JP2017100312A - Compensation method, program, compensation device, and compensation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately compensate for an image comprising pixels or the like formed by ink droplets discharged from a plurality of discharge nozzles.SOLUTION: This compensation method includes: a step for detecting the positions of undischarged pixels formed by defective discharge nozzles by an omitted nozzle detection unit 119; and a step for compensating for an object to be formed by correcting normal pixels formed by normal discharge nozzles and set adjacent to the defective discharge nozzles by using a processing mask by an adjacent pixel dot correction unit 135. The adjacent pixel dot correction unit 135 executes switching between a mask pattern A and a mask pattern B different in image compensation intensity on the basis of at least one of the positions of the defective discharge pixels and printing conditions.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a compensation method, a program, a compensation device, and a compensation system.

2. Description of the Related Art There is known an ink jet recording type image forming apparatus that forms an image on a recording medium by ejecting ink droplets from a plurality of ejection heads provided in the recording head. In an ink jet image forming apparatus, due to drying of the nozzle surface of the recording head, thickening of the ink, or the like, the ejection path of the ink droplet is bent, so that the ink droplet does not land at the correct position on the recording medium. In some cases, no ink droplets are ejected from the nozzles, causing non-ejection.
Therefore, in order to form a good image even if there is a defective ejection nozzle that cannot eject ink droplets normally, a dot is added to the pixel adjacent to the pixel to be recorded by the defective ejection nozzle, or the dot size of the adjacent pixel A halftone processing technique for correcting the above is known.
Patent Document 1 discloses an invention in which a normal dither mask and a non-ejection compatible dither mask are provided as dither masks used for binarization processing, and the normal dither mask is replaced with a non-ejection correspondence dither mask in the non-ejection nozzle portion. It is disclosed. According to the present invention, it is possible to prevent pixel omission caused by a non-ejection nozzle and gradation deterioration in halftone.

However, in the above prior art, when the addition of dots and the correction of the dot size are excessive, there is a problem that the ink adhesion amount becomes excessive and the portion becomes conspicuous.
The present invention has been made in view of the above-described circumstances, and appropriately forms an object such as an image composed of unit elements such as pixels formed by liquid such as ink droplets discharged from a plurality of discharge nozzles. The purpose is to compensate.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a compensation method for compensating a forming object constituted by unit elements formed by liquids ejected from a plurality of ejection nozzles, respectively. The detecting means detects the position of the defective unit element formed by the defective ejection nozzle, and the compensating means uses the processing mask to form the normal unit element formed by the normal ejection nozzle and adjacent to the defective unit element. Compensating for the formation object by correcting, and the compensation means is configured to detect the formation object based on at least one of a position of the defective unit element and a condition relating to the formation of the unit element. A first processing mask and a second processing mask having different compensation strengths are switched.

  ADVANTAGE OF THE INVENTION According to this invention, the formation target comprised by the unit element which the liquid each discharged from a some discharge nozzle forms can be compensated appropriately.

1 is a schematic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. 2A and 2B are diagrams illustrating a configuration of a recording head, in which FIG. 3A is a diagram illustrating a mounting state of the recording head on a carriage, and FIG. 2B is an enlarged view of the recording head. It is a schematic diagram explaining compensation processing for non-ejection pixels, (a) shows before compensation processing, (b) is a diagram showing after compensation processing. (A)-(c) is a figure explaining the generation | occurrence | production principle of the black stripe which arises when the compensation process of a non-ejection pixel is excessive. 1 is a block diagram illustrating a hardware configuration of an ink jet recording apparatus according to an embodiment of the present invention. It is a block diagram explaining the functional structure of the image compensation apparatus which concerns on one Embodiment of this invention. (A), (b) is a figure explaining the detection method of a missing nozzle. (A), (b) is a figure explaining the detection method of a missing nozzle. It is a figure explaining the method of counting the continuous number of non-ejection pixels on dot arrangement data. (A)-(c) is a figure explaining the method of counting the continuous number of non-ejection pixels from the combination of a defective nozzle. It is a figure which shows an example of the table which memorize | stores the continuous pattern of a non-ejection pixel, and the pattern information of the combination of a defect nozzle. (A)-(c) is a figure explaining the replacement of the dot by a mask pattern. (A)-(c) is a figure explaining the replacement of the dot by a mask pattern. It is a figure explaining switching of a mask pattern. It is the flowchart which showed the image compensation process which concerns on one Embodiment of this invention. It is the flowchart which showed the image compensation process which concerns on other embodiment of this invention. 10 is a flowchart illustrating image compensation processing according to still another embodiment of the present invention.

An embodiment of the present invention will be described with reference to an example of an ink jet recording apparatus. The present invention has the following characteristics in a technique for correcting a non-ejection pixel by adding a dot to a pixel at a position adjacent to the non-ejection pixel or increasing the dot size. In short, the feature is that the correction mask pattern at the position corresponding to the non-ejection pixel is switched to the optimum mask pattern in accordance with the number of consecutive non-ejection pixels or the print setting information.
The features of the present invention described above will be described in detail with reference to the following drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .

  In the following description, a recording sheet and a recording sheet are synonymous and are an example of a recording medium. Further, a defective nozzle and a non-ejection nozzle are synonymous and are examples of defective ejection nozzles. The non-ejection pixel is an example of a defective pixel.

[Inkjet recording device]
FIG. 1 is a schematic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention.
An ink jet recording apparatus 1 which is an example of an image forming apparatus forms an image while scanning an ink jet head in the width direction of the recording sheet, conveys the recording sheet after one or more scans are completed, This is a so-called serial type ink jet recording apparatus that forms a recording line. In FIG. 1, the arrow A direction is the width direction of the ink jet recording apparatus and the recording sheet, and the arrow B direction orthogonal to the arrow A direction is the recording sheet conveyance direction.

The ink jet recording apparatus 1 includes an image forming unit 2 that is an image forming unit, a sheet transport unit 3 that is a transport unit of a recording sheet, and a roll paper storage unit 4 that stores roll paper as a recording sheet. These parts are arranged inside the apparatus main body 1a.
The image forming unit 2 is a part for forming an image on a recording sheet (recording medium) conveyed by the sheet conveying unit 3, and guide rods 13 laid on both side plates located at both ends in the width direction of the apparatus main body 1 a. And a guide rail 14. The guide rod 13 and the guide rail 14 hold the carriage 15 so as to be able to reciprocate in the direction of arrow A.
The carriage 15 has a recording head 15a (ejection head: see FIG. 2) that ejects ink droplets (droplets, liquid) of black (K), yellow (Y), magenta (M), and cyan (C). It is installed. Each recording head is integrally provided with a sub tank that supplies ink to each recording head.

The main scanning mechanism 10 that reciprocates the carriage 15 in the direction of arrow A includes a carriage drive motor 21 disposed on one side in the width direction of the recording sheet, a drive pulley 22 that is rotationally driven by the carriage drive motor 21, and a recording sheet. The driven pulley 23 is disposed on the other side in the width direction of the belt, and the belt member 24 is provided between the driving pulley 22 and the driven pulley 23.
The driven pulley 23 is tensioned outward by a tension spring, that is, in a direction away from the drive pulley 22.
A part of the belt member 24 is fixedly held by a belt fixing portion provided on the back side of the carriage 15, thereby pulling the carriage 15 in the width direction of the recording sheet.

Further, in order to detect the main scanning position of the carriage 15, an encoder sheet 40 (see FIG. 2) is disposed along the width direction of the recording sheet of the carriage 15. The main scanning position of the carriage 15 is detected by reading an encoder sheet by an encoder sensor provided on the carriage 15.
In the recording area of the main scanning area of the carriage 15, the roll paper 30 as a recording sheet is intermittently conveyed in the direction of arrow B by the sheet conveying unit 3.

  Each color supplied to the sub-tank of the recording head 15a is located outside the carriage movement area in the width direction of the recording sheet or in one end side area (right side in the drawing) of the main scanning area in the width direction of the recording sheet. A main cartridge 18 containing ink is detachably attached to the apparatus main body 1a.

In addition, a blank discharge receiver that receives ink droplets that do not contribute to image recording discharged by the blank discharge operation is provided on the other end side of the carriage movement region (the blank discharge position on the left side in the drawing). . The idle ejection operation is an operation for ejecting ink droplets from each recording head 15a in order to discharge the thickened ink. Each recording head 15a performs idle ejection at the idle ejection position for maintaining and recovering ejection performance when a predetermined condition is satisfied.
Further, a maintenance / recovery mechanism 19 that performs maintenance / recovery of the recording head 15a is disposed on one end side of the carriage movement region, that is, on the carriage home position side (right side in the drawing). The maintenance / recovery mechanism 19 includes a cap for capping each nozzle surface of the recording head 15a, a wiper blade as a blade member for wiping the nozzle surface, and the like.
Depending on the specifications of the ink jet recording apparatus 1, for example, an empty discharge receiver may be provided on the carriage home position side (right side in the drawing) and included in the maintenance / recovery mechanism 19 like the cap and the wiper blade. Further, a configuration may be adopted in which idle discharge receptacles are provided on both the carriage home position side and the idle discharge position side.

The roll paper storage unit 4 is a paper supply unit, and the roll paper 30 is set as a recording sheet for image recording. A plurality of types of roll papers having different sizes in the width direction of the recording sheet can be set in the roll paper storage unit 4.
The roll paper 30 is accommodated in the roll paper accommodating portion 4 by mounting flanges 31 on both sides of the paper roll and placing the flanges 31 on the flange receivers 32.
A support roller is provided inside the flange receiver 32, and the support roller contacts the outer periphery of the flange 31, so that the flange 31 rotates and the roll paper 30 is sent out to the sheet conveyance path.
However, the configuration of the apparatus is not limited to the above, and the present invention can be applied to a serial type ink jet recording apparatus that supports only a small cut sheet as a recording sheet.

[Recording head]
The configuration of the recording head that ejects ink droplets will be described. 2A and 2B are diagrams illustrating the configuration of the recording head. FIG. 2A is a diagram illustrating a mounting state of the recording head on a carriage, and FIG. 2B is an enlarged view of the recording head.
As shown in FIG. 2A, a recording head 15a is mounted on a carriage 15 that is held by a guide rod 13 and a guide rail 14 so as to be reciprocally movable in the main scanning direction. As shown in FIG. 2B, the recording head 15a is a nozzle having a plurality of ejection nozzles that eject ink droplets of K (black), C (cyan), M (magenta), and Y (yellow). The lines K1 to K4, C1 to C2, M1 to M2, and Y1 to Y2 are included. The odd-numbered nozzle rows (K1, K3, C1, M1, Y1) and the even-numbered nozzle rows (K2, K4, C2, M2, Y2) of each color are arranged at positions shifted from each other by ½ of the nozzle pitch. In this way, the print resolution per scan is doubled.

Here, in order to improve the monochrome image printing speed, two recording heads having nozzle rows that discharge K ink are arranged in a vertical row (sub-scanning direction), and one of them discharges C, M, and Y inks. The recording head provided with the nozzle row is in parallel with the other, and the other is not in parallel. In addition, the nozzle rows that discharge C, M, and Y inks avoid color differences (bidirectional color differences) due to the landing order of ink colors in bidirectional printing in which printing is performed both in the forward movement and in the backward movement in the main scanning direction. Therefore, they are arranged symmetrically in the main scanning direction.
Note that the arrangement of the recording head is not limited to this, and for example, the nozzle rows K3 to K4 are provided on the opposite side of the sub-scanning direction with respect to K1 to K2 (with the positions being switched in the sub-scanning direction). The arrangement order of C, M, and Y inks may be changed as long as the color order of C, M, and Y inks is symmetrically arranged with respect to the main scanning direction.

[Dot correction by non-ejection pixel compensation processing]
FIGS. 3A and 3B are schematic diagrams for explaining compensation processing for non-ejection pixels. FIG. 3A is a diagram showing before compensation processing, and FIG. 3B is a diagram showing after compensation processing.
When there is a pixel (hereinafter referred to as a non-ejection pixel) where an ink dot is not formed by a defective nozzle that does not eject an ink droplet (an example of a defective ejection nozzle), the nozzle that normally ejects the ink droplet (normal ejection nozzle) It is possible to compensate for the non-ejection pixels by correcting the dots of the pixels that are formed and adjacent to the non-ejection pixels (normal pixels). Here, the K1 nozzle row shown in FIG. 2 will be described as an example.
As shown in FIG. 3A, when there are two consecutive defective nozzles in the K1 nozzle row, white stripes are formed on the recording medium due to non-ejection pixels formed by the defective nozzles. Therefore, as shown in FIG. 3B, white streaking is suppressed by expanding the dot size of the pixel adjacent to the non-ejection pixel or adding a dot to a pixel position where a dot is not originally formed. Can do.

[Black streaks that occur when non-ejection pixel compensation processing is excessive]
When the above compensation processing is excessive, there is a problem that black streaks are formed on the recording medium. FIGS. 4A to 4C are diagrams for explaining the principle of black streaking that occurs when compensation processing for non-ejection pixels is excessive.
FIG. 4A is a schematic diagram illustrating a state after pixel compensation processing. FIG. 4A, unlike FIG. 3A, shows a case where there is only one missing nozzle in the K1 nozzle row. FIG. 4B shows a pixel compensation process when “multi-scan printing” is performed in which the recording head is moved a plurality of times in the main scanning direction at a recording resolution (high resolution) higher than the nozzle density. It is a schematic diagram which shows this state. In the case of FIGS. 4A and 4B, if pixel extension processing and dot addition are executed as in FIG. 3B as pixel compensation processing, the pixel compensation processing becomes excessive. On the contrary, there may be a black streak at the pixel compensated portion.

  Further, according to the experiments by the present inventors, the dot size on the surface of the recording paper formed by the reference amount of liquid ejected from the ejection nozzle varies depending on the type of the recording paper as shown in FIG. Is known. For example, if correction processing similar to that for paper that tends to decrease in dot size, such as coated paper, is performed on paper that tends to increase in dot size, such as plain paper, the latter pixel compensation becomes excessive. .

Therefore, in the image compensation system including the following image compensation device shown in the embodiment of the present invention, when pixel compensation is predicted to be excessive, it is possible to suppress the expansion of the dot size and the addition of dots. Prevents black streaks due to compensation processing.
That is, the image compensation processing is performed by performing pattern matching using, for example, the mask pattern (processing mask) shown in FIGS. 12A and 13A. In the present embodiment, when it is predicted that the image compensation will be excessive, it is caused by the image compensation processing by performing the pattern matching by switching to the mask pattern that suppresses the expansion of the dot size and the addition of the dots. Prevent black streaks.

[Image compensation system]
FIG. 5 is a block diagram showing a hardware configuration of an ink jet recording apparatus according to an embodiment of the present invention.
As shown in the figure, a host PC 90 such as a personal computer as an image compensation apparatus is connected to the ink jet recording apparatus 1 as an image forming apparatus so as to be capable of bidirectional communication via a network such as a LAN or WAN, or a parallel cable. Has been. The ink jet recording apparatus 1 and the host PC 90 form an image compensation system.

<Hardware configuration of ink jet recording apparatus>
A control unit 100 of the ink jet recording apparatus 1 includes a CPU (Central Processing Unit) 101 that controls the entire apparatus, a program executed by the CPU 101, a ROM (Read Only Memory) 102 that stores other fixed data, and image data. RAM (Random Access Memory) 103 for temporarily storing data, a non-volatile memory (NVRAM) 104 for holding data even while the apparatus is powered off, various signal processing, rearrangement, etc. And an ASIC 105 for processing input / output signals for controlling the entire apparatus.

Further, the control unit 100 drives and controls the I / F 106 for transmitting and receiving data and signals to and from the host PC 90 such as a personal computer constituting the image compensation apparatus according to the present invention, and the recording head 15a. A drive waveform generation unit 107 and a head driver 108 for generating a drive waveform, a main scanning motor drive unit 111 for driving the main scanning motor 110, a sub-scanning motor driving unit 113 for driving the sub-scanning motor 112, An AC bias supply unit 114 that supplies an AC bias to the charging roller 34, an environmental sensor 118 that detects environmental temperature and / or environmental humidity, and an I / O 116 that inputs detection signals from the environmental sensor 118 and the defective nozzle detection unit 119. Etc. The main scanning motor 110 corresponds to the carriage drive motor 21 shown in FIG. 1, and moves the carriage 15 forward and backward in the main scanning direction by being rotationally driven. Further, the sub-scanning motor 112 is driven to rotate, thereby causing the transport belt 33 to transport the roll paper 30 in the sub-scanning direction (transport direction).
The control unit 100 is connected to an operation panel 117 for inputting and displaying information necessary for the apparatus.

Here, the control unit 100 receives print data including image data from the host PC 90 side by the I / F 106 via a cable or a network. In addition to the host PC 90, the control unit 100 may receive print data including image data from an image reading device typified by an image scanner, an imaging device typified by a digital camera, and the like by the I / F 106. .
In this example, generation and output of print data to the control unit 100 is performed by a printer driver on the host PC 90 side.
Then, the CPU 101 reads and analyzes the print data in the reception buffer included in the I / F 106, performs data rearrangement processing in the ASIC 105, and transfers the image data to the drive waveform generation unit 107.
The conversion of the print data for outputting an image into bitmap data is performed by developing the image data into bitmap data by a printer driver on the host PC 90 side and transferring it to this apparatus. You may store font data.

The drive waveform generation unit 107 includes a D / A converter that performs D / A conversion on the drive pulse pattern data, and includes a single drive pulse (drive signal) or a plurality of drive pulses (drive signals). The waveform is output to the head driver 108.
The head driver 108 selectively records drive pulses constituting a drive waveform supplied from the drive waveform generator 107 based on image data (dot pattern data) corresponding to one line of the recording head 15a input serially. The recording head 15a is driven by being applied to the pressure generating means of the head 15a.

For example, the head driver 108 includes a shift register that inputs a clock signal and serial data, a latch circuit that latches a register value of the shift register with a latch signal, and a level conversion circuit (level shifter) that changes the output value of the latch circuit. In addition, an analog switch array (switch means) that is controlled to be turned on / off by the level shifter, and the like, and by controlling the on / off of the analog switch array, the required drive included in the drive waveform from the drive waveform generator 107 is obtained. The waveform is selectively applied to the pressure generating means of the recording head 15a to drive the recording head 15a.
Here, the drive waveform is composed of a plurality of drive pulses, and by giving one or a plurality of drive pulses, four types of gradations of large droplets, medium droplets, small droplets, and no droplets can be reproduced. .

The defective nozzle detection unit 119 (position detection means) is a means for detecting a defective nozzle (defective ejection nozzle). The defective nozzle detection unit 119 includes, for example, a scanner unit or a photo sensor disposed at an empty discharge position located on the left side of the carriage movement region of the ink jet recording apparatus 1 shown in FIG. Is output from the I / O 116 to the control unit 100. The CPU 101 (position determination unit) of the control unit 100 that has acquired the detection signal from the defective nozzle detection unit 119 determines the position of the defective nozzle by determining whether the nozzle is normal or defective based on the detection signal. To do. Information regarding the position of the defective nozzle (defect information, defective ejection nozzle information) is transmitted from the control unit 100 to the printer driver of the host PC 90 through the host I / F 106.
The defective nozzle detection process is performed based on a defective nozzle detection request from the printer driver of the host PC 90. Based on the detection request, the control unit 100 gives a command to the recording head to eject ink droplets. The missing nozzle detection unit 119 acquires a detection signal based on the response state of each nozzle of the recording head.

<Image compensation device>
FIG. 6 is a block diagram illustrating the functional configuration of the image compensation apparatus according to the embodiment of the present invention.
The host PC 90 functioning as an image compensation device temporarily stores a CPU (Central Processing Unit) that controls the entire device, a program executed by the CPU, a ROM (Read Only Memory) that stores other fixed data, and image data. It is composed of a general personal computer equipped with a RAM (Random Access Memory) for storing, an HDD (Hard Disk Drive) for storing a mask pattern used for image compensation, and the like. The host PC 90 also includes input means such as a mouse and keyboard, display means such as a display for displaying settings, and the like.

The printer driver 91 of the host PC 90 converts image data given from application software or the like from a color space for monitor display (RGB color system) to a color space for a recording apparatus (CMYK color system). Module) processing unit 131, correction processing unit 132 that performs density correction, and halftone processing unit (halftone processing unit) 133 that includes a multi-value / low-value matrix that replaces image data with a pattern arrangement of dots ejected from the recording apparatus. It is out.
The halftone processing unit 133 converts the input multi-valued image data into n values (n is an integer of 2 or more), and generates data for forming an image with n types of dots having different sizes. For example, when n = 4, the halftone processing unit 133 outputs image data to be expressed by four types of dots, large droplets, medium droplets, small droplets, and no droplets.

The printer driver 91 includes a non-ejection pixel continuous number counting unit 134 (counting unit) that counts the number of non-ejection pixels continuous from the missing information of the nozzles of the recording head 15 a acquired from the inkjet recording apparatus 1. The process of counting the number of consecutive non-ejection pixels by the non-ejection pixel continuous number counting unit 134 will be described later.
The printer driver 91 may further include a total amount restriction processing unit that restricts the total number of ink adhesion amounts.
The printer driver 91 includes an adjacent pixel dot correction unit 135 (image compensation unit) that corrects a pixel adjacent to a non-ejection pixel with respect to an image after halftone processing by the halftone processing unit 133. The adjacent pixel dot correction unit 135 switches the mask pattern 137 (see FIG. 14) to be used based on the information from the non-ejection pixel continuous number counting unit 134 and the print mode information (setting information 136), and selects the target pixel. By correcting, non-ejection pixels formed by the defective nozzle are compensated. The non-ejection pixel compensation process will be described later.

All or part of the functions of the printer driver 91 described above may be provided in the ink jet recording apparatus 1 or may be divided and arranged in another apparatus. For example, the non-ejection pixel continuous number counting unit 134, the adjacent pixel dot correcting unit 135, and the mask pattern 137 may be arranged in the ink jet recording apparatus 1, and other parts may be arranged in the printer driver 91.
The functional units provided by the printer driver 91 are realized by the CPU of the host PC 90 reading out the printer driver program stored in the HDD or the like, developing it in the RAM, and executing it. The program is provided as a file in an installable or executable format and recorded on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD, or And distributed by being downloaded from the server via the network.

[Deficient nozzle detection method]
A method for detecting a defective nozzle (non-ejection nozzle) will be described. 7 and 8 are diagrams for explaining a defective nozzle detection method.
The non-ejection nozzle detection pattern shown in FIG. 7A is an example of a check pattern used when checking the reproduction of the horizontal line corresponding to the nozzle and visually judging the non-ejection nozzle. When this non-ejection nozzle detection pattern is used, for example, as shown in FIG. 7B, if the third nozzle is non-ejection, the dot corresponding to the third nozzle is missing.
When the non-ejection nozzle detection pattern shown in FIG. 7 is used, the user inputs the position (missing information) of the non-ejection nozzle from an input unit such as a keyboard or a mouse provided in the host PC 90.

Further, the non-ejection nozzle detection pattern shown in FIG. 8A is automatically set by the control unit 100 shown in FIG. 5 using a scanner unit, a photo sensor, or the like (corresponding to the missing nozzle detection unit 119 shown in FIG. 5). It is an example of a check pattern for detecting a non-ejection nozzle. In this non-ejection nozzle detection pattern, each print area is printed using only a specific nozzle of the recording head. When this non-ejection nozzle detection pattern is used, for example, as shown in FIG. 8B, if the seventh nozzle is non-ejection, the density measurement value by the photosensor or the like of the pattern corresponding to the seventh nozzle is normal. It is possible to determine that this nozzle is not ejecting without reaching the level.
The detection method of the defective nozzle is not limited to these. For example, the operation of ejecting ink by driving the recording head is executed, and laser light is irradiated to the ink ejected from the recording head, and ink is ejected from the nozzle based on the presence or absence of reflected light of the laser light. A non-ejection nozzle may be specified by detecting the situation. Alternatively, a non-ejection nozzle may be specified based on the presence or absence of charge movement on the electrode plate by discharging charged ink droplets onto the electrode plate.
Information (missing information) regarding the position of the non-ejection nozzle obtained as described above is stored in an HDD, RAM, or the like provided in the host PC 90, and is used in image compensation processing executed by the printer driver of the host PC 90.

[Counting the number of consecutive non-ejection pixels]
A method in which the non-ejection pixel continuous number counting unit counts the number of consecutive non-ejection pixels will be described.
<Counting based on dot arrangement data>
FIG. 9 is a diagram for explaining a method of counting the number of consecutive non-ejection pixels on the dot arrangement data. FIG. 9 shows a method of counting input data from the arrangement of ink dots.
The scanning direction of the recording head is the X direction, the conveyance direction of the recording paper is the Y direction, and the target pixel position is (X, Y) = (n, n). In this counting method, the pixel position adjacent to the target pixel is counted in the Y direction, and when the adjacent pixel of the target pixel is a non-ejection pixel, the non-ejection pixel continuous number α is counted up.

On the other hand, when the adjacent pixel is not a non-ejection pixel, the counting in the direction is finished. In the example of FIG. 9, since (n, n−1) is not a non-ejection pixel on the upstream side of the target pixel in the Y direction, the counting ends there. On the other hand, since (n, n + 1) and (n, n + 2) are non-ejection pixels on the downstream side in the Y direction of the target pixel, 2 is counted up and (n, n + 3) counted next is not a non-ejection pixel. Therefore, the counting ends there. From the above, the non-ejection pixel continuation number in the target pixel (n, n) is 0 on the upstream side and 2 on the downstream side, so the non-ejection pixel continuation number α is 2.
However, the description of the method for counting the number of consecutive non-ejection pixels described above is an example, and the counting direction and the count-up method for the number of consecutive non-ejection pixels are not limited to this. The number of consecutive pixels may be counted up while counting the number of non-ejection pixels in the X direction, or the number of consecutive non-ejection pixels on the upstream and downstream sides in the Y direction may be managed as a total number as in the explanation example. Alternatively, the number of consecutive non-ejection pixels on the upstream side and the downstream side may be handled separately.

<Counting based on the combination of defective nozzles>
In FIG. 9, the number of consecutive non-ejection pixels is counted based on the dot arrangement data, but the method of counting the number of non-ejection pixels is not limited to this. FIG. 10 is a diagram illustrating a method of counting the number of consecutive non-ejection pixels from a combination of defective nozzles. Here, a combination pattern of defective nozzles in which the number of consecutive non-ejection pixels is 3 in the sub-scanning direction (vertical direction in the figure) is illustrated.
When determining the case where non-ejection pixels are continuous from the combination of defective nozzles, it is necessary to consider the cases of FIGS. FIG. 10A illustrates a case where three nozzles arranged in a staggered pattern (alternately) are simply missing in one recording head. FIG. 10B shows a case where a defective nozzle of one recording head and a defective nozzle of the other recording head are continuous when a plurality of recording heads are connected in the sub-scanning direction. Further, in FIG. 10C, when recording by “multi-scan printing”, a pixel position where a certain defective nozzle records in the first scan and a pixel position where another defective nozzle records in the second scan are continuous. Shows the case.

<Pattern Table for Combination of Continuous Number of Non-ejecting Pixels and Defect Nozzle>
FIG. 11 is a diagram illustrating an example of a table storing the number of consecutive non-ejection pixels and the pattern information of combinations of defective nozzles.
The continuous number of non-ejection pixels and the generation pattern thereof shown in FIGS. 10A to 10C, as shown in FIG. 11, the number of consecutive non-ejection pixels and the missing nozzle number (CH: channel). Can be managed as a table as pattern information of the combination. 11A to 11C correspond to FIGS. 10A to 10C, respectively. By managing as a table, it is not necessary to count based on dot arrangement data every time information on the number of consecutive non-ejection pixels is required as shown in FIG. 9, and it is determined which nozzle is a normal nozzle or a defective nozzle. Only by this, it is possible to obtain the number of consecutive non-ejection pixels.

[Replacing dots by mask pattern]
The dot replacement using the mask pattern by the adjacent pixel dot correction unit 135 (see FIG. 6) of the host PC will be described. 12 and 13 are diagrams for explaining dot replacement by a mask pattern. For the mask pattern, for example, a plurality of patterns are formed and used for each dot size in accordance with the arrangement of dots around the defective ejection nozzle.

FIG. 12A shows an example of a mask pattern for replacing dots. FIG. 12B is a diagram illustrating an image before replacement of dots (thick line indicates a pattern matching execution range). FIG. 12C is a diagram showing an image after the dot replacement (the bold line indicates the pattern matching implementation range).
Here, when the halftone processing unit 133 (see FIG. 6) of the host PC 90 converts the image data, n in the n value (n ≧ 2) is three types of dot diameters and no droplets. The description will be made assuming that the total is four values (n = 4). Here, for the sake of convenience, the size of the dots is classified by “diameter”, but the dots may be, for example, large drops, medium drops, and small drops, and are not necessarily limited to circular ones.

FIG. 12A shows a mask pattern M1 for converting the second (or second) smaller dot diameter to the maximum dot diameter among the three types of dot diameters “with droplets”.
The mask pattern M1 corresponds to 3 × 4 = 12 nozzles. Among these, the horizontal line portion corresponds to the defective ejection nozzle, no dot, the hatched portion replaces the dots (in the example shown, replacement is performed every other dot in the upper and lower stages), and the blank portion is not replaced. Means that.
Specifically, the pattern matching execution range (that is, the pixel corresponding to the defective discharge nozzle and the defective discharge nozzle corresponding to the mask pattern M1) indicated by the bold line of the n-value (four values in this case) image data shown in FIG. Pattern matching between the mask pattern M1 in FIG. 12A and the n-value image data is performed in the range of the mask pattern M1 when the parts are combined.

  As a result, as shown in FIG. 12C, among the image data in FIG. 12B, the first implementation range A1 replaces the second small dot in the third row from the top and the second from the left. This is the target and is replaced with the largest dot as shown in FIG. That is, when the portion of the second smallest dot in the image data matches the portion of the mask pattern M1 where the dot is to be replaced, the dot at that location is replaced with the largest dot.

In the second implementation range A2, since the mask pattern and the image data do not match, the replacement is not performed. In the third implementation range A3, the second smallest dot at the left end in the first row from the top and the second and fourth dots from the left in the third row are the largest dots as shown in FIG. Has been replaced.
In this way, the pixels around the pixel corresponding to the defective ejection nozzle are converted into a dot pattern having an effect of compensating the image (FIG. 12C). Here, as described above, the four dots are replaced with the maximum dot diameter.
Since the above mask pattern is applied to the dot arrangement after the multi-value error diffusion processing corresponding to the n value (n ≧ 2), the mask pattern corresponding to each dot size after the n value is used. Can be set.
Further, at the same time as the mask pattern M1 shown in FIG. 12A, the mask pattern M2 shown in FIG. 13A can be used to replace the dots. By doing in this way, the influence of a defective discharge nozzle can be relieve | moderated further.

  FIG. 13A is a diagram illustrating a mask pattern M2 for converting the smallest dot into the second (second) smallest dot. FIG. 13B shows an image before the dot replacement (thick line indicates the pattern matching execution range). FIG. 13C shows the replacement with the mask pattern M1 in FIG. 8) is a diagram illustrating an image (thick line is a pattern matching execution range) after each replacement by the mask pattern M2. Note that the mask patterns M2 and M1 are the same as those described for M1, except that the pattern and the size of the dot replacement are different. Further, the image before the dot replacement shown in FIG. 13B is the same as FIG. 12B.

Here, the mask patterns M1 and M2 are simultaneously applied to the same four-valued image data as in FIG. As a result, in addition to the dot replacement by the mask pattern M1 shown in FIG. 12C, the dot replacement by the mask pattern M2 is further performed to obtain the dot of FIG. 13C.
Specifically, in the first implementation range A1, the third dot from the top left and the third dot from the left that match the mask pattern M2, and the third dot from the left in the third step in the second implementation range A2. However, in the third implementation range A3, the second and fourth dots from the left in the first row and the third dot from the left in the third row are replaced with the second smallest dot from the smallest dot, respectively. .

[Switching mask pattern]
The switching of the mask pattern according to the continuous number of non-ejection pixels or the print mode will be described. FIG. 14 is a diagram for explaining switching of mask patterns.
As described with reference to FIGS. 12 and 13, the adjacent pixel dot correction unit 135 (see FIG. 6) of the host PC 90 executes image compensation processing for non-ejection pixels by replacing the dots using the mask pattern.

However, when the number of non-ejection pixels is large (see FIG. 3A), when the recording resolution is low, such as “one-pass printing” in which the recording head 15a forms an image of the scanning area in one main scan. (Low-resolution printing mode, see FIG. 3A), or when the dot size on the recording paper tends to be small as in coated paper (see FIG. 4C), increase the compensation strength. It is necessary to suppress white streaks.
In such a case, the mask pattern A that causes more dot correction is used. In the mask pattern A, all pixels adjacent to the non-ejection pixels (all pixels located at the upper and lower stages of the non-ejection pixels) are pixels to be processed for dot replacement. Since the mask pattern A has a large number of pixels to be processed, more dots are added or the dot size is expanded.

On the contrary, when the number of consecutive non-ejection pixels is small (see FIG. 4A), the recording resolution is high as in “multi-scan printing” in which the recording head 15a forms an image of the scanning region by a plurality of main scans. In the case of high resolution recording mode (see FIG. 4B), or when the dot size on the recording paper tends to be large like plain paper (see FIG. 4C), the compensation intensity of the image is high. If it is too high, black streaks may occur.
In such a case, the pattern B in which the number of correction dots is suppressed as compared with the pattern A is used. Pattern B is a pattern in which replacement is performed for each dot in the upper and lower stages of the non-ejection pixels. Compared to pattern A, pattern B has a smaller number of pixels to be processed, and therefore, addition of dots and expansion of the dot size are suppressed compared to pattern A.
According to the present embodiment, it is possible to perform the optimum non-ejection pixel compensation process by using the optimum mask pattern according to the degree of influence of the defective nozzle on the image.

[Image compensation processing flow-1]
FIG. 15 is a flowchart showing image compensation processing according to an embodiment of the present invention. This flowchart mainly shows the processing of the adjacent pixel dot correction unit 135.
In step S1, the adjacent pixel dot correction unit 135 determines whether or not the target pixel in the input image data is a candidate for a processing target pixel. Here, the processing target pixel candidate is a pixel of interest adjacent to the non-ejection pixel.
If the target pixel is not a candidate for the pixel to be processed (NO in step S1), the process of step S5 is executed. If it is determined that the target pixel is a candidate for the processing target pixel (YES in step S1), the process of step S2-1 is executed.
In step S <b> 2-1, the non-ejection pixel continuous number counting unit 134 counts the number of non-ejection pixel continuations and outputs it to the adjacent pixel dot correction unit 135.

In step S <b> 3-1, the adjacent pixel dot correction unit 135 checks whether or not the non-ejection pixel continuous number α is equal to or greater than a predetermined threshold value.
If it is equal to or greater than the threshold value (yes in step S3-1), the adjacent pixel dot correction unit 135 performs non-ejection using a first processing mask (a mask corresponding to the pattern A in FIG. 14) with more processing target pixels. Pixel compensation processing is executed (step S4).
When it is less than the threshold value (no in step S3-1), the adjacent pixel dot correction unit 135 performs non-ejection using a second processing mask (a mask corresponding to the pattern B in FIG. 14) with fewer processing target pixels. Pixel compensation processing is executed (step S5).

In step S <b> 6, the adjacent pixel dot correction unit 135 confirms whether or not processing has been performed for all pixels.
When the pixel to be processed remains (no in step S6), the target pixel is moved, and the processing after step S1 is executed.
If there are no remaining pixels to be processed (YES in step S6), the process ends.
Thus, the adjacent pixel dot correction unit 135 switches the processing mask used for dot correction according to the number of consecutive non-ejection pixels.

[Image compensation processing flow-2]
FIG. 16 is a flowchart showing image compensation processing according to another embodiment of the present invention. This flow is an example in which processing masks used for dot correction are switched focusing on the recording resolution. Hereinafter, only the parts different from the flow of FIG. 15 will be described.
In step S <b> 2-2, the adjacent pixel dot correction unit 135 acquires recording resolution information from the setting information 136.
In step S <b> 3-2, the adjacent pixel dot correction unit 135 confirms whether the recording resolution is low. The adjacent pixel dot correction unit 135 uses the first processing mask in the low resolution recording mode (step S4), and uses the second processing mask in the high resolution recording mode (step S5).

[Image compensation processing flow-3]
FIG. 17 is a flowchart showing image compensation processing according to still another embodiment of the present invention. This flow is an example in which processing masks used for dot correction are switched by paying attention to the type of recording paper. Hereinafter, only the parts different from the flow of FIG. 15 will be described.
In step S <b> 2-3, the adjacent pixel dot correction unit 135 acquires recording paper information from the setting information 136.
In step S3-3, the adjacent pixel dot correction unit 135 checks whether or not the recording sheet is a sheet that tends to have a small dot size. The adjacent pixel dot correction unit 135 uses the first processing mask when the recording paper tends to have a small dot size as in coated paper (step S4), and the recording paper has a large dot size as in coated paper. If this is the case, the second process mask is used (step S5).
As described above, according to the above embodiment, the mask pattern is switched in accordance with the degree of influence of the defective nozzle on the image, so that the non-ejection pixel compensation process does not become insufficient or excessive. Compensation processing can be performed.

[Applicable objects of the present invention]
As described above, the present invention has been described with reference to an example of an ink jet recording apparatus (image forming apparatus). It is.
Here, the “apparatus that discharges liquid” is an apparatus that includes a liquid discharge head or a liquid discharge unit and drives the liquid discharge head to discharge the liquid. The apparatus for ejecting liquid includes not only an apparatus capable of ejecting liquid to an object to which liquid can adhere, but also an apparatus for ejecting liquid toward the air or liquid.
This “apparatus for discharging liquid” may include means for feeding, transporting, and discharging a liquid to which liquid can adhere, as well as a pre-processing apparatus and a post-processing apparatus.

For example, as a “liquid ejecting device”, an image forming device that forms an image on paper by ejecting ink, a powder is formed in layers to form a three-dimensional model (three-dimensional model) There is a three-dimensional modeling apparatus (three-dimensional modeling apparatus) that discharges a modeling liquid onto the powder layer.
Further, the “apparatus for ejecting liquid” is not limited to an apparatus in which significant images such as characters and figures are visualized by the ejected liquid. For example, what forms a pattern etc. which does not have a meaning in itself, and what forms a three-dimensional image are also included.

The above-mentioned “applicable liquid” means that the liquid can be attached at least temporarily and adheres and adheres, or adheres and penetrates. Specific examples include recording media such as paper, recording paper, recording paper, film, and cloth, electronic parts such as electronic substrates and piezoelectric elements, powder layers (powder layers), organ models, and test cells. Yes, unless specifically limited, includes everything that the liquid adheres to.
The material of the above-mentioned “material to which liquid can adhere” is not limited as long as liquid such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics can be adhered even temporarily.

  The “liquid” is not particularly limited as long as it has a viscosity and surface tension that can be ejected from the head, and the viscosity is 30 mPa · s or less at room temperature, normal pressure, or by heating and cooling. Preferably there is. More specifically, solvents such as water and organic solvents, colorants such as dyes and pigments, functional materials such as polymerizable compounds, resins, and surfactants, and biocompatible materials such as DNA, amino acids, proteins, and calcium. , Edible materials such as natural pigments, solutions, suspensions, emulsions, and the like. These include, for example, inkjet inks, surface treatment liquids, components of electronic devices and light emitting devices, and formation of electronic circuit resist patterns It can be used in applications such as liquids for use, three-dimensional modeling material liquids, and the like.

In addition, the “device for ejecting liquid” includes a device in which the liquid ejection head and the device to which the liquid can adhere move relatively, but is not limited thereto. Specific examples include a serial type apparatus that moves the liquid discharge head, a line type apparatus that does not move the liquid discharge head, and the like.
In addition to the “device for discharging liquid”, a processing liquid coating apparatus for discharging a processing liquid onto a sheet for applying a processing liquid to the surface of the sheet for the purpose of modifying the surface of the sheet, or a raw material There is an injection granulator for granulating raw material fine particles by spraying a composition liquid dispersed in a solution through a nozzle.

[Summary of Embodiments, Actions, and Effects of the Present Invention]
<First embodiment>
This aspect is a compensation method for compensating for an object to be formed (image) composed of unit elements (pixels) formed by liquid ejected from a plurality of ejection nozzles, and includes position detection means (defect nozzle detection unit 119). ) Detects the position of the defective unit element (non-ejection pixel) formed by the defective ejection nozzle, and the compensation means (adjacent pixel dot correction unit 135) forms the normal ejection nozzle and is adjacent to the defective unit element. Compensating the formation target object by correcting the normal unit element using a processing mask, and the compensation means is based on at least one of a position of the defective unit element and a condition relating to the formation of the unit element. The first processing mask (mask pattern A) and the second processing mask (mask pattern B) having different compensation strengths of the formation target are switched.

The magnitude of the influence of the defective unit element on the object to be formed varies depending on the position of the defective unit element and the conditions related to the formation of the unit element. Here, the continuous number of defective unit elements can be used as the condition relating to the position of the defective unit elements. As the conditions related to the formation of the unit element, the size of the unit element formed by the reference amount of liquid discharged from the discharge nozzle, the density of the unit element constituting the formation target, and the like can be used.
According to this aspect, the object to be formed can be appropriately compensated by switching the processing masks having different compensation strengths based on the position of the defective unit element and the conditions relating to the formation of the unit element.

<Second embodiment>
The compensation method according to this aspect includes a step in which the counting unit (non-ejection pixel continuous number counting unit 134) counts the number of consecutive defective unit elements (non-ejection pixels), and the compensation unit (adjacent pixel dot correction unit 135) includes The first processing mask (mask pattern A) is used when the number of consecutive defective unit elements is greater than or equal to a predetermined value, and the second processing mask (mask pattern B) is used when the number of defective unit elements is less than the predetermined value. And
In the case of an ink jet recording apparatus, the continuous number of defective unit elements is the number of continuous recording heads having a plurality of ejection nozzles in the moving direction (main scanning direction) or continuous in the sub-scanning direction orthogonal to the main scanning direction. In addition to the number, the number of non-ejection pixels included in an aggregate of pixels constituted by non-ejection pixels adjacent in the main scanning direction and the sub-scanning direction can be used. When the number of continuous is large, it is necessary to increase the compensation strength so that the compensation processing is not excessive. When the number is small, it is necessary to reduce the compensation strength so that the compensation processing is not excessive.
According to this aspect, the object to be formed can be appropriately compensated by switching between the processing masks having different compensation strengths based on the continuous number of defective unit elements.

<Third embodiment>
In the compensation method according to this aspect, the compensation means (adjacent pixel dot correction unit 135) has a unit element (pixel) size (pixel dot size) formed by a reference amount of liquid ejected from the ejection nozzle. The first processing mask (mask pattern A) is used when the value is equal to or smaller than the predetermined value, and the second processing mask (mask pattern B) is used when the value is larger than the predetermined value.
In the case of an ink jet recording apparatus, an image that is an object to be formed is formed on a recording sheet, but the dot size of pixels formed by a reference amount of ink droplets ejected from ejection nozzles varies depending on the type of recording sheet. know. For example, if correction processing similar to that for paper that tends to decrease in dot size, such as coated paper, is performed on paper that tends to increase in dot size, such as plain paper, the latter pixel compensation becomes excessive. . Therefore, it is necessary to increase the compensation strength so that the compensation processing is not excessive for coated paper or the like, and it is necessary to reduce the compensation strength so that the compensation processing is not excessive for plain paper or the like.
According to this aspect, the formation target can be appropriately compensated by switching the processing masks having different compensation strengths based on the size of the unit element formed by the reference amount of liquid ejected from the ejection nozzle. .

<Fourth embodiment>
In the compensation method according to this aspect, the compensation means (adjacent pixel dot correction unit 135) is configured to perform the first processing mask (mask) when the density (resolution) of unit elements (pixels) constituting the formation target is equal to or less than a predetermined value. The pattern A) is used, and the second processing mask (mask pattern B) is used when it is larger than a predetermined value.
In the case of an ink jet recording apparatus, the recording resolution (pixel density) can be adjusted by the number of reciprocations of the recording head in the main scanning direction. When the recording resolution is low, the width of white stripes formed by the defective ejection nozzles is widened, whereas when the recording resolution is high, the width of white stripes formed by the same amount of defective ejection nozzles is narrower than the former. Therefore, when the recording resolution is low, it is necessary to increase the compensation strength so that the compensation processing is not excessive. When the recording resolution is high, it is necessary to reduce the compensation strength so that the compensation processing is not excessive.
According to this aspect, the formation target can be appropriately compensated by switching the processing masks having different compensation strengths based on the density of unit elements constituting the formation target.

<Fifth embodiment>
In the compensation method according to this aspect, the number of normal unit elements corrected by the first processing mask (mask pattern A) is greater than the number of normal unit elements corrected by the second processing mask (mask pattern B). It is also characterized by many.
In this aspect, when it is necessary to increase the compensation intensity, a processing mask that increases the number of normal unit elements to be corrected is used. When it is necessary to reduce the compensation intensity, the normal unit element to be corrected is corrected. Use a processing mask that reduces the number of
According to this aspect, the formation target can be appropriately compensated by using the processing mask having an appropriate compensation intensity based on the position of the defective unit element and the conditions relating to the formation of the unit element.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet recording apparatus (image forming apparatus), 1a ... Main body, 2 ... Image forming part, 3 ... Sheet conveyance part, 4 ... Roll paper accommodating part, 10 ... Main scanning mechanism, 13 ... Guide rod, 14 ... Guide Rail, 15 ... Carriage, 15a ... Recording head, 18 ... Main cartridge, 19 ... Maintenance recovery mechanism, 21 ... Carriage drive motor, 22 ... Drive pulley, 23 ... Driven pulley, 24 ... Belt member, 30 ... Roll paper, 31 ... Flange 33 ... Conveying belt 34 ... Charging roller 40 ... Encoder sheet 90 ... Host PC (compensator)

JP 2004-202955 A

Claims (8)

A compensation method for compensating for an object to be formed composed of unit elements formed by liquid ejected from a plurality of ejection nozzles,
Position detecting means for detecting a position of a defective unit element formed by the defective discharge nozzle;
Compensating means for compensating the object to be formed by correcting a normal unit element formed by a normal discharge nozzle and adjacent to the defective unit element by using a processing mask, and
The compensation means switches between a first processing mask and a second processing mask having different compensation strengths of the object to be formed based on at least one of a position of the defective unit element and a condition relating to the formation of the unit element. A compensation method characterized by the above. The counting means includes a step of counting a continuous number of the defective unit elements;
The compensation means uses the first processing mask when the number of consecutive defective unit elements is equal to or greater than a predetermined value, and uses the second processing mask when the number is less than a predetermined value. Item 2. The compensation method according to Item 1.   The compensation means uses the first processing mask when the size of the unit element formed by the reference amount of liquid ejected from the ejection nozzle is equal to or smaller than a predetermined value, and is larger than the predetermined value. The compensation method according to claim 1, wherein the second processing mask is used.   The compensation means uses the first processing mask when the density of the unit elements constituting the forming object is equal to or lower than a predetermined value, and uses the second processing mask when the density is larger than the predetermined value. The compensation method according to claim 1, wherein:   5. The number of normal unit elements corrected by the first processing mask is larger than the number of normal unit elements corrected by the second processing mask. 6. The compensation method according to one item.   The program for making a computer perform the compensation method as described in any one of Claims 1 thru | or 5. A compensation device that compensates an object to be formed of unit elements formed by liquid discharged from a plurality of discharge nozzles,
Compensating means for compensating the formation object by correcting a normal unit element formed by a normal discharge nozzle adjacent to a defective unit element formed by a defective discharge nozzle using a processing mask,
The compensation means switches between a first processing mask and a second processing mask having different compensation strengths of the object to be formed based on at least one of a position of the defective unit element and a condition relating to the formation of the unit element. Compensation device characterized by the above. A forming unit that includes a discharge head having a plurality of discharge nozzles each discharging liquid, and that forms an object to be formed by a plurality of unit elements created by the liquid discharged from the discharge nozzle;
Position detecting means for detecting the position of the defective unit element formed by the defective discharge nozzle;
Compensation system comprising: a compensation unit that compensates the formation target by correcting a normal unit element formed by a normal discharge nozzle and adjacent to the defective unit element using a processing mask,
The compensation means switches between a first processing mask and a second processing mask having different compensation strengths of the object to be formed based on at least one of a position of the defective unit element and a condition relating to the formation of the unit element. Compensation system characterized by that.

Images