JP4561257B2 - Inkjet recording apparatus and inkjet recording method - Google Patents

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. Related Art An ink jet recording apparatus including a recording head that performs an image recording operation according to image data by ejecting ink from nozzles is known. 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, the density of nozzles has increased in recent years, and the number of nozzles in the recording head has increased. Further, in response to a demand for higher printing speed, the recording head is fixed, and recording of one line in the direction (main scanning direction) orthogonal to the direction (sub-scanning direction) in which a print medium such as paper is conveyed (recording head) is performed. One-pass image recording is performed by ejecting ink from the plurality of nozzles once. In such an ink jet recording apparatus, after performing the quantization for converting the gradation value of each pixel of the image data into a gradation value that can be recorded by the recording head, the magnitude corresponding to the converted gradation value is obtained. The dots are recorded.

  Further, as shown in Patent Document 1, the density of the entire image when recorded is determined based on the quantization error between the gradation value before conversion and the gradation value after conversion generated by quantization. In order to suppress a density different from the density of the entire image recorded based on the tone value, error diffusion is performed to diffuse the quantization error of the pixel of interest to each peripheral pixel around the pixel of interest, and the diffused quantum By adding the accumulated quantization error for each pixel of the quantization error to the gradation value before conversion by quantization of the corresponding pixel, the quantization error of the pixel of interest is absorbed by the surrounding pixels, and the whole image is simulated It represents the density of the entire original image.

  Here, in order to obtain a good image quality by one-pass image recording, good ink ejection is desired at all nozzles, but in reality, good ink ejection is performed at all nozzles in terms of processing accuracy and cost. Since the number of nozzles per head is increased, it is difficult to manufacture a recording head that does not include defective nozzles that are difficult to perform normal dot recording. 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.

  A technique for suppressing image quality deterioration due to such a defective nozzle is disclosed (for example, see Patent Document 2).

In the technique of Patent Document 2, it is prohibited to eject ink droplets from the defective nozzle by converting the gradation value of the pixel recorded by the defective nozzle to the minimum value, and the pixel recorded by the nozzle adjacent to the defective nozzle is recorded. Control is performed so that the corresponding dots are recorded at a size approximately twice that of normal recording. In order to enlarge the dot, the density is increased by increasing the gradation value of the pixel corresponding to the dot when quantizing. Thus, by increasing the density of the pixels recorded by the nozzles adjacent to the defective nozzles, it is possible to suppress the occurrence of white streaking due to the pixels recorded by the defective nozzles.
JP 2003-103768 A Japanese Patent Laid-Open No. 11-348246

  In the above prior art, it is possible to suppress the occurrence of white streak caused by the defective nozzle by increasing the density of the pixel recorded by the nozzle adjacent to the defective nozzle, but the quantum of the pixels recorded by the defective peripheral nozzle around the defective nozzle. When the density before conversion due to the conversion is high, if the quantization error of the pixel recorded by the defective nozzle and the nozzle adjacent to the defective nozzle is diffused to the peripheral pixels by error diffusion, the quantization of the pixel recorded by the defective nozzle is performed. There is a problem that it becomes difficult to absorb the error in the peripheral pixels, and the high density region is expanded from the target pixel to an excessively wide range of peripheral pixels, resulting in image quality deterioration.

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

  In order to solve the above problems, an ink jet recording apparatus of the present invention has a recording head that records dots corresponding to each pixel by ejecting ink droplets from each of a plurality of nozzles, and a gradation value corresponding to the density. Addition means for adding the cumulative quantization error input to the gradation value of each corresponding pixel of the image data representing the data of each pixel, and a defect in which normal dot formation is impossible for the pixel of interest of the image data When recording with a nozzle, the gradation value to which the accumulated quantization error of the pixel of interest is added is converted to a minimum value, and when the pixel of interest is recorded with a defective peripheral nozzle located around the defective nozzle, and When recording with normal nozzles other than the defective nozzle and the defective peripheral nozzle, the gradation value added with the accumulated quantization error of the pixel of interest is converted into a gradation value with which the recording head can record dots. A quantization error determined by the quantization means and the gradation value before conversion and the gradation value after conversion of the target pixel is determined for each peripheral pixel in a predetermined area including adjacent pixels adjacent to the target pixel. A first error diffusion window in which a distribution amount to be distributed is set so as to decrease as the distance from the pixel of interest increases, and each distribution amount of each adjacent pixel becomes larger than the first error diffusion window. Storage means that pre-stores a second error diffusion window that defines a distribution amount for each peripheral pixel, and when the target pixel is recorded by the normal nozzle, or the low-concentration target pixel is the defective nozzle or the defective peripheral When recording by the nozzle, the quantization error of the target pixel is diffused to each of the peripheral pixels based on the first error diffusion window, and the target pixel of medium density is set to the defective nozzle or the defective peripheral node. When recording with the nozzle, the quantization error of the pixel of interest is diffused to each peripheral pixel based on the second error diffusion window, and when the pixel of interest with high density is recorded with the defective nozzle or the defective peripheral nozzle , Diffusing the quantization error of the pixel of interest only to adjacent pixels or prohibiting the diffusion of the quantization error of the pixel of interest, and inputting the accumulated quantization error of each pixel of the diffused quantization error to the adding means Based on the error diffusion means and the image data whose gradation value has been converted by the quantization means, the dot formation of the pixel having the smallest gradation value is prohibited, and the larger the gradation value, the larger the dot recorded. And a control means for controlling the recording head.

  Further, in the ink jet recording method of the present invention, dots corresponding to each pixel are recorded by ejecting ink droplets from each of the plurality of nozzles, and the data of each pixel is represented by gradation values according to the density. When recording a target pixel of image data with a defective nozzle that cannot form a normal dot, the gradation value to which the accumulated quantization error of the target pixel is added is converted to a minimum value, and the target pixel is converted into the defective pixel. When recording with a defective peripheral nozzle located around the nozzle and when recording with a normal nozzle other than the defective nozzle and the defective peripheral nozzle, the gradation value to which the accumulated quantization error of the pixel of interest is added is The recording head converts the dot into a recordable gradation value, and the quantization error determined by the gradation value before conversion of the pixel of interest and the gradation value after conversion includes an adjacent pixel adjacent to the pixel of interest. Each within a given area A first error diffusion window that defines a distribution amount to be distributed so that the distance from the pixel of interest increases for each side pixel, and the distribution amount of each adjacent pixel compared to the first error diffusion window. A second error diffusion window in which a distribution amount for each peripheral pixel is set to be large is stored in advance, and when the target pixel is recorded by the normal nozzle, or the low-concentration target pixel is the defective nozzle or the When recording with a defective peripheral nozzle, the quantization error of the pixel of interest is diffused to each of the peripheral pixels based on the first error diffusion window, and the medium pixel of interest is recorded with the defective nozzle or the defective peripheral nozzle. The quantization error of the target pixel is diffused to each of the surrounding pixels based on the second error diffusion window, and the high-concentration target pixel is transferred to the defective nozzle. Alternatively, when recording with the defective peripheral nozzle, the quantization error of the pixel of interest is diffused only to adjacent pixels or the diffusion of the quantization error of the pixel of interest is prohibited, and the accumulated quantization error for each pixel is accumulated. Input a quantization error, add the input cumulative quantization error to the gradation value of each corresponding pixel of the image data, and based on the image data whose gradation value is converted by the quantization means, It is characterized in that the recording head is controlled so that the dot formation of the pixel having the minimum tone value is prohibited, and the larger dot is recorded as the gradation value becomes larger.

  The adding means of the inkjet recording apparatus of the present invention is a cumulative quantization error of a quantization error input to a gradation value of each corresponding pixel of image data in which the data of each pixel is represented by a gradation value according to density. Is added. The quantization means adds the accumulated quantization error of the pixel of interest when recording the pixel of interest in each pixel of the image data with a defective nozzle that cannot normally form dots among the plurality of nozzles of the recording head. The obtained gradation value is converted into a minimum value. In addition, when the quantization unit records the pixel of interest with a defective peripheral nozzle located around the defective nozzle, or when recording with a normal nozzle other than the defective nozzle and the defective peripheral nozzle, the quantization quantization error of the pixel of interest is increased. The added gradation value is converted into a gradation value by which the recording head can record dots.

  The error diffusion means calculates the quantization error between the gradation value before being converted by the quantization means for the pixel of interest and the gradation value after the conversion for each peripheral pixel around the pixel of interest. Is diffused to surrounding pixels around the pixel of interest, and the accumulated quantization error for each pixel of the diffused quantization error is input to the adding means.

  When the target pixel is recorded with the defective nozzle, the gradation value of the target pixel is converted to the minimum value, so that the quantization error of the target pixel recorded with the defective nozzle is the target pixel recorded with the defective peripheral nozzle and the normal nozzle. It is larger than the quantization error. Further, when recording the target pixel with a defective nozzle, the higher the density of the target pixel according to the gradation value before the conversion by the quantization means, the greater the quantization error compared to the low density. . In general, since similar gradation values often continue in adjacent pixels, the density of pixels recorded with defective nozzles and the density of pixels recorded with defective peripheral nozzles are often similar. . Therefore, if the quantization error of the pixel of interest is diffused to each peripheral pixel based on the same error diffusion window regardless of the concentration of the pixel of interest, the higher the concentration of the pixel of interest recorded by the defective nozzle and the defective peripheral nozzle, The quantization error of the pixel cannot be absorbed by the peripheral pixels, and the high density region extends from the target pixel to an excessively wide range of peripheral pixels, causing image quality degradation.

  Therefore, the storage means stores the first error diffusion window and the second error diffusion window in advance. The first error diffusion window is an error in which the quantization error of the pixel of interest is determined as a distribution amount that decreases as the distance from the pixel of interest increases for each peripheral pixel in a predetermined area including adjacent pixels adjacent to the pixel of interest. It is a diffusion window. The second error diffusion window is an error diffusion window in which the distribution amount of adjacent pixels adjacent to the target pixel is determined to be larger than that of the first error diffusion window. When the target pixel is recorded with the normal nozzle, or when the low-density target pixel is recorded with the defective nozzle or the defective peripheral nozzle, the error diffusion means determines the quantization error of the target pixel based on the first error diffusion window. Diffuse to each pixel. Further, the error diffusion means diffuses the quantization error of the target pixel to each of the peripheral pixels based on the second error diffusion window when recording the medium density target pixel with the defective nozzle or the defective peripheral nozzle. Further, the error diffusing unit prohibits the diffusion of the quantization error of the pixel of interest only to the adjacent pixel or the diffusion of the quantization error of the pixel of interest when recording the high density pixel of interest with the defective nozzle or the defective peripheral nozzle.

  The control unit prohibits the dot formation of the pixel having the minimum gradation value based on the image data obtained by converting the gradation value of each pixel by the quantization unit. In this way, by prohibiting the dot formation of the pixel having the minimum gradation value, the dot formation can be prohibited 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 formed as the gradation value of each pixel converted by the quantization unit increases. The recording head records dots corresponding to each pixel by ejecting ink droplets from each of the plurality of nozzles under the control of the control means.

  As described above, when recording a high-density pixel of interest with a defective nozzle and a defective peripheral nozzle, the pixels recorded with the defective peripheral nozzle are already in a state where large dots can be easily recorded. Diffusion only to the pixels or diffusion of the quantization error of the pixel of interest to surrounding pixels is not performed. For this reason, generation | occurrence | production of the white stripe by a defective nozzle can be suppressed, and it can suppress that a high concentration area | region spreads to an excessive range by error diffusion. In addition, when recording a target pixel of medium density with a defective nozzle and a defective peripheral nozzle, the quantization error of the target pixel is diffused more to adjacent pixels than the diffusion of the quantization error of the low density target pixel to the peripheral pixels. As a result, large dots are likely to be recorded in pixels that are recorded with defective peripheral nozzles. For this reason, white stripes due to defective nozzles can be suppressed. Also, when recording a pixel of interest with a normal nozzle and when recording a pixel of low density with a defective nozzle and a defective peripheral nozzle, the quantization error of the pixel of interest is set to each peripheral pixel within a predetermined region from the pixel of interest. Since the diffusion is performed in accordance with the distribution amount that decreases as the distance increases, the quantization error of the pixel of interest can be diffused according to the distance from the pixel of interest.

  Therefore, based on the error diffusion window according to the density, when the high-concentration target pixel is recorded by the defective nozzle or the defective peripheral nozzle, the quantization error of the target pixel is diffused only to the adjacent pixels or the quantization error of the target pixel is diffused. When the target pixel of medium density is recorded by the defective nozzle and the defective peripheral nozzle, the distribution amount of the quantization error of the target pixel to the adjacent pixels is increased compared to the distribution amount at the low density, Since it diffuses to the pixels, it suppresses the excessively high density area from spreading around the defective nozzle due to error diffusion, and suppresses the generation of white streak due to the defective nozzle because the ratio of large dots increases around the defective nozzle. Therefore, it is possible to suppress image quality deterioration due to a defective nozzle.

  The second error diffusion window may determine a distribution amount for each peripheral pixel in a region including the adjacent pixels that are narrower than the predetermined region of the first error diffusion window. When recording a target pixel of medium density with a defective nozzle and a defective peripheral nozzle, the quantization error can be diffused more intensively around the target pixel than with a low density target pixel. It is possible to suppress the high density region from being excessively extended to a wide range of peripheral pixels.

  The quantization means includes a pixel that is recorded by a nozzle at one end in the arrangement direction of a plurality of nozzles of the recording head, a pixel that is recorded by a nozzle at the other end, and a nozzle that is recorded by a nozzle at one end in the non-arrangement direction. The pixel of interest is sequentially changed toward the pixel to be recorded in step S1 to convert the gradation value to which the accumulated quantization error of the pixel of interest is added, and the error diffusing unit converts the gradation value by the quantization unit. Can be sequentially diffused. In this way, by alternately reading the gradation value of the pixel of interest in the nozzle arrangement direction and the counter arrangement direction, it is possible to suppress the quantization error of the pixel of interest from being diffused only to the peripheral pixels 79 in one direction. Can do.

  According to the ink jet recording apparatus and the ink jet recording method of the present invention, when a high density pixel of interest is recorded by a defective nozzle or a defective peripheral nozzle, the quantization error of the pixel of interest is diffused based on an error diffusion window corresponding to the density. When recording a target pixel of medium density with a defective nozzle and defective peripheral nozzles, increase the amount of quantization error of this pixel of interest to adjacent pixels compared to the amount of distribution when the density is low, and quantization error Is diffused to the surrounding pixels, so that large dots around the defective nozzle prevent white streaks from being produced by the defective nozzle, and error diffusion causes a high-density area from the target pixel recorded by the defective nozzle to an excessively wide range of surrounding pixels. It is possible to prevent the dots corresponding to the peripheral pixels of a wide range of high density from being spread over and excessively. It is possible to suppress the quality deterioration has the effect that.

  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, a large ink droplet (see FIG. 4B) from the nozzle 33B (see FIG. 4B), the nozzle 33B to small ink droplets (see FIG. 4 (D)), or prohibition of dot formation (not shown), control of medium droplet ejection, etc., such as large droplets, medium droplets, small droplets, and no droplets The dot size can be controlled.

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

  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). In 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 / density conversion unit 62, an image processing unit 64, a recording data creation unit 66, and an image recording unit 68. It is configured to include. The color / density 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 / density 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 / density 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, the gradation value is represented by 8 bits, the maximum value is 255, and the minimum value is 0. The gradation value may be expressed by other bits. Further, the color / density conversion unit 62 converts the gradation value of each pixel according to the characteristics of the paper Q and ink, so that the relationship between the density and the gradation value at the time of recording changes from the minimum density to the maximum density. The density conversion process is executed so as to be linear. The tone value of each pixel of the color-converted image data and the density when recorded on the paper Q are saturated in the region where the tone 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. If 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, the color / density conversion unit 62 performs density conversion processing so that the relationship between the density and the gradation value is linear.

  As will be described in detail later, the image processing unit 64 further converts the image data in which the gradation value of each pixel has been converted by the color / density conversion unit 62 into image data having the number of gradations that can be recorded by the inkjet recording apparatus 12. Quantization and the quantization error between the gradation value of each pixel before conversion and the gradation value after conversion by quantization generated by quantization, and processing within each pixel of color / density converted image data Add the error diffusion that diffuses to the surrounding pixels around the target pixel of interest, and the accumulated quantization error for each pixel of the diffused quantization error to the gradation value before conversion by quantization of each corresponding pixel Addition processing is executed. The image processing unit 64 is provided with a memory 65. The memory 65 stores the quantization error of the target pixel for each peripheral pixel in the predetermined area including the adjacent pixels adjacent to the target pixel according to the density corresponding to the gradation value of each pixel before conversion by quantization. A plurality of types of error diffusion windows having different distribution amounts for the same peripheral pixels, in which the distribution amounts to be distributed are determined for each peripheral pixel, are stored in advance.

  In the present embodiment, as shown in FIG. 6, the first error diffusion window 70 and the second error diffusion window according to the density determined by the gradation value of the pixel before conversion by quantization as a plurality of types of error diffusion windows. Each of the diffusion window 72 and the third error diffusion window 74 is stored in advance.

  The first error diffusion window 70 is an error diffusion window corresponding to a low density, and the distance from the target pixel 76 is set for each peripheral pixel 79 in the predetermined region 77 including the adjacent pixel 78 adjacent to the target pixel 76. A distribution amount that decreases as the value increases is determined in advance. Here, the distance from the target pixel 76 specifically indicates the distance from the nozzle that records the target pixel 76 to the nozzle that records each of the peripheral pixels 79.

  The second error diffusion window 72 is an error diffusion window corresponding to the medium density, and determines the distribution amount so that the distribution amount to the adjacent pixels 78 is larger than that of the first error diffusion window 70, and The distribution amount is determined for each peripheral pixel 79 in the region 77 where the region where the quantization error of the pixel of interest 76 is diffused is narrower than that of the one error diffusion window 70.

  The third error diffusion window 74 corresponds to a high density, and in order to inhibit the quantization error of the pixel of interest 76 from diffusing to the peripheral pixels 79, an error diffusion in which the distribution amount to each of the peripheral pixels 79 is not determined. It is a window.

  In this embodiment, the memory 65 has three types of error diffusion windows with different distribution amounts of the same peripheral pixels 79 as error diffusion windows for diffusing the quantization error of the target pixel 76 to each of the peripheral pixels 79. Although stored in advance, the number of types of error diffusion windows to be stored may be three or more, and is not limited to three.

  In addition, the memory 65 previously indicates defective nozzles that are difficult to normally eject ink droplets due to non-ejection or ejection failure of the ink droplets among the plurality of inkjet recording heads 33 provided in each color recording head 32. Position information detected at the manufacturing stage of the recording head 32 is stored in the image processing unit 64 as position information indicating the position of the defective nozzle.

  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. 7 is executed.

  In step 100, the gradation value of the pixel of interest 76 is read from the pixel of the image data that has been color-converted and density-converted by the color / density converter 62.

  In the next step 102, the cumulative quantization error of the pixel corresponding to the quantization error is added to the gradation value of the pixel of interest 76.

  In the next step 104, based on the position information indicating the position of the defective nozzle stored in the memory 65 and the position information on the image recorded on the paper Q of the pixel of interest 76, the target image read in step 100 is read. It is determined whether or not the pixel 76 is a pixel to be recorded with a defective nozzle.

  If NO in step 104, the process proceeds to step 106, and it is determined whether or not the pixel of interest 76 read in step 100 is a pixel to be recorded by a defective peripheral nozzle whose distance from the defective nozzle is a predetermined distance or less. Then, the process proceeds to step 108. The pixels recorded by the defective peripheral nozzle are, for example, pixels recorded by a nozzle adjacent to the defective nozzle and a nozzle further adjacent to the adjacent nozzle.

  In step 108, based on the gradation value to which the cumulative quantization error of the pixel of interest 76 is added, it is determined whether the density of the pixel of interest when recording is high, medium, or low. . For example, when the gradation value is within the range of 0 to 31, the low density is determined. When the gradation value is within the range of the gradation value 32 to 159, the medium density is determined. When it is within the range of the tone value 255, it is determined that the density is high.

  In the next step 110, quantization is performed to convert the gradation value of the pixel of interest 76 to which the accumulated quantization error has been added after color / density conversion into a gradation value that can be recorded by the recording head 32, and then to step 112. move on. In the present embodiment, as shown in FIG. 8, the gradation value that has undergone color / density conversion and is added with the accumulated quantization error is represented by gradation value 0, gradation value 85, gradation value 170, or gradation. Conversion is performed so as to obtain 4 gradations of tone value 255. By the quantization in step 110, the dot size when recording is set so that the dot size increases as the gradation value increases. Specifically, any one of “no droplet”, “small droplet”, “medium droplet”, and “large droplet” as the dot size at the time of recording of the pixel recorded by the defective peripheral nozzle by the processing of step 110. Is set. Note that the number of gradations that can be recorded by the recording head 32 is not limited to the above-described four gradations, and may be, for example, three or five or more types of gradations.

  On the other hand, if the result in step 104 is affirmative, the process proceeds to step 126, where the same processing as in step 108 is executed to determine whether the density of the pixel of interest 76 is high density, medium density, or low density. Determine.

  Next, in step 128, “no drop” is set as the dot size when recording by converting the gradation value of the pixel of interest 76 which has undergone color / density conversion and the accumulated quantization error added to the minimum value 0. . By the process of step 126, it is possible to prohibit the recording of the pixel dots with the defective nozzle.

  In the next step 112, the quantization error between the gradation value of the pixel that has undergone color / density conversion and to which the accumulated quantization error has been added and the gradation value after quantization is calculated. For example, as shown in FIG. 8, since the gradation value 150 before conversion by quantization of the pixel of interest 76 recorded by the defective nozzle is converted to a gradation value 0 after conversion, the quantization error is 150. Become. Further, when the gradation value 200 before conversion due to quantization of the pixels recorded by the defective peripheral nozzles is converted into the gradation value 255 after conversion, the quantization error becomes −55. When the pixel of interest 76 is recorded with a defective nozzle, the gradation value of the pixel of interest 76 is converted to a gradation value of 0. Therefore, the quantization error of the pixel of interest 76 recorded with a defective nozzle is caused by defective peripheral nozzles and normal nozzles. This is larger than the quantization error of the pixel of interest 76 to be recorded. Furthermore, when recording the pixel of interest 76 with a defective nozzle, the higher the density according to the gradation value before conversion by quantization of the pixel of interest 76, the greater the quantization error compared to the case of low density. Become. In general, since similar gradation values often continue in adjacent pixels, the density of the target pixel 76 recorded by the defective nozzle and the density of the target pixel 76 recorded by the defective peripheral nozzle are the same density. Often becomes. Therefore, if the quantization error of the pixel of interest 76 is diffused to each of the peripheral pixels 79 based on the same error diffusion window regardless of the concentration of the pixel of interest 76, the defective pixel and the pixel of interest 76 recorded by the defective peripheral nozzle have a high density. The higher the value is, the more the quantization error of the pixel of interest 76 is not absorbed by the peripheral pixels, and the high density region extends from the pixel of interest 76 to an excessively wide range of peripheral pixels, which may cause image quality degradation.

  In the next step 114, an error diffusion window corresponding to the density of the pixel of interest 76 before quantization determined in step 126 or 108 is read from the memory 65. For example, when recording the low density pixel of interest 76 with a defective nozzle or defective peripheral nozzle, the first error diffusion window 70 is read, and when recording the medium concentration of pixel of interest 76 with a defective nozzle or defective peripheral nozzle, the second error diffusion window 70 is read. The third error diffusion window 74 is read when the high-concentration target pixel 76 is recorded by the defective nozzle or the defective peripheral nozzle.

  In the next step 116, the quantization error calculated in step 112 is based on the distribution amount determined for each peripheral pixel 79 of the pixel of interest 76 shown in the error diffusion window read in accordance with the density in step 114. And diffused to each of the peripheral pixels 79. When the low-concentration pixel of interest 76 is recorded by the defective nozzle or the defective peripheral nozzle by the processing of step 116, the quantization error of the pixel of interest 76 is calculated based on the first error diffusion window 70 as the distance from the pixel of interest 76. Is diffused to each of the surrounding pixels 79 with a distribution amount that becomes smaller as the value increases.

  Further, when recording the target pixel 76 of medium density with the defective nozzle or the defective peripheral nozzle, the distribution amount to the adjacent pixels 78 is larger than the first error diffusion window 70 based on the second error diffusion window 72. And is diffused to each of the peripheral pixels 79 in the region 77 narrower than the first error diffusion window 70. That is, when recording the target pixel 76 of medium density with the defective nozzle or the defective peripheral nozzle, the quantization error of the target pixel 76 is intensively distributed to the adjacent pixel 78 adjacent to the target pixel 76, and when the density is low. The quantization error is distributed to peripheral pixels within a narrow range including the adjacent pixels 78 as compared to the quantization error diffusion range.

  Furthermore, when the gradation value of the pixel of interest before quantization is a gradation value indicating high density, the quantization error of the pixel of interest is not diffused based on the third error diffusion window 74.

  On the other hand, if the result in Step 106 is negative, the process proceeds to Step 120, and the gradation value of the pixel of interest 76 to which the accumulated quantization error is added after color / density conversion is quantized, similar to the process in Step 110. .

  In the next step 122, as in the above step 112, the quantization of the tone value of the pixel of interest 76 to which the cumulative quantization error has been added and the tone value of the pixel of interest 76 to which the cumulative quantization error has been added and the converted tone value by quantization is performed. Calculation error is calculated.

  In the next step 124, the first error diffusion window 70 corresponding to the low density is read from the memory 65 as a reference error diffusion window, and in the next step 125, the above step 116 is performed according to the read error diffusion window. The quantization error is diffused to the peripheral pixels 79 of the target pixel 76 in the same manner as error diffusion when the low-density target pixel 76 is recorded by the defective nozzle or the defective peripheral nozzle.

  The above processing is repeated until the dot level setting is completed for all the pixels of the image data. When the dot level setting is completed for all the pixels, this routine is terminated.

  As described above, in the ink jet recording apparatus 12 of the present invention, the dot recording by the defective nozzle is prohibited, and in accordance with the gradation value before conversion by quantization of the pixel of interest 76 recorded by the defective nozzle and the defective peripheral nozzle. When the density is high, the pixels already recorded by the defective peripheral nozzles are high density at which large dots can be easily recorded. Therefore, the quantization error of the pixel of interest 76 is not diffused to the peripheral pixels 79. By doing so, it is possible to suppress the occurrence of white streak due to the defective nozzles and not to perform error diffusion, so that it is possible to suppress the high density region from spreading to an excessive range due to error diffusion. . Further, when the density corresponding to the gradation value before conversion by quantization of the target pixel 76 recorded by the defective nozzle and the defective peripheral nozzle is medium density, the target pixel when the quantization error of the target pixel 76 is low density Compared to the diffusion of the quantization error to the peripheral pixels 79, the distribution is concentrated on the adjacent pixels 78, so that it is possible to easily record a large dot from the nozzle adjacent to the defective nozzle. Furthermore, since the quantization error is diffused to the peripheral pixels 79 in a narrow area compared to the area where the quantization error of the pixel of interest 76 is diffused at the low density, the high density area due to error diffusion becomes excessively wide. Can be suppressed. Further, when the density corresponding to the gradation value before conversion of the pixel of interest 76 recorded by the defective nozzle and the defective peripheral nozzle is low, or when the pixel of interest 76 is recorded by the normal nozzle, the quantization error of the pixel of interest 76 Since each of the surrounding pixels in the predetermined area is diffused according to the distribution amount which becomes smaller as the distance from the target pixel becomes larger, and the dots are distributed in a mottled manner, white streaks due to defective nozzles are not conspicuous. A diffusion window can be used together.

  Therefore, based on the error diffusion window according to the density, when recording the high density pixel of interest with the defective nozzle or the defective peripheral nozzle, the quantization error diffusion of the pixel of interest is prohibited, and the medium density pixel of interest is designated as the defective nozzle and When recording with defective peripheral nozzles, the amount of quantization error of the pixel of interest that is distributed to neighboring pixels is increased compared to the amount of distribution when the density is low, and diffuses to the peripheral pixels. It is possible to suppress the occurrence of white streaks due to the defective nozzle because it suppresses the excessively high density area from spreading and the dots around the defective nozzle become large due to the quantization error generated by the defective nozzle. It is possible to suppress the image quality deterioration due to.

  The second error diffusion window may determine a distribution amount for each peripheral pixel in a region including the adjacent pixels that are narrower than the predetermined region of the first error diffusion window. When recording a target pixel of medium density with a defective nozzle and a defective peripheral nozzle, the quantization error can be diffused more intensively around the target pixel than with a low density target pixel. It is possible to suppress the high density region from being excessively extended to a wide range of peripheral pixels.

  Accordingly, based on the error diffusion window according to the density, when recording the high density pixel of interest 76 with the defective nozzle or the defective peripheral nozzle, the quantization error diffusion of the pixel of interest 76 is prohibited, and the medium density pixel of interest 76 is changed. When recording with defective nozzles and defective peripheral nozzles, the distribution amount of the quantization error of the pixel of interest 76 to the adjacent pixels 78 is made larger than the distribution amount when the density is low, and is diffused to the peripheral pixels. As a result, it is possible to prevent an excessively high density area from spreading around the defective nozzle, and to easily generate large dots around the defective nozzle, thereby suppressing the occurrence of white streaks due to the defective nozzle. Deterioration can be suppressed.

  In this embodiment, when the density corresponding to the gradation value before conversion by quantization of the pixel of interest 76 recorded by the defective nozzle and the defective peripheral nozzle is high, the pixels already recorded by the defective peripheral nozzle are large. Although the case where the quantization error of the pixel of interest 76 is not diffused to the peripheral pixels 79 because of the high density at which dots are easily recorded has been described, depending on the gradation value before conversion by quantization of the pixel of interest 76 When the density is high, the quantization error may be diffused only to the adjacent pixel 78 adjacent to the target pixel 76.

  In step 100, the gradation value of the pixel of interest 76 in the color / density-converted image data is read as shown in FIG. 9 at one nozzle in the arrangement direction of the nozzles for recording each pixel. In this case, reading is alternately performed from the pixel to be recorded by the nozzle at the other end to the pixel to be recorded by the nozzle at the other end, and from the pixel to be recorded by the nozzle at one end in the opposite arrangement direction to the pixel to be recorded by the other end nozzle. Thus, by alternately reading the gradation value of the pixel of interest 76 in the nozzle arrangement direction and the counter arrangement direction, the quantization error of the pixel of interest 76 is prevented from being diffused only to the peripheral pixels 79 in one direction. can do.

Further, in this embodiment, the case where the quantization error is diffused based on the error diffusion window corresponding to the density before quantization in the defective peripheral nozzle has been described. However, as shown in FIG. during diffusion may prohibit the diffusion of quantization error for the peripheral pixels 79 to be printed by the defective nozzle 33B _1. In this case, after the process of step 114 and before the process of step 116, the distribution amount corresponding to the peripheral pixel 79 recorded by the defective nozzle of the corresponding error diffusion window is corrected to 0, and error diffusion is performed after the correction. After that, the distribution amount may be returned to the value before correction.

  In this way, error diffusion to pixels to be recorded with a defective nozzle can be prohibited, so that error diffusion processing can be performed efficiently.

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 maintenance state of the inkjet recording device of this invention. 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. It is a schematic diagram which shows an example of several types of error diffusion window according to a density | concentration. It is a flowchart which shows the process performed by an image process part. It is a schematic diagram which shows the flow of quantization and error diffusion. It is a schematic diagram which shows the advancing direction with respect to the arrangement direction of the nozzle of the error diffusion process of each pixel of image data. FIG. 6 is a schematic diagram showing that error diffusion is not performed on pixels recorded with a defective nozzle.

Explanation of symbols

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

Claims (4)

A recording head for recording dots corresponding to each pixel by ejecting ink droplets from each of the plurality of nozzles;
Adding means for adding the cumulative quantization error input to the gradation value of each corresponding pixel of the image data in which the data of each pixel is represented by the gradation value according to the density;
When recording the target pixel of the image data with a defective nozzle incapable of normal dot formation, the gradation value to which the cumulative quantization error of the target pixel is added is converted to a minimum value, and the target pixel is When recording with a defective peripheral nozzle located in the vicinity of the defective nozzle, and when recording with a normal nozzle other than the defective nozzle and the defective peripheral nozzle, the gradation value to which the accumulated quantization error of the pixel of interest is added Quantization means for converting dots into recordable gradation values by the recording head;
The quantization error determined by the gradation value before conversion of the pixel of interest and the gradation value after conversion is expressed as a distance from the pixel of interest for each peripheral pixel in a predetermined area including adjacent pixels adjacent to the pixel of interest. A first error diffusion window in which a distribution amount to be distributed is set so as to become larger, and a distribution for each neighboring pixel so that a distribution amount of each adjacent pixel becomes larger than the first error diffusion window. Storage means for storing in advance a second error diffusion window that defines the amount;
When the pixel of interest is recorded by the normal nozzle, or when the pixel of interest having a low density is recorded by the defective nozzle or the defective peripheral nozzle, the quantization error of the pixel of interest is based on the first error diffusion window. When the target pixel of medium density is recorded by the defective nozzle or the defective peripheral nozzle, the quantization error of the target pixel is determined for each peripheral pixel based on the second error diffusion window. When diffusing and recording the high-density pixel of interest with the defective nozzle or the defective peripheral nozzle, the quantization error of the pixel of interest is diffused only to adjacent pixels or the quantization error of the pixel of interest is prohibited from being diffused, Error diffusion means for inputting a cumulative quantization error for each pixel of the diffused quantization error to the adding means;
Based on the image data in which the gradation value is converted by the quantization means, the dot formation of the pixel having the minimum gradation value is prohibited, and the larger the gradation value, the larger the dots are recorded. Control means for controlling the head;
An ink jet recording apparatus comprising:   The inkjet recording apparatus according to claim 1, wherein the second error diffusion window has a distribution amount determined for each peripheral pixel in an area including the adjacent pixels that is narrower than the predetermined area of the first error diffusion window.   The quantization means includes a pixel that is recorded by a nozzle at one end in the arrangement direction of a plurality of nozzles of the recording head, a pixel that is recorded by a nozzle at the other end, and a nozzle that is recorded by a nozzle at one end in the non-arrangement direction. The pixel of interest is sequentially changed toward the pixel to be recorded in step S1 to convert the gradation value to which the accumulated quantization error of the pixel of interest is added, and the error diffusing unit converts the gradation value by the quantization unit. The inkjet recording apparatus according to claim 1, wherein the quantization error of the pixel of interest having been converted is sequentially diffused. By ejecting ink droplets from each of the plurality of nozzles, dots corresponding to each pixel are recorded,
When the target pixel of the image data in which the data of each pixel is represented by the gradation value according to the density is recorded by a defective nozzle that cannot form a normal dot, the cumulative quantization error of the target pixel is added. When the gradation value is converted to the minimum value and the pixel of interest is recorded with a defective peripheral nozzle located around the defective nozzle, and when recording with a normal nozzle other than the defective nozzle and the defective peripheral nozzle, Converting the gradation value to which the cumulative quantization error of the pixel of interest is added into a gradation value with which the recording head can record dots,
The quantization error determined by the gradation value before conversion of the pixel of interest and the gradation value after conversion is expressed as a distance from the pixel of interest for each peripheral pixel in a predetermined area including adjacent pixels adjacent to the pixel of interest. A first error diffusion window in which a distribution amount to be distributed is set so as to become larger, and a distribution for each neighboring pixel so that a distribution amount of each adjacent pixel becomes larger than the first error diffusion window. Pre-store a second error diffusion window defining the amount;
When the pixel of interest is recorded by the normal nozzle, or when the pixel of interest having a low density is recorded by the defective nozzle or the defective peripheral nozzle, the quantization error of the pixel of interest is based on the first error diffusion window. When the target pixel of medium density is recorded by the defective nozzle or the defective peripheral nozzle, the quantization error of the target pixel is determined for each peripheral pixel based on the second error diffusion window. When diffusing and recording the high-density pixel of interest with the defective nozzle or the defective peripheral nozzle, the quantization error of the pixel of interest is diffused only to adjacent pixels or the quantization error of the pixel of interest is prohibited from being diffused, Enter the accumulated quantization error for each pixel of the diffused quantization error,
Add the accumulated quantization error to the gradation value of each corresponding pixel of the image data,
Based on the image data in which the gradation value is converted by the quantization means, the dot formation of the pixel having the minimum gradation value is prohibited, and the larger the gradation value, the larger the dots are recorded. Control the head,
Inkjet recording method.

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