JP6218531B2 - Line-type inkjet recording device - Google Patents

Description

  The present invention relates to a line-type inkjet recording apparatus in which a line head in which a plurality of nozzles for ejecting ink are arranged in the main scanning direction is arranged for each color at intervals in the sub-scanning direction orthogonal to the main scanning direction.

  In the field of ink-jet recording apparatuses, line-type ink-jet recording apparatuses that enable high-speed printing by performing image formation (printing) in the main scanning direction in a so-called one pass are becoming widespread.

  In this type of ink jet recording apparatus, a line head in which a plurality of nozzles for ejecting ink are arranged in the main scanning direction is used. In particular, in an inkjet recording apparatus capable of color printing of two or more colors, line heads for different colors are arranged at intervals in the sub-scanning direction orthogonal to the main scanning direction. Each color line head is composed of a plurality of head blocks arranged in the main scanning direction and attached to the head holder.

  Then, ink droplets are ejected from each nozzle of the line head when the printing paper being conveyed in the sub-scanning direction passes below the line head of each color. As a result, ink droplets of each color overlap and land on the same pixel of the printing paper, and a color image is formed on the printing paper.

  By the way, in a color-compatible ink jet recording apparatus, a landing position shift of ink droplets of two or more colors to be landed on the same pixel of printing paper is a cause of inconvenience that the color of the pixel is changed to a different hue. Become. Such a landing position shift of the ink droplet occurs when a mounting position shift with respect to the head holder exists in a part of the head block constituting the line head.

  If a change occurs in the color tone of the pixel corresponding to the nozzle of the head block due to the deviation of the landing position of the ink droplet due to the deviation of the mounting position of the head block, the color tone of the pixel corresponding to the adjacent head block in the main scanning direction A color difference will occur between the two.

  With regard to the ink droplet landing position displacement accompanying the head block mounting position displacement, each ink droplet is ejected onto the same pixel from two nozzles spaced in the sub-scanning direction. It has been proposed in the past to compensate for the landing position deviation of the ink droplets from each nozzle by performing random control (for example, Patent Document 1).

JP 2006-168241 A

  By the way, in a line-type inkjet recording apparatus that prints an image for one line in the main scanning direction with ink droplets ejected from nozzles of a plurality of head blocks, ink droplets ejected from nozzles of adjacent head blocks. It is important to make the joints between the image portions printed in the above inconspicuous. This is because if the color of the solid image across the joint between adjacent head blocks changes to the boundary of the joint, the image quality is degraded.

  In this regard, the above-mentioned previous proposals show that the dot interval changes due to the deviation of the landing position of the ink droplet, and white stripes (when the dot interval is wide) or black stripes (when the dot interval is narrow) are displayed on the print paper image. This is intended to prevent occurrence, and when there is a solid image that straddles the joint between adjacent head blocks, the solid image does not have the same hue on both sides of the joint.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to each head block generated in a color image formed of two colors due to a displacement of the mounting position of the head block constituting the line head. It is an object of the present invention to provide a line type ink jet recording apparatus capable of effectively suppressing a difference in hue in a corresponding head row unit.

In order to achieve the above object, a line type ink jet recording apparatus according to the present invention described in claim 1 comprises:
Printing paper in which a plurality of line heads each having a plurality of nozzle blocks arranged in the main scanning direction are arranged for each color at intervals in the sub-scanning direction orthogonal to the main scanning direction and conveyed in the sub-scanning direction In a line-type inkjet recording apparatus that forms ink images of two colors on the printing paper by landing ink droplets from corresponding nozzles of the line heads of the respective colors on the same pixel,
Both pixel portions are obtained from data relating to the hues of the pixel portions corresponding to two head blocks adjacent in the main scanning direction, obtained from the color image test-printed on the printing paper with ink droplets from the line head. Color difference data calculating means for calculating data relating to the color difference between,
Based on the data relating to the color difference calculated by the color difference data calculating means, one head block of the two head blocks is reduced so as to reduce the color difference between the pixel portions corresponding to the two head blocks. Generating means for generating correction data for correcting the ejection amount of at least one color ink droplet;
Based on the correction data generated by the correction data generation means, correction means for correcting the ejection amount of ink droplets ejected from one of the two head blocks corresponding to the pixel portion having the color difference. When,
It is characterized by providing.

The line type ink jet recording apparatus of the present invention according to claim 1, before Symbol correction data, a plurality of correction units arrangement pattern is the same as one another of ink droplets discharged from the nozzles of the two head blocks And generating a color difference of the correction unit grid based on a degree of overlap of the two color dots in the correction unit grid of pixel portions respectively corresponding to the two head blocks. Features.

Further, according to the line type ink jet recording apparatus of the present invention described in claim 1, before Symbol dominant color color number of dots are often present in the correction unit lattice of the two colors, the dominant color of the color number of dots is small In this case, the correction data is generated so as to increase or decrease the ejection amount of the ink droplet of the dominant color in the correction unit grid.

  According to the present invention, the difference in hue in the head row unit corresponding to each head block, which occurs in a color image formed by two overlapping colors due to the displacement of the mounting position of the head block constituting the line head, is effective. Can be suppressed.

  That is, in the line-type inkjet printer to which the present invention is applied, if there is a line head that is not arranged at the correct position among the line heads of each color, a part of the ink droplets of each color formed on the same pixel. The landing position shifts. Then, the hue of the image formed on the pixel changes from the hue of the image to be originally formed.

  According to the line type ink jet recording apparatus of the present invention described in claim 1, the hue of the pixel portions corresponding to the two head blocks adjacent in the main scanning direction from the test color image test printed on the printing paper. Based on this, data relating to the color difference between the two pixel portions is calculated. When printing a color image, based on the calculated correction data, the ejection amount of ink droplets from the nozzles of one head block is corrected so as to reduce the color difference between the two pixel portions. The

  Therefore, even if there is a head block whose mounting position is shifted in the line head of each color, it is possible to effectively suppress the occurrence of a color difference between the pixel portions corresponding to two adjacent head blocks. it can.

Further, according to the line type ink jet recording apparatus of the present invention as set forth in claim 1, complement the overlapping degree of the ink droplets of each color of the positive unit cell is greater than when the degree of overlap is small, of one of the color The area where the dot and the dot of the other color overlap is large. Therefore, when the number of drops of one color dot is increased or decreased, a change in the rate at which the other color dot is concealed by the one color dot increases.

  For this reason, by generating correction data for the head block corresponding to the pixel portion including the correction unit grid having the larger degree of overlapping of the ink droplets of each color, the correction data is generated by increasing or decreasing the number of ink droplet ejection drops. The color difference between pixel portions corresponding to one head block can be corrected efficiently.

Furthermore, according to the line type ink jet recording apparatus of the present invention as set forth in claim 1, when the discharge amount of ink droplets dominant color number of dots are often present in the compensation unit cell increases or decreases the correction data, the Rather than increasing or decreasing the ejection amount of the dominant color ink droplets with the correction data, the degree of increase or decrease of the area where the dominant color dots overlap the controlled color dots is reduced. For this reason, the color difference between the pixel portions corresponding to two adjacent head blocks can be adjusted so as to be reduced with high resolution.

1 is a block diagram showing a schematic configuration of a line type ink jet printer to which the present invention is applied and its control system. FIG. 2 is an explanatory diagram illustrating an image forming path of the printer unit illustrated in FIG. 1 from the side. (A) is explanatory drawing which shows the head holder of FIG. 2 from the downward direction, (b) is explanatory drawing which expands and shows the side cross section of the head holder. It is explanatory drawing which shows the nozzle row | line | column provided in the head block of K (black) and R (red), respectively. (A) is explanatory drawing which shows an example of the color image printed with the inkjet printer of FIG. 1, (b) is explanatory drawing which expands and shows a part of color image of (a). It is a flowchart which shows the determination procedure of the correction object area | region which applies the correction data in a color image, and the production | generation procedure of the correction data in the color image applied to the determined correction object area | region. It is a flowchart which shows the determination procedure of the correction | amendment unit lattice of FIG. (A) is explanatory drawing which shows the correction data when the dot of four dominant colors exists in a correction unit grid, (b) is the correction data when the dot of three dominant colors exists in a correction unit grid. It is explanatory drawing shown. It is a flowchart which shows the production | generation procedure of the correction data of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals, and the description thereof is omitted or simplified.

(Overall configuration of line-type inkjet printer)
FIG. 1 is a block diagram showing a schematic configuration of a line type ink jet printer to which the present invention is applied and its control system. As shown in FIG. 1, a line-type inkjet printer (hereinafter abbreviated as “inkjet printer”) 1 of this embodiment includes a scanner unit 101 that reads a document image on a document and outputs an image signal, and a scanner unit. A printer unit 102 that prints (records) a document image on a printing paper S (one side or both sides, see FIG. 2) based on an image signal output from 101, a display 103 for various display inputs, and control for overall control Unit 10 is provided.

  FIG. 2 is an explanatory view showing an image forming path CR1 in which image formation is performed from the side in the printer unit 102 of the ink jet printer 1 according to the present embodiment, and FIG. 3A is an upper side of the image forming path CR1. 2 is an explanatory view showing the head holder 500 of FIG. 2 arranged from below, and FIG. 3B is an explanatory view showing an enlarged side cross section of the head holder 500.

(Line head configuration and layout)
The printer unit 102 of the inkjet printer 1 according to the present embodiment has a line head 110 that is an image forming unit for each color. As shown in FIG. 3A, the line heads 110 of the respective colors extend along the main scanning direction X and are arranged at equal intervals in the sub-scanning direction Y, respectively. The line heads 110 for each color are configured by arranging a plurality of head blocks 110 a in the main scanning direction X, and each head block 110 a is attached to a head holder 500.

  As shown in FIG. 2, the printing apparatus according to the present embodiment includes an image forming path CR1 as the transport path. In the image forming path CR1, the printing paper S is transported in the sub-scanning direction Y by the transport belt 160 at a speed determined by the printing conditions. Above the image forming path CR1, the line heads 110 of the respective colors are arranged to face the conveyance belt 160, and from the nozzles of the head blocks 110a provided in the line head 110 to the printing paper S on the conveyance belt 160. Each color ink is ejected in line units (line head 110 units), and a plurality of images are formed so as to overlap each other. The line head 110 of this embodiment includes K (black) and R (red) line heads 110.

  As shown in FIG. 3B, the line heads 110 of the respective colors are arranged at intervals in the sub-scanning direction Y, and each have a plurality of head blocks 110a. As shown in FIG. 3A, the plurality of head blocks 110a of each color are arranged side by side in the main scanning direction X, and are arranged with the positions in the sub-scanning direction Y being shifted every other. As a result, the distance between the nozzles (not shown) at the extreme ends of the two adjacent head blocks 110a matches the distance between the adjacent nozzles of each head block 110a.

  Each head block 110a can change the number of ink ejection drops for each nozzle. Depending on the number of drops to be ejected (number of droplets), the size (gain) and density of dots in each pixel of the printing paper S change.

  By the way, in the printing apparatus according to the present embodiment, the print resolution of R (red) is 300 dpi, whereas the print resolution of K (black) is 600 dpi. Therefore, as shown in the explanatory diagram of FIG. 4, each head block 110 a of the R (red) line head 110 has one nozzle row 110 b provided in each head block of the K (black) line head 110. Two rows are provided in 110a.

  The two nozzle rows 110b provided in the K (black) head block 110a are arranged with their positions shifted in the main scanning direction X by a half pitch of the nozzle interval. For this reason, the nozzles 110c of one of the K (black) nozzle rows 110b are arranged in the same position as the nozzles (not shown) of the R (red) nozzle row 110b in the main scanning direction X. Further, the nozzles 110c of the other nozzle row 110b for K (black) are shifted by a half pitch of the nozzle interval with respect to the nozzles (not shown) of the nozzle row 110b for R (red) in the main scanning direction X. Placed in position.

  As the printing resolution of K (black) is made higher than that of R (red), the size (gain) of dots formed by K (black) ink droplets is changed to R (red) ink liquid. It is necessary to make it smaller than the size (gain) of the dot formed by the droplet. Therefore, in the printing apparatus according to the present embodiment, the maximum number of ink droplets ejected by each nozzle 110c of the K (black) nozzle row 110b is set to each nozzle (not shown) of the R (red) nozzle row 110b. ) Is set to a drop number smaller than the maximum drop number of ink droplets to be ejected.

(Deposition position deviation and color change between head block rows)
By the way, as described with reference to FIG. 2, the head blocks 110 a of the line heads 110 of the respective colors are attached to a common head holder 500. When the head block 110a is attached to the head holder 500 with a deviation from the original position, ink droplets ejected from the nozzles of the head block 110a land with a deviation from the position of the corresponding pixel on the printing paper S. .

  For example, when a certain head block 110a is attached to the head holder 500 so as to be shifted in the sub-scanning direction Y from the original position, ink droplets ejected from the nozzles of the head block 110a land on the printing paper S. The position is shifted in the sub-scanning direction Y.

  In the inkjet printer 1 described above, in addition to single color printing, color printing may be performed in which ink droplets of two or more colors land on the same pixel to form a heavy color. At this time, if there is a shift in the mounting position of the head block 110a in the line head 110 of any color, the hue of the pixel portion of the printing paper S corresponding to the head block 110a changes from the normal hue. The reason is that the size of the overlapping portion of the ink droplet whose landing position has shifted from the head block 110a whose mounting position has shifted and the ink droplet of another color that has landed on the same pixel changes from the normal size. It is.

  Due to the above-described change in hue, on the printing paper S, the same color is applied between the pixel portion corresponding to the nozzle of the head block 110a and the pixel portion corresponding to the nozzle of the adjacent head block 110a. Even if this image is printed, a color difference occurs.

  FIG. 5A is an explanatory diagram showing an example of a color image printed by the ink jet printer of FIG. 1, and FIG. 5B is an explanatory diagram showing an enlarged portion surrounded by a frame of the color image of FIG. The portion surrounded by the frame includes a pixel portion corresponding to the joint between the first and second head blocks 110a.

  For example, when two colors K (black) and R (red) are used and the color image of FIG. 5A is printed at a printing resolution of 300 dpi, one nozzle array of K (black) shown in FIG. Ink droplets of K (black) and R (red) are ejected from the nozzles 110b and the nozzles of the R (red) nozzle row 110b, respectively.

  At this time, the nozzle row 110 that discharges K (black) ink droplets from each nozzle is displaced in the main scanning direction X by a half pitch of the nozzle interval with respect to R (red). In the main scanning direction X, R (red) ink droplet dots are formed on the printing paper S in the middle of the two K (black) dots.

  Here, the pixel portion corresponding to the first head block 110a (head row 1) and the second head block 110a (head row 2) surrounded by a frame in the color image of FIG. It is assumed that a solid image having the same hue exists in a portion straddling the pixel portion to be processed. Further, as shown in an enlarged view in FIG. 5B, this solid image has one dot between two dots of R (red) and K (black) in the main scanning direction X and the sub-scanning direction Y. It is assumed that the colors are arranged every other time.

  Then, it is assumed that the second head block 110a of the R (red) line head 110 has a mounting position shift in the main scanning direction X and the sub-scanning direction Y. Then, in the pixel portion corresponding to the second head block 110a (head row 2) of the printing paper S, the landing position of the R (red) ink droplet is changed from the normal position to the main scanning direction X and the sub-scanning direction Y. Sneak away.

  As a result, the R (red) ink droplets in the pixel portion corresponding to the first head block 110a (head row 1) and the pixel portion corresponding to the second head block 110a (head row 2). The landing position will be different. Then, the position and size (area) of the R (red) ink droplet that is concealed by overlapping with the K (black) ink droplet are different between the head row 1 and the head row 2. Therefore, a color difference occurs between K (black) and R (red) in the overlapping color between the pixel portion corresponding to the head row 1 and the pixel portion corresponding to the head row 2.

  Therefore, when the color image of FIG. 5A is once test-printed on the printing paper S, K (black) and R (red) are separated between the pixel portions corresponding to the head row 1 and the head row 2 as described above. )), It is conceivable that the color image of FIG. 5A is actually printed while suppressing the color difference.

  In order to suppress the color difference between the pixel portions corresponding to the head row 1 and the head row 2, the R (by the ink droplet of K (black) in the pixel portion corresponding to either or both of the head rows 1 and 2 ( It is conceivable to change the concealment position and size (area) of the red ink droplet. The concealment position and size (area) of the R (red) ink droplet by the K (black) ink droplet can be changed by increasing or decreasing the dot gain of the ink droplet of either color.

  Therefore, in the inkjet printer 1 of the present embodiment, the ejection amount of the ink droplets ejected from the nozzles according to the mounting position displacement of the head block 110a with respect to the head holder 500 is changed to the nozzles in the head block 110a of the line head 110 of each color. The unit can be adjusted by the control unit 10. Correction data is used to adjust the ejection amount of ink droplets. Details of the correction data will be described later.

(Electric configuration of line-type inkjet printer and peripheral equipment)
As shown in FIG. 1, an external interface unit 15 of a client terminal 14 to be described later is connected to the control unit 10 of the inkjet printer 1 via an external interface unit 11. The control unit 10 receives an original image print job from the client terminal 14, converts the original image data of the received print job into gradation data for printing, and based on this, the original image is printed on the printing paper S. Test printing and main printing are executed in the printer unit 102.

  The control unit 10 of the inkjet printer 1 that causes the printer unit 102 to perform a printing operation includes a CPU 90. A display 103 is connected to the CPU 90. The display 103 is an input operation unit that allows a user to select and input a menu for converting the read image into electronic data or self-diagnosis when the inkjet printer 1 is used in a scanner mode in which the scanner unit 101 reads an image from the printing paper S. Can be used as

  The CPU 90 of the control unit 10 controls the operations of the scanner unit 101 and the printer unit 102 according to the contents input and set from the display 103 based on the program and setting information stored in the ROM 91.

  Note that the control unit 10 is provided with a RAM 92, and the menu selection content input from the display 103 is stored in the RAM 92 as needed. The RAM 92 is provided with a frame memory area. In this frame memory area, the original image raster data generated by the CPU 90 from the postscript data of the print job input from the client terminal 14 to the control unit 10 is temporarily output until it is output to the printer unit 102. Is remembered.

  The control unit 10 is provided with an external storage device 93. In the external storage device 93, the display 103, the printer engine of the printer unit 102, and the firmware of the scanner unit 101 are stored separately for each area to be used.

  The client terminal 14 is configured by a PC (personal computer) or the like, and includes a CPU 16 that executes various processes based on a control program stored in the ROM 17, a RAM 18 that functions as a working area of the CPU 16, a keyboard, An input unit 19 composed of a mouse or the like and an output unit 20 composed of a liquid crystal display or the like are provided.

  In addition to the external interface unit 15 described above, an external storage device 21 that stores various application programs and data and a disk drive 22 that reads various programs and data from the disk-shaped recording medium 50 are connected to the CPU 16. Yes.

  When a print command is input from the input unit 19 while the application program is running, the CPU 16 generates a print job by reading out data of a document image to be printed from the external storage device 21 and outputs the print job to the control unit 10. To do. This print job can be output to the control unit 10 by the CPU 16 executing the printer driver program stored in the external storage device 21 functioning as a printer driver.

(Head row color difference correction process)
The control unit 10 of the inkjet printer 1 described above applies the correction data obtained from the test print result to the correction target area obtained from the test print result of the color image by the inkjet printer 1, and based on the color image print job. The process for correcting the increase / decrease in the number of ejection drops from the nozzle determined in this way is performed. As a result, the color difference between the head rows of the color image on the printing paper S can be corrected, and the change in the color tone of the image on the printing paper S can be suppressed.

  A determination of a correction target area to which correction data in a color image is applied and a procedure for generating correction data in a color image to be applied to the determined correction target area will be described with reference to the flowchart of FIG.

  First, the control unit 10 determines a target region and ink color for correcting the ink ejection timing when a color image is printed on the printing paper S. Specifically, as shown in FIG. 6, the control unit 10 reads a color image test-printed on the printing paper S with the scanner unit 101 in order to determine the target area and target ink color of the ejection drop number correction ( Step S101, 102).

  In this test printing, when the control unit 10 receives a print job from the client terminal 14, it performs a test print of only one color image before executing the print job and performing a main print of the color image. It is. Here, it is assumed that the test print result of the color image in FIG.

  Then, the control unit 10 extracts positions corresponding to joints (five places in the main scanning direction X) of two adjacent head blocks 110a and 110a from the color image of FIG. 5A read by the scanner unit 101. (Step S103). The position of the joint can be extracted by analyzing the nozzle arrangement of each head block 110a in one line head 110 and the dot arrangement in the main scanning direction X in the color image read by the scanner unit 101. .

  Next, the control unit 10 has the same solid color solid image of a certain area or more on both sides in the main scanning direction X across each joint in the color image of FIG. 5A read by the scanner unit 101. It is confirmed by referring to the image data of the color image in the print job (step S104).

  If there is no solid image larger than a certain area on both sides of any joint (NO in step S104), it is determined that color difference correction between the head columns is unnecessary (step S105), and the series of procedures is terminated. If there is a joint where a solid image of a certain area or more exists on both sides (YES in step S104), the color difference correction target which is a candidate for performing color difference correction between the head arrays on the corresponding joint and the solid image portions on both sides thereof. The candidate area is determined (step S106). However, it is assumed that one candidate area for color difference correction does not include two or more joints at the same time.

  Subsequently, the control unit 10 checks whether or not there is a color difference equal to or greater than a threshold value in the shades of the solid images on both sides across the joint of the determined candidate areas for color difference correction (step S107). Whether there is a color difference equal to or greater than the threshold value is determined by using the color information (RGB) on the color image data in FIG. 5A read by the scanner unit 101 from the test print result, for example, the YCbCr color system or Lab table. This can be confirmed by converting to a color system and comparing each solid image portion on both sides across the joint of each color difference correction target candidate region.

  If there is no color difference equal to or greater than the threshold value between solid images on both sides of any joint (NO in step S107), it is determined that color difference correction between the head arrays is unnecessary (step S105), and the series of procedures is terminated. . If there is a joint having a color difference equal to or greater than the threshold value between the solid images (YES in step S107), the control unit 10 selects the color difference correction target candidate region corresponding to the joint having the largest color difference between the solid images as the color difference correction target region. Based on this, a correction unit cell is determined (step S108).

  The correction unit grid is a unit pixel area obtained by dividing a color difference correction target area composed of a solid solid image into a plurality of main scanning directions X and sub-scanning directions Y. Accordingly, K (black) and R (red) ink droplets are arranged in the same pattern in each correction unit cell. Then, with respect to this correction unit lattice, correction contents for correcting the color difference between the head columns in the color difference correction target area are defined as correction data.

  Here, the procedure for determining the correction unit lattice in step S108 will be described with reference to the flowchart of FIG.

  First, the control unit 10 obtains a grid of 10 ^ n0 × 10 ^ n0 (dot) in the solid color solid image of the color difference correction target area from the color image test print result data of FIG. 5A read by the scanner unit 101. The arrangement pattern of K (black) and R (red) ink droplets ejected to each pixel of the printing paper S in order to form a heavy solid image is extracted as a heavy color printing pattern ( Step S108a).

  Next, the control unit 10 selects two colors K (black) and R (red) used in the color image in the color difference correction target area from the extracted heavy color print pattern, and the number of dots in the color difference correction target area. The color is classified into a large number of colors (dominant color) and a small number of dots (dominated color) (step S108b). Here, as is apparent from FIG. 5B, K (black) is the dominant color and R (red) is the controlled color.

  Subsequently, the control unit 10 determines whether or not there is only one dot of the ink droplet of the controlled color (red) in the {(10 × n0) × (10 × n0)} (dot) grid. Is confirmed (step S108c). If there are two or more dots (NO in step S108c), the variable n0 is decreased by 1 (step S108d), and the process returns to step S108a.

  On the other hand, if there is only one dot in the grid of {(10 × n0) × (10 × n0)} (dot) as the dot of the ink droplet of the dominant color (red) (YES in step S108c) After determining the grid of {(10 × n0) × (10 × n0)} (dot) at the time point as the size of the correction unit cell and storing it in the buffer area of the RAM 92 or the external storage device 93 (step S108e), A series of procedures are terminated, and the procedure proceeds to step S109 in FIG.

  In step S109 of FIG. 6, the control unit 10 extracts correction unit grids from the pixel portions corresponding to the head columns on both sides of the joint of the color difference correction target area, and obtains the color of the image in each correction unit grid. For this hue, the color information (RGB) corresponding to each correction unit grid in the color image data of FIG. 5A read by the scanner unit 101 is converted into, for example, the YCbCr color system or the Lab color system. This can be obtained.

  Next, the control unit 10 checks whether or not the color difference between the pixel portions corresponding to the head columns on both sides of the joint, that is, the color difference is equal to or greater than a certain threshold value (step S110). If it is less than the threshold value (NO in step S110), the control unit 10 assumes that there is no large color difference between the two pixel portions, and discharges from each nozzle of the head block 110a for the head rows on both sides of the joint. It is determined that there is no need to correct the number of drops of ink droplets to be performed (step S111). In this case, a series of procedures is terminated without generating correction data.

  If the color difference between the pixel portions corresponding to the head columns on both sides of the joint is equal to or greater than a certain threshold (YES in step S110), the control unit 10 has a large color difference between both pixel portions. As described above, correction contents of the number of ink droplet ejection drops for reducing (suppressing) the color difference between the two are obtained.

  Here, in order to reduce the color difference between the pixel portions corresponding to the head columns on both sides of the joint, a unit cell of the dots of the dominant color (K (black)) and the dots of the controlled color (R (red)) It is effective to increase or decrease the degree of overlap in the interior. The degree of overlap between the dominant color dot and the controlled color dot can be represented by the area ratio (the concealment rate) where the dominant color dot that overlaps the controlled color dot hides the controlled color dot.

  Then, the concealment rate of the dot of the dominant color (R (red)) is the center of gravity of the dots of the plurality of dominant colors (K (black)) and the center of gravity of the dots of the dominant color (R (red)). Can be easily grasped from the positional relationship. In the following description, it is assumed that the concealment rate of the dot of the controlled color (R (red)) is determined based on the position of the center of gravity.

  First, the control unit 10 calculates the distance between the centroid positions of the centroid positions of all the dots of the dominant color (K (black)) and the centroid positions of the dots of the controlled color (R (red)) in the correction unit grid. The pixel portions corresponding to the head rows on both sides of the image are compared with each other (step S112).

  For the head block 110a of the head row corresponding to the pixel portion having the longer distance between the center of gravity positions in the correction unit lattice (NO in step S112), the ink liquid ejected from the nozzle to the pixel of the pixel portion It is determined that it is not necessary to correct the drop number of drops (step S111). In this case, a series of procedures is terminated without generating correction data.

  On the other hand, with respect to the head block 110a of the head row corresponding to the pixel portion with the shorter distance between the center of gravity positions in the correction unit grid (YES in step S112), the ink liquid ejected from the nozzle to the pixel of the pixel portion It is determined that it is a target for performing droplet drop number correction (target color difference correction target) (step S113). Accordingly, there is a case where not the head row of the head block 110a whose mounting position with respect to the head holder 500 is shifted, but the head row of the head block 110a adjacent to the head block 110a is the target of inter-head color difference correction.

  Here, a pixel portion with a short distance between centroid positions in the correction unit lattice has a larger area in which the dominant color dots and the controlled color dots overlap than a pixel portion with a long centroid position distance. Therefore, the change in the concealment rate of the dot of the controlled color when the number of drops of the dominant color dot is increased or decreased becomes large. Therefore, by setting the head block 110a of the head row corresponding to the pixel portion having a short distance between the center of gravity positions as the color difference correction target between the heads, the hue can be efficiently corrected by increasing / decreasing the number of ink droplet ejection drops. .

  Also, if the number of dominant color dots in the correction unit grid is different, the barycentric positions of all the dominant color dots change. As shown in FIG. 8A, when there are four dominant color dots in the correction unit cell, the first column (head column 1) has a short distance between the center of gravity positions of the dominant color and the controlled color. ) Is the head block 110a to be corrected. Also, as shown in FIG. 8B, when there are three dominant color dots in the correction unit cell, the second column (head column 2) has a short distance between the center of gravity positions of the dominant color and the controlled color. ) Is the head block 110a to be corrected. Therefore, when the number of dominant color dots in the correction unit grid is different, the position of the dot to be corrected defined by the correction data may change.

  Then, the control unit 10 generates correction data for the number of drops of ink droplets ejected from the head row of the head block 110a to be subjected to inter-head color difference correction, which is used when the color image is actually printed, and the buffer of the RAM 92 The data is stored in the area or the external storage device 93 (step S114). In the generation of correction data, as shown in FIG. 9, the control unit 10 determines the distance between the centroid positions in the correction unit grid among both sides of the joint corresponding to the head block 110a (head row) of the inter-head color difference correction target. The shorter pixel portion is divided into a plurality of correction unit lattices, and it is confirmed whether or not the correction unit lattice includes a pixel at the boundary between the color difference correction target region and the outside thereof (step S114a).

  When the pixel of the boundary between the color difference correction target region and the outside thereof is included (YES in step S114a), the control unit 10 excludes the pixel of the correction unit lattice from the inter-head color difference correction target (step S114b). This is to prevent an area where the inter-head color difference correction is performed and an area where the inter-head color difference correction is not performed adjacent to each other between the color difference correction target area and the outside thereof, thereby preventing a new color difference between the areas.

  If the boundary pixel is not included (NO in step S114a), the control unit 10 ejects ink droplets that are ejected to the dominant color dots (pixels) that most overlap the dominant color dots in the correction unit grid. Correction data for increasing or decreasing the number of drops is corrected and stored in the buffer area of the RAM 92 or the external storage device 93 (step S114c).

  Specifically, the hue obtained in step S109 in FIG. 6 of the pixel portion corresponding to the head block 110a (head column) of the inter-head color difference correction target is determined between the barycentric positions in the correction unit lattice on both sides of the joint. In the case of approaching the hue of the pixel portion with the longer distance, correction data is generated to reduce the number of ink droplet ejection drops to the dominant color dot (pixel) to be increased or decreased by one.

  On the contrary, between the barycentric positions in the correction unit lattice among the both sides of the joint to the hue calculated in step S109 in FIG. 6 of the pixel portion corresponding to the head block 110a (head column) of the inter-head color difference correction target. When the color of the pixel portion with the longer distance is made closer, correction data that increases the number of ink droplets discharged to the dominant color dot (pixel) to be increased or decreased by one is generated.

  However, the correction of the number of ink droplets discharged by correction data is more than the increase so that the luminance difference and color difference between the image of the color difference correction target area and the image of the surrounding area are not greatly changed by the correction. It is desirable to reduce the content.

  Note that when the type of the printing paper S changes, the dot gain changes, the dot diameter changes, and the degree of change in hue when the number of ink droplet ejection drops increases or decreases. In addition, even if the printing paper S is the same, if the density of heavy colors or the printing resolution of K (black) is different, the dot diameter of the dominant color or the governed color dot changes, so the number of ink droplet ejection drops is also reduced. The degree of color change when increasing or decreasing changes. For this reason, the increase / decrease contents of the number of ejection drops of ink droplets defined by the correction data cause the dot gain to change, and the type of printing paper S used for color image printing and the density of heavy colors (dominant color and It is desirable to generate in consideration of the dot diameter of the dominant color), the print resolution of K (black), and the like.

  Further, when the position of the nozzle of the head block 110a differs in the main scanning direction X by the line head 110 of each color (for example, as in the present embodiment, one nozzle row 110b of K (black) and R (red) ), The nozzle position is shifted by a half pitch of the nozzle interval, etc.), the contents of the landing position shift of the ink droplet when the mounting position shift of the head block 110a occurs, The content of the color change changes. For this reason, it is desirable to generate the correction data in consideration of the positional relationship of the nozzles of the head block 110a in the line head 110 of each color.

  When the correction data is generated, the control unit 10 applies the correction data generated from the test print result to the print gradation data converted from the image data of the color image, and K (black) and R (red). ) Is corrected in units of the head block 110a. Then, the ink droplets are respectively ejected from the nozzles provided in the head blocks 110a in the corresponding rows of the K (black) and R (red) line heads 110 with the corrected number of ejection drops, thereby obtaining a color image. Is performed (step S115).

  As is clear from the above description, in the present embodiment, steps S109 and S110 in the flowchart of FIG. 6 are processing corresponding to the color difference data calculating means in the claims. Moreover, in this embodiment, step S114 in FIG. 6 is a process corresponding to the production | generation means in a claim. Furthermore, in this embodiment, step S115 in FIG. 6 is processing corresponding to the correcting means in the claims.

(Action / Effect)
As described above, when there is a difference in hue between each head row, the number of drops of ink droplets of either K (black) or R (red) is determined using the correction data generated from the test print result described above. The color image is actually printed by correcting each nozzle row as appropriate. As a result, even if the head blocks 110a in the same row in the line heads 110 of the respective colors are attached to the head holder 500 while being displaced in the main scanning direction, the pixels corresponding to the head rows The color difference between the parts can be suppressed.

  Note that, in the above-described embodiment, the color difference correction in which the color difference between the solid images on both sides of the head row joints from the color image of the test-printed printing paper S, which is the basis for generating the correction data, exceeds a certain level. The target candidate area is determined, and the color difference correction target candidate area having the largest color difference among them is set as the color difference correction target area. However, any one of the color difference correction target candidate areas having a color difference of a certain level or more in the hue of the solid images on both sides across the joint may be set as the color difference correction target area regardless of whether the color difference is the largest. Good.

  In addition, when obtaining the color difference of the pixel portions corresponding to the head columns on both sides of the joint of the color difference correction target region, the configuration for obtaining the color difference based on the color information of the correction unit grid extracted from each pixel portion is omitted, and both sides of the joint are omitted. The color difference may be obtained from the color information of the pixel portion corresponding to the head row.

  Furthermore, the color data of the pixel portions corresponding to the head columns on both sides of the joint may be acquired by a device other than the ink jet printer 1 from the test-printed color image.

  In the above-described embodiment, the case where color printing is performed using K (black) and R (red) has been described as an example. However, the present invention can be widely applied to a line type ink jet recording apparatus that performs color printing by an ink jet method by superimposing two color inks.

DESCRIPTION OF SYMBOLS 1 Line type inkjet printer 10 Control unit 11 External interface part 14 Client terminal 15 External interface part 16 CPU
17 ROM
18 RAM
DESCRIPTION OF SYMBOLS 19 Input part 20 Output part 21 External storage device 22 Disk drive 50 Disk-shaped recording medium 90 CPU
91 ROM
92 RAM
93 External storage device 101 Scanner unit 102 Printer unit 103 Display 110 Line head 110a Head block 110b Nozzle array 110c Nozzle 160 Conveying belt 500 Head holder CR1 Image forming path S Printing paper X Main scanning direction Y Sub-scanning direction

Claims (1)

Printing paper in which a plurality of line heads each having a plurality of nozzle blocks arranged in the main scanning direction are arranged for each color at intervals in the sub-scanning direction orthogonal to the main scanning direction and conveyed in the sub-scanning direction In a line-type inkjet recording apparatus that forms ink images of two colors on the printing paper by landing ink droplets from corresponding nozzles of the line heads of the respective colors on the same pixel,
Both pixel portions are obtained from data relating to the hues of the pixel portions corresponding to two head blocks adjacent in the main scanning direction, obtained from the color image test-printed on the printing paper with ink droplets from the line head. Color difference data calculating means for calculating data relating to the color difference between,
Based on the data relating to the color difference calculated by the color difference data calculating means, one head block of the two head blocks is reduced so as to reduce the color difference between the pixel portions corresponding to the two head blocks. Generating means for generating correction data for correcting the ejection amount of at least one color ink droplet;
Based on the correction data generated by the correction data generation means, correction means for correcting the ejection amount of ink droplets ejected from one of the two head blocks corresponding to the pixel portion having the color difference. And
The correction data targets a plurality of correction unit lattices having the same arrangement pattern of ink droplets ejected from the nozzles of the two head blocks, and the correction of pixel portions corresponding to the two head blocks, respectively. Based on the overlapping degree of the two color dots in the unit cell, the color difference of the correction unit cell is generated to be reduced,
Of the two colors, when a color having a large number of dots existing in the correction unit grid is a dominant color, and a color having a small number of dots is a controlled color, the correction data includes the dominant color in the correction unit grid. Generated to increase or decrease the ejection amount of ink droplets,
Line type ink jet recording apparatus according to claim and this.