JP2003019819A - Printer, printing method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a printer which can form dots having different density and diameter that the dots are not used properly while taking account of the limit of ink duty. SOLUTION: The printer comprises a head provided with two kinds of ink, i.e., dark and light inks, for at least one color and can form dots with large and small diameters. Based on inputted image data, the quantity of ink being ejected per unit area is set for each color with reference to a correlation table such that the limit of ink duty is kept. Subsequently, the manner of generating dots having different diameters is determined for each color such that the quantity of ink being ejected actually approaches the set quantity of ink. According to the arrangement, dots having different density and diameter can be used properly while keeping the limit of ink duty.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a head that includes inks having different densities for at least one hue and that can form two or more types of dots having different ink amounts for each ink, and eject from the heads. The present invention relates to a printing apparatus, a printing method, and a recording medium capable of printing a multi-tone image with ink.

[0002]

2. Description of the Related Art Recently, as an output device of a computer,
Color printers of a type in which several colors of ink are ejected from a head have become widespread, and are widely used for printing images processed by computers and the like in multiple colors and multiple gradations. Regarding such a printing device, a printing device and a printing method using dark and light ink have been proposed for the purpose of further improving the printing quality in a region where the image density is low, that is, a so-called highlight portion (for example, Japanese Patent Application No. 8- 209232). This prepares high density ink and low density ink for the same color,
By controlling the ejection of both inks, it is intended to realize printing excellent in gradation expression.

Further, as another means for expressing multi-gradation, it is possible to print by changing the density per unit area in multiple steps by forming two types of dots having different ink density and ink amount. A printing device has also been proposed (for example, Japanese Patent Laid-Open No. 59-201864). This is 1 pixel 4
It is possible to print an image with multi-stage density by forming dots and changing the frequency of appearance of high density dots and low density dots in pixels.

On the other hand, in a printer that ejects ink to form dots, the amount of ink per unit area, that is, the ink duty, is controlled so as not to exceed a predetermined value according to the printing paper. If the ink is ejected in excess of this value, the paper is likely to be torn, and bleeding occurs, which deteriorates the image quality of the printed image.

[0005]

However, in a printing apparatus capable of forming two types of dots having different ink densities and ink amounts, no consideration has been given to the ink duty. In the first place, in such a printing device,
The two are only formed in a predetermined pattern according to the gradation of the input pixel, and no consideration has been given to how to deal with the limitation of the ink duty. Further, no consideration has been given to controlling the amount of ink used for dot formation as a whole, such as dealing with not only the ink duty but also how to use inks having different densities in a well-balanced manner.

The present invention has been made in view of the above problems, and in a printing apparatus, when it is necessary to control the amount of ink used for dot formation, for example, when the ink duty is limited, the ink density is reduced. It is another object of the present invention to provide a technique for effectively utilizing two or more types of dots having different ink amounts.

[0007]

Means for Solving the Problems and Their Actions / Effects In order to solve at least some of the above problems, the present invention employs the following means. The printing apparatus of the present invention is a printing apparatus capable of printing an image by forming a plurality of dots on a printing medium, and at least one input unit for inputting image data for each pixel forming the image. Heads that are provided with two or more types of inks having different densities for the respective hues and that can form two or more types of dots having different ink amounts for the respective inks, and for the inks with different densities, each pixel based on the image data For the ink amount expectation value setting means for setting the expectation value of the ink amount used for forming the dot for each and the ink having the different density,
Multi-value quantization means for selecting which of the two or more types of dots should be formed, including non-formation of dots, based on the expected value of the set ink amount, and performing multi-value conversion; The gist is to provide a dot forming means for forming the selected dot.

In the printing method of the present invention, printing is performed by using a head having two or more kinds of inks having different densities for at least one hue and capable of forming two or more kinds of dots having different ink amounts for each ink. A printing method for printing an image by forming a plurality of dots on a medium, wherein image data is input for each pixel that constitutes the image, and for inks having different densities, based on the image data, An expected value of the amount of ink used for dot formation is set for each pixel, and at least for inks having different densities, whichever of the two or more types of dots is selected based on the set expected value of the amount of ink. The gist is to perform multi-valued selection by selecting whether or not to form dots, including formation of dots, and to form the selected dots.

In such a printing apparatus and printing method, with respect to two or more kinds of ink having different densities provided for at least one hue, first, an expected value of the amount of ink used for dot formation is set for each pixel, and then, Select the type of dots to be formed. By adopting such means, it is possible to appropriately control the amount of ink used for dot formation.

Here, the expected value of the ink amount means an ideal ink amount ejected to each pixel in order to express the gradation value of the image data. The amount of ink that the head of the printing apparatus of the invention can provide for dot formation is actually limited to a predetermined number of types, but the expected value of the amount of ink is not limited to such a number and is not limited to a predetermined value. It can take continuous values within the range. Generally, the expected value is used as a term indicating the probability, but in the present specification, it does not have such a meaning, and is used as a term meaning a value expected to be ejected to each pixel.

As the expected value of the ink amount, it is not necessary to use the strict ink amount necessary for expressing the gradation value of the image data, but the characteristics of the dot forming means for actually ejecting ink, etc. Can be determined in consideration of the factors. The expected value of the ink amount may be set larger or smaller than the strict amount of ink required to express the gradation value. Of course, for a certain gradation value, the expected value of the ink amount may be set to be large, and another gradation value may be set to be small.

In the above printing apparatus, the image data is data including a gradation value for at least one color component in a color space, and the expected ink amount value setting means sets the expected value of the ink amount to the expected value. By referring to the expected value storage means stored as a table corresponding to the combination of gradation values of a plurality of color components in the color space, and the table stored in the expected value storage means based on the input image data, Means for setting the expected value of the ink amount for each pixel.

The expected value of the amount of ink ejected for each pixel can be determined according to the combination of the gradation values of a plurality of color components in the color space. According to the above means, it is possible to set the expected value of the ink amount for each pixel based on the table thus determined.

Further, in the above printing apparatus, the table stored in the expected value storage means has the same expected value of each ink regardless of whether the hue is the same as the expected value of each ink. It is desirable to use a table that stores the values determined in association with the expected values of the ink amounts of other colors in association with the combinations of gradation values of a plurality of color components in the color space.

In the table stored in the expected value storage means, the expected value of the ink amount of each color is determined in association with the expected values of the ink amounts of other colors, thereby controlling the total ink amount, The image quality can be improved. For example, consider a case where the amount of ink ejected per unit area has an upper limit value. In the case where the printing apparatus prints a predetermined density using two kinds of dark and light inks for cyan, when the expected value of the ink amount of other hues is small, there is a margin with respect to the upper limit value, so that cyan Can be set to use a large amount of light ink in which dots are relatively inconspicuous. On the other hand, when the amount of ink of other hues is large, there is no room for the predetermined amount, so it is possible to use a relatively small amount of dark ink having a high density for cyan.

In the above printing apparatus, various methods can be adopted as the multivalued means, and the dither method or the error diffusion method may be used.

When the types of dots that can be formed by the printing device are limited, the previously set expected value of the ink amount and the ink amount actually used for dot formation do not always match. Therefore, there is an error in the ink amount for each pixel. According to the printing apparatus including each of the above units, even if an error occurs in each pixel, it is possible to perform multi-value quantization for the entire image so that the error becomes small. Further, according to the above-mentioned dither method, multi-value quantization can be executed at high speed, and according to the error diffusion method, an error can be appropriately suppressed and a good image quality can be obtained.

Further, the multi-value forming means is a type which is an expected value of the ink amount for each type of dots that can be formed by the head, based on the expected value of the ink amount determined by the expected ink amount value determining means. Also as a multi-valued means having type-specific expected value setting means for setting different expected values and means for judging the presence or absence of dot formation for each dot type based on the set type-specific expected value Good.

With such means, the expected value of the ink amount is set for each type of dot, and the generation is controlled for each type of dot so that the error is eliminated in the entire image. Are relatively uniformly distributed in the image. In general, dots having a large amount of ink are more noticeable, and therefore, when such dots are locally formed, the image quality is greatly impaired. According to the above means, the dots having a large amount of ink are evenly distributed, so that a good image quality in which the dots are not conspicuous can be obtained.

In the printing apparatus, two or more types of dots formed by the head for the same hue have approximately the same average density per unit area when dots are formed with at least one recording density. It is desirable to include two or more types of dots.

When there are two or more types of dots having the same average density per unit area, there is a degree of freedom that any dot can be used in the density for recording an image using these dots. . As a result,
While controlling the ink amount, it is possible to properly use the both according to various conditions such as improvement of image quality. Note that generally, the relationship between the average density per unit area and the recording density of dots differs depending on the type of dot. In order to obtain the above-described effect in the present invention, it is sufficient that there is at least one density such that the average density is approximately the same when two or more types of dots are formed with the same density and compared.

In each of the printing apparatuses described above, the ink amount expectation value setting means calculates the total amount of ink used for forming dots per unit area, regardless of whether the hue is the same or not. It can be a means for setting the expected value of the ink amount within a range not exceeding a predetermined amount determined according to the print medium.

According to such a printing apparatus, it is possible to control so that the total amount of ink supplied per unit area does not exceed a predetermined amount determined according to the printing medium. Generally, there is an upper limit to the amount of ink that can be absorbed by the print medium, and if printing is performed with an ink amount that exceeds the upper limit, the print medium is prone to tearing, and bleeding may occur, thus impairing image quality. In the printing apparatus described above, the ink amount can be controlled so as not to exceed the upper limit, and thus various problems can be avoided.

It should be noted that the predetermined amount determined according to the print medium includes various factors such as the bleeding characteristic of the print medium, the drying time of the ink, the image quality of the printed image, and the deformation of the print medium due to the absorption of the ink. It is the ink amount that is set as a preferable value after the determination. Naturally, such a predetermined amount is not uniquely determined by the print medium, and has a different value depending on the printing speed, the color of the ink used for printing, and the like. By considering such an upper limit, the expected value of the ink amount is set to a value different from the ideal value that should be set from the viewpoint of obtaining good image quality when there is no limitation on the ink amount. . From this viewpoint, as an aspect in which the expected value of the ink amount is set in consideration of the predetermined amount,
For example, when the print medium is a so-called plain paper, and when the special paper manufactured for the purpose of high-quality printing has a low ink penetration amount, the expected value of the ink amount corresponding to the image of the same gradation value is changed. There are cases.

The predetermined amount is the total amount of ink supplied per unit area, and may locally exceed the predetermined amount. For example, even if the specific pixel exceeds the predetermined amount, the amount of ink ejected in the vicinity thereof is small, and the expected value of the ink amount is set so as not to exceed the predetermined amount as a whole. I wish I had it.

In the above printing apparatus, a head capable of forming inks having different densities or inks having different ink amounts is used as ink particles due to the pressure applied to the inks by applying a voltage to the electrostrictive element provided in the ink passage. A mechanism for discharging is conceivable. In addition, a mechanism for ejecting ink particles by the pressure applied to the ink in the ink passage by bubbles generated by energization of the heating element provided in the ink passage forms dots with ink having different densities, It is also possible to form dots of different amounts. According to these configurations, it is easy to make the ink particles fine and to control the amount of the ink appropriately, and it is also easy to prepare a large number of ejection nozzles on the head. When providing a large number of nozzles,
A plurality of nozzles for ejecting ink particles can be arranged for each color and each density of ink along the transport direction of the paper to be printed. By preparing a plurality of nozzles, it is possible to contribute to the improvement of printing speed.

Since the printing apparatus of the present invention described above can be configured by implementing a part of the functions thereof by a computer, the present invention takes an aspect as a recording medium recording such a program. You can also

A first recording medium of the present invention is a recording medium in which a program for printing an image by forming a plurality of dots on a printing medium is recorded so that it can be read by a computer, and at least one hue For the inks with different densities prepared for the function to set the expected value of the ink amount used for dot formation for each pixel based on the image data, and for the inks with different densities, the expected ink amount set Based on the value, a function of selecting which of the two or more types of dots should be formed including non-formation of dots and performing multi-valued, and a function of forming the selected dots are provided. It is a recording medium recording a program to be realized by a computer.

A second recording medium of the present invention is a recording medium in which data used for printing an image by forming a plurality of dots on a printing medium is recorded so that it can be read by a computer, and at least For inks with different densities prepared for one hue, the total amount of ink used to form dots per unit area, regardless of whether or not the hues are the same, is a predetermined amount that is determined according to the print medium. A storage medium in which data related to expected values of ink amounts used to form dots for each pixel, which is determined within a range that does not exceed, is recorded in association with gradation value combinations of a plurality of color components in a color space. Is.

By executing the program recorded on the first recording medium on the computer, the printing apparatus of the present invention described above can be realized. Further, when such a program is prepared separately, the printing device of the present invention can be realized by the computer using the data recorded in the second recording medium.

As a storage medium, a flexible disk, a CD-ROM, a magneto-optical disk, an IC card,
Various computer-readable media such as a ROM cartridge, a punched card, a printed matter on which codes such as a bar code are printed, an internal storage device (memory such as RAM and ROM) of the computer, and an external storage device can be used. Further, it also includes an aspect as a program supply device for supplying a computer program, which causes a computer to realize the functions of the steps or means of the invention described above, via a communication path.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on Examples. (1) Apparatus Configuration FIG. 2 shows a schematic structure of the printer 22 of the present invention, and FIG. 1 shows the configuration of a color image processing system as a system example using the printer 22 of the present invention. In order to clarify the function of the printer 22, first, an outline of the color image processing system will be described with reference to FIG. This color image processing system includes a scanner 12, a personal computer 90,
It has a color printer 22. The personal computer 90 includes a color display 21 and a keyboard,
An input unit 92 including a mouse or the like is provided. Scanner 1
Reference numeral 2 reads color image data from a color original and supplies original color image data ORG composed of three color components of red (R), green (G) and blue (B) to the computer 90.

Inside the computer 90, a CPU, a RAM, a ROM and the like (not shown) are provided, and 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 the final color image data F is sent from the application program 95 via these drivers.
NL will be output. An application program 95 for retouching an image reads the image from the scanner 12, performs a predetermined process on the image, and displays the image on the CRT display 21 via the video driver 91. When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives the image information from the application program 95, and the printer 22 prints the signal FNL (here, cyan, light cyan, magenta, and light magenta). , Binarized signals for six colors of yellow, black, and black). In the example shown in FIG. 1, inside the printer driver 96, a rasterizer 97 for converting color image data handled by the application program 95 into image data in dot units (hereinafter referred to as pixels), and image data in dot units In contrast, the expected ink amount value setting module 98 and the expected ink amount value setting module 98 for setting the expected ink ejection amount for each color in consideration of the characteristics of the ink colors and the colors used by the printer 22 are referred to. Expected value table CT
And a halftone module 99 for generating so-called halftone image information that expresses the density in a certain area depending on the presence or absence of dot formation for each pixel based on the expected value of the set ink amount. . Printer 2
Reference numeral 2 receives the printable signal FNL and records image information on a recording sheet.

Next, the schematic configuration of the printer 22 will be described with reference to FIG. As shown in the figure, the printer 22 includes a mechanism for conveying the paper P by a paper feed motor 23 and a carriage motor 24 for moving the carriage 31 to the platen 2.
6, a mechanism that reciprocates in the axial direction, a mechanism that drives the print head 28 mounted on the carriage 31 to control ink ejection and dot formation, and the paper feed motor 2
3, a carriage motor 24, a print head 28, and a control circuit 40 that controls the exchange of signals with the operation panel 32.

On the carriage 31 of the printer 22,
Cartridge 71 for black ink (Bk) and cyan (C
1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y) six color ink cartridges 72 can be mounted. For two colors, cyan and magenta, two kinds of light and shade ink are provided. The density of these inks will be described later. A total of six ink ejection heads 61 to 66 are formed on the print head 28 below the carriage 31, and at the bottom of the carriage 31,
An introduction pipe 67 (see FIG. 3) that guides the ink from the ink tank is erected on the head for each color. Carriage 3
When the black (Bk) ink cartridge 71 and the color ink cartridge 72 are mounted from above, the introduction tube 67 is inserted into the connection hole provided in each cartridge, and each ink cartridge transfers to the ejection heads 61 to 66. It is possible to supply the ink.

A mechanism for ejecting ink will be briefly described. FIG. 3 is an explanatory diagram showing a schematic configuration of the inside of the ink ejection 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 tube 67 by using the capillary phenomenon as shown in FIG. The print heads 28 are led to the respective color heads 61 to 66. It should be noted that when the ink cartridge is mounted for the first time, the operation of sucking the ink to the heads 61 to 66 of the respective colors is performed by a dedicated pump, but in the present embodiment, the suction pump and the cap that covers the print head 28 at the time of suction are used. Illustration and description of the configuration and the like are omitted.

As will be described later, the heads 61 to 66 for each color are provided with 32 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 arranged. FIG. 4 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown, the piezo element PE is
It is installed at a position in contact with an ink passage 68 that guides ink to the nozzle Nz. As is well known, the piezo element PE is an element which has a crystal structure which is distorted by application of a voltage and which converts electric-mechanical energy at extremely high speed. In this 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 extends for the voltage application time as shown in the lower part of FIG. One side wall of 68 is deformed. As a result, the volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE,
Ink corresponding to this contraction becomes particles Ip and is ejected at high speed from the tip of the nozzle Nz. Printing is performed by impregnating the paper particles P mounted on the platen 26 with the ink particles Ip.

In the printer 22 having the hardware configuration described above, the platen 26 and other rollers are rotated by the paper feed motor 23 to convey the paper P (hereinafter referred to as sub-scanning), while the carriage 31 is moved to the carriage motor 24.
And reciprocating (hereinafter referred to as main scanning) by the piezo element P of each color head 61 to 66 of the print head 28.
By driving E, each color ink is ejected to form dots to form a multicolor image on the paper P.

The mechanism for conveying the paper P is the paper feed motor 2
A gear train for transmitting the rotation of 3 to the sheet conveying rollers as well as the platen 26 is provided (not shown). Further, the mechanism for reciprocating the carriage 31 is such that an endless drive belt 36 is stretched between a carriage shaft 24 and a slide shaft 34 that is installed in parallel with the shaft of the platen 26 and slidably holds the carriage 31. Pulley 38 and carriage 31
The position detection sensor 39 for detecting the origin position of

5 and 6 show the ink discharge head 6
It is explanatory drawing which shows the arrangement of the inkjet nozzle Nz in 1-66. The printer 22 of this embodiment can form three types of dots having different ink amounts for each color. If the dots are formed in a circle, then
Dots having different dot diameters are formed. Hereinafter, in this sense, “dots having different ink amounts” and “dots having different dot diameters” are used synonymously.

In order to form dots having different dot diameters, for example, as shown in FIG. 5, a method of providing nozzles having different diameters for each color can be considered, but in this embodiment, as shown in FIG. 6, all are the same. By using nozzles having different diameters, dots having different dot diameters are formed by the control described later. The arrangement of these nozzles is such that ink is ejected for each color.
It consists of a set of nozzle arrays and has 32 nozzles Nz.
Are arranged in a staggered pattern with a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. 32 nozzles N included in each nozzle array
The zs do not have to be arranged in a staggered pattern and may be arranged in a straight line. However, the staggered arrangement as shown in FIG. 6 has an advantage that the nozzle pitch k can be easily set small in manufacturing.

Here, the principle of forming three types of dots having different dot diameters using a head having a constant nozzle diameter will be described. FIG. 7 is an explanatory diagram showing the relationship between the drive waveform of the nozzle Nz and the ejected ink Ip when ejecting the ink. The drive waveform shown by the broken line in FIG. 7 is a waveform when a normal dot is ejected. Section d2
In FIG. 7, once a negative voltage is applied to the piezo element PE, the piezo element PE deforms in the direction of increasing the cross-sectional area of the ink passage 68, which is opposite to the case described above with reference to FIG. As shown in the state A, the ink interface Me called a meniscus is in a state of being dented inside the nozzle Nz. On the other hand, using the drive waveform shown by the solid line in FIG.
When the negative voltage is rapidly applied as shown in the section d2, the meniscus is indented largely 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 from the state in which the meniscus is not recessed inward (state A) as shown in states B and C, and the state b is changed from state in which the meniscus is largely indented (state a) to state b. Small ink droplets are ejected as shown in state c.

As described above, the dot diameter can be changed according to the change rate when the drive voltage is made negative (sections d1 and d2). In this embodiment, based on such a relationship between the drive waveform and the dot diameter, the drive waveform for forming a small dot having a small dot diameter and the medium dot having the second dot diameter are formed. Drive waveform for 2
There are different types available. FIG. 8 shows drive waveforms used in this embodiment. The drive waveform W1 is a waveform for forming a small dot, and the drive waveform W2 is a waveform for forming a medium dot. By using both of them properly, it is possible to form two types of dots having small and medium dot diameters from the nozzle Nz having a constant nozzle diameter.

Large dots can be formed by forming dots using both the drive waveforms W1 and W2 shown in FIG. This state is shown in the lower part of FIG. Figure 8
The lower diagram shows the paper P after the small and medium dot ink droplets IPs and IPm ejected from the nozzles.
It shows the state up to. When two types of dots, small and medium, are formed using the drive waveform of FIG. 8, the medium dot has a larger change amount of the piezo element PE, and therefore the ink droplet IP is ejected vigorously. Due to such a difference in the flight speed of ink, when the small dots are first ejected and then the medium dots are ejected while the carriage 31 moves in the main scanning direction, the scanning speed of the carriage 31 and the ejection of both dots are performed. If the timing is adjusted according to the distance between the carriage 31 and the paper P, both ink droplets can reach the paper P at the same timing. In this embodiment, the large dot having the largest dot diameter is thus formed from the two types of drive waveforms shown in FIG.

The internal structure of the control circuit 40 of the printer 22 will be described, and a method of driving the head 28 composed of the plurality of nozzles Nz shown in FIG. 6 will be described using the above-mentioned drive waveforms. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, this control circuit 40
Inside the CPU, a CPU 41, a PROM 42, a RAM 43, and a PC for exchanging data with the computer 90.
A peripheral input / output unit (PIO) 45 that exchanges signals with the interface 44, the paper feed motor 23, the carriage motor 24, the operation panel 32, and the like, a timer 46 that measures time, and dots on / off of the heads 61 to 66. There is provided a transfer buffer 47 for outputting the signal, and these elements and circuits are mutually connected by a bus 48. The control circuit 40 is also provided with an oscillator 51 that outputs a drive waveform (see FIG. 8) at a predetermined frequency, and a distributor 55 that distributes the output from the oscillator 51 to the heads 61 to 66 at a predetermined timing. ing. Control circuit 40
Receives dot data processed by the computer 90, temporarily stores the dot data in the RAM 43, and outputs the dot data to the transfer buffer 47 at a predetermined timing. Therefore, the image processing for forming a multi-tone image is not performed on the printer 22 side. The control circuit 40 simply controls on / off in dot units, that is, only controls whether or not to form dots.

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. As shown, the head 6
One of the nozzle rows 1 to 66 is provided in a circuit in which the transfer buffer 47 is on the source side and the distribution output device 55 is on the sink side. Each piezo element PE forming the nozzle row
Of the electrodes is connected to each output terminal of the transfer buffer 47, and the other is collectively connected to the output terminal of the distribution output device 55. From the distribution output device 55 to the transmitter 51
Since the CPU 41 determines ON / OFF for each nozzle and outputs a signal to each terminal of the transfer buffer 47, an ON signal is output from the transfer buffer 47 side according to the drive waveform. The piezo element P that I received
Only E is driven. As a result, the ink particles Ip are ejected all at once from the nozzles of the piezo element PE that have received the ON signal from the transfer buffer 47.

As shown in FIG. 8, the driving waveform is such that the small dot waveform W1 and the medium dot n waveform W2 are alternately output. Therefore, when it is desired to form a small dot for a certain pixel, the small dot is formed. The ON signal is sent to the nozzle row in synchronization with the drive waveform W1 for medium
It is sufficient to send an OFF signal to the nozzle row in synchronization with 2. When forming a medium dot, on the contrary, an OFF signal may be sent to the nozzle row in synchronization with the drive waveform W1 and an ON signal may be sent to the nozzle row in synchronization with the drive waveform W2. When forming a large dot, an ON signal may be sent in synchronization with both drive waveforms. By doing so, the printer 22 of the present embodiment can form dots with large, medium, and small dot diameters during one main scan with each nozzle array.

However, three kinds of drive waveforms for forming large, medium, and small dots and three oscillators for outputting the respective drive waveforms are prepared, and the drive waveforms are selectively selected according to the dot diameter to be formed. By using
You may make it form the dot which consists of each diameter. Further, the dot diameters need not be limited to the three types of large, medium and small, and the number of types of drive waveforms may be increased so that more dot diameters can be output. You may use only a kind.

As shown in FIG. 6, since the heads 61 to 66 are arranged along the carrying direction of the carriage 31,
The timings at which the respective nozzle rows reach the same position on the paper P are deviated. Therefore, the CPU 41 outputs the ON / OFF signal of each dot via the transfer buffer 47 at a required timing after considering the positional deviation of each nozzle of the heads 61 to 66, and outputs the dot of each color. Is forming. In addition, as shown in FIG.
Similarly, the output of the ON / OFF signal is controlled in consideration of the fact that 66 also has the nozzles formed in two rows.

In the present embodiment, large, medium and small dots (hereinafter referred to as light large dot
The density is divided into 6 levels: light medium dot and light small dot) and large, medium and small dots formed with high density dark ink (henceforth, dark large dot, dark medium dot and dark small dot). It uses different dots. On the other hand, for example, a person who sets the dark small dots and the light large dots to have substantially the same density may be used. When the two densities are substantially the same, it means that the average densities per unit area when the two are recorded at a certain recording density are substantially the same. With this setting, the number of gradations that can be expressed for each pixel is reduced, but the degree of freedom in selecting dark small dots and light large dots can be increased.

In the present embodiment, as described above, the printer 22 having the head for ejecting ink using the piezo element PE is used, but a printer for ejecting ink by another method may be used. For example, it may be applied to a printer of a type that energizes a heater arranged in the ink passage and ejects ink by bubbles generated in the ink passage. In such a printer, since the dots having different dot diameters can be formed by changing the energization time and the energization area of the heater, the present invention can be applied.

(2) Dot Generation Processing Routine Next, the dot generation processing routine in the embodiment according to the present invention will be described. FIG. 11 shows the flow of the dot generation processing routine according to the first embodiment. This routine is a part of the processing in the halftone module 99 of the printer driver 96, and is a routine executed by the CPU of the computer 90 in this embodiment.

When the dot generation processing routine is executed,
The CPU inputs pixel gradation data (step S10).
0). The data input here is image data composed of RGB after converting a color image into image data in dot units. In this embodiment, the pixel gradation data is 8
It is given in bits and has a gradation value range of 0 to 255 for each hue.

Next, the CPU executes the processing for determining the expected value of the ink amount to be ejected for the six color inks provided in the printer 22 (step S200). The expected value of the ink amount is set so that the color corresponding to the input image data is printed. At this time, the expected value of the ink amount of each color is determined so that the total of the ink amounts of all six colors does not exceed the ejectable ink amount per unit area of the printing paper (hereinafter referred to as ink duty). For cyan and magenta provided with two types of dark and light inks, how much each dark and light ink is used is set in order to express the density given as image data. Since various processing contents are possible for this processing,
The case will be described later separately.

When the expected value of the amount of ink to be ejected for each color is determined by the processing of step S200, the CPU
Performs processing for setting the diameter of the dot to be formed based on the expected value of the ink amount (step S300).
Since various kinds of processing contents can be considered for this processing as well, a case will be separately described below.

According to the above processing, the ink amount of each color is determined according to the input image data while the ink duty limit is being observed, and the dot diameter is determined within a range not exceeding the ink amount. As a result, in the image to be printed, the ink duty limit is always observed.

(3) Expected ink amount determination process for each color Various types of processes are conceivable for the process for setting the expected value of the ink amount ejected per unit area while keeping the ink duty limit for each color. . In the following, as an example of this processing, processing of three modes will be sequentially described.

First, the expected ejection amount of ink of each color as the first mode will be described with reference to the flowchart of FIG. When this routine is started, the CPU refers to the expected value table IT for each color,
The expected value of the ejected ink amount is determined (step S21).
0). Here, what is called each color means the color of each ink, and does not mean the hue. That is,
In this routine, the cyan ink and the light cyan ink are separately processed, and the expected values of the ink amounts are set respectively.

Here, the expected value table IT will be described. 13 and 14 show examples of expected value tables in this embodiment. FIG. 13 is a table which gives expected values of cyan ink according to the red and green gradation values of the input pixel gradation data. FIG. 14 is a table which gives expected values of light cyan ink in the same format. For convenience of illustration, the blue data is shown for a certain value and a constant value. Actually, there are 256 points in the graph of FIG. 13 according to the change in blue. Note that FIG.
14 and FIG. 14, the data corresponding to all combinations (256 × 256 × 256 points) of gradation values of blue, red and green are actually stored in the form of a table in the computer 90. It is stored in ROM. The expected values of the inks shown in FIGS. 13 and 14 are not limited to the cyan ink and the light cyan ink, but also the expected values of the magenta ink and other inks are taken into consideration. It is set not to exceed. Tables similar to those in FIGS. 13 and 14 are set for the other inks.

In step S210, the CPU sets the expected value of the ink ejection amount by reading the value corresponding to the image data from each table. After performing this processing for all colors (step S215), the process returns from the discharge ink amount expected value determination processing routine to the dot generation processing routine.

According to the expected value of the ejected ink amount, the expected value data of the ejected ink amount is stored in the form of a table according to all the combinations of the gradation data, so that the processing content is very simple. Therefore, there is an advantage that processing can be performed at high speed. In addition, there is an advantage that even if the expected value data of the ink ejection amount is very non-linear data, it can be easily applied.

In the above description, it is explained that the processing for determining the expected value of the ejected ink amount for each color is once ended when the processing is completed for each pixel. However, while storing the results for each pixel in the memory, each raster or The iterative process may be performed on the entire image.

In the above description, the processing is performed for each color, but a table prepared for each color is not used, but a set of expected values of the ink amount of each ink is set corresponding to the input data. It is also possible to set all the ink amounts at once by using the table stored as above.

Next, the ejection amount expected value determination process for each color as the second mode will be described with reference to the flowchart of FIG. This mode is a method of determining the expected value of the ink ejection amount by reducing the number of data points in the expected value table IT shown in FIGS. 13 and 14 and performing an interpolation operation as appropriate. That is, in the second mode, the expected value table IT (FIGS. 13 and 1) that gives the expected value of the ink ejection amount.
4) is a table that does not store data for all combinations of blue, red, and green, but stores data only for specific grid points.

When the discharged ink amount expected value determination processing routine is started, the CPU selects a grid in which pixel gradation data exists (step S220). In the second mode, since the expected value table IT exists only for a specific grid point, there may be no expected value data of the corresponding ink ejection amount depending on the pixel gradation data. The CPU selects which lattice the pixel gradation data belongs to in order to perform the interpolation calculation later.

The lattice will be specifically described with reference to FIG. FIG. 16 is an explanatory diagram showing grid points based on red and green data. For convenience of illustration, the case where blue has a certain value is shown. As already explained, the red and green data values are 0-255.
Up to 256 gradation values, and in the plane of FIG. 16 in which blue is fixed to a certain value, there are 256 × 256 pixel data represented by the combination of both. In the first mode, expected value data of the ink amount to be ejected for each of these points is stored.

On the other hand, in the second mode, as shown in FIG. 16, for red data and green data,
Assuming a grid obtained by equally dividing each gradation value from 0 to 255 into eight grids, expected value data of the ink ejection amount is stored only for grid points that are intersections. Therefore, for example, the gradation value 6
Although 3 and the like are values that can be taken as pixel data, the expected value table IT is in a state in which there is no corresponding data.

In this embodiment, as shown in FIG. 16, grid points exist for each gradation value 32. Gradation value 0 at this grid point
It is assumed that they are indicated by numbers 0, 1, 2, ... 8 in this order (hereinafter, this number is referred to as a grid point number). In the present embodiment, it is possible to determine which grid the pixel gradation data belongs to by dividing each value of the red data and the green data by 32 and rounding up after the decimal point. For example, for the gradation value 63, the result of the above-mentioned calculation is the value 2, so that it is determined that it exists in the grid between the grid point number 2 and the grid point number 3. Although the grid points are arranged at equal intervals in this embodiment, the grid points do not necessarily have to be arranged at equal intervals, and the red data and the green data do not need to be divided in the same division. . By the same method as selecting the grid for red and green, a grid for which pixel gradation data exists is selected for blue. By such processing, one rectangular parallelepiped in which the pixel gradation data exists is selected in the three-dimensional color space of blue, red, and green.

After the grid to which the pixel gradation data belongs is selected in this way, the interpolation calculation of the expected value data of the ink amount is performed using the grid points forming the grid (step S23).
0). There are eight grid points forming the grid. Various methods are well known as the operation for performing the so-called linear interpolation of the data of such eight grid points, and therefore detailed description thereof is omitted here.

The expected value of the ink amount to be ejected is obtained by interpolation calculation, this process is executed for all colors (step S235), and then the ejected ink amount expected value determination process routine returns to the dot generation process routine.

According to this mode, since the interpolation calculation is required, the processing speed is inferior to that of the first mode, but the data amount of the ink amount table IT is small and the memory amount is saved. There is an advantage that you can.

The process of setting the expected value of the ink amount is to give a set of data for each color such as cyan and light cyan based on a set of input data having three elements of blue, red and green. The processing is similar to the so-called color correction processing. Therefore, it is possible to apply various techniques used in the color correction processing in addition to the above-described two aspects. For example, in each of the above-described modes, the method of using the expected value table IT that stores the expected value data of the ink amount is used, but when the expected value data is represented as a function of the pixel gradation data, it takes such a method. The expected value of the ink amount may be obtained based on the function.

(4) Dot diameter setting process Various dot diameter setting processes for setting the diameter of the dot to be formed based on the expected value of the ink amount obtained by the ink amount expected value determination process described above. The following modes are possible. Hereinafter, three modes will be sequentially described as an example of the dot diameter setting process. It should be noted that each of the following aspects can be adopted independently of which aspect of the above-described processing is applied as the ink amount expected value determination processing. When the dot diameter can be continuously changed, it is possible to set the dot diameter so that the expected value of the set ink amount and the actually ejected ink amount match. Only a limited number of dot diameters can be formed. Therefore, for each pixel, an error occurs between the expected value of the set ink amount and the ejected ink amount. In this embodiment, the dot diameter to be formed for each pixel is selected by various processes described below so that such an error can be suppressed to be small in the entire printed image.

The first dot diameter setting process will be described with reference to the flowchart shown in FIG. Here, the case where the expected value of the ink amount of cyan ink is set to the value Cd will be described as an example.

When the dot diameter setting process is started, the CPU inputs expected ink amount value data Cd (step S30).
2). This data is the expected value data of the ink amount to be ejected per unit area, which is obtained in the previously-described expected ink amount value determination process.

Next, it is determined whether the expected ink amount value data Cd is smaller than the predetermined value Vs (step S).
304). The predetermined value Vs is a value indicating the ink amount assumed to be ejected by the dot having the smallest dot diameter (hereinafter referred to as small dot) (hereinafter referred to as small dot ink amount). If the expected ink amount value data Cd is smaller than the small dot ink amount Vs, it is determined whether or not a small dot is formed.
It is determined whether or not hs or more (step S30).
6). When it is smaller than the threshold value ths, it is determined that the small dots are not formed, and the dot diameter setting data Cd is set.
The value 0 is substituted for r (step S308). Threshold ths
If it is larger than that, it is determined that a small dot should be formed, and the value Vs corresponding to the small dot ink amount is substituted into the dot diameter setting data Cdr (step S310).

The predetermined value V used in step S304
s and the value Vs substituted for the dot diameter setting data Cdr
May use different values as long as they are values determined based on the amount of ink ejected to form small dots. For example, the value that is actually used to form a dot, that is, the value that is substituted into the dot diameter setting data Cdr, may be smaller than the value used as the determination reference in step S304. By doing so, even if the amount of ink actually ejected varies from nozzle to nozzle, it is possible to keep the ink duty limit.

Here, the threshold ths will be described. In this embodiment, the threshold value matrix of distributed dither is adopted for the setting of this threshold value. The idea of the threshold value in the dither method will be described later. In the present embodiment, especially 64 × 64
A systematic dither method was applied using a global matrix of degree (blue noise matrix). In this dither matrix, any 16 × 16 region inside the matrix of 64 × 64 has a threshold value (0
The threshold value is set so that there is no large bias in the appearance of (~ 255).

In step S306, since the expected ink amount value data Cd can take only values 0 to Vs,
The threshold value ths is obtained by normalizing the above-mentioned dither matrix in the range of values 0 to Vs. That is, each value th of the above-mentioned dither matrix is converted by using the following equation so that the threshold value ths matches this range. ths = th × Vs / 255

Here, the concept of the dither method will be described with reference to FIG. Here, Vs will be described as the value 64. As shown in FIG. 18, it is assumed that the expected ink amount value data is Vs or less in a region including certain 4 × 4 pixels. The threshold value ths in such a region is given by a table obtained by normalizing the dither matrix, and threshold values having values 0 to 64 appear as shown in FIG. By comparing this threshold value and expected ink amount value data for each pixel,
As shown in FIG. 18, it is determined whether the small dots are on or off. As described above, the dither matrix is set so that the threshold values appear evenly. Therefore, if small dots are turned on / off by such a method, there is an error between the expected value of the ink amount and the actually ejected ink amount for each pixel. This error is small.

When it is determined in step S304 that the expected ink amount Cd is larger than the small dot ink amount Vs, the next expected ink amount Cd is a dot having the second dot diameter (hereinafter referred to as medium dot). It is determined whether or not the amount Vm of ink that is supposed to be ejected due to the misuse is smaller (step S312). When it is smaller than the ink amount Vm, the expected ink amount value data Cd is equal to the predetermined threshold value t.
It is determined whether it is larger than hm (step S31
4) If it is smaller than the threshold value thm, it is determined that small dots are formed instead of medium dots, and the value Vs corresponding to the small dot ink amount is substituted into the dot diameter setting data Cdr (step S316). . If it is larger than the threshold value ths, it is determined that a medium dot should be formed, and the value Vm corresponding to the medium dot ink amount is substituted into the dot diameter setting data Cdr (step S318). When it is smaller than the threshold value thm, it does not mean that a medium dot is not formed,
The reason why small dots are formed is that if medium dots are not formed, an error with respect to the expected ink amount value Cd becomes large, which is not preferable.

The threshold value thm is determined by the dither matrix described above. In step S314, the expected ink amount value data takes values Vs to Vm. Therefore, by using the following equation for each value th of the dither matrix,
The threshold value thm is normalized to match this range. thm = thx (Vm-Vs) / 255 + Vs

If it is determined in step S312 that the expected ink amount Cd is larger than the medium dot ink amount Vm, it is determined whether the dot having the largest dot diameter (hereinafter referred to as large dot) is on or off. . It is determined whether the expected ink amount value data Cd is larger than a predetermined threshold value thl (step S320). If it is smaller than the threshold value thl, it is determined that a medium dot is formed instead of a large dot. The value Vm corresponding to the medium dot ink amount is assigned to the diameter setting data Cdr (step S32).
2). If it is larger than the threshold value thl, it is determined that a large dot should be formed, and the value Vl corresponding to the large dot ink amount is substituted into the dot diameter setting data Cdr (step S324).

The threshold value thl is determined by the dither matrix described above. In step S320, the expected ink amount value data Cd takes values Vm to Vl.
By using the following formula for each value th of the dither matrix, the threshold value thl is normalized so as to match this range. thm = th × (V1-Vm) / 255 + Vm

In this way, the dot diameter of the dots to be formed is set, including the presence or absence of dot formation. The CPU executes this process for all colors (step S32).
6), the dot diameter setting process is ended.

According to this aspect, it is possible to properly form the dots having the respective dot diameters according to the set expected value of the ink amount. As described above, by using the dither matrix, it is possible to avoid the occurrence of locally biased dots, and as a whole image, the ink amount ejected with respect to the expected value of the set ink amount The error can be kept small.

In the above description, the thresholds ths and th
Although sm and thl are set based on the dither matrix, these thresholds may be set by generating a random number for each pixel.

Next, the dot diameter setting process of the second mode will be described with reference to the flowchart of FIG. When the dot diameter setting process is started, the CPU inputs the expected ink amount value data Cd (step S340), adds the diffusion error from the neighboring pixels which have already been processed, and adds the correction data Cd.
x is created (step S342). In the second mode, the ink amount expected value C in which the actually ejected ink amount is set
As a process for approaching d, an error diffusion process is adopted as described later. In the error diffusion processing, since the error of the ink amount generated in the processed pixel is previously distributed to the pixels around the pixel by giving a predetermined weight, the corresponding error is read out in step S342, and this is read now. It is reflected in the pixel to be printed from. FIG. 20 illustrates how the peripheral pixels are weighted and how much the error is distributed with respect to the pixel PP of interest. With respect to the pixel PP of interest, several pixels in the scanning direction of the carriage 31 and several adjacent pixels on the rear side in the transport direction of the paper P have a predetermined density error (1 /
4, 1/8, 1/16) will be allocated. The error diffusion process will be described later in detail.

The CPU uses the correction data Cdx and a predetermined threshold value T
Comparison with h1 to Th3 is performed (step S344-
352). The predetermined threshold value has a relationship of Th1 <Th2 <Th3. If the correction data Cdx is smaller than the threshold Th1 (step S344), it is determined that dots are not formed, and the value 0 is substituted for the data Cdr for setting the dot diameter (step S346). Correction data Cdx
Is larger than the threshold value th1 and smaller than the threshold value th2 (step S348), it is determined that a small dot should be formed, and the value Vs is substituted for the dot diameter data Cdr (step S350). If the correction data Cdx is larger than the threshold value th2 and smaller than the threshold value th3 (step S35).
2) It is determined that a medium dot should be formed, and the value Vm is substituted for the dot diameter data Cdr (step S354). If the correction data Cdx is larger than the threshold value th3 (step S352), it is determined that a large dot should be formed, and the value Vl is substituted for the dot diameter data Cdr (step S356).

As described above, what kind of dots should be formed is set including the case where dots are not formed. Next, the CPU executes error calculation and error diffusion processing based on the setting (step S358). The error referred to here is an error between the correction data Cdx after the correction in step S342 and the actually ejected ink amount Cdr. The error is 0 in the correction data Cdx, for example.
Values up to 255 can be continuously taken, whereas the actually ejected ink amount Cdr is an error caused by being able to take only fixed discrete values. For example, if the ink amount Vl of a large dot is 255 and a large dot is formed even though the correction data Cdx has a value of 199, there is an ink amount error of 255-199 = 56. Is happening. This means that the ejected ink amount is too large as compared with the set ink amount. Since the ejected ink amount is given by Cdr, the error ERR is obtained by ERR = Cdx−Cdr.

The error diffusion is a process of diffusing the error thus obtained by adding a predetermined weight (see FIG. 20) to the pixels around the pixel PP currently being processed. Since the error should be diffused to the unprocessed pixels, it is diffused only to the pixels arranged in the scanning direction of the carriage and the conveying direction of the paper, as shown in FIG. If the error is 56 based on the above example, 14 corresponding to 1/4 of the error 56 is diffused to the pixel P1 adjacent to the pixel PP currently being processed. This error is reflected in step S342 when the pixel P1 is processed next. For example, if the data of the pixel P1 is the value 214,
The diffused error 14 is subtracted from this, and the correction data is set to the value 200. By repeating this process, although the ink amount error is included in each pixel, the image is printed with the ink amount corresponding to the set expected ink amount value data for the entire image.
By this processing, the dot diameter including the presence / absence of dot formation is set for all colors (step S36).
0), this routine is once ended.

If such a process is used, the process becomes complicated as compared with the first mode, but the process speed is inferior.
It is possible to reliably eliminate the error in the ink amount and obtain a better image. Note that the weight values shown in FIG. 20 are merely examples, and other weight values may be used.

Next, the dot diameter setting process according to the third mode will be described with reference to the flowchart of FIG.
In the third mode, similar to the second mode, the error diffusion method is used for processing. However, in the second mode, the dots having the respective diameters are integrally processed. In this mode, the dots having different diameters are individually processed.

When the dot diameter setting process is started, the CPU
Inputs expected ink amount data Cd (step S37).
0), the expected ink amount value for each dot diameter is set based on the data Cd (step S372). The expected ink amount for each dot diameter is determined based on a preset table.
An example of such a table is shown in FIG. FIG. 22 is a diagram in which the expected value of the ink amount of the dots having the respective dot diameters is replaced with the occurrence rate of each dot according to the expected ink amount value Cd. The expected value of the ink amount is obtained by multiplying the ink amount ejected to form each dot by the dot generation rate. If the expected ink amount Cd is relatively small, for example, in the section Cd1, it means that only small dots should be formed. Therefore, in the section Cd1, the expected values of the ink amounts for the medium dots and the large dots are both 0. In other sections (sections Cd2, Cd3, Cd4), similarly, the expected value of the ink amount corresponding to each dot diameter is set. The expected value of the ink amount for each of the small dot, the medium dot, and the large dot thus set is set to Cds,
Cdm and Cdl.

Next, the CPU adds the diffusion error from the neighboring pixels which have already been processed and adds the correction data Cdsx, Cd.
mx and Cdlx are created (step S374). Cd
sx, Cdmx, and Cdlx are results obtained by individually correcting the ink amounts Cds, Cdm, and Cdl of the small dot, the medium dot, and the large dot by the diffusion error. As described above, in the third mode, the processing is independently executed for each dot diameter.

Next, the CPU uses the correction data Cdsx, the error Errs for the small dots as the temporary setting value of the error, and the correction data Cdsx,
The correction data Cdm is included in the error Errm for the medium dot.
x, the correction data Cd for the error Errl for large dots
lx is substituted (step S376). This value is a value corresponding to the error when the dots having the respective dot diameters are not formed in the following processing.

After temporarily setting the error in this way, it is first determined whether or not the correction data Cdlx for the large dot is larger than a predetermined threshold value thr (step S378), and the threshold value thr.
If it is larger than the above, it is determined that a large dot should be formed, the value Vl is substituted for the dot diameter data Cdr, and the error Errl corresponding to the large dot is changed to the difference between the correction data Cdlx and the value Vl ( Step S380).

The correction data Cdlx for large dots is the threshold th.
When it is smaller than r, that is, when a large dot is not formed, the correction data Cdmx for the medium dot is the predetermined threshold value th.
It is determined whether it is larger than r (step S382),
When it is larger than the threshold value thr, it is determined that a medium dot should be formed, the value Vm is substituted for the dot diameter data Cdr, and the error Errm corresponding to the medium dot is changed to the difference between the correction data Cdmx and the value Vm. Yes (step S38
4).

The correction data Cdmx for medium dots is the threshold value th.
When it is smaller than r, that is, when the medium dot is not formed, the correction data Cdsx for the small dot is the predetermined threshold value th.
It is determined whether it is larger than r (step S386),
When it is larger than the threshold value thr, it is determined that a small dot should be formed, the value Vs is substituted for the dot diameter data Cdr, and the error Errs corresponding to the small dot is changed to the difference between the correction data Cdsx and the value Vs. Yes (step S38
8). If the correction data Cdsx for small dots is smaller than the threshold value thr, no dot is formed.

By the above processing, which dot should be formed including the presence or absence of dot formation is set.
In addition, the error was set according to the result. For the dots that are not formed, the error data temporarily set in step S376 remains.

Next, the CPU performs a process of diffusing this error (step S390). The weight used to diffuse the error is the same as the weight used in the second mode. In the third aspect, the error diffusion is also based on the error E corresponding to each dot diameter.
The diffusion process is executed independently for each of rrs, Errm, and Errl. The above processing is performed for all colors (step S392), and this routine is once ended.

According to this processing, as in the second mode,
The error can be appropriately eliminated in the entire image, and a good image can be obtained. In the third aspect, the second aspect is used for the following reason.
It is possible to obtain an image that is even better than that of the embodiment. That is, in the second aspect, since the dots having all the diameters are integrally subjected to the error diffusion processing, there is a possibility that the dots having the large dot diameter are locally biased. When such a deviation occurs in an ink having a particularly high density, the graininess is conspicuous and the image quality is deteriorated. On the other hand, in the third aspect, as a result of performing the error diffusion processing for each dot diameter, the dots having the respective dot diameters are dispersed and generated in the entire image, so that the above-mentioned bias is less likely to occur and it is preferable. The image can be obtained.

Based on the result of the dot generation processing routine described above, the CPU executes the processing for the printer 22 to form each dot. Since various processes are known for this process depending on the configuration of the printer 22, the description based on the flowchart is omitted here.
In the present embodiment, as described above, the large, medium, and small dots can be arbitrarily formed from the individual nozzles during one main scan of the carriage 31, so what dot diameter should be formed by the above-described processing? Even if it is set to, it can be realized relatively easily.

On the other hand, the above-described dot diameter setting process is performed at once by a printer that selectively uses three types of drive waveforms prepared for large, medium, and small dots, that is, a set of nozzle arrays. It can also be applied to a printer in which the possible dot diameter is constant. In such a printer, dots having different dot diameters are formed in a mixed manner by scanning applying a well-known overlap type dot recording method. An example of such scanning will be described below.

In FIG. 23, 6 × was obtained using a head having 6 nozzles.
A scanning example in which large and small dots are mixed in the area 6 will be schematically shown. In FIG. 23, the left side shows the state of ink ejection corresponding to the number of head scans, and the right side shows the state of dots formed. The number attached to each dot corresponds to the scanning order of the head. As shown in FIG. 23, in the first main scanning, large dots are formed every other dot in the main scanning direction using the nozzles in the lower half of the head. Next, after the paper is conveyed by 3 dots in the sub scanning direction, small dots are formed every other dot in the main scanning direction by using all the nozzles. Then, after the paper is further conveyed by 3 dots in the sub-scanning direction, large dots are formed by using the upper half nozzles. According to this aspect, by printing each raster by scanning twice, large and small dots can be mixed and printed at the same ratio.

According to the printing apparatus described above, the expected ink amount of each color is determined according to the input image data while the ink duty limit is being observed, and the ejected ink amount is expected. Since the dot diameter is determined within a range that does not exceed the value, it is possible to properly use various dots having different densities and dot diameters under the condition that the ink duty limit is always observed. Further, there is also an advantage that the best image quality can be obtained for the following reasons.

Dots having different dot diameters can express multi-gradation, make the granularity of dots inconspicuous,
It is properly used so as to prevent dot formation unevenness due to mechanical manufacturing error of the head of the printer 22, that is, banding. For example, when dots with a large dot diameter are locally concentrated in high-density ink, the graininess becomes very noticeable, so dots with a small dot diameter should be selected to prevent such a situation. It is used in a proper mixture. Such a formation pattern for dots having different dot diameters may be a preferable pattern for each color, and it is not necessary to consider the influence of other colors or dot diameters.

If the dot diameter is not set under the condition that the ink duty limit is satisfied in advance, the dot may not be formed in a preferable pattern as a result due to the ink duty limit. According to the printing apparatus using the above-described means, it is possible to form dots having various dot diameters for each color in a preferable pattern based on the expected value of the ink ejection amount that is determined so as to keep the ink duty limit. Therefore, a good image can be formed.

Furthermore, the above-mentioned means also have the following advantages. When an attempt is made to increase the number of types of dots having different densities per unit area for a certain hue, there are a method of increasing the density of ink in multiple stages and a method of increasing the dot diameters. Generally, it is difficult to increase the type of ink density because it is necessary to newly install an ink cartridge and head, but it is relatively easy to change the dot diameter to another type by increasing the type of drive waveform described above. Can be realized. When the number of dot diameters is increased to achieve more gradations, the above-described means allows the ink ejection amount determined by the correlation with other colors to be used as it is, and can be processed independently with each color ink. This can be dealt with by slightly changing the dot diameter selection process. Therefore, the above-mentioned means has the advantage that it is advantageous in terms of the development of further increasing the gradation expression of the once designed printing device.

Further, since the printing apparatus includes processing by the computer, it is possible to adopt an embodiment as a recording medium recording a program for realizing each function described above. Examples of such a storage medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which codes such as a bar code are printed, and an internal storage device (RAM, ROM, etc.) of a computer. Various computer-readable media, such as memory) and external storage, are available. Further, an aspect as a program supply device for supplying a computer program that causes a computer to realize the functions of the respective steps or means of the above-described invention through a communication path is also possible.

Although various embodiments of the present invention have been described above, the present invention is not limited to these, and various embodiments can be implemented without departing from the scope of the invention. For example, although the various processes described above are executed by the computer 90, the printer 22 may be provided with the function of executing such processes and may be executed by the printer 22 side.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image processing system using a printer of the present invention.

FIG. 2 is a schematic configuration diagram of a printer of the present invention.

FIG. 3 is an explanatory diagram showing a schematic configuration of a dot recording head of the printer of the present invention.

FIG. 4 is an explanatory diagram showing a dot formation principle in the printer of the present invention.

FIG. 5 is an explanatory diagram illustrating an example of nozzle arrangement in a printer.

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

FIG. 7 is an explanatory diagram showing the principle of forming dots having different dot diameters according to the present invention.

FIG. 8 is an explanatory diagram showing drive waveforms of nozzles and dots formed by the drive waveforms in the printer 22 of the present invention.

FIG. 9 is an explanatory diagram illustrating an internal configuration of the printer 22.

FIG. 10 is an explanatory diagram showing a drive circuit configuration of a head.

FIG. 11 is a flowchart showing the flow of a dot generation processing routine.

FIG. 12 is a flowchart showing a flow in a first mode of a discharge ink amount determination processing routine for each color.

FIG. 13 is an explanatory diagram showing a cyan ink amount table.

FIG. 14 is an explanatory diagram showing a light cyan ink amount table.

FIG. 15 is a flowchart showing a flow in a second mode of a discharge ink amount determination processing routine for each color.

FIG. 16 is an explanatory diagram showing a state of a grid of the ink amount table in the second mode.

FIG. 17 is a flowchart showing a flow in a first mode of a dot diameter setting processing routine.

FIG. 18 shows dot on / off using a dither matrix.
It is explanatory drawing which shows the method of OFF determination.

FIG. 19 is a flowchart showing a flow in a second mode of a dot diameter setting processing routine.

FIG. 20 is an explanatory diagram showing weighting factors in error diffusion processing.

FIG. 21 is a flowchart showing a flow in a third mode of a dot diameter setting processing routine.

FIG. 22 is an explanatory diagram showing a table that gives the ink amount for each dot diameter in the third mode.

FIG. 23 is an explanatory diagram showing a mode of recording large and small dots in a mixed manner.

[Explanation of symbols]

12 ... Scanner 21 ... Color display 22 ... Color printer 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Print head 31 ... Carriage 32 ... Operation panel 34 ... Sliding 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 ... PIO 46 ... Timer 47 ... Transfer buffer 51 ... Oscillator 55 ... Distribution output devices 61, 62, 63, 64, 65, 66 ... Ink ejection head 67 ... Introducing pipe 68 ... Ink passage 71 ... Black ink cartridge 72 ... Color ink cartridge 90 ... Personal computer 91 ... Video driver 92 ... Input section 95 ... Application program 96 ... Printer driver 97 ... Rastara Iser 98 ... Expected ink amount setting module 99 ... Halftone module

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 10, 2002 (2002.9.1)
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Continued front page    F-term (reference) 2C056 EA06 EA09 EB58 EB59 EC07                       EC42 EC72 EC76 ED01 ED05                       ED07 EE08 FA02 FA10                 2C057 AF25 AF26 AG15 AG44 AH13                       AL31 AM14 AM15 AM28 AN01                       CA01 CA07

Claims (13)

[Claims] 1. A printing apparatus capable of printing an image by forming a plurality of dots on a printing medium, the input means inputting image data for each pixel forming the image, and at least one hue. For each pixel, based on the image data, for a head having two or more types of ink with different densities and capable of forming two or more types of dots with different ink amounts for each ink, Any one of the two or more types of dots based on the expected value of the ink amount set for the ink amount expected value setting means for setting the expected value of the ink amount used for dot formation Multi-valued means for performing multi-valued selection by selecting whether to form each dot including non-formation of dots, and a dot shape for forming the selected dot Printing and means. 2. The printing apparatus according to claim 1, wherein the image data is data including a gradation value for at least one color component in a color space, and the ink amount expected value setting unit is the Expected value storage means for storing the expected value of the ink amount as a table corresponding to a combination of gradation values of a plurality of color components in the color space, and stored in the expected value storage means on the basis of input image data. And a means for setting the expected value of the ink amount for each pixel by referring to the table. 3. The printing apparatus according to claim 2, wherein the table stored in the expected value storage means has the same hue as the expected value of each ink for which the expected value of the ink amount should be set. A printing device that is a table that stores values determined in relation to expected values of ink amounts of other colors regardless of whether or not they correspond to combinations of gradation values of a plurality of color components in the color space. . 4. The printing apparatus according to claim 1, wherein The multi-value conversion unit is a printing device that uses a dither method. 5. The printing apparatus according to claim 1, wherein The printing apparatus, wherein the multi-value quantization means is an error diffusion method. 6. The printing device according to claim 1, wherein the multi-value quantization unit forms dots that can be formed by the head, based on the expected value of the ink amount determined by the expected ink amount determination unit. Type-specific expected value setting means for setting the type-specific expected value that is the expected value of the ink amount for each type, and for each of the dot types, the presence or absence of dot formation is determined based on the set type-specific expected value. A printing device which is a multi-valued device having a means for performing. 7. The printing apparatus according to claim 1, wherein two or more types of dots formed by the head for the same hue have a unit area per unit area when dots are formed with at least one recording density. A printing apparatus that includes two or more types of dots that have approximately the same average density. 8. The printing apparatus according to claim 1, wherein the expected ink amount value setting unit forms dots per unit area regardless of whether the hues are the same or not. A printing apparatus, which is a unit that sets an expected value of the ink amount within a range in which the total amount of the supplied ink does not exceed a predetermined amount that is determined according to the print medium. 9. The printing apparatus according to claim 1, wherein the head includes a mechanism that ejects ink particles by a pressure applied to the ink by applying a voltage to an electrostrictive element provided in an ink passage. Printing device. 10. The printing apparatus according to claim 1, wherein the head ejects ink particles by pressure applied to ink in the ink passage by bubbles generated by energization of a heating element provided in the ink passage. A printing device equipped with a discharge mechanism. 11. A plurality of inks having different densities for at least one hue and capable of forming two or more kinds of dots having different ink amounts for each ink are used to form a plurality of inks on a print medium. A printing method for printing an image by forming dots, wherein image data is input for each pixel forming the image, and for inks having different densities, a dot for each pixel is formed based on the image data. An expected value of the amount of ink to be used for formation is set, and for at least the inks having different densities, which one of the two or more types of dots is to be formed is determined based on the set expected value of the amount of ink. A printing method in which the selected dots are formed including the non-formation, and the selected dots are formed. 12. A recording medium in which a program for printing an image by forming a plurality of dots on a printing medium is recorded so that it can be read by a computer, and inks having different densities prepared for at least one hue. The function of setting the expected value of the ink amount used for dot formation for each pixel based on the image data, and the two types of ink of different densities based on the set expected value of the ink amount A program for realizing by a computer the function of performing multi-valued selection by selecting which of the above dots to be formed including the dot non-formation and the function of forming the selected dot Recording medium recorded. 13. A recording medium in which data used for printing an image by forming a plurality of dots on a print medium is recorded so that it can be read by a computer, and the density is prepared for at least one hue. For the different inks, regardless of whether the hue is the same or not, the total amount of ink used for forming dots per unit area is determined within a range that does not exceed a predetermined amount determined according to the print medium, A storage medium in which data relating to expected values of the amount of ink used to form dots for each pixel is recorded in association with a combination of gradation values for a plurality of color components in a color space.