JPH11277730A - Printer and method for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate disadvantage wherein the number of dots capable of forming an image without shift of pixels is limited and gradation representation is limited in terms of a moving speed of a head in a multi-value printer which can represents the gradation having three or more values by each pixel. SOLUTION: In a multi-value printer, an image is formed by a kind of a dot to be formed by the printer is made to correspond to two or more pixels adjacent with each other in the main scanning direction. For example, in the case where a small dot IP1, a medium dot IP2, a large dot IP3 can be formed, a small dot and a medium dot are formed as a pixel c1 and a large dot is formed as a pixel c2 adjacent to the pixel c1. The above correspondence relationship is repeated so that the first main scanning P1 is executed. Next, the second main scanning P2 is executed by a correspondence relationship wherein a large dot is formed as a pixel c1 and a small dot and a medium dot are formed as a pixel c2. As a result, it is possible to form an arbitrary dot without shift in each pixel so that gradation representation of the printer can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus for printing a multi-tone image by driving a head having nozzles capable of continuously forming dots at intervals smaller than the pixel interval in the main scanning direction. Related to the printing method.

[0002]

2. Description of the Related Art Conventionally, as an output device of a computer, there has been proposed an ink jet printer which forms dots by using several colors of ink ejected from a plurality of nozzles provided in a head and records an image. Are widely used to print processed images in multiple colors and multiple tones. In recent years, in order to enrich the gradation expression, an ink-jet printer, that is, a so-called multi-value printer capable of expressing two or more gradations of ON / OFF for each dot has been proposed. For example, a printer that can express three or more types of densities for each dot by changing the dot diameter and ink density, and a multi-gradation can be expressed by superposing a plurality of dots for each pixel It is a printer.

FIG. 8 is an explanatory diagram showing how dots of different diameters are formed by a multi-level printer. In this printer, a head includes a piezo element PE, and ejects ink droplets according to a voltage applied to the piezo element. FIG.
As shown in the upper rows W1, W2, and W3, if the voltage waveform applied to the piezo element, that is, the drive waveform, is changed, the ink droplets IP1, IP2, and IP3 respectively change the small, medium, and large dots ( Below, small dots,
Medium dots and large dots). In the driving waveform shown in FIG. 8, the larger the ink droplet, the higher the amplitude of the driving waveform and the higher the flying speed of the ink.

Consider a case where the carriage 31 incorporating the head forms dots while moving in the main scanning direction, that is, in the direction shown in the middle of FIG. FIG. 23 schematically shows how small dots and medium dots are formed first. 23, dw1 and dw2 are drive waveforms for forming small and medium dots, and IP1 and IP2 are ink droplets ejected by the respective drive waveforms. c1
The squares to which reference numerals c4 indicate the pixels on which dots are formed on the paper.

As described above, since the flying speed varies depending on the dot diameter, the driving waveform dw1 for forming the small dot IP1 and the driving waveform dw1 for forming the medium dot IP2 as shown in the upper part of FIG. If the drive waveform dw2 and the drive waveform dw2 are output continuously by adjusting the timing, both can be formed in the same pixel c1. If a mask signal that prohibits the ejection of ink from the head is sent while the drive waveform dw2 is being output, only the small dot IP1 can be formed. Similarly, it is also possible to form only the medium dot diameter. As a result, in the multi-value printer shown in FIG.
It is possible to express four values of "formation of small diameter dot", "formation of large diameter dot", and "formation of small diameter dot and large diameter dot overlapped".

[0006]

However, in such a multi-value printer, there is a limit to increasing the number of types of driving waveforms to increase the gradation values that can be expressed for each pixel. FIG. 2 shows how dots are formed when the drive waveform dw3 is further increased in the multilevel printer shown in FIG.
It is shown in FIG. Ink droplet I ejected by drive waveform dw3
P3 is larger than the ink droplet IP2 and has a higher flying speed. However, since the carriage moves in the main scanning direction while outputting the drive waveforms dw1, dw2, and dw3,
If the moving speed of the carriage is high, the ink droplet IP3
May not be formed in the pixel c1, but may be formed at a position protruding in the main scanning direction as shown in FIG. If the dots are formed so as to protrude from the pixels, the quality of the printed image will be greatly reduced. Originally, multi-valued printers aim at high-quality printing by increasing the number of gradations that can be expressed for each pixel, so that such deterioration in image quality cannot be overlooked.

[0007] Even if the ink droplet IP3 could be formed on the pixel c1 in FIG. 24, the same problem would occur if the types of driving waveforms were further increased. Therefore, in a multi-valued printer that forms dots having different diameters by continuously outputting two or more types of drive waveforms, there is a limit to the number of gradations that can be expressed for each pixel.

This problem can be solved by reducing the speed at which the carriage moves in the main scanning direction. However, in this case, another problem of lowering the printing speed occurs. Further, in FIG. 24, it is possible to treat a large pixel (pixel indicated by a broken line in FIG. 24) that includes the position where the ink droplet IP3 is formed in the pixel as a unit. This means a decrease, which leads to a decrease in image quality.

In the above description, a printer using a piezo element has been described as an example. However, a similar problem may occur in a printer or the like which discharges ink droplets by energizing a heater to generate bubbles in ink. A similar problem may occur not only with dots having different diameters but also with a multi-valued printer that forms dots using inks with different densities or a printer that expresses multiple gradations by forming a single type of dot on top of another.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and in a multi-valued printer, it is possible to prevent a dot from protruding from a pixel and to form a gradation of a multi-valued printer. It is an object of the present invention to provide a technology capable of improving image quality and improving image quality.

[0011]

Means for Solving the Problems and Their Functions and Effects In order to solve at least part of the above-mentioned problems, the printing apparatus of the present invention employs the following configuration. The printing apparatus of the present invention
While performing main scanning in which the head is reciprocated relative to the print medium, the head is driven to form dots, thereby forming a raster as a pixel row arranged at regular intervals in the main scanning direction. A printing device that prints an image corresponding to the image data obtained on the print medium, wherein the head includes a nozzle capable of continuously forming two or more dots at an interval smaller than the interval between the pixels. By controlling the driving of the head, a predetermined correspondence relationship is established between two or more dots that can be formed at an interval smaller than the pixel interval and two or more pixels adjacent in the main scanning direction. The gist of the present invention is to include a head control unit that forms dots according to the image data.

According to the printing method of the present invention, while performing main scanning in which the head reciprocates relative to the printing medium, the head is driven to form dots, so that the head is driven at regular intervals in the main scanning direction. A printing method of forming a raster as a line of arranged pixels and printing an image corresponding to input image data on the print medium, wherein the head continuously prints two or more dots at a smaller interval than the pixel. A head having nozzles that can be formed by controlling the driving of the head to form two or more dots that can be formed at a smaller interval than the pixel and two or more pixels that are adjacent in the main scanning direction. The point is that dots corresponding to the image data are formed in a predetermined correspondence relationship with the image data.

According to the printing apparatus and the printing method,
Two or more dots that can be formed at intervals smaller than the pixel interval can be periodically formed in a predetermined correspondence relationship with two or more pixels adjacent in the main scanning direction. To explain with reference to the example shown in FIG. 24, three types of dots IP1, IP2, and IP3 are formed corresponding to two or more pixels adjacent in the main scanning direction. For example, dot IP1,
IP2 corresponds to pixel c1, and dot IP3 corresponds to pixel c2.
It is formed corresponding to. Of course, the dot IP1 may correspond to the pixel c1, and the dots IP2 and IP3 may correspond to the pixel c2. Further, since it corresponds to two or more pixels, the dot IP1 may correspond to the pixel c1, the dot IP2 may correspond to the pixel c2, and the dot IP3 may correspond to the pixel c3.

In the case where the types of dots that can be formed further increase, various correspondences can be set in the same manner. Naturally, the types of dots that can be formed are not limited to the three types shown in FIG. 24, and more or fewer types may be used. In addition, not only the dots having different diameters as shown in FIG. 24 but also the dots having different ink densities can be set in the same manner, or the correspondence may be determined for a single type of dot. In the case of a single type of dot, for example, a correspondence relationship can be set in which two dots are formed on the pixel c1 described above and no dot is formed on the pixel c2.
As described above, the correspondence can be variously set in accordance with the number of dots that can be formed by the head at intervals smaller than the interval between the pixels.

If the correspondence relationship is set in advance such that the dots IP1 and IP2 correspond to the pixel c1 and the dot IP3 corresponds to the pixel c2, the printing apparatus and the printing method use the dot relationship based on the correspondence relationship. Are formed periodically. That is, according to the example of FIG. 24, the dots IP1 and IP2 are formed in the pixel c3, and the dot IP3 is formed in the pixel c4. The same applies to the other correspondences described above. According to the above-described printing apparatus and printing method, by forming dots in association with two or more pixels in this manner, each dot can be formed without protruding from each pixel, and image quality can be improved. .

When the above-described one correspondence relationship between dots and pixels is set, it is possible that an arbitrary dot cannot be formed at each pixel constituting a raster as a dot row in the main scanning direction. For example, in the above example, the pixel c1 has the dot IP
3 cannot be formed, and conversely, the pixel c2 has dots IP1,
In other words, IP2 cannot be formed.

Therefore, in the above-described printing apparatus, the head control means forms the dots to be formed in the main scanning direction by dividing the dots into a plurality of main scans, and the correspondence is determined for each of the plurality of main scans. It is preferable that the means is a means for controlling the driving of the head so as to form dots in different correspondences.

In this case, since dots are formed by a plurality of main scans having different correspondences between the types of dots and the pixels, an arbitrary dot can be formed for each pixel. Explaining in accordance with the above example, the dots IP1, IP2, IP2
For example, in a printing apparatus that forms dots 3 periodically, in the first main scan, dots are formed by associating the dots c1 with the dots IP1 and IP2 and the c2 with the dot IP3. In the second main scan, a dot IP3 is placed on the pixel c1.
And the same raster is formed by associating the dots IP1 and IP2 with the pixel c2. This makes it possible to form all the pixels of the dots IP1, IP2, and IP3 on both the pixels c1 and c2. The same applies to the case where dots are formed by other correspondences.

It should be noted that any one of the above types of dots may be formed for each main scan, but an arbitrary dot can be formed for each pixel. For example, only the dot IP1 is formed in all the pixels in the first main scan, and only the dot IP2 is formed in the second main scan. The printing apparatus described above has better image quality than the printing apparatus that performs such recording. Such characteristics are obtained by periodically forming a plurality of types of dots for each main scan.

When a single type of dot is formed in each main scan, looking at each type of dot, each raster is formed in one main scan. When such printing is performed, if a dot formation position is shifted due to a mechanical manufacturing error of the nozzle, the entire raster is formed with a shift, which causes a deterioration in image quality. On the other hand, according to the printing apparatus, each raster is formed by a plurality of main scans while periodically forming a plurality of types of dots. It is formed. As a result, a shift that may occur in the dot formation position can be averaged over the entire raster, and the image quality can be improved.

In a printing apparatus that forms a raster by a plurality of main scans, it is preferable that the plurality of main scans be the number of main scans corresponding to the number of pixels for which the correspondence is determined. .

In this case, each raster can be constituted by the minimum necessary main scanning. Therefore, in a printing apparatus in which each raster is formed by a plurality of main scans, the printing speed can be improved most.

In the printing apparatus according to the present invention, the two or more dots may be two or more types of dots having different diameters.

In order to form two or more types of dots having different diameters, it is necessary to periodically output a signal corresponding to each diameter to the head. If the type of dots is increased in such a state, the dots are likely to be formed shifted from the pixels, so that the present invention can be effectively used.

Further, as one example, the two or more types of dots are three types of dots having a large diameter, a medium diameter, and a small diameter, respectively. The correspondence may be such that a pixel having a large diameter is associated with a pixel adjacent to the pixel.

In such a case, the number of gradations that can be expressed for each pixel can be increased by forming dots of the above three types. Further, since small- and medium-diameter dots are formed in association with one pixel, every other type of dot can be formed in the main scanning direction by one main scan. As a result, even if each raster is formed by one main scan, the recording rate of each type of dot can be sufficiently ensured. Further, in order to form an arbitrary dot in each pixel, it is sufficient to form each raster by two main scans, so that the printing speed is not significantly reduced.

[0027]

Other aspects of the present invention In the above-described printing apparatus of the present invention, when each raster is formed by one main scan, the types of dots that can be formed for each pixel are limited. In consideration of this, image processing for creating print data is required. Therefore, the present invention can also take an aspect as a printing apparatus provided with means for realizing such image processing, as described below.

According to another aspect of the present invention, there is provided a printing apparatus which performs main scanning in which a head reciprocates relative to a printing medium, and drives the head to form dots, thereby forming dots in the main scanning direction. A printing apparatus that forms a raster as a pixel row arranged at regular intervals and prints an image corresponding to input image data on the print medium, wherein the head is at least two at intervals smaller than the interval of the pixels. Is a head provided with nozzles that can form dots continuously, and is provided in advance between two or more dots that can be formed at a smaller interval than the pixel and two or more pixels that are adjacent in the main scanning direction. Storage means for storing the determined correspondence; multivalue means for multiplying the input image data into gradation values which can be expressed by the head for each pixel; Image data and the storage For the pixels and can form dots does not correspond on the basis of the correspondence stored in the stage,
A pixel rearrangement unit that replaces the image data of the pixel with a pixel that is adjacent to the pixel and that can form a dot corresponding to the image data, based on the image data replaced by the rearrangement unit; This is an aspect as a printing apparatus including: a head control unit that controls driving of a head to form dots in the correspondence stored in the storage unit.

In such a printing apparatus, the multi-value conversion means multi-values the image data into gradation values that can be expressed for each pixel. Here, multi-value conversion is performed without considering the correspondence between pixels and dots to be formed. Therefore, for example, there is a possibility that a gradation value at which a large dot is to be formed is assigned to a pixel which is not associated with a large dot. In the above printing apparatus, when such a pixel exists, the data is replaced by data of an adjacent pixel in which a large dot can be formed by the dot rearrangement means. If the distance between pixels is sufficiently small to replace pixels with adjacent pixels, such replacement does not cause deterioration in image quality. As a result, according to the printing apparatus of this aspect, dots can be appropriately formed according to the multi-valued image data.

In the above description, the case where three types of dots having different diameters are used is taken as an example. However, even when the type of dots changes or the correspondence changes, the dots are appropriately formed by the same processing. Is possible.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. (1) Apparatus Configuration: FIG. 1 is a block diagram showing the configuration of a printing apparatus as one embodiment of the present invention. As shown, the scanner 12 and the color printer 22 are connected to the computer 90, and a predetermined program is loaded and executed on the computer 90, so that the computer 90 functions as a printing apparatus as a whole. This computer 90
Is centered on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program,
The following components are connected to each other by a bus 80. R
The OM 82 previously stores programs and data necessary for the CPU 81 to execute various types of arithmetic processing.
Reference numeral 83 denotes a memory for temporarily reading and writing various programs and data necessary for the CPU 81 to execute various arithmetic processes. The input interface 84 controls input of signals from the scanner 12 and the keyboard 14, and the output interface 85 controls output of data to the printer 22. The CRTC 86 is a CRT2 capable of color display.
1 to the disk controller (DD).
C) 87 controls the exchange of data with the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). On the hard disk 16,
The RAM 83 stores various programs loaded and executed, various programs provided in the form of device drivers, and the like.

In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. This SIO 88 is connected to the modem 18 and the modem 1
8 is connected to a public telephone line PNT. The computer 90 is connected to an external network via the SIO 88 and the modem 18. By connecting to a specific server SV, it is also possible to download a program required for image processing to the hard disk 16. In addition, it is also possible to load a necessary program from a flexible disk FD or a CD-ROM, and cause the computer 90 to execute the program.

FIG. 2 is a block diagram showing a software configuration of the printing apparatus. In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and image data FNL to be transferred to the printer 22 is output from the application program 95 via these drivers. Application program 9 for retouching images
5 reads an image from the scanner 12 and performs a predetermined process on the
An image is displayed on the T display 21. Scanner 1
2 is read from a color original, and is red (R), green (G), and blue (B).
Is the original color image data ORG composed of the three color components.

This application program 95
When a print command is issued, the printer driver 96 of the computer 90 transmits the image information to the application program 9.
5 and converted into a signal that can be processed by the printer 22 (here, a multivalued signal for each color of cyan, magenta, yellow, and black). FIG.
In the example shown in FIG. 5, a resolution conversion module 97, a color correction module 98,
Color correction table LUT and halftone module 99
And a rasterizer 100.

The resolution conversion module 97 serves to convert the resolution of the color image data handled by the application program 95, that is, the number of pixels per unit length into a resolution that can be handled by the printer driver 96. The image data whose resolution has been converted in this way is still RGB.
The color correction module 98 refers to the color correction table LUT and uses the printer 22 for each pixel, cyan (C), magenta (M), yellow (Y), and black, with reference to the color correction table LUT. (K) is converted into data of each color. The data thus color-corrected is, for example, 2
It has a gradation value with a width such as 56 gradations. The halftone module executes halftone processing for expressing such gradation values in the printer 22 by forming dots in a dispersed manner. The image data processed in this way is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 22, and output as final image data FNL. In this embodiment, the printer 22 only plays a role of forming dots in accordance with the image data FNL, and does not perform image processing. Of course, the above-described processing may be performed by the printer 22.

Next, a schematic configuration of the printer 22 will be described with reference to FIG. As shown in the drawing, the printer 22 includes a mechanism for transporting a sheet P by a paper feed motor 23 and a
6, a mechanism for reciprocating in the axial direction, a mechanism for driving a print head 28 mounted on a carriage 31 to eject ink and form dots, and a mechanism for driving these paper feed motors 23,
It comprises a carriage motor 24, a print head 28, and a control circuit 40 which controls the exchange of signals with the operation panel 32.

The mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes a sliding shaft 34 laid parallel to the axis of the platen 26 and holding the carriage 31 slidably.
A pulley 38 for extending an endless drive belt 36 between the carriage motor 24 and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.

The carriage 31 includes a cartridge 71 for black ink (Bk) and five colors of cyan (C1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y). A color ink cartridge 72 containing ink can be mounted. For two colors, cyan and magenta, two types of inks are provided. A total of six ink discharge heads 61 to 66 are formed on the print head 28 below the carriage 31. At the bottom of the carriage 31, an introduction pipe 67 (which guides ink from the ink tank to each color head). (See FIG. 4). Carriage 31
When the cartridge 71 for black (Bk) ink and the cartridge 72 for color ink are mounted from above, the introduction pipe 67 is inserted into the connection hole provided in each cartridge, and each ink cartridge is connected to the ejection heads 61 to 66. Supply of ink becomes possible.

A mechanism for discharging ink and forming dots will be described. FIG. 4 is an explanatory diagram showing a schematic configuration inside the ink discharge head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 by utilizing the capillary phenomenon as shown in FIG. Print head 28 of each color 6
1 to 66. When the ink cartridge is first mounted, the operation of sucking the ink into the heads 61 to 66 of the respective colors by a dedicated pump is performed. In this embodiment, a pump for suction and a cap for covering the print head 28 at the time of suction are provided. The illustration and description of such a configuration are omitted.

As will be described later, the heads 61 to 66 of each color are provided with 48 nozzles Nz for each color (see FIG. 6), and each nozzle is one of the electrostrictive elements. A piezo element PE having excellent responsiveness is provided. FIG. 5 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the upper part of FIG. 5, the piezo element PE has an ink passage 68 for guiding ink to the nozzle Nz.
It is installed in a position in contact with. As is well known, the piezo element PE is an element that distorts the crystal structure due to the application of a voltage and converts electro-mechanical energy very quickly. In the present embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE expands by the voltage application time as shown in the lower part of FIG. One side wall 68 is deformed. As a result,
The volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE, and the ink corresponding to the contraction is discharged as particles Ip at a high speed from the tip of the nozzle Nz. Printing is performed by the ink particles Ip penetrating into the paper P mounted on the platen 26.

FIG. 6 is an explanatory diagram showing the arrangement of the ink jet nozzles Nz in the ink discharge heads 61 to 66. The arrangement of these nozzles is composed of six sets of nozzle arrays that eject ink for each color, and 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. The 48 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, but may be arranged on a straight line. However, the arrangement in a staggered pattern as shown in FIG. 6 has an advantage that the nozzle pitch k can be easily set small in manufacturing.

Although the printer 22 of the present invention is provided with the nozzles Nz having a constant diameter as shown in FIG. 6, three types of dots having different diameters can be formed using the nozzles Nz. This principle will be described. FIG.
FIG. 4 is an explanatory diagram showing a relationship between a driving waveform of a nozzle Nz when ink is ejected and an ink Ip ejected. The drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. In the section d2, once a negative voltage is applied to the piezo element PE, the piezo element PE is deformed in a direction in which the cross-sectional area of the ink passage 68 is increased, contrary to the case described above with reference to FIG. As shown in the state A of FIG. 7, the ink interface Me called the meniscus is in a state recessed inside the nozzle Nz. On the other hand, when a negative voltage is suddenly applied as shown in a section d2 using the drive waveform shown by the solid line in FIG. 7, the meniscus is greatly depressed inward as compared with the state A as shown in the state a.
Next, when the voltage applied to the piezo element PE is made positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, large ink droplets are ejected as shown in states B and C from the state where the meniscus is not much depressed inward (state A). As shown in the state c, a small ink droplet is ejected.

As described above, the dot diameter can be changed in accordance with the change rate when the drive voltage is made negative (section d1, d2). It is easy to imagine that the dot diameter can be changed according to the magnitude of the peak voltage of the driving waveform. In this embodiment, based on such a relationship between the driving waveform and the dot diameter, the driving waveform for forming the small dot IP1 having the small dot diameter and the medium dot IP2 having the second dot diameter are formed. Drive waveform for forming and large dot IP3 with the largest diameter
There are three types of drive waveforms for forming. FIG. 8 shows a driving waveform used in this embodiment. The driving waveform W1 is a waveform forming the small dot IP1, the driving waveform W
Reference numeral 2 denotes a waveform forming a medium dot IP2, and drive waveform W3 denotes a waveform forming a large dot. As shown in FIG. 8, as the dot diameter increases, the flying speed increases. By properly using these drive waveforms, it is possible to form three types of small, medium, and large dots from the nozzle Nz having a fixed nozzle diameter. In the printer 22 of the present embodiment, these drive waveforms are output continuously and periodically in the order of W1, W2, and W3 as the carriage 31 moves.

The timing for outputting the drive waveforms W1, W2, W3 will be described. As described above, since the flying speed of the medium dot IP2 formed by the driving waveform W2 is lower than the flying speed of the small dot IP1 formed by the driving waveform W1, it is possible to form dots in the same pixel. is there. Although the large dot IP3 has a higher flying speed than the medium dot IP2, the large dot IP3 cannot be formed in the same pixel as the small dot IP1 due to the relationship with the moving speed of the carriage 31. In this embodiment, the small dot IP
The output timing of the drive waveforms W1 and W2 is adjusted so that 1 and the medium dot IP2 are formed in the same pixel. The large dot IP3 is the small dot IP1 and the medium dot I
The output timing of the drive waveform W3 is adjusted so that the pixel at which P2 is formed is formed at a pixel adjacent to the moving direction of the carriage 31.

Next, the internal configuration of the control circuit 40 of the printer 22 will be described, and the plurality of nozzles Nz shown in FIG.
A method for driving the head 28 made of will be described.
FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, the control circuit 40 includes a CPU 8
1, PROM 42, RAM 43, and a computer 90
Interface 44 for exchanging data with the PC
, A peripheral input / output unit (PIO) 45 for exchanging signals with the paper feed motor 23, the carriage motor 24, the operation panel 32, etc., a timer 46 for timing, and a head 6.
A driving buffer 47 for outputting a dot on / off signal is provided for each of the pixels 1 to 66, and these elements and circuits are interconnected by a bus 48. The control circuit 40 includes a transmitter 51 that outputs a drive waveform (see FIG. 8) at a predetermined frequency, and a distributor 55 that distributes an output from the transmitter 51 to the heads 61 to 66 at a predetermined timing.
Is also provided. The control circuit 40 includes a computer 90
And temporarily stores the dot data in the RAM 43 and outputs it to the driving buffer 47 at a predetermined timing.

A mode in which the control circuit 40 outputs a signal to the heads 61 to 66 will be described. FIG. 10 is an explanatory diagram showing the connection of one nozzle row of the heads 61 to 66 as an example. One nozzle row of the heads 61 to 66 is provided in a circuit in which the driving buffer 47 is on the source side and the distribution output unit 55 is on the sink side, and each piezo element PE constituting the nozzle row has its electrode One is connected to each output terminal of the driving buffer 47, and the other is connected to the output terminal of the distribution output unit 55 collectively. From the distribution output device 55, as shown in FIG.
1 is output. When ON / OFF is determined for each nozzle from the CPU 81 and a signal is output to each terminal of the driving buffer 47, the piezo element PE which has received the ON signal from the driving buffer 47 side according to the driving waveform.
Only be driven. As a result, the ink particles Ip are simultaneously discharged from the nozzles of the piezo element PE that have received the ON signal from the transfer buffer 47.

As shown in FIG. 6, since the heads 61 to 66 are arranged along the transport direction of the carriage 31,
The timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Therefore, the CPU 81 outputs the ON / OFF signal of each dot via the transfer buffer 47 at a necessary timing, taking into account the displacement of the nozzles of the heads 61 to 66, and outputs the dot of each color. Has formed. Also, as shown in FIG.
The output of the ON / OFF signal is controlled in the same manner as in 66, taking into account that the nozzles are formed in two rows.

In the printer 22 having the hardware configuration described above, the carriage 31 is reciprocated by the carriage motor 24 (hereinafter, referred to as main scanning) while the paper P is transported by the paper feed motor 23 (hereinafter, referred to as sub-scanning). ), And at the same time, the respective color heads 61 to 6 of the print head 28
By driving the piezo elements PE of No. 6, each color ink is ejected, dots are formed, and a multicolor image is formed on the paper P.

In this embodiment, the printer 22 having the head for discharging ink using the piezo element PE is used as described above. However, a printer for discharging ink by another method may be used. Good. For example, the present invention may be applied to a printer of a type in which a heater disposed in an ink passage is energized and ink is ejected by bubbles generated in the ink passage.

(2) Dot formation control: Next, a dot formation control process in the printing apparatus of the present embodiment will be described. FIG. 11 shows the flow of the dot formation control processing routine. This is a process executed by the CPU 81 of the computer 90.

When this processing is started, the CPU 81
Image data is input (step S100). This image data is stored in the application program 95 shown in FIG.
, And values 0 to 255 for each color of R, G, and B for each pixel constituting the image.
Is data having 256 gradation values. The resolution of the image data changes according to the resolution of the original image data ORG and the like.

The CPU 81 converts the resolution of the input image data into a resolution for printing by the printer 22 (step S105). If the image data is lower than the printing resolution, resolution conversion is performed by generating new data between adjacent original image data by linear interpolation.
Conversely, if the image data is higher than the print resolution, resolution conversion is performed by thinning out the data at a fixed rate.
Note that the resolution conversion processing is not essential in the present embodiment, and printing may be executed without performing such processing.

Next, the CPU 81 performs a color correction process (step S110). The color correction processing is to use image data composed of R, G, and B gradation values in
This is a process of converting into data of gradation values of each color of M, Y, and K. This processing is performed for C, M, Y, C, M, Y,
A color correction table LUT storing combinations of K (FIG. 2)
Reference). Various well-known techniques can be applied to the processing itself for performing color correction using the color correction table LUT.
And the like described in US Pat.

The CPU 81 performs multi-value processing on the color-corrected image data (step S12).
0). The multi-value conversion means that the gradation value (256 gradations in this embodiment) of the original image data is converted into a gradation value that can be expressed by the printer 22 for each pixel. As will be described later, in the present embodiment, multi-valued conversion to four gradations of “no dot formation”, “small dot formation”, “medium dot formation”, and “large dot formation” is performed. May be multi-valued to more gradations, including gradation values expressed by superposition of. The multi-value processing can be performed by various methods, and the processing by the error diffusion method and the processing by the dither method are typical. The error diffusion method generally has an excellent image quality, and the dither method has a characteristic that high-speed processing is possible. In the present embodiment, it is possible to use both of them selectively by the user.

First, the multi-value processing by the error diffusion method will be described. Fig. 1 shows the flow of multi-value processing by the error diffusion method.
It is shown in FIG. When this process is started, the CPU 81 inputs the image data Cd (Step S122). The input image data Cd is data that has been subjected to color correction processing (step S110 in FIG. 11) and has 256 gradations for each of C, M, Y, and K colors. Diffusion error correction data Cdx is generated for this data (step S124). In the error diffusion process, an error in the gradation expression generated for the processed pixel is distributed in advance by assigning a predetermined weight to pixels around the pixel. Therefore, in step S124, the corresponding error is read out and this is read out. From the pixel to be processed. FIG. 13 exemplifies how the peripheral pixels are weighted and the error is distributed to the target pixel PP.
The density error is given a predetermined weight (１ ／, 1) for several pixels in the scanning direction of the carriage 31 with respect to the pixel PP of interest, and for several adjacent pixels behind the paper P in the transport direction.
/ 8, 1/16). The error diffusion processing will be described later in detail.

The diffusion error correction data C thus generated
dx is compared with the first threshold th1 (step S
126) If the data Cdx is smaller than the threshold th1, a value 0 meaning that no dot is formed is substituted for the value Cdr representing the multi-value quantization result (step S12).
8). The threshold value th1 is a value serving as a reference for determining whether or not to form a dot as described above. This threshold th1
Can be set to any value, but in the present embodiment, it was set based on the following concept.

FIG. 14 shows the relationship between the recording rates of large, medium and small dots and the gradation values of image data in this embodiment. In this embodiment, as shown in FIG. 14, only small dots are formed at gradation values 0 to gr1, small dots and medium dots are formed at gr1 to gr2, and medium dots and large dots are formed at gr2 and higher. Is set to At a gradation value of gr1 or more, a dot of any of large, medium, and small is formed, and pixels that do not form a dot hardly occur. The above threshold th
1 is set so that the formation or non-formation of small dots occurs as shown in FIG. 14 in the range of gradation values 0 to gr1. In this embodiment, th1 = gr1 / 2 is set.

If the correction data Cdx is greater than or equal to the first threshold th1, then the correction data Cdx and the second threshold t
The value of h2 is compared with the value of h2 (step S130), and if the correction data Cdx is smaller than the second threshold th2, a value 1 meaning the formation of a small dot is substituted for the value Cdr representing the multi-value quantization result ( Step S132). The threshold value th2 is set based on the dot recording rate in FIG. 14 similarly to the threshold value th1, and in this embodiment, th2 = (gr1 + gr2) /
2 is set.

If the correction data Cdx is equal to or larger than the second threshold value th2, the correction data Cdx and the third threshold value t
A comparison is made between h3 and h3 (step S134). If the correction data Cdx is smaller than the third threshold th3, a value 2 meaning the formation of a medium dot is substituted for the value Cdr representing the multi-value quantization result (step S134). Step S136). Similarly to the threshold th1, the threshold th3 is set based on the dot recording rate in FIG. 14, and in this embodiment, th3 = (gr2 + 255) /
2 is set. When the correction data Cdx is equal to the third threshold th
If it is 3 or more, a value 3 meaning the formation of a large dot is substituted for the value Cdr representing the multi-valued result (step S1).
38). In the present embodiment, the quaternization is performed by the above processing. However, when the number of types of dots that can be formed increases and it is necessary to perform more multi-value conversion, the above-described threshold value is increased to increase the number of dots. Can be processed.

Next, the CPU 81 calculates an error caused by the multi-value conversion, and executes a process of diffusing the error to peripheral pixels (step S140). The error refers to a value obtained by subtracting the tone value of the original image data from the evaluation value of the density represented by each dot after multi-value conversion. For example, considering a pixel having a gradation value of 255 in the original image data, the evaluation value of the density by forming a large dot is equivalent to the gradation value of 255, and the evaluation value of the density by forming a medium dot is equivalent to the gradation value of gr2. When it is determined that a large dot is formed for this pixel (C
In the case of (dr = 3), no error occurs because the tone value of the original image data and the density evaluation value expressed are both equal to 255. On the other hand, when it is determined that a medium dot is to be formed (Cdr = 2), an error equivalent to Err = gr2-255 occurs.

The error calculated in this way is diffused to peripheral pixels at the rate shown in FIG. For example, when an error corresponding to the gradation value 4 is calculated in the pixel PP of interest, an error corresponding to the gradation value 1 which is ４ of the error is diffused to the adjacent pixel P1. Will be. Similarly, errors are diffused at other pixels in the ratio shown in FIG. The error diffused in this manner is reflected on the image data Cdx in step S124 described above, and diffusion error correction data Cdx is generated. When the processing for all the pixels is completed by the above repetition (step S14)
2), the CPU 81 once ends the multi-value processing by error diffusion, and returns to the dot formation control processing routine (FIG. 11).
By the above processing, the result value Cdr is set to the value 0 for each pixel.
-3 are assigned.

Next, the multivalue processing by the dither method will be described with reference to the flowchart shown in FIG. When this process is started, the CPU 81 inputs the image data Cd (Step S152). The input image data Cd is data that has been subjected to color correction processing (step S110 in FIG. 11). Next, the magnitude of the image data Cd is compared with the gradation value gr1 (step S154).
As shown in FIG. 14, the tone value gr1 is a tone value that is a boundary between a low tone area where only small dots are formed and an intermediate tone area where both small dots and medium dots are formed. In the step S154, it is determined whether or not the image data Cd has a low gradation.

As described above, the printer 22 of this embodiment can express four values for each dot. FIG.
As shown in FIG. 4, the image data has a low gradation to be expressed by either “dot non-formation” or “small dot formation” and “small dot formation” or “medium dot” in accordance with the gradation value. , And high gradation to be expressed by either "formation of medium dots" or "formation of large dots". In the present embodiment, before performing the multi-value conversion by the dither method, it is determined to which of these areas the image data belongs. In this way, as described below, quaternization can be performed with one type of dither matrix.

If the gradation value Cd of the image data corresponds to a low gradation smaller than the value gr1, the CPU 81 sets the gradation value Cd
Is compared with the threshold value TH1 (step S15).
6). As the threshold value TH1, a different value is set for each pixel by the dither matrix. In this embodiment, a blue noise matrix in which values from 0 to 255 appear in 16 × 16 square pixels is used. However, in step S156, the image data Cd can take only a value smaller than gr1. Therefore, the threshold value Th1 is set by multiplying each value of the dither matrix by gr1 / 255. The reason why the threshold value TH1 is set in this way is that the same dither matrix is used for the intermediate gradation and the high gradation. A total of three types of dither matrices dedicated to each gradation may be prepared.

In the low gradation, one of the states of “no dot formation” or “small dot formation” is adopted. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH1, the value 0 indicating the non-formation of the dot is substituted into the value Cdr representing the result of the multi-value conversion (step S1).
58). In the opposite case, a value 1 meaning the formation of a small dot is substituted for the value Cdr (step S160).

FIG. 16 shows the concept of multi-value conversion by the dither method. Here, as a general case, both the image data Cd and the dither table can take values from 0 to 255. As shown in FIG.
Each pixel of d is compared with the corresponding portion of the dither table. When the modulus of the image data Cd is larger than the threshold value indicated in the dither table, the dot is turned on, and when the modulus of the image data Cd is smaller, the dot is turned off. FIG.
The hatched pixels in the figures mean the pixels that turn on the dots.

In step S154, if the gradation value Cd of the image data is equal to or more than the value gr1, that is, if it corresponds to the intermediate gradation, the image data Cd and the gradation value gr2
By comparing the magnitude with (step S162),
It is determined whether the image data Cd belongs to the middle gradation or the high gradation. When the image data Cd is smaller than the value gr2, that is, when the image data Cd belongs to the halftone,
After subtracting the value gr1 from the image data Cd (step S164), the value gr1 is compared with the threshold value TH2 (step S166). The reason why the value gr1 is subtracted in step S164 is that the same dither matrix as in the case of low gradation can be applied. In this case, the image data Cd is data taking values from 0 to (gr2−gr1).
Each value of the dither matrix is (gr2-gr1) / 25
By multiplying by 5, the threshold value TH2 can be set.

In the intermediate gradation, one of the states “formation of small dots” or “formation of medium dots” is adopted. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH2, a value 1 meaning the formation of a small dot is substituted into the value Cdr representing the result of the multi-value conversion (step S16).
8) In the opposite case, the value 2 meaning the formation of a medium dot is substituted (step S170).

If the gradation value Cd of the image data is equal to or greater than the value gr2 in step S162, that is, if it corresponds to a high gradation, the value gr2 is subtracted from the image data Cd (step S172), and the threshold value TH3 is set. Are compared with each other (step S176). The reason why the value gr2 is subtracted in step S172 is that the same dither matrix as in the case of low gradation can be applied. In this case, since the image data Cd is data taking values from 0 to (255-gr2), (255) is added to each value of the dither matrix.
−gr2) / 255 to set the threshold value TH3.

In the high gradation, one of the states of “formation of medium dot” and “formation of large dot” is adopted. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH3, the value 2 meaning the formation of the medium dot is substituted into the value Cdr representing the result of the multi-value conversion (step S1).
76). In the opposite case, a value 3 meaning the formation of a large dot is substituted for the value Cdr (step S178). By the above processing, one pixel of the image data converted to the print resolution is quaternized. If the gradation value further increases, multi-value processing can be performed by repeatedly executing the processing corresponding to steps S162 to S170 according to the gradation value. The CPU 81 repeatedly executes the above processing, and when the processing for all the pixels is completed (step S180), the multi-value processing by the dither method is temporarily terminated, and the process returns to the dot formation control routine of FIG.

Next, the CPU 81 performs rasterizing (step S210). This means that the data for one raster is rearranged in the order in which it is transferred to the head of the printer 22. FIG. 17 shows the contents of the rasterizing process in this embodiment.

When the rasterizing process is started, the CPU 8
1 inputs image data (step S202). Further, a value 0 is substituted for the variable DN, and a value 1 is substituted for the variable CN to perform initialization (step S202). The variable DN is a value that indicates the order of data that is rasterized and transferred to the printer 22. The variable CN is a pixel number. The pixel numbers are numbers assigned to the pixels constituting the raster in the main scanning direction, and correspond to c1, c2, c3,... Shown in FIG. In FIG. 19, for convenience, they are represented by variables such as c1 and c2.
Integers are given in the order of

Next, it is determined whether the raster to be processed is a raster whose image is to be recorded in the first main scan or a raster whose image is to be recorded in the second main scan (step S204). In this embodiment, each raster is 2
Since it is assumed that the data is formed in the main scans, it is determined which data should be prepared for which main scan. If data to be used for the first main scan is to be prepared, a value of 0 is substituted for the variable F (step S208). If data to be used for the second main scan is to be prepared, a value of 1 is substituted for the variable F. (Step S206).

Here, the meaning of the variable F will be described.
In the present embodiment, as described above, three types of dots, large, medium, and small, can be formed.
One dot is formed by associating each dot with one pixel. That is, as shown in FIG. 18, the small dot IP1 and the medium dot IP1
2 is formed on the pixel c1, and the large dot IP3 is formed on the pixel c2. FIG. 19 shows how dots are continuously formed according to this correspondence. Each square shown in FIG. 19 indicates a pixel, and a black circle indicates a small dot IP.
1. A circle surrounding small dots means a medium dot IP2, and a circle having the largest diameter means a large dot IP3. P in FIG.
Numeral 1 indicates the state of dots formed in the first main scan. If a raster is formed according to the correspondence shown in FIG.
As shown by P1 in FIG. 19, small dots and medium dots are formed in the pixels c1, c3, and c5, and large dots are formed in the pixels c2 and c4.

At this time, large dots cannot be formed in the pixels c1, c3, and c5. Therefore, in this embodiment, each raster is set to 2
The first main scan and the second main scan have different correspondences between dot types and pixels, so that an arbitrary dot can be formed in each pixel. (See the bottom row of FIG. 19). In FIG.
The state of dots formed in the second main scan on the same raster as P1 is indicated by P2. This time, pixels c1, c
The correspondence is changed so that large dots are formed in the pixels 3 and c5, and small dots and medium dots are formed in the pixels c2 and c4. The variable F set in steps 206 and 208 in FIG. 17 is a variable for controlling the use of this correspondence relationship. When the value F is set to 0, the variable F is set in the correspondence relationship shown by P1 in FIG. A dot is formed and the value of the variable F is set to 1
Is set, it means that dots are formed in the correspondence shown by P2 in FIG.

After setting the variable F, the CPU 81 determines whether the remainder obtained by dividing the pixel number CN by 2 is equal to the variable F (step S210). Note that the process of step S210 is described in the flowchart of FIG.
"CN% 2 = F?" Here, “%” is a remainder operator. By this operation, it is determined whether the pixel number CN is an odd number or an even number. When the pixel number is an even number, the result of the above calculation is 0, and when the pixel number is an odd number, the result is 1.

As described above, the variable F is set to a value of 0 when a raster is formed in the first main scan P1, and is set to a value of 1 when a raster is formed in the second main scan P2.
Is set. In the main scan P1, a large dot is formed on even-numbered pixels (corresponding to P1 in FIG. 19), and in the main scan P2, a large dot is formed on odd-numbered pixels (P2 in FIG. 19).
Equivalent). Therefore, in other words, the variable F is set to a value of 0 for a main scan in which a large dot is to be formed in an even-numbered pixel, and a value of 1 for a main scan in which a large dot is to be formed in an odd-numbered pixel. Is set. After all, the variable F specifies a pixel to form a large dot in the form of the calculation result of “CN% 2”. Therefore, the CPU 81
In step S210, when the calculation result of "CN% 2" matches the value of the variable F, it is determined whether or not the pixel is a pixel for which a large dot should be turned on (step S210). S230). If the image data is to form a large dot, a value 1 meaning dot formation is assigned to the data PD [DN] transferred to the driving buffer 40 of the printer 22 (step S234), and If the data does not form a dot, the value 0, which is mask data, is substituted (step S232).

When the value 1 is set in the data PD [DN], the ink is ejected from the nozzles by the input of the driving waveform as described above with reference to FIG. 10 to form dots. When the value 0 is set, although the drive waveform is output from the distribution output unit 55 (see FIG. 9),
Since the circuit on the source side of the nozzle is turned off, no dot is formed. In the data PD [DN], only information indicating dot on / off is stored, and information on the type of dot is not stored. Printer 22 of this embodiment
In this case, since the arrangement of the data PD and the driving waveform (see FIG. 18) output periodically correspond one-to-one,
As long as it is turned off, dots of the type corresponding to the drive waveform can be formed.

In step S210, the operation "C
N% 2 ”does not match the value of the variable F,
U81 determines that the pixel under processing is a pixel for forming a small dot and a medium dot. Therefore, it is determined whether or not the image data is to form a small dot (step S212). If it is to be formed, the data PD [DN] is to be formed.
Is substituted into the data PD [DN] when the data PD [DN] is not formed (step S216).
214). Further, the data number DN is increased by the value 1 (step S218), and the ON / OFF of the medium dot is recorded in the data PD to be transferred immediately after the data PD in which the ON / OFF of the small dot is recorded. That is, it is determined whether or not the image data is to form a medium dot (step S22).
0), if a value should be formed, the value 1 is substituted for the data PD [DN] (step S224), and if not, a value 0 is substituted for the data PD [DN] (step S22).
2).

In the above processing, on / off of small dots and medium dots or on / off of large dots is set according to the pixel number CN. The CPU 81 sets the data number DN and the pixel number CN to the value 1 in preparation for the processing of the next pixel.
The above processing (steps S204 to S240) is repeated until the processing of all pixels constituting each raster is completed (step S242). The rasterized data is output to the printer 22 in the dot formation control processing routine (FIG. 11) (step S250 in FIG. 11). In the above description, the flow of processing for one raster has been described.
This embodiment has 48 nozzles as shown in FIG. 6, and can form 48 rasters at the same time. Therefore, in practice, the entire process is repeatedly executed for the number of nozzles, and data is output to the printer 22.

The large dot IP3 cannot be formed in the same pixel as the small dot IP1 and the medium dot IP2 in one main scan. If it is used for printing as it is, dots will be formed at positions shifted from the pixels, which will lead to deterioration of image quality and the like. On the other hand, according to the printing apparatus described above, in each main scan, small and medium dots and large dots are formed in different pixels, and each raster is formed in two main scans. Accordingly, the large dot IP3 can be formed without causing the above-described deviation from the pixel. As a result, in the printing apparatus, the number of gradations that can be expressed for each pixel can be increased, and the image quality can be improved.

In this embodiment, the small dot IP1, the medium dot IP2, and the large dot IP3 are printed according to the correspondence shown in FIG. 18, but this correspondence can be set in various ways. For example, as shown in FIG. 20, one dot may correspond to each pixel. That is,
The small dot IP1 may be formed at the pixel c1, the medium dot IP2 may be formed at the pixel c2 adjacent to the pixel c1, and the large dot IP3 may be formed at the adjacent pixel c3. The intervals D1 and D2 at which the respective drive waveforms dw1, dw2 and dw3 are output are adjusted so as to realize such association. FIG. 21 shows how dots are formed in such a case. The meanings of the symbols and the like are the same as those in FIG. 19 described above. If each dot is periodically formed in the above-described correspondence relationship, a small dot IP1 is formed in the pixels c1 and c4 in the first main scan as shown by P1 in FIG.
2, a medium dot IP2 is formed in c5, and a large dot IP3 is formed in pixel c3. In this case, P in FIG.
As shown in P2 and P3, three main scans having different correspondences are performed to form an arbitrary dot on each pixel (see the lowermost row in FIG. 21). In a case where it is difficult to form the small dot IP1 and the medium dot IP2 in the same pixel, it can be said that it is desirable from the viewpoint of image quality to form dots in the above-described correspondence.

In the present embodiment, the printer 22 capable of forming three types of dots has been described as an example. However, the present invention can be similarly applied to a case where the number of types of dots that can be formed is larger or smaller. Further, the present invention is also applicable to a printer that forms a single type of dot. For example, assume that the dots IP1, IP2, and IP3 in FIG. 18 described above are all the same type of dots. In the first main scan, as shown at P1 in FIG. 19, printing is performed in a correspondence relationship in which two dots are formed on the pixel c1 and no dots are formed on the pixel c2. In the second main scan, as shown in P2, the correspondence between pixels formed by overlapping dots and pixels not formed is different from that in the first scan. In this way, as shown in the lowermost part of FIG. 19, up to three dots can be formed for each pixel, and the gradation expression can be increased. Of course, the present invention can be applied to a case where a larger number of dots are formed in an overlapping manner.

In this embodiment, each raster is formed by two main scans as shown in FIG.
The second main scan P2 can be omitted. If each raster is formed by one main scan, the printing speed can be increased. When only the main scan P1 in FIG. 19 is performed, the large dot IP3 cannot be formed in the pixel c1.
Therefore, if the image data is to form a large dot IP3 in the pixel c1, the printed image may be degraded in gradation expression. Therefore, in such a case, it is desirable to take measures to prevent the gradation expression from being impaired. Various measures can be taken. For example, in the dot formation control processing, rasterization (FIG. 11)
Immediately before step S200), there is a method of performing a dot rearrangement process having the following contents.

The dot rearrangement process will be specifically described with reference to FIG. For example, it is assumed that the multi-valued image data represents the formation of dots shown in the upper part of FIG. When dots are formed in the correspondence shown in P1 of FIG.
Small dots and medium dots set for the pixel c1 in the upper part of FIG. 22 can be formed. Adjacent pixel c
Since only large dots can be formed in 2, small dots and medium dots set in the upper part of FIG. 22 cannot be formed. Similarly, a large dot cannot be formed in the pixel c3. Therefore, as a dot rearrangement process, as shown in the lower part of FIG. 22, both data are exchanged, a large dot is formed at the pixel c2, and a small dot and a medium dot are formed at the pixel c3. Since only a large dot can be formed in the pixel c4, a similar idea
Replace with the data of pixel c5. By this processing, the image data is corrected to the form shown in the lower part of FIG.

In this way, all dots can be formed in one main scan, so that gradation expression is not impaired.
Strictly speaking, the original image data must be printed faithfully to move the dot formation position. Has a very small effect. In the above-described example of the dot rearrangement process, replacement with pixels adjacent in the main scanning direction is performed. However, replacement with pixels adjacent in the sub-scanning direction may be performed.

Further, as another means for preventing the gradation expression from being impaired, the density in the case where small dots and medium dots are formed in an overlapped manner and the density in the case where large dots are formed alone are almost the same. The ink amount of each dot may be adjusted. If this means is adopted, there is an advantage that the processing can be sped up in that there is no need to perform complicated processing such as dot rearrangement.

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various embodiments can be made without departing from the gist of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of software.

FIG. 3 is a schematic configuration diagram of a printer of the present invention.

FIG. 4 is an explanatory diagram illustrating a schematic configuration of a dot recording head of the printer of the present invention.

FIG. 5 is an explanatory diagram showing a dot formation principle in the printer of the present invention.

FIG. 6 is an explanatory diagram showing an example of a nozzle arrangement in the printer of the present invention.

FIG. 7 is an enlarged view of a nozzle arrangement in the printer of the present invention and an explanatory diagram showing a relationship with formed dots.

FIG. 8 is an explanatory diagram illustrating the principle of forming dots having different diameters by the printer of the present invention.

FIG. 9 is an explanatory diagram showing an internal configuration of a control device of the printer.

FIG. 10 is an explanatory diagram showing a driving waveform of a nozzle and dots formed by the driving waveform in the printer of the present invention.

FIG. 11 is a flowchart illustrating a flow of a dot formation control routine.

FIG. 12 is a flowchart showing a flow of a multi-value processing by error diffusion.

FIG. 13 is an explanatory diagram showing weights when an error is diffused.

FIG. 14 is an explanatory diagram showing a relationship between a recording rate and a gradation value of each of large, medium, and small dots.

FIG. 15 is a flowchart showing a flow of a multi-value processing by a dither method.

FIG. 16 is an explanatory diagram showing the concept of dot on / off determination by the dither method.

FIG. 17 is a flowchart illustrating a flow of a rasterizing process.

FIG. 18 is an explanatory diagram illustrating how dots are formed in the present embodiment.

FIG. 19 is an explanatory diagram showing correspondence between types of dots and pixels in the present embodiment.

FIG. 20 is an explanatory diagram showing another state of dot formation in the present embodiment.

FIG. 21 is an explanatory diagram showing another correspondence between types of dots and pixels.

FIG. 22 is an explanatory diagram illustrating an example of dot rearrangement.

FIG. 23 is an explanatory diagram showing the correspondence between dot types and pixels in a conventional printer.

FIG. 24 is an explanatory diagram showing how dots are formed when the types of dots are increased in a conventional printer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 12 ... Scanner 14 ... Keyboard 15 ... Flexible drive 16 ... Hard disk 18 ... Modem 21 ... Color display 22 ... Color printer 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Print head 31 ... Carriage 32 ... Operation panel 34 ... Slider Driving shaft 36 Drive belt 38 Pulley 39 Position detection sensor 40 Control circuit 41 CPU 42 Programmable ROM (PROM) 43 RAM 44 PC interface 45 Peripheral input / output unit (PIO) 46 Timer 47 Transfer Buffer 48 Bus 51 Transmitter 55 Distribution output 61, 62, 63, 64, 65, 66 Ink ejection head 67 Introducing pipe 68 Ink passage 71 Black ink cartridge 72 Color ink Cartridge 80 81 ... CPU 82 ... ROM 83 ... RAM 84 ... Input Interface 85 ... Output Interface 86 ... CRTC 87 ... Disk Controller (DDC) 88 ... Serial Input / Output Interface (SIO) 90 ... Personal Computer 91 ... Video Driver 95 ... Application Program 96 ... Printer driver 97 Resolution conversion module 98 Color correction module 99 Halftone module 100 Transfer buffer

Claims (6)

[Claims] 1. A raster, which is a pixel row, arranged at regular intervals in the main scanning direction by driving the head to form dots while performing main scanning in which the head reciprocates relative to a print medium. A printing apparatus that prints an image corresponding to input image data on the print medium, wherein the head is capable of continuously forming two or more dots at a smaller interval than the pixel. Controlling the driving of the head to determine in advance between two or more dots that can be formed at a smaller interval than the pixel and two or more pixels adjacent in the main scanning direction. A printing apparatus comprising: a head control unit that forms dots in accordance with the image data in a given correspondence relationship. 2. The printing apparatus according to claim 1, wherein the head control means forms dots to be formed in the main scanning direction by dividing the dots into a plurality of main scans, and A printing apparatus as means for controlling the driving of the head so as to form dots in a different correspondence relationship for each main scan. 3. The printing apparatus according to claim 2, wherein the plurality of main scans are the number of main scans corresponding to the number of pixels for which the correspondence is determined. 4. The printing apparatus according to claim 1, wherein the two or more dots are two or more types of dots having different diameters. 5. The printing apparatus according to claim 4, wherein the two or more types of dots have a large diameter, a medium diameter, respectively.
A printing apparatus comprising three types of small-diameter dots, wherein the correspondence relationship is that one pixel is associated with a small-diameter dot and a medium-diameter dot, and a pixel adjacent to the pixel is associated with a large-diameter dot. 6. A raster which is a pixel row arranged at regular intervals in the main scanning direction by driving the head to form dots while performing main scanning in which the head reciprocates relative to a print medium. And a printing method for printing an image corresponding to input image data on the print medium, wherein the head is capable of continuously forming two or more dots at intervals smaller than the interval between the pixels. A head provided with nozzles, wherein the driving of the head is controlled so that two or more dots that can be formed at an interval smaller than the interval between the pixels and two or more pixels adjacent in the main scanning direction are determined in advance. A printing method for forming dots according to the image data in a predetermined correspondence relationship.