JP2013252626A - Printing apparatus, printing method and printing data generating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology of suppressing printable time from being shortened while suppressing clogging of a nozzle in print using a line head.SOLUTION: A printing apparatus includes: a line head; an acquiring unit for acquiring image data; a storage unit for storing a dither mask that has M pixel sizes in a column direction and N pixel sizes in a row direction, and includes different thresholds including a first threshold for setting the corresponding pixel to have a dot formation regardless of the image data; a half tone processing unit for generating dot data indicating dot arrangement patterns for forming the image by using the dither mask in the image data; and a printing unit for printing with the line head using the generated dot data. The dither mask has at least one first threshold for each column.

Description

  The present invention relates to a printing apparatus, a printing method, and a printing data generation apparatus.

  As a printer that is an example of a printing apparatus, an ink jet printer that performs printing by discharging ink from a plurality of nozzles is known (for example, Patent Document 1).

JP 2007-15359 A

  Here, in the ink jet printer, when ink is not ejected from the nozzle for a certain period of time, the ink moisture may evaporate from the nozzle opening, and the viscosity of the ink may increase. When the viscosity of the ink increases, the ink ejection operation may become unstable. For this reason, it is preferable to perform control so that a certain amount of ink is ejected from each nozzle at regular time intervals. In a serial scanning type printer that performs printing while a head having nozzles moves in the main scanning direction, flushing is performed by retracting the head to a position off the printing medium during the printing operation. Here, the flushing is an ink ejection operation for preventing clogging of the nozzles separately from the ink ejection operation for printing.

  On the other hand, in a printer (line printer) having a line head, printing is executed without the line head moving in the main scanning direction. For this reason, it is difficult to perform special flushing different from the printing operation by retracting the head to a position off the printing medium during the printing operation. In particular, when printing is performed on a print medium that is long in the transport direction, it is difficult to perform special flushing at a time interval necessary to prevent an increase in ink viscosity. In addition, if flushing is performed during the printing operation or between the printing operation and the next printing operation, the printable time may be shortened and the printing efficiency may be reduced.

  In view of the above-described problems, an object of the present invention is to provide a technique capable of suppressing a printable time from being shortened while suppressing clogging of nozzles in printing using a line head.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A printing apparatus that prints an image on a print medium,
A line head including a nozzle row in which a plurality of nozzles that eject ink are arranged in an arrangement direction orthogonal to a conveyance direction of the print medium;
An acquisition unit for acquiring image data representing the image;
A dither mask having M pixel sizes in the column direction and N pixel sizes in the row direction, and a plurality of different threshold values including a first threshold value for setting corresponding pixels regardless of the image data to have dot formation. A storage unit for storing the dither mask,
A halftone processing unit that generates dot data representing a dot arrangement pattern for forming the image by using the dither mask for the image data;
A printing unit that executes printing by the line head using the generated dot data; and
The dither mask has at least one first threshold for each column of the dither mask;
When a predetermined image represented by a group of pixels arranged in S (where S ≧ M) in the arrangement direction and T (where T ≧ N) in the transport direction is printed on a print medium by the printing unit In addition,
The printing apparatus, wherein the pixel group includes at least one pixel on which ink is landed using the first threshold value for each pixel column that is an array of pixels along the transport direction.
According to the printing apparatus described in application example 1, dot data representing a dot arrangement pattern is generated using a dither mask having a first threshold value of at least one for each column. That is, at least in each region where an image is formed, at least one dot is set for each pixel column, and there is a pixel on which ink has landed using the first threshold value. Thereby, ink can be discharged from each nozzle to prevent clogging of the head while performing printing related to the image data. Thereby, generation | occurrence | production of the clogging of a nozzle can be reduced. Further, since the number of times of performing special flushing different from the printing operation can be reduced, it is possible to suppress a reduction in printable time.

[Application Example 2] The printing apparatus according to Application Example 1,
In the pixel group, an arbitrary pixel block which is a set of M pixels arranged in the arrangement direction and N pixels arranged in the transport direction is arranged in the first column for each pixel column that is an array of pixels along the transport direction. A printing apparatus having at least one pixel landed with ink by using a threshold value.
According to the printing apparatus described in the application example 2, at least one pixel can land the ink using the first threshold value for each pixel column in the pixel block unit.

[Application Example 3] The printing apparatus according to Application Example 1 or Application Example 2,
The printing apparatus is capable of printing on the print medium using two colors of ink,
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the two color inks,
The halftone processing unit
The dither mask is arranged to generate the dot data for each of the two colors so that the pixels set as having dot formation according to the first threshold are in different positions between the two colors. apparatus.
According to the printing apparatus described in the application example 3, the first threshold value is set so that the pixels where dot formation is performed are set at different positions between the two colors, and the first threshold value is set, thereby discharging the pixels. The possibility that two color inks are mixed on the print medium can be reduced. As a result, it is possible to suppress deterioration in the image quality of the image formed on the print medium.

[Application Example 4] The printing apparatus according to Application Example 3,
The printing apparatus in which the two colors are cyan and magenta.
According to the printing apparatus described in the application example 4, it is possible to reduce the possibility that the discharged cyan ink and magenta ink are mixed by setting the first threshold value. When cyan ink and magenta ink are mixed, the color becomes blue and the color becomes conspicuous. However, since the possibility that the discharged cyan ink and the magenta ink are mixed can be reduced by setting the first threshold value, it is possible to suppress deterioration in image quality.

[Application Example 5] The printing apparatus according to Application Example 1 or Application Example 2,
The printing apparatus is capable of printing on the print medium using black and one color other than the black,
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the black and the other one color ink,
The halftone processing unit
The dot for each color of the black and the other color is arranged by arranging the dither mask so that the pixel set as having dot formation by the first threshold is the same for the black and the other color. A printing device that generates data.
According to the printing apparatus described in the application example 5, the black ink ejected by the first threshold and the other color ink land on the same pixel position, and therefore the other color ink ejected by the first threshold value. Can reduce the possibility of being noticeable.

[Application Example 6] The printing apparatus according to Application Example 1 or Application Example 2,
The printing apparatus is capable of printing on the print medium using a plurality of types of inks having different characteristics.
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the plurality of types of ink.
The storage unit stores a plurality of types of the dither masks having different numbers of the first threshold values for each column,
The halftone processing unit
One of the plurality of types of dither masks included in the image data and corresponding to the characteristics of the corresponding ink for each of a plurality of types of ink amount data representing the gradation of the ink recording amount for each of the plurality of types of ink. And using the selected dither mask.
According to the printing apparatus described in the application example 6, halftone processing can be executed using an appropriate dither mask for the corresponding ink amount data according to the ink characteristics.

[Application Example 7] The printing apparatus according to Application Example 6,
The plurality of types of ink are:
The first type ink and the second type ink having a higher rate of increase in viscosity due to moisture evaporation at the same rate than the first type ink,
The plurality of types of dither masks are:
A first type of dither mask, and a second type of dither mask in which the number of the first threshold value for each column is greater than that of the first type of dither mask,
The halftone processing unit
For the first type ink amount data, the first type dither mask is selected and used,
A printing apparatus that selects and uses the second type of dither mask for the second type of ink amount data.
According to the printing apparatus described in Application Example 7, the second type ink having a higher rate of increase in viscosity than the first type ink increases the number of times ink is ejected for each nozzle according to the first threshold value. Thereby, more appropriate ink ejection can be performed according to the rate of increase in the viscosity of the ink. Here, the magnitude of the “viscosity increase rate (%)” is, for example, the viscosity increase rate associated with the same rate of water evaporation rate (for example, 20% of water evaporation rate) with respect to the ink in the initial state (when not used). Can be determined by the size of. Here, the moisture evaporation rate (%) can be expressed by the following equation (1). The rate of increase in viscosity (%) can be expressed by the following formula (2).

(Formula 1) (Wta−Wtb) × 100 / Wta
(Formula 2) (Vb−Va) × 100 / Va
Here, Wta is the total weight (g) of the ink in the initial state, Wtb is the total weight (g) of the ink after evaporation of water, Va is the viscosity (mPa · s) of the ink in the initial state, and Vb is This is the viscosity (mPa · s) of the ink after evaporation of water (when the total weight of the ink is Wtb).

[Application Example 8] The printing apparatus according to any one of Application Examples 1 to 7,
Each nozzle of the line head has a first dot formation amount of a predetermined amount of ink ejected to one pixel region by one ejection operation, and a second dot formation amount larger than the first dot formation amount. Can be selectively discharged for each pixel,
The halftone processing unit
Of the dot data, ink discharge amount data for causing the nozzle to discharge the first dot formation amount is added to data corresponding to a pixel set to have dot formation by the first threshold. , Printing device.
According to the printing apparatus described in application example 8, since the ink ejected from the nozzles by the first threshold is the first dot formation amount that is smaller than the second dot formation amount, the print medium The ink landing on the top can be made inconspicuous. Thereby, it is possible to further suppress the image quality deterioration.

Application Example 9 The printing apparatus according to any one of Application Examples 1 to 8, further comprising:
When the width of the image printed on the print medium is smaller than the length of the nozzle row, generating pseudo image data so that the length of the nozzle row becomes the width of the image to be printed, A pseudo data generation unit that regards the pseudo image data as the image data and causes the halftone processing unit to generate the dot data;
The pseudo data generation unit uses the pixel data of the image data for pixel data at the same position as the image data, and the first threshold value for new pixel data not stored in the image data. A printing apparatus that generates the pseudo image data by using data indicating that dot formation is present only in the printer.
According to the printing apparatus described in the application example 9, a dither mask can be used for the pseudo image data corresponding to the length of the nozzle row. Thereby, even when the width of the image to be printed is smaller than the nozzle row, the ink can be ejected at least once using the first threshold value for all the nozzles constituting the nozzle row.
Here, “the length of the nozzle row” refers to a distance along the arrangement direction connecting the centers of a pair of nozzles at both ends of the plurality of nozzles constituting the nozzle row.

Application Example 10 In the printing apparatus according to any one of Application Examples 1 to 9,
In the dither mask, the first threshold value is not stored in the storage element adjacent to the special storage element in which the first threshold value is stored among the plurality of storage elements in which the threshold value is stored. Printing device.
According to the printing apparatus described in application example 10, since the pixels that are set to have dot formation by the first threshold value are not adjacent to each other, the dots formed on the print medium by the first threshold value are less noticeable. It is possible to further suppress deterioration in image quality.

[Application Example 11] In the printing apparatus according to any one of Application Examples 1 to 10,
The dither mask is a printing apparatus having a blue noise characteristic or a green noise characteristic.
According to the printing apparatus described in the application example 11, it is possible to favorably disperse the dots formed on the print medium.

  The present invention can be realized in various forms. In addition to the configuration as the printing apparatus described above, the printing method and printing for generating dot data for printing an image on a printing medium. The present invention can be realized in the form of a data generation device, a computer program for realizing the functions of these devices or methods, a recording medium on which the computer program is recorded, and the like.

1 is a schematic configuration diagram of a printer 20 in a first embodiment. 3 is a flowchart showing a flow of printing processing in the printer 20. It is a figure for demonstrating the dither mask 62 and a halftone process. It is a figure for demonstrating a halftone process notionally. It is a schematic block diagram of the printer 20a in 2nd Example of this invention. It is a figure for demonstrating the 2nd type dither mask 62b. It is a detailed flow of the processing content which the halftone process part 42a performs.

Next, embodiments of the present invention will be described in the following order.
A. First embodiment:
B. Second embodiment:
C. Variations:

A. First embodiment:
A-1. Configuration of printing device:
FIG. 1 is a schematic configuration diagram of a printer 20 according to the first embodiment of the present invention. The printer 20 of this embodiment is an ink jet printer that forms an image on a paper P as a print medium by ejecting ink. The printer 20 is a line printer that performs printing with a line head 50 that extends in a direction orthogonal to the transport direction.

  The printer 20 includes a platen 80 that supports the paper P on a predetermined surface (hereinafter, also referred to as “support surface SS”), a transport mechanism that transports the paper P in the transport direction on the support surface SS of the platen 80, and A line head 50 that ejects ink from a plurality of nozzles 51 and a control unit 30 that controls the exchange of signals are provided.

  The transport mechanism that transports the paper P has a paper feed motor 74. The rotation of the paper feed motor 74 is transmitted to the paper transport roller (same) via a gear train (not shown), and the paper P is transported along the transport direction by the rotation of the paper transport roller.

  The printer 20 includes a plurality of ink cartridges 55 that contain inks of four colors, cyan (C), magenta (M), yellow (Y), and black (K). The ink stored in the ink cartridge 55 is supplied to the line head 50 via the ink flow path 72. Note that the colors of ink used in the printer 20 are not limited to the above four colors.

  The line head 50 includes nozzle rows 50a to 50d in which a plurality of nozzles 51 are arranged along an arrangement direction orthogonal to the conveyance direction of the print medium P. Each nozzle row 50a-50d is provided corresponding to four colors of ink. In this embodiment, the nozzle row 50a discharges black ink, the nozzle row 50b discharges yellow ink, the nozzle row 50c discharges magenta ink, and the nozzle row 50d discharges cyan ink. The nozzle rows 50a to 50c are arranged at positions shifted in the transport direction of the print medium P. The plurality of nozzles 51 included in each of the nozzle rows 50a to 50d are arranged in a staggered manner, but can be said to be arranged along the arrangement direction as a whole.

  The control unit 30 includes a CPU 40, a ROM 59, a RAM 52, and an EEPROM 60 that are connected to each other via a bus. The control unit 30 develops a program stored in the ROM 59 or the EEPROM 60 in the RAM 52 and executes it to control the overall operation of the printer 20, and also obtains an acquisition unit 41, an image analysis unit 43, a halftone processing unit 42, a print It also functions as the unit 46 and the pseudo data generation unit 48.

  A dither mask 62 is stored in the EEPROM 60. The dither mask 62 is used for halftone processing, and is constituted by a plurality of different threshold values. The dither mask 62 has M pixel sizes (M × N pixel sizes) in the column direction and N pixels in the row direction. In this embodiment, the dither mask 62 has a so-called blue noise characteristic. The dither mask 62 may have a so-called green noise characteristic instead of the blue noise characteristic. Since the dither mask 62 has a blue noise characteristic and a green noise characteristic, dots formed on the print medium can be favorably dispersed. Details of the dither mask 62 will be described later.

  A memory card slot 98 is connected to the control unit 30, and image data ORG can be read and acquired from a memory card MC inserted into the memory card slot 98. In this embodiment, the image data ORG acquired from the memory card MC is data composed of three color components of red (R), green (G), and blue (B). The operation panel 99 receives an instruction from the user.

A-2. Details of the printing process:
FIG. 2 is a flowchart showing the flow of printing processing in the printer 20. The printing process here is started when the user performs an instruction to print a predetermined image stored in the memory card MC using the operation panel 99 or the like. When the printing process is started, the acquisition unit 41 reads and acquires RGB format image data ORG to be printed from the memory card MC via the memory card slot 98 (step S110).

  When the image data ORG is acquired, the image analysis unit 43 refers to a lookup table (not shown) stored in the EEPROM 60 and converts the image data ORG in the RGB format into the image data G in the CMYK format for the image data ORG. Color conversion is performed (step S120). In the present embodiment, color conversion in the CMYK format is performed by expressing the gradation value of each color in a range of 64 gradations from 0 to 63. That is, the image analysis unit 43 generates ink amount data in which the ink recording amount is expressed in gradation for each ink color used in the printer 20.

  Further, the image analysis unit 43 determines whether or not the width of the image printed on the print medium P by the image data G is smaller than the lengths of the nozzle rows 50a to 50d (step S122). That is, it is determined whether or not the number of pixels in the arrangement direction formed on the print medium P by the image data G is smaller than the number of nozzles 51 in each of the nozzle rows 50a to 50d. When the width of the image is smaller than the nozzle row (step S122: YES), the pseudo data generation unit 48 generates an image having the same width as the length of each nozzle row 50a to 50d on the print medium P based on the image data G. The pseudo image data Ga is generated so as to be formed (step S126). On the other hand, when the image analysis unit 43 determines that the width of the image is the same as that of the nozzle row (step S122: NO), the halftone processing unit 42 performs halftone processing using the image data G.

  The pseudo image data Ga is generated as follows. That is, the pseudo data generation unit 48 uses the data of the image data G as it is as the pixel data at the same position (same coordinates) as each pixel data of the image data G. In addition, when there is no pixel data of the image data G in the same position among the pixel data of the pseudo image data Ga to be generated, the pseudo data generation unit 48 newly sets the pixel data in which the gradation value of each color is set to zero. To generate. That is, the newly added data to the original image data G sets ink amount data representing special gradation values that are not normally ejected. In other words, for the new pixel data that is not stored in the image data G, the pseudo data generation unit 48 generates new data by using data that indicates dot formation only at the first threshold value. In the present embodiment, the newly added data is set to data in which the gradation value of each color becomes zero. When the pseudo data generation unit 48 generates the pseudo image data Ga, the half tone processing unit 42 described below causes the half tone processing unit 42 to regard the pseudo image data Ga as the image data G and execute halftone processing.

  Thereafter, the halftone processing unit 42 performs halftone processing for converting the image data G (Ga) into dot ON / OFF data (dot data) representing the dot arrangement pattern of each color (step S130). Specifically, the halftone processing unit 42 acquires the coordinate data of the target pixel position of the image data and the target pixel data, and among the gradation values of the target pixel data and a plurality of different threshold values constituting the dither mask 62 The magnitude relationship with the threshold value corresponding to the target pixel data is compared. Then, the halftone processing unit 42 determines the presence / absence of dot formation of the pixel corresponding to the target pixel data according to the magnitude relationship between the gradation value of the target pixel data and the corresponding threshold value of the dither mask 62. The process of comparing the magnitude relationship is performed on the ink amount data of each color (black, cyan, magenta, yellow). The halftone process is not limited to the binarization process for whether or not dots are formed, and may be a multi-value process such as the presence or absence of dot formation for large dots and small dots. Further, the image data provided to step S130 may be subjected to image processing such as resolution conversion processing or smoothing processing.

  When the halftone process is performed, the CPU 40 performs an interlace process for rearranging data to be printed using the line head 50 in accordance with the nozzle arrangement of the printer 20 and the paper feed amount (step S150). When the interlace process is performed, the printing unit 46 drives the line head 50, the motor 74, and the like to execute printing (step S160).

  FIG. 3 is a diagram for explaining the dither mask 62 and halftone processing. FIG. 4 is a diagram for conceptually explaining halftone processing. In FIG. 3, the line head 50 and the nozzle 51 are also illustrated for easy understanding. FIG. 3 illustrates a nozzle row 50a that discharges black ink among a plurality of nozzle rows.

  As shown in FIG. 3, the dither mask 62 is a dither mask having a size of 32 × 64 pixels. That is, the dither mask 62 is composed of 2048 storage elements. Then, 32 threshold values of 0 to 63 are prepared, and each threshold value is stored in 2048 storage elements one by one. In FIG. 3, only the threshold value 0, which is the first threshold value, is shown. Also, the threshold value 0 is distributed and arranged so that the dither mask 62 has a blue noise characteristic. This point is equivalent to a dither mask having a normal blue noise characteristic, that is, a blue noise mask. However, the dither mask 62 of this embodiment is different from the normal blue noise mask in that the threshold 0 is stored for each column of the dither mask 62, and this restriction is added. Further, the thresholds 1 to 63 other than the first threshold may be a normal blue noise characteristic mask without such a restriction. That is, the dither mask 62 of the present embodiment is added with the characteristic that a specific threshold value as the first threshold value is always stored in each column in addition to the characteristic as a normal blue noise mask. Become.

  The halftone processing unit 42 compares the magnitude relationship between the gradation value of the pixel data and the threshold value stored in the storage element. More specifically, the halftone processing unit 42 sets the pixel corresponding to the target pixel data as having dot formation if the gradation value of the target pixel data of the image data is equal to or greater than the threshold value stored in the corresponding storage element. To do. On the other hand, if the gradation value of the target pixel data of the image data is less than the threshold value stored in the corresponding storage element, the halftone processing unit 42 sets the pixel corresponding to the target pixel data without dot formation. . The above comparison is performed for all the pixel data for each color component (cyan, magenta, yellow, black) of the image data. That is, as shown in FIG. 4, the dither mask 62 is repeatedly used for each pixel data arranged in the transport direction and the arrangement direction. In this embodiment, the dither mask 62 is repeatedly used for each unit, with a pixel data group of a predetermined area (32 × 64 pixel area) as one unit.

  Here, the threshold value 0 functions as a first threshold value for setting the corresponding pixel to have dot formation regardless of the ink amount data (tone value data) of the target pixel data. In other words, in the present embodiment, the halftone processing unit 42 uses the dither mask 62 to represent a dot arrangement pattern in which each nozzle 51 ejects ink with the first threshold at a rate of once per 64 pixels. Dot data can be formed. That is, it is represented by a pixel group in which S pixels are arranged in the arrangement direction (where S ≧ M. In this embodiment, M = 32) and T pixels (where T ≧ N. In this embodiment, N = 64). When the predetermined image to be printed is printed on the print medium, the pixel group includes at least one pixel on which ink is landed using a first threshold value for each pixel row that is an array of pixels along the transport direction. Have. In other words, an arbitrary pixel block that is a set of M pixels arranged in the arrangement direction and N pixels in the transport direction in the pixel group constituting the predetermined image is an array of pixels along the transport direction. Each pixel column has one pixel on which ink is landed using the first threshold value.

A-3. effect:
In the first embodiment, the dither mask 62 has one threshold value 0 that is the first threshold value for each column of the dither mask 62. Thus, at least one pixel group constituting the printed image is set to have dot formation for each pixel column that is an array of pixels along the transport direction, and ink is landed using the first threshold value. Existed pixels. Accordingly, each nozzle 51 ejects ink at least once when printing an image on one print medium P. As a result, it is possible to reduce the possibility that the ink is dried in the nozzle 51 and the 51 nozzle is clogged. In addition, by performing ink ejection using the first threshold value, the number of times of performing special flushing different from the printing operation can be reduced. As a result, it is possible to suppress a reduction in printable time. In addition, in any pixel block having the same pixel size as the dither mask 62 in the pixel group constituting the image formed on the print medium P, at least one pixel uses the first threshold value for each pixel column. Can land ink.

  In the first embodiment, when the width of the image printed on the print medium P by the image data G is smaller than the length of the nozzle rows 50a to 50d, the pseudo image data Ga is generated to generate the pseudo image data. Halftone processing is performed on Ga (steps S126 and S150). That is, the pseudo image data Ga is generated so that an image having the same number of pixels as the number of nozzles 51 included in each of the nozzle rows 50a to 50d is formed in the transport direction. Therefore, regardless of the size of the image formed by the image data G, when the image is printed on one print medium P, all the nozzles 51 eject ink at least once with the first threshold value. Can do. That is, for example, even when a margin is set on the print medium P during printing, ink ejection can be performed with the first threshold value with respect to the nozzle 51 located at a position overlapping the margin portion in the transport direction.

  In the first embodiment, one first threshold is set for each column of the dither mask 62. However, the number of first thresholds arranged in each column is limited to one. Rather, it may be two or more. Note that if the number of the first thresholds arranged in each row is large, there is a possibility that the image quality of the image is deteriorated. Therefore, the ink ejection by the first threshold is performed at a rate of 16 times or less for 256 pixels in the transport direction. Preferably, the first threshold value is stored in the storage element of the dither mask 62 as is performed, and the storage element of the dither mask 62 is set so that ink discharge is performed at a rate of once or less per 256 pixels. More preferably, the first threshold is stored.

B. Second embodiment:
FIG. 5 is a schematic configuration diagram of the printer 20a according to the second embodiment of the present invention. FIG. 6 is a diagram for explaining the second type dither mask 62b. The difference from the printer 20 of the first embodiment is the content of data stored in the EEPROM 60a and the processing content executed by the halftone processing unit 42a of the control unit 30a. The other configurations and the processing contents executed by the respective units are the same as those in the first embodiment, and therefore the same configurations are denoted by the same reference numerals and the description thereof is omitted.

  The EEPROM 60a stores a first-type dither mask 62a and a second-type dither mask 62b having different storage ratios of the first threshold value to a plurality of storage elements. Since the first type dither mask 62a is the same as the dither mask 62 of the first embodiment, the description thereof is omitted. Similar to the first type dither mask 62a, the second type dither mask 62b has blue noise characteristics. The second type dither mask may have a so-called green noise characteristic instead of the blue noise characteristic.

  The correspondence table 65 is stored in the EEPROM 60a. The correspondence table 65 performs halftone processing on the first type and the second type dither masks 62a and 62b with respect to the ink amount data (cyan, magenta, yellow, black) for each color of the image data G after color conversion. It is a table which determines whether to use for. Whether the halftone processing unit 42a uses the first type or the second type dither mask 62a, 62b with reference to the correspondence table 65 for the ink amount data for each color stored in the image data G To decide. The detailed contents of the correspondence table 65 will be described later.

As shown in FIG. 6, the second type dither mask 62b is a dither mask having a size of 32 × 64 pixels. Then, 32 threshold values of 0 to 63 are prepared, and each threshold value is stored in 2048 storage elements one by one. In FIG. 6, only the threshold values 0 and 1 that are the first threshold values are illustrated. In the second type dither mask 62 b, the threshold value 0 and the threshold value 1 are stored one by one for each row arranged in the arrangement direction of the plurality of nozzles 51. Further, the threshold value 0 and the threshold value 1 are distributed and arranged so that the dither mask 62b has a blue noise characteristic. When halftone processing is performed using the second type dither mask 62b, the following condition 1 is used.
<Condition 1>
-If Data value + 1 ≥ threshold, set with dot formation-If Data value + 1 <threshold, set no dot formation Here, Data value is the ink amount data (tone value data) of the target pixel data is there.

  That is, the threshold value 0 and the threshold value 1 function as a first threshold value for setting the corresponding pixel to have dot formation regardless of the ink amount data (tone value data) of the target pixel data. In other words, the halftone processing unit 42a uses the second type dither mask 62b, so that each nozzle 51 represents a dot arrangement pattern in which ink is ejected by the first threshold at a rate of once per 32 pixels. Data can be formed. In the above condition 1, dot formation is set with the gradation value of the pixel-of-interest data being 62 or 63. However, in the ink jet in which dot bleeding occurs, the density change of the image is near a large gradation value. Is a small area, it hardly affects the deterioration of image quality.

  In the correspondence table 65 shown in FIG. 5, whether to use the first type dither mask 62a or the second type dither mask 62b is set according to the characteristics of the ink used in the printer 20a. . Specifically, the first type of dither mask 62a is used for inks whose viscosity increase rate is less than or equal to a predetermined value, and the second type of dither mask 62b is used for inks whose viscosity increase rate is greater than a predetermined value. Is set to be used. In the present embodiment, among the image data G, the dither mask 62b of the second type is used for the ink amount data of cyan ink used for discharging cyan, and is used for discharging ink of other colors. The first type dither mask 62a is set to be used for the ink amount data. Here, the ink amount data of each ink color is also referred to as “ink color data”.

  FIG. 7 is a detailed flow of the processing contents executed by the halftone processing unit 42a of the second embodiment. The halftone processing unit 42 acquires the image data G (Ga) (step S132a), refers to the correspondence table 65, and selects either the first type dither mask 62a or the second type dither mask 62b for each ink color data. Is selected (step S134a). Then, the presence or absence of dot formation is determined using the dither mask selected for all pixels for each ink color data (step S136a).

  As described above, in the printer 20a of the second embodiment, as in the first embodiment, at least one pixel is set to have dot formation in the pixel row arranged in the transport direction. As a result, the same effects as those of the first embodiment can be obtained. In addition, in the printer 20a of the second embodiment, the second type in which the first threshold value is set to be larger for one column for the ink (for example, cyan) whose ink viscosity increase rate is larger than the other inks. Halftone processing is performed using the dither mask 62b. Thus, ink ejection using the first threshold can be performed more appropriately according to the characteristics of the ink.

C. Variations:
As mentioned above, although one Example of this invention was described, this invention is not limited to such an Example, A various structure can be taken in the range which does not deviate from the meaning. For example, the following modifications are possible.

C-1. First modification:
In the halftone processing of the above embodiment (steps S130 and 130a), it is preferable to use the dither masks 62, 62a and 62b for the color data of the image data G and Ga as follows.

C-1-1. First preferred method of use:
For example, when an image is formed using at least two colors of ink, the dither masks 62, 62a, and 62b are set so that the pixels that are set to have dots formed by the first threshold value are located at different positions between the two colors. Is preferably arranged in the image data G and Ga to perform halftone processing. For example, when the same dither masks 62, 62a, and 62b are used for each ink amount data of cyan ink and magenta ink, the dither masks 62, 62a, and 62b are used while being shifted with respect to each ink amount data. At this time, when the dither masks 62, 62a, 62b are shifted and used for a plurality of colors of ink, the dither masks 62, 62a are arranged so that the dots of the plurality of colors of ink ejected according to the first threshold have good dispersibility. 62b may be determined. In this way, the overall dispersibility of the dots (flushing dots) formed by the first threshold value with respect to the ink having a conspicuous color can be improved, and deterioration in image quality can be further suppressed. For example, when halftone processing is performed on the ink amount data corresponding to magenta ink, the dither masks 62, 62, and 62b are used while being shifted by 16 pixels in the arrangement direction with respect to the ink amount data corresponding to cyan ink. . By doing so, it is possible to reduce the possibility that the two color inks ejected from the nozzles 51 by the first threshold are mixed on the print medium P. Thereby, for example, it is possible to reduce the possibility that a plurality of types of inks that change to a conspicuous color due to color mixing are mixed. For example, when cyan ink and magenta ink are mixed, the color becomes blue and is easily noticeable. However, by using the dither masks 62, 62a, and 62b in a shifted manner as described above, it is possible to prevent the inks ejected by the first threshold from being mixed with each other, and the possibility that the image quality is lowered can be reduced.

C-1-2. Second preferred method of use:
For example, in the case where an image is formed on the print medium P using at least black and other colors, the pixels set as having dot formation by the first threshold are set to the same position in black and other colors. It is preferable that the dither masks 62, 62a and 62b are arranged in the image data to perform halftone processing. For example, when an image is formed using black, cyan, magenta, and yellow inks, the same dither masks 62, 62a, and 62b are used in the same manner for the ink amount data corresponding to each ink color. That is, the same dither masks 62, 62a, and 62b are used for each ink amount data without shifting the pixels. For black ink, even when inks of other colors are mixed, there is almost no darkening (density increase) from the beginning. That is, since the black ink ejected by the first threshold and the other color ink land on the same pixel position, the possibility that the other color ink ejected by the first threshold is conspicuous can be reduced.
Here, the yellow ink is excluded from the target of the other color above, and it is not necessary to use the dither masks 62, 62a, 62b so as to overlap the black ink. This is because yellow ink is not noticeable.

C-2. Second modification:
In the above embodiment, the amount of ink ejected once by the first threshold is not particularly limited. For example, each nozzle 51 can eject ink of large dots, medium dots, and small dots for each pixel. In this case, it is preferable that the ink ejection by the first threshold value is performed with small dots. Here, the large dots, medium dots, and small dots have different amounts of ink ejected to one pixel region by one ejection operation, and the ink amounts decrease in the order of large dots, medium dots, and small dots. For example, when the halftone processing units 42 and 42a generate dot data, ink is ejected to the nozzle 51 with small dots with respect to data set to have dot formation by the first threshold. This can be realized by adding ink discharge amount data for generating the ink. By performing ink ejection with the first threshold value using small dots, the flushing dots can be made less noticeable. Here, the ink amount of the large dot corresponds to the “second dot formation amount” described in the means for solving the problem, and the ink amount of the small dot corresponds to the “first dot” described in the means for solving the problem. Corresponds to “dot formation amount”.

C-3. Third modification:
In the above embodiment, the dither masks 62, 62a, and 62b having 32 × 64 pixels have been described as an example. However, the size of the dither masks 62, 62a, and 62b is not limited to this. For example, the size in the transport direction may be 256 pixels or more. By setting the size of the dither masks 62, 62a, and 62b in the transport direction to 256 pixels or more, the ratio of ink ejection by the first threshold can be reduced to 1/256 or less, and the presence of flushing dots can be made less noticeable.

C-4. Fourth modification:
In the above embodiment, the printers 20 and 20a have the pseudo data generation unit 48, the process of determining whether or not to generate the pseudo image data Ga during the printing process (step S122 in FIG. 2), and the pseudo image. Although the process of generating the data Ga (step S126 in FIG. 2) was provided, it can be omitted. That is, halftone processing may be performed on the image data G converted into the CMYK format regardless of the size of the printed image. Even in such a case, at least one ink ejection is performed with respect to the plurality of nozzles 51 used in the image forming region regardless of the ink amount data included in the image data. Can do.

C-5. Fifth modification:
The storage method of the first threshold value for the plurality of storage elements of the dither masks 62, 62a, 62b is not limited to the above embodiment, and it is sufficient that at least one first threshold value is stored for each column. Here, the dither masks 62, 62a and 62b are created so that the first threshold value is not stored in the storage element adjacent to the storage element storing the first threshold value (also referred to as “special storage element”). It is preferable. By doing so, it is possible to prevent the flushing dots from being formed in adjacent pixels, to make the flushing dots less noticeable, and to further suppress the deterioration of the image quality.

C-6. Sixth modification:
In the above embodiment, the control units 30 and 30a of the printers 20 and 20a include the acquisition unit 41, the halftone processing units 42 and 42a, the image analysis unit 43, the pseudo data generation unit 48, and the dither masks 62, 62a, and 62b. However, a printing data generation device (for example, a personal computer) different from the printer 20 may include the units 41, 42, 42a, 43, 48, 62, 62a, 62b. That is, the processing of steps S110 to S130 shown in FIG.

C-7. Seventh modification:
In the second embodiment, the first type dither mask 62a and the second type dither mask 62b having different numbers of stored first threshold values for one column are used for each ink color data. Although an example of selecting the dither masks 62a and 62b has been described, instead of this, as described below, the same effect as that of the second embodiment can be realized by using only the second type dither mask 62b.

That is, in steps S134a and S136a of the second embodiment, the ink color data using the second type of dither mask 62b is processed with the same contents in this modified example. On the other hand, in steps S134a and S136a of the second embodiment, for ink color data using the first type dither mask 62a, the following condition 2 is used instead of condition 1 when performing halftone processing. . In addition, when performing halftone processing under condition 2, compared to performing halftone processing according to condition 1, the second type is applied by an appropriate number of pixels (for example, 16 pixels in the row direction and 32 pixels in the column direction). The dither mask 62b is used while being shifted in parallel.
<Condition 2>
-If Data value ≥ threshold, set dot formation.-If Data value <threshold, set no dot formation.

20, 20a ... Printer 30, 30a ... Control unit 40 ... CPU
DESCRIPTION OF SYMBOLS 41 ... Acquiring part 42, 42a ... Halftone process part 43 ... Image analysis part 46 ... Printing part 48 ... Pseudo data generation part 50 ... Line head 50a-50d ... Nozzle row 51 ... Nozzle 55 ... Ink cartridge 62, 62a, 62b ... Dither mask 65 ... Corresponding table 72 ... Ink flow path 74 ... Motor 80 ... Platen 98 ... Memory card slot 99 ... Operation panel P ... Printing medium G ... Image data MC ... Memory card Ga ... Pseudo image data ORG ... Image data

Claims (13)

A printing device for printing an image on a print medium,
A line head including a nozzle row in which a plurality of nozzles that eject ink are arranged in an arrangement direction orthogonal to a conveyance direction of the print medium;
An acquisition unit for acquiring image data representing the image;
A dither mask having M pixel sizes in the column direction and N pixel sizes in the row direction, and a plurality of different threshold values including a first threshold value for setting corresponding pixels regardless of the image data to have dot formation. A storage unit for storing the dither mask,
A halftone processing unit that generates dot data representing a dot arrangement pattern for forming the image by using the dither mask for the image data;
A printing unit that executes printing by the line head using the generated dot data; and
The dither mask has at least one first threshold for each column of the dither mask;
When a predetermined image represented by a group of pixels arranged in S (where S ≧ M) in the arrangement direction and T (where T ≧ N) in the transport direction is printed on a print medium by the printing unit In addition,
The printing apparatus, wherein the pixel group includes at least one pixel on which ink is landed using the first threshold value for each pixel column that is an array of pixels along the transport direction. The printing apparatus according to claim 1,
In the pixel group, an arbitrary pixel block which is a set of M pixels arranged in the arrangement direction and N pixels arranged in the transport direction is arranged in the first column for each pixel column that is an array of pixels along the transport direction. A printing apparatus having at least one pixel landed with ink by using a threshold value. The printing apparatus according to claim 1 or 2, wherein
The printing apparatus is capable of printing on the print medium using two colors of ink,
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the two color inks,
The halftone processing unit
The dither mask is arranged to generate the dot data for each of the two colors so that the pixels set as having dot formation according to the first threshold are in different positions between the two colors. apparatus. The printing apparatus according to claim 3,
The printing apparatus in which the two colors are cyan and magenta. The printing apparatus according to claim 1 or 2, wherein
The printing apparatus is capable of printing on the print medium using black and one color other than the black,
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the black and the other one color ink,
The halftone processing unit
The dot for each color of the black and the other color is arranged by arranging the dither mask so that the pixel set as having dot formation by the first threshold is the same for the black and the other color. A printing device that generates data. The printing apparatus according to claim 1 or 2, wherein
The printing apparatus is capable of printing on the print medium using a plurality of types of inks having different characteristics.
The nozzle row of the line head is provided at a position shifted in the transport direction for each of the plurality of types of ink.
The storage unit stores a plurality of types of the dither masks having different numbers of the first threshold values for each column,
The halftone processing unit
One of the plurality of types of dither masks included in the image data and corresponding to the characteristics of the corresponding ink for each of a plurality of types of ink amount data representing the gradation of the ink recording amount for each of the plurality of types of ink. And using the selected dither mask. The printing apparatus according to claim 6,
The plurality of types of ink are:
The first type ink and the second type ink having a higher rate of increase in viscosity due to moisture evaporation at the same rate than the first type ink,
The plurality of types of dither masks are:
A first type of dither mask, and a second type of dither mask in which the number of the first threshold value for each column is greater than that of the first type of dither mask,
The halftone processing unit
For the first type ink amount data, the first type dither mask is selected and used,
A printing apparatus that selects and uses the second type of dither mask for the second type of ink amount data. The printing apparatus according to any one of claims 1 to 7,
Each nozzle of the line head has a first dot formation amount of a predetermined amount of ink ejected to one pixel region by one ejection operation, and a second dot formation amount larger than the first dot formation amount. Can be selectively discharged for each pixel,
The halftone processing unit
Of the dot data, ink discharge amount data for causing the nozzle to discharge the first dot formation amount is added to data corresponding to a pixel set to have dot formation by the first threshold. , Printing device.
Printing device. The printing apparatus according to any one of claims 1 to 8, further comprising:
When the width of the image printed on the print medium is smaller than the length of the nozzle row, generating pseudo image data so that the length of the nozzle row becomes the width of the image to be printed, A pseudo data generation unit that regards the pseudo image data as the image data and causes the halftone processing unit to generate the dot data;
The pseudo data generation unit uses the pixel data of the image data for pixel data at the same position as the image data, and the first threshold value for new pixel data not stored in the image data. A printing apparatus that generates the pseudo image data by using data indicating that dot formation is present only in the printer. The printing apparatus according to any one of claims 1 to 9,
In the dither mask, the first threshold value is not stored in the storage element adjacent to the special storage element in which the first threshold value is stored among the plurality of storage elements in which the threshold value is stored. Printing device. The printing apparatus according to any one of claims 1 to 10,
The dither mask is a printing apparatus having a blue noise characteristic or a green noise characteristic. A printing method for printing an image on the print medium using a line head including a nozzle array in which a plurality of nozzles that eject ink are arranged in an arrangement direction orthogonal to the conveyance direction of the print medium,
An acquisition step of acquiring image data representing the image;
A dither mask composed of a plurality of different threshold values including a first threshold value for setting the corresponding pixel with dot formation regardless of the image data, and having a pixel size of M in the column direction and N in the row direction A dot data generation step of generating dot data representing a dot arrangement pattern for forming the image by using a dither mask having the image data,
Using the generated dot data, and performing a printing by the line head,
The dither mask has at least one first threshold for each column of the dither mask;
When a predetermined image represented by a group of pixels arranged in S (where S ≧ M) in the arrangement direction and T (where T ≧ N) in the transport direction is printed on a print medium by the printing process In addition,
The printing method, wherein the pixel group includes at least one pixel on which ink is landed using the first threshold value for each pixel row that is an arrangement of pixels along the transport direction. For generating dot data for printing an image on the print medium using a line head including a nozzle array in which a plurality of nozzles for ejecting ink are arranged in an arrangement direction orthogonal to the conveyance direction of the print medium A data generation device for printing,
A dither mask having M pixel sizes in the column direction and N pixel sizes in the row direction, and includes a plurality of first threshold values for setting corresponding pixels with dot formation regardless of image data representing the image. A storage unit for storing dither masks having different threshold values;
A halftone processing unit that generates a dot arrangement pattern for forming the image using the dither mask, and
The dither mask has at least one first threshold for each column of the dither mask;
The halftone processing unit
When a predetermined image represented by a group of pixels arranged in S (however, S ≧ M) in the arrangement direction and T (where T ≧ N) in the carrying direction is printed on a print medium by the line head In addition, the dot pattern is generated so that the pixel group includes at least one pixel landed with ink using the first threshold value in each pixel row that is an array of pixels along the transport direction. Data generator.

Images