JP6286971B2 - Inkjet recording device - Google Patents

Description

  The present invention relates to an ink jet recording apparatus.

  Conventionally, in image formation in an ink jet recording apparatus, there has been a strong demand for higher definition of images and higher recording speed. In order to solve this problem, there is known an ink jet recording apparatus including a recording head having a nozzle row in which a plurality of nozzles are arranged in rows at predetermined intervals.

  In addition, such an ink jet recording apparatus is known in which a recording head as described above is provided for each color of YMCK. The ink jet recording apparatus configured as described above converts the input image data into discharge image data for each color of YMCK, and assigns these discharge image data to the recording heads of the respective colors. Then, each pixel constituting the ejection image data allocated to the recording head of each color is allocated to each of a plurality of nozzles, and an ink droplet is ejected from each nozzle to form an image on a recording medium, thereby forming an image by color. Is possible.

  By the way, it is known that the conventional ink jet recording apparatus has a displacement with respect to the nozzle array direction due to a manufacturing error or the like, and when an image is formed in such a state, an ink droplet is landed at an assumed position on the recording medium. In other words, the landing position of the ink droplet is shifted between colors, which causes image deterioration such as color shift.

  In view of such a situation, there is a conventional ink jet recording apparatus that eliminates the displacement in the nozzle row direction (for example, Patent Documents 1 and 2).

JP 2009-83175 A JP 2006-264152 A

  By the way, in the conventional ink jet recording apparatus, in order to realize high definition and high speed, the nozzle interval is extremely small, and the nozzle row tends to be long. In this case, the number of nozzles per recording head is the same, but an error occurs in the nozzle interval due to a manufacturing error, and the accumulation may cause a difference in the number of nozzles per unit length. Further, in recent years, there is an ink that needs to eject ink droplets at a high temperature. In such a case, a change due to thermal distortion due to heating cannot be ignored. Therefore, also in these cases, a deviation in the nozzle row direction occurs.

  However, in any of the inventions described in the above patent documents, the displacement in the nozzle row direction is eliminated on the assumption that the number of nozzles per unit length is the same, and the number of nozzles per unit length is It is not possible to eliminate the deviation that occurs when an error occurs in the.

  The subject of this invention is providing the inkjet recording device which can reduce the color shift which arises when the number of nozzles per unit length differs.

In order to solve the above problems, the invention described in claim 1 is provided with a plurality of recording heads each having a nozzle row in which a plurality of nozzles are arranged at a predetermined interval, arranged in a direction perpendicular to the nozzle row direction. Inkjet for converting the image data into ejection image data for each recording head and forming an image on the recording medium by ejecting ink from each nozzle of the plurality of recording heads according to the ejection image data while conveying the recording medium In the recording device,
The number of nozzles per predetermined unit length in the nozzle row direction is specified for each of the plurality of recording heads, and the number of reference nozzles per predetermined unit length is defined as the reference nozzle number, and the reference nozzle number and the plurality of recording heads. And a controller that corrects the ejection image data by calculating an error from the number of nozzles per predetermined unit length and inserting or deleting pixels according to the calculated nozzle number error. To do.

According to a second aspect of the present invention, in the ink jet recording apparatus of the first aspect,
The control unit includes the number of nozzles that is equal to or less than the number of nozzles per predetermined unit length of the recording head having the smallest number of nozzles per predetermined unit length among the plurality of recording heads as the reference nozzle number and the reference nozzle number. An error with the number of nozzles per predetermined unit length for each of the plurality of recording heads is calculated, and the ejection image data is corrected by inserting pixels according to the calculated error in the number of nozzles. .

According to a third aspect of the present invention, in the ink jet recording apparatus according to the first aspect,
The control unit includes the number of nozzles that is equal to or larger than the number of nozzles per predetermined unit length of the recording head having the largest number of nozzles per predetermined unit length among the plurality of recording heads as the reference nozzle number, An error from the number of nozzles per predetermined unit length for each of the plurality of recording heads is calculated, and the ejection image data is corrected by deleting pixels according to the calculated error in the number of nozzles. .

The invention according to claim 4 is the ink jet recording apparatus according to any one of claims 1 to 3,
The control unit inserts or deletes pixels so that correction positions are different for each recording head.

The invention according to claim 5 is the ink jet recording apparatus according to any one of claims 1 to 4,
The control unit inserts or deletes pixels so as not to be continuous in a direction perpendicular to the nozzle row direction of the ejection image data.

A sixth aspect of the present invention is the ink jet recording apparatus according to the fifth aspect,
The control unit includes a plurality of pixels in the nozzle row direction and a direction perpendicular to the nozzle row direction, and is formed in a matrix, and mask data in which positions where pixels are inserted or deleted are defined. The position at which the pixel is inserted or deleted is determined by performing mask processing on the ejection image data using.

The invention according to claim 7 is the inkjet recording apparatus according to claim 6,
In the mask data, only the position for inserting or deleting one pixel is defined in the nozzle row direction, and the position for inserting or deleting the pixel does not have a period in the entire mask data, The pattern data is formed to have substantially uniform intervals.

  According to the present invention, it is possible to reduce color misregistration caused by the difference in the number of nozzles per unit length.

1 is a perspective view illustrating a schematic configuration of an ink jet recording apparatus. FIG. 2 is a plan view for schematically explaining a recording head. It is a block diagram which shows the functional structure of an inkjet recording device. It is a schematic block diagram explaining image formation. It is a flowchart explaining a correction area | region setting process. It is a figure explaining line chart image data. It is a flowchart explaining a distortion correction process. It is a flowchart explaining a correction process. It is a figure explaining a mask pattern. It is a figure explaining the example of application of this invention. It is a figure explaining the example of application of this invention. It is a figure explaining the application example of another aspect of this invention. It is a perspective view which shows the other example of the inkjet recording device which concerns on this Embodiment.

  Hereinafter, an ink jet recording apparatus according to an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In addition, in the following description, what has the same function and structure attaches | subjects the same code | symbol, and abbreviate | omits the description. In the following description, “image data” refers to, for example, data of the entire image formed on one recording medium, and “pixel” refers to one dot constituting “image data”. Data.

As shown in FIG. 1, the ink jet recording apparatus 2 has a platen 6 that supports a recording medium 4. A transport roller 8 for transporting the recording medium 4 is provided before and after the platen 6. When the transport roller 8 is driven, the recording medium 4 is transported from the rear to the front while being supported by the platen 6.
In the following description, the conveyance direction of the recording medium 4 is referred to as “Y direction”, and the direction orthogonal to the conveyance direction is referred to as “X direction”. The Y direction and the X direction are directions on the horizontal plane.

  Above the platen 6, recording heads 10, 12, 14, and 16 are provided from the upstream side to the downstream side in the Y direction. Each recording head 10, 12, 14, 16 is a line head extending in the X direction. For example, the recording head 10 ejects cyan (C) ink toward the recording medium 4. Further, the recording head 12 discharges magenta (M) ink toward the recording medium 4. Further, the recording head 14 ejects yellow (Y) ink toward the recording medium 4. Further, the recording head 16 ejects black (K) ink toward the recording medium 4. The arrangement order of the recording heads 10, 12, 14, 16 can be arbitrarily set.

  Further, a line sensor 18 as an image reading unit is provided on the downstream side of the recording head 16 above the platen 6. The line sensor 18 extends in the X direction, and can read an image formed on the recording medium 4 and specify a position where the image is formed.

When the recording head 10 is viewed in plan view from below, as shown in FIG. 2, the recording head 10 has a large number of nozzles N formed in rows at a predetermined interval over a range longer than the length of the recording medium 4 in the X direction. Has been. That is, the recording head 10 has a nozzle row. The number of nozzles N can be set arbitrarily. Note that the number of nozzle rows is not limited to one, but may be two or more. The recording head 10 includes, for example, an ejection unit such as a piezo element (piezoelectric element) inside, and the ejection of each ink droplet from each nozzle N can be controlled independently by the operation of the ejection unit.
In this embodiment, the line head is configured by one long recording head in which a large number of nozzles N are formed in a row. For example, a plurality of recording heads are arranged in the nozzle row direction. You may make it comprise a line head by arranging in zigzag form.
The ink used in the present embodiment is four colors of cyan (C), magenta (M), yellow (Y), and black (K). However, the present invention is not limited to this. For example, light cyan (LC) Other colors such as light magenta (LM) and light yellow (LY) can also be used. In this case, a recording head corresponding to each color is further provided.
Since the recording heads 12, 14, and 16 have the same configuration as the recording head 10, only the recording head 10 will be described in the following description, and the description of the recording heads 12, 14, and 16 will be omitted. .

Next, the functional configuration of the inkjet recording apparatus 2 will be described with reference to FIG.
The ink jet recording apparatus 2 includes a transport unit 20 and a control unit 30 in addition to the recording heads 10, 12, 14, 16 and the line sensor 18 described above.

  The transport unit 20 includes a transport roller 8 and a transport motor 20 a that rotates the transport roller 8. The transport motor 20a is driven and controlled by the control unit 30, and is configured to transport the recording medium 4 in the Y direction (see FIG. 1) by rotating the transport roller 8 in a predetermined direction.

  The control unit 30 controls each unit of the inkjet recording apparatus 2, and includes a CPU (Central Processing Unit) 31, a RAM (Random Access Memory) 32, a ROM (Read Only Memory) 33, and the like.

  The CPU 31 reads out various application programs related to various functions as the ink jet recording apparatus 2 stored in the ROM 33, develops them in a work area in the RAM 32, and comprehensively controls the ink jet recording apparatus 2 according to the program.

  The RAM 32 includes, for example, a program storage area for expanding a processing program executed by the CPU 31, a data storage area for storing input data, a processing result generated when the processing program is executed, and the like.

  The ROM 33 stores a system program that can be executed by the inkjet recording apparatus 2, various processing programs that can be executed by the system program, various data that are used when the various processing programs are executed, and the like.

Next, a processing procedure for executing image formation performed in the inkjet recording apparatus 2 configured as described above will be described with reference to FIG. Image formation in the present embodiment is realized by the functions of the respective units as shown in FIG.
In the present embodiment, the control unit 30 is configured to realize the functions of the following units by software processing. However, the control unit 30 may be implemented by including a circuit for causing these units to function, a dedicated processor, and the like. Good.

  As shown in FIG. 4, the control unit 30 includes an ink amount limiting unit 301, an edge detection unit 302, a distortion correction unit 303, a shading correction unit 304, a primary gamma correction unit 305, a halftone processing unit 306, and a nozzle missing correction unit. 307, a conveyance direction correction unit 308, and an image formation processing unit 309. The control unit 30 converts the input image data into ejection image data that is image data for each of the recording heads 10, 12, 14, and 16, and then the ink amount limiting unit 301 and the edge detection unit 302 for each ejection image data. , The distortion correction unit 303, the shading correction unit 304, the primary gamma correction unit 305, the halftone processing unit 306, the nozzle missing correction unit 307, and the conveyance direction correction unit 308, and then the image forming processing unit The image forming process according to 309 is executed.

  The ink amount restriction unit 301 restricts the amount of ink of each color of YMCK. Specifically, for example, the ink amount restriction unit 301 sets the amount of ink of each color to a maximum of 400%, while maintaining the color reproduction accuracy to increase the amount of ink of each color to, for example, a maximum of 320%. Make corrections such as limiting. The degree of restriction of the amount of ink of each color can be arbitrarily set.

  The edge detection unit 302 generates Tag information for storing an edge part when performing halftone processing.

  The distortion correction unit 303 corrects image distortion caused by a difference in the number of nozzles per unit length. Details will be described later.

  The shading correction unit 304 corrects non-uniformity in density caused by a difference in ink discharge amount for each recording head, a bent flight of ink, a variation in ink discharge amount for each nozzle, and the like.

  The primary gamma correction unit 305 performs gamma correction for suppressing dot gain that occurs when halftone processing is performed.

  The halftone processing unit 306 performs halftone processing using an AM screen or FM screen.

  The nozzle missing correction unit 307 detects the ejection failure of the nozzle N and performs image data interpolation based on this.

  The transport direction correction unit 308 corrects landing deviation due to variations in ink ejection speed for each nozzle N.

  The image formation processing unit 309 forms an image on the recording medium 4 by controlling the recording heads 10, 12, 14, and 16 based on the image data that has been subjected to various corrections as described above.

  Next, correction area setting processing executed by the control unit 30 of the inkjet recording apparatus 2 configured as described above will be described with reference to FIG.

  First, the control unit 30 generates line chart image data as measurement image data (step S101).

  Specifically, the control unit 30 generates line chart image data CH as shown in FIG. The line chart image data CH has a predetermined line-by-line image (line image) extending in the Y direction, which is a direction perpendicular to the X direction that is the nozzle array direction, for each recording head 10, 12, 14, 16 of each color. This is image data formed at intervals of the number of nozzles (for example, 100). That is, the line chart image data CH forms a cyan line chart CC by the recording head 10, forms a magenta line chart CM by the recording head 12, and forms a yellow line chart CY by the recording head 14. This is data for forming a black line chart CK by the head 16. Each of the line charts CC, CM, CY, and CK is composed of two line images. That is, the line chart CC is composed of cyan line images LC1 and LC2. The line chart CM includes magenta line images LM1 and LM2. The line chart CY is composed of yellow line images LY1, LY2. The line chart CK includes black line images LK1 and LK2. The above-mentioned predetermined nozzle number interval can be set in the range of 2 ≦ predetermined nozzle number interval ≦ Y, where Y is the total number of nozzles in the nozzle row direction of one print head, but it is the minimum necessary for correction. From the viewpoint of acquiring information, it is sufficient if the accuracy is within a range where 0.5 to 1.5 pixels can be detected as the accumulated position error.

  After generating the line chart image data CH as described above, the control unit 30 controls the recording heads 10, 12, 14, 16 and outputs the line chart to the recording medium 4 (step S102).

  Subsequently, the control unit 30 reads a line chart formed on the recording medium 4 by the line sensor 18 (step S103).

  The control unit 30 executes an error determination process for determining an error based on the read line chart (step S104).

In the error determination process, first, a predetermined unit length and a reference nozzle number are obtained from a line image formed with each color of CMYK. Specifically, the interval between the line images is obtained for each line chart, the color having the largest interval is specified, and this is set as a predetermined unit length. At this time, the number of nozzles between the line images of the color becomes the reference nozzle number which is the reference nozzle number per predetermined unit length. Note that the number of reference nozzles may be smaller than this.
Subsequently, the number of nozzles per predetermined unit length obtained as described above is obtained for each color. Specifically, the number of nozzles per predetermined unit length can be determined for each color by comparing the predetermined unit length determined as described above with the interval between line images of other colors.
Then, an error between the number of nozzles per predetermined unit length obtained as described above and the number of reference nozzles is obtained for each color.
In this embodiment, the interval between the line images is obtained for each line chart, the color having the largest interval is specified, and this length is set as a predetermined unit length, and the nozzles between the line images of the color at this time The number is the reference number of nozzles. For example, the length between line images of the color with the largest interval is divided into a plurality, and the divided one length is set as a predetermined unit length, and the number of nozzles included in the predetermined unit length May be the reference number of nozzles. In this way, the error in the number of nozzles per predetermined unit length can be reduced, and the number of correction areas to be described later can be reduced. Further, a length obtained by multiplying the length between the line images of the color with the largest interval may be set as the predetermined unit length.

  Next, based on the error between the number of nozzles per predetermined unit length for each color and the number of reference nozzles obtained in the error determination process, the control unit 30 selects a correction area that is an area for inserting pixels in the ejection image data. Setting is performed (step S105). The correction area is set according to an error for each predetermined unit length. For example, in the discharge image data of a certain color, when the error between the number of nozzles per predetermined unit length and the number of reference nozzles is 3 nozzles, 3 locations are provided for each number of pixels corresponding to the number of nozzles per predetermined unit length. The correction area is set. As will be described later, one pixel is inserted in the X direction for each correction region set in this way.

  Next, the distortion correction process will be described with reference to FIG. The distortion correction process is a process executed by the distortion correction unit 303 in the control unit 30 functioning. This distortion correction processing is executed for each color of ejection image data.

  First, the control unit 30 determines whether or not the coordinates of a target pixel for determining whether or not to correct image data (hereinafter, may be referred to as a target pixel) is equal to or less than the maximum value in the Y direction (Y axis). Is determined (step S201). When the control unit 30 determines that the coordinate of the pixel of interest is less than or equal to the maximum value in the Y axis (step S201: Y), whether or not the coordinate of the pixel of interest is less than or equal to the maximum value in the X direction (X axis). Is determined (step S202). When the control unit 30 determines that the coordinate of the pixel of interest is equal to or smaller than the maximum value on the X axis (step S202: Y), whether or not the pixel of interest is within the correction region set as described above. Is determined (step S203).

  When the control unit 30 determines that the target pixel is within the range of the correction area (step S203: Y), the control unit 30 performs a correction process for inserting the pixel into the target pixel (step S204), and then performs an X of the target pixel. The coordinate of the axis is incremented by 1 (step S205), and the process of step S202 is executed. Details of the correction process will be described later. On the other hand, when the control unit 30 does not determine that the target pixel is within the range of the correction area (step S203: N), the control unit 30 executes the process of step S205 without executing the process of step S204.

  In addition, when the control unit 30 does not determine in step S202 that the coordinate of the target pixel is equal to or less than the maximum value on the X axis (step S202: N), the control unit 30 increments the Y axis coordinate of the target pixel by 1, After the X-axis coordinate is set to the origin position (step S206), the process of step S201 is executed.

  If the control unit 30 does not determine that the coordinate of the pixel of interest is equal to or less than the maximum value on the Y axis in step S201 after repeatedly executing the above-described processing (step S201: N), the control unit 30 ends this processing.

  In the present embodiment, pixel data can be inserted in the correction area as described above.

  Next, the correction process executed in step S204 of the distortion correction process will be described with reference to FIG.

First, the control unit 30 performs a mask process for applying a mask pattern to the ejection image data (step S301). This masking process is a process for determining a pixel correction position, which will be described later. Here, the “correction position” refers to the position of the pixel where the pixel is inserted. In the present embodiment, one mask pattern is applied to one correction region in the X direction. Specifically, the control unit 30 arranges a mask pattern P as shown in FIG. 9 continuously in the Y direction so as to match a predetermined coordinate on the X axis. The mask pattern P is pattern data formed in a matrix with 16 × 32 pixels as one unit, and only one dot indicating the correction position is defined in the nozzle row direction (X direction), and the correction position However, the pattern data is formed so as to have substantially even intervals in the 16 × 32 pixels (in the entire mask pattern P) without a cycle. In other words, the mask pattern is formed in a matrix having a plurality of pixels in the nozzle row direction and a direction perpendicular to the nozzle row direction, and the correction positions are defined. The mask pattern P is pattern data that approximates a blue noise pattern. Thus, in the present embodiment, the correction position can be determined so as not to be continuous in the direction (Y direction) perpendicular to the nozzle row direction (X direction) of the ejection image data. In the present embodiment, the pattern of the mask pattern P is different for each color of CMYK. For example, if the cyan mask pattern is as shown in FIG. 9, the magenta mask pattern is shifted by 4 pixels in the X direction, and the yellow mask pattern is shifted by 8 pixels in the X direction. Suppose that the black mask pattern is shifted by 12 pixels in the X direction. Thus, in the present embodiment, the correction position can be determined so that the position differs for each recording head.
In the present embodiment, it is possible to suppress the occurrence of moire patterns due to periodicity by configuring the mask pattern P as described above.
The mask pattern applicable in the present embodiment may be pattern data that approximates noise of other colors such as white noise, as long as only one dot is formed in the X direction. Further, it may be pattern data having regularity.
In addition, the size of the mask pattern applicable in the present embodiment can be set as appropriate.

  Next, the control unit 30 determines whether or not the coordinate of the target pixel is a position where a dot is made in the mask pattern P (step S302). When the control unit 30 determines that the coordinate of the target pixel is a position where a dot is made in the mask pattern P (step S302: Y), the control unit 30 executes a pixel insertion process (step S303). Specifically, the control unit 30 shifts each pixel on the right side in the X direction from the coordinate of the target pixel by one pixel to the right, and inserts the pixel into the coordinate of the target pixel. As a pixel to be inserted, a pixel adjacent to the left side in the X direction is applied as it is (nearest neighbor). Note that the method of generating a pixel to be inserted is not limited to the nearest neighbor described above, and various methods such as obtaining a pixel value by a bilinear method, a bicubic method, or the like can be applied.

  The control unit 30 determines whether or not the target pixel is an edge portion (step S304). When the control unit 30 determines that the target pixel is an edge portion (step S304: Y), the control unit 30 performs a filtering process for smoothing the pixel (step S305), and then ends this process. For example, a median filter is suitable for the filter processing, but is not limited thereto. On the other hand, when the control unit 30 does not determine that the pixel of interest is an edge portion (step S304: N), this process ends without executing the process of step S305.

  Further, when the control unit 30 does not determine in step S302 that the coordinate of the target pixel is the position where the hit point is performed in the mask pattern P (step S302: N), the process ends.

  Next, an application example of this embodiment will be described.

In the example shown in FIG. 10, the number of nozzles in the unit length T is such that 20 nozzles are arranged in the recording head 12, whereas 21 nozzles are arranged in the recording head 10.
In this case, when an image is formed by ejecting ink droplets from each nozzle without applying the present invention, the image formed by the recording head 10 is reduced by one nozzle to the left of the image formed by the recording head 12. Appear. As a result, color misalignment or the like occurs between the image formed by the recording head 10 and the image formed by the recording head 12, and the image quality is degraded.
On the other hand, according to the present embodiment, for example, as shown in FIG. 11, each pixel on the right side in the X direction is shifted by one pixel in the right direction from the ninth as described above. The pixel is inserted into the pixel. As the pixel to be inserted, the pixel adjacent to the left side in the X direction, that is, the eighth pixel is applied as it is.
Then, the image formed by the recording head 10 is enlarged by one nozzle on the right side, and color misregistration is reduced.

The unit length T described above can be set to a length that satisfies a range of 2 ≦ T ≦ Y, where Y is the total number of nozzles in the nozzle row direction of one recording head. Setting in accordance with the nozzle pitch between the nozzles in a certain X direction is preferable from the viewpoint of reducing color misregistration. For example, when the nozzle pitch in the X direction, which is the nozzle row direction, is 20 μm, the position error is corrected in units of 20 μm by inserting or deleting one pixel, so the error of each nozzle pitch in the recording head is accumulated to 20 μm. By setting the unit length T to be such that the position error can be further reduced. Therefore, in the above-described embodiment, an example in which the unit length T is 20 nozzles is shown. However, for example, when using a recording head whose position error per nozzle pitch is known to be ± 0.2 μm, Color misregistration can be further reduced by setting the unit length T to 100 nozzles that are considered to have an accumulated positional error of 20 μm.
Further, in the present embodiment, as described above, the image is enlarged in the X direction by the method of inserting the pixels into the ejection image data to reduce the color misregistration. It is also possible to reduce the color misregistration by reducing the image in the X direction by deleting the image.

  Specifically, first, in the correction area setting process described above, after obtaining the interval between the line images for the line chart formed on the recording medium 4, the color with the smallest interval is specified, and this is determined in a predetermined unit. Long. At this time, the number of nozzles between the line images of the color becomes the reference number of nozzles per predetermined unit length (step S104 in FIG. 5). Note that the number of reference nozzles may be larger than this.

  Then, based on the error between the number of nozzles per predetermined unit length for each color and the number of reference nozzles, a region for deleting pixels in the ejection image data is set as a correction region (step S105 in FIG. 5).

  Thereafter, in a correction process (step S204 in FIG. 7) in the distortion correction process, a pixel deletion process is performed instead of the pixel insertion process (step S303 in FIG. 8). Specifically, the pixel in the target pixel is deleted, and each pixel on the right side in the X direction from the coordinate of the target pixel is shifted by one pixel.

  Next, application examples of the above-described embodiment will be described.

According to the embodiment described above with respect to the nozzle arrangement mode shown in FIG. 10, for example, as shown in FIG. 12, the eighth pixel is deleted, and each pixel on the right side in the X direction from the pixel. That is, the ninth and subsequent pixels are shifted leftward by one pixel.
Then, the image formed by the recording head 12 is reduced by one nozzle on the left side, and color misregistration is reduced.

  As described above, according to the present embodiment, the inkjet recording apparatus 2 is configured so that the recording heads 10, 12, 14, and 16 having nozzle rows in which a plurality of nozzles N are arranged at predetermined intervals are the nozzle row direction. A plurality of print heads arranged in the vertical direction are converted into discharge image data for each of the recording heads 10, 12, 14, 16, and the plurality of recording heads 10, 12 are transferred according to the discharge image data while transporting the recording medium 4. , 14 and 16, ink is ejected from the nozzles N to form an image on the recording medium 4. The control unit 30 specifies the number of nozzles per predetermined unit length in the nozzle row direction for each of the plurality of recording heads 10, 12, 14, and 16. The control unit 30 calculates the error between the reference number of nozzles and the number of nozzles per predetermined unit length for each of the plurality of recording heads 10, 12, 14, 16 using the reference number of nozzles per predetermined unit length as the reference nozzle number. To do. The control unit 30 corrects the ejection image data by inserting or deleting pixels in accordance with the calculated error in the number of nozzles. As a result, color misregistration caused by the difference in the number of nozzles per unit length can be reduced by adjusting the image by enlarging or reducing in the nozzle row direction.

  Further, according to the present embodiment, the control unit 30 includes the number of nozzles per predetermined unit length of the recording head having the smallest number of nozzles per predetermined unit length among the plurality of recording heads 10, 12, 14, and 16. An error between this reference nozzle number and the number of nozzles per predetermined unit length for each of the plurality of recording heads 10, 12, 14, and 16 is calculated with the following nozzle number as the reference nozzle number. The control unit 30 corrects the ejection image data by inserting pixels in accordance with the calculated error in the number of nozzles. As a result, color misregistration can be reduced only by correction by inserting pixels into the ejection image data.

  Further, according to the present embodiment, the control unit 30 includes the number of nozzles per predetermined unit length of the recording head having the largest number of nozzles per predetermined unit length among the plurality of recording heads 10, 12, 14, and 16. Using the above number of nozzles as the reference nozzle number, an error between this reference nozzle number and the number of nozzles per predetermined unit length for each of the recording heads 10, 12, 14, 16 is calculated. The control unit 30 corrects the ejection image data by deleting pixels according to the calculated error in the number of nozzles. As a result, color misregistration can be reduced only by correcting the ejection image data by deleting pixels.

  Further, according to the present embodiment, the control unit 30 inserts or deletes pixels so that the correction positions are different for each of the recording heads 10, 12, 14, and 16. As a result, it is possible to suppress deterioration in image quality caused by the correction positions matching between colors.

  Further, according to the present embodiment, the control unit 30 inserts or deletes pixels so as not to be continuous in a direction perpendicular to the nozzle row direction of the ejection image data. As a result, it is possible to reduce deterioration in image quality due to the appearance of regular images such as streak irregularities in the corrected ejection image data.

  Further, according to the present embodiment, the control unit 30 has a plurality of pixels in the nozzle row direction and a direction perpendicular to the nozzle row direction, and is formed in a matrix, and insertion or deletion of pixels is performed. The position where the pixel is inserted or deleted is determined by performing mask processing on the ejection image data using the mask pattern in which the position where the pixel is performed is defined. As a result, the correction position can be easily determined, so that the processing efficiency is improved.

  Further, according to the present embodiment, the mask pattern defines only the position where one pixel is inserted or deleted in the nozzle row direction, and the position where the pixel is inserted or deleted is the entire mask data. Since the pattern data is formed so as to have substantially uniform intervals without a period, the dot positions of the mask pattern are evenly distributed, so that the correction positions in the discharge image data are well distributed and the correction is good. Can be made to do.

  The description in the embodiment of the present invention is an example of the ink jet recording apparatus according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of each functional unit constituting the ink jet recording apparatus can be appropriately changed.

  In the present embodiment, an example of an ink jet recording apparatus capable of performing image formation by a so-called line head method in which image formation is performed only by transporting a recording medium has been described. For example, as illustrated in FIG. The recording heads of the respective colors described above are mounted side by side in the X direction, the recording medium is conveyed in the Y direction, and the carriage 504 is conveyed in the direction orthogonal to the recording medium conveyance direction (X direction). In addition, it can also be employed in the ink jet recording apparatus 2A that ejects ink from above. The recording head has a nozzle row in which a plurality of nozzles are arranged at predetermined intervals, and the nozzle row direction is parallel to the conveyance direction of the recording medium.

  In this embodiment, either one of pixel insertion and deletion is performed on the ejection image data. However, both pixel insertion and deletion may be performed simultaneously.

  In this embodiment, the pixel correction position is determined so that the position is different for each print head (color). However, the pixel correction position may be the same between the print heads.

  In this embodiment, the correction position is determined so as not to be continuous in the direction (Y direction) perpendicular to the nozzle row direction of the ejection image data. However, the correction position is set to be continuous in the Y direction. Also good.

  In this embodiment, the correction position is determined using the mask pattern. However, the correction position may be determined by performing a predetermined calculation, for example, without using the mask pattern.

  In the present embodiment, a line sensor 18 is provided to read a line image formed by the recording heads 10, 12, 14, and 16, and based on this, image formation between the recording heads 10, 12, 14, and 16 is performed. Although the position error is specified, the line sensor is not provided and the line image is read by a reading device separate from the ink jet recording apparatus 2, and the error in the image forming position between the recording heads 10, 12, 14, and 16 is detected. The result may be specified and the result may be input to the inkjet recording apparatus 2.

  In the present embodiment, a line chart composed of two line images is output, the number of nozzles per predetermined unit length is obtained for each recording head, and pixels are inserted or deleted based on this. A line image is formed for each predetermined number of nozzles, the number of nozzles per predetermined unit length is obtained for each line image, and pixels are inserted or deleted for each corresponding region between the line images based on this. You may do it. In this way, it is possible to cope with a case where the nozzle interval varies depending on the position.

  In the present embodiment, an example in which a hard disk, a semiconductor nonvolatile memory, or the like is used as a computer-readable medium of the program according to the present invention is disclosed, but the present invention is not limited to this example. As another computer-readable medium, a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data according to the present invention via a communication line.

2 Inkjet recording device 4 Recording medium 10, 12, 14, 16 Recording head 30 Control unit N Nozzle P Mask pattern

Claims (7)

A plurality of recording heads each having a nozzle array in which a plurality of nozzles are arranged at predetermined intervals are arranged in a direction perpendicular to the nozzle array direction, and the input image data is converted into ejection image data for each recording head, and recording is performed. In an inkjet recording apparatus that forms an image on a recording medium by ejecting ink from each nozzle of the plurality of recording heads according to the ejection image data while conveying the medium.
The number of nozzles per predetermined unit length in the nozzle row direction is specified for each of the plurality of recording heads, and the number of reference nozzles per predetermined unit length is defined as the reference nozzle number, and the reference nozzle number and the plurality of recording heads. And a controller that corrects the ejection image data by calculating an error from the number of nozzles per predetermined unit length and inserting or deleting pixels according to the calculated nozzle number error. Inkjet recording apparatus.   The control unit includes the number of nozzles that is equal to or less than the number of nozzles per predetermined unit length of the recording head having the smallest number of nozzles per predetermined unit length among the plurality of recording heads as the reference nozzle number and the reference nozzle number. An error with the number of nozzles per predetermined unit length for each of the plurality of recording heads is calculated, and the ejection image data is corrected by inserting pixels according to the calculated error in the number of nozzles. The ink jet recording apparatus according to claim 1.   The control unit includes the number of nozzles that is equal to or larger than the number of nozzles per predetermined unit length of the recording head having the largest number of nozzles per predetermined unit length among the plurality of recording heads as the reference nozzle number, An error from the number of nozzles per predetermined unit length for each of the plurality of recording heads is calculated, and the ejection image data is corrected by deleting pixels according to the calculated error in the number of nozzles. The ink jet recording apparatus according to claim 1.   The ink jet recording apparatus according to claim 1, wherein the control unit inserts or deletes pixels so that a correction position is different for each recording head.   5. The inkjet according to claim 1, wherein the control unit inserts or deletes pixels so as not to be continuous in a direction perpendicular to the nozzle row direction of the ejection image data. 6. Recording device.   The control unit includes a plurality of pixels in the nozzle row direction and a direction perpendicular to the nozzle row direction, and is formed in a matrix, and mask data in which positions where pixels are inserted or deleted are defined. The inkjet recording apparatus according to claim 5, wherein a position at which a pixel is inserted or deleted is determined by performing mask processing on the ejection image data using an image.   In the mask data, only the position for inserting or deleting one pixel is defined in the nozzle row direction, and the position for inserting or deleting the pixel does not have a period in the entire mask data, The ink jet recording apparatus according to claim 6, wherein the ink jet recording apparatus is pattern data formed to have substantially uniform intervals.

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