JP5994919B2 - Printing apparatus, printing method, and computer program - Google Patents

Description

  The present invention relates to a technique for printing on a print medium.

  Conventionally, in a serial type printing apparatus, printing is performed by driving a print head relative to a print medium in the main scanning direction and the sub-scanning direction. In the print head, nozzle rows that eject ink of each color are arranged side by side in the main scanning direction (see Patent Document 1). For this reason, for example, if the nozzle row for discharging yellow ink and the nozzle row for discharging black ink are formed in this order in the main scanning direction on the print head, Therefore, yellow ink is ejected before black ink.

  As described above, when different inks are ejected to the same printing position, bleeding is likely to occur in the ink ejected later according to the dry state of the ink ejected earlier. Therefore, for example, if the ink ejected later is an ink that has a lower lightness and is more conspicuous than the ink ejected earlier, the bleeding of the ink becomes more conspicuous. In addition, when the ink ejected earlier has a characteristic of being easily mixed with other inks, the ink ejected later is more likely to spread.

  Such a problem becomes particularly prominent during bidirectional printing (see Patent Document 1) in which ink is ejected both when the print head moves forward and when it moves backward. In bi-directional printing, the order of ink ejected is switched between forward and backward movements, so the likelihood of bleeding also fluctuates, even if the same color is printed during forward and backward movements. This is because density unevenness may occur.

JP 2007-145031 A

  In view of the various problems described above, the problem to be solved by the present invention is to improve the image quality by suppressing the occurrence of bleeding due to the difference in the drying time of the ink in the serial type printing apparatus.

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.
In the first aspect of the present invention, printing is performed by driving a print head relative to a print medium in a main scanning direction that is the width direction of the print medium and a sub-scanning direction that intersects the main scanning direction. A device,
An acquisition unit for acquiring image data;
A low-visibility ink preceding ejection nozzle that ejects low-visibility ink to a predetermined print area on the print medium;
A low-visibility ink trailing ejection nozzle that ejects the low-visibility ink after the low-visibility ink is ejected from the low-visibility ink preceding ejection nozzle for the predetermined printing area;
A high-visibility ink preceding ejection nozzle that ejects high-visibility ink to a predetermined print area on the print medium;
A high-visibility ink trailing discharge nozzle that discharges the high-visibility ink after the high-visibility ink is discharged from the high-visibility ink preceding discharge nozzle with respect to the predetermined printing area;
Including a print head;
A dot forming unit that controls the print head and forms dots corresponding to the image data on the print medium with the low-visibility ink and the high-visibility ink;
When the dot recording rate according to the image data is less than a predetermined dot recording rate,
The number of times of forming dots in the predetermined print area by the high-visibility ink preceding discharge nozzle is greater than the number of times of forming dots in the predetermined print area by the high-visibility ink subsequent discharge nozzle,
When the dot recording rate according to the image data exceeds a predetermined dot recording rate,
The number of times dots are formed in the predetermined print area by the high-visibility ink preceding discharge nozzle is less than the number of times dots are formed in the predetermined print area by the high-visibility ink subsequent discharge nozzle.
It is characterized by that.

Application Example 1 A printing apparatus that performs printing by driving a print head relative to a print medium in a main scanning direction that is the width direction of the print medium and a sub-scanning direction that intersects the main scanning direction. A print head having a plurality of nozzles for ejecting ink, an acquisition unit for obtaining image data, and controlling the print head to eject the ink, thereby causing dots corresponding to the image data to be printed on the print medium. A dot forming unit for forming the dot, and the dot forming unit forms a suppression dot, which is a target dot to suppress bleeding, on the print medium, among the plurality of nozzles. A printing apparatus that causes the print head to eject ink corresponding to the suppression dots from a preceding nozzle that ejects ink earlier than other nozzles.

  In the case of a printing apparatus having such a configuration, the timing of ejecting ink to the print medium from among a plurality of nozzles provided in the print head is the other nozzles among the plurality of nozzles provided in the print head. It can be formed by an earlier preceding nozzle. Therefore, drying of the suppression dots is promoted, and it becomes possible to suppress the occurrence of bleeding.

Application Example 2 In the printing apparatus according to Application Example 1, in the print head, the first nozzle row having a plurality of nozzles ejecting the first ink along the sub-scanning direction; A second nozzle row having a plurality of nozzles ejecting a second ink, which is an ink corresponding to a suppression dot, along the sub-scanning direction is arranged in the main scanning direction, and the preceding nozzle is Among the second nozzle rows, the nozzles are arranged on the side that first reaches the print medium when the print head is driven in the sub-scanning direction, and the dot formation unit A printing apparatus that discharges the second ink with a nozzle usage rate higher than a nozzle usage rate provided in a position corresponding to the preceding nozzle in the first nozzle row.

  With the printing apparatus having such a configuration, the second ink can be ejected relative to the same printing position earlier than the first ink. Therefore, drying of the second ink can be promoted.

[Application Example 3] In the printing apparatus according to Application Example 2, the dot forming unit compares each threshold value of a dither mask including a plurality of threshold values with pixel data constituting an image, thereby comparing the dot data. A formation position is determined. For the first ink, a dot formation position is determined using a first dither mask, and for the second ink, a second dither mask is determined. A printing apparatus that determines the dot formation position using the. With such a configuration, it is possible to eject the first ink and the second ink using two types of dither masks.

Application Example 4 In the printing apparatus according to Application Example 3, the size of the second dither mask in the main scanning direction and the sub-scanning direction is determined by performing main scanning and sub-scanning on the print head, respectively. A printing apparatus that is an integral multiple of the size of a nozzle arrangement pattern that repeatedly appears on the print medium when dots are formed on the print medium by the second nozzle array. With such a configuration, the position of the dot formed on the print medium can be uniquely associated with the nozzle that forms the dot. As a result, the usage rate of each nozzle in the second nozzle row can be easily varied using the second dither mask.

Application Example 5 In the printing apparatus according to Application Example 4, in the second dither mask, a threshold value corresponding to a position where a dot is formed by the preceding nozzle is set to a value at which a dot is easily formed. Printing device. With such a configuration, the usage rate of the preceding nozzle can be increased simply by appropriately arranging the threshold values. The value at which dots are easily formed is, for example, a threshold having a small value.

Application Example 6 In the printing apparatus according to any one of Application Examples 3 to 5, the size of the first dither mask in the main scanning direction and the sub-scanning direction is different from that of the print head. A printing apparatus that is an integral multiple of the size of a nozzle arrangement pattern that repeatedly appears on the print medium when dots are formed on the print medium by the first nozzle row after main scanning and sub-scanning. With such a configuration, the usage rate of each nozzle in the first nozzle row can be easily varied using the first dither mask.

Application Example 7 In the printing apparatus according to Application Example 6, the threshold corresponding to the position where the dot is formed by the nozzle at the position corresponding to the preceding nozzle in the first nozzle row is a dot Printing device set to a value that is difficult to form. With such a configuration, it is possible to reduce the usage rate of nozzles at positions corresponding to the preceding nozzles in the first nozzle row only by appropriately arranging the threshold values. The value that makes it difficult to form dots is, for example, a large threshold value.

[Application Example 8] The printing apparatus according to any one of Application Example 2 to Application Example 7, wherein the number of nozzles of the preceding nozzle is set according to a single sub-scanning amount of the print head. apparatus. With such a configuration, the second ink can be ejected to an unprinted area on the print medium, so that density unevenness can be more effectively suppressed.

Application Example 9 In the printing apparatus according to Application Example 1, the printing apparatus includes a dot recording rate conversion unit that converts the acquired image data into a dot recording rate that represents a density of dots per unit area of the printing medium. The suppression dot is a printing apparatus in which the converted dot recording rate is a dot lower than a predetermined value. With such a configuration, sparsely formed dots can be suppressed.

[Application Example 10] In the printing apparatus according to Application Example 1 or Application Example 9, the dot forming unit changes a position where dots are formed in each main scan while the print head is main-scanned a plurality of times. Thus, dots are filled in a band corresponding to the width of the print head in the sub-scanning direction, and the preceding nozzle includes, among the plurality of nozzles, a first main scan in the band. A printing apparatus including nozzles for forming dots. With such a configuration, the suppression dots can always be formed in the first main scanning in the printing of each band in the printing of each band. Therefore, drying of the suppression dots can be promoted and occurrence of bleeding can be suppressed.

  The present invention can be configured as a printing method or a computer program in addition to the configuration as the printing apparatus described above. The computer program may be recorded on a computer-readable recording medium. As the recording medium, for example, various media such as a flexible disk, a CD-ROM, a DVD-ROM, a magneto-optical disk, a memory card, and a hard disk can be used.

1 is a diagram illustrating a schematic configuration of a printing system 10 as an embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a computer 100. FIG. FIG. 2 is a diagram illustrating a schematic configuration of a printer. FIG. 3 is a diagram illustrating an arrangement of nozzle rows formed on the bottom surface of a print head 241. It is a figure which shows the concept which raises the usage rate of a preceding nozzle group. It is a figure which shows a mode that a dot is formed on a printing medium. It is a figure which shows the position where a dot is formed by the preceding nozzle group. It is a figure which shows a part of 2nd dither mask D2. It is a figure which shows the dot formation position at the time of printing a solid image with a dot recording rate of 5% with the second dither mask D2. It is a figure which shows the dot formation position at the time of printing a solid image with a dot recording rate of 30% with the second dither mask D2. It is a flowchart of a printing process. It is a flowchart which shows a halftone process routine. It is a figure which shows the example of the dot recording rate table DT. It is a figure which shows the usage rate of each nozzle in 2nd Example. It is a figure which shows a part of 1st dither mask D1b. It is a figure which shows the dot formation position at the time of printing a solid image with a dot recording rate of 60% with the first dither mask D1b. It is a figure which shows the usage rate of each nozzle in 3rd Example. It is a figure which shows a part of 1st dither mask D1c. It is a figure which shows the dot formation position at the time of printing a solid image with a dot recording rate of 50% with the first dither mask D1c. It is a figure which shows the dot formed by the nozzle numbers 0-6 when the 1st dither mask D1c is used. It is a figure which shows the dot formed with the nozzle numbers 7-14 when the 1st dither mask D1c is used. It is a figure which shows the dot formed by the nozzle numbers 15-22 when the 1st dither mask D1c is used. It is a figure which shows the dot formed by the nozzle numbers 23-29 when the 1st dither mask D1c is used. It is a figure which shows a part of 2nd dither mask D2c. It is a figure which shows the dot formation position at the time of printing a solid image with a dot recording rate of 50% with the second dither mask D2c. It is a figure which shows the dot formed by the nozzle numbers 0-6 when the 2nd dither mask D2c is used. It is a figure which shows the dot formed by the nozzle numbers 7-14 when the 2nd dither mask D2c is used. It is a figure which shows the dot formed by the nozzle numbers 15-22 when the 2nd dither mask D2c is used. It is a figure which shows the dot formed by the nozzle numbers 23-29 when the 2nd dither mask D2c is used. It is a flowchart which shows the halftone process routine in 4th Example. It is a figure which shows the characteristic of the dither mask for forming a low density dot prior to a high density dot. It is a figure which shows the characteristic of the other dither mask for forming a low density dot prior to a high density dot.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A-1. General configuration of the printing system:
A-2. Computer and printer configuration:
A-3. The principle of bleeding suppression:
A-4. Printing process:
B. Second embodiment:
C. Third embodiment:
D. Fourth embodiment:
E. Variations:

A. First Example A-1. General configuration of the printing system:
FIG. 1 is a diagram showing a schematic configuration of a printing system 10 as an embodiment of the present invention. As shown in the figure, the printing system 10 of this embodiment includes a computer 100 and a printer 200 that actually prints an image under the control of the computer 100. The printing system 10 functions as a printing device in a broad sense as a whole.

  A predetermined operating system is installed in the computer 100 shown in FIG. 1, and the application program 20 operates under this operating system. A video driver 22 and a printer driver 24 are incorporated in the operating system. The application program 20 inputs image data IMG from the digital camera 120 through the peripheral device interface 108, for example. Then, the application program 20 displays an image represented by the image data IMG on the display 114 via the video driver 22. The application program 20 outputs the image data IMG to the printer 200 via the printer driver 24. Image data IMG input from the digital camera 120 by the application program 20 is data composed of three color components of red (R), green (G), and blue (B).

  The printer driver 24 corresponding to the “dot forming unit” of the present application includes an image acquisition module 40, a color conversion module 42, a halftone module 44, and a print data output module 46. The image acquisition module 40 acquires image data to be printed from the application program 20.

  The color conversion module 42 refers to a color conversion table LUT prepared in advance, and color components (cyan (C), magenta (M), yellow) that the printer 200 can express the color components R, G, B of image data. (Y) and black (K).

  The halftone module 44 performs a halftone process in which the image data after color conversion is represented by a binarized (more precisely, multivalued) dot distribution. In this embodiment, a known systematic dither method is used as the halftone process.

  The print data output module 46 rearranges the data representing the dot arrangement of each color obtained by the halftone process in accordance with the dot formation order by the print head 241 of the printer 200 and outputs the data to the printer 200 as print data.

  The halftone module 44 of this embodiment uses a general dither mask having blue noise characteristics (hereinafter referred to as “first dither mask D1”) for dots formed with low-visibility ink that is difficult to see bleeding. Perform halftone processing. On the other hand, with respect to dots (suppressed dots) that are formed with highly visible ink that is prominently blurred, a special dither mask (hereinafter referred to as “second dither mask D2”) is used. Has the function of suppressing bleeding. The principle that can suppress bleeding by using a special dither mask will be described in detail later.

  Note that the terms “low visibility” and “high visibility” do not indicate the absolute properties of ink, but merely indicate relative properties. For example, when two types of ink are driven into a print medium, ink with relatively low brightness becomes “high visibility ink”, and ink with relatively high brightness becomes “low visibility ink”. Specifically, in the case of cyan ink and yellow ink, cyan ink is “high visibility ink” and yellow ink is “low visibility ink”. In the case of black ink and cyan ink, the black ink is “high visibility ink” and the cyan ink is “low visibility ink”. Thus, according to the relative expressions “low visibility” and “high visibility”, the position of cyan ink is reversed depending on the comparative ink. However, in this embodiment, in order to classify the type of ink included in the printer 200, black and magenta are treated as high visibility ink and cyan and yellow are treated as low visibility ink for convenience.

A-2. Computer and printer configuration:
FIG. 2 is a diagram illustrating a schematic configuration of the computer 100. The computer 100 is a well-known computer configured by connecting a ROM 104, a RAM 106, and the like with a bus 116 around a CPU 102.

  The computer 100 includes a disk controller 109 for reading data such as the flexible disk 124 and the compact disk 126, a peripheral device interface 108 for exchanging data with peripheral devices, and a video interface 112 for driving the display 114. It is connected. A printer 200 and a hard disk 118 are connected to the peripheral device interface 108. Further, if the digital camera 120 or the color scanner 122 is connected to the peripheral device interface 108, it is possible to perform image processing on an image captured by the digital camera 120 or the color scanner 122. If the network interface card 110 is installed, the computer 100 can be connected to the communication line 300 to acquire data stored in the storage device 310 connected to the communication line. When the computer 100 acquires image data to be printed, the printer driver 24 controls the printer 200 to print the image data.

  Next, the configuration of the printer 200 will be described with reference to FIG. As shown in FIG. 3, the printer 200 includes a transport mechanism that transports the print medium P by the paper feed motor 235, a main scanning mechanism that reciprocates the carriage 240 in the axial direction of the platen 236 by the carriage motor 230, and the carriage 240. A mechanism for driving the mounted print head 241 to eject ink and forming dots, and a control circuit 260 that controls the exchange of signals with the paper feed motor 235, the carriage motor 230, the print head 241, and the operation panel 256. It is composed of

  The main scanning mechanism for reciprocating the carriage 240 in the axial direction of the platen 236 is an endless arrangement between the carriage motor 230 and a slide shaft 233 that is installed in parallel with the platen 236 axis and slidably holds the carriage 240. A pulley 232 for extending the drive belt 231 and a position detection sensor 234 for detecting the origin position of the carriage 240 are included.

  An ink cartridge 243 containing cyan ink (C), magenta ink (M), yellow ink (Y), and black ink (K) is mounted on the carriage 240. In the print head 241 provided at the lower portion of the carriage 240, nozzle rows 244 to 247 for ejecting ink are formed for each color. These nozzles can form dots of a plurality of types by ejecting a plurality of types (large, medium, and small) of ink droplets having different ink amounts. Taking large dots as a reference, medium dots are formed with an ink amount of about ½ of large dots and small dots with an amount of about ¼ of ink.

  FIG. 4 is a diagram illustrating the arrangement of nozzle rows formed on the bottom surface of the print head 241. As illustrated, the print head 241 includes nozzle rows 244 to 247 formed with a plurality of nozzles arranged in the sub-scanning direction. In this embodiment, each nozzle row is composed of 30 nozzles. These nozzle rows 244 to 247 are supplied with ink from an ink cartridge 243 mounted on the carriage 240 and discharge cyan ink C, magenta ink M, yellow ink Y, and black ink K, respectively. In the following description, it is assumed that the head nozzle number in the sub-scanning direction is “29” and the nozzle number on the rear end side is “0”. As shown in FIG. 4, in this embodiment, the nozzle rows corresponding to the respective ink colors are configured such that the nozzles are arranged in a row in the sub-scanning direction. It is not limited. For example, the nozzles may be arranged in a plurality of rows for one ink color, or the nozzles may be arranged in a staggered manner.

  As shown in FIG. 3, the control circuit 260 included in the printer 200 is configured by connecting a CPU, a ROM, a RAM, a PIF (peripheral device interface), and the like via a bus. Upon receiving print data output from the computer 100 via the PIF, the control circuit 260 drives the carriage motor 230 to reciprocate the print head 241 with respect to the print medium P in the main scanning direction. By driving the paper feed motor 235, the print medium P is moved in the sub-scanning direction. The control circuit 260 performs printing by driving the nozzles at an appropriate timing based on the print data in accordance with the movement of the carriage 240 reciprocally (main scanning) or the movement of paper feeding of the printing medium (sub scanning). Ink dots of appropriate colors are formed at appropriate positions on the medium P. In this way, the printer 200 can print a color image on the print medium P. In this embodiment, the print medium is transported in the sub-scanning direction, but the position of the print medium may be fixed and the carriage 240 may be transported in the sub-scanning direction.

A-3. The principle of bleeding suppression:
As described above, the printing system 10 according to the present embodiment has a function of suppressing bleeding of high-visibility ink on a printing medium. In order to realize such a function, the printing system 10 performs control to increase the usage rate of the leading nozzle in the sub-scanning direction of the nozzle row that ejects high-visibility ink as compared with the trailing-end nozzle. . Hereinafter, the leading nozzle group that increases the usage rate is referred to as a “preceding nozzle group”. A nozzle group on the rear end side that relatively lowers the usage rate is referred to as a “following nozzle group”. In this embodiment, the number of nozzles that increase the usage rate is the number of nozzles included in the band width in which the print head 241 moves by one sub-scan (7 in this embodiment).

  FIG. 5 is a diagram illustrating the concept of increasing the usage rate of the preceding nozzle group. In this figure, the horizontal axis indicates the number (0 to 29) of each nozzle constituting the nozzle row, and the vertical axis indicates the usage rate for each nozzle. FIG. 5 shows the usage rate of the low visibility ink nozzles and the usage rate of the high visibility ink nozzles when the dot recording rate for a predetermined printing area is 5%.

  As shown in FIG. 5, in this embodiment, for example, for low visibility ink, each nozzle ejects ink at the same usage rate (5%) as shown. On the other hand, for the high visibility ink, the usage rate of the nozzles of the preceding nozzle group (nozzle numbers 22 to 29) is increased to about 20%, and the usage rate of the nozzles of the subsequent nozzle group (nozzle numbers 0 to 21) is increased. By setting the ratio to approximately 0%, the ink is ejected so that the average usage rate of the entire nozzle array is 5%.

  In this embodiment, the usage rate of the preceding nozzle group is increased by varying the usage rate for each nozzle in the nozzle row. In this way, the print head 241 that prints an image by gradually feeding paper (sub-scanning) can eject the high-visibility ink earlier than the low-visibility ink to the same printing position in time. it can. As a result, drying of the high visibility ink can be promoted, and bleeding of the high visibility ink can be suppressed. In FIG. 5, only the usage rate of the No. 22 nozzle is an intermediate value between the preceding nozzle group and the other nozzles. This is because the dots formed by the No. 22 nozzle are formed exactly at the middle position between the bands (see FIG. 7), and thus the occurrence of a striped pattern at such portions is suppressed.

  In the present embodiment, a special dither mask (second dither mask D2) is half-colored corresponding to high-visibility ink in order to vary the usage rate of each nozzle constituting the nozzle row as shown in FIG. Used during tone processing. Hereinafter, the principle that the usage rate of each nozzle can be changed by the second dither mask D2 will be described.

  As a premise, in this embodiment, as a mode of drive control of the print head 241, the overlap number is “2”, the nozzle pitch is “2”, and the paper feed amount is “15”. Bidirectional printing is performed in which ink is ejected both during movement. The number of overlaps refers to the number of times of main scanning necessary to fill all the lines formed in the main scanning direction (horizontal direction) with dots. That is, when the overlap number is “2”, one line in the main scanning direction is completed in two main scans. The nozzle pitch refers to the interval between two nozzles formed in the nozzle row. In this embodiment, since the nozzle pitch is “2”, dots are formed every other line in the main scanning of the print head 241 once. The paper feed amount refers to the amount (number of lines) by which the print head 241 is conveyed in the sub-scanning direction for each main scanning. In this embodiment, the paper feed amount is “15”. Hereinafter, this paper feed amount may be referred to as “band width”. In this embodiment, the width of the preceding nozzle group (= 8 [number of nozzles] × 2 [nozzle pitch] −1) is made to coincide with this band width.

  FIG. 6 is a diagram illustrating how dots are formed on a print medium by a certain nozzle row. FIG. 6A shows a state in which a nozzle array composed of 30 nozzles (Nos. 0 to 29) is sub-scanned (paper fed) by 15 dots each time main scanning is performed. FIG. 6B shows the order in which dots are formed in a predetermined 2 × 2 local area on the print medium. As shown in this figure, in this embodiment, each dot in the local area is filled in the order of upper left, lower right, upper right, and lower left. This order is called “filling order”. As for the size of the local region, the horizontal direction (main scanning direction) matches the number of overlaps (“2” in this embodiment), and the vertical direction (sub-scanning direction) corresponds to the nozzle pitch (“2” in this embodiment). Match. The filling order has a property of changing every time the print head 241 is sub-scanned. In this embodiment, when the filling order changes four times, the original filling order is restored. The repeating unit of the filling order is a product of the nozzle pitch and the number of overlaps. The filling order is set by the printer driver 24 giving a predetermined command to the control circuit 260 of the printer 200. When receiving the setting of the filling order from the printer driver 24, the control circuit 260 forms dots in accordance with the set filling order.

  FIG. 6C shows a state in which dots are formed on the print medium according to the drive control mode and the filling order as described above. Each grid shown in FIG. 6C indicates one dot, and the numbers in the grid indicate the numbers of nozzles that form the dots. In this embodiment, as shown in FIG. 6A, eight main scans (four forward scans + four reverse scans) and eight sub-scans are performed, as shown in FIG. 6C. In addition, the printing range of 2 × 60 dots is filled with dots. Dots are formed on the entire print medium by repeatedly applying this 2 × 60 dot pattern (hereinafter referred to as “nozzle arrangement pattern”) in the main scanning direction and the sub-scanning direction. That is, when printing is performed according to the drive control mode and the filling order as described above, as shown in FIG. 6C, the dots formed on the print medium are the positions of the dots and the dots. The number of the nozzle to be formed uniquely corresponds. Then, if the dots at the positions indicated by the nozzle numbers 22 to 29 in FIG. 6C are likely to be generated by the halftone process, the usage rate of the preceding nozzle group is increased. The fact that dots are easily formed is none other than that the threshold value corresponding to the position is low in the systematic dither method. Therefore, in this embodiment, a dither mask corresponding to the size of the nozzle arrangement pattern shown in FIG. 6C is prepared as the second dither mask D2, and the arrangement of the threshold values for the second dither mask D2 is optimized. Then, the usage frequency of each nozzle is adjusted.

  FIG. 7 is a diagram illustrating positions where dots are formed by the preceding nozzle group. FIG. 7 shows a state where eight nozzle arrangement patterns shown in FIG. 6C are connected in the main scanning direction. In the figure, hatched portions are positions where dots are formed by the preceding nozzle groups (nozzle numbers 22 to 29) shown in FIG. As described above, in this embodiment, bleeding of the high-visibility nozzle is suppressed by increasing the usage rate of the preceding nozzle group as compared with the succeeding nozzle group. Therefore, if a dither mask having a threshold (that is, a threshold having a small value) at which dots are easily formed at the hatched position in FIG. 7 is prepared, the usage rate of the nozzles of the preceding nozzle group is increased more than other nozzles. It becomes possible.

  FIG. 8 is a diagram showing a part of the second dither mask D2 generated based on the above concept. In the second dither mask D2, the size of the nozzle arrangement pattern shown in FIG. 6C is 8 × in the main scanning direction and 1 × in the sub-scanning direction, and the size is 16 × 60. That is, the second dither mask D2 has 960 (= 16 × 60) elements. In the second dither mask D2, threshold values from 0 to 255 are arranged for each element while allowing duplication of values. In FIG. 8, similarly to FIG. 7, elements in which dots are formed by the preceding nozzle group (nozzle numbers 22 to 29) are hatched. The threshold value can be arranged on each element as follows. First, for the elements corresponding to the nozzle numbers 22 to 29, small threshold values are arranged uniformly. Thereafter, the remaining threshold values are arranged for other elements. Finally, the arrangement balance of the entire threshold is adjusted for all nozzle numbers. As a method for uniformly arranging the thresholds, for example, predetermined granularity evaluation values (for example, RMS granularity, autocorrelation function, Wiener spectrum, etc.) are obtained before and after the thresholds are arranged, and the changes are optimized. There is a method of arranging a threshold in

  FIG. 9 is a diagram showing dot formation positions when a solid image with a dot recording rate of 5% is printed by the second dither mask D2 shown in FIG. In the figure, the blacked-out portions indicate the positions where dots are formed. As shown in FIG. 9, when the second dither mask D2 shown in FIG. 8 is used, when the dot recording rate is 5%, the hatched portion in FIG. 8, that is, the preceding nozzle group (nozzle numbers 22 to Dots are formed only at positions corresponding to 29). Therefore, if the dot recording rate is up to 5%, all dots can be formed by the preceding nozzle group.

  FIG. 10 is a diagram showing dot formation positions when a solid image with a dot recording rate of 30% is printed using the second dither mask D2. As shown in FIG. 10, when the second dither mask D2 shown in FIG. 8 is used, dots are also formed by nozzles other than the preceding nozzle group when the dot recording rate is 30%. .

  The computer 100 separately stores the above-described second dither mask D2 and the first dither mask D1 having a general blue noise characteristic in advance, and uses these dither masks in accordance with the color to be processed. Perform halftone processing. Hereinafter, a printing process for performing printing using these dither masks will be described in detail.

A-4. Printing process:
FIG. 11 is a flowchart of print processing executed by the computer 100 according to this embodiment. This printing process is performed by the CPU 102 as hardware executing a program prepared as the printer driver 24. When the printing process is started, the computer 100 first inputs RGB format image data from the application program 20 (step S100).

  When the image data is input, the computer 100 uses the color conversion module 42 to convert the RGB format image data input in step S100 into CMYK format image data (step S200).

  When the CMYK format image data is obtained, the computer 100 uses the halftone module 44 to perform halftone processing for each color of cyan (C), magenta (M), yellow (Y), and black (K). Data that can be transferred to the printer 200 is generated (step S300). The data that can be transferred to the printer 200 is data (referred to as dot data) indicating the size of ink droplets formed on the print medium P by the printer 200, and it is determined whether or not to form small dots, medium dots, or large dots. It is data.

  When the halftone process is completed, the computer 100 outputs each dot data for C, M, Y, and K generated by the halftone process to the printer 200 as print data using the print data output module 46 (step). S400).

  The printer 200 receives print data output from the computer 100, and prints an image by ejecting ink onto a print medium according to the received print data. In the present embodiment, the printer 200 sets the number of overlaps to “2”, the nozzle pitch to “2”, the paper feed amount to “15”, and performs bidirectional printing, so that the print head 241, the carriage motor 230, and the paper The printing mechanism such as the feed motor 235 is controlled.

Of the print processing described above, details of the halftone processing executed in step S300 will be described in detail below.
FIG. 12 is a flowchart showing a halftone processing routine. This halftone process is performed for each of C, M, Y, and K colors. As shown in the figure, when this process is started, the computer 100 first designates one of the target colors from C, M, Y, and K (step S302), and reads the gradation data of the pixel of interest (step S302). S304). The initial position of the pixel of interest is the upper left corner of the image data.

  When the gradation data of the pixel of interest is read, the computer 100 determines whether the currently processed color is a high visibility ink color (magenta or black) (step S306). If the color currently being processed is a high-visibility ink color, the computer 100 selects the second dither mask D2 as a dither mask to be applied in the binarization process described later in order not to make blurring noticeable (step) S308). On the other hand, if the currently processed color is a low-visibility ink color (cyan or yellow), the computer 100 selects the first dither mask D1 (step S310).

  When the dither mask to be used is selected in step S308 or step S310, the computer 100 subsequently acquires the dot recording rate corresponding to the gradation data read in step S304 with reference to the dot recording rate table DT. (Step S312). The dot recording rate refers to the density of dots per unit area of the print medium. The dot recording rate table DT is a table in which the occurrence rates of small, medium, and large dots that are generated in the pixel according to the gradation data of the pixel of interest are defined.

  FIG. 13 is a diagram illustrating an example of the dot recording rate table DT. As shown in FIG. 13, the dot recording rate table DT defines the formation ratios of large, medium, and small dots. In the dot recording rate table DT, the recording rate S of small dots gradually increases until the recording rate reaches the maximum in the range of gradation data from 0 to 40, and then the range of gradation data reaches 40. The recording rate is set to gradually decrease until it reaches zero. Similarly, the recording rate M for medium dots gradually increases until the recording rate reaches a maximum in the range of gradation data from 15 to 40, and then becomes 0 in the range of the gradation data up to 100. It is set to decrease gradually. Further, the recording rate L of large dots is set so as to increase gradually until the recording rate reaches the maximum in the range of image data from 100 to 255 (exactly, in the range of gradation data of 200 or more, it increases gradually. Is lower than a range of less than 200).

  When the dot recording rate is acquired in step S312, the computer 100 reads a threshold value corresponding to the position of the pixel of interest from the dither mask (first dither mask D1 or second dither mask D2) selected in step S308 or step S310 ( Step S314). When the threshold value is read in this way, the computer 100 performs binarization by the systematic dither method using the threshold value and the dot recording rate acquired in step S312 (step S316). Since the systematic dither method is a well-known technique, a detailed description is omitted. In short, the systematic dither method corresponds to the dot recording rate corresponding to the gradation data of the pixel of interest and the position of the pixel of interest. This is a method of comparing the threshold value in the dither mask and determining that a dot is to be formed if the dot recording rate is larger, and determining that no dot is formed if the dot recording rate is smaller. In this embodiment, since the dot recording rate takes a value from 0 to 100 and the threshold value takes a value from 0 to 255, in the binarization process in step S316, the dot recording rate acquired in step S312 is obtained. Is set to 2.55 times and then compared with a threshold value.

  Here, referring to the dot recording rate table DT shown in FIG. 13, the dot recording rates of two or more types of dots may be read for one gradation data. For example, in the dot recording rate table DT of FIG. 13, two types of recording are performed with respect to the gradation data CS1, such that the recording rate S for small dots is “48” and the recording rate M for medium dots is “16”. The rate is read. In such a case, the computer 100 determines the size of dots to be formed for the pixel of interest by the following procedure.

(1) First, the large dot recording rate L is compared with a threshold value. If the large dot recording rate L is larger than the threshold value, it is determined that a large dot is to be formed at the target pixel.
(2) If the recording rate L for large dots is smaller than the threshold value, the sum (L + M) of the recording rate L for large dots and the recording rate M for medium dots is compared with the threshold value. As a result, if this sum (L + M) is larger than the threshold value, it is determined that a medium dot is to be formed in the target pixel.
(3) If the sum (L + M) is smaller than the threshold, the sum (L + M + S) of the recording rate of large dots, the recording rate of medium dots, and the recording rate of small dots is compared with the threshold. As a result, if this sum (L + M + S) is larger than the threshold value, it is determined that a small dot is to be formed on the pixel of interest. On the other hand, if this sum (L + M + S) is smaller than the threshold value, it is determined that no dot is formed on the target pixel.

  Here, it is assumed that the recording rate L for large dots is “0”, the recording rate M for medium dots is “40”, the recording rate S for small dots is “122”, and the threshold is “75” (both 0). To a value in the range of from 255 to 255). Then, in the step (1), since the recording rate of large dots is smaller than the threshold value, it is not determined that large dots are formed, and the process proceeds to step (2). In step (2), the sum (L + M) of the large dot recording rate L and the medium dot recording rate M is 40 (= 0 + 40), but the value is still smaller than the threshold value (= 75). Go to 3). In step (3), the sum (L + M + S) of the large dot recording rate, the medium dot recording rate, and the small dot recording rate is 162 (= 0 + 40 + 122), which is larger than the threshold (= 75). It is determined to form a dot. In this way, if the recording rate of each dot size is added one after another and compared with the threshold value, it is possible to determine which size of dot is formed with only one threshold value.

  When the halftone process for the pixel of interest is completed by the process described above, the computer 100 designates the pixel at the next position (step S318), and determines whether the process for all the pixels has been completed (step S318). Step S320). If the processing for all the pixels has not been completed, the computer 100 returns the processing to step S304 and repeats the above processing. On the other hand, if the processing for all the pixels has been completed, it is determined whether the processing for all the ink colors has been completed (step S322). If the processing for all ink colors has been completed, the halftone processing is terminated. If the processing has not been completed, the processing returns to step S302 to continue the processing for the next ink color.

  When the above-described halftone process is completed, the print data generated by the halftone process is transmitted to the printer 200. Upon receiving this print data, the printer 200 drives the print head 241 with the overlap number being “2”, the nozzle pitch being “2”, and the paper feed amount being “15” as described above. Bidirectional printing is performed to eject ink of each color both during the forward movement and during the backward movement.

  According to the printing process described above, high-visibility ink is intensively printed by the preceding nozzle group, and low-visibility ink is printed uniformly over the entire nozzle array. Therefore, when viewing the same printing position on the print medium, the high visibility ink is ejected relatively earlier than the low visibility ink. Accordingly, even when the order of ink ejection is changed from C, M, Y, K to K, Y, M, C in the forward and backward directions of bidirectional printing, the order is the same. Regardless of the change, the high visibility ink is always ejected relatively earlier than the low visibility ink. As a result, drying of highly visible ink that tends to be noticeable in bleeding is promoted, and density unevenness caused by low visibility ink that is subsequently printed at the same position is suppressed.

  In this embodiment, the width of the preceding nozzle group is made to coincide with the width of the paper feed amount of the print head. Therefore, highly visible ink can be ejected to an unprinted area on the print medium, and density unevenness can be further effectively suppressed.

  Furthermore, according to the present embodiment, the usage rate of each nozzle can be controlled simply by switching the dither mask to be applied to the halftone process between the first dither mask D1 and the second dither mask D2. Therefore, density unevenness can be suppressed at low cost without adding a special circuit.

B. Second embodiment:
In the first embodiment described above, drying of the highly visible ink was promoted by increasing the usage rate of the preceding nozzle group. On the other hand, for the low visibility ink, the entire nozzle array is used on average by using a general dither mask. On the other hand, in the second embodiment, the usage rate of each nozzle is positively changed even for the low visibility ink.

  FIG. 14 is a diagram showing the usage rate of each nozzle in the second embodiment. As can be seen from FIG. 14, in this embodiment, for the high visibility ink, control is performed to increase the usage rate of the preceding nozzle group, as in the first embodiment. In addition, in this embodiment, for low visibility ink, the usage rate of the preceding nozzle group is set to “0”, while the usage rate of the succeeding nozzle group of the nozzle numbers 0 to 21 is increased, thereby reducing the nozzles. Ink is discharged so as to achieve the targeted dot recording rate (60% in the case of FIG. 14) over the entire row.

  In the present embodiment, in order to increase the usage rate of the succeeding nozzle group for ejecting the low visibility ink, the nozzle arrangement pattern shown in FIG. 7 has a small value in a portion other than the hatched portion. Prepare a dither mask with thresholds. In other words, in order to reduce the usage rate of the preceding nozzle group, a dither mask in which a large threshold value is arranged in a hatched portion is prepared. Hereinafter, such a dither mask is referred to as a “first dither mask D1b”. FIG. 15 shows a part of the first dither mask D1b. This first dither mask D1b is a dither mask used in place of the first dither mask D1 in the halftone processing routine shown in FIG.

  FIG. 16 is a diagram showing dot formation positions when a solid image with a dot recording rate of 60% is printed using the first dither mask D1b. As shown in FIG. 16, when the first dither mask D1b shown in FIG. 15 is used, if the dot recording rate is up to 60%, the succeeding nozzle group (nozzle numbers 0 to 21) not hatched. Only by this, low visibility ink is ejected.

  As described above, in this embodiment, by using the first dither mask D1b and the second dither mask D2, the nozzles that discharge the high-visibility ink and the low-visibility ink are respectively set to the preceding nozzle group. And the succeeding nozzle group can be completely separated. Therefore, the low-visibility ink is not ejected while the high-visibility ink is being ejected, and the drying of the high-visibility ink can be further promoted. As a result, the occurrence of density unevenness in the print medium is further suppressed.

C. Third embodiment:
In the first embodiment described above, the usage rate of the nozzles other than the preceding nozzle group is set to “0” in the nozzle row that ejects high visibility ink. In the second embodiment, in the nozzle row that ejects low visibility ink. The usage rate of nozzles other than the subsequent nozzle group was set to “0”. In contrast, in the third embodiment, the usage rate of each nozzle is continuously varied according to the nozzle number.

  FIG. 17 is a diagram showing the usage rate of each nozzle in the third embodiment. As can be seen with reference to FIG. 17, in this embodiment, as for the high-visibility ink, as the nozzle number increases (the nozzle on the head side), the usage rate increases, and conversely, for the low-visibility ink. As the nozzle number increases (the nozzle on the head side), the usage rate decreases. By doing so, it becomes possible to eject the high-visibility ink relatively earlier than the low-visibility ink.

  FIG. 18 is a diagram showing a part of the first dither mask D1c that realizes the usage rate of the low-visibility ink shown in FIG. FIG. 19 is a diagram showing dot formation positions when a solid image with a dot recording rate of 50% is printed using the first dither mask D1c. 20 to 23 show which nozzles form each dot shown in FIG. Specifically, FIG. 20 shows dots formed by nozzle numbers 0-6, and FIG. 21 shows dots formed by nozzle numbers 7-14. FIG. 22 shows dots formed by the nozzle numbers 15 to 22, and FIG. 23 shows dots formed by the nozzle numbers 23 to 29. As shown in these figures, when the first dither mask D1c shown in FIG. 18 is used, the proportion of dots formed decreases as the nozzle number increases. That is, if the first dither mask D1c shown in FIG. 18 is used, the nozzle usage rate can be lowered as the nozzle number increases.

  FIG. 24 is a diagram showing a part of the second dither mask D2c that realizes the usage rate of the high-visibility ink shown in FIG. FIG. 25 is a diagram showing dot formation positions when a solid image having a dot recording rate of 50% is printed by the second dither mask D2c. 26 to 29 show which nozzles form each dot shown in FIG. Specifically, FIG. 26 shows dots formed by nozzle numbers 0-6, and FIG. 27 shows dots formed by nozzle numbers 7-14. FIG. 28 shows dots formed by nozzle numbers 15 to 22, and FIG. 29 shows dots formed by nozzle numbers 23 to 29. As shown in these drawings, when the second dither mask D2c shown in FIG. 24 is used, the proportion of dots formed increases as the nozzle number increases. That is, if the second dither mask D2c shown in FIG. 24 is used, the nozzle usage rate can be increased as the nozzle number increases.

D. Fourth embodiment:
In the first to third embodiments described above, the dither mask is switched according to whether the ink to be used is high visibility ink or low visibility ink. On the other hand, in the fourth embodiment, the dither mask is switched according to the dot recording rate. The configuration of the printing system of this embodiment is the same as that of the first embodiment.

  FIG. 30 is a flowchart showing a halftone processing routine in the fourth embodiment. In the halftone processing routine of this embodiment, first, the computer 100 designates one of the processing target colors from C, M, Y, and K (step S352), and reads the gradation data of the pixel of interest (step S354). ).

  When the gradation data of the pixel of interest is read, the computer 100 refers to the dot recording rate table DT (see FIG. 13) and acquires the dot recording rate corresponding to the gradation data read in step S354 (see FIG. 13). Step S356). When the dot recording rate is acquired, the computer 100 determines whether the acquired dot recording rate is 5% or less (step S358). If the dot recording rate is 5% or less, the computer 100 selects the second dither mask D2 (step S360). On the other hand, when the acquired dot recording rate exceeds 5%, the computer 100 selects the first dither mask D1 (step S362). In step S356, when a plurality of dot recording rates are acquired, a predetermined coefficient is added to the dot recording rates of each size (S, M, L), and an average of them is obtained. The average value is used for the process of step S358.

  When the selection of the dither mask is completed, the computer 100 reads a threshold value corresponding to the position of the pixel of interest from the dither mask (first dither mask D1 or second dither mask D2) selected in step S360 or step S362 (step S364). ). When the threshold value is read in this way, the computer 100 uses the threshold value and the dot recording rate acquired in step S356 to perform binarization (more accurately, multi-value) by the systematic dither method (step S366).

  When the binarization for the pixel of interest is finished, the computer 100 designates the pixel at the next position (step S368), and determines whether or not the processing for all the pixels is completed (step S370). If the processing for all the pixels has not been completed, the computer 100 returns the processing to step S354 and repeats the above processing. On the other hand, if the processes for all the pixels are completed, it is determined whether the processes for all the ink colors are completed (step S352). If the processing for all ink colors has been completed, the halftone processing is terminated. If the processing has not been completed, the processing returns to step S352, and the processing for the next ink color is continued.

  In the halftone process of the fourth embodiment described above, the second dither mask D2 is selected if the dot recording rate is low regardless of the type of ink. Therefore, regardless of the color of the ink, low density dots are formed by the preceding nozzle group prior to high density dots. As a result, even when ink with high visibility is printed sparsely, the dots are printed before surrounding dots, so that bleeding is suppressed.

  In this embodiment, printing by the preceding nozzle group is performed by applying the second dither mask D2 to ink dots having a low dot recording rate. On the other hand, for example, dots with a low dot recording rate may be formed in the first filling order in the band (for example, the filling order of number 0 in FIG. 6). Specifically, in the halftone processing flowchart shown in FIG. 30, when the computer 100 determines in step S358 that the dot recording rate is 5% or less, in step S360, the computer 100 fills in the order of filling zero. If it exceeds 5%, it is determined in step S362 that dots are to be formed in any of the first to third filling orders. Then, the computer 100 generates print data by associating the filling order determined in these processes with the target dot. The computer 100 transmits the print data generated in this way to the printer 200 in step S400 of the printing process shown in FIG. The printer 200 analyzes the received print data and forms each dot on the print medium in the designated filling order. As described above, if the process of changing the filling order for forming the dots according to the dot recording rate is performed, it is possible to prioritize the formation of sparse dots without using different dither masks. The processing described above can be applied not only when forming sparse dots, but also when forming dots corresponding to high-visibility ink. Specifically, in step S358, it is determined whether the color currently being processed corresponds to a high visibility ink. If the color is a high visibility ink, it is determined in step S360 that dots are formed in the order of filling 0. To do. By doing so, it becomes possible to form dots corresponding to the high-visibility ink in the first filling order in the band.

  In the halftone process shown in FIG. 30, low-density dots are formed prior to high-density dots by switching the dither mask to be used according to the dot recording rate. However, even with a single dither mask, low density dots can be formed prior to high density dots.

  FIG. 31 is a diagram illustrating the characteristics of a dither mask for forming low density dots prior to high density dots. In the dither mask having the characteristics shown in FIG. 31, at the dot recording rate of 3% or less, the usage rate of the preceding nozzle group is increased and the usage rate of the subsequent nozzle group is set to zero. Then, when the dot recording rate is higher than 3%, the usage rate of the succeeding nozzle group is gradually increased, and when the dot recording rate exceeds 30%, the usage rates of all the nozzles are made substantially equal. If a dither mask having such characteristics is used for all colors, low density dots can be formed prior to high density dots by the preceding nozzle group without switching the dither mask to be used. For example, using a dither mask having the characteristics shown in FIG. 31, dots are formed with yellow having a high density (for example, a dot recording rate of 30% or more) and cyan having a low density (for example, a dot recording rate of 3% or less). In this case, high density yellow will form dots equally by all nozzles, but low density cyan will form dots preferentially by the preceding nozzle group. For this reason, cyan dots are formed with the entire density in a state where only a part of the total density of other dots such as yellow dots is formed, and it becomes possible to suppress bleeding of the cyan dots. .

  FIG. 32 is a diagram illustrating characteristics of another dither mask for forming low density dots prior to high density dots. In the dither mask having the characteristics shown in FIG. 32, at a dot recording rate of 3% or less, the usage rate of the preceding nozzle group is increased and the usage rate of the subsequent nozzle group is set to zero. When the dot recording rate is higher than 3%, the usage rate of the subsequent nozzle group is gradually increased, and the usage rate of the subsequent nozzle group is set to the usage rate of the preceding nozzle group in the vicinity where the dot recording rate exceeds 20%. Higher than the rate. If a dither mask with such characteristics is used for all colors, low density dots can be formed prior to high density dots by the preceding nozzle group without switching the dither mask to be used. The subsequent nozzle group can be preferentially used for these dots. Therefore, when printing high density yellow and low density cyan, it is possible to further suppress the bleeding of cyan dots.

E. Variations:
As mentioned above, although the various Example of this invention was described, it cannot be overemphasized that this invention is not limited to these Examples, and can take a various structure in the range which does not deviate from the meaning. For example, the following modifications are possible.

E-1. Modification 1:
In each of the embodiments described above, control is performed to increase the usage rate of the preceding nozzle group and the succeeding nozzle group by using a special dither mask. However, such control can also be performed by an error diffusion method. Hereinafter, a method of controlling the nozzle usage rate by the error diffusion method will be described.

Here, a halftone processing procedure by a general error diffusion method will be described first. If the gradation data of each pixel takes a value from 0 to 255, in the normal error diffusion method,
(1) The error distributed from the processed pixel is added to the gradation data of the target pixel.
(2) The gradation data after the error addition is compared with a predetermined threshold value (for example, a fixed value such as 127) and binarized to either 0 (dot off) or 255 (dot on).
(3) Error calculation between the binarized value (0 or 255) and the gradation data after error addition.
(4) The calculated error is distributed to the surrounding unprocessed pixels at a predetermined ratio (for example, 1/4 is distributed to the four neighboring pixels).
(5) Move the processing target to the next pixel.
Halftone processing is performed by the procedure. For example, the halftone process of the low visibility ink in the first embodiment can be performed according to this procedure.

  On the other hand, the procedure (2) is changed as follows for the halftone processing of the high visibility ink in the first embodiment. That is, when the dot recording rate of the pixel of interest is 5% or less (13 as gradation data) and the nozzle number corresponding to the pixel of interest is 0 to 22, the gradation data is forcibly set to 0 (dots). If this condition is not met, processing similar to (2) above is performed. If the procedure (2) is changed in this way, also in the error diffusion method, the subsequent nozzle group (nozzle numbers 0 to 22) in the nozzle row that ejects the high visibility ink as in the first embodiment described above. The usage rate of the preceding nozzle group (nozzle numbers 23 to 29) can be increased while making the usage rate of) almost zero.

  For the halftone processing of the low visibility ink in the second embodiment, the procedure (2) is changed as follows. That is, when the dot recording rate of the pixel of interest is 60% (153 as gradation data) or less and the nozzle numbers are 22 to 29, the gradation data is forcibly set to 0 (dot off). If the condition is not met, the same processing as in (2) above is performed. If the procedure (2) is changed in this way, also in the error diffusion method, as in the second embodiment, the preceding nozzle group (nozzle numbers 23 to 29) in the nozzle row that ejects low visibility ink. The usage rate of the succeeding nozzle group (nozzle numbers 0 to 22) can be increased while the usage rate is substantially zero.

  Further, as in the third embodiment, in order to continuously change the usage rate of each nozzle according to the nozzle number, the threshold value in the procedure (2) may be changed. For example, when the nozzle number is large, if the threshold value is set to a large value, the probability that dots are formed in the pixel is reduced accordingly. On the other hand, if the nozzle number is small and the threshold is set to a small value, the probability that a dot is formed in that pixel increases accordingly. As described above, if the threshold value is linearly changed according to the nozzle number by using a predetermined function, the usage rate of each nozzle is continuously set according to the nozzle number as in the third embodiment. It becomes possible to make it variable. If the function for determining the threshold is a function that can obtain a polygonal line or a curve, it is possible to bring the nozzle usage rate closer to the target. Further, if the function changes not only with the nozzle number but also with the gradation data (dot recording rate), the usage rate of the nozzle can be controlled also with the gradation data.

E-2. Modification 2:
In each of the above-described embodiments, printing is performed in the printing system 10 including the computer 100 and the printer 200. On the other hand, the printer 200 itself may perform printing by inputting image data from a digital camera or various memory cards. That is, the CPU in the control circuit 260 of the printer 200 may perform printing by executing processing equivalent to the above-described printing processing and halftone processing.

E-3. Modification 3:
In each of the above-described embodiments, the ink is divided into a high-visibility ink and a low-visibility ink, and various controls are performed to suppress bleeding of the high-visibility ink. On the other hand, for example, each of the above-described embodiments can be applied in order to suppress bleeding of ink that easily mixes with other inks in terms of physical properties due to, for example, the relationship between surface tension and permeability to a printing medium. It is. That is, by treating ink that is easily mixed with other inks as the “high visibility ink” in each of the above-described embodiments, it is possible to suppress bleeding of ink that is easily mixed physically.

DESCRIPTION OF SYMBOLS 10 ... Printing system 20 ... Application program 22 ... Video driver 24 ... Printer driver 40 ... Image acquisition module 42 ... Color conversion module 44 ... Halftone module 46 ... Print data output module 100 ... Computer 102 ... CPU
104 ... ROM
106 ... RAM
DESCRIPTION OF SYMBOLS 108 ... Peripheral device interface 109 ... Disk controller 110 ... Network interface card 112 ... Video interface 114 ... Display 116 ... Bus 118 ... Hard disk 120 ... Digital camera 122 ... Color scanner 124 ... Flexible disk 126 ... Compact disk 200 ... Printer 230 ... Carriage motor 231 ... Drive belt 232 ... Pulley 233 ... Slide shaft 234 ... Position detection sensor 235 ... Paper feed motor 236 ... Platen 240 ... Carriage 241 ... Print head 243 ... Ink cartridges 244 to 247 ... Nozzle array 256 ... Operation panel 260 ... Control circuit 300 ... Communication line 310 ... Storage device

Claims (7)

A printing apparatus that prints by driving a print head relative to a print medium in a main scanning direction that is the width direction of the printing medium and a sub-scanning direction that intersects the main scanning direction,
An acquisition unit for acquiring image data;
A low-visibility ink preceding ejection nozzle that ejects low-visibility ink to a predetermined print area on the print medium;
A low-visibility ink trailing ejection nozzle that ejects the low-visibility ink after the low-visibility ink is ejected from the low-visibility ink preceding ejection nozzle for the predetermined printing area;
A high-visibility ink preceding ejection nozzle that ejects high-visibility ink to a predetermined print area on the print medium;
A high-visibility ink trailing discharge nozzle that discharges the high-visibility ink after the high-visibility ink is discharged from the high-visibility ink preceding discharge nozzle with respect to the predetermined printing area;
Including a print head;
A dot forming unit that controls the print head and forms dots corresponding to the image data on the print medium with the low-visibility ink and the high-visibility ink ;
When the dot recording rate according to the image data is less than a predetermined dot recording rate,
The number of times of forming dots in the predetermined print area by the high-visibility ink preceding discharge nozzle is greater than the number of times of forming dots in the predetermined print area by the high-visibility ink subsequent discharge nozzle,
When the dot recording rate according to the image data exceeds a predetermined dot recording rate,
The number of times dots are formed in the predetermined print area by the high-visibility ink preceding discharge nozzle is less than the number of times dots are formed in the predetermined print area by the high-visibility ink subsequent discharge nozzle.
A printing apparatus characterized by that.   The printing apparatus according to claim 1,
  The printing apparatus according to claim 1, wherein the high-visibility ink is an ink having lightness lower than that of the low-visibility ink.   The printing apparatus according to claim 1 or 2, wherein
  The printing apparatus according to claim 1, wherein the low-visibility ink is an ink that is less prone to bleeding than the high-visibility ink.   A printing apparatus according to any one of claims 1 to 3, wherein
  The print head is
    A high-visibility ink trailing discharge nozzle group comprising a plurality of nozzles that discharge the high-visibility ink including the high-visibility ink trailing discharge nozzle;
    A high-visibility ink preceding discharge nozzle group consisting of a plurality of nozzles that discharge the high-visibility ink that is not included in the high-visibility ink subsequent discharge nozzle group and includes the high-visibility ink preceding discharge nozzle group. ,
  The number of nozzles belonging to the high-visibility ink preceding ejection nozzle group is smaller than the number of nozzles belonging to the high-visibility ink subsequent ejection nozzle group.   The printing apparatus according to any one of claims 1 to 4, wherein:
  The printing apparatus, wherein the predetermined printing area is a raster line extending in a main scanning direction. A printing method for each relatively driven to print the print head relative to the print medium in the sub-scanning direction crossing the width direction serving as the main scanning direction and the main scanning direction of the print medium,
And as Engineering you get the image data,
A low-visibility ink preceding ejection nozzle that ejects low-visibility ink to a predetermined print area on the print medium;
A low-visibility ink trailing ejection nozzle that ejects the low-visibility ink after the low-visibility ink is ejected from the low-visibility ink preceding ejection nozzle for the predetermined printing area;
A high-visibility ink preceding ejection nozzle that ejects high-visibility ink to a predetermined print area on the print medium;
A high-visibility ink trailing discharge nozzle that discharges the high-visibility ink after the high-visibility ink is discharged from the high-visibility ink preceding discharge nozzle with respect to the predetermined printing area;
Controlling a print head including said by said high visibility ink with low visibility ink, and a dot corresponding to the image data Cheng Hao you formed on the printing medium,
When the dot recording rate according to the image data is less than a predetermined dot recording rate,
The number of times of forming dots in the predetermined print area by the high-visibility ink preceding discharge nozzle is greater than the number of times of forming dots in the predetermined print area by the high-visibility ink subsequent discharge nozzle,
When the dot recording rate according to the image data exceeds a predetermined dot recording rate,
The number of times dots are formed in the predetermined print area by the high-visibility ink preceding discharge nozzle is less than the number of times dots are formed in the predetermined print area by the high-visibility ink subsequent discharge nozzle.
A printing method characterized by the above. Computer program for controlling a printing device for each driven relative to print the print head relative to the print medium in the sub-scanning direction crossing the width direction serving as the main scanning direction and the main scanning direction of the print medium Because
And that function to get the image data,
A low-visibility ink preceding ejection nozzle that ejects low-visibility ink to a predetermined print area on the print medium;
A low-visibility ink trailing ejection nozzle that ejects the low-visibility ink after the low-visibility ink is ejected from the low-visibility ink preceding ejection nozzle for the predetermined printing area;
A high-visibility ink preceding ejection nozzle that ejects high-visibility ink to a predetermined print area on the print medium;
A high-visibility ink trailing discharge nozzle that discharges the high-visibility ink after the high-visibility ink is discharged from the high-visibility ink preceding discharge nozzle with respect to the predetermined printing area;
Controlling a print head including said by said high visibility ink with low visibility ink, a computer program for realizing the said print medium to form to that feature of the dot corresponding to the image data to a computer,
When the dot recording rate according to the image data is less than a predetermined dot recording rate,
The number of times of forming dots in the predetermined print area by the high-visibility ink preceding discharge nozzle is greater than the number of times of forming dots in the predetermined print area by the high-visibility ink subsequent discharge nozzle,
When the dot recording rate according to the image data exceeds a predetermined dot recording rate,
The number of times dots are formed in the predetermined print area by the high-visibility ink preceding discharge nozzle is less than the number of times dots are formed in the predetermined print area by the high-visibility ink subsequent discharge nozzle.
A computer program characterized by that.

Images