of the target position (here, dot formation position (i0, j0)) of T (k) to be calculated and information on the spatial distance at which droplet interference occurs. Select a possible position (s) and place it in an element of array N. For example, in FIG. 5, a range 50 surrounded by a broken line with respect to the target position (i0, j0) is a range where droplet interference occurs spatially, and a range 52 surrounded by a solid line is a range where droplet interference occurs temporally. Then, each position (each position of 8 pixels excluding the target position) in a range 50 surrounded by a broken line in the figure is input to an element of the array N.

N = {V (i0-1, j0-1), V (i0-1, j0),..., V (i0 + 1, j0 + 1)}
Next, the dot formation time information stored in the array V (i, j) at the position that is an element of the array N is extracted, and the difference from the dot formation time at the target position (i0, j0) is calculated. The position satisfying the condition for causing the droplet interference is determined as the position causing the droplet ejection interference with respect to the target position (i0, j0). Then, all the positions that cause such droplet interference are input to the position (i0, j0) of the array DI (i, j) (step S124). For example, an AND condition (overlapping range) of a range 50 (spatial condition) surrounded by a broken line and a range 52 (temporal condition) surrounded by a solid line in FIG. Therefore, the information on the position (i0-1, j0) is written in the position (i0, j0) of the array DI (i, j) shown in FIG.

  Hereinafter, in the flowchart of FIG. 2, the value of the variable k is increased by “1” (step S126), the process returns to step S118, the position is changed, and the same processing is repeated (steps S118 to S126). When processing is completed for all pixel positions, a NO determination is made in step S118, and the process exits from the loop. Thus, the array DI (i, j) as shown in FIG. 5 is completed.

[Determination of repeating units]
In the threshold matrix used for digital halftoning, since the unit matrix is used repeatedly, it is desirable that the dependency relationship has a repeated structure. Therefore, after the dependency relationship is determined, the repetition unit of the dependency relationship is determined. As described with reference to FIGS. 2 to 5, since the array DI (i, j) representing the dependency is determined in advance by the step of determining the dependency, the dependency is determined based on the array DI (i, j). Is required. The outline of the processing method is to express the contents of the array DI (i, j) as a graph structure and determine the repetition of the graph structure by a known method. In this example, a method for obtaining a repetition unit from a graph structure will be described as an example of a method for obtaining a dependency repetition unit. However, the method for determining a repetition unit is not limited to this example.

  Here, the conversion method to the graph structure will be outlined.

  From each position that is an element of the array DI (i, j) with the position (i, j) of the array DI (i, j) as a point, a line ( Draw an arrow line with the position (i, j) at the tip of the line. A line having this direction is called a “directed edge”. By drawing a directed edge with respect to the points of the array DI, it becomes possible to grasp in a two-dimensional graph structure how each point is dependent on the surrounding points.

  FIG. 6 is a graphical representation of the array DI (i, j) illustrated in FIG. In FIG. 6, a line (directed edge) having a direction with respect to a position (point) indicated by a white circle is indicated by an arrow. By using a graph structure with directed edges (arrows), it is possible to display in an easy-to-understand manner from which surrounding points each point of the array DI (i, j) is affected. In the case of FIG. 6, since one point and one directed edge are repeated, two positions related to these are the minimum units (repeating units) of the repeating structure.

  Although the illustrated example is a very simple case, depending on conditions, when a graph is created based on the array DI (i, j), a circuit (a relationship in which influences circulate) may exist. An example is shown in FIG. When the dot formation positions are in a relationship that affects each other, a circuit is generated. This occurs when the simultaneous droplet ejection is temporally less than the time interval at which droplet interference occurs mutually and the dot formation positions are adjacent.

  If a circuit has occurred, it is desirable to eliminate the circuit itself from the dependency by adjusting the droplet ejection time. However, if the circuit cannot be eliminated by methods such as adjusting the droplet ejection time, the directed edge with the largest time difference (the one that seems to have the least effect) is removed to eliminate the circuit. Further, as shown in FIG. 7A, when the left and right influence each other, the circuit is canceled by deciding to remove the directed edge toward the left (or right).

  Next, processing for determining a repetitive structure from a graph structure will be described.

  FIG. 8 is a flowchart showing the procedure for determining the repetitive structure. When the decision flow in the figure starts, first, an arbitrary position is selected from the graph representation of the array DI (i, j) as an origin, and the selected position is connected to the selected edge via a directed edge. The set is set as a temporary minimum unit (step S210). At this time, if the shape of the minimum unit is not a rectangle, the minimum rectangle including the minimum unit is set as a temporary minimum unit.

  Next, in a column adjacent to the temporary minimum unit in the column direction and having the same number of columns as the temporary minimum unit (all sizes in the row direction), the column of the temporary minimum unit (all in the row direction is It is determined whether the structure is the same as (size) (step S212). FIG. 9 shows a conceptual diagram thereof. In FIG. 9, the rectangle indicated by reference numeral 60 is a provisional minimum unit, and the hatched area (including the provisional minimum unit 60 area) indicated by reference numeral 61 is a column of provisional minimum units (the row direction is the entire size). ) Area. A hatched area indicated by reference numeral 62 is located adjacent to the temporary minimum unit and represents an area having the same number of columns as the temporary minimum unit (all sizes in the row direction).

  That is, it is determined whether or not the area denoted by reference numeral 61 in FIG. 9 and the area denoted by reference numeral 62 have the same structure (repetitive structure in the column direction) (step S212 in FIG. 8). In this determination, matching is determined including the directed edge included in the temporary minimum unit, the directed edge that exits from the temporary minimum unit, and the directed edge that enters the temporary minimum unit. .

  If the two structures do not match, the temporary minimum unit is expanded by one column in the column direction (step S214 in FIG. 8), and the process returns to step S212. FIG. 10 is a conceptual diagram showing a state where the temporary minimum unit 60 described in FIG. 9 is expanded by one column in the column direction, and the region indicated by reference numeral 60 ′ in the drawing is the “temporary minimum unit” after the column expansion. Is shown.

  On the other hand, if the two structures match in step S212 of FIG. 8, the process proceeds to step S216. In step S216, it is determined whether or not the region having the same number of rows as the temporary minimum unit and the same structure as the temporary minimum unit is located adjacent to the temporary minimum unit in the row direction. FIG. 11 shows a conceptual diagram thereof. In FIG. 11, a hatched area indicated by reference numeral 64 is located adjacent to the temporary minimum unit 60 in the row direction, and an area having the same number of columns as the temporary minimum unit 60 (all sizes in the row direction). Represents.

  That is, it is determined whether or not the temporary minimum unit area indicated by reference numeral 60 in FIG. 11 and the adjacent area in the row direction indicated by reference numeral 64 have the same structure (repeating structure in the row direction). In this determination, as in step S212, the matching is determined including the directed edge included in the provisional minimum unit, the directed edge exiting from the minimum unit, and the directed edge entering the minimum unit.

  If the structures do not match in step S216, the temporary minimum unit is expanded by one line in the line direction (step S218), and the process returns to step S216. FIG. 12 is a conceptual diagram showing a state where the temporary minimum unit is expanded by one line in the row direction, and an area indicated by reference numeral 60 ″ in the drawing indicates the “temporary minimum unit” after the line expansion.

  On the other hand, if the two structures match in step S216 of FIG. 8, the process proceeds to step S220. In step S220, the provisional minimum unit is finally determined as the “minimum unit”. When the minimum unit of the dependency relationship is determined through the above-described steps, this processing flow is finished.

[Knowledge of amount of dot displacement by dependency]
The amount of displacement due to the droplet ejection state at the position where the concentration at the target position is dependent on the droplet interference is known. It is assumed that the density of the target position in a state where all the positions in the dependency relationship are dotless is known separately.

  As a knowledge method, it is desirable to be based on the result of actual printing. Since the content of the droplet interference changes if the type of the recording medium changes, it is desirable to know the dependency and the amount of dot displacement for each recording medium. Examples of knowledge include determination by device type (model), determination by an actual individual, and the like.

  The method for determining the amount of dot displacement is as follows: (1) The density displacement of the target position due to the dot state is determined independently for the positions in the dependency relationship (one-to-one relationship for one position that affects the target position). And (2) a method of obtaining the density displacement of the target position according to the dot state of the combination in advance by considering all combinations. Note that the dot state is not only when there are only two states, ON and OFF, but also when the dot size can be modulated (for example, when the dot size can be changed to large, medium, and small), all the dots It is desirable to know the size combinations.

  When the density displacement due to the dot state is obtained independently (on a one-to-one basis) for the positions in the dependency relationship, the combinations at two positions for each dot size. Depending on the combination of dot sizes, there may be no displacement of the amount. This is because the dependency is determined by assuming the maximum dot size and the amount of displacement is obtained.

  The knowledge of the amount of dot displacement determined as described above is stored in the array DX (i, j, m, s, t). i, j represents a position, m is an address indicating an element of the dependency when there are a plurality of positions (positions affecting the position of interest) in the array DI (i, j), and s is The dot size at the position of interest, t is the dot size at the dependency position. Note that s and t are not required for systems without dot size modulation.

  On the other hand, in the case of calculating the density displacement at the target position in consideration of the dot states of all combinations in advance, for convenience of calculation, an array CMB (s, t1, t2, t3,. t4, ...) is used. Here, s represents the dot size at the target position, and t1, t2, t3, t4,... Represent the dot size (including the dot off state) at the dependency position. This array CMB (s, t1, t2, t3, t4,...) Is for arranging all combinations of dot states in dependency relation in a certain order (permutation). In order to associate the elements of the array CMB (s, t1, t2, t3, t4,...) With the address, an array that generates an address from the combination of dependency states is used, and ads = CMB (s, t1, t2, t3 , t4,...), the knowledge of the dot displacement determined for the dot state of the combination indicated by the address is stored in the array DX (i, j, ads).

[Examples of specific methods for obtaining knowledge of dot displacement by dependency]
As described above, the dependency and the amount of dot displacement vary depending on the conveyance speed (paper feed speed) of the recording medium, the characteristics of the recording medium, the characteristics of the ink, and the like. Therefore, in order to realize higher-quality image reproduction (halftoning), the dependency relationship and the dot displacement amount are determined with respect to the conditions of the conveyance speed of the recording medium, the recording medium type, and the ink type. It is necessary to use a parameter or threshold matrix.

  In addition, regarding the knowledge of the dependency relationship and the amount of dot displacement, there are one depending on the type (model) of the device and one based on characteristics unique to each machine (individual). When determining the dependency on droplet interference caused by the device type (model), in principle, it is only necessary to determine once for the same model (same specifications), and the determined information is transferred to other aircraft of the same model. Applicable.

  On the other hand, assuming a calibration-like usage corresponding to machine differences (individual differences), since the locality of the nozzle characteristics exists in the ink ejection head (printing head) of the inkjet recording apparatus, the dependency relationship is widened. Even if it is calculated, the knowledge of the amount of dot displacement needs to be determined for all nozzles. In determining the threshold matrix, it is necessary to calculate each threshold matrix size (calculate with the number of pixels of the entire column width). If the line head is assumed, the repetition unit in the row direction is effective, and therefore it is not necessary to calculate the number of pixels in the total number of rows in the row direction.

  As an example of a method for knowing the amount of dot displacement, the dot landing position and the dot size (for each nozzle) are printed for each nozzle by printing a predetermined test pattern using the target inkjet recording apparatus and reading the printing result. The amount of droplets) is measured in advance for each nozzle of the machine.

  For example, as shown in FIG. 13 (a), droplets that are isolated from each nozzle (single dots that do not overlap with other dots) are ejected, and the droplet ejection results are read by an image sensor or the like. And the dot size (dot diameter when circular dots are assumed). For a system capable of dot size modulation, it is preferable to perform the same measurement for all dot size types, but at least the maximum dot size is measured. In this way, dot landing position and dot size information is obtained for all nozzles.

  Further, the dot displacement amount at the target position can be obtained from the data of the dot displacement amount (see FIG. 14) with respect to the combination of the dot landing position and the dot size in each dependency relationship, which is separately known. The table shown in FIG. 14 is a table showing dot displacement amounts with respect to combinations of dot landing positions and dot sizes at relative positions. FIG. 15 shows the positional relationship of relative positions corresponding to the table of FIG.

  As shown in FIG. 15, it is assumed that a dependency relationship is generated between “position 1”, “position 2”, “position 3”,... Know the dot displacement amount of the target position for the combination of the dot position and the dot size at each position of the one having the greatest influence (that is, one that can include all the dependencies affecting the target position) ( (See FIG. 14). The combination includes the case of “no dot” for each position. FIG. 13C illustrates a state in which the “position of interest” dot is displaced in relation to the “position 3” dot and the “position 4” dot as an example of the combination.

  In addition to the mode of specifying the amount of dot displacement using the table as shown in FIG. 14, as another example of the method of knowing the amount of dot displacement, a combination of dot sizes corresponding to the dependency at each position It is also possible to actually deposit dots corresponding to the above on the recording medium, measure the droplet ejection result with a dot measuring device, and use this measurement result to find out. By actually printing a dot pattern under various conditions and measuring the optical density at the target position, it is possible to acquire information regarding the amount of dot displacement at each position.

  Alternatively, instead of an aspect in which the dot displacement amount is known for a combination of positions having a dependency relationship, as shown in FIG. 13B, the position of the target pixel and the position of the dependency relationship are independently displayed. A mode in which the amount of displacement is determined and known (one to one with one) is also possible. In this case, finally, a means for determining the displacement amount of the target pixel position from the information of the displacement amounts from a plurality of positions having a dependency relationship is necessary.

As an example of such a determination means, for example, the displacement amount from each position obtained independently is di (i = 0,1,2,3...), The displacement amount at the position of interest (the result of the determination, In the combination, this displacement amount value is directly stored) when ΔD is
ΔD = f (d0, d1, d2, d3,...)
A means for calculating using the function f determined in advance is used. Although this function f is not particularly limited, for example, a linear combination of di (i = 0, 1, 2, 3...) Can be considered. In this case, the coefficient of each term is appropriately determined from experiments and the like.

[Determination of threshold matrix size]
The size of the threshold matrix to be finally obtained needs to satisfy the conditions of an integral multiple of the repeating unit and a visually effective size (for example, 128 × 128 pixels to 512 × 512 pixels). A threshold matrix size that satisfies this condition is determined.

  After determining the threshold matrix size, the dependency array is cut out with the threshold matrix size and stored in the array DIE (i, j). The array DI (i, j) described with reference to FIGS. 5 to 6 is intended for the entire image (all image planes), but what is required in the threshold matrix is a certain repeating unit. Therefore, a process of cutting out the repeating unit with the final size of the threshold matrix is performed. Naturally, when a part of the region (threshold matrix size region) is cut out from the entire image region, the dependency is cut off at the portion adjacent to the cut-out region (the cut-out boundary portion). In order to compensate for this divided dependency, the directed edge is replaced (converted).

  At this time, only for the directed edges that enter from outside the area of the threshold matrix size cut out by referring to the graph structure (ignoring directed edges that exit from the area), the dependency within the area The directed edge is converted so that the above is completed (the row size and the column size MOD of the threshold matrix size are calculated and set as the dependency positions). When a circuit is generated after this conversion, if the circuit length is not sufficiently long, the threshold matrix size is increased by an integral multiple of the repeating unit. In other words, make the circuit length large enough to ignore the effect. The threshold matrix threshold is determined using the dependency of the threshold matrix size thus determined.

[Determination of threshold value]
Next, a method for determining the threshold will be described.

  In a state where dots are sparse, it is not necessary to consider dependency relations from the beginning, so that a well-known dot arrangement determination flow can be used, and detailed description thereof is omitted. The dot size corresponding to the dot arrangement is determined for each dot in a known dot arrangement determination flow, and a check based on the dependency is performed at the time of determination. If the dot is off at the position having the dependency relationship or the dot displacement amount is zero, the dependency relationship does not affect the determination of the dot at the target position, and thus detailed description is omitted. In addition, not only newly added dot positions but also dependency relations are checked between existing dot positions.

  If it is found that the amount of dot displacement is not zero due to the dependency, the dot position (including change of the dot size) added by the known dot arrangement determination flow is once canceled.

  There are several methods for determining the additional dot position after cancellation. For example, there are the following method 1 and method 2.

(Method 1) Method to test all positions Test all possible combinations, and evaluate dot arrangement in a state where changes in the amount of dot displacement due to the combinations are included (a known method is used for the evaluation method). Then, the best dot is determined as the additional dot position.

(Method 2) Method of narrowing down to a highly likely position first Calculate the density distribution based on the existing dot arrangement, and calculate the density distribution that is visible when viewed at a predetermined observation distance (preferably about 100 mm to 300 mm). Then, a position (a range in consideration of the amount of dot displacement) that falls within a predetermined density range from the minimum value of the density distribution (bright spot, that is, a place where there is no dot) is selected as a candidate. If the number of selected candidate positions is larger than the predetermined number, the density width is adjusted so as to fall within the allowable range from the predetermined number, and then the candidate positions are selected again.

  On the other hand, if the number of selected candidate positions is too small, the density width is adjusted so as to be within the allowable range from the predetermined number, and then the candidate position is selected again. With regard to the positions thus selected, all combinations are tested, and dot arrangement is evaluated in a state where changes in the amount of dot displacement due to the combinations are included, and the best evaluation is determined as an additional dot position.

  Alternatively, a density histogram is created from the existing dot arrangement, all combinations are tested from the minimum density corresponding to a predetermined number of pixels, and the dot arrangement is evaluated with changes in the amount of dot displacement caused by the combination included. The best dot is determined as the additional dot position.

  A threshold value is added for the dot position determined by (Method 1) or (Method 2) described above.

  As a method for evaluating dot arrangement (dot pattern), the method proposed by Robert and Ulichney is generally used ("Digital Halftoning"; published by The MIT Press). That is, the two-dimensional power spectrum of the dot arrangement is converted into polar coordinates, and an index corresponding to the average and variance of the spectrum at all angles is used for the spatial frequency fr corresponding to the radius of the polar coordinates. The average index of the polar power spectrum is called “R.A.P.S (Radially Averaged Power Spectrum)”, and the dispersion index is called “Anisotropy”. R.A.P.S is an index relating to the visibility of dot arrangement, and Anisotropy is an index relating to anisotropy of dot arrangement. According to Robert Ulichney, the anisotropy of dots is inconspicuous if Anisotropy is -10 dB [dB] or less.

  FIG. 16 is a flowchart illustrating an example of a threshold determination procedure. This flowchart is applied to a system without dot size modulation, and is an example in which evaluation is performed by narrowing down candidates as described in (Method 2) above.

  First, the threshold matrix is initialized, and each threshold is initialized to zero. The position where the first threshold value is stored is a predetermined position, and the threshold value is incremented by 1 after the threshold value is input to the predetermined position (step S310).

  Next, it is determined whether or not all positions have been calculated (step S312). If there are uncalculated positions, the process proceeds to step S314. In step S314, a density distribution is calculated based on a dot model (a model in which specific conditions such as dot size and density are set) at positions where threshold values have already been determined. Then, with respect to the result of filtering the obtained density distribution with a spatial filter corresponding to visual observation from a predetermined observation distance, a position corresponding to the minimum density among positions where no threshold is input (determined) is set as the next threshold value. It is selected as an input position candidate (referred to as “threshold candidate”) (step S316). At this time, if there are a plurality of candidates, the position having the best dot arrangement is selected as the threshold candidate. For the evaluation of dot arrangement, a known method such as “R.A.P.S” or “Anisotropy” is used.

  Next, it is confirmed whether or not dot displacement occurs for the selected threshold candidate position based on the dependency array DIE (i, j) (step S318). Then, it is determined whether or not dot displacement occurs (step S320). If dot displacement does not occur (NO determination), the process proceeds to step S322, and the candidate position is input to the next threshold position (threshold value is input). The threshold value is input here.

  On the other hand, if it is determined in step S320 that dot displacement occurs (YES determination), the process proceeds to step S324. In step S324, as a result of filtering the density distribution with a spatial filter corresponding to visual observation from a predetermined observation distance, a predetermined number of pixels from a lower density among the positions where no threshold is input as threshold candidates. Evaluate dot placement, including dependencies (calculating how array DIE and array DX change). Then, the candidate position with the best dot arrangement is determined as the next threshold position, and the threshold value is input to the position (step S326).

  After step S322 or step S326, the threshold value is increased by 1 (step S328), and the process returns to step S312. Steps S312 to S328 are repeated until threshold values have been input for all positions in the threshold matrix. When all positions have been calculated, a YES determination is made in step S312, and the process routine is exited and the process ends. Thus, the threshold matrix is completed.

  FIG. 17 is a flowchart illustrating another example of the threshold determination procedure. This flowchart is applied to a system that performs dot size modulation. In FIG. 17, steps that are the same as those in the flowchart shown in FIG. 16 are given the same step numbers, and descriptions thereof are omitted. In place of steps S312, S316, and S324 in FIG. 16, steps S312 ', S316', and S324 'are taken into consideration in FIG. The processing content of each step is as described in FIG.

  In the case of a system that can change the dot size, since a plurality of types of dots having different dot sizes can be formed at one dot formation position, the threshold matrix not only defines on / off of dots but also at the same position. Since switching of the dot size is also defined, a hierarchical structure (three-dimensional structure) corresponding to the number of types of dot sizes is formed.

  FIG. 18 is a conceptual diagram showing how threshold values of a threshold value matrix corresponding to dot size modulation are determined. For example, in a system in which the dot size can be changed in three types, small, medium, and large, for each dot formation position, the threshold level (first layer) TH1 at which the small size dot is turned on and the small size dot on Threshold level (second layer) TH2 when switching from medium size to medium size dot and threshold level (third layer) TH3 when switching from medium size dot on to large size dot A threshold value is set (input) for each structure. Steps S312 'to S328' of Fig. 17 are repeated until all threshold values of each layer are determined for all dot formation positions. When all positions and dot sizes have been calculated, a YES determination is made in step S312 ', and the process routine is exited and the process ends. Thus, the threshold matrix is completed.

  As described above, by performing digital halftoning using the threshold matrix obtained by the threshold matrix creation method according to the embodiment of the present invention, the optimum dot arrangement including the dot displacement based on the dependency relationship is determined. And high-quality images can be obtained.

  The threshold matrix creation method described above can be realized using a computer. That is, a program (threshold matrix creation program) for causing a computer to execute the algorithm of the threshold matrix creation method described above is created, and the computer is operated by this program so that the computer functions as a threshold matrix creation device. it can.

[Description of Computer System as an Example of Threshold Matrix Generation Device]
FIG. 19 is a block diagram illustrating a system configuration example of a computer. The computer 70 includes a main body 72, a display (display means) 74, and an input device (input means for inputting various instructions) 76 such as a keyboard and a mouse. In the main body 72, a central processing unit (CPU) 80, a RAM 82, a ROM 84, an input control unit 86 for controlling signal input from the input device 76, a display control unit 88 for outputting a display signal to the display 74, A hard disk device 90, a communication interface 92, a media interface 94, and the like are included, and these circuits are connected to each other via a bus 96.

  The CPU 80 functions as an overall control device and arithmetic device (arithmetic means). The RAM 82 is used as a temporary data storage area or a work area when the CPU 80 executes a program. The ROM 84 is a rewritable nonvolatile storage unit that stores a boot program for operating the CPU 80, various setting values, network connection information, and the like. The hard disk device 90 stores an operating system (OS), various application software (programs), data, and the like.

  The communication interface 92 is a means for connecting to an external device or a communication network according to a predetermined communication method such as USB, LAN, or Bluetooth. In this example, a reading device such as a scanner (not shown) can be connected via the communication interface 92. The media interface 94 is means for performing read / write control of an external storage device 98 represented by a memory card, magnetic disk, magneto-optical disk, and optical disk.

  Information indicating the mutual dependency between dots, and information on the amount of dot displacement due to the dependency may be obtained by actually reading and measuring a dot pattern using a device such as a scanner, or by experiments or the like in advance. The grasped value may be input from the input device 76 or may be acquired as data through the communication interface 92 or the media interface 94.

  The threshold value matrix creating program according to the embodiment of the present invention is stored in the hard disk device 90 or the external storage device 98, and the program is read out as needed and expanded in the RAM 82 and executed. Alternatively, an aspect in which the program is provided by a server installed on a network (not shown) connected via the communication interface 92 is possible, and an aspect in which an arithmetic processing service by the program is provided by a server on the Internet. Is also possible.

  The operator can input necessary items such as a desired matrix size and various initial value settings by operating the input device 76 while viewing an application window (not shown) displayed on the display 74, and can display the calculation result. It can be confirmed on the display 74.

  In FIG. 19, an example in which the computer 70 realizes a function as a threshold matrix creation device has been described. However, an embodiment in which a dedicated device having a threshold matrix creation function according to the present invention is configured is also possible.

[Description of Inkjet Recording Apparatus Using Threshold Matrix]
Next, an example of an ink jet recording apparatus to which the threshold matrix created by the threshold matrix creating method described above is applied will be described.

  FIG. 20 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. As shown in the figure, the ink jet recording apparatus 110 includes a plurality of ink jet recording heads (hereinafter referred to as “ink jet recording heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 112 having 112K, 112C, 112M, and 112Y, an ink storage / loading unit 114 that stores ink to be supplied to each of the heads 112K, 112C, 112M, and 112Y, and recording paper as a recording medium The paper feeding unit 118 that supplies the paper 116, the decurling unit 120 that removes curl of the recording paper 116, and the nozzle surface (ink ejection surface) of the printing unit 112 are disposed so as to improve the flatness of the recording paper 116. A belt conveyance unit 122 that conveys the recording paper 116 while holding it, a print detection unit 124 that reads a printing result by the printing unit 112, and recorded And a discharge unit 126 for discharging recording paper (printed matter) to the outside.

  The ink storage / loading unit 114 has an ink tank that stores ink of a color corresponding to each of the heads 112K, 112C, 112M, and 112Y, and each tank has a head 112K, 112C, 112M, and 112Y via a required pipe line. Communicated with. Further, the ink storage / loading unit 114 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 20, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 118, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media (media) can be used, an information recording body such as a barcode or a wireless tag that records media type information is attached to a magazine, and information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of recording medium to be used (media type) and to perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 116 delivered from the paper supply unit 118 retains curl due to having been loaded in the magazine. In order to remove the curl, heat is applied to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction of the magazine in the decurling unit 120. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration using roll paper, a cutter (first cutter) 128 is provided as shown in FIG. 20, and the roll paper is cut to a desired size by the cutter 128. Note that the cutter 128 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 116 is sent to the belt conveyance unit 122. The belt conveyance unit 122 has a structure in which an endless belt 133 is wound between rollers 131 and 132, and at least portions facing the nozzle surface of the printing unit 112 and the sensor surface of the printing detection unit 124 are horizontal (flat). Surface).

  The belt 133 has a width that is greater than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 20, an adsorption chamber 134 is provided at a position facing the nozzle surface of the printing unit 112 and the sensor surface of the printing detection unit 124 inside the belt 133 spanned between the rollers 131 and 132. The recording paper 116 is sucked and held on the belt 133 by sucking the suction chamber 134 with a fan 135 to a negative pressure. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  When the power of the motor (reference numeral 188 in FIG. 25) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, the belt 133 is driven in the clockwise direction in FIG. The held recording paper 116 is conveyed from left to right in FIG.

  Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region). Although details of the configuration of the belt cleaning unit 136 are not illustrated, for example, there are a method of niping a brush roll, a water absorption roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  It is possible to use a roller / nip conveyance mechanism instead of the belt conveyance unit 122. However, if the roller / nip conveyance is performed in the printing area, the roller is brought into contact with the printing surface of the sheet immediately after printing, so that the image is likely to bleed. There's a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 140 is provided on the upstream side of the printing unit 112 on the paper conveyance path formed by the belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 112K, 112C, 112M, and 112Y of the printing unit 112 has a length corresponding to the maximum paper width of the recording paper 116 targeted by the inkjet recording device 110, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 21).

  The heads 112K, 112C, 112M, and 112Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. 112K, 112C, 112M, and 112Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 116.

  A color image can be formed on the recording paper 116 by discharging different colors of ink from the heads 112K, 112C, 112M, and 112Y while the recording paper 116 is being conveyed by the belt conveyance unit 122.

  As described above, according to the configuration in which the full-line heads 112K, 112C, 112M, and 112Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 116 and the printing unit in the paper feeding direction (sub-scanning direction). An image can be recorded on the entire surface of the recording paper 116 by performing the operation of relatively moving the 112 once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  The print detection unit 124 illustrated in FIG. 20 includes an image sensor (line sensor or area sensor) for imaging the droplet ejection result of the printing unit 112, and the dependency relationship between dots from the droplet ejection image read by the image sensor. And a means for measuring the amount of dot displacement, and also a means for checking ejection defects such as nozzle clogging and landing position deviation. A test pattern or practical image printed by the heads 112K, 112C, 112M, and 112Y of each color is read by the print detection unit 124, and the dependency of each head is measured and ejection determination is performed. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 142 is provided following the print detection unit 124. The post-drying unit 142 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 144 is provided following the post-drying unit 142. The heating / pressurizing unit 144 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 145 having a predetermined uneven surface shape while heating the image surface, and transfers the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 126. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 110 is provided with a sorting means (not shown) that switches the paper discharge path in order to select the prints of the main image and the prints of the test print and send them to the discharge units 126A and 126B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by the cutter (second cutter) 148. Although not shown in FIG. 20, the paper output unit 126A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the respective heads 112K, 112C, 112M, and 112Y for each color are common, the heads are represented by reference numeral 150 in the following.

  FIG. 22A is a plan perspective view showing an example of the structure of the head 150, and FIG. 22B is an enlarged view of a part thereof. 22C is a plan perspective view showing another example of the structure of the head 150, and FIG. 23 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 151). It is sectional drawing which follows the 23-23 line in FIG.22 (a).

  In order to increase the dot pitch printed on the recording paper 116, it is necessary to increase the nozzle pitch in the head 150. As shown in FIGS. 22A and 22B, the head 150 of this example includes a plurality of ink chamber units (liquid chambers) each including a nozzle 151 serving as an ink discharge port, a pressure chamber 152 corresponding to each nozzle 151, and the like. Droplet ejecting elements) 153 are arranged in a zigzag matrix (two-dimensionally), and thus are projected so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are formed over a length corresponding to the entire width of the recording paper 116 in a direction substantially orthogonal to the feeding direction of the recording paper 116 is not limited to this example. For example, instead of the configuration of FIG. 22 (a), as shown in FIG. 22 (c), short head modules 150 ′ in which a plurality of nozzles 151 are two-dimensionally arranged are arranged in a staggered manner and connected. A line head having a nozzle row having a length corresponding to the entire width of the recording paper 116 may be configured.

  The pressure chamber 152 provided corresponding to each nozzle 151 has a substantially square planar shape (see FIGS. 22 (a) and (b)), and the nozzle 151 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 154 is provided on the other side. The shape of the pressure chamber 152 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 23, each pressure chamber 152 communicates with the common flow path 155 through the supply port 154. The common channel 155 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 152 via the common channel 155.

  An actuator 158 having an individual electrode 157 is joined to a pressure plate (vibrating plate also serving as a common electrode) 156 constituting a part of the pressure chamber 152 (the top surface in FIG. 23). By applying a driving voltage between the individual electrode 157 and the common electrode, the actuator 158 is deformed to change the volume of the pressure chamber 152, and ink is ejected from the nozzle 151 due to the pressure change accompanying this. For the actuator 158, a piezoelectric element using a piezoelectric body such as lead zirconate titanate or barium titanate is preferably used. When the displacement of the actuator 158 returns to its original state after ink ejection, new ink is supplied from the common flow path 155 through the supply port 154 to the pressure chamber 152.

  As shown in FIG. 24, the ink chamber units 153 having the above-described structure are arranged in a constant arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern.

  That is, with a structure in which a plurality of ink chamber units 153 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 151 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When the nozzles are driven by a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 151 arranged in a matrix as shown in FIG. 24, main scanning as described in (3) above is preferable. That is, nozzles 151-11, 151-12, 151-13, 151-14, 151-15, 151-16 are made into one block (other nozzles 151-21,..., 151-26 are made into one block, Nozzles 151-31,..., 151-36 as one block,..., And by sequentially driving the nozzles 151-11, 151-12,. One line is printed in the width direction of 116.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. This is defined as sub-scanning.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as a main scanning direction, and the direction in which the sub scanning is performed is referred to as a sub scanning direction. In other words, in the present embodiment, the conveyance direction of the recording paper 116 is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In this embodiment, a method of ejecting ink droplets by deformation of an actuator 158 typified by a piezo element (piezoelectric element) is adopted. However, the method of ejecting ink is not particularly limited in implementing the present invention. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Explanation of control system]
FIG. 25 is a block diagram illustrating a system configuration of the inkjet recording apparatus 110. As shown in the figure, the inkjet recording apparatus 110 includes a communication interface 170, a system controller 172, an image memory 174, a ROM 175, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182 and a head driver 184. It has.

  A communication interface (corresponding to an image input unit) 170 is an interface unit that receives image data sent from the host computer 186. As the communication interface 170, a serial interface such as USB, IEEE 1394, Ethernet, or wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 186 is taken into the inkjet recording apparatus 110 via the communication interface 170 and temporarily stored in the image memory 174. The image memory 174 is a storage unit that stores an image input via the communication interface 170, and data is read and written through the system controller 172. The image memory 174 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 110 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the image memory 174, the motor driver 176, the heater driver 178, and the like, and performs communication control with the host computer 186, read / write control of the image memory 174 and ROM 175, and the like. At the same time, a control signal for controlling the motor 188 and the heater 189 of the transport system is generated.

  The ROM 175 stores programs executed by the CPU of the system controller 172 and various data necessary for control. The ROM 175 also stores a threshold matrix data used for the halftoning process and a program for ejecting a test pattern for examining the dependency. That is, the ROM 175 corresponds to a threshold matrix storage unit. The ROM 175 may be a non-rewritable storage unit or a rewritable storage unit such as an EEPROM. The image memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 176 is a driver (driving circuit) that drives the conveyance motor 188 in accordance with an instruction from the system controller 172. The heater driver 178 is a driver that drives the heater 189 such as the post-drying unit 142 in accordance with an instruction from the system controller 172.

  The print control unit 180 has a signal processing function for performing various processes such as processing and correction for generating a print control signal from image data (original image data) in the image memory 174 in accordance with the control of the system controller 172. And a control unit that supplies the generated print data (dot data) to the head driver 184.

  The print control unit 180 includes an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the print control unit 180. In FIG. 25, the image buffer memory 182 is shown in a mode associated with the print control unit 180, but can also be used as the image memory 174. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  An outline of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 170 and stored in the image memory 174. At this stage, for example, RGB image data is stored in the image memory 174.

  In the ink jet recording apparatus 110, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 174 is sent to the print control unit 180 via the system controller 172, and the print control unit 180 uses the halftone process using the threshold matrix to generate the ink color. Converted to dot data for each.

  That is, the print control unit 180 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. A threshold value matrix created by applying the present invention (in this example, a threshold value matrix is prepared for each color) is incorporated in the print control unit 180 and used for the above-described conversion process from original image to dot data. . Thus, the dot data generated by the print control unit 180 is stored in the image buffer memory 182.

  The head driver 184 generates a drive signal for driving the actuator 158 corresponding to each nozzle 151 of the head 150 based on the print data (that is, dot data stored in the image buffer memory 182) given from the print control unit 180. Output. The head driver 184 may include a feedback control system for keeping the head driving condition constant.

  When the drive signal output from the head driver 184 is applied to the head 150, ink is ejected from the corresponding nozzle 151. An image is formed on the recording paper 116 by controlling ink ejection from the head 150 in synchronization with the conveyance speed of the recording paper 116.

  As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head driver 184 based on the dot data generated through the required signal processing in the print control unit 180. Thereby, a desired dot size and dot arrangement are realized.

  As described with reference to FIG. 20, the print detection unit 124 is a block including an image sensor. The print detection unit 124 reads an image printed on the recording paper 116, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection. Variation, optical density, etc.) and the detection result is provided to the print controller 180. It should be noted that other discharge detection means (corresponding to discharge abnormality detection means) may be provided instead of or in combination with the print detection unit 124.

  As another ejection detection means, for example, a pressure sensor is provided in or near each pressure chamber 152 of the head 150, and a detection signal obtained from the pressure sensor is used when ejecting ink or driving a pressure measurement actuator. Using a mode (internal detection method) to detect abnormal discharge or an optical detection system consisting of a light source and a light receiving element such as a laser light emitting element, the liquid droplets discharged from the nozzle are irradiated with light such as laser light and transmitted. There may be a mode (external detection method) in which flying droplets are detected based on the amount of light (amount of received light).

  The print control unit 180 performs various corrections on the head 150 based on information obtained from the print detection unit 124 or other discharge detection means (not shown) as necessary, and performs preliminary discharge, suction, wiping, and the like as necessary. Control to perform the cleaning operation (nozzle recovery operation) is performed.

  The ink jet recording apparatus 110 also includes an ink information reading unit 190 that acquires information about the type of ink used (ink type information), and a media type detection that acquires information about the type of recording paper 116 (media type). The information obtained from each of these units is sent to the system controller 172.

  As a means for acquiring ink type information, for example, the ink physical property information is read from the shape of the cartridge of the ink tank (a specific shape that can identify the ink type) or a barcode or IC chip incorporated in the cartridge. Means can be used. In addition, the operator may input necessary information using a user interface.

  The media type detection unit 192 is a unit that detects the type (paper type) and size of the recording paper 116. For example, a means for reading information such as a barcode attached to the magazine of the paper feeding unit 118 described in FIG. 20, a sensor (paper width detection sensor, detecting the thickness of the paper) disposed at an appropriate location in the paper conveyance path For example, a sensor for detecting the reflectance of the paper), and an appropriate combination thereof is also possible. Further, in place of or in combination with these automatic detection means, it is possible to specify information such as paper type and size by input from a predetermined user interface.

  The system controller 172 and the print control unit 180 select an optimum threshold matrix based on information obtained from the ink information reading unit 190 and the media type detection unit 192, and also select the ink amount (droplet size, ejection drive timing, or These combinations) are controlled. That is, the system controller 172 or the print control unit 180, or the combination of the system controller 172 and the print control unit 180 functions as “halftoning processing unit” and “test pattern formation control unit” in the present invention, and results of the halftoning processing. It functions as droplet ejection control means for performing droplet ejection control based on the above.

  According to the ink jet recording apparatus 110 having the above configuration, even when droplet interference occurs, it is possible to obtain a good image with little deterioration in image quality due to dot displacement.

  As already described, the mutual dependency between dots is determined by a temporal element and a spatial element. That is, when the printing speed (relative speed of the recording medium with respect to the head) is changed, the landing time difference between the droplets changes, and the dependency changes. In addition, when the type of ink or the type of recording medium (a combination thereof) is changed, the behavior of the droplets on the recording medium changes, and the affected space amount changes. Therefore, in the case of a system in which at least one of the printing speed, ink type, and recording medium type can be changed, it is preferable to change the threshold matrix used in accordance with the change.

  At this time, the threshold matrix may be recalculated or a plurality of threshold matrices corresponding to each condition may be stored in advance, and the corresponding threshold matrix may be read and replaced in accordance with the use conditions. is there.

  Alternatively, an embodiment in which the threshold matrix creation function described in FIGS. 1 to 19 is incorporated in the inkjet recording apparatus 110 is also possible. In this case, a threshold matrix creation program is stored in the ROM 175 described with reference to FIG. Then, if necessary, a test pattern for checking the dependency is printed, the print result of the test pattern is read by the print detection unit 124, and the read information is analyzed to obtain information on the dependency between dots and the amount of dot displacement. get. Based on the information thus obtained, a threshold matrix can be generated as described above and used for the halftoning process.

  In the above embodiment, an ink jet recording apparatus using a full line type print head has been exemplified, but the scope of application of the present invention is not limited to this. For example, as shown in FIGS. 26 (a) and 26 (b), a line head (hereinafter referred to as a print head 250) having a length insufficient for the width Wm of the recording medium (recording paper 116 or other printing medium) 216 is used. The present invention can also be applied to the case where an image is formed by scanning a plurality of times.

  26A and 26B, the double-headed arrow 250A drawn in the print head 250 schematically represents the nozzle alignment direction and the length of the nozzle row, and the white arrow 252 represents the print head scanning direction. Represents. FIG. 26A shows the state of the first scanning, and FIG. 26B shows the state of the Nth scanning (N is an integer of 2 or more) performed by changing the scanning position.

  As shown in the figure, the print head 250 has its longitudinal direction (nozzle alignment direction) arranged along the width direction of the recording medium 216, and drives a head scanning means (not shown) such as a support mechanism such as a carriage and a travel guide and the like. For example, a drive means such as a motor for moving the print head in a scanning direction (in the direction of the white arrow 252) and in the width direction of the recording medium 216 (in the horizontal direction in FIG. 26).

  An image is formed on the recording medium 216 by performing scanning a plurality of times in the print head scanning direction 252 while changing the position (scanning position) of the print head 250 with respect to the width direction of the recording medium 216.

  Although an example in which the print head 250 is moved will be described here, scanning may be performed by moving the print head 250 relative to the recording medium 216, or a mode in which the recording medium 216 side is moved, or printing. A mode in which scanning is performed by combining movement of both the head 250 and the recording medium 216 is also possible.

  As shown in FIGS. 26 (a) and 26 (b), the print head 250 scans different positions in each scan. The nozzles that moved relatively on the recording medium 216 by these scans are shown in FIG. As shown, the print head 250 has a nozzle row 255A having a length corresponding to the width Wm of the recording medium 216 by regarding the nozzle as a corresponding position on the line head 255 having a virtual recording medium width (Wm). It can be regarded as a part of the virtual line head 255. That is, the present invention can be applied to this virtual line head (full line type head) 255 in the same manner as in the embodiment of the full line type head 150 described above.

  Further, as shown in FIGS. 28A and 28B, when the print head 250 is shuttle-scanned to form an image, it can be similarly converted into a virtual line head, and the algorithm of the present invention is applied. Is possible.

  In FIGS. 28A and 28B, the same or similar components as those in FIGS. 26A and 26B are denoted by the same reference numerals, and description thereof is omitted.

  28A and 28B, the print head 250 is arranged such that its longitudinal direction (nozzle alignment direction) is along the feed direction of the recording medium 216 (media feed direction indicated by the white arrow 254). The print head 250 is scanned in a direction substantially orthogonal to the feed direction.

  An image is formed on the recording medium 216 by scanning a plurality of times while changing the relative position between the recording medium 216 and the printing head 250 by a combination of scanning by the printing head 250 and movement of the recording medium 216. The

[Second Embodiment: Example Using Error Diffusion Method]
Next, another embodiment of the present invention will be described. An embodiment using the error diffusion method instead of the method using the threshold matrix described in the first embodiment will be described below.

  FIG. 29 is a flowchart showing a schematic procedure of an image forming method using the error diffusion method. As shown in FIG. 5A, first, the dependency relationship is determined (step S410), and knowledge of the displacement amount due to the dependency relationship is obtained (step S420). Subsequently, the processing order of error diffusion processing is determined (step S430), and error diffusion processing is performed according to the determined order (step S440). Then, at the time of dot formation in the error diffusion process, the density of the pixel of interest is corrected in consideration of the dot displacement based on the dependency, and the error is calculated based on the corrected value.

  Alternatively, as shown in FIG. 29 (b), it is possible to add a process of “determination of repeating unit (step S415) between step S410 and step S420. The determination of the repeating unit is performed by the error diffusion method. Although not an indispensable process, a repeating unit can be used in the sense of reducing the range of checking dependency relationships and further reducing the amount of dependency information.

[Determination of processing order]
In view of the nature of the droplet interference, the order of the processing positions that reverses the actual droplet ejection time is undesirable. Therefore, it is preferable to select the order in which the pixels are processed so as not to contradict the dependency.

(When there is a consistent processing order)
The case where there is a consistent processing order means that the dot formation determination has been completed for all pixels having a dependency relationship with the target pixel. An example is shown in FIG.

  In this case, the dot formation of the target pixel is compared with a threshold value, the density of the target pixel is corrected (dot displacement) based on the dependency during dot formation, and the error is calculated based on the corrected value. A known technique is used for error diffusion. In addition to the raster scan order that is normally used, it is possible to perform processing that skips pixels within the same line. At that time, an error diffusion coefficient is prepared in accordance with the surrounding positional relationship.

  FIG. 31 is a flowchart showing a processing procedure when there is a consistent processing order. As shown in the figure, first, it is determined whether or not all positions have been calculated (step S510). If NO, the process proceeds to step S512. In step S512, an error E (i, j) from the already processed peripheral pixels is obtained. Next, a processed dot size at a position having a dependency relationship is obtained (step S514).

Next, a combination array CMB (sk, t1, t2, t3, t4,...) Is created from the dot sizes at positions that are in a dependency relationship for all the dot sizes sk that can be taken by the target position, and from this combination array. An address is generated by associating adsk = CMB (sk, t1, t2, t3, t4,...). Then, a dot displacement amount ΔDk = DX (i, j, adsk) indicating how much dot displacement is generated for a certain combination (how much density can actually be expected) is obtained, and the dot size sk of the target pixel is obtained. Is compared with the density Dk corresponding to the sum of the error E (i, j) and the density I (i, j) of the pixel of interest (E (i, j) + I (i, j)). A dot size having a small value (including dot on / off) is determined, and a generated error Eo (i, j) generated for the determination is calculated (step S516). That is, the dot size sk that minimizes F _ijk = | E (i, j) + I (i, j) − (Dk + ΔDk) | is obtained, and the generated error Eo (i, j) generated for this determination is obtained. Calculate (step S516).

  Next, the generated error Eo (i, j) is diffused to the unprocessed position (step S518), and the next pixel position is set as the target pixel position in accordance with the processing position order (step S520). Thereafter, the process returns to step S510, and the processes of steps S510 to S520 are repeated. When the dot formation determination is completed for all positions, the determination is YES in step S510 and the process ends.

  Note that a mode in which step S516 in FIG. 31 is replaced with step S516 'in FIG. 32 is also possible. In FIG. 32, the same steps as those in FIG. 31 are denoted by the same step numbers, and the description thereof is omitted.

In step S516 ′ in FIG. 32, the sum of the error E (i, j) and the density I (i, j) of the target pixel is compared with the multi-value threshold T (i, j, a) to determine the target pixel position. The dot size a is determined. Then, for the determined dot size a, ads = CMB (a, t1, t2, t3, t4,...) Is obtained from the dot size at a position having a dependency relationship. Further, a dot displacement amount ΔD = DX (i, j, ads) is obtained, and the density D corresponding to the dot size a of the target pixel is expressed by the following equation:
Eo (i, j) = D + ΔD + E (i, j) −I (I, j)
The generated error Eo (i, j) is calculated.

  Steps S518 and S520 subsequent to step S516 'are as described in FIG.

(If there is no consistent processing order)
Next, a processing method when there is no consistent processing order will be described. The case where there is a consistent processing order means that some of the pixels having a dependency relationship with the target pixel have not been subjected to dot formation determination. An example is shown in FIG.

  In this case, the dot formation of the target pixel is compared with the threshold value, and it is assumed that no dot is formed for the unprocessed position B. At the time of dot formation, the density of the target pixel is corrected (dot displacement) based on the dependency relationship. The error is calculated based on the obtained value. The density correction amount at this time is stored. A known technique is used for error diffusion. Next, when the dot formation at the unprocessed position B is determined, the density correction amount at this position is newly calculated again. If the density correction amount is different from the stored density correction amount, the newly generated error is determined at this position B. Treated as an error and diffuses as an error at position B.

  FIG. 33 is a flowchart showing a processing procedure when there is no consistent processing order. First, it is determined whether or not all positions have been calculated (step S610). If NO, the process proceeds to step S612. In step S612, an error E (i, j) from the already processed peripheral pixels is obtained. Next, it is assumed that the processed dot size of the position in the dependency relationship is obtained, while the dot is turned off for the unprocessed position in the dependency relationship (step S614).

Next, a combination array CMB (sk, t1, t2, t3, t4,...) Is created from the dot sizes at positions that are in a dependency relationship for all the dot sizes sk that can be taken by the target position, and from this combination array. An address is generated by associating adsk = CMB (sk, t1, t2, t3, t4,...). Then, a dot displacement amount ΔDk = DX (i, j, adsk) indicating how much dot displacement is generated for a certain combination (how much density can actually be expected) is obtained, and the dot size sk of the target pixel is obtained. And the sum of the error E (i, j) and the density I (i, j) of the target pixel (E (i, j) + I (i, j)) A dot size with a small difference (including dot on / off) is determined, and a generated error Eo1 (i, j) generated for this determination is calculated (step S616). That is, the dot size sk that minimizes F _ijk = | E (i, j) + I (i, j) − (Dk + ΔDk) | is obtained, and the generated error Eo1 (i, j) generated for this determination is obtained. Calculation is performed (step S616).

  Next, the dot displacement amount ΔDk corresponding to the dot whose target pixel position has been determined is stored (step S618), and the already processed pixel position is extracted from the pixel positions that include the target pixel position in the dependency relationship (step S620). ). That is, since the dot formation of the target pixel has been determined, the target pixel position is extracted in order to review the pixel position affected by the target pixel.

  At this time, the processed pixel position affected by the target pixel is extracted by using the array DI indicating the dependency described above. However, as a technical method for calculation in step S618, instead of using the array DI that shows the dependency relationship from the viewpoint of the pixel that affects the target pixel, a table of pixels that affect the target pixel in advance (dependency It is also possible to prepare an array in which the relationship is reversed and prepare the extraction process in step S618 using this array.

  In this way, with respect to the pixel position extracted in step S618, it is determined whether or not dot formation at all positions having a dependency relationship has been determined, and the position at which it has been determined that dot formation at all positions having a dependency relationship has been determined. For PL, the dot displacement amount ΔD′L is calculated again based on the dependency relationship (step S622).

  Next, the process proceeds to step S624, and the difference between the dot displacement amount ΔD′L recalculated in step S622 and the dot displacement amount ΔDL stored in step S618 is calculated for all the determined positions PL. Find the sum. The calculated sum Σ (ΔD′L−ΔDL) is set as a generation error Eo2 (i, j) (step S624). Since the dot formation of the pixel of interest has been determined, the number of pixels to be determined in the surroundings is not limited to one, and when there are a plurality of such pixels, the true value and the value that has been tentatively obtained for each of these pixels All the differences are calculated, and the sum of these is obtained as the generated error Eo2 (i, j).

  Next, the sum of the generated error Eo1 (i, j) and the generated error Eo2 (i, j) obtained in step S616 is determined as the generated error Eo (i, j) at the target pixel position (Eo (i, j) = Eo1 (i, j) + Eo2 (i, j)), and diffuses to the unprocessed position as an error (step S626).

  Then, according to the order of the processing positions, the next pixel position is set as the target pixel position (step S628). Thereafter, the process returns to step S610, and the processes of steps S610 to S628 are repeated. When the dot formation determination is completed for all positions, the determination is YES in step S610, and the process flow ends.

  By performing the halftoning process using the error diffusion method described with reference to FIGS. 29 to 33, the optimum dot arrangement can be determined even when droplet interference occurs, and a high-quality image can be obtained.

The flowchart which showed the general | schematic procedure of the preparation method of the threshold value matrix which concerns on embodiment of this invention. Flow chart showing the procedure for determining the dependency Plane schematic diagram showing an example of print head Chart showing an example of the array V (i, j) corresponding to each dot formation position Chart showing an example of the array DI (i, j) for storing the result of the dependency relationship Chart showing graph representation of array DI (i, j) Diagram showing examples of circuits that can occur in the graph structure Flow chart showing the procedure for determining the repetitive structure Conceptual diagram used to explain the process of determining whether or not the provisional minimum unit and the region of the same number of columns adjacent in the column direction have the same structure Conceptual diagram used to explain how to extend the temporary minimum unit by one column in the column direction The conceptual diagram used in order to explain the process of determining whether or not the temporary minimum unit and the area of the same number of adjacent rows in the row direction have the same structure Flow chart showing the calculation procedure of the conceptual diagram threshold matrix used to explain how the temporary minimum unit is expanded by one line in the row direction (A) is a diagram showing a single dot, (b) is a diagram showing an example of determining the dot displacement in a one-to-one (one-to-one) relationship with the position of interest and the existence relationship, and (c) is an existence relationship. Figure showing an example of determining dot displacement from a combination of dots at multiple positions Chart showing an example of a table describing the amount of dot displacement for a combination of dot landing position and dot size at the relative position The figure which showed the positional relationship corresponding to each position shown in the table shown in FIG. A flowchart showing an example of a threshold determination procedure The flowchart which shows the other example of the determination procedure of a threshold value Conceptual diagram when determining threshold values of threshold matrix for dot size modulation 1 is a block diagram showing a system configuration example of a computer that performs threshold matrix creation processing according to an embodiment of the present invention; 1 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image forming apparatus according to the present invention. FIG. 20 is a plan view of the main part around the printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing a structural example of an ink jet recording head Enlarged view of the main part of Fig. 22 (a) Plane perspective view showing another structure example of a full-line head Sectional drawing which follows the 23-23 line in Fig.22 (a) Enlarged view showing the nozzle arrangement of the head shown in FIG. Main part block diagram which shows the system configuration | structure of the inkjet recording device which concerns on this embodiment. Schematic diagram showing an example of an embodiment for forming an image using a scanning print head Explanatory drawing showing the relationship between multiple scanning and virtual line head Schematic diagram showing another embodiment for forming an image using a scanning print head Flow chart showing a schematic procedure of an image forming method using the error diffusion method Schematic diagram showing examples of processed and unprocessed positions that have a dependency relationship with the target position Flow chart showing an example of image processing procedure by error diffusion method when there is a consistent processing order Flow chart showing another example of image processing procedure by error diffusion method when there is a consistent processing order Flow chart showing an example of image processing procedure by error diffusion method when there is no processing order without contradiction

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 ... Head, 32 ... Nozzle, 60 ... Temporary minimum unit, 70 ... Computer, 72 ... Main body, 74 ... Display, 76 ... Input device, 80 ... CPU, 110 ... Inkjet recording apparatus (equivalent to image forming apparatus), 112 ... printing section, 112K, 112C, 112M, 112Y ... head (corresponding to recording head), 116 ... recording paper (corresponding to recording medium), 122 ... belt conveying section (corresponding to conveying means), 150 ... head, 150A ... nozzle Surface 151, nozzle, 152 pressure chamber, 153 ink chamber unit (corresponding to droplet ejection element), 170 communication interface (corresponding to image input means), 172 system controller, 175 ROM (threshold matrix storage means) 180 ... print control unit (image processing apparatus, halftoning processing means, test pattern) Corresponds to the formation control means)

Claims (9)

A dependency information acquisition step for obtaining information for specifying a dependency relationship between dots in which droplet interference occurs;
A dot displacement amount specifying step for specifying a dot displacement amount expected at the position of interest based on the information acquired in the dependency relationship information acquiring step;
A dot placement calculation step for performing a calculation for determining dot placement using the information of the dot displacement amount specified in the dot displacement amount specifying step;
A dot arrangement determining method characterized by comprising: A dependency information acquisition step for obtaining information for specifying a dependency relationship between dots in which droplet interference occurs;
A repeating unit determining step for determining a repeating unit of the dependency in the image from the information acquired in the dependency relationship information acquiring step;
A threshold matrix size determining step of determining a threshold matrix size by an integer multiple of the repeating unit determined in the repeating unit determining step;
A dot displacement amount specifying step for specifying a dot displacement amount expected at the position of interest based on the information acquired in the dependency relationship information acquiring step;
For the dot arrangement candidates corresponding to the threshold matrix threshold values determined in the threshold matrix size determining step, the dots including the change in the dot displacement amount due to the dependency specified in the dot displacement amount specifying step are included. A threshold determination step of performing an evaluation of the arrangement and inputting a threshold to an undetermined position in the threshold matrix based on the dot arrangement determined based on the evaluation result;
A threshold value matrix creation method characterized by comprising: The threshold determination step includes
A candidate selection step of selecting a dot arrangement candidate corresponding to the threshold matrix threshold value of the size determined in the threshold matrix size step;
For the dot arrangement selected in the candidate selection step, a dot arrangement evaluation step for evaluating dot arrangement in a state including a change in dot displacement amount due to the dependency specified in the dot displacement amount specifying step;
The threshold value matrix creating method according to claim 2, wherein:   The program for making a computer perform each process in the preparation method of the threshold value matrix of Claim 2 or 3. Dependency information acquisition means for obtaining information for specifying a dependency relationship between dots in which droplet interference occurs,
Repetitive unit determining means for determining the repetitive unit of the dependency in the image from the information acquired by the dependency information acquiring means;
Threshold matrix size determining means for determining a threshold matrix size by an integer multiple of the repeating unit determined by the repeating unit determining means;
Dot displacement amount specifying means for specifying the amount of dot displacement expected at the target position based on the information acquired by the dependency relationship information acquisition means;
For dot placement candidates corresponding to the threshold matrix threshold values determined by the threshold matrix size determining means, the dots including the change in dot displacement due to the dependency specified in the dot displacement specifying step are included. Threshold value determination means for performing an evaluation of the arrangement and inputting a threshold value to an undetermined position in the threshold value matrix based on a dot arrangement determined based on the evaluation result;
An apparatus for creating a threshold value matrix. Threshold matrix storage means for storing threshold matrix data created by the threshold matrix creation method according to claim 2;
Image input means for inputting multi-gradation digital image data;
Halftoning processing means for generating dot data by area gradation by applying the threshold matrix to the digital image data input from the image input means;
An image processing apparatus comprising: Threshold matrix storage means for storing threshold matrix data created by the threshold matrix creation method according to claim 2;
Image input means for inputting multi-gradation digital image data;
Halftoning processing means for generating dot data by area gradation by applying the threshold matrix to the digital image data input from the image input means;
A recording head having a droplet discharge element array in which a plurality of droplet discharge elements that are driven based on the dot data generated by the halftoning processing means are arranged;
Conveying means for conveying at least one of the recording head and the recording medium to relatively move the recording head and the recording medium;
An image forming apparatus comprising: An apparatus for creating a threshold matrix according to claim 5;
Threshold matrix storage means for storing threshold matrix data created by the threshold matrix creating device;
Image input means for inputting multi-gradation digital image data;
Halftoning processing means for generating dot data by area gradation by applying the threshold matrix to the digital image data input from the image input means;
A recording head having a droplet discharge element array in which a plurality of droplet discharge elements that are driven based on the dot data generated by the halftoning processing means are arranged;
Conveying means for conveying at least one of the recording head and the recording medium to relatively move the recording head and the recording medium;
An image forming apparatus comprising: 9. The image forming apparatus according to claim 7, further comprising test pattern formation control means for controlling driving of the droplet discharge element so as to eject a test pattern for checking the dependency relationship.

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