JPH11254709A - Apparatus and method for printing, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve gradational expression of a high image-density area by providing inks of different concentrations for at least one hue and selecting a dot density and a dot diameter to form dots while allowing a total recording density of dots to exceed 100%. SOLUTION: In a printing apparatus forming a plurality of dots on a printing medium thereby forming an image, inks of different concentrations are provided for at least one hue and a head that can form two or more kinds of dots of different dot diameters for each ink is installed. A dot density and a dot diameter are selected on the basis of image data so as to allow a total recording density of dots to exceed 100% in a range where recording densities of dots formed by the inks of different concentrations do not exceed 100% respectively. Moreover, two kinds of driving waveforms for forming small and middle dots are prepared, thereby enabling large dots to be formed with the use of the driving waveforms.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-gradation head using inks having different densities for at least one hue and capable of forming two or more types of dots having different dot diameters for each ink. The present invention relates to a printing apparatus capable of printing an image, a printing method, and a recording medium.

[0002]

2. Description of the Related Art In recent years, as an output device of a computer,
2. Description of the Related Art A color printer that discharges several colors of ink from a head has become widespread, and is widely used to print an image processed by a computer or the like in multiple colors and multiple gradations. With respect to such a printing apparatus, a printing apparatus and a printing method using dark and light inks have been proposed for the purpose of further improving the print quality in an area where the image density is low, that is, in a so-called highlight portion (for example, Japanese Patent Application No. H8-208686). 209232). This is to prepare 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.

In the case where only light ink having a relatively low density is provided instead of the light and dark inks and an area having a high image density is printed, the center of the dots formed by the light ink, that is, the dot recording positions are overlapped with each other. Some form.
However, in a printer that forms dots by discharging ink, in order to avoid color mixing and decrease in throughput,
In such a manner, the dot recording positions are not usually superimposed and recorded.

Further, as another means for expressing multi-gradation, by forming two types of dots having different ink densities and dot diameters, it is possible to print by changing the density per unit area in multiple steps. A printing device has also been proposed (for example, JP-A-59-201864). This means that one pixel is 4
It is possible to print an image with multiple levels of density by changing the appearance frequency of high density dots and low density dots in pixels by using dots.

On the other hand, in a printer that forms dots by discharging ink, the amount of ink per unit area, that is, the ink duty, is controlled so as not to exceed a predetermined value corresponding to the printing paper. If the ink is discharged in excess of such a value, the paper is likely to be torn, and bleeding or the like will occur, thereby deteriorating the image quality of the printed image.

[0006]

However, in general, in a printer which is provided with dark and light inks and expresses multiple gradations, a region having a low image density, that is, a region having a high image density, although the print quality in a so-called highlight portion is improved. Could not be improved sufficiently.

In order to improve the gradation expression in such an area,
A method of overlapping the dot recording positions is also conceivable, but simply overlapping the dot recording positions causes another problem that the throughput is reduced. In addition, the ink duty limit may be exceeded.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a technique for improving the gradation expression in a high image density region in a printing apparatus without significantly lowering the throughput. Aim.

[0009]

Means for Solving the Problems and Their Functions and Effects In order to solve at least a part of the above problems, the present invention employs the following means. A first printing apparatus according to the present invention is a printing apparatus capable of printing an image by forming a plurality of dots on a print medium, and input means for inputting image data for each pixel constituting the image. A head comprising inks having different densities for at least one hue, and capable of forming two or more types of dots having different dot diameters for each ink; and at least one hue,
As long as the recording density of the dots formed by the inks having different densities does not exceed 100%, the total recording density of the dots formed for the hue is allowed to exceed 100%, and the dots to be formed are allowed. The present invention comprises a dot form selecting means for selecting a density and a dot diameter based on the image data, and a dot forming means for forming a dot with the selected density and dot diameter.

[0010] The printing method of the present invention uses a head provided with inks having different densities for at least one hue and capable of forming two or more types of dots having different dot diameters for each ink, on a printing medium. A printing method for printing an image by forming dots of
Image data is input to each pixel constituting an image, and at least one hue is formed for each hue within a range where the recording density of dots formed by the inks having different densities does not exceed 100%. Allowing the total recording density of the dots to exceed 100%, selecting the density and dot diameter of the dots to be formed based on the image data, and forming the dots with the selected density and dot diameter. Is the gist.

In the printing apparatus and the printing method, inks having different densities are provided for at least one hue, and the dots are formed so as to allow the total recording density of dots formed for such a hue to exceed 100%. The density and dot diameter of the dot to be performed are selected. At this time, the recording densities of dots formed by inks having different densities do not exceed 100%. In a region where the dot recording density exceeds 100%, it means that there is a portion where two or more dots are formed at one dot recording position. On the other hand, the recording density of the dots formed using the ink having a specific density of the above hue is 100%.
, The dots formed using the same ink are recorded at mutually different recording positions.

As described above, by forming some of the dots at the same recording position, it is possible to improve the gradation expression in a region where the print density is high. In addition, since it is possible to record dots formed by different inks and not dots formed by a specific ink, what can be recorded in the same storage position by the printing apparatus and the printing method,
The printing speed of the image, that is, the throughput is not reduced.

Here, the term dot recording density is defined. Generally, in a printing apparatus that forms dots and prints an image, dots are formed such that the centers of the dots are arranged at a substantially constant pitch in a printing area, and the number of dots that can be formed per unit area is a fixed value. Become. In this specification, the center position of the dot recorded in this way is defined as the dot recording position. The ratio of the number of dots actually formed to the number of dots that can be formed per unit area is defined as the dot recording density. However, since the dot recording density cannot be strictly defined and slightly varies depending on the area setting, in this specification, when the dot recording density is 100%,
It means a recording density having a width that can be regarded as 100%.

In the above printing apparatus, the dot forming means records all dots at different recording positions in an area where the total recording density does not exceed 100%.
Forming dots with the selected density and dot diameter,
In the region where the total recording density exceeds 100%, while dots formed by the same density ink are recorded at different recording positions, a part of the dots formed by the inks having different densities are recorded by the same dot recording. A means for forming dots with the selected density and dot diameter while permitting recording at the position may be employed.

According to this printing apparatus, in the area where the total dot recording density does not exceed 100%, that is, in the area where the printing density is relatively low, all the dots are recorded at different recording positions. Image quality can be obtained. In a region where the total dot recording density exceeds 100%, that is, in a region where the printing density is relatively high, two or more dots are recorded at one dot recording position (hereinafter, dots are formed by overlapping, etc.). This makes it possible to express in multiple gradations, and it is possible to prevent a reduction in printing speed by limiting such printing to dots formed by inks having the same hue and different densities.

In general, in a printing apparatus that prints an image using dots, dots recorded at different recording positions are also formed so as to partially overlap each other. However, this does not mean that the recording positions of the dots are the same. Further, the fact that the recording positions of the dots in this case are the same does not need to be exactly the same, and also includes a case where the recording positions are sufficiently close in comparison with the pitch at which the dots are formed.

In the above printing apparatus, the dot forming means may be a means for forming dots within a range in which the total amount of each ink ejected per unit area does not exceed a predetermined amount determined according to a printing medium.

In this printing apparatus, when the total amount of each ink ejected per unit area exceeds a predetermined amount determined according to the printing medium, the dots are overlapped in an area where the dot recording density exceeds 100%. Even if recording is permitted, such recording is prohibited. Therefore,
According to the above-described printing apparatus, dots are formed so that the total amount of each ink ejected per unit area does not exceed a predetermined amount determined according to the printing medium. It is possible to prevent the image quality from deteriorating due to the above factors.

In the above-described printing apparatus, the two or more types of dots formed by the head may include two or more types of dots that have substantially the same density per unit area.

According to such a printing apparatus, two or more types of dots having the same density per unit area are used (for example, a dot having a large dot diameter using low-density ink, a dot having a small dot diameter using high-density ink, and the like). ), The degree of freedom in properly using both of the image data is increased. Therefore, it is possible to form dots in an appropriate combination in accordance with various conditions, such as a total amount of ink ejected per unit area and an improvement in gradation expression in a region where the image density is high. .

In the above-described printing apparatus, the head capable of forming inks having different densities or inks having different dot diameters includes ink droplets formed by applying pressure to the ink by applying a voltage to an electrostrictive element provided in an ink passage. The mechanism which discharges is considered. Further, by a mechanism that ejects ink particles by pressure applied to ink in the ink passage by bubbles generated by energizing a heating element provided in the ink passage, it is possible to form dots with inks having different densities, It is also possible to form different dots. According to these configurations, it is easy to make the ink particles fine and to appropriately control the amount of ink, and it is also easy to prepare a large number of ejection nozzles on the head. When a large number of nozzles are provided, a plurality of nozzles for discharging ink particles can be arranged along the transport direction of the paper to be printed for each ink of each color and each density. By preparing multiple nozzles,
This can contribute to an improvement in printing speed.

The second 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 inputs image data for each pixel constituting the image. An input unit, a head including inks having different densities for at least one hue, and capable of forming two or more types of dots having different dot diameters for each ink; and forming at least one hue using the same density ink. While recording the dots to be formed at different recording positions, it is possible to record a part of the dots formed by the inks having different densities at the same dot recording position, and to adjust the density and the dot diameter of the dots to be formed. A dot form selecting means for selecting based on the image data; and a dot forming means for forming dots with the selected density and dot diameter. And summarized in that comprises and.

According to this printing apparatus, dots formed by inks having different densities can be formed so as to overlap dots formed by inks having different densities without overlapping dots formed by inks having the same density. The same effect as that of the printing apparatus can be obtained. Further, in such a printing apparatus, it is not necessary to determine whether or not to form dots in a superimposed manner based on the dot recording density, so that there is an advantage that the processing relating to dot formation can be performed at high speed.

The above-described printing apparatus of the present invention can also be configured by realizing a part of its functions by a computer. Therefore, the present invention takes an aspect as a recording medium on which such a program is recorded. You can also.

A first recording medium according to the present invention is a recording medium on which a program for printing an image by forming a plurality of dots on a printing medium is readable by a computer, and includes at least one hue. The total recording density of the dots formed for the hue is allowed to exceed 100%, provided that the recording density of the dots formed by two or more types of inks having different densities provided does not exceed 100%. A program for realizing, by a computer, a function of selecting a density and a dot diameter of a dot to be formed based on input image data and a function of forming a dot with the selected density and a dot diameter. It is a recording medium on which recording is performed.

The program recorded on the recording medium is
The printing apparatus of the present invention described above can be realized by being executed by the computer.

As a recording medium, a flexible disk, CD-ROM, magneto-optical disk, IC card,
Various computer-readable media such as a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, an internal storage device (memory such as RAM and ROM) and an external storage device of the computer can be used. The present invention also includes an embodiment as a program supply device that supplies a computer program for causing a computer to realize the functions of each step or each unit of the above-described invention via a communication path.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. (1) Configuration of Apparatus FIG. 2 shows a schematic structure of the printer 22 of the present invention, and FIG. 1 shows a configuration of a color image processing system as an example of a system 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,
And a color printer 22. The personal computer 90 includes a color display 21 and a keyboard,
An input unit 92 such as a mouse is provided. Scanner 1
2 reads color image data from a color original and supplies the computer 90 with original color image data ORG including three color components of red (R), green (G), and blue (B).

The computer 90 includes a CPU, a RAM, a ROM and the like (not shown), and an application program 95 runs under a predetermined operating system. The operating system incorporates a video driver 91 and a printer driver 96, and the application program 95 sends the final color image data F through these drivers.
NL will be output. An application program 95 for retouching an image reads an image from the scanner 12 and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image. 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 sends the image information to a signal that can be printed by the printer 22 (here, each color of cyan, magenta, yellow, and black). (A binarized signal). In the example shown in FIG. 1, inside the printer driver 96, a rasterizer 97 that converts color image data handled by the application program 95 into image data in dot units, and a printer 22 for image data in dot units are provided. A color correction module 98 that performs color correction in accordance with the characteristics of the ink color and color used, a color correction table CT referred to by the color correction module 98, and the presence or absence of ink in dot units based on the color corrected image information And a halftone module 99 that generates so-called halftone image information expressing the density in a certain area. The printer 22 receives the printable signal and records image information on a recording sheet.

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 driving a print head 28 mounted on a carriage 31 to control ink ejection and dot formation, and a paper feed motor 2
3, a control circuit 40 for exchanging signals with the carriage motor 24, the print head 28 and the operation panel 32.

The carriage 31 of the printer 22 includes
Black ink (Bk) cartridge 71 and cyan (C
1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y) ink cartridges 72 containing five color inks can be mounted. For two colors, cyan and magenta, two types of inks are provided. The concentration 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) for leading the ink from the ink tank is provided upright for each color head. Carriage 3
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 from each ink cartridge to the ejection heads 61 to 66. Can be supplied.

The mechanism for discharging ink will be briefly described. FIG. 3 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. The print heads 28 are guided to the respective color heads 61 to 66 of the print head 28. 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 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 provided. FIG. 4 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the figure, the piezo element PE
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 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 extension of the piezo element PE,
The ink corresponding to the contraction amount becomes the particles Ip and is ejected 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.

The printer 22 having the above-described hardware configuration rotates the platen 26 and other rollers by the paper feed motor 23 and conveys the paper P (hereinafter, referred to as sub-scanning) while moving the carriage 31 to the carriage motor 24.
(Hereinafter, referred to as main scanning), and at the same time, the piezo elements P of the respective color heads 61 to 66 of the print head 28.
By driving E, each color ink is ejected to form a dot to form a multicolor image on the paper P.

The mechanism for transporting the paper P is a paper feed motor 2
A gear train for transmitting the rotation of No. 3 not only to the platen 26 but also to the sheet transport roller is provided (not shown). The mechanism for reciprocating the carriage 31 includes an endless drive belt 36 extending between the carriage motor 24 and a slide shaft 34 erected in parallel with the axis of the platen 26 and slidably holding the carriage 31. Pulley 38 and carriage 31
And a position detection sensor 39 for detecting the origin position of the camera.

FIGS. 5 and 6 show the ink ejection head 6.
FIG. 6 is an explanatory diagram showing an arrangement of inkjet nozzles Nz in Nos. 1 to 66. The printer 22 of the present embodiment can form dots having two types of large and small dot diameters for each color. 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 the present embodiment, as shown in FIG. Using a nozzle, dots having different dot diameters are formed by control described later. The arrangement of these nozzles is such that ink is ejected for each color.
Sets of nozzle arrays, 32 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. In addition, 32 nozzles N included in each nozzle array
z does not need to be arranged in a staggered manner, and 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.

Here, the principle of forming two types of dots having different dot diameters using a head having a constant nozzle diameter will be described. Actually, the printer 22 of the present embodiment
Can form three types of dots, large, medium, and small, with different dot diameters. Of these dots, two types of large and small dots are used. Hereinafter, the principle of forming three types of large, medium, and small dots will be described.

FIG. 7 shows the nozzle N when the ink is ejected.
FIG. 4 is an explanatory diagram showing a relationship between a driving waveform of z and ink Ip to be 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 ink path 6 is reversed in the opposite manner as described above with reference to FIG.
Since the piezo element PE is deformed in the direction of increasing the cross-sectional area of No. 8, the ink interface Me called a meniscus is depressed inside the nozzle Nz as shown in the state A of FIG. 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, the state in which the meniscus is not much depressed inward (state A)
Large ink droplets are ejected as shown in states B and C, and small ink droplets are ejected as shown in states b and c from the state in which the meniscus is largely dented inward (state a).

As described above, the dot diameter can be changed according to 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 the present embodiment, a driving waveform for forming a small dot having a small dot diameter is determined based on such a relationship between the driving waveform and the dot diameter.
Two types of driving waveforms for forming a medium dot having the third dot diameter are prepared. FIG. 8 shows a driving waveform used in this embodiment. The driving waveform W1 is a waveform for forming small dots, and the driving waveform W2 is a waveform for forming medium dots. By selectively using both types, two types of small and medium dots can be formed from the nozzle Nz having a fixed nozzle diameter.

Further, a large dot can be formed by forming a dot using both the drive waveforms W1 and W2 of FIG. This situation is shown in the lower part of FIG. FIG.
The lower part of the drawing shows the sheet P after the ink droplets IPs and IPm of small dots and medium dots ejected from the nozzles are ejected.
Up to. When two types of small and medium dots are formed using the drive waveform of FIG. 8, the ink droplet IP is ejected vigorously because the change amount of the piezo element PE is larger in the medium dot. Due to such a difference in the flying speed of the ink, when the carriage 31 moves in the main scanning direction, first ejects a small dot, and then ejects a medium dot. 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, a large dot having the largest dot diameter can be formed from the two types of driving waveforms in FIG. 8 in this manner.

A description will be given of the internal configuration of the control circuit 40 of the printer 22 and a method of driving the head 28 having a plurality of nozzles Nz shown in FIG. 6 using the above-described drive waveform. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG.
Is a PC that exchanges data with the computer 90 in addition to the CPU 41, the PROM 42, and the RAM 43.
An interface 44, 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 measuring time, and turning on / off dots for the heads 61 to 66. And a transfer buffer 47 for outputting the above signal. These elements and circuits are mutually connected by a bus 48. The control circuit 40 also includes a transmitter 51 for outputting a driving waveform (see FIG. 8) for forming small dots at a predetermined frequency, and an output from the transmitter 51 to a head 61.
Also, a distributor 55 for distributing at a predetermined timing is provided. The control circuit 40 receives the dot data processed by the computer 90 and temporarily stores it in the RAM.
43 and output to the transfer buffer 47 at a predetermined timing. Therefore, image processing for forming a multi-tone image is not performed on the printer 22 side. Control circuit 4
A value of 0 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 signals 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 arrays 1 to 66 is provided in a circuit in which the transfer buffer 47 is on the source side and the distribution output unit 55 is on the sink side. Each piezo element PE that constitutes a nozzle row
One of the electrodes is connected to each output terminal of the transfer buffer 47, and the other electrode is connected to the output terminal of the distribution output device 55 collectively. From the distribution output device 55, the transmitter 51
Since the drive waveform is output from the CPU 41, ON / OFF is determined for each nozzle from the CPU 41, and a signal is output to each terminal of the transfer buffer 47. Then, an ON signal is output from the transfer buffer 47 side according to the drive waveform. Piezo element P received
Only E is 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. 8, the driving waveform is such that the waveform W1 for small dots and the n waveform W2 for medium dots are output alternately. Signal to the nozzle array in synchronization with the driving waveform W1 for
An off signal may be sent to the nozzle row in synchronization with the second row. When forming a medium dot, conversely, 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. To form a large dot, an ON signal may be sent in synchronization with both drive waveforms. By doing so, the printer 22 of this embodiment can form dots with large, medium, and small dot diameters during one main scan with each nozzle array.

As described above, the printer 22 of this embodiment can form three types of large, medium, and small dots. However, in the dot generation processing described below, only the large and small dots Is used.
All large, medium, and small dots may be used. Also,
In order to form dots having different dot diameters, two types of driving waveforms for forming large and small dots and two oscillators for outputting the respective driving waveforms are prepared, and the driving waveforms are formed according to the dot diameter to be formed. May be selectively used.

Next, the composition of the ink provided in the printer 22 of this embodiment will be described. As explained earlier,
The printer 22 according to the present embodiment includes, in its print head 28, heads 63 and 65 for light cyan ink and light magenta ink, in addition to so-called CMYK four-color inks. FIG. 11 shows the components of these inks. The normal density cyan ink (indicated by C1 in FIG. 11) has 3.6% by weight of the direct blue 99 as a dye, and the light cyan ink (indicated by C2 in FIG. 11) has the direct blue 99 as a dye in cyan ink. 0.9% by weight, which is 1/4 of C1. In addition, the magenta ink (shown by M1 in FIG. 11) having a normal concentration contains 2.8% by weight of Acid Red 289 as a dye,
The light magenta ink (indicated by M2 in FIG. 11) converts acid red, which is a dye, to １ ／ of the magenta ink M1.
0.7% by weight. The yellow ink Y has 1.8% by weight of direct yellow 86 as a dye, and the black ink Bk has 4.8% by weight of food black 2 as a dye. The density of the yellow ink and the black ink is only one. The viscosity of each ink is adjusted to about 3 [mPa · s], and the surface tension is also adjusted in addition to the viscosity of each color ink. The same can be achieved regardless of the ink to be formed. In the present embodiment, of these inks, black ink is stored in a single cartridge 71, and color ink is stored in an integrated ink cartridge 72 shown in FIG.

It has already been described that the printer 22 of this embodiment can form dots having two types of dot diameters. In this embodiment, dots having a small dot diameter (hereinafter, referred to as small dots) are formed with an ink weight of 5 ng (nanogram), and dots having a large dot diameter (hereinafter, referred to as large dots) are formed with an ink weight of 20 ng. The brightness of each dot is approximately represented by the product of the weight of the dye and the weight of the ink. The brightness of the dots thus represented is also shown in FIG. As shown in FIG. 11, the lightness (lightness 18.0) of the small dots formed by the cyan ink C1 is equal to the lightness (lightness 18.0) of the large dots formed by the light cyan ink C2.
Brightness of small dots formed with magenta ink M1 (brightness 1
4.0) and the lightness (lightness 14.0) of the large dot formed with the light magenta ink M2 are equal.

If dots having different densities and dot diameters are prepared for the purpose of expressing multiple gradations, small dots formed of light ink with low density (hereinafter referred to as light small dots) are used to prepare high density dark dots. It is possible to set the brightness to change in four steps up to a large dot formed of ink (hereinafter, referred to as a large dot), but in this embodiment, a large dot formed of a light ink having a low density (hereinafter referred to as a light large dot) is set. Dots) and small dots formed of dark ink with high density (hereinafter referred to as dark and small dots) were set with the same brightness. In this way, the degree of freedom in selecting both dots can be increased. In the present embodiment, the two types of dots are set so as to have the same brightness, but the brightnesses of the two do not need to exactly match, but need only be approximately the same brightness.

In the present embodiment, as described above, the printer 22 having a head for discharging ink using the piezo element PE is used, but a printer for discharging ink by another method may be used. 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. In such a printer, dots with different dot diameters can be formed by changing the current supply time and current supply area to the heater, so that the present invention can be applied.

(2) Dot Generation Processing Routine Next, a dot generation processing routine in the embodiment according to the present invention will be described. In the following, cyan 1 is used for simplicity.
The process of generating four types of dots (dark small dots, dark large dots, light small dots, light large dots) formed for colors will be described. Similarly, the same processing as the processing described below is applied to magenta that can form four types of dots. In addition, for yellow and black which are not provided with dark and light inks, a process in which the portion corresponding to the use of dark and light dots and light and large dots in the following process is omitted is applied.

FIG. 13 shows the flow of the dot generation processing routine. This routine is a part of the process 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 data obtained by converting a color image into dot-based image data, and then performing color correction on the RGB image data in accordance with the ink color CMY used by the printer 22 and the characteristics of color development. It is.
In this embodiment, the gradation data is given by 8 bits, and has a gradation value in the range of 0 to 255.

Next, the CPU performs a process of determining on / off of a large dot based on the image data Data (step S110). Details of the processing for determining the ON / OFF of the large dot are shown in the dark dot formation determination processing routine of FIG. In this processing routine, first, referring to the table of FIG. 15 based on the image data Data,
A process for generating the level data Dth is performed (step S
112). FIG. 15 shows the gradation data of the original image.
4 is a graph for setting the recording rate of four types of dots (dark small dot, dark large dot, light small dot, light large dot). The graph of FIG. 15 is actually stored on the ROM as tabulated data. The image data Data takes values from 0 to 255 for each color (8 bits for each color). The table of FIG. 15 shows the ratio of each dot in the finally obtained printed matter, and when given gradation data is given, the type of dot formed for the pixel currently being processed and the on / off state. Is not directly determined.

The dot recording rate shown in FIG. 15 is set so that the gradation value of the input data can be appropriately represented and the ink duty does not exceed the limit. Since the limit value of the ink duty changes according to the printing paper, a plurality of tables shown in FIG. 15 may be prepared, and may be selectively used according to the printing paper.

Based on the gradation values of the input image data,
The level data Dth corresponding to the image data is obtained by referring to the table represented by the white square “□” symbol in FIG. 15 (the right vertical axis in FIG. 15). For example, when printing a solid area where the inputted cyan tone value is 63, the recording rate of the large dot is 0%, and the level data Dth is also 0. The gradation value is 191
When printing a solid area, the recording rate of a large dot is 7
5%, and the level data Dth has a value of 191.
Becomes

Next, the level data Dt thus obtained is obtained.
It is determined whether or not h is larger than the threshold value Dref1 (step S114). This threshold value Dref1 is a determination value of whether or not to form a dot by dark ink at the pixel of interest.
A fixed value can be set in all regions. In this embodiment,
An organizational dither method using a global matrix (blue noise matrix) of about 64 × 64 was applied to the setting of the threshold. In this dither matrix, 64 × 6
Any 16 × 16 inside a matrix of size 4
The threshold is determined so that the appearance of the thresholds (0 to 255) is not biased even in the region of. When such a global matrix is used, the occurrence of a false contour or the like is suppressed.

Here, the concept of the dither method will be described with reference to FIG. For convenience of explanation, a part (4 × 4 part) of the matrix is shown. The threshold value Dref1 in such an area is given by a dither matrix. By comparing the threshold value Dref1 with the level data Dth for each pixel, it is determined whether a large dot is on or off as shown in FIG. That is, when the level data Dth is larger than the threshold value Dref1, it is determined that the dark dot of the pixel is turned on (step S116). When the level data Dth is smaller than the threshold value Dref1, the dark dot of the pixel is changed. It is determined to turn off (step S11)
8). As described above, since the dither matrix is set so that the threshold value appears without bias, if on / off of the large dot is determined by such a method, the recording rate shown in FIG. A dark dot is recorded.

If it is determined that the large dot is to be turned on by such processing, the processing for that is executed (step S120). This process is a process of setting dot formation data to be input to the nozzles Nz that eject ink including the size of the dot diameter (see FIG. 10).
If the dark dot is turned off, it is next determined whether dark dots are on or off by the same method (step S13).
0). In this case, a table indicated by a white circle “○” symbol in FIG. 15 is used.

In the present embodiment, in order to avoid the formation of the large dot and the small dot in the same pixel, when the large dot is turned on, it is not determined whether the small dot is on or off. On the other hand, if the on / off determination is performed on the dark dot and the dark dot under the same condition, there is a high possibility that the dark dot is turned off when the dark dot is turned off. In order to avoid such inconvenience, a method applied in this embodiment will be described with reference to FIG.

The uppermost row in FIG.
It shows how OFF is determined by the dither method. The determination method is as described above. In FIG. 17, the level data of the large dot is represented by Dl. Also, for convenience of illustration, the range of 4 × 4 is shown. FIG.
In the second row from the top, the on / off state of dark and small dots is determined by the dither method. However, the level data D obtained by modifying the level data Ds for the dark dots
On / off determination is made using s'. This correction was performed by adding the level data Dl of the large dot obtained based on the graph of FIG. 15 to the level data Ds of the small dot obtained based on the graph of FIG. The corrected level data D thus obtained
s' has a larger value than the original dark dot level data Ds. This situation is shown in the lower two rows of FIG. In this embodiment, the on / off state of the dark dot is determined by comparing the level data Ds ′ thus corrected with the threshold value of the dither matrix. By using the level data Ds' corrected in this way, it is possible to appropriately perform the on / off determination of the small dot using the same dither matrix used for the on / off determination of the large dot.

With the above processing, ON / OFF of the large and small dots is set. Note that various processes other than the process described in the present embodiment can be applied as a process for avoiding the formation of the large dot and the small dot in an overlapping manner. For example, instead of steps S110 and S130, it is first determined whether or not to turn on the dark dot. When turning on the dark dot, it is determined whether or not the dot is to be a large dot or a small dot. It may be performed.

If the large dot or the small dot is turned on, it is determined whether or not the dot recording rate exceeds 100% (step S150). The dot recording rate referred to here is the total value of the recording rates of all the dots obtained based on the table of FIG.

For example, when the gradation value of the image data is the value 191, the recording rate of the large and small dots is 75% as is clear from the table of FIG.
%. At this time, the recording rate of light large dots is only about 1% from the table of FIG. 15, and the recording rate of light small dots is 0% for the data having the same gradation value 191. Therefore, in this case, the dot recording rate of all dots is 1
It will not exceed 00%.

On the other hand, when the gradation value of the input data of the image is 12
For No. 7, the recording ratio of dark and small dots is 56%. At this time, since the recording rate of the light large dots is 73% for the data having the same gradation value 127, the total value of the recording rates of all the dots is 100% or more. In the area indicated by section A in FIG. 15, the dot recording rate may exceed 100%.

If the dot recording rate does not exceed 100%, the dot generation processing routine is terminated without determining whether the light dots are on or off. If the dot recording rate does not exceed 100%, it means that recording is possible without overlapping the dark and light dots, and in such a case, it is better to record without overlapping both. This is because a high image quality can be obtained.

When the dot recording rate exceeds 100% and when neither the large dot nor the large dot is formed (step S140), it is determined whether or not to record the large dot (step S140). S160). The determination method is basically the same as the method shown in FIG. However, if the on / off determination is performed using the same dither matrix for the dark dot and the light dot, the light dot is more likely to be turned off when the dark dot is turned off. I have. That is, by changing the positions of the pixels that are likely to be turned on between the dark dot and the light dot, it is ensured that each is appropriately formed. In this embodiment, as shown in FIG. 18, a dither matrix TM is used for dark dots, and a dither matrix UM in which each threshold value is symmetrically moved in the sub-scanning direction is used for light dots. In this embodiment, a 64 × 64 matrix is used as described above, but FIG. 18 shows a 4 × 4 matrix for convenience. Naturally, a completely different dither matrix can be used for dark dots and light dots. Further, as another method for appropriately forming light dots, it is also possible to apply a method of correcting light dot level data as in the case of ON / OFF determination of dark and small dots.

As a result of the judgment of the light large dot using the above-described dither matrix UM, when it is judged that the light large dot should be turned on, the processing for that is performed (step S170). If it is determined that the light large dot is not turned on, the light small dot is turned on / off (step S180). The determination method is the same as the method shown in FIG. In addition, similarly to the case where the level data is corrected in the on / off determination of the dark small dot (see FIG. 17), the on / off determination is made here by correcting the level data for the light small dot. The same dither matrix UM is used for light large dots and light small dots. In this way, appropriate formation of light large dots and light small dots is ensured, and when light large dots are turned on, both light and small dots are formed in the same pixel by not performing on / off determination of light small dots. To avoid Various methods can be applied as a method of avoiding the formation of the light large dot and the light small dot in the same pixel. If it is determined that the light and small dots should be turned on, a process for that is performed (step S190).

As described above, whether or not to form four types of dots (dark small dot, dark large dot, light small dot, light large dot) is set. As is clear from the above description, the dots formed by the same ink, that is, the large dot and the small dot, and the large dot and the small dot are not simultaneously turned on. On the other hand, dots recorded with different inks, that is, dark dots and light dots, may be turned on at the same time when the dot recording rate exceeds 100%. In such a case, a dark dot and a light dot are formed at the same dot recording position in an overlapping manner.

FIG. 19 shows an example in which dots are formed in an overlapping manner. FIG. 19 shows a case where a light large dot (shown by a large circle in the figure) and a dark small dot (shown by a small circle in the figure) are formed so as to overlap each other. In the case where both are formed to overlap, not only such a pattern but also various patterns can occur. Further, not only a regular pattern as shown in FIG. 19 but also a pattern in which dots formed in an overlapping manner appear at random may occur.

Based on the result of the dot generation processing routine described above, the CPU executes 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 this embodiment, since the large and small dots can be arbitrarily formed from the individual nozzles during one main scan of the carriage 31 as described above, how the dot diameter to be formed by the above processing is Even if it is set, it can be realized relatively easily.

In the above-described dot generation processing routine, the formation of dots is determined using a so-called dither method. However, dot on / off determination may be performed using another method. An example of such a technique is an error diffusion method. The error diffusion method is a method of determining dot on / off for each pixel based on the magnitude relationship between image data and a predetermined threshold. This decision
Since the error between the gradation value of the image data of each pixel and the density evaluation value expressed by turning on / off the dots is performed while diffusing the error to the surrounding pixels, the error can be eliminated as a whole and the image quality is excellent. Has characteristics. Since dot on / off determination by the error diffusion method is well known, further detailed description is omitted. This error diffusion method may be used for dot on / off determination in steps S110, S130, S160, and S180 in FIG. Further, it is naturally possible to use the dither method and the error diffusion method shown in the above embodiments in combination.

On the other hand, the above-described dot diameter setting processing is performed at a time by a printer that selectively uses two types of drive waveforms prepared for large and small dots, ie, a set of nozzle arrays at a time. The present invention can be applied to a printer in which the obtained dot diameter is constant. In such a printer, dots having different dot diameters are mixedly formed by scanning using a well-known overlap type dot recording method. An example of such scanning will be described below.

FIG. 20 shows a 6 × nozzle using a head having six nozzles.
A scanning example when large and small dots are mixed in the area No. 6 is schematically shown. In FIG. 20, the state of ink ejection corresponding to the number of scans of the head is shown on the left side, and the state of dots formed on the right side. The number assigned to each dot corresponds to the scanning order of the head. As shown in FIG. 20, in the first main scan, large dots are formed every other dot in the main scan direction using the lower half nozzles of the head. Next, after the paper is conveyed by three dots in the sub-scanning direction, small dots are formed in each dot in the main scanning direction using all the nozzles. Then, after the paper is further conveyed by three dots in the sub-scanning direction, large dots are formed using the upper half nozzles. According to this aspect, by printing each raster in two scans, it is possible to print by mixing large and small dots at the same ratio.

According to the above-described printing apparatus, the gradation expression in an area where the print density is high can be improved by recording a part of dots in a superimposed manner. Also,
What can be recorded at the same storage position by the printing apparatus and the printing method are dots formed by different inks, that is, dots formed by different heads, and not dots formed by a specific ink. The dots formed by different inks, that is, different heads,
Since dots can be formed by overlapping in one main scan,
There is no decrease in throughput.

Further, even when dots are recorded in an overlapping manner,
Since the table of FIG. 15 is set so as to keep the ink duty limit, it is possible to prevent a decrease in image quality due to bleeding or the like caused by excessive ink ejection. In addition to the method used in this embodiment in order to keep the ink duty limit, the table in FIG. 15 is set only from the viewpoint of gradation expression, and is used when dots are formed beyond the ink duty limit. May be provided with a process for inhibiting the formation of dots.

In the printing apparatus described above, when forming a deep dot, the on / off determination of the light dot is performed only when the dot recording rate exceeds 100% (step S150 in FIG. 13). reference). In other words, it is permitted to form dark and light dots only when the dot recording rate exceeds 100%, but such determination may be omitted. In this case, dots may be formed in an overlapping manner even in a region where the recording rate does not exceed 100%. By performing such processing, the processing can be sped up as much as the determination of the dot recording rate is not performed.

In the printing apparatus described above, the ink density and the dot diameter can be changed by two types, respectively, but the type of the ink density or the dot diameter may be further increased. In addition, although the dark and small dots and the light and large dots use ink having the same lightness (see FIG. 11), the present invention is not limited to such inks, and the present invention can be applied even when the lightness of both is different. Also, in the above description,
Although a head that forms dots by ejecting ink is used, the present invention can be applied to any printing apparatus that includes two or more types of ink of different shades, such as a so-called thermal transfer type or thermal sublimation type printing apparatus. Can be applied.

Further, since the printing apparatus includes processing by a computer, it is possible to adopt an embodiment as a recording medium on which a program for realizing each of the functions described above is recorded. Examples of such a recording 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 a code such as a barcode is printed, a computer internal storage device (such as a RAM or ROM). Various computer readable media are available, such as memory and external storage. Further, an embodiment as a program supply device for supplying, via a communication path, a computer program that causes a computer to realize the functions of each step or each unit of the above-described invention is also possible.

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. For example, although the various processes described above are executed by the computer 90, the function of executing such processes may be provided in the printer 22, and the functions may be executed by the printer 22.

[Brief description of the 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 illustrating 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 showing an example of nozzle arrangement in the printer of the present invention.

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 nozzle drive waveforms in the printer 22 of the present invention.

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

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

FIG. 11 is an explanatory diagram showing ink compositions and characteristics.

FIG. 12 is an explanatory diagram showing an ink cartridge in the printer of the present invention.

FIG. 13 is a flowchart illustrating a flow of a dot generation processing routine.

FIG. 14 is a flowchart showing a dark dot formation determination processing routine.

FIG. 15 is a graph showing the relationship between the input data gradation value and the dot recording rates of large, dark, small, light, and light dot.

FIG. 16 shows an example of turning on / off dots using a dither matrix.
FIG. 4 is an explanatory diagram illustrating a method of OFF determination.

FIG. 17 is an explanatory diagram illustrating a method of determining dot on / off by correcting level data.

FIG. 18 is an explanatory diagram showing a dither matrix created by symmetrically moving the dither matrix in the sub-scanning direction.

FIG. 19 is an explanatory diagram showing an example of dot recording by the printer of the present invention.

FIG. 20 is an explanatory diagram showing a mode in which large and small dots are mixedly recorded by the printer of the present invention.

[Explanation of symbols]

DESCRIPTION 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 Transmitter 55 Distribution output 61, 62, 63, 64, 65, 66: ink discharge head 67: introduction tube 68: ink passage 71: black ink cartridge 72: color ink cartridge 90: personal computer 91: video driver 92: input unit 95: application program 96: printed Iba 97 ... rasterizer 98 ... color correction module 99 ... half-tone module

Continuing on the front page (72) Inventor Liu So, 3-5-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (72) Inventor Shigeaki Kazuya 3-5-35 Yamato, Suwa-shi, Nagano Seiko Epson Corporation

Claims (9)

[Claims] 1. A printing apparatus capable of printing an image by forming a plurality of dots on a print medium, comprising: input means for inputting image data for each pixel constituting the image; and at least one hue. Are provided with inks having different densities, and have different dot diameters for each ink.
A head capable of forming more than one type of dots; and a recording density of dots formed by inks having different densities of at least one hue is 100%.
Dot form selection that selects the density and dot diameter of the dots to be formed based on the image data, while allowing the total recording density of the dots formed for the hue to exceed 100% within a range not exceeding. And a dot forming means for forming dots with the selected density and dot diameter. 2. The printing apparatus according to claim 1, wherein the dot forming unit is configured to record all dots at different recording positions in an area where the total recording density does not exceed 100%. A dot is formed with the selected density and dot diameter. In an area where the total recording density exceeds 100%, the dots formed by the same density ink are recorded at different recording positions while the inks having different densities are recorded. A printing apparatus which is means for forming dots with the selected density and dot diameter while allowing a part of the dots formed by the above to be recorded at the same dot recording position. 3. The printing apparatus according to claim 2, wherein the dot forming unit further controls the dot formation so that the total amount of each ink ejected per unit area does not exceed a predetermined amount determined according to a printing medium. A printing device which is a means for forming a printer. 4. The printing apparatus according to claim 1, wherein two or more types of dots formed by the head are:
A printing apparatus in which two or more types of dots having substantially the same density per unit area are included. 5. The printing apparatus according to claim 1, wherein the head has a mechanism for ejecting ink particles by a pressure applied to the ink by applying a voltage to an electrostrictive element provided in an ink passage. Printing equipment. 6. The printing apparatus according to claim 1, wherein the head is configured to remove ink particles by a pressure applied to ink in the ink passage by bubbles generated by energizing a heating element provided in the ink passage. A printing device equipped with an ejection mechanism. 7. A printing apparatus capable of printing an image by forming a plurality of dots on a printing medium, comprising: input means for inputting image data for each pixel constituting the image; and at least one hue. Are provided with inks having different densities, and have different dot diameters for each ink.
A head capable of forming more than one type of dots, and, for at least one hue, a part of dots formed by inks having different densities while recording dots formed by the same ink at different recording positions. To be recorded in the same dot recording position,
A printing apparatus comprising: a dot form selecting unit that selects a density and a dot diameter of a dot to be formed based on the image data; and a dot forming unit that forms a dot with the selected density and the dot diameter. 8. A plurality of dots are formed on a print medium by using a head having inks having different densities for at least one hue and capable of forming two or more types of dots having different dot diameters for each ink. A printing method for printing an image by inputting image data for each pixel constituting the image, and for at least one hue, the recording density of dots formed by the inks having different densities is 100%.
The density and dot diameter of the dots to be formed are selected based on the image data, while allowing the total recording density of the dots formed for the hue to exceed 100% within a range not exceeding. Printing method for forming dots with the specified density and dot diameter. 9. A recording medium on which a program for printing an image by forming a plurality of dots on a print medium is readable by a computer, wherein at least one type of hue is provided. As long as the recording densities of the dots formed by the inks having different densities do not exceed 100%, the total recording density of the dots formed for the hue is allowed to exceed 100%, A recording medium storing a program for realizing a function of selecting a density and a dot diameter based on input image data and a function of forming a dot with the selected density and dot diameter by a computer.