Inkjet printers and printing methods

Abstract

To provide an ink jet printer which can achieve both of the granularity of a print image and the reduction of ink mist.SOLUTION: A plurality of dot tables respectively defining a correspondence between an ink value and a component ratio of each ink droplet are registered in an ink jet printer according to the present invention. The plurality of dot tables have mutually-different component ratios of the smallest first ink droplets in at least partial ink values. The ink jet printer associates any of the plurality of dot tables with a print image or each object in the print image (S11, S12A, S12B). The ink jet printer discharges a plurality of ink droplets on the basis of the component ratio of each ink droplet defined by the dot table corresponding to the print image or each object when forming the print image or each object (S16).SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an inkjet printer and a printing method. [Background technology]

[0002] Inkjet printers, which form images by ejecting ink onto a recording medium, have been known for some time. Typical inkjet printers are configured to eject multiple types of ink droplets of different sizes. For example, Patent Document 1 discloses an inkjet printer capable of forming three or more ink droplets of different sizes.

[0003] Furthermore, as disclosed in Patent Document 2, for example, a conversion table that defines the relationship between the ink value of print image data and the composition ratio of multiple types of ink droplets of different sizes has been known for some time. Using such a conversion table, the composition ratio of ink droplets corresponding to the ink value of print image data can be calculated. According to such a conversion table, when the ink value of print image data is small, the proportion of small dot ink droplets is high. Also, when the ink value of print image data is large, the proportion of small dot ink droplets is low and the proportion of large dot ink droplets is high. An inkjet printer is configured to eject multiple types of ink droplets of different sizes according to the composition ratio calculated by the conversion table. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-159463 [Patent Document 2] Japanese Patent Publication No. 2013-201666 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The conversion tables described above (hereinafter referred to as dot tables) are adjusted in various ways by inkjet printer designers and others. For example, a dot table can be created to prioritize the use of small dot ink droplets up to areas with relatively high ink values. In that case, the ink value at which large dot ink droplets begin to be ejected will be relatively high. Alternatively, a dot table can be created so that the ejection of large dot ink droplets begins in areas with relatively low ink values.

[0006] In image formation, a higher proportion of small ink droplets results in a finer image texture, improving the so-called granularity. However, a higher proportion of small ink droplets tends to increase the amount of ink mist dispersed during the droplet's flight. If this ink mist adheres to and hardens on the nozzle of the recording head, it may prevent ink from being ejected from the nozzle or cause the ink's flight direction to bend. From the standpoint of print image granularity, a higher proportion of small ink droplets is desirable, while from the standpoint of reducing ink mist, a lower proportion is desirable. However, balancing these two factors is not always easy.

[0007] This invention has been made in view of the above, and its objective is to provide an inkjet printer that can achieve both granularity in printed images and reduction of ink mist. It also aims to provide a printing method that can achieve both granularity in printed images and reduction of ink mist. [Means for solving the problem]

[0008] The inkjet printer disclosed herein comprises an ink head for ejecting a plurality of ink droplets, and a control device for controlling the ink head. The control device comprises an ejection control unit, a dot table registration unit, a data storage unit, and a dot table selection unit. The ejection control unit causes the ink head to eject a plurality of ink droplets, including the smallest first ink droplet and one or more other ink droplets larger than the first ink droplet. The dot table registration unit stores a plurality of dot tables, each defining a correspondence between ink values ​​and the composition ratio of each ink droplet. The plurality of dot tables have different composition ratios of the first ink droplet for at least some ink values. The data storage unit stores data of the printed image. The dot table selection unit associates one of the plurality of dot tables with the printed image or each object within the printed image. When forming the printed image or each object, the ejection control unit causes the ink head to eject a plurality of ink droplets based on the composition ratio of each ink droplet determined by the dot table corresponding to the printed image or each object.

[0009] Furthermore, the printing method disclosed herein is a method for printing an image using an inkjet printer capable of ejecting a plurality of ink droplets, each including a smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, comprising the steps of: associating a print image or each object in a print image with one of a plurality of pre-prepared dot tables that each define a correspondence between ink values ​​and the composition ratio of each ink droplet; and forming the print image or each object based on the composition ratio of each ink droplet defined by the dot table corresponding to the print image or each object. The plurality of dot tables have different composition ratios of the first ink droplet for at least some ink values.

[0010] According to the inventor's findings, the degree to which poor granularity affects the appearance varies depending on the image. For example, according to the inventor's findings, poor granularity is often not very noticeable in dark, solid-color images. For example, poor granularity is often relatively noticeable in bright images.

[0011] Therefore, the above inkjet printer is configured to associate one of several dot tables with different composition ratios of the smallest first ink droplets with the printed image or each object within the printed image. The above printing method also includes the step of associating one of several dot tables with different composition ratios of the smallest first ink droplets with the printed image or each object within the printed image. With the above inkjet printer and printing method, it is possible to associate a dot table suitable for the image, for example, associating a dot table with a relatively small composition ratio of first ink droplets with a dark solid image, and associating a dot table with a relatively large composition ratio of first ink droplets with a bright image. Therefore, with the above inkjet printer and printing method, it is possible to achieve both granularity of the printed image and reduction of ink mist. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view of an inkjet printer according to one embodiment. [Figure 2] This is a front view showing the main components of the printer. [Figure 3] This is a partial cross-sectional view of the area near the nozzle of the ink head. [Figure 4] This waveform diagram shows an example of a drive signal for dispensing S, M, and L droplets. [Figure 5] This is a block diagram of the printer according to the first embodiment. [Figure 6] This chart shows the first dot table registered in the dot table registration section. [Figure 7] This chart shows the second dot table registered in the dot table registration section. [Figure 8] It is a schematic diagram showing an example of a printed image including a plurality of objects. [Figure 9] It is a flowchart showing an example of a process for forming a printed image including a plurality of objects. [Figure 10] It is a block diagram of a printer according to the second embodiment. [Figure 11] It is a flowchart showing an example of a process for forming one object in a printed image in the second embodiment. [Figure 12] It is a block diagram of a printer according to the third embodiment. [[ID=B]] [Figure 13] It is a graph showing a conversion table between a first dot table and a second dot table. [Figure 14] It is a flowchart showing an example of a process for forming one object in a printed image in the third embodiment.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of an inkjet printer according to the present invention will be described with reference to the drawings. The embodiments described here are not, of course, intended to particularly limit the present invention. Also, although several embodiments are described below, members and parts having the same function are denoted by the same reference numerals, and overlapping descriptions are omitted or simplified.

[0014] (First Embodiment) FIG. 1 is a perspective view of an inkjet printer (hereinafter, printer) 10 according to an embodiment. FIG. 2 is a front view showing the main part of the printer 10. In FIGS. 1 and 2, reference numerals L and R indicate left and right, respectively. Reference numerals F and Rr indicate front and rear, respectively. However, these are merely directions for convenience of explanation and do not limit the installation state of the printer 10 in any way.

[0015] The printer 10 is used to print onto the recording medium 5. The recording medium 5 is the object onto which ink is ejected. The recording medium includes not only paper such as plain paper, but also various materials such as polyvinyl chloride (PVC), polyester resins, aluminum, iron, and wood.

[0016] The printer 10 comprises a casing 2 and guide rails 3 located within the casing 2. The guide rails 3 extend in the left-right direction. A carriage 1, equipped with an ink head 15 for ejecting ink, is engaged with the guide rails 3. The carriage 1 reciprocates along the guide rails 3 in the left-right direction (scanning direction) by a carriage movement mechanism 8. The carriage movement mechanism 8 has pulleys 19b and 19a located on the left and right ends of the guide rails 3. A carriage motor 8a is connected to pulley 19a. The carriage motor 8a may also be connected to pulley 19b. The pulley 19a is driven by the carriage motor 8a. An endless belt 6 is wound around both pulleys 19a and 19b. The carriage 1 is fixed to the belt 6. As the pulleys 19a and 19b rotate and the belt 6 travels, the carriage 1 moves in the left-right direction.

[0017] The recording medium 5 is transported in the paper feeding direction by a paper feeding mechanism (not shown). Here, the paper feeding direction is the front-to-back direction. A platen 4 supporting the recording medium 5 is provided inside the casing 2. A grid roller (not shown) is provided on the platen 4. A pinch roller (not shown) is provided above the grid roller. The grid roller is connected to a feed motor 7 (see Figure 5). The grid roller is driven and rotated by the feed motor 7. When the grid roller rotates with the recording medium 5 sandwiched between it and the pinch roller, the recording medium 5 is transported in the front-to-back direction.

[0018] The printer 10 has multiple ink cartridges 11. These multiple ink cartridges 11 store ink of different colors. For example, the printer 10 has five ink cartridges 11, each storing cyan ink, magenta ink, yellow ink, black ink, and white ink.

[0019] An ink head 15 is provided for each color of ink. Each ink head 15 and the ink cartridge 11 are connected by an ink supply path 12. The ink supply path 12 is an ink flow path that supplies ink from the ink cartridge 11 to the ink head 15. The ink supply path 12 is made of, for example, a flexible tube. A liquid delivery pump 13 is provided in the ink supply path 12. However, the liquid delivery pump 13 is not always necessary and can be omitted. Part of the ink supply path 12 is covered by a cable protection guide device.

[0020] The ink head 15 ejects ink toward the recording medium 5, forming ink dots on the recording medium 5. By arranging many of these dots, an image or the like is formed on the recording medium 5. The ink head 15 is equipped with multiple nozzles 25 (see Figure 3) for ejecting ink on the side facing the recording medium 5 (the lower surface of the ink head 15 in this embodiment).

[0021] Figure 3 is a partial cross-sectional view of the ink head 15 near one nozzle 25. The ink head 15 comprises a hollow case 21 having an opening 21a and a diaphragm 22 attached to the case 21 so as to close the opening 21a. The diaphragm 22 together with the case 21 partitions a pressure chamber 23 in which ink is stored. The diaphragm 22 partitions a portion of the pressure chamber 23. The diaphragm 22 is elastically deformable inward and outward from the pressure chamber 23. The diaphragm 22 is configured to be deformable to increase and decrease the volume of the pressure chamber 23. The diaphragm 22 is typically a resin film or a metal foil.

[0022] The case 21 has an ink inlet 24 into which ink flows. The ink inlet 24 only needs to be connected to the pressure chamber 23, and its position is not limited in any way. Ink is supplied to the pressure chamber 23 from the ink cartridge 11 through the ink inlet 24, and the ink is stored there. The nozzle 25 is formed on the lower surface 21b of the case 21.

[0023] An actuator 26 is in contact with the surface of the diaphragm 22 opposite to the pressure chamber 23 side. The actuator 26 is a piezoelectric element. Part of the actuator 26 is fixed to a fixing member 29. The actuator 26 is connected to the control device 100 via a flexible cable 27. Signals are supplied to the actuator 26 via the flexible cable 27. In this embodiment, the actuator 26 is a laminate in which piezoelectric material and conductive layers are alternately laminated. When the actuator 26 receives a signal from the control device 100, it expands or contracts, functioning to elastically deform the diaphragm 22 to the outside or inside of the pressure chamber 23. A longitudinal vibration mode piezoelectric element (PZT) is used here. The longitudinal vibration mode PZT is expandable and contractible in the lamination direction, for example, it contracts when discharged and expands when charged. However, the type of actuator 26 is not particularly limited.

[0024] In an ink head 15 with this configuration, for example, by lowering the potential of the actuator 26 from the reference potential, the actuator 26 contracts. In response, the diaphragm 22 elastically deforms outward from its initial position, causing the pressure chamber 23 to expand. Note that expansion of the pressure chamber 23 means that the volume of the pressure chamber 23 increases due to the deformation of the diaphragm 22. Next, by raising the potential of the actuator 26, the actuator 26 extends in the stacking direction. As a result, the diaphragm 22 elastically deforms inward, causing the pressure chamber 23 to contract. Note that contraction of the pressure chamber 23 means that the volume of the pressure chamber 23 decreases due to the deformation of the diaphragm 22. Due to this expansion and contraction of the pressure chamber 23, the pressure inside the pressure chamber 23 fluctuates. This pressure fluctuation inside the pressure chamber 23 pressurizes the ink inside the pressure chamber 23, and it is ejected from the nozzle 25. Subsequently, by returning the potential of the actuator 26 to the reference potential, the diaphragm 22 returns to its initial position and the pressure chamber 23 expands. At this time, ink flows into the pressure chamber 23 from the ink inlet 24.

[0025] The ink head 15 is configured to simultaneously form multiple ink droplets of different sizes. Here, the ink head 15 ejects S droplets, M droplets, and L droplets of different sizes. The ink head 15 ejects ink droplets while changing the composition ratio of S droplets, M droplets, and L droplets according to the total amount of ink in the S droplets, M droplets, and L droplets (hereinafter referred to as the ink value). The composition ratio of S droplets, M droplets, and L droplets is commanded by the control device 100.

[0026] Figure 4 is a waveform diagram showing an example of a drive signal for ejecting S, M, and L droplets. As shown in Figure 4, the printer 10 generates a drive signal containing five drive pulses P1 to P5 for each drive cycle. When forming an L droplet, the control device 100 supplies all drive pulses P1 to P5 to the actuator 26. When forming an M droplet, the control device 100 supplies the third drive pulse P3 and the fifth drive pulse P5 to the actuator 26. When forming an S droplet, the control device 100 supplies only the fifth drive pulse P5 to the actuator 26. However, the drive signal shown in Figure 4 is merely an example, and the form of the drive signal is not limited.

[0027] Figure 5 is a block diagram of the printer 10. As shown in Figure 5, the control device 100 is electrically connected to the feed motor 7 of the paper feeding mechanism, the carriage motor 8a of the carriage movement mechanism 8, the liquid supply pump 13, and the ink head 15. The control device 100 controls the operation of these components. The control device 100 is typically a computer. The control device 100 includes, for example, an interface (I / F) for receiving print data from external devices such as a host computer, a central processing unit (CPU) for executing instructions of the control program, a ROM for storing programs executed by the CPU, RAM used as a working area for expanding the program, and a storage device such as memory for storing the program and various data.

[0028] As shown in Figure 5, the control device 100 includes a dot table registration unit 110, a data storage unit 120, a dot table selection unit 130, an input unit 140, a color conversion unit 150, a halftone processing unit 160, and an output control unit 170. The control device 100 may include other processing units, but these are not shown or described here.

[0029] Multiple dot tables are registered in the dot table registration unit 110. Each of the multiple dot tables defines the correspondence between ink values ​​and the composition ratio of each ink droplet (here, S droplets, M droplets, and L droplets). For at least some ink values, the composition ratio of S droplets differs among the multiple dot tables. The number of dot tables registered in the dot table registration unit 110 is not limited, but in this case, there are two.

[0030] Figure 6 is a chart showing the first dot table T1 registered in the dot table registration unit 110. Figure 7 is a chart showing the second dot table T2 registered in the dot table registration unit 110. The horizontal axis in Figures 6 and 7 represents the ink value, with the ink value when all dots are L droplets being 100%. The vertical axis in Figures 6 and 7 represents the composition ratio of S droplets, M droplets, and L droplets, with the maximum number of dots that can be ejected per unit area being 100%. However, the first dot table T1 and the second dot table T2 are merely examples, and other configurations are possible.

[0031] Rs1 in Figure 6 represents the composition ratio of S droplets in the first dot table T1. As shown in Figure 6, the first dot table T1 is configured to dispense only S droplets up to an ink value of I1. In the first dot table T1, the number of S droplets increases linearly until the ink value reaches I1. The composition ratio of S droplets when the ink value is I1 is Vs1. After that, the number of S droplets decreases linearly so that the composition ratio becomes 0% at an ink value of I2.

[0032] Rm1 in Figure 6 represents the composition ratio of M droplets in the first dot table T1. As shown in Figure 6, the first dot table T1 starts ejecting M droplets at an ink value of I1. In the first dot table T1, the number of M droplets increases linearly until the ink value reaches I2. When the ink value is I2, only M droplets are ejected. After that, the number of M droplets decreases linearly so that the composition ratio becomes 0% when the ink value reaches 100%.

[0033] Rl1 in Figure 6 represents the composition ratio of L droplets in the first dot table T1. As shown in Figure 6, the first dot table T1 starts ejecting L droplets at ink value I2. In the first dot table T1, the number of L droplets increases linearly until the ink value reaches 100%. When the ink value is 100%, only L droplets are ejected.

[0034] Rs2 in Figure 7 represents the composition ratio of S droplets in the second dot table T2. As shown in Figure 7, the second dot table T2 is configured to dispense only S droplets up to an ink value I3, which is smaller than the ink value I1. In the second dot table T2, the number of S droplets increases linearly until the ink value reaches I3. The composition ratio of S droplets when the ink value is I3 is Vs2. After that, the number of S droplets decreases linearly so that the composition ratio becomes 0% at the ink value I2.

[0035] Rm2 in Figure 7 represents the composition ratio of M droplets in the second dot table T2. As shown in Figure 7, the second dot table T2 starts ejecting M droplets at an ink value of I3. In the second dot table T2, the number of M droplets increases linearly until the ink value reaches I2. When the ink value is I2, only M droplets are ejected. After that, the number of M droplets decreases linearly so that the composition ratio becomes 0% when the ink value reaches 100%.

[0036] Rl2 in Figure 7 represents the composition ratio of L droplets in the second dot table T2. As shown in Figure 7, the second dot table T2 starts ejecting L droplets at ink value I2. In the second dot table T2, the number of L droplets increases linearly until the ink value reaches 100%. When the ink value is 100%, only L droplets are ejected.

[0037] Thus, for ink values ​​from 0% to I3, both the first dot table T1 and the second dot table T2 eject only S droplets of ink, and the composition ratio of S droplets is the same. For ink values ​​from I3 to I2, the composition ratio of S droplets and M droplets differs between the first dot table T1 and the second dot table T2. In this case, the composition ratio of L droplets is 0%. For ink values ​​from I2 to 100%, both the first dot table T1 and the second dot table T2 eject M droplets and L droplets of ink, and the composition ratio of M droplets and L droplets is the same between the first dot table T1 and the second dot table T2.

[0038] The relationship between the first dot table T1 and the second dot table T2 is not limited to the above, but the second dot table T2 is configured such that the proportion of S droplets is less than or equal to that of the first dot table T1 for all ink values, and that the proportion of S droplets is smaller than that of the first dot table T1 for at least some ink values. Hereinafter, "the proportion of S droplets is the same or smaller for all ink values, and the proportion of S droplets is smaller for at least some ink values" will also be simply referred to as "a low S droplet occurrence rate." The opposite will be referred to as "a high S droplet occurrence rate."

[0039] The data storage unit 120 stores the data of the printed image. In this case, the data storage unit 120 temporarily stores image data transmitted from an external computer or the like.

[0040] The dot table selection unit 130 is configured to associate one of the first dot table T1 and the second dot table T2 with each object in the printed image. Depending on how the dot table selection unit 130 associates a dot table with each object in the printed image, the printer 10 can have several variations. In this embodiment, the dot table selection unit 130 includes a first selection unit 131 that associates either the first dot table T1 or the second dot table T2 with each object in the printed image based on user specification. The control device 100 also includes an input unit 140 configured to allow the user to specify the dot table association for each object in the printed image.

[0041] The input unit 140 displays an operation screen, for example, on a display device of an external computer connected to the printer 10. The user operates the operation screen to associate the first dot table T1 or the second dot table T2 with each object in the printed image. The first selection unit 131 associates the dot table specified in the input unit 140 with each object in the printed image.

[0042] The color conversion unit 150 performs color conversion on each object in the printed image using an ICC profile to obtain the ink value, in this case CMYK ink value, for each object. In this embodiment, the color conversion unit 150 selects an ICC profile corresponding to the dot table (in this case, the first dot table T1 or the second dot table T2) associated with each object. Each object is converted to a CMYK ink value using this selected ICC profile. The color conversion process is performed for each object.

[0043] The halftone processing unit 160 performs halftone processing on each color-converted object. This converts the CMYK ink values ​​of each object into ink dot data.

[0044] The ejection control unit 170 causes the ink head 15 to eject a plurality of ink droplets, including the smallest S droplet and one or more other ink droplets larger than the S droplet. As described above, in this embodiment, the ejection control unit 170 causes the ink head 15 to eject the smallest S droplet, the M droplet which is larger than the S droplet, and the L droplet which is even larger than the M droplet. However, the types of ink droplets ejected from the ink head 15 may be two or four or more. When forming each object, the ejection control unit 170 causes the ink head 15 to eject S droplets, M droplets, and L droplets based on the composition ratio of each ink droplet determined by the dot table corresponding to each object (here, the first dot table T1 or the second dot table T2). The ejection control unit 170 causes the ink head 15 to eject S droplets, M droplets, and L droplets by selectively supplying some or all of the drive signals.

[0045] The following describes an example of the process for forming a printed image containing multiple objects. Figure 8 is a schematic diagram showing an example of a printed image containing multiple objects. Figure 9 is a flowchart showing an example of the process for forming a printed image containing multiple objects. In the example shown in Figure 8, the printed image contains a first object O1 and a second object O2. In this example, the first object O1 is assumed to be an image with a generally light color scheme. The second object O2 is assumed to be a solid color image with a dark color scheme. A solid color image is an image that is uniformly filled with one color (which may be a single ink or a mixture of multiple inks). The second object O2 may also be a high-density image with a high dot density. However, the types of objects that the first object O1 and the second object O2 are are not limited, and it is at the user's discretion which of the first dot table T1 and the second dot table T2 to associate with the first object O1 and the second object O2, respectively.

[0046] As mentioned above, in image formation, a higher proportion of small S droplets results in a finer image texture, improving the so-called granularity. However, a higher proportion of S droplets in an ink droplet tends to increase the amount of ink mist dispersed during the droplet's flight. If this ink mist adheres to and hardens on the nozzle 25 of the ink head 15, it may prevent ink from being ejected from the nozzle 25 or cause the ink's flight direction to bend. From the viewpoint of granularity in printed images, a higher proportion of S droplets is desirable, but from the viewpoint of reducing ink mist, a lower proportion of S droplets is desirable. Balancing these two aspects has not always been easy in the past.

[0047] In response to the above problem, the inventors of the present invention have found that the degree to which poor granularity affects the appearance varies depending on the image. According to the inventors' findings, for example, poor granularity is often not very noticeable in dark solid images. On the other hand, for example, poor granularity is often relatively noticeable in bright images. Therefore, in the case of an image like Figure 8, it is preferable to associate the first object O1 with the first dot table T1 which has a high rate of S droplet generation. Furthermore, it is preferable to associate the second object O2 with the second dot table T2 which has a low rate of S droplet generation.

[0048] Figure 9 shows the process of forming a printed image when a first dot table T1 is associated with a first object O1 and a second dot table T2 is associated with a second object O2. As shown in Figure 9, in the processing of the first object O1, in step S01A, the composition ratio of each ink droplet of the first object O1 is determined based on the first dot table T1. In step S02A, the first object O1 is color-converted by a first ICC profile corresponding to the first dot table T1. In the processing of the second object O2, in step S01B, the composition ratio of each ink droplet of the second object O2 is determined based on the second dot table T2. In step S02B, the second object O2 is color-converted by a second ICC profile corresponding to the second dot table T2.

[0049] The color-converted data of the first object O1 and the color-converted data of the second object O2 are subjected to halftone processing in step S03. In step S04, an image is formed based on the dot data of the printed image obtained by the halftone processing.

[0050] As described above, the printer 10 according to this embodiment is configured to associate one of the first dot table T1 and the second dot table T2 with each object in the printed image. Therefore, with such a printer 10, for example, a dot table with a relatively small proportion of S droplets (in this case, the second dot table T2) can be associated with a dark solid image, and a dot table with a relatively large proportion of S droplets (in this case, the first dot table T1) can be associated with a bright image. By selecting a suitable dot table according to the image in this way, the granularity of images where granularity is desired can be improved, and ink mist can be reduced when forming images where granularity is not important. Therefore, it is possible to achieve both granularity of the printed image and reduction of ink mist.

[0051] The printer 10 according to this embodiment is configured so that the user can specify the mapping of dot tables to each object in the printed image. How to evaluate the graininess of the image and the risk of ink mist is up to the user. Therefore, with the printer 10 according to this embodiment, it is possible to balance the reduction of image graininess and ink mist according to the user's circumstances and preferences.

[0052] (Second Embodiment) In the second embodiment, a dot table is automatically associated with each object in the printed image. Figure 10 is a block diagram of the printer 10 according to this embodiment. As shown in Figure 10, the dot table selection unit 130 according to this embodiment includes a second selection unit 132 that associates either a first dot table T1 or a second dot table T2 with each object in the printed image. The second selection unit 132 is set to associate the first dot table T1 with objects whose brightness is equal to or greater than a predetermined first brightness, and to associate the second dot table T2 with objects whose brightness is less than the first brightness. The brightness of each object is calculated based on the data of the printed image stored in the data storage unit 120. The brightness here refers to, for example, the average value, median value, maximum value, minimum value, etc., of the brightness of each part of each object.

[0053] The printer 10 may be configured to allow the user to select between a mode in which the mapping of dot tables to each object in the printed image is performed automatically and a mode in which the user performs the mapping. In that case, as shown in Figure 10, the control device 100 may further include a first selection unit 131 and an input unit 140.

[0054] Figure 11 is a flowchart illustrating an example of the process for forming a single object in a printed image. As shown in Figure 11, in the process for forming a single object in a printed image, step S11 determines whether the object's brightness is greater than or equal to a predetermined first brightness. If the object's brightness is greater than or equal to the predetermined first brightness (if the result of step S11 is YES), step S12A associates the object with a first dot table T1. This determines the composition ratio of each ink droplet in the object based on the first dot table T1. Subsequently, step S13A selects a first ICC profile corresponding to the first dot table T1. Step S14A colors the object using the first ICC profile. This determines the ink values ​​of the object. The color-converted image data is then halftoned in step S15. In the halftoning process of step S15, dot data for each ink (here, CMYK and W) is created according to the ink values ​​obtained by the color conversion and the composition ratio of each ink droplet based on the first dot table T1. In step S16, printing is performed based on the dot data obtained through halftone processing.

[0055] If the object's brightness is less than a predetermined first brightness (the result of step S11 is NO), the object is associated with a second dot table T2 in step S12B. This determines the composition ratio of each ink droplet in the object based on the second dot table T2. Then, in step S13B, a second ICC profile corresponding to the second dot table T2 is selected. In step S14B, the object is color-converted using the second ICC profile. Steps S15 and S16 are the same as for objects with a brightness of first brightness or greater.

[0056] Thus, in this embodiment, the first dot table T1 is associated with objects whose brightness is equal to or greater than a predetermined first brightness level, and the second dot table T2 is associated with objects whose brightness is less than the first brightness level. Since images with high brightness tend to show poor granularity relatively well, the first dot table T1, which has a high rate of S droplet generation, is associated with images whose brightness is equal to or greater than the first brightness level. Since images with low brightness tend to show poor granularity relatively well, the second dot table T2, which has a low rate of S droplet generation, is associated with images whose brightness is less than the first brightness level. This reduces ink mist.

[0057] Note that more than three dot tables may be registered. For example, if a first dot table T1, a second dot table T2, and a third dot table with a lower S-drop rate than the second dot table T2 are registered, the second dot table T2 may be associated with objects whose brightness is less than the first brightness level but greater than or equal to the second brightness level (the second brightness level is lower than the first brightness level), and the third dot table may be associated with objects whose brightness is less than the second brightness level. The same applies if four or more dot tables are registered.

[0058] (Modification 1 of the second embodiment) In one modification of the second embodiment, as shown in Figure 10, the dot table selection unit 130 may include a third selection unit 133 that associates a first dot table T1 with objects whose print density is less than a predetermined first density. In that case, the third selection unit 133 may be set to associate a second dot table T2 with objects whose print density is equal to or greater than the first density. Print density here refers to, for example, the average, median, maximum, and minimum values ​​of the print density of each part of each object. According to the inventors' knowledge, images with low print density are images where poor granularity is relatively noticeable, while images with high print density are images where poor granularity is relatively inconspicuous. Therefore, the degree to which granularity affects the appearance of an image can be classified into multiple categories based on print density.

[0059] (Modification 2 of the second embodiment) In another modification of the second embodiment, as shown in FIG. 10, the dot table selection unit 130 may include a fourth selection unit 134 that associates a first dot table T1 with an object composed of line drawings. Since line drawings preferably show sharp outlines, they correspond to images that are sensitive to granularity. Since it is known that line drawings can be distinguished from other objects, the description of the method for distinguishing line drawings is omitted. For objects other than line drawings, for example, a corresponding dot table may be selected based on brightness or printing density.

[0060] (Modification Example 3 of the Second Embodiment) In still another modification of the second embodiment, as shown in FIG. 10, the dot table selection unit 130 may include a fifth selection unit 135 that associates a first dot table T1 with an object in which the ratio of the area belonging to a predetermined color gamut is equal to or greater than a first threshold value. In one preferred example, the predetermined color gamut is the color gamut of skin color. According to the findings of the inventor of the present application, the color gamut of skin color is a color gamut in which the poor granularity is relatively prominent, and in a region where skin color occupies a certain proportion, the poor granularity is relatively likely to be prominent. For objects other than those described above, for example, a corresponding dot table may be selected based on brightness or printing density. Here, the "skin color" mentioned here refers to L * value is set in the range of 0 or more and 100 or less on the L * axis, and a * value is set in the range of -128 or more and 127 or less on the a * axis, and b * value is set in the range of -128 or more and 127 or less on the b * axis. In the L * a * b * color space, the L * value is 60 or more and 90 or less, the a * value is 0 or more and 20 or less, and the b * value is 0 or more and 30 or less refers to the color gamut. However, the fifth selection unit 135 may set the above-described threshold value for the color gamut of colors other than skin color, and associate the first dot table T1 with an object in which the ratio of the area belonging to the color gamut is equal to or greater than the threshold value.

[0061] Although Figure 10 shows all of the first to fifth selection units 131 to 135 and the input unit 140, the dot table selection unit 130 may include all of the first to fifth selection units 131 to 135 and the input unit 140, or it may include only some of them. For example, the printer 10 may be configured so that the user can select whether to select a dot table based on brightness, print density, line drawing, or color gamut. Alternatively, for example, the printer 10 may be configured to select an object to which the first dot table T1 or second dot table T2 corresponds based on one of the following: brightness, print density, line drawing, or color gamut, and then to additionally select an object to which the first dot table T1 or second dot table T2 corresponds based on the other one. The same applies when further additional objects are selected. However, these methods are merely preferred examples. The printer 10 is not limited to which of the first to fifth selection units 131 to 135 it includes, nor is it limited to the order in which the functions of the included units are performed.

[0062] (Third embodiment) The printer 10 according to the third embodiment is configured to adjust the ink values ​​of objects to which other dot tables are associated in order to match one dot table, when different dot tables are associated with multiple objects in a printed image. Figure 12 is a block diagram of the printer 10 according to the third embodiment. As shown in Figure 12, the printer 10 according to this embodiment includes a conversion table registration unit 180, an ink value correction unit 190, and a color conversion unit 150A having a different function from that of the first and second embodiments.

[0063] In this embodiment, the color conversion unit 150A is configured to convert the color of all objects in the printed image using an ICC profile corresponding to one predetermined dot table from among a plurality of dot tables. In this embodiment as well, it is assumed that the printer 10 has a first dot table T1 and a second dot table T2 registered. Here, the color conversion unit 150A converts the color of all objects in the printed image using an ICC profile corresponding to the first dot table T1.

[0064] The conversion table registration unit 180 has a conversion table Te (see Figure 13) registered for converting ink values ​​between multiple dot tables. The ink value correction unit 190 determines the composition ratio of each ink droplet based on another dot table (here, the second dot table T2) that is different from one predetermined dot table (here, the first dot table T1), and converts the ink value of the object whose color has been converted by the ICC profile corresponding to the predetermined dot table (here, the first dot table T1) based on the conversion table Te. The conversion process between the conversion table Te and the ink value will be described below.

[0065] Figure 13 is a graph showing the conversion table Te between the first dot table T1 and the second dot table T2. The horizontal axis of the conversion table Te represents the ink value of the first dot table T1. The vertical axis of the conversion table Te represents the ink value of the second dot table T2. On the graph G1 of the conversion table Te, the print density of the single-color ink is the same between the first dot table T1 and the second dot table T2.

[0066] As shown in Figures 6 and 7, for ink values ​​from 0% to I3, the composition ratio of each ink droplet is the same between the first dot table T1 and the second dot table T2. Therefore, in this range, the slope of graph G1 in Figure 13 is "1" (the dotted line L1 represents the line with a slope of "1"). In this range, graph G1 and line L1 coincide. For ink values ​​from I3 to I2, the composition ratio of each ink droplet differs between the first dot table T1 and the second dot table T2. Therefore, in this range, graph G1 does not coincide with line L1. In the range where graph G1 and line L1 do not coincide, there is a slight difference in print density between using the first dot table T1 and using the second dot table T2. This difference in print density is due to the difference in how the ink dots spread after impact. In this example, in the range of ink values ​​from I3 to I2, the print density is higher when using the first dot table T1 than when using the second dot table T2. In other words, the ink value required to achieve the same print density is smaller when using the first dot table T1 than when using the second dot table T2. Between ink values ​​I2 and 100%, the composition ratio of each ink droplet is the same between the first dot table T1 and the second dot table T2. Therefore, in the above range, graph G1 and line L1 coincide.

[0067] The conversion table Te is a conversion table that corrects the ink values ​​of each object after color conversion to match the print density between objects using the first dot table T1 and objects using the second dot table T2. The conversion table Te is created based on the colorimetric results of test patch images printed using the first dot table T1 and test patch images printed using the second dot table T2, respectively. Here, the conversion table Te is a conversion table for correcting the ink values ​​of objects whose composition ratio of each ink droplet is determined based on the second dot table T2 and which have been color converted by the ICC profile corresponding to the first dot table T1. When the ink values ​​of the first dot table T1 are entered into the conversion table Te, the ink values ​​of the second dot table T2 on graph G1 corresponding to the ink values ​​of the first dot table T1 are obtained.

[0068] Figure 14 is a flowchart illustrating an example of the formation process for a single object in a printed image. As shown in Figure 14, in the formation process for a single object in a printed image, step S21 determines whether the object's brightness is greater than or equal to a predetermined first brightness. If the object's brightness is greater than or equal to the predetermined first brightness (if the result of step S21 is YES), step S22A associates the object with a first dot table T1. Based on this, the composition ratio of each ink droplet in the object is determined. In step S23A, the object is color-converted using a first ICC profile corresponding to the first dot table T1. No ICC profile selection takes place in step S23A. The ICC profile used in step S23A is predetermined and is the first ICC profile.

[0069] If the object's brightness is less than a predetermined first brightness (the result of step S21 is NO), the object is associated with the second dot table T2 in step S22B. This determines the composition ratio of each ink droplet in the object based on the second dot table T2. In step S23B, the object is color-converted using the first ICC profile corresponding to the first dot table T1. No ICC profile is selected in step S23A. Even if the second dot table T2 is selected in step S22B, the ICC profile used in step S23B is the first ICC profile. The ICC profile used in step S23B is predetermined.

[0070] As a result of step S23B, a slight difference in print density occurs between the object using the first dot table T1 and the object using the second dot table T2. Therefore, in step S24B following step S23B, the ink value of the object is corrected using the conversion table Te. This makes it possible to match the print density between the object using the first dot table T1 and the object using the second dot table T2.

[0071] The color-converted image data is halftoned in step S25. In step S26, printing is performed based on the halftoned print image data.

[0072] According to the method of the third embodiment, it is possible to achieve both granularity of the printed image and reduction of ink mist, while also reducing the effort required to create ICC profiles and the memory capacity of the printer 10. With this method, it is not necessary to create multiple ICC profiles corresponding to multiple dot tables. Therefore, the effort required to create ICC profiles can be reduced. In addition, since the number of ICC profiles to be stored can be reduced, the memory capacity for storing ICC profiles can be reduced.

[0073] The dot table used as the basis for print density may also be the second dot table T2. If there are three or more registered dot tables, the dot table used as the basis for print density is not limited. In addition, although the dot table was selected based on the brightness of the object in the description of the third embodiment above, the dot table may be selected based on other criteria (e.g., print density, line drawing, color gamut). Alternatively, the dot table may be selected by the user.

[0074] Several preferred embodiments have been described above. However, the inkjet printer of the present invention is not limited to the embodiments described above.

[0075] For example, in the embodiment described above, the dot table to be used was selected for each object in the printed image. However, the dot table to be used may be selected for each printed image.

[0076] In the embodiments described above, the selection of the dot table to be used was performed automatically by the printer 10 or by the user using the printer 10's operation screen. However, similar printing methods are possible with other printers as well. The printing method of the present invention only needs to include the steps of associating one of a plurality of pre-prepared dot tables with a print image or each object within a print image, and forming the print image or each object based on the composition ratio of each ink droplet determined by the dot table corresponding to the print image or each object, and is not limited to a method using a specific printer. Note that the plurality of dot tables described above have different composition ratios of the first ink droplets for at least some ink values.

[0077] In the embodiments described above, image brightness and print density were given as examples of criteria for selecting the dot table to be used. However, the criteria for selecting the dot table to be used are not limited to any other criteria that can evaluate the effect of the composition ratio of small dot ink droplets on the granularity of the image.

[0078] The configuration of the printer 10 according to the above embodiment is illustrative and does not limit the printer's configuration.

[0079] Unless otherwise specified, the embodiments described above do not limit the present invention. [Explanation of Symbols]

[0080] 5. Recording media 10 Printers 15 Inkheads 100 Control device 110 Dot Table Registration Section 120 Data Storage Unit 130 Dot Table Selection Section 131 1st Selection Department 132 2nd Selection Department 133 Third Selection Department 134 4th Selection Department 135 5th Selection Department 140 Input section 150 Color Conversion Unit 150A Color conversion unit (third embodiment) 160 Halftone Processing 170 Discharge control unit 180 Conversion Table Registration Section 190 Ink Value Correction Unit O1 First Object O2 Second Object T1 First Dot Table T2 Second Dot Table T Conversion Table

Claims

1. An ink head that ejects multiple ink droplets, A control device for controlling the ink head, Equipped with, The control device is A discharge control unit that causes a plurality of ink droplets to be ejected from the ink head, including the smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, A dot table registration unit where multiple dot tables are registered, each defining the correspondence between ink values ​​and the composition ratio of each ink droplet, A data storage unit that stores the data of the printed image, An input section configured to allow specifying the mapping of a dot table to each object in a printed image, A dot table selection unit includes a first selection unit that associates each object in the printed image with a dot table specified in the input unit from among the plurality of dot tables, Equipped with, When forming each object, the ejection control unit ejects multiple ink droplets from the ink head based on the composition ratio of each ink droplet determined by the dot table corresponding to each object. The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, The invention includes a second dot table in which, for all ink values, the composition ratio of the first ink droplet is less than or equal to that of the first dot table, and for at least some ink values, the composition ratio of the first ink droplet is smaller than that of the first dot table, and the composition ratio of the first ink droplet increases until the ink value reaches a predetermined first ink value, and then decreases once the ink value reaches the first ink value, and further includes a second dot table in which the maximum value of the composition ratio of the first ink droplet is smaller than the maximum value of the composition ratio of the second smallest second ink droplet, and is also smaller than the maximum value of the composition ratio of the first ink droplet in the first dot table. Inkjet printer.

2. An ink head that ejects multiple ink droplets, A control device for controlling the ink head, Equipped with, The control device is A discharge control unit that causes a plurality of ink droplets to be ejected from the ink head, including the smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, A dot table registration unit where multiple dot tables are registered, each defining the correspondence between ink values ​​and the composition ratio of each ink droplet, A data storage unit that stores the data of the printed image, A dot table selection unit that associates one of the plurality of dot tables with each object in a printed image or within a printed image, Equipped with, When forming a printed image or each object, the ejection control unit ejects multiple ink droplets from the ink head based on the composition ratio of each ink droplet determined by a dot table corresponding to the printed image or each object. The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, A second dot table in which the composition ratio of the first ink droplet is less than or equal to that of the first dot table for all ink values, and in at least some ink values ​​the composition ratio of the first ink droplet is smaller than that of the first dot table, Includes, The dot table selection unit includes a second selection unit that associates the first dot table with printed images or objects whose brightness is equal to or greater than a predetermined first brightness, and associates the second dot table with printed images or objects whose brightness is less than the first brightness. Inkjet printer.

3. An ink head that ejects multiple ink droplets, A control device for controlling the ink head, Equipped with, The control device is A discharge control unit that causes a plurality of ink droplets to be ejected from the ink head, including the smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, A dot table registration unit where multiple dot tables are registered, each defining the correspondence between ink values ​​and the composition ratio of each ink droplet, A data storage unit that stores the data of the printed image, A dot table selection unit that associates one of the plurality of dot tables with each object in a printed image or within a printed image, Equipped with, When forming a printed image or each object, the ejection control unit ejects multiple ink droplets from the ink head based on the composition ratio of each ink droplet determined by a dot table corresponding to the printed image or each object. The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, A second dot table in which the composition ratio of the first ink droplet is less than or equal to that of the first dot table for all ink values, and in at least some ink values ​​the composition ratio of the first ink droplet is smaller than that of the first dot table, Includes, The dot table selection unit includes a third selection unit that associates the first dot table with printed images or objects whose print density is less than a predetermined first density, and associates the second dot table with printed images or objects whose print density is equal to or greater than the first density. Inkjet printer.

4. The dot table selection unit includes a fourth selection unit that associates the first dot table with a printed image or object composed of line drawings. The inkjet printer according to claim 2 or 3.

5. The dot table selection unit includes a fifth selection unit that associates the first dot table with printed images or objects in which the ratio of areas belonging to a predetermined color gamut is equal to or greater than a first threshold. The inkjet printer according to claim 2 or 3.

6. The predetermined color gamut has an L ＊ value in the range of 0 or more and 100 or less on the L ＊ axis, an a ＊ value in the range of -128 or more and 127 or less on the a ＊ axis, and a b ＊ value in the range of -128 or more and 127 or less on the b ＊ axis. In the L ＊ a ＊ b ＊ color space, L ＊ The value is between 60 and 90. a ＊ The value is between 0 and 20, b ＊ The color gamut is between 0 and 30. The inkjet printer according to claim 5.

7. An ink head that ejects multiple ink droplets, A control device for controlling the ink head, Equipped with, The control device is A discharge control unit that causes a plurality of ink droplets to be ejected from the ink head, including the smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, A dot table registration unit where multiple dot tables are registered, each defining the correspondence between ink values ​​and the composition ratio of each ink droplet, A data storage unit that stores the data of the printed image, A dot table selection unit that associates one of the multiple dot tables with each object in the printed image, Equipped with, When forming each object, the ejection control unit ejects multiple ink droplets from the ink head based on the composition ratio of each ink droplet determined by the dot table corresponding to each object. The aforementioned multiple dot tables have different composition ratios for at least some ink values, The control device is A conversion table registration unit in which a conversion table for converting ink values ​​between the aforementioned multiple dot tables is registered, A color conversion unit that converts the color of all object data in a printed image using an ICC profile corresponding to one predetermined dot table from among the multiple dot tables, The composition ratio of each ink droplet is determined based on a dot table different from the predetermined dot table, and the ink value correction unit converts the ink value of an object whose color has been converted by an ICC profile corresponding to the predetermined dot table based on the conversion table. It also has, Inkjet printer.

8. A method for printing an image using an inkjet printer capable of ejecting a plurality of ink droplets, each containing a smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, The process involves associating each object in a printed image with one of several pre-prepared dot tables that define the correspondence between ink values ​​and the composition ratio of each ink droplet, and The steps include forming each object based on the composition ratio of each ink droplet as determined by the dot table corresponding to each object, Includes, The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, A second dot table is set such that the composition ratio of the first ink droplet is less than or equal to the first dot table for all ink values, and for at least some ink values ​​the composition ratio of the first ink droplet is smaller than the first dot table, and the composition ratio of the first ink droplet increases until the ink value reaches a predetermined first ink value, and then begins to decrease once the ink value reaches the first ink value, and furthermore the maximum value of the composition ratio of the first ink droplet is smaller than the maximum value of the composition ratio of the second ink droplet, which is the second smallest, and is also smaller than the maximum value of the composition ratio of the first ink droplet in the first dot table, A printing method that includes [this].

9. A method for printing an image using an inkjet printer capable of ejecting a plurality of ink droplets, each comprising a smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, The steps include associating a printed image or each object within a printed image with one of several pre-prepared dot tables that define the correspondence between ink values ​​and the composition ratio of each ink droplet, and The steps include forming a printed image or each object based on the composition ratio of each ink droplet as determined by a dot table corresponding to the printed image or each object, Includes, The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, A second dot table in which the composition ratio of the first ink droplet is less than or equal to that of the first dot table for all ink values, and in at least some ink values ​​the composition ratio of the first ink droplet is smaller than that of the first dot table, Includes, A printing method comprising the step of associating the dot tables, wherein the first dot table is associated with printed images or objects whose brightness is equal to or greater than a predetermined first brightness, and the second dot table is associated with printed images or objects whose brightness is less than the first brightness.

10. A method for printing an image using an inkjet printer capable of ejecting a plurality of ink droplets, each comprising a smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, The steps include associating a printed image or each object within a printed image with one of several pre-prepared dot tables that define the correspondence between ink values ​​and the composition ratio of each ink droplet, and The steps include forming a printed image or each object based on the composition ratio of each ink droplet as determined by a dot table corresponding to the printed image or each object, Includes, The aforementioned multiple dot tables have different composition ratios for at least some ink values, The first dot table and, A second dot table in which the composition ratio of the first ink droplet is less than or equal to that of the first dot table for all ink values, and in at least some ink values ​​the composition ratio of the first ink droplet is smaller than that of the first dot table, Includes, A printing method comprising the step of associating the dot tables, wherein the first dot table is associated with printed images or objects whose print density is less than a predetermined first density, and the second dot table is associated with printed images or objects whose print density is equal to or greater than the first density.

11. A method for printing an image using an inkjet printer capable of ejecting a plurality of ink droplets, each comprising a smallest first ink droplet and one or more other ink droplets larger than the first ink droplet, The process involves associating each object in a printed image with one of several pre-prepared dot tables that define the correspondence between ink values ​​and the composition ratio of each ink droplet, and The steps include: converting the color of all objects in the printed image using an ICC profile corresponding to one predetermined dot table from among the multiple dot tables; The composition ratio of each ink droplet is determined based on a dot table different from the predetermined dot table, and the ink value of the object color-converted by the ICC profile corresponding to the predetermined dot table is converted based on a conversion table that converts ink values ​​between the multiple dot tables. The steps include forming each object based on the composition ratio of each ink droplet as determined by the dot table corresponding to each object, Includes, A printing method wherein the multiple dot tables have different composition ratios for the first ink droplets at least for some ink values.

Images