JP2009279933A - Image recording method and image recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record an image by a line head under a condition having overlapping of a plurality of short length heads. <P>SOLUTION: An image recording apparatus is equipped with: a line head composed of a long length recording element row by arranging a plurality of short length recording element rows under a condition that on mutually adjoining end parts, the recording elements have overlapping regions; a halftone processing part wherein multiple value image data are executed with halftone-processing in accordance with specified halftone processing rules and recording materials are output from the recording elements to generate dots to be recorded; a distribution processing part wherein it is distributed that recording is performed by either one of adjoining short length recording element rows in the overlapping region by a distribution processing rules determined in accordance with the halftone processing rules; and a driving means for driving the recording elements so that dots distributed by the distribution processing part may be recorded by the recording elements of respective short length element rows included in the line head. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a long recording element in which a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at adjacent ends. The present invention relates to an image recording method and an image recording apparatus that perform printing by forming dots by adhering to a recording medium from a recording element using a line head configured as a column.

In an inkjet printer or the like, an image is formed on a recording paper (recording medium) by ejecting ink (recording material) from a plurality of nozzles (recording elements).
As such a printer, there is an image recording apparatus using a long line head that covers the main scanning direction of recording paper. In such an image recording apparatus, recording in the main scanning direction is performed with the line head fixed, and the recording paper is conveyed in a direction (sub-scanning direction) orthogonal to the line head direction (main scanning direction). Can be formed.

  Here, a long line head that covers the width of the recording paper has a higher manufacturing cost, a lower yield during manufacturing, a lower reliability, and a part of the recording element compared to a short head. Even if it is broken, it is necessary to replace the entire expensive line head, and there is a disadvantage that the cost for repair is high.

  With respect to such a problem, in Patent Document 1 (Japanese Patent Publication No. 4-38589), a long line head is configured as shown in FIG. 12 by arranging a plurality of short heads (short heads) in the nozzle row direction. A method has been proposed.

  However, with such a configuration, although the basic problem of the long head can be solved, a new problem arises when the short head is combined, that is, the adjustment between the heads is very difficult. Come.

  In particular, recently, there is an urgent need to deal with this problem because the printing resolution tends to be high. For example, when an image is recorded with a resolution of 1440 dpi (dot / 25.4 mm), the recording element pitch is about 17 μm.

  Various proposals have been made for a new problem when a long head is configured by combining short heads. For example, thinning out in the nozzle row direction, thinning out in the inter-nozzle direction, shaking the boundary, and shifting the overlapping position for each color in the case of a color head.

  Patent Document 2 (Japanese Patent No. 3702711) discloses a method in which several recording elements of a short head are overlapped and distributed to each head regularly or randomly using a random number according to the position.

Japanese Examined Patent Publication No. 4-38589 Japanese Patent No. 3702711

  However, the method disclosed in Patent Document 2 has the following problems. FIG. 13 shows an error diffusion pattern with a dot rate of 50% (dot rate = (dot-formed pixel / dot-formable pixel) × 100). Random numbers are generated in the overlapping area of the printing elements, and each head is assigned to each head according to the random number. FIG.

  As shown in (a1) and (a2) of FIG. 13, distribution is performed in an overlapping portion (overlapping region) between two adjacent short heads. When dots are output by these two short heads, if the two short heads are arranged in an ideal state, the dots are formed on the recording paper without any problem as shown in FIG. 13B. .

Further, in the pattern of FIG. 13B, assuming a resolution of 1440 dpi and a dot diameter of 40 μm, an actual print is reproduced as shown in FIG.
Here, in FIG. 14 (a), FIG. 14 (b) assumes a case in which there is a deviation or deviation in the arrangement of adjacent short heads. In FIG. 14B, it is assumed that one head is displaced by a distance of 1/2 nozzle from the original position in a direction in which the heads are separated from each other.

  As can be seen from FIG. 14 (b), a deviated position of each head is generated, so that a blank portion that is visually conspicuous is generated due to the deviation in the overlapping portion where the dot density of both the heads is lowered. Become. Here, three conspicuous blank portions are generated and surrounded by broken-line circles. In this case, visually, not only a blank can be seen, but also a pseudo contour may occur.

  As a result of the inventor of the present application verifying such inconvenience, when disassembling the dot pattern generated by the halftone process into two adjacent short heads, in the dot pattern of each head after sorting, It has been found that such a phenomenon occurs when the distribution is concentrated locally on one head (contains many low-frequency components). The basis for this will be briefly described with reference to FIGS.

  FIG. 15 shows a result of sorting a dot pattern with a dot rate of 100% using a random number rule containing many low frequencies when disassembling into two adjacent short heads (FIGS. 15 (a1) and 15 (a2)). FIG. 15 (b1) and FIG. 15 (b2) are results of distribution using a distribution rule having a blue noise characteristic in which low frequency components are small and every adjacent dot interval is distributed at a predetermined distance.

  Also, FIG. 16A shows that when forming an image with two adjacent short heads based on the sorting results of FIG. 15A1 and FIG. FIG. 10 is a simulation image assuming actual recording when dots are formed in a state where they are displaced in a relatively distant direction. FIG.

  Similarly, in FIG. 16B, when forming an image with two adjacent short heads based on the sorting results of FIG. 15B1 and FIG. 15B2, each head is equivalent to 1/2 nozzle. FIG. 10 is a simulation image assuming actual recording when dots are formed in a state where they are displaced in a relatively distant direction. FIG.

  As in the conventional example, FIGS. 15A1 and 15A2 distributed using a random number pattern including many low-frequency components have a large distribution unevenness in the dot pattern assigned to each head in the head overlap after the distribution (low). 15 (b1) and (b2), which are distributed using a blue noise characteristic pattern with a small amount of low-frequency components), the dots are not distributed to one head at the head overlap portion after the distribution. There is no large gap in the dot pattern that each head is responsible for.

  As a result, in FIG. 16 (a), the gaps caused by the displacement of the head are large and the gaps are coarsely distributed, whereas in FIG. 16 (b), the gaps caused by the displacement of the head are small and the gaps. Was found to be finely distributed.

  That is, if there is a large deviation in the allocated pattern, the density variation part (the part where the gap is generated) tends to be solidified when the short head is misaligned (FIG. 16A). On the other hand, as shown in FIG. 16B, by distributing the distribution locations so as not to be biased toward one head, the density variation locations (locations where gaps are generated) are dispersed and are difficult to see. By doing so, at least a 100% dot rate can be distributed to each head without deviation.

  However, with respect to a dot rate area of less than 100%, if there is no relationship between the distribution processing rule having the blue noise characteristic and the dot data after halftone, interference between patterns occurs, and the short head is decomposed. The later pattern becomes white noise (a state including a lot of low frequency components), and distribution of non-uniform dot data in a halftone with a dot rate of less than 100% as shown in FIG. 13B (FIG. 13A1). ) And (a2)) are not improved.

  Interference between patterns described here is interference moiré that occurs in gradation reproduction by halftone doting as seen in offset printed matter, but the phenomenon that is a problem in the present invention is somewhat different from this. Is different. In the case of halftone dots, since the regular patterns overlap each other, the interference pattern appears as a periodic pattern. On the other hand, in the case of interference between patterns having blue noise characteristics, since the patterns themselves are pseudo-random, the interference pattern generated by overlapping the patterns becomes white noise. A specific example of pattern interference is shown in FIG.

  FIG. 17A shows a halftone pattern having a blue noise characteristic with a dot rate of 30%, and FIG. 17B shows a 50% having a different blue noise characteristic that has nothing to do with the halftone pattern. It is a distribution rule. FIG. 17 (c1) is a diagram in which FIG. 17 (a) and FIG. 17 (b) are overlapped, and a portion where the black dot in (a) and the white region in the distribution rule in (b) overlap is extracted. FIG. 17 (c2) is a diagram in which FIG. 17 (a) and FIG. 17 (b) are overlapped, and a portion where the black dot of (a) and the black region of the distribution rule of (b) overlap is extracted. It is. In this way, even if the 50% sorting rule has a blue noise characteristic, if there is no relationship with the dot pattern, interference occurs between the dot pattern and the sorting rule pattern, Due to this interference, the pattern after sorting becomes white noise.

  The present invention solves the above-described problems, and a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in a state in which the recording elements have overlapping regions at end portions adjacent to each other. When image recording is performed using a line head arranged in one direction and configured as a long recording element array, the image quality deteriorates due to misalignment of dots in the overlapping area of adjacent short recording element arrays at the overlapping portion. It is an object of the present invention to realize an image recording method and an image recording apparatus that do not occur.

The present invention for solving the above-described problems is as follows.
(1) In the first aspect of the present invention, a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at adjacent ends. An image recording method using a line head arranged as a long recording element array, wherein multi-value input image data is read from a position corresponding to the input image data in a threshold matrix held in advance Halftone processing by comparing with the threshold value, a halftone processing step of generating a halftone data corresponding to a dot to be recorded by outputting a recording material from a recording element, and the halftone data in the overlapping region, Adjacent to each dot according to a distribution processing rule determined so as not to interfere with the halftone data according to the threshold matrix The recording element is recorded so as to be recorded by the recording element of each short length element array included in the line head. An image recording method, wherein the threshold matrix is a threshold matrix designed to suppress a low-frequency component of a halftone pattern generated in the halftone processing step. is there.

  Here, the threshold matrix designed to suppress low-frequency components refers to components in the low frequency band excluding DC components that feel visually uneven, such as blue noise threshold matrix and green noise threshold matrix, as other high-frequency components. The threshold matrix created so as to be suppressed in comparison.

  (2) In the invention according to claim 2, a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state in which the recording elements have overlapping areas at adjacent ends. A halftone by comparing a line head arranged as a long recording element array, multi-value input image data, and a threshold value read from a position corresponding to the input image data in a threshold matrix held in advance A halftone processing unit that generates a halftone data corresponding to a dot to be recorded by outputting a recording material from a recording element and processing the halftone data in the overlapping region according to the threshold matrix. Recording is performed with any short recording element row adjacent to each dot according to a distribution processing rule determined so as not to interfere with tone data. A distribution processing unit that distributes, and a driving unit that drives the recording elements so as to record the dots distributed by the distribution processing unit by the recording elements of the respective short element rows included in the line head, The threshold value matrix is an image recording apparatus that is a threshold value matrix designed to suppress a low frequency component of a halftone pattern generated in the halftone processing unit.

  Here, the threshold matrix designed to suppress low-frequency components refers to components in the low frequency band excluding DC components that feel visually uneven, such as blue noise threshold matrix and green noise threshold matrix, as other high-frequency components. The threshold matrix created so as to be suppressed in comparison.

  (3) In the invention according to claim 3, the distribution processing rule makes the threshold reading position in the distribution processing unit coincide with the threshold reading position of the halftone processing unit, and the threshold value read corresponding to the position is read. The image recording apparatus according to claim 2, wherein the image recording apparatus is a rule for sorting using a pattern created by using.

  (4) In the invention according to claim 4, the distribution processing rule makes the threshold reading position in the distribution processing unit coincide with the threshold reading position of the halftone processing unit, and the threshold value read corresponding to the position is read. The image recording apparatus according to claim 2, wherein the image recording apparatus is a rule that distributes using.

  (5) The invention according to claim 5 is characterized in that the recording material is ink and the recording element is a nozzle for ejecting the ink. It is an image recording device of description.

According to the present invention described above, the following effects can be obtained.
(1) In the invention of the image recording method according to the first aspect, the plurality of short recording element arrays in which the plurality of recording elements are arranged in one direction are in a state in which the recording elements have overlapping regions at adjacent ends. When image recording is performed using a line head arranged in one direction and configured as a long recording element array, the input multi-value input image data and the input image data in the threshold matrix held in advance are used. Distribution in which halftone data is generated by comparison with a threshold value read from a corresponding position, and the generated halftone data is determined not to interfere with the halftone data according to the above threshold matrix in the overlap region. According to the processing rule, it is distributed which short recording element row is adjacent to each dot, and in this way the distribution process step Recorded by the respective short element array of the recording elements included Ri divided was dots in the line head.

  This threshold matrix is a matrix designed to suppress low frequency components in the dot pattern processed by the threshold matrix. In addition, specific examples of matrices designed to suppress low-frequency components include low-frequency components other than high-frequency components, such as the blue noise threshold matrix and the green noise threshold matrix, that are not visually perceptible DC components. There is a threshold matrix created to be suppressed compared to the components.

  Accordingly, a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at end portions adjacent to each other. By using a distribution processing rule determined so as not to interfere with halftone data using a threshold matrix used for halftone processing when recording an image using a line head configured as a column, halftone processing and As a result, an increase in low frequency components due to pattern interference between the halftone pattern and the distribution pattern described above is suppressed in the decomposed pattern.

  Further, since the dot pattern generated in the threshold matrix uses a threshold matrix in which low frequency components are suppressed, each piece of data after decomposition can maintain a state in which the low frequency components are suppressed. Therefore, even if there is a misalignment of dots in the overlapping area of adjacent short recording element arrays, it is difficult for a blank area to be gathered in the recorded dots and image quality does not deteriorate.

  (2) In the invention of the image recording apparatus according to the second aspect, the plurality of short recording element arrays in which the plurality of recording elements are arranged in one direction are arranged in a state where the recording elements have overlapping regions at adjacent ends. When image recording is performed using a line head arranged in one direction and configured as a long recording element array, the input multi-value input image data and the input image data in the threshold matrix held in advance are used. Distribution in which halftone data is generated by comparison with a threshold value read from a corresponding position, and the generated halftone data is determined not to interfere with the halftone data according to the above threshold matrix in the overlap region. According to the processing rule, it is assigned which short recording element row is adjacent to each dot, and in this way the distribution processing unit assigns it. Recorded by the recording element of each short element array contained the resulting dot line head.

  This threshold matrix is a matrix designed to suppress low frequency components in the dot pattern processed by the threshold matrix. In addition, specific examples of matrices designed to suppress low-frequency components include low-frequency components other than high-frequency components, such as the blue noise threshold matrix and the green noise threshold matrix, that are not visually perceptible DC components. There is a threshold matrix created to be suppressed compared to the components.

  As a result, a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at end portions adjacent to each other. When recording an image using a line head configured as a halftone process, the threshold matrix used for the halftone process is used so that the distribution process rule is determined so as not to interfere with the halftone data. As a result, an increase in low-frequency components due to pattern interference between the halftone pattern and the distribution pattern described above is suppressed in the decomposed pattern.

  Further, since the dot pattern generated in the threshold matrix uses a threshold matrix in which low frequency components are suppressed, each piece of data after decomposition can maintain a state in which the low frequency components are suppressed. Therefore, even if there is a misalignment of dots in the overlapping area of adjacent short recording element arrays, it is difficult for a blank area to be gathered in the recorded dots and image quality does not deteriorate.

  (3) In the invention of the image recording apparatus according to the third aspect, the plurality of short recording element arrays in which the plurality of recording elements are arranged in one direction are arranged in a state in which the recording elements have overlapping regions at adjacent ends. When image recording is performed using a line head arranged in one direction and configured as a long recording element array, a sorting rule is used, the threshold matrix used when halftone processing is performed, and the threshold reading order In the same state, the rules are assigned using a pattern created from a threshold value obtained corresponding to the position.

  Here, the threshold value matrix used for the halftone process is designed so that the dot grouping generated by the threshold value process does not occur even if the binarization process is performed with any threshold value constituting the matrix. For example, a 50% dot pattern generated using a threshold matrix includes a 25% dot pattern generated using a threshold matrix. Therefore, the dot pattern assigned to one short recording element by the sorting rule is set to the threshold value by using the threshold value matrix used when the halftone process is performed as the sorting rule and the same threshold reading order. The same pattern as the pattern subjected to threshold processing using the matrix is obtained.

  As a result, the halftone process and the distribution process are in a correlated state, pattern interference can be prevented, and as a result, an increase in low frequency components of the decomposed pattern can be suppressed. Therefore, by performing such sorting, even if there is a dot shift in the overlapping area of adjacent short recording element arrays, it is difficult for a blank area to be gathered in the recorded dots and image quality is deteriorated. No longer occurs.

  (4) In the invention of the image recording apparatus according to claim 4, the plurality of short recording element arrays in which the plurality of recording elements are arranged in one direction are in a state in which the recording elements have overlapping regions at adjacent end portions. When image recording is performed using a line head arranged in one direction and configured as a long recording element array, a sorting rule is used, the threshold matrix used when halftone processing is performed, and the threshold reading order In the same state, the distribution rule is set by using a threshold value corresponding to the position.

  By doing so, the halftone process and the distribution process are in a correlated state, pattern interference can be prevented, and as a result, an increase in low frequency components of the decomposed pattern can be suppressed. Therefore, by performing such sorting, even if there is a dot shift in the overlapping area of adjacent short recording element arrays, it is difficult for a blank area to be gathered in the recorded dots and image quality is deteriorated. No longer occurs.

  (5) In the invention of the image recording apparatus according to claim 5, the plurality of short recording element arrays in which the plurality of recording elements are arranged in one direction are in a state in which the recording elements have overlapping regions at the end portions adjacent to each other. When a line head arranged in one direction and configured as a long recording element array is used to record an image by ejecting ink toward a recording medium, dots in the overlapping area of adjacent short recording element arrays are displayed. Even if there is a misalignment or the like, it becomes difficult to form a blank area in the recorded dots, and image quality does not deteriorate.

1 is a block diagram illustrating a configuration of an image recording apparatus according to an embodiment of the present invention. It is explanatory drawing which shows arrangement | positioning of the recording element of the image recording apparatus of embodiment of this invention. 1 is a perspective view illustrating a configuration of an image recording apparatus according to an embodiment of the present invention. It is a flowchart which shows the process of embodiment of this invention. It is a flowchart which shows the process of embodiment of this invention. It is a flowchart which shows the process of embodiment of this invention. It is a schematic diagram which shows the process of the image recording device of embodiment of this invention. It is explanatory drawing which shows the process of the image recording device of embodiment of this invention. It is explanatory drawing which shows the process of the image recording device of embodiment of this invention. It is a flowchart which shows the process of embodiment of this invention. It is a flowchart which shows the process of embodiment of this invention. It is explanatory drawing which shows the structure of a general elongate line head. It is explanatory drawing which shows the mode of the recording by the conventional image recording apparatus. It is explanatory drawing which shows the mode of the recording by the conventional image recording apparatus. It is explanatory drawing which shows the mode of distribution by 100% dot density. It is explanatory drawing which shows a mode when the position shift of a head has occurred with 100% dot density. It is explanatory drawing which shows a distribution rule.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, an image recording method and an image recording apparatus according to an embodiment of the present invention will be described.
In the following embodiments, an ink jet printer will be described as a specific example as an image recording apparatus. Accordingly, the recording material corresponds to ink, and the recording element corresponds to a nozzle that ejects ink.

(1) Configuration of the embodiment:
In this embodiment, the description will be focused on the configuration requirements regarding the characteristics of the image recording apparatus 100. Therefore, basic configuration requirements such as a power supply circuit and a power switch that are common as an image recording apparatus and are well-known are omitted.

  The control unit 101 is a control unit that performs various types of control of image formation. In the present embodiment, in particular, a plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction have recording elements at end portions adjacent to each other. When an image is recorded using a line head arranged in one direction and configured as a long recording element array with an overlapping area, half-value image data is half-processed according to a predetermined halftone processing rule. A halftone processing step for generating halftone data corresponding to dots to be recorded by outputting a recording material from a recording element by performing tone processing, and the halftone data in the overlapping region is determined so as not to cause interference. According to the distribution processing rule, a distribution processing step for distributing which short recording element row is adjacent to each dot, and a distribution processing step. The dots distributed by the flop, performing each recording step of driving the recording elements to record by the recording element of the short element array, the various controls at the time of execution that is included in the line head.

  In the above halftone processing step, as a predetermined halftone processing rule, half-value input image data is compared with a threshold value read from a position corresponding to the input image data in a threshold matrix held in advance. Tone processing is performed, and the recording material is output from the recording element to generate halftone data corresponding to the dot to be recorded. Further, in the above distribution processing step, in the overlap region, the halftone data is determined in any short recording element row adjacent to each dot according to the distribution processing rule determined so as not to interfere with the halftone data according to the threshold value matrix. Record or sort. The threshold matrix is a threshold matrix designed to suppress the low frequency component of the halftone pattern generated in the halftone processing step.

  The storage unit 105 is a storage unit that holds various data. In this embodiment, in particular, a low frequency component in a spatial frequency of a pseudo random pattern obtained by using a matrix such as a blue noise matrix or a green noise matrix as a matrix pattern. Are stored in various known matrices that are suppressed compared to other frequency components.

  The rasterization processing unit 110 is image processing means for converting image data of various formats such as vector data given from the outside such as a computer into raster data such as a bitmap. If the input data resolution is different from the print resolution, enlargement / reduction processing is performed at this point, and the data resolution after rasterization is made the same as the print resolution.

  The halftone processing unit 120 is a halftone processing unit that generates dots in a state where a halftone is expressed by multi-valued data by area gradation based on the number of dots based on a predetermined halftone processing rule. The halftone processing unit 120 performs threshold processing on the rasterized data using a matrix value such as a blue noise matrix or a green noise matrix stored in the storage unit 105 as a predetermined halftone processing rule. Then, halftone data corresponding to the dot to be recorded is generated. That is, in the halftone processing unit 120, as a predetermined halftone processing rule, halftone is obtained by comparing multivalued input image data with a threshold value read from a position corresponding to the input image data in a threshold matrix held in advance. The halftone data corresponding to the dots to be recorded is generated by outputting the recording material from the recording element. Here, the threshold matrix is a threshold matrix designed to suppress the low frequency component of the halftone pattern generated in the halftone processing step.

  The distribution processing unit 130 executes a distribution process for distributing halftone data to which adjacent short recording element array is to be recorded in an overlapping area of short heads, which will be described later, according to a distribution processing rule determined so as not to cause interference. It is a processing means. Here, the distribution processing unit 130 uses any of the short recording element arrays adjacent to each dot according to the distribution processing rule determined so that the halftone data does not interfere with the halftone data according to the threshold matrix in the overlapping region. Record or sort with. In this distribution processing unit 130, according to the present invention, a dot that is determined to be printed by halftone processing is assigned by AB which head is formed by a distribution processing rule that is determined so as not to cause interference. Thus, the halftone process and the distribution process are in a state of being correlated (or matched).

  The driving unit 140 is a driving unit (driver) that drives each recording element included in each short head (short recording element array), which will be described later, to discharge ink. In this embodiment, the driving unit 140A and the driving unit 140B It is configured with.

  In the line head 150, a plurality of short line heads (short recording element arrays) in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at adjacent ends. And a line head configured as a long recording element array. In this embodiment, the line head 150 is composed of short heads 150A and 150B.

  In addition, as the line head 150 in this embodiment, the state comprised by two short heads like FIG. 1 is shown in FIG. Here, a region where dots are formed during image recording only by the short head 140A is defined as a region aa. Similarly, a region where dots are formed during image recording by only the short head 140B is defined as a region bb. A region where dots are formed by both the short head 140A and the short head 140B is defined as a region ab. FIG. 2 shows the line head 150 as viewed from the ink ejection side. Here, the number of recording elements included in each short head is schematically shown. In actuality, a larger number of recording elements are arranged in accordance with the density of image recording. In practice, the line head 150 is configured by combining more short heads.

  Further, as shown in the perspective view of FIG. 3, the image recording apparatus 100 uses the drive rollers R <b> 1 and R <b> 2 to record the recording paper in a direction (sub-scanning direction) orthogonal to the longitudinal direction (main scanning direction) of the line head 150. While being conveyed, ink is ejected from the recording elements of the line head 150 onto the recording paper. Alternatively, the line head 150 and the recording paper may be relatively moved in the transport direction (sub-scanning direction), for example, by moving the line head 150.

If necessary, the ink on the recording paper is irradiated with heat or ultraviolet rays from the fixing unit 160 to fix the image recorded with the ink.
(2) Overall processing of the embodiment:
Hereinafter, an operation (image recording method) by the image recording apparatus will be described with reference to a flowchart.

FIG. 4 is a flowchart showing the overall schematic operation of the image recording apparatus 100 of the present embodiment when recording an image.
In the image recording apparatus 100, image data in various formats such as vector data given from outside such as a computer is converted into raster data such as a bitmap format in the rasterization processing unit 110 (step S401 in FIG. 4). At this time, external vector format data and converted bitmap format raster data are stored in the storage unit 105 as necessary.

  If the image is composed of multi-valued data having gradation, halftone processing is performed in order to finally represent the gradation in a binary manner with ink ejection / no ink ejection. (Step S402 in FIG. 4).

That is, the halftone processing unit 120 generates dots in a state in which halftones are expressed from multi-valued data by area gradation based on a predetermined halftone processing rule.
In the halftone processing unit 120, as a predetermined halftone processing rule, a low frequency component of a halftone pattern generated by threshold processing such as a blue noise matrix and a green noise matrix stored in the storage unit 105 is included. The rasterized data is thresholded using threshold matrix values designed to be suppressed, and halftone data corresponding to dots to be recorded is generated.

  In the present embodiment, a halftone data is generated by using a 64 dot × 64 dot matrix pattern, comparing the rasterized multi-value pixel values with the corresponding matrix values, and performing quantization.

  Here, regarding the overlapping area (area ab in FIG. 2), it is in charge of recording for each dot by executing a data distribution process to determine which of the short heads 150A / 150B included in the line head 150 is to be recorded. The head to be determined is determined (step S403 in FIG. 4).

  That is, the distribution processing unit 130 uses the distribution processing rule according to the threshold matrix used in the above halftone, and performs processing to distribute which short recording element array is adjacent in the overlapping area of short heads described later. Execute. In this distribution processing unit 130, according to the present invention, which head is to be formed by AB is assigned using the threshold value used when the dot at the position is generated, which is determined to be printed by halftone processing.

  Then, the short head 150A for the area aa, the short head 150B for the area bb, and the short head 150A or 150B determined by the sorting process for the area ab, ink is ejected onto the recording paper to record an image. (Step S404 in FIG. 4).

(3) Detailed processing of the embodiment:
(3-1) Halftone processing:
Here, the halftone processing (step S402 in FIG. 4) by the halftone processing unit 120 will be described in detail with reference to FIG.

  As the halftone processing, the halftone processing unit 120 generates halftoned data by comparing each pixel of the bitmap format raster data with a threshold matrix corresponding to a sequential position. .

First, with regard to raster data in bitmap format, initial coordinates x = 0 and y = 0 are set as the target coordinates.
(Step S501 in FIG. 5). However, in these coordinates, the x-axis direction is the nozzle row direction (longitudinal direction of the line head 150 = main scanning direction), and the y-axis direction is the transport direction (sub-scanning direction orthogonal to the main scanning direction) (see FIG. 2). .

Then, it is determined whether y of the target coordinate is smaller than the maximum coordinate value ymax of the image data in the y direction, and the process is completed when it reaches ymax (NO in step S502 in FIG. 5).
Further, it is determined whether x of the target coordinate is smaller than the maximum coordinate value xmax of the image data in the x direction, and when xmax is reached (NO in step S503 in FIG. 5), y is incremented and x is increased. It is set again to 0 (step S508 in FIG. 5), and the process is executed for the next line.

  Here, for the pixel at the target coordinate, the density value PX (x, y) of the pixel is compared with the threshold TH (x ′, y ′) in the matrix when the pixel at the target coordinate is assigned to the threshold matrix. (Step S504 in FIG. 5).

  If the threshold matrix is C pixels in the x direction and D pixels in the y direction, the remainder when x is divided by C is x ', and the remainder when y is divided by D is y'. become. That is, TH (x ′, y ′) means that the above x ′ and y ′ are applied to the threshold value matrix and the threshold value in the threshold value matrix is read out.

  As in this embodiment, when a 64 × 64 dot matrix pattern is used, the threshold matrix has a matrix size of 64 pixels in the x direction and 64 pixels in the y direction, and the coordinates of the pixel of interest PX are ( x ′, y ′ are the remainder when x is divided by 64 and the remainder when y is divided by 64, respectively. Then, the above x ′ and y ′ are applied to the threshold value matrix, and the threshold value in the threshold value matrix is read out.

  If PX (x, y)> TH (x ′, y ′) (YES in step S504 in FIG. 5), dots are formed at the position of the threshold TH in the matrix (step in FIG. 5). S505).

  On the other hand, unless PX (x, y)> TH (x ′, y ′) (NO in step S504 in FIG. 5), dots are not formed at the position of the threshold TH in the matrix (step in FIG. 5). S506). In this way, dot formation / non-formation is determined by comparing the pixel density of the target coordinate and the threshold matrix, and halftone processing is executed.

  Further, the pixel of interest is incremented by one pixel in the x direction (step S507 in FIG. 5), and the dot formation / non-formation determination is made by comparing the pixel density at the above-mentioned coordinate of interest with the threshold matrix threshold (FIG. 5). Steps S504, S505, and S506 in the middle are continued to the maximum value xmax in the x direction (Steps S507 and S503 in FIG. 5).

  When the x coordinate of the target image reaches the maximum value xmax in the x direction (NO in step S503 in FIG. 5), y is incremented and x is set to 0 again (in FIG. 5). Step S508), the process is executed for the next line. Then, halftone processing is executed for all the pixels, and the above processing is terminated when the target coordinates reach xmax and ymax (end in FIG. 5).

  FIG. 7 is an explanatory diagram schematically showing the above processing. Here, a state in which the image data Ad is recorded on the recording paper P by the line head 150 is schematically shown. In FIG. 7, a C pixel × D pixel matrix Am corresponds to the threshold matrix described above, and image data Ad represents the entire input image. In general, the threshold matrix is small with respect to the size of the image data. Therefore, as described above, by comparing the remaining threshold values obtained by dividing the coordinates of the image of interest by the size of the threshold matrix, the same effect as that obtained by repeatedly adapting the threshold matrix in the x direction and the y direction is obtained.

(3-2) Data distribution processing:
Here, with reference to FIG. 6, the data distribution process (step S403 in FIG. 4) by the distribution process 130 will be described in detail.

  This distribution processing unit 130 performs data distribution processing, in particular, which of the short heads 150A / 150B performs recording on the overlapping area (area ab in FIG. 2) of a plurality of short heads included in the line head 150. The head in charge of recording is determined for each dot.

  In this distribution processing unit 130, as a predetermined distribution processing rule, firstly, distribution processing for determining the halftone data generated by the halftone processing unit 120 so as not to interfere with the halftone data according to the threshold matrix. Data for each head is created using rules.

  Here, as a desirable example, in the distribution processing unit 130, when determining the distribution processing rule, the threshold reading position is matched with the threshold reading position of the halftone processing unit, and distribution is performed using the threshold value read corresponding to the position. Sorting process is performed using the rule.

  About each dot of the data produced | generated by the halftone process by the above halftone process part 120, as a data distribution process, it determines which of the short head 150A / 150B is used for recording, and the head in charge of recording for every dot is determined. .

  Although it is obvious which short head should be used to record dots that do not belong to the overlapping area, in this embodiment, it is determined which short head should be used to record all dots in the image data, and flag format data. Is granted.

  First, for dot data generated by halftone processing, the coordinates of interest are set to initial values x = 0 and y = 0 (step S601 in FIG. 6). Here, also in the distribution processing unit 130, as in the halftone processing unit 120, the x-axis direction is the nozzle row direction and the y-axis direction is the transport direction.

Then, it is determined whether y of the target coordinate is smaller than the maximum coordinate value ymax of the image data in the y direction, and the process is completed when it reaches ymax (NO in step S602 in FIG. 6).
Further, it is determined whether x of the target coordinate is smaller than the maximum coordinate value xmax of the image data in the x direction, and when xmax is reached (NO in step S603 in FIG. 6), y is incremented and x is set. It is set again to 0 (step S608 in FIG. 6), and the process is executed for the next line.

Here, x of the target coordinate is the maximum value in the x direction of the area aa of only the short head 150A (
It is determined whether it is smaller than the maximum value xaa_max in the x direction within the range that does not become the overlapping area ab with the short head 150B (step S604 in FIG. 6).

  If the coordinate x of interest is smaller than the maximum value xaa_max in the x direction of the area aa of only the short head 150A (YES in step S604 in FIG. 6), the CPU 101 determines that the dot is within the area aa. Is stored in the storage unit 105 in association with the dot (step S607 in FIG. 6).

  When the coordinate x of the attention coordinate is larger than the maximum value in the x direction of the area aa of only the short head 150A (maximum value in the x direction in a range not overlapping with the short head 150B) xaa_max (step in FIG. 6) In NO in S604, the coordinate x of the attention coordinate is larger than the minimum value in the x direction of the region bb of only the short head 150B (minimum value in the x direction in a range that does not become the overlapping region ab with the short head 150B) xbb_min. Is determined (step S605 in FIG. 6).

  If the coordinate x of interest is larger than the minimum value xbb_min in the x direction of the area bb of only the short head 150A (YES in step S605 in FIG. 6), the CPU 101 causes the head 150B to be a dot within the area bb. Is stored in the storage unit 105 in association with the dot (step S608 in FIG. 6).

  When the coordinate x of interest is larger than the maximum value in the x direction of the area aa of only the short head 150A (the maximum value in the x direction in the range that does not become the overlapping area ab with the short head 150B) xaa_max (in FIG. 6). NO in step S604), and if it is smaller than the minimum value xbb_min in the x direction of the area bb of only the short head 150A (NO in step S605 in FIG. 6), the dot within the area ab that is the overlapping area Therefore, the CPU 101 determines which short head should be used for output as follows, and stores a flag indicating that the short head is used for output in the storage unit 105 in association with the dot. (Step S607 or S608 in FIG. 6).

  Here, the distribution processing unit 130 uses a distribution processing rule determined so as not to generate interference according to the halftone processing rule as a predetermined distribution processing rule when executing the distribution processing. In this embodiment, a matrix pattern having a correlation between the halftone processing rule and the distribution processing rule is used as the predetermined distribution processing rule. As a specific example, the same matrix pattern is assigned to the same dot position in the halftone processing rule and the distribution processing rule.

  Hereinafter, the same matrix pattern as the threshold matrix used in the halftone process is used, the reading start position and the reading order are the same as the halftone processing unit, and the process using the read threshold is used for sorting. This will be specifically described.

  Here, with respect to the dot at the target coordinate, the threshold TH (x ′, y ′) in the matrix when the dot at the target coordinate is assigned to the threshold matrix and the relative x-coordinate value in the overlapping region are the maximum threshold values in the matrix. The relative coordinate threshold conversion value THmax−α (x−xaa_max) obtained by normalization to the value THmax is compared (step S606 in FIG. 6).

  Here, the threshold value TH (x ′, y ′) is the same value as that used in the halftone process. If the threshold matrix is C pixels in the x direction and D pixels in the y direction, x is C. The remainder when dividing is x ′, and the remainder when y is divided by D is y ′. The threshold value read from the threshold matrix by applying x ′ and y ′ to the threshold matrix.

Also, the relative coordinate threshold conversion value THmax-α (x-xaa_max) is
More details are as follows.
THmax-α (x-xaa_max)
= THmax- (THmax / (xbb_min-xaa_max)) (x-xaa_max)
For example, if the maximum threshold value THmax in the threshold matrix is 255 and the number of dots in the overlapping area is 14 dots, the relative coordinate threshold conversion value is
THmax-α (x-xaa_max)
= 255- (255/14) (x-xaa_max)
Can be expressed as

  In addition, here, a specific example in which α is a fixed proportionality coefficient and the relative coordinate threshold value conversion value changes linearly according to the dot position (x−xaa_max) of the overlapping region is shown, but the present invention is not limited thereto. Is not to be done. That is, an expression that changes the relative coordinate threshold conversion value in a quadratic curve may be determined.

  If TH (x ′, y ′)> THmax−α (x−xaa_max) (YES in step S606 in FIG. 6), dots are formed by the short head 150B (step S608 in FIG. 6).

  On the other hand, unless TH (x ′, y ′)> THmax−α (x−xaa_max) (NO in step S606 in FIG. 6), dots are formed by the short head 150A (step S607 in FIG. 6).

  In this way, the distribution processing unit 130 executes the distribution process using the distribution processing rule determined so as not to generate interference according to the halftone processing rule (steps S604, S605, S606 in FIG. 6). S607, S608).

  Further, the coordinate of interest is incremented by one pixel in the x direction (step S609 in FIG. 6), and the above-described dot distribution processing of the coordinate of interest (steps S604, S605, S606, S607, and S608 in FIG. 6) is performed. The process continues until the maximum value xmax in the x direction (steps S609 and S603 in FIG. 6).

  When x of the coordinate of interest reaches the maximum value xmax in the x direction (NO in step S603 in FIG. 6), y is incremented and x is set to 0 again (step in FIG. 6). S610), the process is executed for the next line. Then, the sorting process is executed for all the dots, and the above process is terminated when the target coordinates reach xmax and ymax (end in FIG. 6).

  The data created in this way is shown in FIG. FIG. 8A1 shows dot data distributed to one head, and FIG. 8A2 shows dot data distributed to the other head. FIG. 8B is a diagram showing a state where FIG. 8A1 and FIG. 8A2 are overlapped.

  As can be seen by comparing FIG. 13 (a1) and FIG. 13 (a2) of the conventional example and FIG. 8 of the present embodiment, when a random number is used to distribute to each head as in the prior art, a random number pattern is used. The dot data assigned to each head due to the interference between the sorting rule and the halftone pattern contains a lot of low frequency components in each dot pattern, whereas this embodiment (FIG. 8). ), The halftone pattern and the distribution rule are created from the same dither matrix, and interference is suppressed. For this reason, as shown in FIGS. 8 (a1) and 8 (a2), it can be seen that the increase in the low frequency component of the dot pattern assigned to each head is suppressed.

That is, by executing the sort process as described above, even if the dot rate is less than 100%, the dots in the overlapping region are dispersed at high frequency in both short heads.
Further, when a dot diameter assuming actual printing is generated in the pattern of FIG. 8B, the result is as shown in FIG. 9A. Also, FIG. 9B shows a diagram in which one head is displaced in the direction in which the heads are separated from each other by 1/2 nozzles as in the conventional example of FIG.

  As can be seen by comparing the case of FIG. 14 of the conventional example with FIG. 9 of the present embodiment, even if there is a deviation of dots in the overlapping area of adjacent short heads, the dots are collected in the recorded dots. Blank areas are less likely to occur, and image quality is not degraded. That is, according to the present embodiment, it is difficult to form a blank area as shown in FIG. 14B, and as a result, deterioration of image quality is suppressed, and a smooth change is realized even in the overlapping portion between the heads. it can.

(4) Other embodiments:
In the above embodiment, a blue noise matrix is used as a matrix pattern having a correlation used in the halftone process and the distribution process, but various other matrices such as a green noise matrix can be used.

  Further, in the above embodiment, in order to make the explanation easy to understand, a specific example of the line head 150 including the two short heads 150A and 150B is used. However, the present invention can also be applied to a line head including three or more short heads. is there.

  In the above embodiment, the distribution ratio is gradually changed for the connection of 150A and 150B. However, the distribution ratio of the overlapping portion may be fixed to 50%. Even in this case, a better connection can be obtained as compared with the case of distributing using random numbers.

  Further, in the above embodiment, the halftone processing unit 120 and the distribution processing unit 130 are described as separate processing units (different steps) for easy understanding of the description, but the halftone processing unit 120 and the distribution processing unit 130 are described. Can also be integrated. With this configuration, it is possible to increase the processing speed because similar processing is not repeated twice.

At this time, as relative coordinate conversion value,
PX (x, y) -β (x-xaa_max)
= PX (x, y)-(PX (x, y) / (xbb_min-xaa_max)) (x-xaa_max)
It is also good.

By doing this, the region of the connecting portion can be in the range of (xaa_max <x <xbb_min) in any dot density region in the halftone data.
In the above embodiment, the distribution processing unit 130 uses the same threshold value matrix value as that of the halftone processing unit 120. However, when determining the distribution processing rule, the threshold value reading position is set to the threshold value reading position of the halftone processing unit 120. It is also possible to distribute using a distribution pattern created from a threshold value matrix read according to the position.

  Specifically, as in the distribution mask creation process shown in FIG. 10, the x-axis direction (main scanning direction) is from the beginning xaa_max to the end xbb_min of the overlapping portion of the head (steps S601 ′, S602 ′, and S603 in FIG. 10). '-S609', S610 '), and the y-axis direction (sub-scanning direction) creates a THA having a matrix size adapted by the halftone processing unit 120 (steps S606'-S608' in FIG. 10).

  Then, in the x-axis direction (main scanning direction) from the start xaa_max to the end xbb_min of the overlapped portion of the head in the x-axis direction (main scanning direction) as in the data distribution process shown in FIG. 11 (step S601 in FIG. 11). "-S605", S609'-S610 ') and the distribution process rule (steps S606 "-S608" in FIG. 11) are used to execute the distribution process.

Processing as shown in FIGS. 10 to 11 not only provides the same effects as the above-described embodiments, but also reduces the computation load.
Further, in the image recording apparatus 100 described above, the fixing unit 160 is used. However, even in the case of image recording that does not have a fixing unit, the fixing unit is an image recording apparatus that exists outside the image recording apparatus. The present embodiment can also be applied.

The image recording apparatus 100 described above is suitable for an ink jet printer, but can also be applied to a recording apparatus or a printing apparatus of a recording method other than ink jet.
Further, the recording in the above embodiment does not mean only recording by ink ejection, but can also be applied to light emitting display. That is, the above embodiment can be applied even to an image display apparatus that drives a light emission by moving a line head in which a plurality of short heads are combined.

100 image recording apparatus 101 control unit 105 storage unit 110 rasterization processing unit 120 halftone processing unit 130 distribution processing unit 140 driving unit 140A first driving unit 140B second driving unit 150 line head 150A first short head 150B second Short head

Claims (5)

A plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at adjacent ends, and are configured as a long recording element array. An image recording method using a line head,
Dots to be printed by halftone processing by comparing multi-valued input image data with a threshold value read from a position corresponding to the input image data in a threshold matrix held in advance, and outputting a recording material from a recording element A halftone processing step for generating halftone data corresponding to
In the overlapping area, the halftone data is distributed according to the threshold processing matrix so that it is recorded by which short recording element row adjacent to each dot according to the distribution processing rule determined so as not to interfere with the halftone data. Processing steps;
A recording step of driving the recording elements so as to record the dots distributed in the distribution processing step by the recording elements of the respective short element rows included in the line head,
The threshold matrix is a threshold matrix designed to suppress a low frequency component of a halftone pattern generated in the halftone processing step.
An image recording method. A plurality of short recording element arrays in which a plurality of recording elements are arranged in one direction are arranged in the one direction in a state where the recording elements have overlapping regions at adjacent ends, and are configured as a long recording element array. Line head,
Dots to be printed by halftone processing by comparing multi-valued input image data with a threshold value read from a position corresponding to the input image data in a threshold matrix held in advance, and outputting a recording material from a recording element A halftone processing unit for generating halftone data corresponding to
In the overlapping area, the halftone data is distributed according to the threshold processing matrix so that it is recorded by which short recording element row adjacent to each dot according to the distribution processing rule determined so as not to interfere with the halftone data. A processing unit;
Driving means for driving the recording elements so as to record the dots distributed by the distribution processing unit by the recording elements of the respective short element rows included in the line head;
With
The threshold matrix is a threshold matrix designed to suppress a low frequency component of a halftone pattern generated in the halftone processing unit.
An image recording apparatus. The distribution processing rule is a rule in which the threshold reading position in the distribution processing unit is matched with the threshold reading position of the halftone processing unit, and distribution is performed using a pattern created using the threshold value read corresponding to the position. Is,
The image recording apparatus according to claim 2. The distribution processing rule is a rule that matches the threshold reading position in the distribution processing unit with the threshold reading position of the halftone processing unit, and distributes using the threshold value read corresponding to the position.
The image recording apparatus according to claim 2. The recording material is ink;
The recording element is a nozzle for discharging the ink;
The image recording apparatus according to claim 2, wherein the image recording apparatus is an image recording apparatus.