JP5321446B2 - Image data processing apparatus and recording liquid ejection apparatus - Google Patents

Description

  The present invention relates to an image data processing apparatus that processes image data relating to an image recorded on a recording medium by discharging recording droplets from a plurality of discharge ports, and a liquid discharge apparatus including the image data processing apparatus.

  In an inkjet recording apparatus, color bleeding (bleeding) is likely to occur at the edge portion of the boundary between two colors where different colors are adjacent to each other. As a countermeasure, a method is adopted in which the ink discharge amount at the edge portion of the two-color boundary is smaller than that in the region other than the edge portion (see, for example, Patent Document 1).

JP-A-5-162339

  In the above-described technique, since the ink discharge amount is reduced at the edge portion of the boundary between the two colors, the color blur is suppressed, but the banding (white streaks) is easily noticeable due to the ink landing misalignment or the ink droplet discharge failure. Occurs.

  An object of the present invention is to provide an image data processing apparatus and a recording liquid ejecting apparatus capable of suppressing banding from being noticeable while suppressing color bleeding at an edge portion.

  The image data processing apparatus of the present invention has a plurality of ejection openings corresponding to the recording droplets of a plurality of colors, and forms an image by ejecting the recording droplets from the plurality of ejection openings onto a recording medium. Or an image data processing apparatus relating to a recording liquid ejecting apparatus having a plurality of recording liquid ejecting heads, wherein each of the plurality of pixels arranged in a matrix corresponding to the recording medium is assigned to each of the recording liquids of the plurality of colors. Image data storage means for storing image data having density values corresponding to the discharge amount, and for each of the plurality of colors, when recording droplets are discharged from the plurality of discharge ports to form dots on the recording medium In addition, the distance between other dots adjacent to each other in the direction orthogonal to the relative movement direction of the recording liquid ejection head and the recording medium is the same as the distance between the dots and the other adjacent dots. Specific nozzle storage means for storing the discharge ports in which dots different from the distance corresponding to the pixels corresponding to the nozzles are formed, and recording liquid from the discharge ports stored in the specific nozzle storage means based on the image data Specific pixel storage means for specifying and storing a specific pixel that is an ejected pixel, and at least one of the edges where the pixels having different combinations of density values of the plurality of colors are adjacent to each other based on the image data Edge region extracting means for extracting an edge region including a portion, and density value changing means for changing an average value of density values of the plurality of colors relating to pixels located in the edge region. When the specific pixel is included in the edge area, the density value changing unit includes the density values of the plurality of colors relating to pixels located in the edge area other than the specific area including the specific pixel in the edge area. The density value of the plurality of colors is changed so that the average value of the plurality of colors is small, and the change amount of the average value of the density values of the plurality of colors related to the pixels located in the specific area is the non-specific area. Decreasing the density values of the plurality of colors so as to be less than the change amount of the average value of the density values of the plurality of colors relating to the pixels located in the edge region, or the plurality relating to the pixels located in the specific region The average value of the color density values is not changed.

  The recording liquid ejection apparatus of the present invention includes one or more recording liquid ejection heads that eject recording droplets of a plurality of colors onto a recording medium to form an image from a plurality of ejection ports, and the above-described image data processing apparatus. It has.

  According to the present invention, in the recording medium on which the image is recorded, since the discharge amount of the recording liquid in the edge region is reduced, it is possible to prevent the color blur of the edge of the image formed on the recording medium and Of these, the discharge amount of the recording liquid in the specific area is higher than that in the area excluding the specific area, so that banding is suppressed from being noticeable in the image recorded on the recording medium even when the banding is likely to occur in the edge portion. be able to.

  In the present invention, it is preferable that the edge region includes all edges in which the difference in brightness between the pixels adjacent to the edge portion is a predetermined value or more. According to this, since the bleeding becomes significant when the difference in brightness between the pixels adjacent to the edge is equal to or larger than a predetermined value, the density value reduction by the density value reducing means is effective. It is possible to suppress the conspicuous banding of the generated image.

  In the present invention, the density value changing unit reduces the density values of the plurality of colors for each pixel located in the edge region, thereby density values of the plurality of colors relating to the pixel located in the edge region. It is preferable to reduce the average value. According to this, it is possible to suppress the banding of the image recorded on the recording medium from being conspicuous by a simple process of changing the density value (recording liquid ejection amount) of each pixel located in the edge region.

  Further, in the present invention, when the density value changing unit is a pixel corresponding to the ejection port from which the specific pixel cannot eject a recording droplet, the discharge value relating to the pixel located in the specific region is determined. It is preferable to make the reduction amount of the average value of the density value related to at least one of the other colors smaller than the reduction amount of the average value of the density value related to the color corresponding to the exit. According to this, even when there is a non-ejection outlet, it is possible to efficiently suppress the banding from being noticeable.

  In addition, in the present invention, the density value changing unit relates to the specific pixel when only one of the plurality of color density values related to the specific pixel exceeds 0. Reduction of the average value of the density values of the plurality of colors related to the pixels located in the specific region as compared to when the density values of two or more colors among the density values of the plurality of colors exceed 0 It is preferable to reduce the amount. According to this, it is possible to reliably suppress the banding from conspicuous in the edge portion including a single color dot that is easily banded.

  Further, in the present invention, the density value changing means applies the pixel located in the specific region as the brightness of the dot color indicated by the combination of the density values of the plurality of colors related to the specific pixel decreases. It is preferable to reduce the reduction amount of the average value of the density values of the plurality of colors. According to this, it is possible to efficiently suppress the banding from being conspicuous in an area where the banding is conspicuous and the brightness is low.

  Furthermore, in the present invention, as the density value changing unit decreases the density of pixels in which the density value of at least one of the plurality of colors in the specific region relating to the image data exceeds 0, It is preferable that a reduction amount of an average value of density values of the plurality of colors related to pixels located in the specific region is reduced. According to this, it is possible to efficiently suppress the banding from being noticeable in the low concentration region where the banding is easily noticeable.

  In the present invention, the density value changing means reduces the average value of the density values of the plurality of colors relating to the pixels located in the specific area as the recording liquid penetration rate into the recording medium decreases. Is preferably reduced. According to this, it is possible to efficiently suppress the conspicuous banding even in a recording medium in which the banding is conspicuous due to a small amount of liquid bleeding.

  Further, in the present invention, when the density value changing means is an area to which the treatment liquid that lowers the permeability of the recording liquid in the recording medium is applied, the specific area is the area in the recording medium. It is preferable that the reduction amount of each of the average values of the density values of the plurality of colors related to the pixels located in the specific region is smaller than that in the region where the treatment liquid is not applied. According to this, it is possible to efficiently suppress the banding from being noticeable even in an area where the banding is easily noticeable due to a small amount of liquid bleeding.

  Furthermore, in the present invention, it is preferable to further include detection means for detecting the specific pixel. According to this, the characteristic pixel can be reliably detected.

  In the present invention, the specific pixel may be determined by a physical configuration of the recording liquid ejection head. According to this, since it is not necessary to detect a characteristic pixel, processing becomes easy.

  According to the present invention, in the recording medium on which the image is recorded, since the discharge amount of the recording liquid in the edge region is reduced, it is possible to prevent the color blur at the edge portion of the image formed on the recording medium and the edge region. Since the discharge volume of the recording liquid in a specific area is higher than the area excluding the specific area, even if a situation where banding is likely to occur at the edge portion, the banding is suppressed from being noticeable in the image recorded on the recording medium. can do.

1 is a schematic plan view of an inkjet printer according to an embodiment of the present invention. It is sectional drawing along the width direction of the inkjet head shown in FIG. It is sectional drawing regarding the III-III line | wire shown in FIG. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. It is a functional block diagram of the control apparatus shown in FIG. It is a figure which shows the test pattern printed on a paper by the specific pixel detection part shown in FIG. It is a figure which shows the specific example of the reduction process of the density value change part shown in FIG. It is a figure for demonstrating a process when the edge area | region extraction part shown in FIG. 5 detects a process target edge part. It is a figure which shows the specific example of the suppression process of the density | concentration value change part shown in FIG. 6 is a flowchart illustrating an operation procedure of a printing process performed by the control device illustrated in FIG. 5. It is a figure for demonstrating a modification.

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

  As shown in FIG. 1, the ink jet printer 101 includes a transport unit 20 that transports the paper P from the upper side to the lower side of FIG. 1, and inks of magenta, cyan, yellow, and black on the paper P transported by the transport unit 20. There are four inkjet heads 1 that respectively eject droplets, and a control device 16 that controls the entire inkjet printer 101. In the present embodiment, the sub-scanning direction is a direction parallel to the transport direction when the paper P is transported by the transport unit 20, and the main scanning direction is a direction orthogonal to the sub-scanning direction and along the horizontal plane. Direction.

  The transport unit 20 includes two belt rollers 6 and 7 and an endless transport belt 8 wound around the rollers 6 and 7. The belt roller 7 is a driving roller, and rotates when a driving force is applied from a conveyance motor (not shown). The belt roller 6 is a driven roller and rotates as the conveyor belt 8 travels due to the rotation of the belt roller 7. The paper P placed on the outer peripheral surface of the transport belt 8 is transported downward in FIG.

  The four inkjet heads 1 each extend along the main scanning direction and are arranged in parallel to each other in the sub-scanning direction. That is, the ink jet printer 101 is a line type color ink jet printer in which a plurality of ejection openings 108 for ejecting ink droplets in the main scanning direction are arranged. The lower surface of each inkjet head 1 is an ejection surface on which a plurality of ejection ports 108 (see FIG. 4) are arranged.

  The outer peripheral surface of the upper loop of the conveyor belt 8 and the discharge surface are parallel to each other while facing each other. When the paper P transported by the transport belt 8 passes immediately below the four ink jet heads 1, ink droplets of each color are sequentially ejected from the respective ink jet heads 1 toward the upper surface of the paper P, and are then onto the paper P. A desired color image is formed.

  Next, the inkjet head 1 will be described in detail with reference to FIGS. In FIG. 3, the lower housing 87 is omitted.

  As shown in FIG. 2, the inkjet head 1 includes a reservoir unit 71, a head body 2 including a flow path unit 9 and an actuator unit 21, a COF in which one end is connected to the actuator unit 21 and a driver IC 52 is mounted. (Chip On Film: flat flexible substrate) 50 and a control substrate 54 to which the other end of the COF 50 is connected. Further, the inkjet head 1 includes an upper housing 86 and a lower housing 87 that form a box surrounding the reservoir unit 71 and the flow path unit 9, and a head cover 55 that surrounds the control substrate 54 above the upper housing 86. have.

  The reservoir unit 71 is a flow path forming member that is fixed to the upper surface of the head body 2 and supplies ink to the head body 2. The reservoir unit 71 is a stacked body in which four plates 91 to 94 are aligned and stacked, and an ink inflow channel (not shown), an ink reservoir 72, and 10 The ink outflow channels 73 are formed so as to communicate with each other. In FIG. 2, only one ink outflow channel 73 appears. The ink inflow channel is a channel through which ink from the ink tank flows. The ink reservoir 72 is an ink reservoir that temporarily stores the ink that has flowed from the ink inflow passage. The ink outflow channel 73 is a channel through which the ink from the ink reservoir 72 flows out, and communicates with the ink supply port 105 b formed on the upper surface of the channel unit 9. Ink from the ink tank flows into the ink reservoir 72 through the ink inflow channel, passes through the ink outflow channel 73, and is supplied to the channel unit 9 from the ink supply port 105b.

  Further, a recess 94 a is formed on the lower surface of the plate 94. The recess 94 a forms a gap 90 with the upper surface of the flow path unit 9. In the gap 90, the four actuator units 21 on the flow path unit 9 are arranged at equal intervals along the longitudinal direction of the flow path unit 9. Further, the lower surface of the plate 94 has a convex portion (a portion other than the concave portion 94 a) bonded to the flow path unit 9. An ink outflow channel 73 is formed in the convex portion.

  The control board 54 is disposed above the upper housing 86 and controls the driving of the actuator unit 21 via the driver IC 52 of the COF 50.

  Further, the head body 2 will be described with reference to FIGS. 3 and 4. In FIG. 4, for convenience of explanation, the pressure chamber 110, the aperture 112, and the discharge port 108 that are to be drawn by broken lines below the actuator unit 21 are drawn by solid lines.

  As shown in FIG. 3, the head body 2 is a laminated body in which four actuator units 21 are fixed to the upper surface 9 a of the flow path unit 9. As shown in FIGS. 3 and 4, the flow path unit 9 has an ink flow path including a pressure chamber 110 and the like formed therein. The actuator unit 21 includes a plurality of actuators corresponding to the pressure chambers 110, and has a function of selectively giving ejection energy to the ink in the pressure chambers 110.

  The flow path unit 9 is a laminated body in which a plurality of metal plates made of stainless steel are aligned with each other. A large number of individual ink flow paths are formed in the flow path unit 9 from the manifold flow path 105 to the sub-manifold flow path 105a, and from the outlet of the sub-manifold flow path 105a to the discharge port 108 through the pressure chamber 110.

  A total of ten ink supply ports 105 b are opened on the upper surface 9 a of the flow path unit 9 corresponding to the ink outflow flow path 73 (see FIG. 2) of the reservoir unit 71. A discharge surface is formed on the lower surface of the flow path unit 9, and a large number of discharge ports 108 are arranged in a matrix. The ejection ports 108 are arranged at an interval of 600 dpi, which is the resolution in the main scanning direction with respect to the main scanning direction.

  The ink flow in the flow path unit 9 will be described. As shown in FIGS. 3 to 4, the ink supplied from the reservoir unit 71 into the flow path unit 9 through the ink supply port 105 b is distributed from the manifold flow path 105 to the sub-manifold flow path 105 a. The ink in the sub-manifold channel 105 a flows into each individual ink channel and reaches the ejection port 108 via the pressure chamber 110.

  On the downstream side of the four inkjet heads 1 in the transport direction, a line sensor 30 that faces the outer peripheral surface of the transport belt 8 is disposed. The line sensor 30 has a plurality of optical elements arranged in the main scanning direction, and can read an image printed on the paper P by ink droplets ejected from the four inkjet heads 1. Yes.

  Next, the control device 16 will be described with reference to FIG. The control device 16 includes a CPU (Central Processing Unit), a program executed by the CPU, and an EEPROM (Electrically Erasable and Programmable Read Only Memory) that stores data used for these programs in a rewritable manner. It includes RAM (Random Access Memory) for temporary storage. Each functional unit constituting the control device 16 is constructed by cooperation of these hardware and software in the EEPROM. As shown in FIG. 5, the control device 16 controls the entire inkjet printer 101, and includes a conveyance control unit 31, an image data processing unit 33, and a head control unit 34.

  The transport control unit 31 controls the transport motor of the transport unit 20 so that the paper P is transported along the transport direction.

  The image data processing unit 33 performs preprocessing of image data relating to an image to be printed on the paper P. The image data processing unit 33 includes an image data storage unit 41, a specific nozzle detection unit 47, a specific nozzle storage unit 48, a specific pixel detection unit 44, a specific pixel storage unit 45, an edge region extraction unit 42, and a density value change. Part 43. The image data storage unit 41 stores image data relating to an image printed on the paper P. The image data indicates density values (ink ejection amounts) of four colors of magenta, cyan, yellow, and black for each pixel arranged in a matrix corresponding to the print area of the paper P. The density value is a value quantized into four values according to the ink discharge amount, and is indicated by 0 to 3. The density value 3 corresponds to a large drop (12 pl), the density value 2 corresponds to a medium drop (8 pl), the density value 1 corresponds to a small drop (4 pl), and the density value 0 corresponds to no discharge (0 pl).

  The specific nozzle detection unit 47, the specific nozzle storage unit 48, and the specific pixel detection unit 44 correspond to the ejection ports 108 that cause the ink droplet landing positions to shift in the main transport direction for each inkjet head 1, as will be described in detail later. Specific pixel detection processing is performed in which the pixel corresponding to the non-ejection ejection port 108 in which ejection of the ink droplet and the ejection of the ink droplet is disabled is detected as the specific pixel.

  Due to the physical characteristics of the inkjet head 1 and a part of the ejection port 108 being blocked by thickened ink or impurities, the ink droplet landing position is displaced. Further, when the ejection port 108 is completely blocked by thickened ink or impurities, the ejection port 108 cannot be ejected. The physical characteristics of the inkjet head 1 are, for example, variations in the ink ejection characteristics related to the ejection ports 108 due to individual differences of the actuator units 21 and errors in the attachment position with respect to the flow path unit 9. In the present embodiment, a difference in ink discharge characteristics tends to occur between the discharge ports 108 that are adjacent to each other in the main scanning direction on the discharge surface and that correspond to different actuator units 21. For each inkjet head 1, when dots corresponding to all the pixels are formed on the paper P, the distance between the dot relating to the specific pixel and other dots adjacent to each other in the direction orthogonal to the transport direction (main scanning direction) is It differs from the unit distance (600 dpi in this embodiment) regarding a pixel. For this reason, white stripes (banding) extending in the transport direction are likely to occur in the vicinity of the dots corresponding to the specific pixels related to the image printed on the paper P.

  The specific pixel detection process will be described. When the specific nozzle detection unit 47 starts the specific pixel detection process, the head control unit 34 and the conveyance control unit 31 print a test pattern as shown in FIG. In a region facing the actuator unit 21 on the ejection surface, a plurality of ejection ports 108 are arranged in a trapezoidal matrix, and the plurality of ejection ports 108 are ejection ports composed of ejection ports 108 arranged in the main scanning direction. A plurality of rows are formed (see FIGS. 3 and 4). The test pattern is for each ejection port 108 by ejecting ink droplets simultaneously from a predetermined number of ejection ports 108 in order from one side in the main scanning direction for each ejection port array that appears in order from the upstream side in the transport direction. A straight line extending in the transport direction is formed on the paper P. As a result, a straight line group arranged in a trapezoidal matrix is formed on the paper P. Each straight line indicates a position in the main transport direction of dots formed by ink droplets ejected from the corresponding ejection port 108. The specific nozzle detection unit 47 prints a test pattern composed of straight lines relating to all of the ejection ports 108 on the paper P by repeatedly forming a predetermined number of straight lines shifted by one dot in the main scanning direction. In addition, in FIG. 6, the straight line regarding the discharge outlet 108 facing one actuator unit 21 is shown typically. A straight line related to the discharge port 108 facing the other actuator unit 21 is formed in the same manner.

  Further, the specific nozzle detection unit 47 reads the test pattern printed on the paper P by the line sensor 30. The specific nozzle detection unit 47 measures the separation distance between straight lines adjacent to each other in the transport direction in the test pattern from the reading result of the line sensor 30. In FIG. 6, for example, the separation distances between the straight lines AB, the straight lines BC, and the straight lines CD are measured. At this time, the specific nozzle detection unit 47 uses, as the measurement result, an average value of the separation distances at three positions where the positions in the sub-scanning direction (conveyance direction) differ in the straight lines. The specific nozzle detection unit 47 determines, based on the separation distance measured for all the straight lines related to the test pattern, the ejection positions of the ink droplet landing positions and the ejection openings 108 causing the non-ejection of the ink droplets for each inkjet head 1. The corresponding discharge port 108 is specified. Then, the specific nozzle detection unit 47 stores, in the specific nozzle storage unit 48, the ejection port 108 corresponding to the ejection port 108 where the ink droplet landing position is displaced and the ink droplets are not ejected. The specific pixel detection unit 44 detects a specific pixel that is a pixel associated with the ejection port 108 stored in the specific nozzle storage unit 48, and the detected specific pixel and the ejection port 108 in which the specific pixel is not ejected. Whether or not there is is stored in the specific pixel storage unit 45.

  The specific pixel storage unit 45 stores the specific pixel and whether or not the specific pixel is a non-ejection ejection port 108 based on the detection result of the specific pixel detection unit 44.

  As shown in FIG. 7, the edge region extraction unit 42 is based on image data stored in the image data storage unit 41, and edge portions (edges) in which pixels having different combinations of four color density values are adjacent to each other. Among these, a difference in color parameters including at least one of saturation, brightness, and hue of a color (dot color) obtained by combining four color density values between adjacent pixels across the edge portion is greater than or equal to a predetermined value. The processing target edge portion is detected. As a specific example, for pixels adjacent to each other with the edge portion interposed therebetween, the brightness of the pixel is calculated from the density values of the four colors of the pixel and the values shown in the table of FIG. As shown in the table of FIG. 8, in order from the darkest color to the color of each ink, black is weighted as 1, magenta is 2, cyan is 3, yellow is 4, and the amount of ink is large. In order from the first, a large drop is assigned a weight of 1, a medium drop is assigned a weight of 2, and a small drop is assigned a weight of 3, and the lightness is calculated by multiplying the weight of the color and the weight of the amount. That is, for example, the lightness in the case of a yellow medium drop is (4 × 2 =) 8, and the lightness in the case of a black small drop is (1 × 3 =) 3. Then, the brightness difference between adjacent pixels across the edge is determined. That is, for example, when comparing a pixel corresponding to a yellow medium droplet with a pixel corresponding to a black droplet, the brightness of the pixel is 8 and 3, and the difference between them is (8-3 = ) 5 If the difference in brightness is large, bleeding between the adjacent pixels across the edge portion becomes significant. The number of lightness differences at which bleeding becomes noticeable (that is, the predetermined value of the lightness difference) is appropriately set according to the ink component, the type of recording medium, and the like. Further, the edge region extraction unit 42 extracts a predetermined range centering on the detected processing target edge portion (for example, a range of two dots on both sides centering on the edge portion in this embodiment) as an edge region. Note that the difference in color parameters for detecting the processing target edge can be arbitrarily set.

  The density value changing unit 43 performs a reduction process for reducing the average value of the density values of the four colors related to the pixels located in the edge region extracted by the edge region extracting unit 42 for the image data stored in the image data storage unit 41. Do. Specifically, the density value changing unit 43 sets the density value of each pixel having a density value of 2 or more (medium droplet and large droplet) to 1 (small droplet) for each of the four colors among the pixels located in the edge region. ). In this way, by reducing the average value of the density values of the pixels located in the edge region, it is possible to suppress occurrence of color bleeding (bleeding) in the processing target edge portion of the two-color boundary where different colors are adjacent to each other, It is suppressed that the image quality concerning the printed image falls.

  As shown in FIG. 9, the density value changing unit 43 suppresses the reduction amount of the average value of the density values of the four colors related to the pixels located in the specific area including the specific pixels in the edge area subjected to the above-described reduction processing. Perform suppression processing. When the suppression process is started, the density value changing unit 43 determines a specific region including the specific pixel stored in the specific pixel storage unit 45 in the edge region where the reduction process has been performed. In this embodiment, the specific area is a two-dot range centered on the processing target edge as in the edge area, but the specific area is the same as or narrower than the edge area. Any pixel can be arbitrarily determined.

  Then, the density value changing unit 43 converts a reduction amount (hereinafter, simply referred to as a reduction amount) related to the average value of the density values of the four colors related to the pixels located in the specific region into an edge region that does not include the specific region (see FIG. 7)).

  Specifically, when the specific area includes specific pixels related to the positional deviation of the ink droplet landing position, the density value changing unit 43, as shown in FIG. 9A, out of the pixels located in the specific area For each color, the amount of reduction is suppressed by setting the density value of each pixel whose density value is 1 (small droplet) to 2 (medium droplet) by the reduction process. As described above, with respect to specific pixels related to misregistration, the corresponding dot formation position deviates from a desired position with respect to the main transport direction. Therefore, when the density value is reduced to the minimum 1 (small droplet), the main scan direction The distance between adjacent dots increases, and banding is likely to occur in the printed image. Therefore, in the present invention, by reducing the amount of reduction in the specific area and increasing each dot, the distance between adjacent dots in the main scanning direction is reduced, and banding is suppressed from being noticeable in the printed image.

  On the other hand, when the specific area includes specific pixels related to non-ejection of ink droplets, the density value changing unit 43 performs non-ejection related to pixels located in the specific area as shown in FIG. The amount of reduction for other colors is made smaller than the amount of reduction for colors. For example, when the ejection port 108 that ejects cyan ink droplets is non-ejection, among the pixels located in the specific region, at least one of the density values of magenta, yellow, and black is 1 (small droplet) by the reduction process. The density value of the color is set to 3 (large drop) for a plurality of pixels arranged at a predetermined interval among the pixels that become), and the density value of the color is set to 2 (medium drop) for the other remaining pixels. To. Thereby, the reduction amount regarding colors other than cyan relating to the specific region is suppressed. In the specific region corresponding to the non-ejection, the ink ejection amount of the specific color that has become non-ejection becomes zero, and the ink ejection amount becomes insufficient, and the diameter of the dots formed on the paper P becomes smaller than necessary. . For this reason, the distance between adjacent dots increases in the main scanning direction with respect to the dot, and banding is likely to occur in the printed image. Therefore, in the present invention, the ink discharge amount that is insufficient due to non-ejection is supplemented with ink of other colors to prevent the corresponding dot diameter from becoming unnecessarily small, and banding is conspicuous in the printed image. It is suppressed.

  Further, in the suppression process, when the dot corresponding to the specific pixel is a single color (when only the density value of one color exceeds 0), the density value changing unit 43 is a mixed color. Compared with (when the density values of two or more colors exceed 0), the amount of reduction of each color related to the pixel located in the specific region is suppressed. The suppression of the reduction amount is adjusted by returning a part of the pixels whose density values are reduced by the reduction process to the original density values. As a result, the banding is suppressed from being noticeable in the edge portion including the single-colored dots that are easily noticeable.

  Further, in the suppression process, the density value changing unit 43 reduces the reduction amount of each color related to the pixel located in the specific region as the brightness of the dot corresponding to the specific pixel becomes low. As a result, it is possible to suppress the banding from being noticeable in the low brightness area where the banding is easily noticeable.

  Further, in the suppression process, the density value changing unit 43 reduces the reduction amount of each color related to the pixels located in the specific area as the dot density in the specific area (the density of the pixels whose density value exceeds 0) decreases. To do. As a result, the banding is suppressed from being noticeable in the low concentration region where the banding is easily noticeable.

  Further, in the suppression process, the density value changing unit 43 has a formation region formed only by pixels having the same density value for each color as the pixels forming the processing target edge portion, orthogonal to the extending direction of the processing target edge portion. As the number of pixels related to the direction decreases, the reduction amount of each color related to the pixels located in the specific region is reduced. Thereby, it is suppressed that banding stands out in the thin line where banding is more conspicuous.

  Further, in the suppression process, the density value changing unit 43 reduces the reduction amount of each color related to the pixels located in the specific region as the ink penetration rate with respect to the paper P decreases. Thereby, it is possible to suppress the banding from being conspicuous in the paper P in which the banding is easily noticeable due to the low ink penetration rate.

  The density value changing unit 43 stores the image data subjected to the reduction process and the suppression process in the image data storage unit 41.

  The head control unit 34 drives the actuator unit 21 of each inkjet head 1 based on the image data subjected to the reduction process and the suppression process by the density value changing unit 43, thereby causing the desired volume of ink droplets to be generated. It discharges from the discharge outlet 108 at a timing.

  Next, the printing process will be described. When the printing process is started, as shown in FIG. 10, the specific nozzle detection unit 47, the specific nozzle storage unit 48, and the specific pixel detection unit 44 perform specific pixel detection processing to detect specific pixels (S101). The specific pixel detection process is performed only when a predetermined time has elapsed after the inkjet printer 101 is activated or when an instruction is given from the user. Then, the image data transmitted from the host computer is stored in the image data storage unit 41 (S102). The edge region extraction unit 42 detects the processing target edge portion of the two-color boundary based on the image data stored in the image data storage unit 41 (S103), and extracts the edge region including the detected processing target edge portion. (S104). The density value changing unit 43 performs a reduction process for reducing the average value of the density values of the four colors related to the pixels located in the edge region extracted by the edge region extracting unit 42 (S105). Further, the density value changing unit 43 determines a specific region including the specific pixel stored in the specific pixel storage unit 45 in the edge region subjected to the reduction process (S106). Then, the density value changing unit 43 performs a suppression process for suppressing the reduction amount of the average value of the density values of the four colors related to the pixels located in the determined specific area (S107). The head control unit 34 and the conveyance control unit 31 print an image on the paper P based on the image data subjected to the reduction process and the suppression process (S108). Since the present embodiment is a line-type color ink jet printer, the specific pixels relating to the dots formed on the paper P by the specific nozzles stored in the specific nozzle storage unit 48 are constant regardless of the image data. On the other hand, in the case of a serial type inkjet head in which the head moves in the main scanning direction, the position of the specific pixel with respect to the paper P is different for each image, so that the specific pixel is detected for each image.

  As described above, according to the ink jet printer 101 of the present embodiment, the density (ink discharge amount) of the dots located in the edge region is reduced in the paper P on which the image is printed. It is possible to prevent color bleeding at the edge portion to be processed. In addition, since the average value of the ink discharge amount corresponding to the specific region in the edge region is higher than the average value of the ink discharge amount in the edge region that does not include the specific region, banding is likely to occur in the processing target edge portion. Even if it occurs, it is possible to suppress the noticeable banding in the image printed on the paper P.

  Further, the density value changing unit 43 processes the image printed on the paper P so that the edge region includes all edge portions in which the brightness difference between pixels adjacent to the edge portion is equal to or greater than a predetermined value. It is possible to surely prevent the color blur of the target edge part and to suppress the banding from being noticeable.

  In addition, the density value changing unit 43 reduces the density value of each color for each pixel located in the edge region in the reduction process and the suppression process, whereby the average value of the density values of each color related to the pixels located in the edge area Therefore, it is possible to prevent the color blur at the processing target edge portion of the image printed on the paper P by a simple process of changing the density value of each pixel located in the edge region, and the banding is conspicuous. Can be suppressed.

  Further, in the suppression process, the density value changing unit 43 reduces the average value of density values related to other colors from the reduction value of the average value of density values related to non-ejection colors related to pixels located in the specific region. Suppress. As a result, for specific pixels related to non-ejection, the ink ejection amount that is insufficient when the non-ejection specific color ink ejection amount becomes 0 reduces the reduction amount of the other color ink ejection amount. Therefore, the corresponding dot diameter is prevented from becoming unnecessarily small, and banding is suppressed from being noticeable in the printed image.

  In addition, when the dot corresponding to the specific pixel is a single color in the suppression process, the density value changing unit 43 compares the color of each color related to the pixel located in the specific area as compared to when the corresponding dot is a mixed color. In order to suppress the reduction amount of the average value of density values, the processing target edge portion including a single color dot that is prominent in banding has a reduction amount smaller than the processing target edge portion including a mixed color dot, and processing including a single color dot It is suppressed that banding is conspicuous in the target edge portion.

  In addition, the density value changing unit 43 reduces the reduction amount of the average value of the density values of the colors related to the pixels located in the specific area as the brightness of the dots corresponding to the specific pixels decreases in the suppression process. Therefore, the banding is suppressed from being noticeable in a region where the banding is conspicuous and the brightness is low.

  Further, in the suppression process, the density value changing unit 43 reduces the respective reduction amount of the average value of the density values of the respective colors related to the pixels located in the specific area as the dot density in the specific area decreases. In the low density region where banding is easily noticeable, the banding is suppressed from being noticeable.

  In addition, in the suppression process, the density value changing unit 43 is orthogonal to the extending direction of the processing target edge portion, in which the formation region formed by only pixels having the same density value for each color as the pixel forming the processing target edge portion is As the number of pixels in the direction to be reduced decreases, the banding becomes more conspicuous in thin lines where banding is more conspicuous in order to reduce the reduction amount of the average value of the density values of each color related to the pixels located in the specific region. Is suppressed.

  Further, the density value changing unit 43 reduces the respective reduction amount of the average value of the density values of the respective colors related to the pixels located in the specific region as the ink penetration rate with respect to the paper P is lowered in the suppression process. Therefore, it is possible to suppress the banding from being noticeable in the paper P where banding is conspicuous because there is little ink bleeding and the dot diameter does not increase.

  In addition, since the specific pixel detection unit 44 detects the characteristic pixel, it is possible to reliably detect the current characteristic pixel and reliably suppress the banding.

<Modification>
In the present embodiment, the density value changing unit 43 reduces the average value of the density values of the respective colors related to the specific area by adjusting the reduction amount of the density value of each color for the pixel located in the specific area in the suppression process. Although the configuration is such that the amount is adjusted, the reduction amount may be adjusted by other methods. For example, as shown in FIG. 11, a part of the reduced density value of each color related to a pixel located in the specific area is diffused to other pixels located in the specific area, so that the pixels located in the specific area are diffused. The structure which adjusts the reduction amount of each color which concerns may be sufficient. According to this, it is possible to suppress the conspicuous banding of the image printed on the paper P while suppressing the deterioration of the image quality. Further, as a configuration for adjusting the reduction amount of the average value of the density values of each color in the specific area, the density values of some pixels are adjusted instead of adjusting all the density values of the pixels located in the specific area. It may be a configuration. By adjusting the reduction amount of the density value of the entire specific region, it is possible to suppress the banding of the image printed on the paper P from being noticeable. The density value changing unit 43 also prevents the banding of the image printed on the paper P in the specific area from being noticeable by not changing (not reducing) the average value of the density values of the respective colors related to the specific area. Can do.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. In the above-described embodiment, the density value changing unit 43 determines the average of density values related to other colors from the reduction amount of the average value of density values related to non-ejection colors related to pixels located in the specific region in the suppression process. Although it is the structure which suppresses the reduction amount of a value, the structure which makes the reduction amount of the average value of the density value regarding all the colors the same may be sufficient.

  Furthermore, in the above-described embodiment, when the dot corresponding to the specific pixel is a single color in the suppression process, the density value changing unit 43 is located in the specific region as compared to when the corresponding dot is a mixed color. Although it is a configuration that suppresses the reduction amount of the average value of the density value of each color related to the pixel, the average of the density value of each color related to the pixel located in the specific region regardless of whether the dot corresponding to the specific pixel is a single color or a mixed color The structure which makes the reduction amount of a value the same may be sufficient.

  In addition, in the above-described embodiment, the density value changing unit 43 uses the average value of the density values of the respective colors related to the pixels located in the specific area as the brightness of the dots corresponding to the specific pixels decreases in the suppression process. However, it is a configuration in which the reduction amount of the average value of the density values of the colors related to the pixels located in the specific region is the same regardless of the brightness of the dot corresponding to the specific pixel. May be.

  Further, in the above-described embodiment, the density value changing unit 43 reduces each of the average values of the density values of the respective colors related to the pixels located in the specific area as the dot density in the specific area decreases in the suppression process. Although the configuration is such that the amount is reduced, it may be configured such that the reduction amount of the average value of the density values of the respective colors related to the pixels located in the specific region is the same regardless of the dot density in the specific region.

  In addition, in the above-described embodiment, in the suppression process, the formation region formed by only the pixels having the same density value for each color as the pixels forming the processing target edge portion is the processing target edge portion. As the number of pixels in the direction orthogonal to the extending direction of the pixel decreases, the reduction amount of the average value of the density values of the colors related to the pixels located in the specific region is reduced. As the number of pixels decreases, the reduction amount of the average value of the density values of the respective colors related to the pixels located in the specific area may be reduced, or the specific area may be reduced regardless of the size or shape of the formation area. A configuration may be used in which the reduction amount of the average value of the density values of the respective colors related to the pixel located is the same.

  Further, in the above-described embodiment, the density value changing unit 43 determines each of the average values of the density values of the respective colors related to the pixels located in the specific area as the ink penetration rate with respect to the paper P decreases in the suppression process. However, from the same viewpoint, when the inkjet printer further includes a head that discharges a processing liquid that lowers the permeability of the ink to the paper P prior to the discharge of the ink droplets, When the concentration value changing unit includes a region where the treatment liquid is applied to the specific region in the suppression process, the concentration value changing unit applies the pixel located in the specific region compared to the case where the treatment liquid is not applied to the specific region. Each reduction amount of the average value of the density values of each color may be reduced. According to this, it is possible to efficiently prevent the banding from conspicuous even in the region where the ink is not smeared and the banding is easily noticeable by applying the treatment liquid. Note that the density value changing unit may have the same amount of reduction in the average value of the density values of the respective colors related to the pixels located in the specific region regardless of the ink penetration rate with respect to the paper P.

  Furthermore, in the above-described embodiment, the specific pixel detection unit 44 detects the specific pixel and stores the detected specific pixel in the specific pixel storage unit 45. The configuration stores specific pixels (for example, pixels corresponding to the ejection ports 108 that are adjacent to each other in the main scanning direction on the ejection surface and correspond to different actuator units 21) according to physical characteristics. May be. According to this, it is not necessary for the ink jet printer to include the line sensor 30, and the cost can be reduced.

  In addition, in the above-described embodiment, the density value changing unit 43 first performs the reduction process, and then performs the suppression process on the result. However, the density value changing unit 43 performs the suppression process in advance. The reflected reduction process may be performed.

  In the above-described embodiment, the four inkjet heads 1 are configured to eject ink droplets of different colors, but two, three, or five or more inkjet heads 1 are configured to eject ink droplets of different colors. There may be a configuration in which one inkjet head ejects ink droplets of a plurality of colors.

  In addition, in the above-described embodiment, an example in which the present invention is applied to a line-type color inkjet printer has been described. However, the present invention can also be applied to a serial-type color inkjet printer. In this case, since banding is likely to occur at the boundary between the band regions through which the serial inkjet head passes in the scanning direction, it is preferable to determine the pixel corresponding to the boundary as the specific pixel.

  The present invention is also applicable to a recording apparatus that ejects liquid other than ink. Further, the present invention is not limited to a printer, and can be applied to a facsimile, a copier, and the like.

  In the above-described embodiment, an example in which the present invention is applied to the inkjet printer 101 has been described. However, the present invention can also be applied to an image data processing apparatus that processes image data.

DESCRIPTION OF SYMBOLS 1 Inkjet head 16 Control apparatus 20 Conveyance unit 21 Actuator unit 30 Line sensor 31 Conveyance control part 33 Image data processing part 34 Head control part 41 Image data storage part 42 Edge area extraction part 43 Density value change part 44 Specific pixel detection part 45 Specific Pixel storage unit 47 Specific nozzle detection unit 48 Specific nozzle storage unit 101 Inkjet printer 108 Discharge port

Claims (12)

It has a plurality of ejection openings corresponding to the recording droplets of a plurality of colors, and one or a plurality of recording liquid ejection heads for forming an image by ejecting the recording droplets from the plurality of ejection openings onto a recording medium. An image data processing apparatus relating to a recording liquid ejection apparatus,
Image data storage means for storing, for each pixel in a plurality of pixels arranged in a matrix corresponding to the recording medium, image data having density values corresponding to the ejection amounts of the recording liquids of the plurality of colors;
For each of the plurality of colors, when recording droplets are ejected from the plurality of ejection ports to form dots on the recording medium, the recording liquid ejection head and the recording medium are perpendicular to each other in a direction perpendicular to the relative movement direction. A specific nozzle storage unit that stores the discharge port in which the distance between the adjacent other dots is different from the distance corresponding to the pixels corresponding to the other dots adjacent to the dots,
Specific pixel storage means for specifying and storing a specific pixel that is a pixel from which the recording liquid is discharged from the discharge port stored in the specific nozzle storage means based on the image data;
An edge region extracting means for extracting an edge region including at least a part of edges where the pixels having different combinations of density values of the plurality of colors are adjacent to each other based on the image data;
Density value changing means for changing an average value of the density values of the plurality of colors related to the pixels located in the edge region;
When the specific pixel is included in the edge area, the density value changing unit includes the density values of the plurality of colors relating to pixels located in the edge area other than the specific area including the specific pixel in the edge area. The density value of the plurality of colors is changed so that the average value of the plurality of colors is small, and the change amount of the average value of the density values of the plurality of colors related to the pixels located in the specific area is the non-specific area. Decreasing the density values of the plurality of colors so as to be less than the change amount of the average value of the density values of the plurality of colors relating to the pixels located in the edge region, or the plurality relating to the pixels located in the specific region An image data processing apparatus characterized in that an average value of density values of colors is not changed.   The image data processing apparatus according to claim 1, wherein the edge region includes all edges in which a difference in brightness between the pixels adjacent to the edge is a predetermined value or more.   The density value changing unit reduces an average value of the density values of the plurality of colors related to the pixels located in the edge region by reducing the density values of the plurality of colors for each pixel located in the edge region. The image data processing apparatus according to claim 1, wherein the image data processing apparatus is an image data processing apparatus. When the specific pixel is a pixel corresponding to the ejection port from which the recording droplet cannot be ejected, the density value changing unit is a density related to the color corresponding to the ejection port related to the pixel located in the specific region. The image data processing according to any one of claims 1 to 3 , wherein a reduction amount of an average value of density values related to at least one of the other colors is made smaller than a reduction amount of the average value of the values. apparatus. When the density value of only one color exceeds 0 among the density values of the plurality of colors related to the specific pixel, the density value changing unit may change the density values of the plurality of colors related to the specific pixel. A reduction amount of an average value of density values of each of the plurality of colors related to a pixel located in the specific region is reduced as compared with a case where density values of two or more of the colors exceed 0. The image data processing apparatus according to any one of claims 1 to 4 . The density value changing unit is configured to increase the density of the plurality of colors related to the pixels located in the specific area as the brightness of the dot color indicated by the combination of the density values of the plurality of colors related to the specific pixel decreases. image data processing apparatus according to any one of claims 1 to 5, characterized in that to reduce the amount of reduction in the average value of the values. The density value changing unit is configured to detect pixels located in the specific area as the density of pixels in which the density value of at least one of the plurality of colors in the specific area related to the image data exceeds 0 decreases. image data processing apparatus according to any one of claims 1 to 6, characterized in that to reduce the amount of reduction in the average value of the plurality of color density values according to. The density value changing means reduces the amount of reduction of the average value of the density values of the plurality of colors related to the pixels located in the specific area as the permeability of the recording liquid to the recording medium decreases. image data processing apparatus according to any one of claims 1 to 7, characterized. The density value changing means is configured such that when the specific area is an area to which a processing liquid that lowers the permeability of the recording liquid in the recording medium is applied, the specific area is not applied with the processing liquid in the recording medium. compared to when an area, any one of claims 1-8, characterized in that to reduce the respective reduction amount of the average value of the density values of the plurality of colors according to the pixels located in the specific region 1 The image data processing apparatus according to the item. Image data processing apparatus according to any one of claims 1 to 9, characterized by further comprising detection means for detecting the specific pixel. The specific pixel, the image data processing apparatus according to any one of claims 1 to 1 0, characterized in that it is determined by the physical configuration of the recording liquid ejection head. One or a plurality of recording liquid ejection heads for ejecting recording droplets of a plurality of colors for forming an image from a plurality of ejection openings onto a recording medium;
Image data processing device and the recording liquid discharging apparatus characterized by comprising a according to any one of claims 1 to 1 1.

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