JP2006076086A - Ink jet recorder and recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce deterioration in image quality due to a poor nozzle. <P>SOLUTION: Gray level is corrected not only for pixels recorded by poor peripheral nozzles adjacent to a poor nozzle but also for pixels recorded by peripheral nozzles between a poor peripheral nozzle and a normal nozzle. In the gray level correction, addition and subtraction of correction amount becoming smaller as the distance from a poor nozzle increases are repeated alternately for each pixel in the direction of a normal nozzle from a poor peripheral nozzle adjacent to the poor nozzle. Consequently, occurrence of white streaks due to a poor nozzle is suppressed and since gray scale transits gradually to a gray level obtained by gray scale transformation in the direction of a normal nozzle from a poor peripheral nozzle, occurrence of black streaks due to pixels recorded by adjacent poor nozzles is suppressed, and occurrence of a significant gray scale difference between pixels recorded by a poor nozzle and a normal nozzle B<SB>6</SB>is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus and an ink jet recording method, and more particularly to an ink jet recording apparatus and an ink jet recording method provided with a recording head for recording dots corresponding to each pixel.

  2. Description of the Related Art There is known an ink jet recording apparatus provided with a recording head that performs an image recording operation according to image data by ejecting ink from nozzles. In such an ink jet recording apparatus, dots corresponding to each pixel of image data are recorded by ejecting ink from a plurality of nozzles.

  In this type of ink jet recording apparatus, in recent years, the density of nozzles has increased and the number of nozzles in the recording head has increased. Also, due to the demand for higher printing speed, recording of one line in the direction (main scanning direction) orthogonal to the direction (sub-scanning direction) in which the recording head is fixed and the print medium such as paper is conveyed is recorded. Image formation by one pass performed by one ink discharge by a plurality of nozzles of the head is performed. In order to obtain good image quality in one pass, good ink ejection is desired for all nozzles, but in reality, it is difficult to perform good ink ejection for all nozzles in terms of processing accuracy and cost. Since the number of nozzles increases, it is difficult to manufacture a recording head that does not include defective nozzles that are difficult to form normally. For this reason, there has been a problem of image quality deterioration due to generation of white streaks due to defective ejection or non-ejection of ink due to a defective nozzle.

  Techniques for suppressing image quality degradation due to such defective nozzles are disclosed (see, for example, Patent Document 1 and Patent Document 2).

In the technique of Patent Document 1, the ejection of ink droplets from a defective nozzle is stopped, and dots corresponding to pixels recorded by two normal nozzles adjacent to the defective nozzle are recorded in a size about twice that of normal recording. Control to do. In the technique of Patent Document 2, the drive circuit for controlling the dot length is switched so as to increase the dot diameter of the nozzle adjacent to the defective nozzle.
Japanese Patent Laid-Open No. 11-348246 JP 2002-086767 A

  However, in the above conventional technique, control is performed so as to increase only the diameter of the ink ejected from the nozzle adjacent to the defective nozzle. Therefore, black streaks are generated by the pixels recorded by the nozzle adjacent to the defective nozzle. There was a problem of causing image quality degradation.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an ink jet recording apparatus and an ink jet recording method capable of reducing image quality deterioration due to defective nozzles.

  In order to solve the above-described problems, an ink jet recording apparatus of the present invention discharges ink droplets from each of a plurality of nozzles, thereby recording a dot corresponding to each pixel and a maximum density when recording. A first pixel that records each pixel of image data in which the data of each pixel is represented by a gradation value having a minimum density when recording and a minimum value when recording is performed with a defective nozzle in which normal dot formation is impossible Classification means for classifying the second pixel to be recorded by a defective peripheral nozzle located around the defective nozzle, and the third pixel to be recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle; The gradation value of the second pixel is converted into the minimum value, and the gradation value and the gradation value when the gradation value of the second pixel and the gradation value of the third pixel are recorded linearly change. Linear relationship Conversion means for converting based on, correction means for correcting the gradation value of the second pixel converted by the conversion means based on a correction amount that decreases as the distance from the defective nozzle increases, and Based on the gradation value of the first pixel and the gradation value of the third pixel converted by the conversion means, and the gradation value of the second pixel corrected by the correction means And a control unit that prohibits the dot formation of the pixel having the minimum value and controls the recording head so that a larger dot is recorded as the gradation value increases.

  Further, the ink jet recording method of the present invention records dots corresponding to each pixel by ejecting ink droplets from each of a plurality of nozzles, and sets the maximum density when recording to the maximum value and the minimum when recording. A first pixel that records each pixel of the image data in which the data of each pixel is represented by a gradation value having a minimum density as a defective nozzle that cannot form a normal dot, and is positioned around the defective nozzle A second pixel that is recorded by a defective peripheral nozzle, and a third pixel that is recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle, and the gradation value of the first pixel is set to the minimum value. And converting the gradation value of the second pixel and the gradation value of the third pixel on the basis of a linear relationship that is determined so that the density and gradation value when recorded are linearly changed. The distance from the defective nozzle is The gradation value of the second pixel converted by the conversion unit is corrected based on the correction amount that becomes smaller as it becomes smaller, and the gradation value of the first pixel and the third value converted by the conversion unit are corrected. On the basis of the tone value of the second pixel and the tone value of the second pixel corrected by the correction means, the dot formation of the pixel having the minimum tone value is prohibited, and the tone value is The recording head is controlled so that a larger dot is recorded as the size increases.

  The classification means of the ink jet recording apparatus of the present invention provides each pixel of image data in which the data of each pixel is represented by a gradation value having a maximum density when recorded as a maximum value and a minimum density when recorded as a minimum value. Are classified into a first pixel, a second pixel, and a third pixel. The first pixel is a pixel that is recorded by a defective nozzle in which normal dot formation is not possible due to ink ejection failure or ejection failure among the nozzles of the recording head. The second pixel is a pixel that is recorded by a defective peripheral nozzle located around the defective nozzle. The third pixel is a pixel that is recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle.

  The conversion unit converts the gradation value of the first pixel into a minimum value. Further, the converting means converts the gradation value of the second pixel and the gradation value of the third pixel based on a linear relationship determined so that the density and the gradation value at the time of recording change linearly. To do. By converting the gradation values of the second pixel and the third pixel based on the linear relationship, the density when recording is not biased toward the high density region, and the relationship between the gradation value and the density changes linearly. Thus, the gradation value is converted.

  The correction unit corrects the gradation value of the second pixel converted by the conversion unit based on a correction amount that decreases as the distance from the defective nozzle increases. As a result of correction by the correction unit, the gradation value of the second pixel converted by the conversion unit is corrected by the largest correction amount for the defective peripheral nozzle closest to the defective nozzle, and the distance from the defective nozzle increases. Correction is performed with a small correction amount.

  Based on the gradation value of the first pixel and the gradation value of the third pixel converted by the conversion means, and the gradation value of the second pixel corrected by the correction means, the control means. Dot formation of pixels with the minimum tone value is prohibited. In this way, by prohibiting the dot formation of the pixel having the minimum gradation value, it is possible to prohibit the printing of the dot by the defective nozzle whose gradation value is converted to the minimum value. In addition, the control unit controls the recording head so that a larger dot is recorded as the gradation value of each pixel corrected by the conversion unit and the correction unit by the conversion unit increases. Further, the control unit controls the third pixel to record dots having a size based on the gradation value converted by the conversion unit, and the second pixel further after being converted by the conversion unit. The recording head is controlled so that dots having a size based on the gradation value corrected by the correcting means are recorded.

  In this way, dots are not recorded for defective nozzles, and dots of a size corresponding to the gradation value converted by the conversion means are recorded for normal nozzles other than defective nozzles and defective peripheral nozzles. Further, for defective peripheral nozzles, since the gradation value converted by the conversion means is recorded with dots having a size corresponding to the gradation value corrected based on the correction amount that becomes smaller as the distance from the defective nozzle further increases, As the distance from the defective peripheral nozzle increases, dots having a density corresponding to the gradation value converted by the conversion unit gradually from the corrected gradation value are recorded.

  Therefore, in order to suppress the occurrence of white streak due to the defective nozzle, even when pixels having a higher density are recorded by correction than the density according to the gradation value converted by the conversion means at the defective peripheral nozzle, As the distance from the defective nozzle increases, pixels having a density closer to the gradation value converted by the conversion means are recorded, so that black streaks can be prevented from being generated by the pixels recorded by the defective peripheral nozzle. Accordingly, it is possible to suppress image quality deterioration due to a defective nozzle.

The correction means of the present invention alternately repeats addition and subtraction of the correction amount to the gradation value of each corresponding second pixel from the defective peripheral nozzle adjacent to the defective nozzle toward the normal nozzle direction. Thus, the gradation value of the second pixel converted by the conversion means can be corrected. By correcting the correction means, the correction amount is added to the gradation value corresponding to the defective peripheral nozzle adjacent to the defective nozzle, and the correction amount is subtracted from the gradation value corresponding to the defective peripheral nozzle adjacent to the normal nozzle direction, Correction amount addition and subtraction are alternately repeated so as to decrease as the distance from the defective nozzle increases toward the normal nozzle direction. By performing such correction, the gradation value of the defective peripheral nozzle adjacent to the defective nozzle is increased and high density pixels are recorded, so that the generation of white stripes by the defective nozzle can be suppressed and the correction is performed. Since the subtraction and addition of the amount are repeated, by increasing the density of the defective peripheral nozzles adjacent to the defective nozzle, it is possible to suppress the increase in the density of the entire image and to record as the distance from the defective nozzle increases. The correction means of the present invention corresponds to the correction means in which the correction amount is converted by the conversion means. By adding to the gradation value of each of the second pixels, the gradation value of the second pixel converted by the conversion means can be corrected. In this way, by adding the correction amount to the gradation value of each of the second pixels, correction is performed so that the gradation value becomes larger than the gradation value converted by the conversion unit as the distance from the defective nozzle is shorter, Since the gradation value can be corrected so as to be closer to the gradation value converted by the conversion means as the distance from the defective nozzle increases, the higher the density pixel is recorded, the smaller the distance from the defective nozzle. As the distance increases, the density of the recorded pixels can be gradually brought closer to the density based on the gradation value obtained by the conversion means.

  The correction amount includes a unit correction amount per unit distance determined by a difference between a gradation value before conversion by the conversion unit and a gradation value after conversion and a distance from the defective nozzle to the normal nozzle, and the defect It can be determined by the distance of the peripheral nozzle from the defective peripheral nozzle. The correction means corrects the gradation value using a correction amount according to the difference between the gradation value before the conversion by the conversion means and the gradation value after the conversion, and the distance from the defective peripheral nozzle to the defective nozzle. The gradation value can be corrected with a correction amount corresponding to the gradation value before conversion, the gradation value after conversion, and the distance from the defective nozzle to the normal nozzle.

  The correction amount can be determined to change linearly with respect to the distance of the defective peripheral nozzle from the defective nozzle, and the correction amount is determined with respect to the distance of the defective peripheral nozzle from the defective nozzle. It can be determined to change nonlinearly. The correction means determines the correction amount so as to change linearly with respect to the distance of the defective peripheral nozzle from the defective nozzle, so that the density of the recorded pixel changes linearly from the defective nozzle toward the normal nozzle. To be able to. Further, the correction means determines the correction amount so as to change nonlinearly with respect to the distance of the defective peripheral nozzle from the defective nozzle, for example, correction between adjacent nozzles as the defective peripheral nozzle is closer to the defective nozzle. If the difference in the amount is increased and the difference in the correction amount is made smaller as the defective peripheral nozzle is farther from the defective nozzle, the change in the density of the high density region that is difficult to be visually recognized is increased, and the density of the low density region that is more easily visible Changes can be smoothed.

  According to the ink jet recording apparatus and the ink jet recording method of the present invention, dots are not recorded for defective nozzles, and dots having a size corresponding to the gradation value converted by the converting means are used for normal nozzles other than defective peripheral nozzles. For the defective peripheral nozzles, dots having a size corresponding to the gradation value corrected based on the correction amount that further reduces the gradation value converted by the conversion means according to the distance from the defective nozzle are recorded. Since the pixel density can be gradually changed from the defective nozzle toward the normal nozzle, the image quality deterioration due to the defective nozzle can be suppressed.

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

  As shown in FIG. 1, a paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12 of the present embodiment, and the paper Q stacked in the paper feed tray 16 is picked up by a pickup roll 18. Can be taken out one by one. The taken paper Q is conveyed by a plurality of conveyance roller pairs 20 constituting a predetermined conveyance path 22.

  Above the paper feed tray 16, an endless transport belt 28 stretched around a drive roll 24 and a driven roll 26 is disposed. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The paper Q transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image data are discharged from the printhead array 30 in a state of facing the printhead array 30. The

  The recording head array 30 has a long yellow (Y), magenta (M), and cyan configuration in which a plurality of inkjet recording heads (not shown) are arranged in the width direction of the paper Q (a direction orthogonal to the transport direction). The recording heads 32 of four colors (C) and black (K) are arranged along the transport direction, and a full-color image can be recorded.

  As shown in FIG. 4B, each of the plurality of inkjet recording heads 33 constituting each color recording head 32 includes a nozzle 33B for ejecting ink, an ink pressure chamber 33C communicating with the nozzle 33B, and an ink pressure chamber 33C. The piezoelectric element 33 </ b> D provided in contact with is included. As is well known, the piezoelectric element 33D has a property that its shape changes when a voltage is applied. By applying pressure to the ink pressure chamber 33C using this shape change, the piezoelectric element 33D Ink droplets are ejected to record dots on the paper Q. At this time, as shown in FIGS. 4A and 4C, by controlling the voltage applied to the piezoelectric element 33D, that is, the drive waveform, the drive voltage, etc., a large drop of ink from the nozzle 33B (FIG. 4). (See (B)), small ink droplets from the nozzle 33B (see FIG. 4D), prohibition of dot formation, ejection of medium ink droplets, etc., and control large droplets, medium droplets, small droplets, And dot size such as no drops can be controlled.

  In the present embodiment, the case where ink is ejected using the piezoelectric element 33D will be described. However, the present invention is not limited to such a form. For example, the ink in the ink pressure chamber 33C is heated. The size of the dots recorded by ejecting the ink droplets may be controlled.

  In the vicinity of the recording head array 30, maintenance mechanisms 34 corresponding to the recording heads 32 are arranged. When maintenance is performed on the recording head 32, as shown in FIG. 2, the recording head array 30 moves upward, and the maintenance mechanism 34 moves into the gap formed between the conveyance belt 28 and enters. . And the recovery process which attracts | sucks the ink in a nozzle is performed in the state facing the nozzle surface.

For example, the transport belt 28 is made of a semiconductive polyimide material (for example, a surface resistance value of 10 ¹⁰ to 10 ¹³ Ω / m ² and a volume resistance value of 10 ⁹ to 10 ¹² Ω · cm), a thickness of 75 μm, and a width. What was shape | molded to 380 mm and peripheral length 1000mm can be used. Moreover, as the drive roll 24 and the driven roll 26, a SUS roll with a diameter of 50 mm can be used as an example.

  As shown in FIG. 3, a charging roll 36 is disposed on the upstream side of the recording head array 30. The charging roll 36 is driven while sandwiching the transport belt 28 and the paper Q between the follower roll 26 and presses the paper Q against the transport belt 28 (see FIG. 3), and is separated from the transport belt 28. (Not shown). At the pressing position, a predetermined potential difference is generated between the grounded driven roll 26 and the sheet Q can be charged and electrostatically attracted to the transport belt 28.

As the charging roll 36, for example, a roll having a diameter of 14 mm, in which conductive carbon is coated on the surface of silicone rubber and the volume resistance value is adjusted to about 10 ⁶ to 10 ⁷ Ω · cm, can be used.

  A registration roll (not shown) is provided further upstream than the charging roll 36, and the paper Q is aligned before reaching the conveyance belt 28 and the charging roll 36.

  A peeling plate 40 is disposed on the downstream side of the recording head array 30, and the paper Q can be peeled from the transport belt 28. As the peeling plate 40, for example, an aluminum plate having a thickness of 0.5 mm, a width of 330 mm, and a length of 100 mm can be used.

  The peeled paper Q is conveyed by a plurality of discharge roller pairs 42 that constitute a discharge path 44 on the downstream side of the peeling plate 40 and discharged to a paper discharge tray 46 provided at the top of the housing 14.

  Below the peeling plate 40, a cleaning roll 48 capable of sandwiching the conveying belt 28 with the driving roll 24 is disposed, and the surface of the conveying belt 28 is cleaned.

  A reversing path 52 composed of a plurality of reversing roller pairs 50 is provided between the paper feed tray 16 and the conveying belt 28, and the sheet Q on which the image is recorded on one side is reversed and held on the conveying belt 28. By doing so, image recording on both sides of the paper Q can be easily performed.

  Between the conveyance belt 28 and the paper discharge tray 46, an ink tank 54 for storing each of the four color inks is provided. The ink in the ink tank 54 is supplied to the recording head array 30 through an ink supply pipe (not shown). As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  In the ink jet recording apparatus 12 of the present embodiment configured as described above, the paper Q taken out from the paper feed tray 16 is transported to the transport belt 28 as described above. Then, it is pressed against the conveyor belt 28 by the charging roll 36 and is held by being attracted (contacted) to the conveyor belt 28 by the voltage applied from the charging roll 36. In this state, the ink droplets are ejected from the recording head array 30 while the paper Q passes through the ejection area SE by circulation of the transport belt, and an image is recorded on the ejection area SE.

  In the present embodiment, the long yellow (Y), magenta (M), cyan (C), and black (K) recording heads 32 having a configuration in which a plurality of inkjet recording heads are arranged, The arrangement is arranged along the transport direction, and a full-color image can be recorded. However, the number of arrangement of each recording head 32 is not limited to four.

  As shown in FIG. 5, the control system of the inkjet recording apparatus 12 according to the present embodiment includes a control unit 60, a color conversion unit 62, an image processing unit 64, a recording data creation unit 66, and an image recording unit 68. It is configured. The color conversion unit 62, the image processing unit 64, and the recording data creation unit 66 may be provided on the external device side such as a personal computer.

  The control unit 60 controls the color conversion unit 62, the image processing unit 64, the recording data creation unit 66, and the image recording unit 68. The image recording unit 68 includes components relating to image recording such as the inkjet recording head 33 in the inkjet recording apparatus 12 described with reference to FIGS. 1 to 3.

  When the image data input from the outside is RGB data, the color conversion unit 62 converts the image data into YMCK data. In the present embodiment, the image data input from the outside has the maximum density when recorded for each pixel R, G, and B as the maximum value, and the minimum density when recorded as the minimum value. This is image data in which data of each pixel is represented by gradation values. Accordingly, similarly to the color-converted image data, for each of Y, M, C, and K pixels, the gradation value having the maximum density when recorded as the maximum value and the minimum density when recorded as the minimum value. Is image data in which data of each pixel is represented. In this embodiment, it is assumed that the maximum value of the gradation value is 255 and the minimum value is 0. The maximum gradation value is not limited to 255.

  As will be described in detail later, the image processing unit 64 performs density conversion processing for converting the density of image data that has been color-converted according to the characteristics of the paper Q and ink, and the image data in which the gradation value of each pixel is converted. Further, so-called halftone processing for converting the image data into the number of gradations that can be recorded by the inkjet recording apparatus 12 is performed. The density conversion process is a process for converting the gradation value of each pixel so that the relationship between the density and the gradation value when recording is linear from the minimum density to the maximum density. The gradation value of each pixel of the image data color-converted by the color conversion unit 62 and the density when recorded on the paper Q are saturated in a region where the gradation value is high. The saturated density is a density at which the density change when recording is saturated with respect to an increase in the gradation value of each pixel. As shown in FIG. 6, as the gradation value of each pixel becomes larger, the density when recording becomes higher, but when reaching a saturation density where the density change when recording becomes saturated as the gradation value increases, Even if the gradation value increases beyond the gradation value corresponding to the saturation density, no change is observed in the density when recording. For this reason, the relationship between the density and the gradation value becomes a nonlinear relationship 70 that changes nonlinearly. As described above, when the image recording is performed based on the gradation value without converting the gradation value of each pixel of the color-converted image data, the density distribution at the time of recording is biased toward the high density region. For this reason, density conversion processing for converting the gradation value of each pixel is performed so that the relationship between the density and the gradation value becomes the linear relationship 72. The image processing unit 64 is provided with a memory 65 for storing various data. In order to perform the density conversion process, the memory 65 stores in advance a density conversion table indicating the correspondence between the gradation value before density conversion and the gradation value after density conversion, as shown in FIG. Based on this density conversion table, for example, the gradation value 255 before density conversion is converted to the gradation value 255 after density conversion, and in the case of the gradation value 150 before density conversion, the gradation value after density conversion is converted. Converted to the value 100.

  In addition, the memory 65 indicates defective nozzles that are difficult to eject ink droplets normally due to non-ejection of ink droplets or defective ejection among a plurality of inkjet recording heads 33 provided for each color recording head 32. Position information is stored in advance. The position information of the defective nozzle is detected in advance at the manufacturing stage of the recording head 32 or at the start of use.

  The recording data creation unit 66 converts the image data processed by the image processing unit 64 into a data structure that can be decoded by the image recording unit 68, rearranges the data in the recording order (transfer order), and transfers the data to the image recording unit 68. Output. At this time, the recording data is created in consideration of the ejection timing and the data arrangement mapped to the arrangement of the inkjet recording head 33 and the nozzle 33B.

  The image recording unit 68 causes ink to be ejected from each nozzle 33 </ b> B of each inkjet recording head 33 in accordance with the YMCK recording data created by the recording data creation unit 66. Thereby, dots are recorded on the paper Q, and an image is recorded.

  In the image processing unit 64, a processing routine shown in FIG. 8 is executed.

  In step 100, the data for each pixel of the image data color-converted by the color converter 62 is read. In the next step 102, the position information indicating the position of the defective nozzle is read from the memory 65, and the position information of the defective nozzle and the position information of the read pixel on the image recorded on the paper Q are described above. It is determined whether or not the pixel read in step 100 is a pixel to be recorded with a defective nozzle.

  If negative in step 102, the process proceeds to step 104, and the distance from the defective nozzle of the nozzle that records the pixel read in step 100 is calculated.

  In the next step 106, it is determined whether or not the pixel is a pixel to be recorded by the defective peripheral nozzle by determining whether or not the distance from the defective nozzle calculated in step 102 is less than a predetermined distance. Then, the process proceeds to step 108.

  In step 108, based on the density conversion table stored in the memory 65, the tone value of the pixel before density conversion is converted into the tone value after density conversion corresponding to this tone value.

  In the next step 112, a correction amount that decreases as the distance increases is calculated according to the distance from the defective nozzle calculated in step 104. The correction amount is calculated by, for example, the following formula (1).

X represents a correction amount. D1 is a gradation value before density conversion, and D2 is a gradation value after density conversion of D1. As shown in FIG. 9, L indicates a predetermined distance used when it is determined in step 106 that the pixel is around the defective nozzle, and the nozzle 33B _{n + 1 at} a position more than the predetermined distance L is This corresponds to normal nozzles other than the above-described defective nozzles and defective peripheral nozzles. In represents a distance from each defective nozzle 33B ₁ to each of the defective peripheral nozzles 33B ₁ to _n . n indicates the number of nozzles from a nozzle for recording the pixel to the defective nozzle 33B _1. Thus, the difference between the tone value D2 after gradation values D1 and density conversion before the density conversion unit corrects per unit distance determined by the distance L from the defective nozzle 33B ₁ to a normal nozzle 33B n + ₁ calculating the amount, the distance from the defective nozzle 33B ₁ of the defective peripheral nozzles 33B ₁ ~ _n, a correction amount X, such as the distance from the defective nozzle 33B ₁ of the defective peripheral nozzles 33B ₁ ~ _n is as large reduced based on To do.

Relationship between the distance from the defective nozzle 33B ₁ of the correction amount and the defective peripheral nozzles 33B ₁ ~ _n, calculated based on the equation (1), for example, as shown in FIG. 10 (A), a non-linear relationship .

  In the next step 114, correction processing for correcting the tone value after density conversion obtained by the density conversion processing in step 108 is executed in accordance with the correction amount calculated in step 112. In the correction process, the gradation value after density conversion is corrected by alternately repeating addition and subtraction of the correction amount for each pixel from the defective peripheral nozzle adjacent to the defective nozzle toward the normal nozzle direction. For example, as shown in FIG. 11, the gradation value 150 before density conversion is converted into a gradation value 100 by density conversion, and the defective peripheral nozzle next to the defective nozzle is processed by the process of step 112 above. Correction amount 10, correction amount 5 of the defective peripheral nozzle next to the defective nozzle 5, correction amount 3 of the defective peripheral nozzle next to the defective nozzle 3, and correction amount 1 of the defective peripheral nozzle next to the defective nozzle 1 Is calculated. In this case, the gradation value after density conversion of the pixel recorded by the defective peripheral nozzle adjacent to the defective nozzle is corrected to the gradation value 110 obtained by adding the correction amount 10 to the gradation value 100 after density conversion. Further, the gradation value after density conversion of the pixel recorded by the defective peripheral nozzle next to the defective nozzle is corrected to a gradation value 95 obtained by subtracting the correction amount 5 from the gradation value 100 after density conversion. The gradation value after density conversion of the pixel recorded by the defective peripheral nozzle next to the defective nozzle is corrected to the gradation value 103 obtained by adding the correction amount 3 to the gradation value 100 after density conversion. The gradation value after density conversion of the pixel recorded by the defective peripheral nozzle next to the defective nozzle is corrected to a gradation value 99 obtained by subtracting the correction amount 1 from the improved value 100 after density conversion.

  As a result of the processing in step 114, the gradation value after density conversion of the pixels recorded by the defective peripheral nozzles is added for each pixel from the defective nozzle to the normal nozzle in a correction amount that decreases as the distance from the defective nozzle increases. And it is corrected to a value obtained by repeating subtraction.

  On the other hand, if the result in Step 106 is negative and the pixel is recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle, the process proceeds to Step 100, and the density conversion process according to the density conversion table is performed as in Step 108. The gradation value of the pixel before density conversion is converted to the gradation value after density conversion.

  Next, in step 116, the image data in which the gradation value of the pixel recorded by the normal nozzle is converted in density in step 110 and the gradation value of the pixel recorded in the defective peripheral nozzle in step 114 are converted in density. Further, the image data corrected according to the distance from the defective nozzle is corrected by the process of step 114 or the density is converted by the process of step 110 so that the number of gradations can be expressed by the inkjet recording apparatus 12. Halftone processing (also referred to as quantization processing) for further converting the gradation value of each pixel is performed. In the present embodiment, quantization to four gradations that can be expressed by the inkjet recording apparatus 12, that is, gradation values indicating “no drop”, “small drop”, “medium drop”, and “large drop”, respectively. Quantization of “0”, “1”, “2”, and “3” into four gradations, that is, halftone processing is performed. The number of gradations that can be expressed by the inkjet recording apparatus 12 is not limited to the above-described four types of gradations, and may be two types, three types, or five or more types of gradations. The quantization operation method uses a generally known error diffusion method, and a detailed description of the error diffusion method is omitted.

  By performing the halftone processing in step 116, the dot size at the time of recording, that is, “large droplet”, “medium droplet” of the defective peripheral nozzle and the pixels recorded by the defective peripheral nozzle and the normal nozzle other than the defective nozzle, respectively. ”,“ Small droplet ”, and“ no droplet ”.

  On the other hand, if the result in step 102 is affirmative, the process proceeds to step 118 where the dot size “no drop” to be recorded is set by setting the minimum value “0” as the gradation value of the pixel to be recorded with the defective nozzle. .

  In the next step 120, it is determined whether or not the dot size has been set for all the pixels of the image data. If the determination is negative, the process returns to step 100. If the determination is affirmative, the routine is ended.

By executing the processing routine from step 100 to step 120, in the conventional technique, as shown in FIG. 12A, the pixel 73B ₂ recorded by the defective peripheral nozzle 33B ₂ adjacent to the defective nozzle 33B ₁ is recorded. only gradation values, FIG. 12 (B) and the correction to increase the concentration (C), the other words by correcting such gradation value increases, the defective peripheral nozzles adjacent to the defective nozzle 33B ₁ The density of the pixel 73B ₂ recorded with 33B ₂ is set higher than that during normal recording. For this reason, only the density at the time of recording of the pixel adjacent to the pixel to be recorded by the defective nozzle is increased, and black streaks are generated on the opposite side of the defective nozzle by this pixel, resulting in image quality deterioration. However, in the inkjet recording apparatus 12 of the present embodiment, as shown in FIG. 12D, not only the pixel 73B ₂ recorded by the defective peripheral nozzle 33B ₂ adjacent to the defective nozzle 33B ₁ but also the defective peripheral nozzle 22B _1. The gradation values of the defective peripheral nozzle 33B ₃ , the defective peripheral nozzle 33B ₄ , and the defective peripheral nozzle 33B ₅ between the normal nozzle B ₆ and the normal nozzle B ₆ are corrected. Correction of the tone values, as shown in FIG. 12 (E) and (F), from the bad surrounding nozzle 33B ₂ adjacent to the defective nozzle 33B ₁ toward the normal nozzles B ₆ direction, from the defective nozzle 33B ₁ Addition and subtraction of the correction amount, which decreases as the distance increases, are repeatedly executed alternately for each pixel. As a result, the density of the defective peripheral nozzle 33B ₂ adjacent to the defective nozzle 33B ₁ becomes higher than the density based on the gradation value obtained by the density conversion, but from the defective peripheral nozzle 33B ₂ toward the normal nozzle 33B _6. The concentration oscillates damped.

Thus, floors only pixels to be recorded in the adjacent defective peripheral nozzle 33B ₂ is it is possible to prevent the higher the concentration, toward the normal nozzles B ₆ direction from the defective peripheral nozzle 33B _2, was based on a correction amount since the concentration to resulting tone value by gradually density conversion from tone values to remain, it is possible to suppress the occurrence of black stripes by the pixels to be recorded in the adjacent defective nozzles 33B _2. In addition, it is possible to prevent a large density difference from occurring between the pixels recorded with the defective nozzle B ₆ and the pixels recorded with the normal nozzle B ₆ .

  Accordingly, it is possible to suppress image quality deterioration due to a defective nozzle.

  Further, since the relationship between the correction amount and the distance calculated based on the above formula (1) is a non-linear relationship as shown in FIG. 10A, the correction amount is determined based on the defect periphery adjacent to the defective nozzle. Since the correction amount can be decreased exponentially from the nozzle correction amount toward normal nozzles, the concentration change is abruptly reduced in high-density regions where the change in concentration is difficult to see, and the concentration change is easy to see. In the area, dots can be recorded so that the density gradually decreases.

In the present embodiment, the correction amount is calculated so as to decrease for each pixel as the distance of the defective nozzle 33B ₂ increases. However, the correction amount may be calculated so as to decrease in units of two pixels. . In this way, as shown in FIG. 12E, the correction amount a to be added to and subtracted from the density-converted gradation value of the adjacent pixel, which is added to and subtracted from the gradation value after density conversion, and this pixel Since the correction amount b to be subtracted from the tone-converted tone value of the pixel adjacent to the same value is the same value, it is possible to suppress the occurrence of a deviation from the value of the tone value after conversion obtained by the density conversion. It is possible to suppress deviation from the converted gradation value obtained by density conversion in the entire image data. In addition, the time required for calculating the correction amount can be shortened, and the processing speed can be increased.

  In the present embodiment, the case where the correction amount is calculated by the equation (1) has been described. However, any equation can be used as long as the correction amount can be calculated such that the correction amount becomes smaller as the distance from the defective nozzle increases. For 1), a different formula may be used depending on, for example, how to reduce the type of paper to be recorded, the type of ink, and the correction amount according to the distance from the nozzle, and is limited to the formula (1). is not.

  Further, in the present embodiment, the correction amount is calculated using the equation (1), and the relationship between the correction amount and the distance becomes nonlinear as shown in FIG. 10A, and the correction is performed as the distance from the defective nozzle increases. Although the case where the amount decreases exponentially has been described, the relationship between the correction amount and the distance is not limited to a non-linear relationship. For example, as shown in FIG. 10B, a linear relationship may be established. In this case, the correction amount may be obtained by using a mathematical formula that is different from the above formula (1) and that the correction amount decreases in a linear relationship as the distance from the defective nozzle increases. In this way, the correction amount can be calculated at high speed.

  In this embodiment, in the gradation value correction processing in step 114, the calculated correction amount is added to the correction amount for each pixel from the defective peripheral nozzle adjacent to the defective nozzle in the normal nozzle direction. Although the case where the gradation value subjected to density conversion is corrected by alternately repeating subtraction has been described, addition and subtraction of the correction amount may be alternately repeated every two pixels. In this case, the correction amount may be a correction amount that decreases for each pixel as the distance from the defective nozzle increases, but may be a correction amount that decreases for every two pixels. In this way, the same correction amount is added and subtracted for every two adjacent pixels as the distance from the defective nozzle increases, so that the density of the entire image data is obtained by the density conversion process. It is possible to suppress the concentration from being different from the concentration based on the value.

  In the present embodiment, in the gradation value correction processing in step 114, the calculated correction amount is added to the correction amount for each pixel from the defective peripheral nozzle adjacent to the defective nozzle toward the normal nozzle. In the above description, the density-converted gradation value is corrected by alternately subtracting, but a correction amount that decreases according to the distance from the defective nozzle is added to the density-converted gradation value. You may make it correct | amend.

  Note that in this embodiment, the density value of the converted pixel is corrected according to the correction amount according to the distance from the defective nozzle, so that the density of the recorded pixel is adjacent to the defective nozzle. In the above description, the control is performed so that the density is gradually shifted from the pixel to be recorded to the pixel to be recorded by the normal nozzle, and this density change is driven by the piezoelectric element 33D. The waveform or driving voltage may be controlled. In this case, a large drop of ink is ejected from a defective peripheral nozzle adjacent to the defective nozzle, and an ink droplet of a dot size corresponding to the image data is gradually discharged from the defective peripheral nozzle toward the normal nozzle. The drive waveform applied to the piezoelectric element 33D and the drive voltage may be controlled. In addition, large ink droplets are ejected from defective peripheral nozzles adjacent to the defective nozzle, and ink droplets of dot sizes corresponding to image data are gradually ejected from the defective peripheral nozzles toward normal nozzles. The control may be performed in the halftone process.

  In the above-described halftone processing in step 116, the case where the quaternary halftone processing is executed in both the defective peripheral nozzle and the normal nozzle has been described. However, the binary halftone processing is executed in the defective peripheral nozzle. May be. In this way, the density of defective peripheral nozzles adjacent to the defective nozzle can be increased.

It is the schematic which shows the inkjet recording device of this invention in an image recording state. It is the schematic which shows the inkjet recording device of this invention in a maintenance state. FIG. 2 is a schematic configuration diagram illustrating a conveyance belt and the vicinity thereof in the inkjet recording apparatus of the present invention. FIG. 7 is an image diagram showing size control of ink droplets ejected from a recording head, (A) is a waveform showing a voltage applied to a piezoelectric element in order to eject large droplets of ink from the recording head, (B) Is a cross-sectional view of the recording head when large droplets are ejected, (C) is a waveform indicating a voltage applied to the piezoelectric element in order to eject small droplets of ink from the recording head, and (D) is FIG. 4 is a cross-sectional view of a recording head when ejecting small droplets. It is a control block diagram of the ink jet recording apparatus according to the present invention. FIG. 6 is a diagram showing the relationship between density and gradation value when recording before and after density conversion processing. It is an example of a look-up table showing the correspondence between the gradation value before density conversion and the gradation value after density conversion. It is a flowchart which shows the process performed by an image process part. It is an image figure which shows a defective nozzle, a defective periphery nozzle, and a normal nozzle. It is a diagram which shows the correction amount which becomes small, so that the distance from a defective nozzle becomes large, (A) is a diagram which shows the case where the relationship between the distance from a defective nozzle and a correction amount is nonlinear, (B ) Is a diagram showing a case where the relationship between the distance from the defective nozzle and the correction amount is linear. Correction amount of pixels recorded by the defective peripheral nozzle next to the defective nozzle, the second defective peripheral nozzle from the defective nozzle, the third defective peripheral nozzle from the defective nozzle, and the fourth defective peripheral nozzle from the defective nozzle FIG. 6 is a schematic diagram illustrating an example of a method for calculating a corrected gradation value and an example of a corrected gradation value. It is the model which shows the suppression method of the image quality degradation by the conventional defective nozzle, and the suppression method of the image quality degradation by the defective nozzle of this invention, (A) recorded the pixel with the recording head containing the defective nozzle in a prior art. FIG. 6B is a schematic diagram digitally showing the correction amount of the gradation value of each pixel in the conventional technique, and FIG. 6C is a gradation diagram of each pixel in the conventional technique. It is a diagram which shows the correction amount of a value in analog. (D) is a schematic diagram showing the density when a pixel is recorded by a recording head including a defective nozzle in the present invention, and (E) shows the correction amount of the gradation value of each pixel in the present invention. FIG. 8F is a diagram schematically illustrating the correction amount of the gradation value of each pixel in the present invention.

Explanation of symbols

12 Inkjet recording apparatus 32 Recording head 33 Inkjet recording head 64 Image processing unit

Claims (7)

A recording head for recording dots corresponding to each pixel by ejecting ink droplets from each of the plurality of nozzles;
Each pixel of the image data in which the data of each pixel is represented by a gradation value with the maximum density at the time of recording as the maximum value and the minimum density at the time of recording as the minimum value. Classification into a first pixel to be recorded by a nozzle, a second pixel to be recorded by a defective peripheral nozzle located around the defective nozzle, and a third pixel to be recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle Classification means to
The gradation value of the first pixel is converted into the minimum value, and the gradation value and gradation value when the gradation value of the second pixel and the gradation value of the third pixel are recorded are linear. Conversion means for converting based on a linear relationship determined to change to
Correction means for correcting the gradation value of the second pixel converted by the conversion means based on a correction amount that decreases as the distance from the defective nozzle increases;
Based on the gradation value of the first pixel and the gradation value of the third pixel converted by the conversion unit, and the gradation value of the second pixel corrected by the correction unit, Control means for prohibiting dot formation of pixels having a minimum tone value and controlling the recording head so that a larger dot is recorded as the gradation value increases;
An ink jet recording apparatus comprising:   The correction means alternately repeats addition and subtraction of the correction amount to the gradation value of each corresponding second pixel from the defective peripheral nozzle adjacent to the defective nozzle toward the normal nozzle direction. The inkjet recording apparatus according to claim 1, wherein the gradation value of the second pixel converted by the conversion unit is corrected.   The correction means adds the correction amount to the gradation value of each of the corresponding second pixels converted by the conversion means, thereby converting the gradation value of the second pixel converted by the conversion means. The inkjet recording apparatus according to claim 1, wherein the correction is performed.   The correction amount includes a unit correction amount per unit distance determined by a difference between a gradation value before conversion by the conversion unit and a gradation value after conversion and a distance from the defective nozzle to the normal nozzle, and the defect The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is determined by a distance of the peripheral nozzle from the defective peripheral nozzle.   5. The inkjet recording apparatus according to claim 1, wherein the correction amount is determined so as to change linearly with respect to a distance of the defective peripheral nozzle from the defective nozzle.   The inkjet recording apparatus according to claim 1, wherein the correction amount is determined so as to change nonlinearly with respect to a distance of the defective peripheral nozzle from the defective nozzle. By ejecting ink droplets from each of the plurality of nozzles, dots corresponding to each pixel are recorded,
Each pixel of the image data in which the data of each pixel is represented by a gradation value with the maximum density at the time of recording as the maximum value and the minimum density at the time of recording as the minimum value. Classification into a first pixel to be recorded by a nozzle, a second pixel to be recorded by a defective peripheral nozzle located around the defective nozzle, and a third pixel to be recorded by a normal nozzle other than the defective nozzle and the defective peripheral nozzle And
The gradation value of the first pixel is converted into the minimum value, and the gradation value and gradation value when the gradation value of the second pixel and the gradation value of the third pixel are recorded are linear. Converted based on a linear relationship determined to change to
Based on a correction amount that decreases as the distance from the defective nozzle increases, the gradation value of the second pixel converted by the conversion unit is corrected,
Based on the gradation value of the first pixel and the gradation value of the third pixel converted by the conversion unit, and the gradation value of the second pixel corrected by the correction unit, Prohibiting dot formation for pixels with the minimum tone value and controlling so that larger dots are recorded as the tone value increases,
Inkjet recording method.

Images