JP2006297919A - Image processing method and apparatus, threshold value matrix generating method, image formation apparatus, and sub-matrix generating method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing technique which can realize high-quality image formation utilizing a threshold matrix having a comparatively large size such as a blue noise mask and halftoning processing which causes image defects due to no ejection (inrecordable) to be less apparent without largely increasing storage capacity. <P>SOLUTION: For an area (partial area) which corresponds to an inrecordable position in a basic threshold matrix and has a predetermined pixel width, threshold values (sub-matrix) for realizing dot arrangement which reduces visibility of image defects due to incapable recording are calculated in advance. A plurality types of such sub-matrices corresponding to differences in inrecordable positions are prepared. Then, based on information of a specified inrecordable position, a corresponding area on the basic threshold value matrix is determined, it is replaced by the sub-matrix in which the area is stored, and a halftoning process is performed by applying the obtained threshold value matrix. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing method and apparatus, a threshold matrix creating method, an image forming apparatus, a sub-matrix creating method, and a program, and in particular, image processing suitable for halftoning processing that makes image defects due to non-ejection of ink in an inkjet printer inconspicuous. Regarding technology.

  In an ink jet printer, there may occur a situation where ink cannot be ejected from a nozzle due to various factors. When a specific nozzle in a nozzle group fails to eject, the dots that should have been ejected by that nozzle are missing, so an unintended streak-like defect in the image recorded on the recording medium ( (Straight stripe) occurs, and the stripe shape becomes very noticeable.

  In particular, in the case of a device configuration that completes printing in one sub-scan using a line-type recording head in which multiple nozzles are arranged (single-pass method), unlike the shuttle (multi-) scan method, another nozzle Therefore, it is difficult to cover the droplet ejection position of the undischarge nozzle (so-called shingling), so that unevenness due to the undischarge nozzle becomes prominent and serious image quality deterioration is caused. For this reason, when a certain nozzle fails to discharge, a measure for making the image quality deterioration conspicuous due thereto is desired.

  Patent Document 1 prepares a normal dither matrix and a dither matrix corresponding to non-discharge in order to make white spots due to non-discharge unnoticeable in an ink jet printer, and selectively dither matrix based on non-discharge position information. The technique which applies is disclosed.

Patent Document 2 proposes a technique for changing the combination of recording dots so that ejection is performed by another recording element instead of the recording dots by the recording element that does not discharge.
Japanese Patent Application Laid-Open No. 2004-202795 JP 2004-202927 A

  However, the technique of changing to a combination that does not include an undischarge nozzle as in Patent Document 1 requires a dither matrix corresponding to the number of combinations when there are a plurality of undischarge nozzles in the dither matrix. There is a drawback that the storage capacity of the matrix data is remarkably increased. In addition, the technique of changing the combination as in Patent Document 2 cannot be handled by the disclosed technique because the combination becomes enormous when considering application to a dither matrix having a size of 2 × 2 pixels or more.

In general, an input image is quantized using a large-size threshold matrix (for example, 256 (columns) × 256 (rows) pixels, 512 (columns) × 512 (rows) pixels, etc.) represented by a blue noise mask. The dot image obtained by converting into a high quality image. When this blue noise mask is used, when the technique disclosed in Patent Document 1 is used for the purpose of reducing streak-like artifacts due to discharge failure (a threshold matrix corresponding to discharge failure nozzles is created in advance). Considering that the matrix switching technique corresponding to the discharge failure position is applied to a large threshold matrix (for example, M = N × N), threshold values to be prepared for switching to discharge failure The number of matrices is M × N (M corresponds to the matrix size, N corresponds to the discharge failure position included in the threshold matrix), that is, N × N × N (N to the third power), It can be seen that all of the threshold matrices corresponding to the above require enormous storage capacity.

  As described above, one non-discharge is in the third order of N, but assuming that two or more non-discharge occurs in one matrix, it is easy to require the fourth order of N. Recognize. If the threshold matrix size is reduced, the storage capacity is reduced correspondingly. However, in this case, the blue noise mask cannot be used, so that there is a problem that high image quality cannot be obtained.

  The present invention has been made in view of such circumstances, and does not significantly increase the storage capacity, and does not discharge (record) high-quality images using a relatively large threshold matrix such as a blue noise mask. It is an object of the present invention to provide an image processing method and apparatus, a threshold matrix creating method, an image forming apparatus, a sub-matrix creating method, and a program capable of realizing both of the above-mentioned correspondence.

  In order to achieve the above object, the image forming method according to the first aspect of the present invention includes a non-recordable position specifying step for specifying a non-recordable position on an image corresponding to a recording element that has become unrecordable, and a multi-value input. A basic threshold value matrix storing step for storing a basic threshold value matrix used for halftoning processing for quantizing image data and converting it into dot data having a smaller number of gradations, and corresponding to the unrecordable positions on the basic threshold value matrix A sub-matrix storage that stores a plurality of types of sub-matrices that are set with a threshold value that can be replaced with a threshold value of a partial area having a predetermined number of pixels including a pixel position, corresponding to unrecordable positions in the basic threshold value matrix. The basic threshold value matrix from the pixel position in the input image data and the non-recordable position specified in the non-recordable position specifying step. A replacement region determination step for determining a corresponding region having a predetermined pixel number width including the unrecordable position in a plurality of sub-matrices stored in the sub-matrix storage step; A sub-matrix selecting step of selecting a sub-matrix used for replacing the corresponding region based on the determination, and a sub-matrix selected in the sub-matrix selecting step for the threshold value of the corresponding region including the unrecordable position on the basic threshold matrix. A threshold replacement step for replacing with a matrix, and a threshold matrix obtained by replacing the corresponding region of the basic threshold matrix with a sub-matrix in the threshold replacement step or the basic threshold matrix is selectively applied to quantize the input image data. And a quantization processing step for performing quantization.

  A digital image is handled as a set (array) of pixels, which is a minimum information unit, and each pixel is given a gradation value (a value representing the degree of shading) according to the image content. Claim: As a technique for halftoning such an original image (multi-valued input image data) and converting it to lower gradation image data (multi-value dot data in consideration of binary or dot size change), According to the first aspect of the present invention, a threshold (sub-area) that realizes a dot arrangement that reduces the visibility of image defects due to recording failure in a region (partial region) having a predetermined pixel width corresponding to the recording disabled position in the basic threshold matrix. Matrix) is calculated in advance, and a plurality of such sub-matrices are prepared corresponding to the difference in the unrecordable position. That is, the threshold value is set in the sub-matrix so as to determine the dot arrangement of neighboring pixels (pixels in a predetermined number of pixels range) in order to suppress the occurrence of uneven stripes (artifacts) due to missing dots at unrecordable positions. Further, when a part of the basic threshold value matrix is replaced with the sub-matrix, the threshold value of the sub-matrix is set so that no artifact is generated in the vicinity of the joint of the replacement area on the matrix.

Based on the information on the unrecordable position specified in the unrecordable position specifying step, the corresponding area on the basic threshold matrix is determined, the area is replaced with the stored submatrix, and the obtained threshold matrix is applied. Halftoning. Thereby, even when a recording element that cannot be recorded is generated, a high-quality image in which image defects are not conspicuous can be obtained.

  In addition, since the sub-matrix to be replaced with a part of the basic threshold matrix is held and the corresponding sub-matrix is selectively applied according to the corresponding region of the unrecordable position, the threshold matrix is set according to the unrecordable position. Compared with a configuration for switching the whole, the amount of data to be stored can be reduced.

  In the unrecordable position specifying step, information related to unrecordable positions may be stored in a storage unit such as a memory in advance, and information may be acquired by reading out necessary information, or a test pattern or the like may be actually printed. The print result may be read and analyzed to obtain information on the unrecordable position.

  Note that “recording impossible” is not limited to the recording element itself being in an unrecordable state for some reason, but the recording element itself is not unrecordable, but the recording element itself is not capable of recording. In the case of showing complete recording, the case where recording becomes impossible by forcibly disabling the defective recording element is included in the control.

  The invention according to claim 2 relates to an aspect of the image processing method according to claim 1, wherein the basic threshold value matrix has a blue noise characteristic, and the predetermined pixel number width of the sub-matrix ranges from 3 to 9 pixels. It is set by.

  The basic threshold value matrix used in the present invention preferably has a blue noise characteristic capable of forming a high quality image. The blue noise mask is designed to provide a visually favorable dot arrangement for the DC component of the image. Although the matrix size is relatively large (for example, 256 (columns) × 256 (rows) pixels to 512 (columns) × 512 (rows) pixels), a sub-matrix to be replaced with a partial region of the basic threshold matrix is Since the predetermined number of pixels of 3 to 9 pixels and the small size, the total data amount including the basic threshold value matrix and the sub-matrix is kept small.

  The invention according to claim 3 provides an image processing apparatus for achieving the object. That is, the image forming apparatus according to claim 3 quantizes the unrecordable position specifying means for specifying the unrecordable position on the image corresponding to the unrecordable recording element and the multi-valued input image data, thereby reducing the number of unrecordable positions. Basic threshold matrix storage means for storing a basic threshold matrix used for halftoning processing for conversion to dot data of the number of gradations, and a predetermined number of pixels including pixel positions corresponding to the unrecordable positions on the basic threshold matrix Sub-matrix storage means for storing a plurality of types of sub-matrices set with thresholds to be replaced with the threshold values of the partial areas having the non-recordable positions in the basic threshold value matrix; and in the input image data The non-recordable position in the basic threshold matrix from the pixel position of the non-recordable position and the non-recordable position specified by the non-recordable position specifying means A replacement area determining means for determining a corresponding area having a predetermined number of pixels in width, and the corresponding area based on the determination of the replacement area determining means from a plurality of sub-matrices stored in the sub-matrix storage means Submatrix selection means for selecting a submatrix used for replacement, threshold replacement means for replacing the threshold value of the corresponding area including the unrecordable position on the basic threshold value matrix with the submatrix selected by the submatrix selection means, Quantization processing means for selectively applying the threshold matrix obtained by replacing the corresponding region of the basic threshold matrix with a sub-matrix by the threshold replacement means or the basic threshold matrix, and quantizing the input image data; , Provided.

  According to the image processing apparatus of the third aspect, similar to the operational effect of the image processing method according to the first aspect, it is possible to reproduce a high-quality image with a small data storage capacity.

  The unrecordable position specifying means may be a means for storing information relating to unrecordable positions in a storage means such as a memory in advance and acquiring information by reading out necessary information, or by actually printing a test pattern or the like. It may be a means (recording impossible position detecting means) for reading the printing result and performing analysis processing to acquire information on the recording impossible position.

  The invention according to claim 4 provides a threshold value matrix creating method for achieving the object. That is, the threshold value matrix creating method according to claim 4 stores a basic threshold value matrix used for halftoning processing for quantizing multi-valued input image data and converting it into dot data having a smaller number of gradations. A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial region having a predetermined number of pixels including a pixel position corresponding to a position of an unrecordable recording element on the basic threshold value matrix; A sub-matrix storage step for storing a plurality of types corresponding to unrecordable positions in the threshold matrix, and a sub for selecting at least one sub-matrix from the plurality of sub-matrices stored in the sub-matrix storage step A matrix selection step and the predetermined position including the non-recordable position on the basic threshold matrix. Characterized in that it comprises a threshold substitution generating a threshold matrix by replacing the threshold of a part of the prime width in the sub-matrix that is selected by the sub-matrix selection step.

  When a plurality of unrecordable positions are specified on the basic threshold matrix, the areas corresponding to the unrecordable positions are replaced with appropriate sub-matrices.

  According to the present invention, the threshold value is appropriately replaced by the sub-matrix corresponding to different unrecordable positions in the basic threshold matrix, and a threshold matrix suitable for image correction at each unrecordable position can be created. . In addition, a threshold value matrix creation apparatus can be provided by providing each means which performs each process in the threshold value matrix creation method of Claim 4.

  The invention according to claim 5 provides an image forming apparatus for achieving the object. That is, the image forming apparatus according to claim 5 includes a recording head in which a plurality of recording elements are arranged, and a transport that transports at least one of the recording head and the recording medium and relatively moves the recording head and the recording medium. Means, a non-recordable position specifying means for specifying a non-recordable position on the image corresponding to the non-recordable recording element in the recording element array of the recording head, and quantizing the multi-value input image data to reduce the number Basic threshold matrix storage means for storing a basic threshold matrix used for halftoning processing for conversion to dot data of the number of gradations, and a predetermined number of pixels including pixel positions corresponding to the unrecordable positions on the basic threshold matrix A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial area having a non-recordable position in the basic threshold value matrix Correspondingly, sub-matrix storage means for storing a plurality of types, and the non-recordable position in the basic threshold matrix from the pixel position in the input image data and the non-recordable position specified in the non-recordable position specifying step A replacement area determining means for determining a corresponding area having a predetermined number of pixels, and a replacement of the corresponding area based on the determination of the replacement area determining means from a plurality of sub-matrices stored in the sub-matrix storage means. Sub-matrix selection means for selecting a sub-matrix to be used, threshold replacement means for replacing the threshold value of the corresponding area including the unrecordable position on the basic threshold matrix with the sub-matrix selected by the sub-matrix selection means, Obtained by substituting the corresponding area of the basic threshold matrix with a sub-matrix by threshold substitution means. Quantization processing means for selectively applying the threshold matrix or the basic threshold matrix to quantize the input image data, and the recording head based on the dot data generated by the quantization of the quantization processing means And a recording control means for controlling the driving of the recording element.

6. An ink jet recording apparatus as one aspect of the image forming apparatus according to claim 5, wherein the recording element is a nozzle for discharging ink droplets for forming dots and a pressure generating means (piezoelectric element) for generating discharge pressure. And a liquid discharge head (recording head) having a liquid droplet discharge element array in which a plurality of liquid droplet discharge elements including a heating element are arranged, and the liquid discharge head based on the dot data generated by the quantization processing means And an ejection control means for controlling ejection of droplets from the nozzle, and an image is formed on the recording medium by the droplets ejected from the nozzle.

  As a configuration example of the recording head, a full-line type recording head having a recording element array in which a plurality of recording elements are arranged over a length corresponding to the entire width of the recording medium can be used.

  In this case, a combination of a plurality of relatively short recording head blocks having a recording element array less than the length corresponding to the entire width of the recording medium, and connecting them together has a length corresponding to the entire width of the recording medium. There is an aspect in which a recording element array is configured.

  A full-line type recording head is usually arranged along a direction orthogonal to the relative feeding direction (relative conveying direction) of the recording medium, but at a certain angle with respect to the direction orthogonal to the conveying direction. There may also be a mode in which the recording head is arranged along an oblique direction with a gap.

  A “recording medium” is a medium that can record an image by the action of a recording head (a medium that can be called an ejection medium, a printing medium, an image forming medium, a recording medium, an image receiving medium, etc.), continuous paper, cut paper In addition, it includes various media regardless of materials and shapes, such as a sealing sheet, a resin sheet such as an OHP sheet, a film, a cloth, a printed board on which a wiring pattern is formed by a liquid discharge head, an intermediate transfer medium, and the like.

  The conveying means for relatively moving the recording medium and the recording head is an aspect in which the recording medium is conveyed with respect to the stopped (fixed) recording head, an aspect in which the recording head is moved with respect to the stopped recording medium, or Any of the modes in which both the recording head and the recording medium are moved is included. When forming a color image using an ink jet recording head, a recording head may be arranged for each color of a plurality of inks (recording liquids), or a plurality of colors of ink are ejected from one recording head. It is good also as a possible structure.

  The invention according to claim 6 is used for the image processing method according to claim 1, the image processing apparatus according to claim 3, the threshold value matrix creating method according to claim 4, or the image forming apparatus according to claim 5. A method for creating a submatrix is provided. That is, the sub-matrix creating method according to claim 6 includes a sub-matrix region setting step of setting a region having a predetermined number of pixels including the unrecordable position on the basic threshold matrix as a sub-matrix replacement region, and the recording In the process of determining the threshold value of the sub-matrix by sequentially determining the dot arrangement in the sub-matrix other than the impossible position, the sub-matrix among the dot arrangement corresponding to the sub-matrix and the basic threshold matrix An evaluation value calculation step for calculating an evaluation value of a density distribution visually recognized for a dot arrangement obtained when combining a dot arrangement corresponding to a non-replaced region that is not replaced with a matrix, and an evaluation value obtained in the evaluation value calculation step A dot arrangement determining step for determining the arrangement of the dots to be added, and the dots According dot arrangement determined by the location determining step, characterized in that it comprises a and a threshold value input step of setting a threshold value corresponding to the position of the additional dots in the sub-matrix.

  The evaluation value is preferably configured to include a value for evaluating at least one of graininess and anisotropy. As an evaluation index of the dot pattern, an aspect in consideration of graininess and anisotropy is preferable. For example, the evaluation value is calculated using an evaluation function including a linear combination of a granularity evaluation function and an anisotropic evaluation function. A more preferable evaluation can be performed by considering both graininess and anisotropy.

  Further, in the submatrix creation method according to claim 6, an initialization step of setting a threshold value at each position of the submatrix having a size corresponding to the replacement region set in the submatrix setting step to an undecided state; A non-record corresponding threshold value setting step for setting a threshold value that does not generate a dot regardless of an input value for a pixel position corresponding to the unrecordable position on the initialized sub-matrix, A mode is possible in which the threshold value is determined through the evaluation value calculation step and the threshold value input step for positions in the sub-matrix other than the position where the threshold value is set in the recording threshold setting step.

  The invention according to claim 7 is a program for causing a computer to execute the steps of the image processing method according to claim 1 or 2, the threshold matrix creation method according to claim 4, or the sub-matrix creation method according to claim 6. I will provide a.

  The program according to the present invention can be applied as an operation program of 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.

  According to the present invention, the threshold value of a partial region (a range of a predetermined number of pixels) corresponding to a non-recordable position on the basic threshold matrix is switched to a sub-matrix so that a dot arrangement suitable for image formation near the non-recordable position is obtained. Since the threshold matrix to be realized is created, even if a recording element that cannot be recorded is generated, a high-quality image in which image defects due to the recording element are not noticeable can be obtained.

  In addition, since the present invention can be applied to a basic threshold matrix having a large matrix size (for example, a basic threshold matrix having blue noise characteristics), high-quality image formation is possible from the viewpoint of the matrix size. Furthermore, by replacing a partial area of the basic threshold matrix with a sub-matrix, a threshold matrix corresponding to non-recording is obtained so that matrix data including correspondence to non-recording (basic threshold matrix data and sub-matrix The data storage capacity can be reduced.

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

[Outline of Image Processing Method According to Embodiment of Present Invention]
In the image processing method according to the embodiment of the present invention, for a basic threshold value matrix having a blue noise characteristic, a threshold having a predetermined width corresponding to an undischarge position is calculated in advance, and this is stored as an undischarge corresponding sub-matrix, Corresponding to the discharge failure position, a part of the basic threshold value matrix is replaced with the discharge failure corresponding submatrix and applied.

FIG. 1 is a diagram showing the concept of image processing according to an embodiment of the present invention. As shown in the drawing, the basic threshold value matrix M is repeatedly applied to the input image IMG in a tile shape to quantize the image and convert it into a pseudo gradation image (dot data). At this time, a specific nozzle of the print head (here, a line head is assumed) fails to discharge, and a streak-like artifact (white) is displayed at the image position (undischarge position) corresponding to the undischarge nozzle as shown in FIG. Let us consider the case where omission occurs. If a sheet (recording medium) is conveyed in the vertical direction in FIG. 1, streak-like defects occur along the sheet conveyance direction (sub-scanning direction).

  In the input image IMG, an undischarged (normal) image region (region of the symbol In in FIG. 1) is quantized by applying the basic threshold matrix M as it is. On the other hand, when the discharge failure position X is included in the image area to which the basic threshold value matrix M is to be applied (the area indicated by reference symbol Ia in FIG. 1), a part of the basic threshold value matrix M (discharge failure position). A matrix in which a column region having a width of a predetermined number of pixels including a position corresponding to X (range indicated by hatching in FIG. 1) is replaced with an undischargeable submatrix is applied.

  That is, as shown in FIG. 2, if the discharge failure position on the basic threshold value matrix M corresponding to the discharge failure position X in the image is X ′, the discharge failure position on the basic threshold value matrix M as shown in FIG. A non-discharge correspondence sub-matrix SM that realizes a dot arrangement in which a streak due to discharge failure is not noticeable in a region (replacement region) MA having a predetermined number of pixels including the discharge failure position X ′ corresponding to X ′. Replace with (X ′). A threshold value that does not use the nozzle corresponding to the discharge failure position X ′ is input to the discharge failure corresponding submatrix SM (X ′). In the basic threshold value matrix M, an area (non-replacement area) that is not replaced by the discharge failure corresponding submatrix SM (X ′) is indicated by MB in the drawing.

  Prior to detailed description, the main features of the image processing method of this example are listed. The image processing method of this example is applied when the discharge failure by the print head generates streak-like artifacts. The concept of “non-discharge” here is not limited to non-discharge due to nozzle clogging, but does not use nozzles that cause defective discharge for some reason, such as landing misalignment or liquid volume defects (control that is not forcibly used). To do).

  As a premise for performing image processing, first, information on the discharge failure position is necessary. A predetermined test pattern is printed in advance and the result of the test print is read to detect the undischarge position or the information is read from the storage means storing the undischarge position in advance. The undischarge position in is identified.

  The undischarge correspondence sub-matrix has a predetermined width (preferably 3 to 7 pixels) with respect to the undischarge position. “3 pixels” is a range including a pixel at the discharge failure position and pixels adjacent to both, and only the pixel positions on both sides of the discharge failure position can be used. “5 pixels” is a range including pixels on both sides adjacent to the outside of the three pixels. The positions on both sides of the discharge failure position are used for correction of discharge failure positions, and further outside the positions of the positions on both sides. This is a preferred size because it can be used for correction to reduce fluctuations. “7 pixels” is a range including pixels on both sides adjacent to the outside of the 5 pixels. Both sides of the undischarge position are used for non-discharge position correction, and the outside is used to reduce fluctuations in the positions of both sides. This is a preferable size because it can be used for correction, and the outside can also be used for correction to reduce fluctuations. Note that the best mode of the size (predetermined width) of the undischargeable sub-matrix is related to the resolution. For example, 3 to 5 pixels are preferable at 1200 dpi, and 3 to 9 pixels are preferable at 2400 dpi.

  When the discharge failure support sub-matrix is replaced with the corresponding area on the basic threshold matrix, in the adjacent area on the basic threshold matrix (near the boundary between the replaced area (non-replaced area) and the replaced area) It is determined that no artifact will occur.

  The undischarge-corresponding sub-matrix is determined so that the graininess does not change greatly in the adjacent area on the basic threshold matrix when the sub-matrix is replaced with the corresponding area on the basic threshold matrix.

  The non-discharge-equivalent sub-matrix is determined so that the densities are approximately equal in the adjacent areas on the basic threshold matrix when replaced with the corresponding areas on the basic threshold matrix.

  The discharge failure corresponding sub-matrix is determined so as to realize a dot arrangement in which discharge failure is visually reduced.

  When the non-discharge sub-matrix is replaced with a corresponding area on the basic threshold matrix, a plurality of evaluation values (non-discharge non-discharge visually, density is approximately equal, It is determined so as to satisfy the conditions of no occurrence of lactate and no significant change in graininess.

  The non-discharge correspondence sub-matrix has a data size of 3 × N × N to 9 × N × N at most even if N types are prepared in order to correspond to all non-discharge positions in the basic threshold matrix. The amount of data is very small even when compared with the N cubed order (N = 64, 128, 256) according to the prior art.

  In addition, when non-discharge occurs at a plurality of positions in the basic threshold matrix, a plurality of non-discharge corresponding sub-matrices are replaced corresponding to each non-discharge position. At this time, when the predetermined number of pixels is within the width (for example, when the predetermined width is 7 pixels, the interval between the two discharge failure positions is less than 6 pixels), the discharge failure corresponding sub-matrices overlap each other. The problem arises.

  For such a situation, the problem can be solved by using at least one of the discharge failure-response sub-matrices having a small predetermined width so that the discharge failure-response sub-matrices do not overlap each other. For example, when the predetermined width is 5 pixels, one of the discharge failure corresponding sub-matrices is changed to 3 pixels or 5 pixels. As described above, it is preferable to further include an undischarge-corresponding sub-matrix having a minimum predetermined width so as to cope with the case where undischarge positions are close to each other.

  Of course, as a non-discharge correspondence sub-matrix, a method of obtaining in advance a case where there are two discharge failures within a predetermined width is also conceivable. In this case, depending on the combination of a plurality of discharge failure positions, the data amount (storage capacity for storing the discharge failure corresponding submatrix) increases. For example, when the predetermined width is 7 pixels, Considering the discharge failure position within 6 to 3 pixels (If the discharge failure position is too close, the correction performance itself deteriorates, so a lower limit is necessary when a certain correction performance is expected. For example, two pixel positions are adjacent to each other. If it is not possible to make corrections), at most 4 (the number of combinations for selecting positions within 6 to 4 pixels) × 14 (predetermined width: 7 pixels + 7 pixels) × N (number of rows) × N (number of columns) Therefore, unlike the prior art, an explosive increase in storage capacity does not occur as in the third cube of N.

  The ejection failure countermeasure sub-matrix has a larger artifact reduction correction effect as the predetermined width is larger. However, the correction performance is saturated when it exceeds a certain size. It is desirable to select an appropriate predetermined width (for example, 5 pixels) that balances the correction effect, non-discharge position proximity, and storage capacity.

[Calculation method for non-discharge sub-matrix]
Next, a calculation method (determination method) of the discharge failure prevention sub-matrix will be described.

  The basic policy of calculation is to obtain a discharge failure corresponding submatrix SM (X) based on the basic threshold value matrix M. However, the discharge failure position is represented by a variable “X”.

First, main concepts related to calculation will be described with reference to FIGS. FIG. 4 is a conceptual diagram showing the relationship between the replacement area MA (X) and the non-replacement area MB (X) of the basic threshold value matrix M. FIG. 5 is a conceptual diagram showing an example of the dot arrangement DMA (X, L) of the replacement area MA (X) of the basic threshold value matrix M and the dot arrangement DMB (X, L) of the non-replacement area MB (X). DMA (X, L) and DMB (X, L) are dot arrangements where the dot is ON at the discharge failure position X and the threshold value is L or less.

  FIG. 6 shows a state in which the replacement area MA (X) of the basic threshold value matrix M is replaced with the discharge failure corresponding submatrix SM (X). The dot arrangement DSM ( An example of the dot arrangement DMB (X, L) of the non-replacement area MB (X) of the basic threshold value matrix M with X, L) is shown.

As shown in FIG. 4 to FIG. 6, the meanings of main characters (symbols) used in the calculation of the discharge failure corresponding sub-matrix of this example are as follows.
A threshold set LM = {L0, L1, L2, L3, ...} included in the basic threshold matrix M
A dot arrangement DMA (X, L) of a replacement area (replacement area) MA (X) of the basic threshold matrix M, a threshold set LA included in the replacement area MA (X) = {L0, L2, L3, L5,. }
The threshold value set LB = {L1, L4, L7, included in the dot arrangement DMB (X, L) of the non-replaced area (non-replaced area) MB (X) and the non-replaced area MB (X) of the basic threshold matrix M ...}. Dot arrangement DSM (X, L) based on undischargeable sub-matrix SM (X)
However, L indicates an input value (input value for the entire matrix) or a gradation value, and the dot arrangement is determined corresponding to the input value L.

  Further, the threshold value LM included in the basic threshold value matrix M is the union of the threshold set LA included in the replacement area MA (X) and the threshold set LB included in the non-replacement area MB (X) (LM = LA + LB, because it is a set operation). LM = LA∪LB).

  The calculation constraints are as follows.

  (1) Regarding the relationship between the dot arrangement DMA (X, L) and the dot arrangement DSM (X, L), the number of dots and the dot size configuration are similar (constraint condition 1-1). In addition, the concentrations are almost equal (constraint condition (1-2).

  (2) Regarding the relationship between the dot arrangement DSM (X, L) and the dot arrangement DMB (X, L), when they are combined, no artifacts occur, and the density step and the edge are difficult to visually recognize (restriction condition 2- 1). In addition, the graininess is not far apart (Restriction 2-2).

  (3) Regarding the dot arrangement DSM (X, L), it is difficult to visually recognize artifacts (straight lines) due to undischarge (constraint condition 3-1).

  By gradually determining the dot arrangement (dot distribution) so as to satisfy the above constraint conditions while gradually increasing the input value L, the threshold value of the discharge failure corresponding submatrix is sequentially filled, and the discharge failure support submatrix. To complete.

7 to 9 are flowcharts showing the procedure for determining the discharge failure support sub-matrix. In the following description, “threshold is not input” means that in the case of a binary value (in the case of only dot ON / OFF), it can be determined by whether or not the threshold is in that position, so the story is simple. However, in the case of multi-value (dot size modulation), the threshold value corresponding to each gradation value (dot size) is at the same position, so the threshold value corresponding to each gradation value (dot size) at the same position is It is assumed that any of them indicates an uninput state. For example, when three types of dot size modulation of large, medium, and small are possible, when focusing on a certain pixel, there is a threshold value (first level threshold value) at which a small-sized dot is first formed from a state without dots, Further, a threshold when changing from a small size to a medium size dot (second level threshold) and a threshold when changing from a medium size to a large size dot (third level threshold) are set hierarchically. Therefore, when any of the threshold values at each level is not input, the expression “the threshold value is not input” is used.

  When the processing of this algorithm is started as shown in FIG. 7 (step S10), first, a basic threshold matrix size (for example, 256 (columns) × 256 (rows) pixels or 512 (columns) × 512 (rows) Pixels, etc.) are set (step S12), and a basic threshold value matrix of the set size is determined (step S14). A known technique can be used to determine the basic threshold matrix. For example, a blue noise mask determination method is used.

  Next, a predetermined width of the discharge failure prevention sub-matrix is set (step S16). This is set to 7 pixels, for example. The algorithm is set by inputting a predetermined value from the outside by an operator.

  Next, the process proceeds to the determination step S18 of the first loop. The first loop is a calculation loop for sequentially changing the discharge failure position X in the basic threshold value matrix. In step S18, whether or not there is an uncalculated column for the discharge failure position X on the basic threshold value matrix. (For the relationship between the discharge failure position X and the basic threshold value matrix, see FIGS. 2, 3, and 10). When there are no more uncalculated columns on the basic threshold matrix, the first loop is exited and the present algorithm is terminated (step S70 in FIG. 7).

  If there is an uncalculated column in step S18, the process proceeds to step S20 to determine whether or not the discharge failure corresponding submatrix SM (X) corresponding to the discharge failure position X protrudes from the basic threshold value matrix M. This is processing corresponding to the case where the discharge failure position X is at the end of the basic threshold value matrix M as shown in FIG. That is, when the discharge failure position X ′ on the basic threshold value matrix M corresponding to the discharge failure position X is at the end of the basic threshold value matrix M as shown in FIG. When trying to secure the value, there may occur a situation where the value falls outside the range of the basic threshold value matrix M. In such a case, the end region ME on the opposite side of the basic threshold value matrix M is moved to the end portion on the undischarge position X ′ side, and converted to the basic matrix M ′ as shown in FIG. 'Is treated as a basic threshold value matrix below (step S22 in FIG. 7). After step S22, the process proceeds to step S24.

  If the discharge failure prevention sub-matrix SM (X) does not protrude from the basic threshold value matrix M in step S20, the process of step S22 is omitted and the process proceeds to step S24.

  In step S24, threshold values at all positions in the discharge failure prevention sub-matrix SM (X) are set (initialized) to an uninput state. Subsequently, a threshold value Lz (for any input value L) at which dots do not appear at all of the discharge failure positions X of the discharge failure handling submatrix SM (X) (all positions on a line corresponding to the discharge failure position X). A predetermined value that does not turn on the dot) is set (step S26).

  Next, the thresholds included in the threshold set LB of the non-replacement area MB (X) arranged in ascending order are input to the array LX (step S28). Then, the threshold value L is extracted from the array LX in ascending order (step S30).

After step S30, the process proceeds to step S32 in FIG. Step S32 is processing for determining a condition for exiting the second loop. The second loop is a loop that repeatedly calculates the threshold value L from the initial value to the end value for the first time. If all the threshold values have been calculated (array LX is empty) or if the end condition is satisfied, Go through 2 loops and proceed to S66. In step S32, it is determined whether or not the array LX is empty (φ). If NO, the process proceeds to step S34, and the presence or absence of a position where the threshold is not input is confirmed. If there is no position where the threshold value is not input in step S34, the end condition is satisfied, so the process exits the second loop and proceeds to step S66.

  If NO is determined in step S32 and it is determined in step S34 that there is a position where the threshold value is not input, the process proceeds to step S36 and the calculation of the second loop is started. In step S36, a dot arrangement DMB (X, L) corresponding to the threshold value L is obtained. Further, the dot arrangement DMA (X, L) corresponding to the threshold value L is also obtained (step S38).

  Here, it is determined whether or not there is a dot corresponding to the discharge failure position in the dot arrangement DMA (X, L) of the replacement area (step S40). If there is no dot corresponding to the discharge failure position in DMA (X, L), the process proceeds to step S42, and the threshold value is set at the SM (X) position corresponding to the position corresponding to the threshold value L in MA (X). Enter L. This means that the arrangement (threshold value) of MA (X) is used as it is in the non-discharge correspondence sub-matrix SM (X) as long as the non-discharge nozzle is not used (originally under the condition that the corresponding nozzle is not used). It means (because the constraints are automatically met). After step S42, the next threshold value L is extracted from the array LX (step S44), and the process returns to step S32.

  On the other hand, if there is a nozzle corresponding to the non-ejection position in DMA (X, L) in step S40, that is, a non-ejection nozzle is used (in the case of conditions, the process proceeds to step S50 in FIG. The process of determining the position of the threshold value L that realizes the dot arrangement that does not use the discharge failure position is entered.If the discharge failure nozzle is started at a certain stage, the threshold value L is always determined in step S40. The result is YES, and the process proceeds to the calculation of FIG.

  That is, first, the dot arrangement DSM (X, L-1) of the discharge failure prevention submatrix SM (X) corresponding to the previous threshold value L-1 is obtained (step S50). In the process of determining the discharge failure sub-matrix in order from the lowest threshold, the threshold is determined until a certain level (until the level where the discharge failure position is not used), and is added at the threshold at which the discharge failure position starts to be used. This is an attempt to appropriately determine the dot arrangement. At this time, it is determined from the constraint conditions where the next additional dot is appropriate based on the dot arrangement state of the previous threshold L-1.

  Here, the dot arrangement DSM (X, L-1) corresponding to the threshold value L-1 is obtained, but other values may be used as long as they are less than L and smaller than the next smaller value than L of the array LX. (L-1 satisfies this condition).

  Next, a density distribution DDM is calculated using a predetermined dot model for the dot arrangement DM in which DSM (X, L-1) and DMB (X, L) are combined (step S52). In other words, the dot arrangement DMB (X, L) in the outer area (non-replacement area MB (X)) that is not replaced and the dot arrangement in the area to be replaced (however, one dot is less) DSM (X, L-1) For the dot arrangement DM combining the above, a density distribution DDM is obtained by applying a predetermined dot model.

  Further, a density histogram HDDM is created for the result of processing the obtained DDM with a spatial filter based on visual characteristics (step S54).

  Next, with respect to the result of processing the DDM with the spatial filter based on the visual characteristics, a position within the DSM region, a threshold value is not input, and a condition satisfying a condition within the predetermined number of pixels from the minimum density in the density histogram DDM is selected. The position is extracted (step S56). This process is a process of narrowing down additional dot position candidates when deciding where the next dot should be added to the discharge failure corresponding sub-matrix. As a method for determining candidates, a condition that there is a high possibility that the next dot will be placed near a place where the density is low in the density distribution DDM (the density unevenness is reduced by adding a dot there), and further The candidate position is selected under the condition that the threshold value is a position that has not been input and that the threshold value is in the undischargeable submatrix to be replaced. In addition, since the threshold Lz has already been input to the column of the discharge failure position X (step S26 in FIG. 7), it is not listed as a candidate position.

  Subsequently, with respect to the candidate positions extracted in step S56, a dot arrangement DM ′ (i) when an applicable gradation value (dot size) is added is obtained, and a predetermined arrangement for the dot arrangement DM ′ (i) is obtained. Using the dot model, the density distribution DDM ′ (i) is obtained (step S58).

  Further, granular evaluation and anisotropy evaluation (artifact) based on visual characteristics are performed on DDM ′ (i), and an evaluation value EDDM ′ (i) is obtained (step S60).

  As an example of a method for calculating the evaluation value EDDM ′ (i), the evaluation value EDDM ′ (i) is defined as a linear combination of a granularity evaluation function and an anisotropy evaluation function, and is defined by the following equation (Formula A).

EDDM ′ (i) = wg × granularity evaluation function (i) + wa × anisotropy evaluation function (i)
... (Formula A)
However, wg and wa are weighting factors. The granularity evaluation function and anisotropy evaluation function are the average index (Radially Averaged Power Spectrum; RAPS) and dispersion index of dot brightness distribution proposed by Robert and Ulichney. (Anisotropy) "can be used.

  A dot pattern is obtained as a result of digital halftoning, and a method proposed by Robert and Ulichney is generally known as a method for evaluating this dot pattern (dot arrangement) ("Digital Halftoning"; published by The MIT Press) ).

  That is, the two-dimensional power spectrum of the halftone image obtained by dot arrangement is converted into polar coordinates, and the index corresponding to the average and variance of the spectrum of all angles for the spatial frequency fr corresponding to the radius of the polar coordinates as shown in FIG. Is used.

  The average index of the polar coordinate power spectrum is called “R.A.P.S” and is expressed by the following equation.

The dispersion index is called “Anisotropy” and is expressed by the following equation.

RAPS is an index related to the visibility of dot arrangement, and Anisotropy is an index related to anisotropy of dot arrangement.

FIG. 12 shows an example of RAPS calculated under certain preferable conditions. In FIG. 12, σ _g is expressed by the following equation.

Here, g represents a standardized input value, and 0 ≦ g ≦ 1.

  In the graph shown in FIG. 12, the visual characteristics are not taken into consideration, but when the known visual characteristics (VTF) as shown in FIG. become. The VTF for calculating R.A.P.S and Anisotropy is not limited to the one proposed by Dooly & Shaw, and a known one can be used.

  FIG. 14 shows an example of Anisotropy calculated under a preferable condition. According to Robert Ulichney, the anisotropy of dots is inconspicuous if Anisotropy is -10 dB [dB] or less.

  In this embodiment, the above-mentioned RAPS is used for the granularity evaluation function (i), and Anisotolopy is used for the anisotropy evaluation function (i), so that the evaluation value EDDM ′ (i) is defined by the above (formula A). Is done.

  The candidate position i extracted in step S56 of FIG. 9 is evaluated while changing the position (i) in order (steps S58 to S60), the position with the best evaluation value is selected, and the threshold value L is input to that position. (Step S62).

  Thus, when the input position of the threshold value L is determined, the next threshold value L is extracted from the array LX (step S64), and the process returns to step S32 in FIG.

  While the threshold value L is sequentially changed, the above-described processing is repeated, and the threshold value is sequentially input to each position of the discharge failure prevention sub-matrix SM (X). Eventually, when there is no position where the threshold is not input, the second loop is exited, and the discharge failure corresponding submatrix SM (X) corresponding to the discharge failure position X is determined (step S66). Subsequently, the undischarge position X is changed to the next position (step S68), and the process returns to step S18 (the beginning of the first loop) in FIG. When the discharge failure corresponding sub-matrix SM (X) corresponding to all discharge failure positions X is determined, a NO determination is made in step S18, the first loop is exited, and this sequence is terminated (step S70).

  It is also possible to replace the steps S56 to S62 described in FIG. 9 with steps S56 'to S62' shown in FIG.

  In steps S56 to S62 of FIG. 9, the candidate position is narrowed down within the range of the number of pixels from the minimum density value in the density histogram HDDM, and then the best position is selected from the narrowed candidate locations. The steps shown in FIG. In the examples of S56 ′ to S62 ′, the calculation is attempted for all the positions where the next added dot may enter without narrowing down the candidate positions. The processing contents of steps S56 'to S62' are as described in FIG. In order to reduce the calculation amount, it is preferable to narrow down candidates as shown in FIG. However, in order to find the truly best position, it is preferable to calculate all possible positions as shown in FIG.

  The basic threshold value matrix M and a plurality of discharge failure corresponding sub-matrices SM (X) corresponding to discharge failure positions are obtained by the method described with reference to FIGS.

  The “blue noise characteristics” will be outlined here. When the dot arrangement is evaluated using the evaluation method described with reference to FIGS. 11 to 14, the characteristics are such that the RAPS is small in the low frequency range, has a peak at the medium frequency, and is constant at the high frequency, and the Anisotropy is When a dot arrangement having −10 decibels [dB] or less has “blue noise characteristics” and the dot arrangement determined by the threshold matrix has blue noise characteristics, the threshold matrix is referred to as a blue noise mask. The graph shown in FIG. 12 also generally shows blue noise characteristics, but a typical graph example is as shown in FIG.

  The above-described basic threshold value matrix M and the method for creating the discharge failure corresponding sub-matrix SM (X) based on the basic threshold value matrix M can be realized using a computer. That is, by creating a program (threshold matrix creation program) that causes a computer to execute the algorithm of the non-discharge-corresponding sub-matrix determination method described in FIG. 7 to FIG. It can function as a creation device.

  FIG. 17 is a block diagram illustrating a system configuration example of a computer. The computer 10 includes a main body 12, a display (display means) 14, and an input device 16 (input means for inputting various instructions) such as a keyboard and a mouse. In the main body 12, a central processing unit (CPU) 20, a RAM 22, a ROM 24, an input control unit 26 that controls signal input from the input device 16, a display control unit 28 that outputs a display signal to the display 14, A hard disk device 30, a communication interface 32, a media interface 34, and the like are included, and these circuits are connected to each other via a bus 36.

  The CPU 20 functions as an overall control device and arithmetic device (arithmetic means). The RAM 22 is used as a temporary data storage area and a work area when the CPU 20 executes a program. The ROM 24 is a rewritable nonvolatile storage unit that stores a boot program for operating the CPU 20, various setting values, network connection information, and the like. The hard disk device 30 stores an operating system (OS), various application software (programs), data, and the like.

  The communication interface 32 is means for connecting to an external device or a communication network according to a predetermined communication method such as USB, LAN, or Bluetooth. The media interface 34 is means for performing read / write control of an external storage device 38 typified by a memory card, magnetic disk, magneto-optical disk, or optical disk.

  The dot arrangement determination processing program and the threshold matrix creation program according to the embodiment of the present invention are stored in the hard disk device 30 or the external storage device 38, and the program is read out as needed and expanded in the RAM 22. Executed. Alternatively, an aspect in which the program is provided by a server installed on a network (not shown) connected via the communication interface 32 is possible, and an aspect in which an arithmetic processing service is provided by the server on the Internet. Is also possible.

  An operator operates the input device 16 while looking at an application window (not shown) displayed on the display 14 and needs to calculate a desired basic threshold matrix size, a non-discharge-capable sub-matrix size (a predetermined number of pixels), and the like. Various values can be input, and the calculation result can be confirmed on the display 14.

  Data of the basic threshold value matrix M and the discharge failure corresponding submatrix SM (X) obtained by the above-described method is stored, and in the actual image processing stage, the basic corresponding to the corresponding position based on the discharge failure position information. An image is quantized (digital halftoning) by applying a matrix in which a part of the threshold matrix M is replaced with a discharge failure corresponding submatrix SM (X).

  At this time, as described with reference to FIG. 10, when the discharge failure position is at the end of the basic threshold value matrix and the discharge failure corresponding submatrix SM (X) protrudes from the range of the basic threshold value matrix, the discharge failure corresponding submatrix When calculating SM (X), the processing as shown in FIG. 10B is performed to obtain the discharge failure corresponding submatrix SM (X) (step S22 in FIG. 7), but at the stage of performing image processing. As shown in FIG. 18, replacement of the discharge failure corresponding sub-matrix SM (X) is performed with respect to two adjacent basic threshold value matrices M corresponding to the discharge failure position X.

  Next, an example of an image processing apparatus that performs image processing using the basic threshold value matrix and the discharge failure prevention sub-matrix created by the above-described threshold value matrix creation method will be described.

[Configuration of image processing apparatus]
FIG. 19 is a block diagram showing the configuration of the image processing apparatus according to the embodiment of the present invention. As shown in the figure, the image processing apparatus 50 according to the present embodiment stores basic threshold value matrix storage means 52 for storing data of the basic threshold value matrix M and data of the discharge failure prevention sub-matrix SM (X). A non-discharge correspondence sub-matrix storage means 54, an undischarge position detection means 56 for detecting an undischarge position, and an undischarge position corresponding to the undischarge position based on the information on the undischarge position obtained from the undischarge position detection means 56. The non-discharge correspondence sub-matrix selection means 58 for selectively taking out the corresponding sub-matrix from the discharge failure-response sub-matrix storage means 54, and the discharge failure-response sub-matrix selected by the discharge failure-response sub-matrix selection means 58 are the basic threshold matrix. Threshold Mat for generating a threshold matrix (hereinafter referred to as “replacement synthesis threshold matrix”) to be applied to the discharge failure position. Replacement matrix 60, threshold matrix setting module 62 for setting a threshold matrix used for quantization according to the image area (position) (selectively setting either a basic threshold matrix or a replacement synthesis threshold matrix), An image input unit 64, a quantization processing unit 66 that quantizes an input image (multi-valued data) using the threshold matrix set by the threshold matrix setting unit 62, and the quantized data generated by the quantization processing unit And a quantized data output means 68 for outputting a dot image on the basis thereof.

  As the basic threshold value matrix storage unit 52 and the discharge failure prevention sub-matrix storage unit 54, a non-volatile memory such as an EEPROM or a storage device such as a hard disk device is preferably used. Separate memories (or storage devices) may be used for the basic threshold value matrix storage unit 52 and the discharge failure prevention sub-matrix storage unit 54, or the basic threshold value matrix is divided by dividing the storage area in one memory (or storage device). You may comprise the memory | storage means 52 and the undischarge corresponding submatrix memory | storage means 54. FIG.

  The discharge failure position detection unit 56 includes, for example, an image sensor that captures the print result of the test pattern, and an information processing device (arithmetic processing device) that analyzes image data obtained from the image sensor and grasps the discharge failure position. Composed. Alternatively, in place of the discharge failure position detection means 56, discharge failure position storage means that stores information on discharge failure positions acquired in advance by a separate means can be used. As the “non-discharge position storage means” here, a non-volatile memory such as an EEPROM or a storage device such as a hard disk device is preferably used.

The discharge failure corresponding submatrix selection unit 58 corresponds to the discharge failure position from the discharge failure corresponding submatrix storage unit 54 in accordance with the discharge failure position information obtained from the discharge failure position detection unit 56 (or discharge failure position storage unit). The non-discharge-corresponding sub-matrix data is read and provided to the threshold matrix replacement means 60. The discharge failure corresponding sub-matrix selection unit 58 also functions as a replacement area determination unit that determines a replacement area (corresponding area having a predetermined number of pixels) including the discharge failure position in the basic threshold value matrix.

  The threshold value matrix replacing unit 60 replaces a part of the basic threshold value matrix read from the basic threshold value matrix storage unit 52 with the discharge failure corresponding sub matrix provided from the discharge failure corresponding sub matrix selection unit 58 (the threshold value matrix ( A process for generating a replacement synthesis threshold matrix is performed. That is, the threshold value matrix replacing unit 60 functions as a threshold value replacing unit that replaces the threshold value of the corresponding region including the discharge failure position on the basic threshold value matrix with the discharge failure corresponding sub-matrix.

  The threshold value matrix setting means 62 determines whether or not the discharge target position is included in the quantization processing target area based on the information obtained from the discharge failure position detection means 56 (or discharge failure position storage means). Processing to switch the matrix is performed.

  The image input means 64 is an interface unit that accepts original image data (eg, multi-value digital image data expressed in 256 gradations) before quantization. Specifically, it may be a communication interface, a media interface such as a removable medium, or a memory controller that fetches data from a memory or the like.

  Multi-valued image data input from the image input means 64 is quantized by the quantization processing means 66 using the threshold value matrix set by the threshold value matrix setting means 62, and there is a binary or dot size modulation. Is converted into multivalued quantized data corresponding to the type of dot size. At this time, a replacement synthesis threshold matrix incorporating a discharge failure sub-matrix is applied to an image region including a discharge failure position. This makes it possible to obtain good quantized data (dot data) in which artifacts due to undischarge are not noticeable.

  It should be noted that each of the non-discharge correspondence submatrix selection means 58, the threshold matrix replacement means 60, the threshold matrix setting means 62, and the quantization processing means 66 can be realized by software.

  The quantized data output unit 68 corresponds to an image forming unit including a print head (liquid ejection head) driven based on the quantized data (dot data) generated by the quantization processing unit 66. By supplying the quantized data generated by the quantization processing means 66 to the quantized data output means 68, the quantized data output means prints an image on a recording paper or other medium.

  According to the image processing apparatus 50 according to the present embodiment, a threshold value obtained by adaptively selecting an optimal discharge failure sub-matrix according to the discharge failure position and replacing a part of the basic threshold matrix with the discharge failure corresponding sub matrix. Since the matrix is applied, it is possible to form a good image with no noticeable artifacts due to discharge failure.

Although a plurality of discharge failure corresponding sub-matrices are prepared according to the discharge failure occurrence position, each discharge failure support sub-matrix has a relatively small size (predetermined width) of about 3 to 9 pixels. The storage capacity of the storage means is relatively small. In addition, a part of the basic threshold matrix is replaced with the discharge failure sub-matrix according to the discharge failure position, and the threshold matrix that can correspond to the discharge failure position is adaptively generated. When viewed as the entire data amount of the threshold matrix that can be handled, the data amount is relatively small. Therefore, in the present embodiment, the basic threshold value matrix and the discharge failure are compared with the configuration in which a large number of discharge failure correspondence matrices (the entire matrix) corresponding to discharge failure positions are prepared by the conventional technique disclosed in Patent Document 1. The storage capacity of the corresponding submatrix data (the sum of the storage capacities of the basic threshold value matrix storage means and the discharge failure corresponding submatrix storage means) can be reduced.

  When discharge failure occurs at a plurality of positions in the basic threshold value matrix, threshold value replacement (switching) by the discharge failure corresponding sub-matrix is performed for each region corresponding to each discharge failure position. At this time, there may be a case where a plurality of discharge failure positions are close to each other, and discharge failure corresponding sub-matrices corresponding to the discharge failure positions may overlap each other. Change the combination of multiple discharge failure support matrixes so that both of the discharge failure support sub-matrices or one of the discharge failure prevention matrixes have a smaller matrix size (pixel width) To be controlled. The combination control of the discharge failure correspondence matrix is performed by the discharge failure correspondence sub-matrix selection unit 58 based on the information from the discharge failure position detection unit 56.

  Next, an ink jet recording apparatus will be described as a specific application example of the image processing apparatus 50 described above.

  FIG. 20 is an overall configuration diagram of an ink jet recording apparatus showing an embodiment of an image processing 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. From the droplet ejection image read by the image sensor, nozzle clogging or It functions as a means for checking ejection defects such as landing position deviation. Test patterns or practical images printed by the heads 112K, 112C, 112M, and 112Y of the respective colors are read by the print detection unit 124, and ejection determination of each head 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.

  The communication interface 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 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 the discharge failure prevention submatrix selection unit 58, the threshold matrix replacement unit 60, the threshold matrix setting unit 62, and the quantization processing unit 66 described with reference to FIG. Serves as a means.

  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 is incorporated into the print control unit 180 and used for the conversion process from the original image to the 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 medium 116, performs necessary signal processing, and the like to perform a print situation (whether ejection is performed, droplet ejection). Variation, optical density, etc.) and the detection result is provided to the print controller 180. That is, the print detection unit 124 functions as the undischarge position detection unit 56 described with reference to FIG. 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 setting of a threshold matrix and various corrections to the head 150 based on information obtained from the print detection unit 124 or other discharge detection means (not shown) as necessary, and preliminary discharge as necessary. Control to perform cleaning operations (nozzle recovery operations) such as suction, wiping, etc.

  According to the inkjet recording apparatus 110 having the above-described configuration, even when nozzle non-ejection occurs, a good image with little deterioration in image quality due to missing dots can be obtained.

  In the above embodiment, an ink jet recording apparatus using a full line type print head is illustrated, 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 performing 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

  In the above embodiment, an inkjet recording apparatus has been described as an example of an image recording apparatus, but the scope of application of the present invention is not limited to this. Other than the inkjet system, a thermal transfer recording apparatus having a line head (an apparatus using a thermal element as a recording element), an LED electrophotographic printer, a silver salt photographic printer having an LED line exposure head (an apparatus using an LED element as a recording element), etc. The present invention can also be applied to various types of image forming apparatuses.

Conceptual diagram of image processing using basic threshold matrix and discharge failure support submatrix Conceptual diagram showing the relationship between basic threshold matrix and discharge failure position Conceptual diagram illustrating the discharge failure position on the basic threshold matrix and the relationship between the replacement area and the non-replacement area Conceptual diagram illustrating the relationship between the replacement area MA (X) and the non-replacement area MB (X) of the basic threshold matrix. Conceptual diagram showing an example of the dot arrangement DMA (X, L) of the replacement area MA (X) and the dot arrangement DMB (X, L) of the non-substitution area MB (X) Conceptual diagram showing an example of the dot arrangement DSM (X, L) of the undischargeable submatrix SM (X) and the dot arrangement DMB (X, L) of the non-replacement area MB (X) Flow chart showing the procedure for determining the discharge failure sub-matrix Flow chart showing the procedure for determining the discharge failure sub-matrix Flow chart showing the procedure for determining the discharge failure sub-matrix Conceptual diagram used to explain an example of a processing method when the discharge failure position is at the end of the basic threshold matrix Diagram showing coordinate system for calculating two-dimensional power spectrum Graph showing an example of the polar power spectrum average index (R.A.P.S) calculated under certain conditions Graph showing the visual characteristics (VTF) of the human eye Graph showing an example of polar power spectrum dispersion index (anisotropy) calculated under certain conditions The principal part flowchart which showed the other process example which can be substituted for a part of flow demonstrated in FIG. Typical R.A.P.S graph of dot arrangement with blue noise characteristics 1 is a block diagram showing an example of a system configuration of a computer that performs threshold matrix creation processing and image processing according to an embodiment of the present invention. Conceptual diagram showing an example in which the discharge failure support submatrix relates to two adjacent basic threshold matrixes 1 is a block diagram showing a configuration of an image processing apparatus 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

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Computer, 12 ... Main body, 20 ... CPU, 24 ... ROM, 50 ... Image processing device, 52 ... Basic threshold matrix storage means, 54 ... Undischarge correspondence submatrix storage means, 56 Undischarge position detection means, 58 ... Not Discharge-corresponding sub-matrix selection means, 60 ... threshold matrix replacement means, 62 ... threshold matrix setting means, 64 ... image input means, 66 ... quantization processing means, 68 ... quantized data output means, 110 ... inkjet recording apparatus, 112 ... Print unit, 112K, 112C, 112M, 112Y ... head, 114 ... ink storage / loading unit, 116 ... recording paper, 118 ... paper feeding unit, 122 ... belt transport unit, 124 ... print detection unit, 131, 132 ...
Roller, 133 ... belt, 134 ... suction chamber, 135 ... fan, 150 ... head, 151 ... nozzle, 152 ... pressure chamber, 153 ... ink chamber unit, 158 ... actuator, 172 ... system controller, 175 ... ROM, 180 ... print Control unit, M ... basic threshold matrix, SM (X) ... non-discharge compatible sub-matrix

Claims (7)

An unrecordable position identifying step for identifying an unrecordable position on the image corresponding to the recording element that has become unrecordable;
A basic threshold value matrix storage step for storing a basic threshold value matrix used for halftoning processing for quantizing multi-valued input image data and converting it into dot data having a smaller number of gradations;
A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial area having a predetermined pixel width including a pixel position corresponding to the non-recordable position on the basic threshold value matrix, and a non-recordable position in the basic threshold matrix Sub-matrix storage process for storing a plurality of types corresponding to
A replacement area determining step of determining a corresponding area having a predetermined number of pixels within the basic threshold matrix from the pixel position in the input image data and the unrecordable position specified in the unrecordable position specifying step. When,
A sub-matrix selection step of selecting a sub-matrix to be used for replacing the corresponding region based on the determination of the replacement region determination step from a plurality of sub-matrices stored in the sub-matrix storage step;
A threshold value replacement step of replacing the threshold value of the corresponding area including the unrecordable position on the basic threshold value matrix with the sub-matrix selected in the sub-matrix selection step;
A quantization processing step of performing quantization of the input image data by selectively applying the threshold matrix obtained by replacing the corresponding region of the basic threshold matrix with a sub-matrix in the threshold replacement step or the basic threshold matrix; ,
An image processing method comprising:   The image processing method according to claim 1, wherein the basic threshold value matrix has a blue noise characteristic, and the predetermined pixel number width of the sub-matrix is set in a range of 3 to 9 pixels. An unrecordable position specifying means for specifying an unrecordable position on an image corresponding to a recording element that has become unrecordable;
Basic threshold value matrix storage means for storing a basic threshold value matrix used for halftoning processing for quantizing multi-value input image data and converting it into dot data having a smaller number of gradations;
A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial area having a predetermined pixel width including a pixel position corresponding to the non-recordable position on the basic threshold value matrix, and a non-recordable position in the basic threshold matrix Sub-matrix storage means for storing a plurality of types corresponding to
Replacement area determining means for determining a corresponding area having the predetermined number of pixels in the basic threshold matrix from the pixel position in the input image data and the unrecordable position specified by the unrecordable position specifying means in the basic threshold matrix. When,
Sub-matrix selection means for selecting a sub-matrix used for replacement of the corresponding area based on the determination of the replacement area determination means from a plurality of sub-matrices stored in the sub-matrix storage means;
Threshold replacement means for replacing the threshold of the corresponding area including the unrecordable position on the basic threshold matrix with a sub-matrix selected by the sub-matrix selection means;
Quantization processing means for selectively applying the threshold matrix obtained by replacing the corresponding region of the basic threshold matrix with a sub-matrix by the threshold replacement means or the basic threshold matrix, and quantizing the input image data; ,
An image processing apparatus comprising: A basic threshold value matrix storage step for storing a basic threshold value matrix used for halftoning processing for quantizing multi-valued input image data and converting it into dot data having a smaller number of gradations;
A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial region having a predetermined pixel number width including a pixel position corresponding to a position of a recording element that cannot be recorded on the basic threshold value matrix is included in the basic threshold value matrix. A sub-matrix storage step for storing a plurality of types corresponding to unrecordable positions;
A sub-matrix selection step of selecting at least one sub-matrix from a plurality of sub-matrices stored in the sub-matrix storage step;
A threshold value replacing step of generating a threshold value matrix by replacing a threshold value of a partial region having a predetermined number of pixels including the unrecordable position on the basic threshold value matrix with a sub-matrix selected in the sub-matrix selecting step;
A threshold value matrix creating method characterized by comprising: A recording head in which a plurality of recording elements 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;
A non-recordable position specifying means for specifying a non-recordable position on an image corresponding to a non-recordable recording element of the recording element array of the recording head;
Basic threshold value matrix storage means for storing a basic threshold value matrix used for halftoning processing for quantizing multi-value input image data and converting it into dot data having a smaller number of gradations;
A sub-matrix in which a threshold value is set to be replaced with a threshold value of a partial area having a predetermined pixel width including a pixel position corresponding to the non-recordable position on the basic threshold value matrix, and a non-recordable position in the basic threshold matrix Sub-matrix storage means for storing a plurality of types corresponding to
Replacement area determining means for determining a corresponding area having the predetermined number of pixels in the basic threshold matrix from the pixel position in the input image data and the unrecordable position specified by the unrecordable position specifying means in the basic threshold matrix. When,
Sub-matrix selection means for selecting a sub-matrix used for replacement of the corresponding area based on the determination of the replacement area determination means from a plurality of sub-matrices stored in the sub-matrix storage means;
Threshold replacement means for replacing the threshold of the corresponding area including the unrecordable position on the basic threshold matrix with a sub-matrix selected by the sub-matrix selection means;
Quantization processing means for selectively applying the threshold matrix obtained by replacing the corresponding region of the basic threshold matrix with a sub-matrix by the threshold replacement means or the basic threshold matrix, and quantizing the input image data; ,
Recording control means for controlling driving of the recording element of the recording head based on dot data generated by quantization of the quantization processing means;
An image forming apparatus comprising: An image processing method according to claim 1, an image processing device according to claim 3, a threshold value matrix creating method according to claim 4, or a method for creating the sub-matrix used in the image forming device according to claim 5. And
A sub-matrix region setting step of setting a region of a predetermined number of pixels including the unrecordable position on the basic threshold matrix as a sub-matrix replacement region;
In the process of determining the threshold value of the sub-matrix by sequentially determining the dot arrangement in the sub-matrix other than the non-recordable position, the dot arrangement corresponding to the sub-matrix and the basic threshold value matrix An evaluation value calculation step of calculating an evaluation value of a density distribution visually recognized for a dot arrangement obtained when combining a dot arrangement corresponding to a non-replacement region that is not replaced by the sub-matrix;
Using the evaluation value obtained in the evaluation value calculation step, a dot arrangement determination step for determining the arrangement of dots to be added,
A threshold value input step for setting a threshold value corresponding to the position of the additional dot in the sub-matrix according to the dot placement determined in the dot placement determination step;
A method of creating a sub-matrix characterized by comprising:   A program for causing a computer to execute the steps of the image processing method according to claim 1 or 2, the threshold matrix creation method according to claim 4, or the sub-matrix creation method according to claim 6.