JP2006051677A - Image recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent variation in the amount of ink droplets in each recording element in an image recording apparatus in which a recording unit in the arrangement direction is improved by arranging a head unit in which a plurality of recording elements are arranged in a direction perpendicular to the arrangement direction To reduce the resulting density unevenness.
Image data is recorded on a recording medium using a recording head in which two or more recording head units in which a plurality of recording elements are arranged are connected in a direction perpendicular to the arrangement direction of the recording elements. The recording head drive units 58 and 59 for driving the plurality of recording elements of the recording head in accordance with the recording head and recording an image on a recording medium with different ink droplet amounts for each recording head unit, and recording by the recording head unit Obtained by the ejection characteristic table 510 in which the recording characteristics for each element are recorded, the density unevenness determination processing section for determining the density on the recording surface based on the head characteristics table, the head characteristics table, and the density unevenness determination processing section. The image recording apparatus includes an image processing unit 52 including a process for performing density unevenness correction processing based on the determination result.
[Selection] Figure 7

Description

  The present invention relates to an on-demand type image recording apparatus, for example.

  As an image recording apparatus, for example, an on-demand type inkjet recording apparatus is known. In such an ink jet recording apparatus, it is important to increase the speed. As the number of recording elements of the ink jet head increases, high-speed printing becomes possible. As a technique for increasing the number of recording elements, there is a technique in which a plurality of head units having a large number of recording elements are integrally arranged so that the arrangement of the recording elements is substantially parallel to form one long recording head. is there. And, by making the length of the head correspond to the width of the recording paper, it becomes a line head, and high-speed printing can be realized.

  The head unit will be described with reference to FIG. As shown in the figure, the head unit includes a recording element portion 2 provided with a large number of ink chambers 1, a main body portion 4 provided with a common ink chamber 3 for supplying ink to each ink chamber 1, and ink in the common ink chamber 3. Ink supply path 5 is provided, and by applying a volume variation in ink chamber 1, ink droplets are ejected from recording element 6 of ink chamber 1 to perform dot printing. Ink consumed in the ink chamber 1 is replenished from the common ink chamber 3.

  As a control method for giving a volume variation in the ink chamber 1, there are a piezoelectric control method using distortion deformation of a piezoelectric member, a thermal control method using heat generation of a heating element, and the like. Printing can be performed on demand by arbitrarily giving a volume fluctuation to each ink chamber 1 by such a control method.

  An ink jet recording apparatus is known in which density unevenness due to variation in ink discharge volume from the ink discharge port at the end of each bed unit is reduced to improve recording quality (see, for example, Patent Document 1). ).

Furthermore, there is known an image recording apparatus that can obtain a high-quality image by reducing the density unevenness of the joints caused by the phase difference of the array of recording elements between adjacent recording heads (see, for example, Patent Document 2). ).
JP 2000-79707 A JP 2003-285434 A

  However, when a head unit having a large number of recording elements is used, it is ideal that the output characteristics of each of the plurality of recording elements are uniform. However, variations in manufacturing and pressure fluctuations in the ink chamber 1 during the ink ejection operation may occur. The ejection volume of ink increases or decreases due to variations in propagation and the like. When the ink ejection volume fluctuates in this way, the output characteristics vary, resulting in uneven density in the recorded image.

 In particular, when line printing (that is, one-pass printing) is performed in an image recording apparatus in which a plurality of such head units are arranged and a line head is formed, density unevenness, gradation deterioration, etc. for each recording element or each head unit. Degradation of image quality appears remarkably, and it is very difficult to correct it.

  By the way, the ejection characteristics of each head unit are investigated in advance, the ejection characteristics are stored as a table in a control memory or the like in the apparatus, and the input image is corrected according to the characteristics to perform the above correction process. It is possible to improve image quality deterioration such as density unevenness and gradation deterioration to some extent.

 However, when a uniform image is printed at a high density (the area where dots are buried is large), a density drop occurs in a part of an area of a certain head unit. This is because there is no method that can sufficiently compensate for the decrease in density.

  The present invention has been made in view of the above points, and its object is to increase the recording resolution in the arrangement direction by arranging a head unit in which a plurality of recording elements are arranged in a direction perpendicular to the arrangement direction. An object of the present invention is to provide an image recording apparatus capable of reducing density unevenness caused by variation in the amount of ink droplets of each recording element.

  The invention according to claim 1 is an image recording apparatus that performs recording on a recording medium using a recording head in which two or more recording head units in which a plurality of recording elements are arranged are connected in a direction perpendicular to the arrangement direction of the recording elements. A recording head driving unit that drives a plurality of recording elements of the recording head according to image data and records an image on a recording medium with a different amount of ink droplets for each recording head unit; and A discharge characteristic table for recording discharge characteristics for each recording element; a density unevenness determination processing unit for determining density on a recording surface based on the discharge characteristics for each recording element recorded in the head characteristic table; and the head characteristic table. And an image processing unit including a process for performing density unevenness correction processing based on the determination result obtained by the density unevenness determination processing unit. That.

 According to a second aspect of the present invention, the pitch of the recording elements of the plurality of recording head units according to the first aspect is set so as to be shifted from each other.

According to a third aspect of the present invention, the recording head driving unit according to the first aspect controls the amount of ink droplets ejected from the plurality of recording head units so that dots are adjacent to each other and no blank portion is generated. The invention according to claim 4 is characterized in that the density unevenness determination processing unit according to claim 1 corrects density unevenness from discharge characteristics recorded in a discharge characteristic table provided for each of a plurality of recording head units. The invention according to claim 5 is characterized in that the density is determined with respect to the density unevenness determination area determined by the density unevenness determination processing unit based on the discharge characteristics recorded in the discharge characteristic table according to claim 1. Unevenness correction is performed.

 According to a sixth aspect of the invention, the image processing unit according to the first aspect performs density unevenness correction on the density unevenness determination area determined by the density unevenness determination processing unit based on the discharge characteristics recorded in the discharge characteristic table. When performing, correction is performed on a recording element to be corrected or a recording element in the vicinity thereof.

  As described above in detail, according to the present invention, recording is performed on a recording medium using a recording head in which two or more recording head units in which a plurality of recording elements are arranged are connected in a direction perpendicular to the arrangement direction of the recording elements. In the image recording apparatus to perform, a plurality of recording elements of the recording head are driven according to image data, and a recording head driving unit that records an image on a recording medium with a different ink droplet amount for each recording head unit is provided. Based on information in the head characteristic table provided in advance, the density unevenness generated in the head can be corrected by performing correction processing on the recording element to be corrected or a recording element in the vicinity of the recording element. An image recording apparatus capable of recording a quality image can be provided.

    Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For example, an ink jet recording apparatus will be described as an example of the image recording apparatus.

  FIG. 1 is a diagram illustrating a configuration of the entire inkjet recording apparatus. In the figure, reference numeral 11 denotes a main body case 11. A drum 12 that rotates in a direction indicated by an arrow in the figure is provided in the case main body 11 and is a recording medium that is a recording medium fed to the drum 12 via paper feed rollers 13 and 14. The medium 15 is wound around.

  A paper feed cassette 16 is provided at the bottom of the main body case 11. The recording medium 15 placed on the placement plate 17 of the paper feed cassette 16 is taken out one by one by a feed roller 18 and fed to the paper feed rollers 13 and 14. Further, the recording medium 15 manually fed from the manual feed tray 19 attached to the side of the main body case 11 so as to be freely opened and closed is fed to the feeding rollers 13 and 14 via the feeding roller 20. Switching between feeding by the feeding roller 18 and feeding by the feeding roller 20 is performed by a feeding switching means 21.

  A charging roller 22 is disposed on the drum 12 so as to oppose the recording medium 15 fed from the paper feeding rollers 13 and 14 to the drum surface. In addition, an ink jet recording head (recording head portion) 23 in which a large number of recording elements are arranged in a line shape is movable on the drum 12 in the direction of the rotation axis of the drum 12, which is the direction in which the recording elements of the recording head 23 are arranged. The printing mechanism 24 arranged in the above is opposed to the printing mechanism 24. Accordingly, the recording medium 15 is conveyed in a direction substantially orthogonal to the arrangement direction of the recording elements of the ink jet recording head 23 by the rotation of the drum 12.

  As shown in FIG. 3, the ink jet recording head unit 23 includes three recording head units 231, 232, and 233 having substantially the same recording characteristics in which a large number of recording elements a are arranged at a predetermined pitch. The recording head unit 232 is bonded to both sides of the recording head unit 232 at the center on one side and the recording head units 231 and 233 are attached to the end sides on the other side. The positional relationship between the recording head unit 232 and the recording head units 231 and 233 is such that all the recording elements are arranged at equal distances. Here, the recording head unit is composed of three recording heads, but the present invention is not limited to this.

  The recording elements of the recording head units 231 and 233 and the recording element a of the recording head unit 232 do not line up in a straight line with respect to the line direction. By controlling the ink discharge timing, control is performed so that the same printing result as that when the recording elements a of the recording head units 231, 232, 233 are arranged on a straight line is obtained.

Further, as shown in FIG. 5, the recording head units 231, 232, and 233 shown in FIG. 3 are arranged in the direction in which the recording elements are arranged on the recording surface in the direction perpendicular to the arrangement direction of the recording elements a. The arrangement is such that the recording resolution is increased. That is, the recording head unit 231 has a configuration in which the recording head units 231a and 231b are stacked. The recording head unit 231b is laminated with a deviation of a half pitch of the recording element from the recording head unit 231a. Similarly,
The recording head unit 232 has a configuration in which recording head units 232a and 232b are stacked. The recording head unit 232b is stacked with a deviation of a half pitch of the recording element from the recording head unit 232a. Further, the recording head unit 233 has a configuration in which recording head units 233a and 233b are stacked. The recording head unit 233b is stacked with a deviation of a half pitch of the recording element from the recording head unit 233a.

  Returning to FIG. 1, the printing mechanism 24 includes a reciprocating mechanism 25 on which an ink jet recording head 23 is mounted, a motor unit 26 having a reciprocating rod and a linear motor, and advancing / retreating means 27. 27, the ink jet recording head 23 is moved back and forth with respect to the drum 12, and the motor unit 26 controls the reciprocation mechanism 25 to move in the direction of the rotation axis of the drum 12. It is designed to reciprocate in the direction.

  The drum 12 is provided with a peeling claw 28 that can be inserted between the drum surface and the recording medium 15, and the recording medium 15 peeled off by the peeling claw 28 is discharged by a recording medium discharge / conveyance mechanism 29. It has become. The recording medium discharging / conveying mechanism 29 includes a belt conveyor 30 that contacts the non-recording surface of the recording medium 15 and a pressing unit 31 that presses the recording medium 15 against the surface of the belt conveyor 30.

  A discharge roller 32 is disposed on the upper side of the main body case 11 so as to discharge the recording medium 15 conveyed by the belt conveyor 30 to the outside of the main body case 11. In the main body case 11, a main motor 33 that rotates and drives each part, an ink cassette 34 that serves as an ink supply source, an ink buffer 35 that temporarily stores ink from the ink cassette 34, and ink in the ink buffer 35 An ink supply tube 36 to be supplied to the ink jet recording head 23 is accommodated.

  In the ink jet recording apparatus, for example, the recording medium 15 is taken out from the paper feed cassette 16 by the paper feed roller 18 and sent to the paper feed rollers 13 and 14 at the time of printing. The recording medium 15 is fed and wound around the rotating drum 12 by the paper feed rollers 13 and 14. The recording medium 15 is attracted to the surface of the drum 12 by the charging roller 22.

  As the drum 12 rotates, the recording medium 15 moves in a direction (Y) perpendicular to the arrangement direction (X) of the recording elements of the recording head 23 as shown in FIG. Image recording is performed by selectively ejecting ink to the recording medium 15 at a predetermined timing based on the image signal.

  Next, a recording head driving unit that drives a plurality of recording elements of the recording head unit according to image data according to the present invention and records an image on a recording medium with a different ink droplet amount for each recording head unit. explain.

 Conventionally, the amount of ink droplets is determined by recording resolution, ink properties, and properties of a recording medium such as paper. In general, assuming that ink is ejected from all the recording elements, it is desirable that the dots formed on the recording surface are large enough to cover the recording surface. If the dots formed on the recording surface are smaller than the size that covers the recording surface, a problem of density reduction occurs. In addition, if the dots formed on the recording surface are too large to cover the recording surface, there is a possibility that bleeding may occur due to an excessive amount of ink.

 In the present invention, the ink droplet amount is such that the dot shape is in a range that does not cause the above problem, and the ink droplet amount ejected from the recording element of each recording head unit of the recording head unit is different.

  6A shows the size of dots formed on the recording surface by the ink ejected from the recording element of the recording head unit 231a, 232a, 233a (see FIG. 4) in the recording heads 231, 232, 233. FIG. . When the maximum recording resolution is D [dpi], the length d between adjacent pixels is d = 25.4 / D, and the dot size is a design value of d * √2. When ink is ejected from all the recording elements of the recording head at this size, the recording surface is completely filled with dots.

 FIG. 6B shows the size of dots formed on the recording surface by the ink ejected from the recording elements of the recording head units 231b, 232b, and 233b (see FIG. 4) in the recording heads 231, 232, and 233. The dot size d ′ has a design value of d ′> d * √2. When ink is ejected from all the recording elements of the recording head at this size, the recording surface is fully filled with dots. That is, the dot diameter d ′ discharged from the recording head units 231b, 232b, and 233b is set to be larger than that of the recording head units 231a, 232a, and 233a.

  Next, the control unit of the ink jet recording apparatus will be described with reference to FIG. In FIG. 7, 51 is a CPU (central processing unit). The CPU 51 is connected to a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, an input / output (I / O) port 54, and an interface (I / F) 55.

 The CPU 51 implements various operations such as a printing operation and a maintenance process by executing program data and the like for controlling each unit stored in the ROM 52.

 The RAM 53 is provided with a memory area and the like used for various data processing executed by the CPU 51.

 Each device described later is connected to the I / O port 54. A host computer 56 is connected to the I / F 55 via a communication cable.

  The CPU 51 and the ROM 52, RAM 53, I / O port 54, and I / F 55 are electrically connected by a bus line 57 such as a control bus, a system bus, and a data bus.

  In the RAM 53, an image processing parameter area 53a for temporarily storing a table and a program necessary for image processing for converting an input recording image into an image optimal for the image recording apparatus, and ejection of each recording head unit. A discharge characteristic area 53b for temporarily storing characteristics read from the discharge characteristic table of each recording head unit, a temporary storage of a correction area calculation program, and a recording element to be subjected to density correction based on the discharge characteristics are determined. A correction area 53c for storing the area, an input image for recording, an image processing program, and an input / output image area 53d for storing an output image converted into an image optimal for the image recording apparatus by the correction processing program; Receive buffer 53e for temporarily receiving print data from the host computer 56 It is provided.

  The I / O port 54 includes an a head driver (recording head driving unit) 58 that drives an ink chamber of the recording head units 231a, 232a, and 233a (hereinafter also collectively referred to as recording head unit a), and the recording. Drives the head driver (recording head drive unit) 58 that drives the ink chambers of the head units 231b, 232b, and 233b (hereinafter collectively referred to as the recording head unit b), the drum 12, the paper feed rollers 13 and 14, and the like. A motor driver 511d for controlling the conveyance motor 511, a power switch 512, a temperature / humidity sensor 515 for detecting the temperature / humidity in the vicinity of the inkjet recording head 23, and an input unit 517 for setting various flags are connected. The I / O port 54 is connected to a maintenance mechanism 514 that is driven during maintenance of the inkjet recording head 23 and a maintenance driver 513 that controls the maintenance mechanism 514.

  Connected to the bus line 57 are an ejection characteristic table 510 storing the ejection characteristics of each recording head unit and an image processing parameter table 514. For example, the ejection characteristic table 510 includes ejection characteristic tables Tbl1 and Tbl2 that store the ejection characteristics of the recording head units 231a and 231b, respectively. Similarly, ejection characteristic tables are provided for the recording head units 232a, 232b, 233a, and 233b.

  Next, density unevenness determination processing for determining an area for correcting density unevenness will be described with reference to the flowchart of FIG. In the present embodiment, density unevenness determination processing is divided into two stages. The first stage is defined as discrimination process 1, and the second stage is defined as discrimination process 2.

  First, the discrimination process 1 will be described with reference to the flowchart of FIG. First, initialization processing (counter i is set to 0) is performed (ST1).

  Next, a process of inputting real values of the array to Y1_i and Y2_i from the addresses associated with the counters from the discharge characteristic tables Tbl1 [i] and Tbl2 [i] stored in the discharge characteristic table 510 is performed (ST2). Here, Tbl1 and Tbl2 are, for example, tables in which the ejection characteristics of the recording head units 231a and 231b are stored, and Tbl1 [i] and Tbl2 [i] are the i-th recording elements of the respective recording head units. Indicates the discharge characteristic value.

  Then, it is determined whether or not the real value Y1_i is included in the predetermined lower threshold Y1_Lth and the upper threshold Y1_Uth. That is, it is determined whether the real value Y1_i is smaller than the lower threshold Y1_Lth or smaller than the upper threshold Y1_Uth. The lower limit threshold Y1_Lth and the upper limit threshold Y1_Uth are as shown in FIG.

  When the determination of ST3 is “NO”, that is, when the real value Y1_i is included in the threshold values of the lower limit threshold value Y1_Lth and the upper limit threshold value Y1_Uth, 0 (ST6) is set in the flag table Tbl1_flag [i], and the real value Y1_i is set. If it is outside the threshold values of the lower limit threshold value Y1_Lth and the upper limit threshold value Y1_Uth, 1 is inserted (ST4).

  Next, a process for determining whether or not the real value Y2_i is included in the predetermined lower limit threshold Y2_Lth and the upper limit threshold Y2_Uth is performed (ST5). When the determination of ST5 is “NO”, that is, when the real value Y1_i is included in the threshold values of the lower limit threshold value Y2_Lth and the upper limit threshold value Y2_Uth, 0 (ST7) is set in the flag table Tbl2_flag [i], and the real value Y1_i is set. If it is outside the threshold values of the lower threshold Y2_Lth and the upper threshold Y2_Uth, 1 is set in the flag table Tbl2_flag [i] (ST8).

  As soon as the processes of ST2 to ST8 are completed, the counter i is incremented by 1 in ST9, and the processes of ST2 to 8 are repeated until the counter i exceeds a specified value N (the number of recording elements of the head unit).

  FIG. 10 is a schematic diagram of the discrimination process 1. A flag is set to “1” for a printing element having ejection characteristics exceeding the upper thresholds Y1_Uth and Y2_Uth, or a printing element having ejection characteristics below the lower thresholds Y1_Lth and Y2_Lth, and is subject to density unevenness correction.

  Next, the discrimination process 2 will be described with reference to the flowchart of FIG.

  First, the counter i is set to 0 and initialization processing is performed (ST11).

  Next, the displacement counter j is set to 1 (ST12). The displacement counter j is a counter used when the displacement from the ejection characteristic Tbl1 [i] of the i-th recording element to the ejection characteristic Tbl [i + j] of the recording element at the j-th position is targeted.

 Then, the ejection characteristics of the i-th recording element of each recording head unit are input to Y1_i and Y2_i. Further, the ejection characteristics of the j-th recording element from the i-th recording element are input to Y1_i + j and Y2_i + j (ST13).

 Next, ΔY1_ij and ΔY2_ij are calculated as the displacement amounts of the ejection characteristics of the i-th printing element and the j-th printing element (ST14).

  Next, it is determined whether or not the ejection characteristic displacement amount ΔY1_ij is larger than a displacement amount threshold value Δy1th [j] (ST15). Here, the displacement amount threshold value is a threshold value that can identify whether or not the displacement between a certain printing element and the j-th printing element from the printing element is visually expressed as density unevenness, and exceeds this threshold value. If it falls, the area is determined as uneven density, and if it falls below, it is determined that there is no uneven density.

  If “YES” in ST15, that is, if it is determined that the displacement amount exceeds the threshold value, 1 is set in the flag tables Tbl1_flag [i] and Tbl1_flag [i + j] (ST16).

On the other hand, if “NO” in the determination in ST15, that is, if it is determined that the displacement amount has fallen below the threshold value, the process in ST16 is skipped.

  Similarly, it is determined whether or not the ejection characteristic displacement amount ΔY2_ij is larger than the displacement amount threshold value Δy2th [j] (ST17).

 If “YES” in ST17, that is, if it is determined that the displacement amount exceeds the threshold value, 1 is set in the flag tables Tbl2_flag [i] and Tbl2_flag [i + j] (ST18). On the other hand, if “NO” is determined in ST17, that is, if the amount of displacement is less than the threshold value, the process of ST18 is skipped.

  When “NO” is determined in ST15 and ST17 described above, or when the processing of ST16 and ST18 is finished, the displacement counter j is incremented by 1 (ST19).

  Then, it is determined whether or not the displacement counter j is greater than a specified value M (ST20). While it is determined “NO” in ST20, the processes after ST13 are repeated.

  By the way, if it is determined as “YES” in ST20, the counter i is incremented by 1 (step S21).

  Then, it is determined whether the value of the counter i is larger than the above-mentioned specified value N (ST22). If it is determined “NO” in ST22, the processes in and after step S12 are repeated. On the other hand, if “YES” is determined in ST22, the series of processing ends.

 FIG. 12 is a schematic diagram of the discrimination process 2 described above. That is, when the difference in ejection characteristics between a certain printing element and an adjacent printing element exceeds a threshold value, it is considered that the density fluctuation is large, and both printing elements are targeted for density unevenness correction. Eventually, the recording elements that are flagged at the stage when the discrimination process 1 and the discrimination process 2 are finished are subjected to density unevenness correction.

  Next, image processing including density correction processing for the determined correction area will be described with reference to the block diagram of FIG.

  FIG. 13 is a block diagram showing a configuration example of an image processing program including density unevenness correction processing stored in the ROM 52. As shown in the figure, the image processing program including density unevenness correction processing includes a color conversion processing unit 81, UCR processing unit 82, gradation correction unit 83, pseudo halftone processing unit 84, and density unevenness correction processing unit 85.

  For example, a standard RGB color signal input on an 8-bit monitor for each color or the like is converted into CMY colors which are color reproduction colors in the printer in the color conversion processing unit 81. Next, in the UCR processing unit 82, the black component is extracted from the CMY colors, the subsequent CMY colors are determined, and finally converted to CMYK colors. Next, the gradation correction unit 83 performs correction according to the actual output characteristics of the printer.

 Next, the pseudo halftone processing unit 84 converts the image signal of one pixel into either ON or OFF, that is, a 1-bit binary image signal for each color, and outputs it. Finally, the density unevenness correction processing unit 85, which is a feature of the present invention, corrects the binary image signal.

  In connection with the present invention, as one of the points to be focused on, the image recording apparatus of the present invention is an ink droplet ejected from the recording elements of the recording head unit arranged in a direction perpendicular to the arrangement direction of the recording elements. It is mentioned that it is a recording apparatus from which quantity differs.

 When the same image processing is performed on the recording head units 231a, 232a, 233a and 231b, 232b, 233b, according to the present invention, the ink droplet amounts of the recording head units 231b, 232b, 233b are 231a, 232a, 233a. Since it exceeds the ink droplet amount, dots of different sizes are alternately arranged as shown in FIG. In view of this, the image signals input to the recording head units 231a, 232a, and 233a are corrected for different dot sizes. As an example, correction processing for the gradation correction processing unit 83 is shown below.

  FIG. 15A shows a gradation correction table for the recording head units 231a, 232a, and 233a, and FIG. 15B shows a gradation correction table for the recording head units 231b, 232b, and 233b. In this embodiment, the amount of ink droplets from the recording head units 231a, 232a, and 233a is 25.4 / D × √2 with respect to the maximum recording resolution D [dpi] for the dot size formed on the recording surface. The amount of ink droplets from the recording head units 231b, 232b, and 233b is designed to be> 25.4 / D × √2 with respect to the maximum recording resolution D [dpi] for the dot size formed on the recording surface. Designed, the dot size is a slightly larger design value.

  The gradation correction table shown in FIG. 15 has a meaning of correcting the deviation of the dot size. At the same time as correcting the gradation, the density difference due to the difference in the dot size is also corrected.

  After the gradation correction processing is performed in the gradation correction processing unit 83, pseudo gradation processing is performed in the pseudo gradation processing unit 84, and dots are formed as shown in FIG. Since the dots are only ON and OFF, by changing the number of dots per unit area, pseudo gradation can be expressed, but different ink droplet amounts are ejected for each recording head unit. In the image recording apparatus, the number of dots per unit area recorded from the recording head unit (231b, 232b, 233b) with a large amount of ink droplets is set to the other recording head unit (231a, 232a, 233a). By setting the number to a small number, the same conditions as when the same ink droplet amount is ejected from both recording head units can be obtained.

  Next, density unevenness correction processing performed in the density unevenness correction processing unit 85 will be described. The correction process is performed on the recording element that is the determination target in the density unevenness determination process. Here, as an example, the correction process for the area that is the target in the density unevenness determination process 1 is illustrated in the flowchart of FIG. The description will be given with reference.

  First, initialization is performed to set the counter i to 0 (ST31). Next, referring to the flag table Tbl_flag of the recording element viewed from the recording medium (integrated with Tbl1_flag and Tbl2_flag as viewed from the recording medium), it is determined whether there is a flag of “1” (ST32). ). If “YES” is determined in ST32, it is determined that the recording element is a target for correcting uneven density, and the process proceeds to ST33. If “NO” is determined, the recording element is corrected for uneven density. It is determined that it is not the target.

  First, a counter j indicating the recording position of the input image signal in the conveyance direction of the recording medium is set to 0 and initialized (ST33).

  Next, with respect to a recording element subject to density unevenness correction, an assumed discharge amount per unit area of an input image value corresponding to the recording element and an adjacent input image value and an assumed discharge amount per unit area to be a correction value Is calculated (ST34 to ST40).

 In ST41 to ST44, an output in which density unevenness of the input image is reduced by using a function DC (x, y) for converting the input image so that the assumed discharge amount per unit area becomes the assumed discharge amount to be corrected. Processing to convert to an image is performed.

  The conversion function can be switched between a case where correction is performed on a recording element to be corrected and a case where correction is applied to an adjacent element.

  By executing the above processing, when a density drop occurs as shown in FIG. 18, dots are added to compensate for this, and density unevenness is reduced.

  As described above, by performing the processing using the correction processing unit, which is a feature of the present invention, it is possible to correct the input image signal value and reduce density unevenness caused by the head unit width.

  In the above-described embodiment, the density unevenness correction performed by the density unevenness correction processing unit 85 is performed after the pseudo gradation processing unit 84, but is performed before the pseudo gradation processing unit 84. Also good.

  Further, as shown in FIG. 8, the density unevenness determination processes 1 and 2 are performed separately, but the present invention is not limited to this and may be a single determination process.

  Further, a flag may be set from the input unit 517 to the flag table. In the above-described embodiment, the input unit 517 is connected to the IO port 54, but the input unit may be connected to the host computer 56.

  In the above embodiment, one recording head is configured by connecting two recording head units so as to be positioned in a direction perpendicular to the arrangement direction of the recording elements. However, three or more recording head units are provided. One recording head may be configured by being connected so as to be positioned in a direction perpendicular to the arrangement direction of the recording elements.

1 is a cross-sectional view of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 2 is a front view illustrating a schematic configuration of an inkjet head unit mounted on the inkjet recording apparatus. FIG. 3 is a perspective view of the ink jet recording head. FIG. 3 is a front view showing a positional relationship between the inkjet recording head and a recording medium. FIG. 3 is a diagram illustrating an example of the arrangement of the inkjet recording head. FIG. 4 is a diagram illustrating an arrangement interval between recording elements and recording heads. 2 is a block diagram showing a system configuration of the inkjet recording apparatus. FIG. FIG. 3 is a block diagram for explaining image processing performed in the inkjet recording apparatus. 5 is a flowchart for explaining density unevenness determination processing 1; FIG. 6 is a diagram illustrating ejection characteristics with respect to a recording element arrangement direction. 7 is a flowchart for explaining density unevenness determination processing 2; FIG. 6 is a diagram illustrating ejection characteristics with respect to a recording element arrangement direction. FIG. 3 is a block diagram for explaining image processing performed in the inkjet recording apparatus. The figure which shows the image signal example after correction | amendment. FIGS. 15A and 15B are diagrams each showing the corrected print density. The figure which shows a density | concentration characteristic. The flowchart which shows a density nonuniformity correction process. The figure which shows an example of a correction table.

Explanation of symbols

    23 ... Recording head, 51 ... CPU, 52 ... ROM, 53 ... RAM, 81 ... Color conversion processing unit, 82 ... UCR processing unit, 83 ... Gradation correction unit, 84 ... Pseudo halftone processing unit, 85 ... Density unevenness correction Processing unit, 231 to 233... Print head unit, 510... Discharge characteristic table,

Claims (6)

In an image recording apparatus for recording on a recording medium, using a recording head in which two or more recording head units in which a plurality of recording elements are arranged are connected in a direction perpendicular to the arrangement direction of the recording elements.
A recording head driving unit that drives a plurality of recording elements of the recording head according to image data and records an image on a recording medium with a different ink droplet amount for each recording head unit;
An ejection characteristic table for recording ejection characteristics for each recording element of the recording head unit; and
An uneven density determination processing unit for determining the density on the recording surface based on the ejection characteristics for each recording element recorded in the head characteristic table;
An image processing unit including a process for performing density unevenness correction processing based on the determination result obtained by the head characteristic table and the density unevenness determination processing unit;
An image recording apparatus comprising: The image recording apparatus according to claim 1, wherein pitches of recording elements of the plurality of recording head units are set to be shifted from each other. The image recording apparatus according to claim 1, wherein the recording head driving unit controls the amount of ink droplets ejected from the plurality of recording head units so that dots are adjacent to each other and no blank portion is generated. . The image recording apparatus according to claim 1, wherein the density unevenness determination processing unit specifies a density unevenness correction area from discharge characteristics recorded in a discharge characteristic table provided for each of the plurality of recording head units. . The image recording according to claim 1, wherein the image processing unit performs density unevenness correction on the density unevenness determination area determined by the density unevenness determination processing unit based on the discharge characteristics recorded in the discharge characteristic table. apparatus. When the image processing unit performs density unevenness correction on the density unevenness determination area determined by the density unevenness determination processing unit based on the discharge characteristics recorded in the discharge characteristic table, the recording element to be corrected or its periphery The image recording apparatus according to claim 1, wherein correction is performed on the recording element.

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