Liquid discharge device

Abstract

To provide a liquid discharge device capable of improving, with preferable balance, density, granularity, printing time, and hue of an image, a control method of the liquid discharge device, and a computer program.SOLUTION: A control part 30 of a liquid discharge device performs: first printing processing of forming a partial image for one path by discharging liquid only while a discharge head 10 is moved to one of a first direction; second printing processing of forming a partial image for one path by discharging liquid while the discharge head 10 is moved to one and the other of the first direction; and selection processing of selecting whether the first printing processing is performed or the second printing processing is performed. In the selection processing, selection is performed on the basis of results of: first determination processing (S16 to S23) of determining whether hue of the partial image satisfies a predetermined first condition; and second determination processing (S4 to S6) of determining whether a size of the liquid discharged from a nozzle and a landing position of the liquid on a recording medium satisfy a predetermined second condition.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a liquid ejection device that ejects liquid. [Background technology]

[0002] A conventional liquid ejection device is a printer as disclosed in Patent Document 1. This printer is a serial inkjet printer that forms an image by ejecting ink while reciprocating a recording head provided on a carriage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-298061 Summary of the Invention [Problem to be solved by the invention]

[0004] Inkjet printers, which form images on a recording medium by ejecting droplets and causing them to land, can cause droplet misalignment on the recording medium due to surface tension between adjacent droplets. Misalignment of droplets can result in a decrease in the color density of the image or a decrease in the graininess of the image surface. In response to this, ejecting adjacent droplets in separate scans (e.g., forward and backward passes) can prevent misalignment. However, this increases printing time and may result in a different overlapping order of droplets on the recording medium between ejecting droplets in a single scan and ejecting droplets in two or more scans, potentially affecting the color of the image.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid ejection apparatus that can achieve a balanced improvement in image density and graininess, as well as print time and image color tone, a control method for the apparatus, and a computer program. [Means for solving the problem]

[0006] A liquid ejection device according to a first aspect of the present disclosure comprises an ejection head having a nozzle surface on which nozzles are formed that eject liquid onto a recording medium based on first image data; a moving unit that supports the ejection head and moves back and forth in a first direction together with the ejection head; and a control unit, wherein the control unit executes a first printing process in which a partial image for one pass is formed by ejecting liquid only while the moving unit moves the ejection head in one of the first directions; a second printing process in which the partial image for one pass is formed by ejecting liquid while the moving unit moves the ejection head in one and the other of the first directions; and a selection process in which the control unit selects whether to execute the first printing process or the second printing process, wherein the selection process makes the selection based on the results of a first judgment process in which the color of the partial image obtained from the first image data satisfies a predetermined first condition, and a second judgment process in which the control unit determines whether the size of the liquid ejected from the nozzle and the landing position on the recording medium, which are obtained from second image data obtained by halftoning the first image data, satisfy a predetermined second condition. [Effects of the Invention]

[0007] According to the liquid ejection device of the present disclosure, the first determination process determines the effect on the color tone of the image, and the second determination process determines the effect on the density and graininess of the image, and based on these results, a selection is made between a first printing process that prints in a single scan and a second printing process that prints over two separate scans. Therefore, by selecting either the first printing process or the second printing process in this manner, it is possible to achieve a balanced improvement in the density and graininess of the image, as well as the printing time and color tone of the image. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a liquid ejection device according to the present disclosure. [Figure 2] FIG. 2 is a block diagram showing the functional configuration of the liquid ejection device. [Figure 3]3A to 3C are schematic diagrams illustrating a case where small ink droplets are unevenly positioned around a large ink droplet having a large volume. [Figure 4] FIG. 4 is a schematic diagram showing an example in which small ink droplets are evenly distributed relative to large ink droplets. [Figure 5] 5A to 5D are schematic diagrams for explaining the first operational example of the printing process. [Figure 6] FIG. 6 is a series of flowcharts showing the first operational example of the printing process. [Figure 7] FIG. 7 is a series of flowcharts showing the first operational example of the printing process. [Figure 8] FIG. 8 is a series of flowcharts showing the first operational example of the printing process. [Figure 9] 9A to 9D are schematic diagrams for explaining the second operation example of the printing process. [Figure 10] FIG. 10 is a series of flowcharts showing the second operation example of the printing process. [Figure 11] FIG. 11 is a series of flowcharts showing the second operation example of the printing process. [Figure 12] FIG. 12 is a series of flowcharts showing the second operation example of the printing process. [Figure 13] FIG. 13 is a series of flowcharts showing the second operation example of the printing process. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of a liquid ejection device according to the present disclosure will be specifically described with reference to the drawings. Note that, in the following, the same or corresponding elements will be designated by the same reference numerals throughout the drawings, and redundant description will be omitted.

[0010] (Configuration of liquid ejection device) 1 is a schematic diagram of a liquid ejection device 1 according to the present disclosure. The liquid ejection device 1 prints an image on a recording medium A using liquid ejected from an ejection head 10 based on image data. An example of such a liquid ejection device 1 applied to an inkjet printer that ejects ink will be described below.

[0011] The liquid ejection device 1 is a serial head type, and alternates between a process of ejecting ink of multiple colors to form an image while the ejection head 10 moves (scans) and a process of transporting the recording medium A. In the following, the direction in which the ejection head 10 moves back and forth is referred to as a first direction (or left-right direction), and the direction perpendicular to the first direction, which was the transport direction of the recording medium A, is referred to as a second direction (or front-rear direction). Furthermore, the direction perpendicular to both the first and second directions is referred to as a third direction (or up-down direction). However, the arrangement direction of the liquid ejection device 1 is not limited to this.

[0012] The ejection head 10 is housed in a housing 2 of the liquid ejection device 1. The ejection head 10 has a nozzle surface 12 in which a plurality of nozzles 11 are formed, which eject liquid onto a recording medium A based on first image data. The nozzle surface 12 has nozzle rows in which the nozzles 11 are aligned in the front-to-rear direction, and the nozzle rows are arranged in multiple rows in the left-to-right direction. For example, one or more nozzle rows are provided for each different color of ink. The ejection head 10 is provided with a drive element for each nozzle 11. The drive element is a piezoelectric element, a heat generating element, an electrostatic actuator, or the like, and when driven, applies pressure to the ink in the ejection head 10 to eject ink from the corresponding nozzle 11.

[0013] The liquid ejection device 1 includes a platen 14 disposed opposite the ejection head 10. The platen 14 is positioned below the ejection head 10 at a predetermined distance, and supports the recording medium A from below with its flat upper surface.

[0014] The liquid ejection device 1 includes a transport unit 15 that transports the recording medium A on a platen 14. The transport unit 15 has, for example, two transport rollers 16 and a transport motor. The two transport rollers 16 are arranged at a distance from each other in the front and rear with the platen 14 sandwiched between them, and are connected to the rotating shaft of the transport motor via a reducer. Therefore, when the transport motor is driven, the two transport rollers 16 rotate about their axes, transporting the recording medium A on the platen 14 in the front-to-rear direction.

[0015] The liquid ejection device 1 includes a reciprocating movement unit 18 that moves the ejection head 10 back and forth in the left-right direction. The reciprocating movement unit 18 includes a carriage (moving unit) 19, two guide rails 20, an endless belt 21, and a movement motor. The carriage 19 is a moving unit according to the present disclosure, which supports the ejection head 10 and moves back and forth in the left-right direction together with the ejection head 10. The two guide rails 20 extend left and right across the platen 14, and are arranged spaced apart in the front and back with the ejection head 10 sandwiched between them. The two guide rails 20 support the carriage 19 so that it can move (scan) in the left-right direction.

[0016] The endless belt 21 is wound around two pulleys 22 provided near the left and right ends of one of the guide rails 20, and is connected to the carriage 19 at a predetermined location. The movement motor has a rotating shaft connected to either the left or right pulley 22 via a reducer. Therefore, when the movement motor is driven to rotate, the reciprocating unit 18 causes the endless belt 21 to run, and the carriage 19 supporting the ejection head 10 moves left and right along the guide rail 20.

[0017] The liquid ejection device 1 is provided with a plurality of tanks 24 that store ink of each color to be supplied to the ejection head 10. These tanks 24 are housed inside the housing 2 by opening an openable cover provided on the housing 2. The liquid ejection device 1 of the present disclosure uses ink of four colors, for example, cyan, yellow, magenta, and black, and is provided with four tanks 24 accordingly. One end of a flexible tube 25 is connected to each tank 24, and the other end is connected to an ink supply port of the ejection head 10, and the ink from each tank 24 is sent to the ejection head 10 through the tube 25.

[0018] Fig. 2 is a block diagram showing the functional configuration of the liquid ejection device 1. As shown in Fig. 2, the liquid ejection device 1 has a functional configuration mainly made up of hardware, including a control unit 30, a storage unit 31 connected to the control unit 30, an interface 32, and a head drive unit 33. The control unit 30 is also connected to the transport unit 15 and the reciprocating unit 18 described above.

[0019] The control unit 30 is, for example, a computer, and includes a processor such as an MPU, or a circuit such as an integrated circuit such as an ASIC. The storage unit 31 is a memory accessible from the control unit 30, and includes, for example, RAM and ROM. The RAM temporarily stores image data, including the first image data and the second image data, as well as various data used in calculations by the control unit 30. The ROM stores computer programs and data for various data processing operations. Therefore, the control unit 30 controls the operation of each part of the liquid ejection device 1 by executing the computer program while referencing the data stored in the storage unit 31.

[0020] The interface 32 is a connection device that connects the control unit 30 to external devices of the liquid ejection device 1. Examples of external devices include other computers, communication networks, recording media, displays, and other liquid ejection devices. The liquid ejection device 1 acquires image data and print setting information from external devices, such as computers, via this interface 32. This image data includes "first image data" that is raster data indicating an image to be printed on the recording medium A and has RGB value gradation information.

[0021] The head driver 33 has a head driver circuit electrically connected to each drive element of the ejection head 10, and controls the operation of each drive element based on instructions from the controller 30. That is, the controller 30 outputs a control signal to the head driver circuit to drive the drive elements, and the head driver circuit generates a drive signal based on the input control signal and outputs this drive signal to each drive element. As a result, each drive element is driven based on the corresponding drive signal and operates to apply a predetermined ejection pressure to the ink in the ejection head 10 at a predetermined timing. Therefore, the ejection timing and size of the ink ejected from each nozzle 11 (the volume of the ink droplet) can be controlled.

[0022] The transport unit 15 has a transport drive circuit electrically connected to the transport motor described above, and the operation of the transport motor is controlled by the control unit 30 via the transport drive circuit. This allows the transport unit 15 to transport the recording medium A on the platen 14 intermittently or continuously in the front-to-rear direction, and also to stop and hold it at a predetermined position on the platen 14.

[0023] The reciprocating unit 18 has a movement drive circuit electrically connected to the movement motor described above, and the operation of the movement motor is controlled by the control unit 30 via the movement drive circuit. This allows the reciprocating unit 18 to move the carriage 19 supporting the ejection head 10 in the left and right directions at different speeds, and to stop the carriage 19 at any position within its movable range. Therefore, the ejection head 10 mounted on the carriage 19 is moved reciprocally in the left and right directions (first direction) relative to the recording medium A by the reciprocating unit 18.

[0024] The liquid ejection device 1 forms an image on the recording medium A in each pass by ejecting ink while moving the ejection head 10 using the reciprocating unit 18. That is, the liquid ejection device 1 transports the recording medium A using the transport unit 15 and stops it at a predetermined position on the platen 14. Next, the reciprocating unit 18 moves the ejection head 10 left and right while ejecting ink to land on the recording medium A. In this way, a partial image for one pass is formed on the stopped recording medium A by the ink ejected while the ejection head 10 moves left and right. Then, after the partial image for one pass is formed, the recording medium A is transported again by the transport unit 15 a predetermined distance and stopped, and the next partial image for one pass is formed by ejecting ink. The liquid ejection device 1 alternately repeats this process of transporting the recording medium A and ejecting ink, thereby printing an entire image consisting of one or more partial images on the recording medium A.

[0025] In addition to the above, the droplet ejection device 1 may also have, as functional hardware configurations, output devices such as a display and a speaker that output various types of information to the outside, and input devices such as a touch panel and a physical switch that accept input of information from the outside.

[0026] Meanwhile, the droplet ejection device 1 has a functional configuration mainly made up of software, which includes a halftone processing unit 40, a first print processing unit 41, a second print processing unit 42, and a selection processing unit 43. The selection processing unit 43 also includes a first judgment processing unit 44 and a second judgment processing unit 45. All of these processing units 40 to 45 function when the control unit 30 executes a computer program stored in the storage unit 31.

[0027] The halftone processing unit 40 performs halftone processing on the first image data including RGB values ​​to generate second image data. The second image data generated by the halftone processing unit 40 is printing data for ejecting ink from the ejection head 10. For example, the second image data is data that expresses the color of each pixel expressed in the original first image data using several colors of ink, such as cyan, yellow, magenta, and black, and using several types of ink droplets of different sizes. This halftone processing can employ known data conversion methods such as dithering and error diffusion.

[0028] The first print processing unit 41 performs printing (first print processing) to form a partial image for one pass by ejecting liquid only while the reciprocating unit 18 moves (scans) the ejection head 10 in one of the first directions. In contrast, the second print processing unit 42 performs printing (second print processing) to form a partial image for one pass by ejecting liquid while the reciprocating unit 18 moves (scans) the head 10 in one and the other of the first directions. Then, the selection processing unit 43 selects whether to perform the first print processing or the second print processing when printing is performed, i.e., performs a selection process.

[0029] Furthermore, a first judgment processing unit 44 included in the selection processing unit 43 determines whether the color of the partial image obtained from the first image data satisfies a predetermined first condition. Furthermore, a second judgment processing unit 45 included in the selection processing unit 43 determines whether the size of the liquid ejected from the nozzle 11 and the landing position on the recording medium A, which are obtained from second image data obtained by halftone processing the first image data, satisfy a predetermined second condition.

[0030] (About the knowledge that led to this disclosure) Referring to Figure 3, we will explain the changes in graininess and density, and changes in color caused by the coalescence of droplets when the second image data shows small droplets of ink Ds unevenly positioned around large droplets of ink Db with a large volume.

[0031] Fig. 3A is a schematic diagram illustrating the misalignment of ink droplets when inks Db and Ds are ejected simultaneously. The left diagram of Fig. 3A shows the state of inks Db and Ds that have landed on a recording medium A when the second image data indicates that small ink droplets Ds are unevenly positioned around a large ink droplet Db with a large volume, and these inks Db and Ds are ejected simultaneously. In this case, the large ink droplet Db is in contact with the small ink droplets Ds that are unevenly positioned around it. As time passes from this state, the inks Db and Ds that are in contact with each other attract each other due to surface tension, and, for example, as shown in the right diagram of Fig. 3A, the large ink droplet Db moves toward the small ink droplets Ds, causing misalignment of the inks (coalescence of the droplets).

[0032] Note that ejecting the inks Db and Ds simultaneously means ejecting the inks Db and Ds during the same scan of the ejection head 10, that is, ejecting the inks Db and Ds by the first printing process described above.

[0033] When such droplet coalescence occurs, the two droplets overlap each other and their height from the surface of the recording medium A increases (the state shown in the right diagram of FIG. 3A) compared to the state immediately after landing (the state shown in the left diagram of FIG. 3A), resulting in a change in granularity. Furthermore, as a result of the position of the landing droplets being shifted, unintended margins Bs (areas where no droplets exist) are created on the recording medium A, which also changes the density of the image.

[0034] In contrast, if the large ink droplet Db and the small ink droplet Ds surrounding the large ink droplet Db are ejected separately rather than simultaneously, the coalescence of the droplets as described above can be prevented. Here, the ejection of the inks Db and Ds separately means that the inks Db and Ds are ejected by the second printing process described above.

[0035] Fig. 3B shows an example in which a small droplet of ink Ds is ejected when the ejection head 10 moves forward (left diagram in Fig. 3B), and then a large droplet of ink Db is ejected when the ejection head 10 moves backward (right diagram in Fig. 3B). Also, Fig. 3C shows an example in which a large droplet of ink Db and a small droplet of ink Ds that is not adjacent to the large droplet of ink Db are ejected when the ejection head 10 moves forward (left diagram in Fig. 3C), and then a small droplet of ink Ds adjacent to the large droplet of ink Db is ejected when the ejection head 10 moves backward (right diagram in Fig. 3C).

[0036] In the cases of Figures 3B and 3C, the ink ejected first on the forward pass dries out before the ink is ejected on the return pass, increasing the viscosity of the surface. Therefore, even if ink ejected on the return pass is adjacent to ink ejected on the forward pass, the droplets are less likely to coalesce. This also makes it less likely that graininess or changes in density will occur.

[0037] However, the overlapping order (vertical positions) of the large ink droplet Db and the adjacent small ink droplet Ds is different between the left diagram of Fig. 3A, which shows simultaneous ejection, and the right diagram of Fig. 3B, which shows divided ejection. Similarly, the overlapping order (vertical positions) of the large ink droplet Db and the adjacent small ink droplet Ds is different between the left diagram of Fig. 3A, which shows simultaneous ejection, and the right diagram of Fig. 3C, which shows divided ejection. In this way, if the overlapping order of the inks on the recording medium A differs, the color of the image will differ, which is undesirable.

[0038] The magnitude of the difference in color (the amount of change in color) caused by a difference in the overlapping order of inks differs depending on the types of inks that overlap. That is, the color of each pixel represented by RGB values ​​in the first image data is expressed by the overlapping of multiple colors of ink. Even if the combination of ink colors used is the same, a difference in the overlapping order of the inks will result in a difference in the expressed color. The magnitude of this difference in color differs depending on the types of ink colors used to express one pixel. In this way, the magnitude of the difference in color when the overlapping order of inks differs varies depending on the RGB value.

[0039] For any RGB value, the magnitude of the difference in color between the first printing process and the second printing process can be quantified and acquired in advance. For example, for any RGB value, the patch created by the first printing process and the patch created by the second printing process are each measured, the Lab values ​​of the two patches are acquired, and the color difference ΔE, which is the difference between the Lab values ​​of each patch, is calculated. Then, a "weighting value" is assigned according to the magnitude of this color difference ΔE. As a result, a weighting value that quantifies the magnitude of the difference in color is assigned to each RGB value.

[0040] Furthermore, the above-described positional deviation of droplets occurs when adjacent small ink droplets Ds are unevenly arranged around a large ink droplet Db. In other words, if the small ink droplets Ds are evenly arranged relative to the large ink droplet Db, the surface tension acting on the large ink droplet Db is balanced, and thus the positional deviation of the ink Db does not occur.

[0041] FIG. 4 is a schematic diagram showing an example in which small ink droplets Ds are evenly arranged relative to large ink droplets Db. In all of Examples 1 to 9, small ink droplets Ds are evenly arranged relative to large ink droplets Db. In this disclosure, "even" and "uneven" with respect to the arrangement of small droplets relative to large droplets are more precisely defined as follows. That is, the arrangement of small droplets relative to large droplets is considered "even" when two or more small droplet pixels Ps corresponding to small droplets are arranged in rotational symmetry around the large droplet pixel Pb at positions adjacent to the large droplet pixel Pb, which is a pixel corresponding to a large droplet. On the other hand, the arrangement is considered "uneven" when two or more small droplet pixels Ps are not arranged in rotational symmetry around the large droplet pixel Pb at positions adjacent to the large droplet pixel Pb.

[0042] Based on the above findings, the liquid ejection device 1 according to the present disclosure executes a first determination process regarding color and a second determination process regarding the size and landing position of the ejected liquid for each partial image for one pass, and selects either the first printing process or the second printing process as the printing method for the partial image for one pass depending on the results. Once the printing method has been determined for all partial images on the recording medium A, printing (printing process) is performed on the recording medium A. Details of the printing process of the liquid ejection device 1 will be described below.

[0043] (Printing process operation example 1) 5A to 5D are schematic diagrams for explaining operation example 1 of the printing process. FIGS. 6 to 8 are a series of flowcharts showing operation example 1 of the printing process. In operation example 1, a second determination process regarding the size and landing position of the ejected liquid is executed, and then a first determination process regarding color is executed to select a printing method.

[0044] 6, the liquid ejection device 1 starts the printing process according to this operation example 1 by receiving a print job inputted from, for example, the interface 32 (step S1). Note that this print job includes first image data, which is image data having RGB values, and the first image data is stored in the storage unit 31.

[0045] When the liquid ejection device 1 receives the print job, it starts the second determination process and first acquires the partial image that has been halftoned (step S2). That is, the liquid ejection device 1 halftones the first partial image, which is the partial image for the first pass in the printing order, from the received first image data, using the halftone processing unit 40. This generates a second partial image, which is the second image data corresponding to the first partial image. This second partial image is a partial image that has been halftoned, and is also stored in the storage unit 31. In this operation example 1, even after the second partial image is generated and stored in the storage unit 31, the corresponding first partial image remains stored in the storage unit 31.

[0046] Next, in the second partial image, for example, the upper left pixel is set as the target (step S3). For example, in the example of FIG. 5A, in the halftoned data (second partial image) of a horizontally long rectangle, pixel p1 at the left end of the top row is set as the target. For this pixel p1, it is determined whether the liquid to be ejected is a large droplet (step S4). If it is determined that it is a large droplet (S4: YES), the surrounding pixels of the target pixel, that is, pixels around and adjacent to the target pixel, are searched for (step S5). Then, it is determined whether the second condition, that uneven small droplets exist in the surrounding pixels, is met (step S6). Whether unevenness exists is determined using the method described using FIG. 4.

[0047] If it is determined that the second condition is met, that is, that uneven small droplets exist in the surrounding pixels (S6: YES), the division flag for this target pixel is turned on (step S7). That is, the fact that the division flag is on is linked to the current target pixel and stored in memory unit 31. In FIG. 5B, pixels px with the division flag turned on are indicated by black circles. Then, it is determined whether the processing of steps S4 to S7 targeting all pixels in the partial image (second partial image) acquired in step S2 has been completed (step S8). Note that if it is determined in step S4 that the target pixel is not a large droplet (S4: NO), or if it is determined in step S6 that the second condition is not met, that is, that uneven small droplets do not exist (S6: NO), the determination in step S8 is also made.

[0048] If it is determined in step S8 that the process is not complete (S8: NO), it is determined whether the previous target pixel was the rightmost pixel of the second partial image (step S9). If the previous target pixel was the rightmost pixel, such as pixel p2 in FIG. 5A (S9: YES), the leftmost pixel p3 of the next column (see FIG. 5A) is set as the new target (step S10), and the process is repeated from step S4. If it is determined in step S9 that the previous target pixel was not the rightmost pixel (S9: NO), the pixel immediately to the right of the previous target pixel is set as the new target (step S11), and the process is repeated from step S4.

[0049] As described above, by the processing of steps S1 to S11, a second determination process is executed to determine whether or not there are pixels of large droplets adjacent to uneven small droplets, that is, whether or not there are pixels that satisfy the second condition, for the pixels included in the partial image for one pass.

[0050] Next, in step S8, if it is determined that the processes of steps S4 to S7 have been completed for all pixels of the current partial image (S8: YES), it is determined whether or not there are any pixels in this partial image whose division flag is on (step S12), as shown in Fig. 7. Here, if it is determined that there are no pixels whose division flag is on (S12: NO), the printing method for this partial image is determined to be the first printing process, that is, a method of printing by ejecting liquid only while the ejection head 10 is moved (scanned) in one of the first directions (step S13).

[0051] That is, step S12 returns NO if all pixels contained in the partial image do not satisfy the second condition; in other words, it is determined that selecting the first printing process, which prints the partial image in only one scan, will not result in changes in graininess or density. Therefore, there is no need to select the second printing process, which prints the image in two separate scans, and the first printing process is selected in step S13. Note that this selection and determination of the printing method is performed by the selection processing unit 43 of the control unit 30, and the partial image and its printing method (here, the first printing process), which are the result of the determination, are linked to each other and stored in the memory unit 31.

[0052] After the first printing process is determined in step S13, the process proceeds to step S27 in Fig. 8, where it is determined whether the process according to operation example 1 (i.e., any one of the processes S13, S24, and S25) has been completed for the partial images corresponding to all paths in the first image data included in the print job (step S27). If completed (S27: YES), printing is performed using the printing method (first printing process or second printing process) corresponding to each partial image based on the information stored in storage unit 31 (step S28). On the other hand, if not completed (S27: NO), the process is performed again from step S2 in Fig. 6.

[0053] In step S12 of FIG. 7, if it is determined that there is a pixel whose division flag is on (S12: YES), then the first determination process (S14 to S23) is executed.

[0054] Specifically, the liquid ejection device 1 acquires a partial image containing RGB values ​​corresponding to the partial image (second partial image) that was the target of the immediately preceding second determination process (step S14). That is, the liquid ejection device 1 acquires a first partial image as such a partial image from the storage unit 31. Then, the liquid ejection device 1 divides this first partial image into a plurality of blocks (step S15). For example, as shown in FIGS. 5C and 5D, the first partial image is divided into a plurality of blocks by dividing it with a plurality of vertical and horizontal lines. Then, in the first partial image, for example, the upper left pixel is set as a target (step S16), and a weight value of this target pixel is acquired (step S17).

[0055] As already explained, the weight value of a pixel is a numerical value assigned according to the color difference ΔE corresponding to the RGB value of the pixel. The liquid ejection device 1 stores data in the storage unit 31 in which the weight values ​​corresponding to each RGB value are tabulated using an LUT (look-up table) or the like. Therefore, in step S17, the liquid ejection device 1 obtains the RGB values ​​of the target pixel from the first partial image, and obtains the weight values ​​corresponding to these RGB values ​​from the table.

[0056] Next, it is determined whether acquisition of weight values ​​has been completed for all pixels of the first partial image corresponding to the partial image acquired in step S2 (step S18). If it is determined in step S18 that acquisition has not been completed (S18: NO), it is determined whether the previous target pixel was the rightmost pixel of the first partial image (step S19). If the previous target pixel was the rightmost pixel (S19: YES), the leftmost pixel in the next column is set as the new target (step S20), and the processing from step S17 is executed again. If it is determined in step S19 that the previous target pixel is not the rightmost pixel (S19: NO), the pixel immediately to the right of the previous target pixel is set as the new target (step S21), and the processing from step S17 is executed again.

[0057] As described above, by repeating the processes of steps S17 to S21, weight values ​​are obtained for all pixels included in the partial image for one pass. The obtained weight values ​​corresponding to each pixel are stored in the storage unit 31.

[0058] If weight values ​​are obtained for all pixels included in this partial image as a result of repeating the processes of steps S17 to S21 (S18: YES), the process proceeds to step S22 in Fig. 8. That is, the liquid ejection device 1 calculates a representative value (representative weight value) of the weight values ​​for each block into which the first partial image was divided in step S15. More specifically, the liquid ejection device 1 obtains the average value (weighted average value) of the weight values ​​of all pixels included in this block as the representative weight value of the block (step S22).

[0059] Next, the liquid ejection device 1 determines whether the first condition, that is, that the weight value is equal to or greater than a predetermined threshold, is satisfied. More specifically, the liquid ejection device 1 determines whether any of the blocks in the first partial image has a weighted average value (representative weight value) equal to or greater than a predetermined value (step S23). Note that in FIGS. 5C and 5D, hatched blocks represent blocks whose weighted average value is less than the predetermined value, and unhatched white blocks represent blocks whose weighted average value is equal to or greater than the predetermined value. Therefore, FIG. 5C is an example of a first partial image that does not satisfy the first condition, and FIG. 5D is an example of a first partial image that satisfies the first condition.

[0060] Here, as in the example of Figure 5C, if it is determined that the first partial image does not satisfy the first condition, i.e., that there are no blocks in the first partial image whose weighted average value is equal to or greater than a predetermined value (S23: NO), the printing method for this partial image is determined to be the second printing process (step S24). In other words, in this case, small droplet pixels are unevenly positioned around large droplet pixels, and it is determined that there is little difference in color even if one pass is printed twice, so the second printing process is selected. This makes it possible to suppress changes in color and reduce changes in graininess and density.

[0061] In contrast, as in the example of Figure 5D, if it is determined that the first partial image satisfies the first condition, i.e., that the above-mentioned block exists (S23: YES), the printing method for this partial image is determined to be the first printing process (step S25). In other words, in this case, small droplet pixels are unevenly positioned around large droplet pixels, but it is determined that printing one pass in two passes would result in a large difference in color, so the first printing process is selected. This causes changes in graininess and density, but prevents changes in color.

[0062] The selection and determination of such a printing method is executed by the selection processing unit 43 of the control unit 30, and the partial image and its printing method, which are the determined results, are linked to each other and stored in the storage unit 31.

[0063] Next, the division flag is reset to OFF (step S26), and it is determined whether the processing according to Operation Example 1 has been completed for the partial images corresponding to all paths in the first image data included in the print job (step S27). If it has not been completed (S27: NO), the processing is executed again from step S2 in Fig. 6. On the other hand, if it has been completed (S27: YES), printing is performed using the printing method (first printing process or second printing process) corresponding to each partial image based on the information stored in storage unit 31 (step S28), and the printing processing according to Operation Example 1 is terminated.

[0064] According to the printing process according to the first operational example described above, if there are no pixels for which the division flag is on in the second determination process for a partial image for one pass, it is determined that there is little (or no) change in graininess or density due to misalignment of droplets after landing, and the first printing process, which prints in one scan, is selected (S13). On the other hand, if there are pixels for which the division flag is on, the second printing process, which prints in two scans, is selected only if there are no blocks whose weighted average value is equal to or greater than a predetermined value (S24). Furthermore, if there are blocks whose weighted average value is equal to or greater than a predetermined value, the first printing process is selected instead of the second printing process, because performing the second printing process would result in a large change in color (S25).

[0065] As a result, the liquid ejection device 1 according to the present disclosure can achieve a balanced improvement in image density and graininess, as well as the time required for printing and the color tone of the image.

[0066] Note that the mode of Operation Example 1 is not limited to the above. For example, in step S12, if there is at least one pixel with the division flag set to ON, the determination is "YES." However, the present invention is not limited to this. Instead, the determination may be "YES" only if there are a predetermined number of pixels with the division flag set to ON greater than 1, and "NO" if there are fewer than the predetermined number.

[0067] (Printing process example 2) 9A to 9D are schematic diagrams for explaining operation example 2 of the printing process. Figures 10 to 13 are a series of flowcharts showing operation example 2 of the printing process. In operation example 2, a first determination process related to color is executed, and then a second determination process related to the size and landing position of the ejected liquid is executed to select a printing method.

[0068] 10, the liquid ejection device 1 starts the printing process according to this second operation example by receiving a print job input from, for example, the interface 32 (step S101). Note that this print job includes first image data, which is image data having RGB values, and the first image data is stored in the storage unit 31.

[0069] When the liquid ejection device 1 receives a print job, it starts a first determination process and first acquires an RGB partial image (step S102). That is, the liquid ejection device 1 acquires a first partial image, which is a partial image for the first pass in the printing order, from the received first image data. This first partial image is an RGB partial image, and is stored in the storage unit 31.

[0070] Next, the first partial image is divided into a plurality of blocks (step S103). For example, as shown in Fig. 9A, the first partial image is divided into a plurality of blocks by dividing it with a plurality of vertical and horizontal lines. Then, in the first partial image, for example, the upper left pixel is set as a target (step S104), and the weight value of this target pixel is obtained by referring to a table stored in the storage unit 31 (step S105).

[0071] Next, it is determined whether acquisition of weight values ​​has been completed for all pixels of the first partial image corresponding to the partial image acquired in step S102 (step S106). If it is determined in step S106 that acquisition has not been completed (S106: NO), it is determined whether the previous target pixel was the rightmost pixel of the first partial image (step S107). If the previous target pixel was the rightmost pixel (S107: YES), the leftmost pixel in the next column is set as the new target (step S108), and the processing from step S105 is executed again. Also, if it is determined in step S107 that the pixel is not the rightmost pixel (S107: NO), the pixel immediately to the right of the previous target pixel is set as the new target (step S109), and the processing from step S105 is executed again.

[0072] As described above, by repeating the processes of steps S105 to S109, weight values ​​are obtained for all pixels included in the partial image for one pass. The obtained weight values ​​corresponding to each pixel are stored in the storage unit 31.

[0073] If weight values ​​are obtained for all pixels included in this partial image as a result of repeating the processes of steps S105 to S109 (S106: YES), the process proceeds to step S110 in Fig. 11. That is, the liquid ejection device 1 calculates a representative value (representative weight value) of the weight values ​​for each block into which the first partial image was divided in step S103. More specifically, the liquid ejection device 1 obtains the average value (weighted average value) of the weight values ​​of all pixels included in this block as the representative weight value of the block (step S110).

[0074] Next, the liquid ejection device 1 determines whether the first condition, that is, that the weight value is equal to or greater than a predetermined threshold, is satisfied. More specifically, the liquid ejection device 1 determines whether any block in the first partial image has a weighted average value (representative weight value) equal to or greater than a predetermined value (step S111). Note that in FIGS. 9B and 9C, hatched blocks represent blocks whose weighted average value is less than the predetermined value, and unhatched white blocks represent blocks whose weighted average value is equal to or greater than the predetermined value. Therefore, FIG. 9B is an example of a first partial image that does not satisfy the first condition, and FIG. 9C is an example of a first partial image that satisfies the first condition.

[0075] 9B, if it is determined that the first partial image satisfies the first condition, that is, if there is a block in the first partial image whose weighted average value is equal to or greater than a predetermined value (S111: YES), the printing method for this partial image is determined to be the first printing process (step S112). In other words, if it is determined in the first determination process that the first condition is satisfied, the second determination process is not performed and the printing method is determined.

[0076] 13, where it is determined whether the processing according to Operation Example 2 (i.e., any one of the processing of S112, S123, and S127) has been completed for the partial images corresponding to all paths in the first image data included in the print job (step S129). If completed (S129: YES), printing is performed using the printing method (first printing processing or second printing processing) corresponding to each partial image based on the information stored in storage unit 31 (step S130). On the other hand, if not completed (S129: NO), the processing from step S102 in FIG. 10 is performed again.

[0077] On the other hand, in the example of Figure 9C, it is determined that the first partial image does not satisfy the first condition, i.e., there are no blocks in the first partial image whose weighted average value is equal to or greater than the predetermined value (S111: NO). In this case, the difference in color between the print results of the first printing process and the second printing process is small, meaning that either printing method can be selected from the perspective of color. Therefore, the second determination process is executed to select a printing method from the perspective of improving graininess and density.

[0078] First, halftone processing is performed on this partial image (step S113). As a result, a second partial image is obtained by halftone processing the first partial image. In operation example 2, if step S113 is reached in the process of processing one partial image, the RGB values ​​of this partial image will not be used thereafter, so the data of the first partial image may be discarded at this point, or the data of the second partial image may be overwritten on the data of the first partial image.

[0079] After step S113, the liquid ejection device 1 sets the upper left block in the second partial image as the target (step S114), and sets the upper left pixel in this block as the target (step S115). For example, in the example of FIG. 9D, in the upper left block of the horizontally long rectangular second partial image, pixel p11 at the left end of the top row is set as the target. Then, for this pixel p11, it is determined whether the liquid to be ejected is a large droplet (step S116). If it is determined that the liquid is a large droplet (S116: YES), it searches for peripheral pixels of the target pixel, i.e., pixels around and adjacent to the target pixel (step S117). Then, it is determined whether a second condition, that uneven small droplets exist in the peripheral pixels, is satisfied (step S118). Whether unevenness exists is determined using the method described with reference to FIG. 4.

[0080] If it is determined that the second condition is met, that is, that uneven droplets exist in the surrounding pixels (S118: YES), the division flag for this target pixel is turned on (step S119). That is, the fact that the division flag is on is linked to the current target pixel and stored in the memory unit 31. In FIG. 9D, pixels px with the division flag turned on are indicated by black circles. Then, the process proceeds to step S127 in FIG. 13, where the printing method for this partial image is determined to be the second printing process (step S127). Thereafter, the division flag is turned off again (step S128), and the processes from step S129 onwards, which have already been described, are executed.

[0081] On the other hand, if it is determined in step S116 of Fig. 11 that the target pixel is not a large drop (S116: NO), or if it is determined in step S118 that the second condition is not satisfied, that is, that there are no uneven small drops (S118: NO), the process proceeds to step S120 of Fig. 12. Then, it is determined whether the execution of the processes of steps S116 to S118 has been completed for all pixels in the currently targeted block (step S120).

[0082] As a result, if it is determined in step S120 that the process is not complete (S120: NO), it is determined whether the previous target pixel was the rightmost pixel of the target block (step S124). If the previous target pixel is the rightmost pixel, such as pixel p12 in FIG. 9D (S124: YES), the leftmost pixel p13 of the next column (see FIG. 9D) is set as the new target (step S125), and the process from step S116 is executed again. Also, if it is determined in step S124 that the pixel is not the rightmost pixel (S124: NO), the pixel immediately to the right of the previous target pixel is set as the new target (step S126), and the process from step S16 is executed again.

[0083] If it is determined in step S120 that the processing is complete (S120: YES), it is determined whether or not the processing according to Operation Example 2 is complete for all blocks in the partial image acquired in step S102 (step S121). If there are any blocks that have not been processed (S121: NO), the next block is set as the target (step S122) in order to perform the second determination processing for the unprocessed blocks, and the processing from step S115 is executed again for this target block. Note that the method for determining the next target for a block may be similar to the method for determining the next target for a pixel (see S124, S125, S126), but is not limited thereto.

[0084] In this way, the second determination process is performed for each block in turn, and while no block that satisfies the second condition is found (S116: NO, S118: NO), a new pixel is set as the next target (S125, S126) or a new pixel is set as the next target in a new block (S122) (S115) by the processes from step S120 onwards until the process is completed for all blocks, and the second determination process from step S116 onwards is continued for this target pixel. Then, when a block that satisfies the second condition is found (S118: YES), the division flag is turned on as described above (S119), and the printing method for this partial image is determined to be the second printing process (S127).

[0085] On the other hand, if it is determined in step S121 that the processing according to operation example 2 has been completed for all blocks (S121: YES), the printing method for this partial image is determined to be the first printing process (step S123). That is, the result in step S121 is YES only when the partial image does not satisfy the first condition related to color (S111: NO) and does not satisfy the second condition related to graininess or density (S118: NO). In this case, either the first printing process or the second printing process can be selected from the perspective of color, and there is no need to select the second printing process from the perspective of graininess or density. Therefore, in such a case, the first printing process, which enables high-speed printing, is selected (S123).

[0086] Note that the mode of Operation Example 2 is not limited to the above. For example, in step S118, if there is at least one pixel that satisfies the second condition, the determination is "YES" and the division flag is turned on, but this is not limited to this. Instead, it may be determined to be "YES" only if there are a predetermined number of pixels that satisfy the second condition greater than 1, and determined to be "NO" if there are fewer than the predetermined number.

[0087] Furthermore, the second determination process (S116 to S118) of the second operation example is not limited to the mode of determining whether the second condition is satisfied by switching the target pixel for each block. For example, similar to the first determination process, the determination may be performed by switching the target pixel for the entirety of one partial image. [Industrial Applicability]

[0088] The present disclosure can be applied to a liquid ejection apparatus, a control method thereof, and a computer program. [Explanation of symbols]

[0089] 1 Liquid discharge device 10 Discharge head 11 nozzles 12 Nozzle surface 15 Conveying section 18 Reciprocating unit 19 Carriage 30 Control Unit

Claims

1. a discharge head having a nozzle surface on which nozzles are formed; a moving unit that supports the ejection head and moves back and forth in a first direction together with the ejection head; a control unit, The control unit a first printing process in which a partial image for one pass is formed by ejecting liquid only while the ejection head is moved in one of the first directions by the moving unit; a second printing process in which a partial image for one pass is formed by ejecting liquid while the ejection head is moved in one and the other of the first directions by the moving unit; a selection process for selecting whether to execute the first printing process or the second printing process; In the selection process, a first determination process for determining whether or not the color of the partial image obtained from the first image data satisfies a predetermined first condition; a second determination process for determining whether or not the size of the liquid ejected from the nozzle and the landing position on the recording medium, which are obtained from second image data obtained by halftone processing the first image data, satisfy a predetermined second condition; making the selection based on the results of Liquid discharge device.

2. The control unit In the first determination process, if a weight value relating to the magnitude of the difference in color between the image when the first printing process is executed and the image when the second printing process is executed, which is set for the RGB values ​​of each pixel constituting the first image data, is equal to or greater than a predetermined threshold, it is determined that the first condition is satisfied. The liquid ejection device according to claim 1 .

3. In the first determination process, the control unit Dividing the partial image into a plurality of blocks; obtaining a representative weight value that is a representative value of the weight values ​​for each of the plurality of blocks; determining that the first condition is satisfied when the representative weight value is equal to or greater than the threshold value; The liquid ejection device according to claim 2 .

4. The control unit In the second determination process, if the arrangement of small droplets relative to large droplets in the second image data is uneven, it is determined that the second condition is satisfied. The liquid ejection device according to claim 1 .

5. The control unit In the second determination process, if two or more small droplet pixels corresponding to small droplets are arranged rotationally symmetrically around a large droplet pixel corresponding to a large droplet and adjacent to the large droplet pixel, the arrangement of the small droplets relative to the large droplet is determined to be uniform, and if two or more small droplet pixels are not arranged rotationally symmetrically around the large droplet pixel, the arrangement is determined to be unequal. The liquid ejection device according to claim 4 .

6. The control unit In the selection process, the first determination process is executed after the second determination process is executed. The liquid ejection device according to claim 1 .

7. The control unit In the second determination process, if it is determined that the two conditions are met because the arrangement of small droplets relative to large droplets in the second image data is uneven, a flag is set to ON; When the flag is on, in the first determination process, it is determined whether or not a weight value relating to the magnitude of the difference in color between the image when the first printing process is executed and the image when the second printing process is executed, which is set to the RGB values ​​of each pixel constituting the first image data, is equal to or greater than a predetermined threshold value. The liquid ejection device according to claim 6 .

8. The control unit In the selection process, the second determination process is executed after the first determination process is executed. The liquid ejection device according to claim 1 .

9. The control unit In the first determination process, if it is determined that the first condition is not satisfied because a weight value relating to the magnitude of the difference in color between the image when the first printing process is executed and the image when the second printing process is executed, which is set for the RGB values ​​of each pixel constituting the first image data, is less than a predetermined threshold, halftone processing is performed on the first image data to generate the second image data, performing halftone processing on the first image data to generate the second image data, and then performing the second determination processing; The liquid ejection device according to claim 8 .

10. The control unit In the second determination process, if it is determined that the arrangement of small droplets relative to large droplets in the second image data is uneven, a flag is set to ON; If the flag is on, the second printing process is selected in the selection process. The liquid ejection device according to claim 7 .

11. a discharge head having a nozzle surface on which nozzles are formed; a moving unit that supports the ejection head and moves back and forth in a first direction together with the ejection head; A method for controlling a liquid ejection device comprising: The liquid ejection device, a first printing process in which a partial image for one pass is formed by ejecting liquid only while the ejection head is moved in one of the first directions by the moving unit; a second printing process in which a partial image for one pass is formed by ejecting liquid while the ejection head is moved in one and the other of the first directions by the moving unit; a selection process for selecting whether to execute the first printing process or the second printing process; In the selection process, a first determination process for determining whether or not the color of the partial image obtained from the first image data satisfies a predetermined first condition; a second determination process for determining whether or not the size of the liquid ejected from the nozzle and the landing position on the recording medium, which are obtained from second image data obtained by halftone processing the first image data, satisfy a predetermined second condition; making the selection based on the result of A method for controlling a liquid ejection device.

12. a discharge head having a nozzle surface on which nozzles are formed; a moving unit that supports the ejection head and moves back and forth in a first direction together with the ejection head; A computer program to be executed by a liquid ejection device comprising: The computer program causes the liquid ejection device to a first printing process in which a partial image for one pass is formed by ejecting liquid only while the ejection head is moved in one of the first directions by the moving unit; a second printing process in which a partial image for one pass is formed by ejecting liquid while the ejection head is moved in one and the other of the first directions by the moving unit; a selection process for selecting whether to execute the first printing process or the second printing process; In the selection process, a first determination process for determining whether or not the color of the partial image obtained from the first image data satisfies a predetermined first condition; a second determination process for determining whether or not the size of the liquid ejected from the nozzle and the landing position on the recording medium, which are obtained from second image data obtained by halftone processing the first image data, satisfy a predetermined second condition; making the selection based on the result of Computer program.

Images