JP2004262186A - Printing while suppressing bleeding at contour - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing device which carries out subtractive color processing by using a density pattern method, wherein the printing device can suppress bleeding of ink in a contour area. <P>SOLUTION: A printing control device generates print data to be supplied to a printing section that can form ink dots on a printing medium according to image data assigned thereto. The printing control device separates the contour area of an image represented by the image data from the other image area other than the contour area, and converts the image data into multi-gradation data representative of gradation values of ink colors available in the printing section, followed by selecting one of a plurality of ink dot patterns prepared beforehand, to thereby subtract the number of colors of the multi-gradation data to the number of gradations reproduceable by the printing section. In the subtractive color processing, a dot pattern having a low ink dot density on the periphery thereof is employed at least in the part of the contour area. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for printing an image on a print medium by discharging ink.
[0002]
[Prior art]
2. Description of the Related Art An ink jet printer that forms an ink dot on a print medium by ejecting ink droplets to print an image is widely used as an output device of an image created by a computer or the like.
[0003]
When printing is performed by an inkjet printer, ink bleeding may occur particularly in the outline region of a line drawing such as a character or an illustration. Such bleeding of the ink is caused by the fact that the ink discharged to the line drawing area cannot be completely absorbed by the print medium to form an ink pool, and the ink having a different hue becomes cloudy. On the other hand, with the increase in printing resolution, for example, a color reduction process called a density pattern method of expressing a gradation by associating a gradation value of one pixel with one of dot patterns in an n × n array has been adopted. Is increasing.
[0004]
[Problems to be solved by the invention]
However, in the conventional density pattern method, since one dot pattern corresponds to one tone value, if the dot density of the dot pattern is reduced in order to suppress bleeding in the outline region, other dot regions other than the outline region There is a problem that white spots are likely to occur in the image area.
[0005]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem in the related art, and has as its object to suppress ink bleeding in a contour region in a printing apparatus that performs color reduction processing using a density pattern method.
[0006]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the above-described problems, the present invention provides a print control device that generates print data to be supplied to a printing unit capable of forming ink dots on a print medium in accordance with given image data. So,
A contour area separation / extraction unit that separates the image represented by the image data into a contour area and another image area other than the contour area,
A color conversion unit that converts the image data into multi-tone data representing tone values of ink colors available in the printing unit;
The printing unit can reproduce the multi-tone data by selecting one of a plurality of ink dot patterns prepared in advance according to the tone value of the multi-tone data. A color-reducing portion for reducing the number of gradations
With
The color reduction section uses a first dot pattern for at least a part of the outline area, and uses a second dot pattern for image areas other than the outline area;
The first dot pattern is characterized in that the density of ink dots in the peripheral portion of the first dot pattern is lower than that of the second dot pattern corresponding to the same gradation value.
[0007]
According to the printing control apparatus of the present invention, a dot pattern having a relatively low density of ink dots in the peripheral portion in the pattern is used for at least a part of the outline region, while other image regions other than the outline region are used. , A dot pattern having a relatively high density of ink dots in the peripheral portion of the pattern is used, so that ink bleeding in the outline region can be suppressed without excessively increasing the occurrence of white spots. .
[0008]
Here, the contour region means a region composed of pixels that are in contact with the boundary where the hue changes or pixels that are in contact with the boundary where no ink dot is formed. The pixel means the minimum element of each color in the multi-tone data. The peripheral portion is a position where the ink dots are arranged and is a portion closest to the outer periphery in the dot pattern.
[0009]
In the above-described printing control device, the first dot pattern may be configured such that the number of ink dots in a peripheral portion of the first dot pattern is smaller than that of the second dot pattern corresponding to the same gradation value. May be configured,
The first dot pattern may be configured such that the area of the peripheral ink dots in the first dot pattern is smaller than that of the second dot pattern corresponding to the same gradation value. Alternatively, both may be combined.
[0010]
In the above printing control device, the dot pattern includes a plurality of dot formation positions corresponding to one pixel of the multi-tone data, and the presence or absence of dot formation at the plurality of dot formation positions is determined by one pixel. It is preferable that the value is determined according to the gradation data. In this way, accurate gradation expression can be realized.
[0011]
In the print control device, it is preferable that the color reduction unit is configured to use the first dot pattern when the print medium is plain paper.
[0012]
This is because plain paper has a slow ink absorption and tends to bleed, so that the effect of using the first dot pattern is remarkable when the print medium is plain paper. The determination as to whether the print medium is plain paper may be made in response to an input from a user, or may be made automatically using a sensor.
[0013]
Note that the present invention can be realized in various modes, for example, a printing method and a printing apparatus, a printing control method and a printing control apparatus, a computer program for realizing the functions of those methods or apparatuses, and a computer program therefor. The present invention can be realized in the form of a recording medium on which a computer program is recorded, a data signal including the computer program and embodied in a carrier wave, and the like.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in the following order based on examples.
A. Equipment configuration:
B. Printing process in an embodiment of the present invention:
C. Modification:
[0015]
A. Equipment configuration:
FIG. 1 is a block diagram illustrating a configuration of a printing system as one embodiment of the present invention. This printing system includes a computer 90 as a print control device and a color printer 20 as a printing unit. Note that the combination of the color printer 20 and the computer 90 can be called a “printing device” in a broad sense.
[0016]
In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 94 and a printer driver 96 are incorporated in the operating system, and print data PD to be transferred to the color printer 20 is output from the application program 95 via these drivers. The application program 95 performs desired processing on the image to be processed, and displays the image on the CRT 21 via the video driver 94.
[0017]
When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives the image data from the application program 95 and converts it into print data PD to be supplied to the color printer 20. In the example shown in FIG. 1, inside the printer driver 96, a resolution conversion module 97, a color conversion module 98, a contour area separation / extraction unit 101, a color reduction module 99, a print data generation module 100, a color conversion module And a table LUT.
[0018]
The resolution conversion module 97 plays a role of converting the resolution of the color image data handled by the application program 95 (that is, the number of pixels per unit length) into a resolution that can be handled by the printer driver 96. The image data whose resolution has been converted in this way is still image information of three colors of RGB. The color conversion module 98 converts the RGB image data into multi-gradation data representing gradation values of a plurality of ink colors that can be used by the color printer 20 for each pixel while referring to the color conversion table LUT.
[0019]
The color-converted multi-tone data has, for example, 256 tone values. The contour area separation / extraction unit 101 separates an image into a contour area and an image area other than the contour area based on the multi-tone data. The color reduction module 99 executes a color reduction process for expressing this gradation value with the number of gradations that can be realized by the color printer 20 using the density pattern method. At this time, the dot pattern is changed depending on whether or not it is a contour area. The details of these processes will be described later.
[0020]
The color reduction data generated by the color reduction processing is rearranged by the print data generation module 100 in the order of data to be transferred to the color printer 20, and output as final print data PD. Note that the print data PD includes raster data indicating a dot recording state during each main scan and data indicating a sub-scan feed amount.
[0021]
Note that the printer driver 96 corresponds to a program for realizing a function of generating the print data PD. A program for realizing the function of the printer driver 96 is supplied in a form recorded on a computer-readable recording medium. 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 bar code is printed, and a computer internal storage device (such as a RAM or ROM). Various computer readable media, such as memory and external storage, can be used.
[0022]
FIG. 2 is a schematic configuration diagram of the color printer 20. The color printer 20 includes a sub-scanning feed mechanism that conveys the printing paper P in the sub-scanning direction by a paper feed motor 22 and a main scanning feed that reciprocates the carriage 30 in the axial direction (main scanning direction) of the platen 26 by the carriage motor 24. Mechanism, a head drive mechanism that drives a print head unit 60 (also referred to as a “print head assembly”) mounted on the carriage 30 to control ink ejection and dot formation, and a paper feed motor 22 and a carriage motor 24, a control circuit 40 for controlling the exchange of signals with the print head unit 60 and the operation panel 32. The control circuit 40 is connected to the computer 90 via the connector 56.
[0023]
The sub-scanning feed mechanism that transports the print paper P includes a gear train (not shown) that transmits the rotation of the paper feed motor 22 to the platen 26 and a paper transport roller (not shown). A main scanning feed mechanism for reciprocating the carriage 30 includes an endless drive belt 36 provided between the carriage motor 24 and a slide shaft 34 laid parallel to the axis of the platen 26 and slidably holding the carriage 30. And a position sensor 39 for detecting the origin position of the carriage 30.
[0024]
In the color printer 20 having the above-described hardware configuration, the carriage 30 is reciprocated by the carriage motor 24 while the paper P is being conveyed by the paper feed motor 22, and at the same time, the piezo elements of the print head 28 are driven and Drops are ejected to form ink dots to form a multi-color and multi-tone image on the paper P.
[0025]
B. Printing process in an embodiment of the present invention:
FIG. 3 is a flowchart illustrating a print processing procedure according to the first embodiment of the present invention. In step S110, the resolution conversion module 97 and the color conversion module 98 of the computer 90 (FIG. 1) generate multi-tone data from the provided RGB data as described above.
[0026]
FIG. 4 is an explanatory diagram showing the contents of the generated multi-tone data. The multi-tone data has four planes which are data of four colors, cyan (C), magenta (M), yellow (Y), and black (K). The plane of each color is data of 256 gradations in which each pixel has a size of 720 dpi × 720 dpi. Here, cyan (C), magenta (M), yellow (Y), and black (K) are ink colors that can be used in the printer 20. Further, it means that the density of the ink dots is higher as the gradation value is larger. The ink dot density means the ratio of the area of the ink dot to the unit area on the print medium.
[0027]
In step S120, the contour area separation / extraction section 101 (FIG. 1) separates and extracts a contour area based on multi-tone data. In this embodiment, the contour region refers to a group of pixels in which the difference between the pixel values of adjacent pixels is larger than a predetermined value. It is assumed that the predetermined value is 100 in this embodiment. The separation and extraction of the contour region can be performed using a Sobel filter or another contour line extraction filter.
[0028]
FIG. 5 is an explanatory view showing an example of cyan multi-tone data (C plane) and magenta multi-tone data (M plane) having an outline area. In the C plane, as can be seen from FIG. 5A, the difference between the pixel values of the two pixels adjacent to the pixel in the B column and the third row and the pixel in the C column and the third row is 138. As a result, the pixels in column B, row 3 and the pixels in column C, row 3 are classified as contour areas. By the same processing, all the pixels adjacent to the dotted line are classified into the outline area.
[0029]
On the other hand, as can be seen from FIG. 5B, the same pixel is classified as a contour area even in the M plane. Focusing on the pixel values of both the C plane and the M plane, it can be seen that the area inside the dotted line has a high magenta density and the area outside the dotted line has a high cyan density. As a result, it is understood that the dotted line shown in FIG. 5 is a contour line in which the hue rapidly changes from cyan to magenta.
[0030]
FIG. 6 is an explanatory diagram showing two planes (C contour plane and M contour plane) indicating whether or not the pixel belongs to the contour area. Each plane indicates whether each pixel in the plane belongs to the contour area. Specifically, when the pixel value is “1”, it indicates that it is a contour area, and when the pixel value is “0”, it indicates that it is another image area other than the contour area. . In this example, since the area in contact with the dotted line is the outline area for both the cyan and magenta ink colors, the C outline plane and the M outline plane have exactly the same pixel values.
[0031]
FIG. 7 is a flowchart showing the color reduction processing procedure (step S140 in FIG. 3) in the embodiment of the present invention. In this color reduction processing, first, the pixel value of the multi-tone plane of each color of the multi-tone data and the pixel value of the contour plane of each color of the contour data are input for each pixel (steps S200 and S210).
[0032]
In step S220, the color reduction module 99 determines whether each pixel belongs to the contour area according to the pixel value of the contour plane. Specifically, when the pixel value of the contour plane is “1”, it is determined that the pixel belongs to the contour area, and the process proceeds to step S240. On the other hand, when the pixel value of the contour plane is “0”, Is determined to be a pixel belonging to another image area other than the contour area, and the process proceeds to step S230.
[0033]
In step S230, the color reduction module 99 selects a dot pattern from the non-contour dot patterns according to the pixel values of the multi-tone plane. On the other hand, in step S240, the color reduction module 99 selects a dot pattern from the contour dot patterns according to the pixel values of the multi-tone plane.
[0034]
FIGS. 8 and 9 are explanatory diagrams respectively showing a non-contour dot pattern and a contour dot pattern in the embodiment of the present invention. In these figures, dots are arranged at a pitch of 2880 dpi for each pixel having a size of 720 dpi × 720 dpi. These dot patterns include a plurality of dot formation positions corresponding to one pixel of the multi-tone data, and the presence or absence of dot formation at these plurality of dot formation positions corresponds to the multi-tone data of one pixel. It has been determined accordingly.
[0035]
Note that the contour dot pattern corresponds to a “first dot pattern” in the claims, and the non-contour dot pattern corresponds to a “second dot pattern” in the claims.
[0036]
In the non-contour dot pattern shown in FIG. 8, ink dots are arranged at a high spatial frequency to suppress graininess. On the other hand, in the contour dot pattern shown in FIG. 9, the ink dots are arranged such that the density of the ink dots in the peripheral portion of the dot pattern is lower than that of the non-contour dot pattern corresponding to the same gradation value. I have. Here, the peripheral portion refers to a position where the ink dots are arranged and a portion closest to the outer periphery in the dot pattern. For example, in the dot patterns shown in FIGS. 8 and 9, the positions of the ink dots belonging to any of the first row, the fourth row, the A column, and the D column.
[0037]
The reason why the ink dots of the contour dot pattern are arranged so that the density of the ink dots in the peripheral portion of the pattern is low is to suppress the formation of ink pools in the contour area. This is because if formation of an ink pool is suppressed, bleeding due to turbidity of inks having different hues is reduced. The resulting dot pattern for contour has a dot arrangement close to a halftone type.
[0038]
FIG. 10 is an explanatory diagram showing the relationship between the gradation value of the multi-gradation data and the dot pattern. The dot pattern numbers correspond to the dot pattern numbers in FIG. 8 and FIG. For example, when the gradation value is 160, the 10th dot pattern is selected. When the gradation value is 0 to 15, the 0th dot pattern not shown in FIGS. 8 and 9 is selected. The number 0 dot pattern is a pattern in which no ink dots are formed.
[0039]
When such processing is performed for all pixels of each color plane (step S250), the dot formation state of each pixel on the print medium is determined. Based on this determination, dot data having the following properties is generated.
[0040]
FIG. 11 is an explanatory diagram showing a dot formation state on a print medium. FIG. 11A shows a dot formation state in the embodiment of the present invention. This is an example in which a dot pattern is properly used depending on whether or not it is a contour area. On the other hand, FIG. 11B shows an example in which the dot patterns are not properly used. This example is shown for comparison with a case where dot patterns are properly used. Black circles indicate cyan ink dots, and white circles indicate magenta ink dots.
[0041]
FIG. 11 shows only the dot pattern of the ink color on the higher tone value side for easy understanding. For example, only the cyan ink dot (the 10th dot pattern) is shown in the pixel in the B column and the 2nd row, and only the magenta ink dot (the 13th dot pattern) is shown in the pixel in the C column and the 3rd row. Have been.
[0042]
Comparing the dot formation state of FIG. 11A with the dot formation state of FIG. 11B, FIG. 11A shows that the number of adjacent ink dots of different colors is smaller than that of FIG. 11B. I understand. For example, focusing on the pixel in column B, row 3 and the pixel in column C, row 3, in FIG. 11B, three sets of ink dots having different colors are adjacent to each other, whereas in FIG. Only one set of adjacent ink dots is adjacent. As a result, in FIG. 11A, it is understood that the possibility that the inks of different colors gather to form an ink pool is lower than that in FIG. 11B.
[0043]
The dot data thus generated is rearranged by the print data generation module 100 in the order of data to be transferred to the color printer 20, and output as print data PD (step S150 (FIG. 3)). The printer 20 executes printing according to the print data PD (step S160).
[0044]
As described above, in the present embodiment, a dot pattern in which the number of ink dots in the peripheral portion of the pattern is relatively small is used for the contour area, and the dot pattern is used for the image area other than the contour area. Since a dot pattern having a relatively large number of ink dots in the peripheral portion is used, it is possible to suppress ink bleeding in the outline region without excessively increasing the occurrence of white spots.
[0045]
In addition, as the dot pattern in which the density of the ink dots in the peripheral portion is relatively low, for example, a dot pattern called a halftone type or a dot concentration type can be used, and a dot in which the density of the ink dots in the peripheral portion is relatively high is used. As the pattern, for example, a dot pattern called a Bayer type or a dot dispersion type can be used.
[0046]
C. Modification:
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0047]
C-1. In the above embodiment, the arrangement of the ink dots is not changed in the outline area or in the image area other than the outline area, and the number of the ink dots is not changed. However, the number of the ink dots may be changed. For example, as shown in FIG. 12, a dot pattern in which 13 to 16 ink dots are formed in an image area other than the outline area has a dot pattern in which 12 ink dots are formed in the outline area. You may comprise so that it may respond.
[0048]
C-2. In the above embodiment, the dot pattern for the contour area differs from the dot pattern for the non-contour area in the arrangement and the number of the ink dots. For example, the size of the ink dot may be reduced. Also, the number of ink dots and the change in size may be combined. Further, the dot pattern does not necessarily have to be a square, and may be, for example, a rectangle.
[0049]
C-3. In the above embodiment, the computer 90 generates the dot data. However, for example, the computer 90 may supply multi-tone data to the printer 20, and the printer 20 may perform the contour area separation extraction processing or the color reduction processing. good. As described above, a part or all of the functions of the printer driver 96 may be executed by the control circuit 40 in the printer 20.
[0050]
C-4. In the above embodiment, the dot pattern is changed according to whether or not the print medium is the contour area. However, for example, the dot pattern may be changed only when the print medium is plain paper. The reason for this is that the present invention has a remarkable effect when the printing medium is plain paper, because plain paper has a slow ink absorption and tends to bleed. The determination as to whether the print medium is plain paper may be made in response to an input from the user, or may be made automatically using a sensor.
[0051]
C-5. In the above embodiment, all the dot patterns of the pixels belonging to the contour area are changed. However, for example, only the dot pattern on the higher tone value side may be changed. The present invention only needs to change at least a part of the dot pattern of the contour area. It is preferable to change the dot pattern at a higher tone value than at a lower tone value. This is because a dot pattern corresponding to a high gradation value has a high density of ink dots.
[0052]
C-6. In the above embodiment, the outline area is extracted by processing the multi-tone data, and the reduction processing of the ink amount is performed using this. However, the method of extracting the contour region is not limited to this. For example, when data defining an outline, such as an outline font, is used for printing, an outline region may be separated and extracted according to outline data generated from the outline data.
[0053]
C-7. In the above embodiment, the outline area is a pixel that is in contact with a boundary where the hue changes, but the outline area is not limited to this, and may be a pixel that is in contact with an area where no ink dot is formed. good. The pixel in this specification means the minimum element of each color in the multi-tone data. In general, the contour area according to the present invention refers to a group of a plurality of pixels adjacent to a boundary line where the density of at least one hue changes rapidly.
[0054]
C-8. The present invention is applicable not only to color printing but also to monochrome printing. Also, the present invention can be applied to printing in which one pixel is expressed by a plurality of ink dots to express multiple gradations. Further, the present invention can be applied to a drum printer. In the drum printer, the drum rotation direction is the main scanning direction, and the carriage traveling direction is the sub scanning direction. Further, the present invention can be applied not only to an ink jet printer but also to an ink dot recording apparatus that generally performs recording on the surface of a print medium using a recording head having a plurality of nozzle rows.
[0055]
C-9. In the above embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware.
[0056]
When some or all of the functions of the present invention are implemented by software, the software (computer program) can be provided in a form stored in a computer-readable recording medium. In the present invention, the "computer-readable recording medium" is not limited to a portable recording medium such as a flexible disk or a CD-ROM, but may be an internal storage device in a computer such as various RAMs or ROMs, a hard disk or the like. And an external storage device fixed to the computer.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a printing system as one embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating a configuration of a printer.
FIG. 3 is a flowchart illustrating a print processing procedure according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram showing the contents of multi-tone data in the embodiment.
FIG. 5 is an explanatory view showing an example of cyan multi-tone data (C plane) and magenta multi-tone data (M plane) having an outline area.
FIG. 6 is an explanatory diagram showing two planes (C contour plane and M contour plane) indicating whether or not the area is a contour area;
FIG. 7 is a flowchart illustrating a color reduction processing procedure according to the embodiment of the present invention.
FIG. 8 is an explanatory view showing a non-contour dot pattern in the embodiment of the present invention.
FIG. 9 is an explanatory diagram showing an outline dot pattern in the embodiment of the present invention.
FIG. 10 is an explanatory diagram showing a relationship between a gradation value of multi-gradation data and a dot pattern.
FIG. 11 is an explanatory diagram showing a dot formation state on a print medium.
FIG. 12 is an explanatory diagram showing a contour dot pattern in a modified example.
[Explanation of symbols]
20: color printer 21: CRT
22 Paper feed motor 24 Carriage motor 26 Platen 28 Print head 30 Carriage 32 Operation panel 34 Sliding shaft 36 Drive belt 38 Pulley 39 Position sensor 40 Control circuit 56 Connector 60 Print head Unit 90 Computer 94 Video driver 95 Application program 96 Printer driver 97 Resolution conversion module 98 Color conversion module 99 Color reduction module 100 Print data generation module 101 Outline area separation and extraction unit

Claims (8)

A print control device that generates print data to be supplied to a printing unit capable of forming ink dots on a print medium in accordance with given image data,
A contour area separation / extraction unit that separates the image represented by the image data into a contour area and another image area other than the contour area,
A color conversion unit that converts the image data into multi-tone data representing tone values of ink colors available in the printing unit;
The printing unit can reproduce the multi-tone data by selecting one of a plurality of ink dot patterns prepared in advance according to the tone value of the multi-tone data. A color-reducing portion for reducing the number of gradations
With
The color reduction section uses a first dot pattern for at least a part of the outline area, and uses a second dot pattern for image areas other than the outline area;
A printing control device, wherein the first dot pattern has a lower density of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value. . The print control device according to claim 1,
The printing control device according to claim 1, wherein the first dot pattern has a smaller number of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value. The print control device according to claim 1 or 2,
The printing control device, wherein the first dot pattern has a smaller area of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value. The print control device according to claim 1, wherein:
The dot pattern includes a plurality of dot formation positions corresponding to one pixel of the multi-tone data, and the presence or absence of dot formation at the plurality of dot formation positions is determined according to the multi-tone data of one pixel. The print control device that has been determined. The print control device according to any one of claims 1 to 4, wherein
The print control device, wherein the color reduction unit uses the first dot pattern when the print medium is plain paper. A printing apparatus capable of forming ink dots on a print medium in accordance with given image data,
A contour area separation / extraction unit that separates the image represented by the image data into a contour area and another image area other than the contour area,
A color conversion unit that converts the image data into multi-tone data representing tone values of ink colors available in the printing unit;
The printing unit can reproduce the multi-tone data by selecting one of a plurality of ink dot patterns prepared in advance according to the tone value of the multi-tone data. A color-reducing portion for reducing the number of gradations
An ink dot forming unit that forms ink dots on a print medium according to the color-reduced data;
With
The color reduction section uses a first dot pattern for at least a part of the outline area, and uses a second dot pattern for image areas other than the outline area;
The printing apparatus according to claim 1, wherein the first dot pattern has a lower density of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value. A printing method for forming ink dots on a print medium according to given image data,
(A) separating an image represented by the image data into an outline region and an image region other than the outline region;
(B) converting the image data into multi-gradation data representing gradation values of ink colors usable in the printing unit;
(C) selecting one of a plurality of ink dot patterns prepared in advance in accordance with the gradation value of the multi-gradation data to select the multi-gradation data from the printing unit; Reducing the number of colors to a reproducible number of gradations,
(D) forming ink dots on a print medium according to the color-reduced data;
With
The step (c) uses a first dot pattern for at least a part of the outline area, and uses a second dot pattern for an image area other than the outline area;
The printing method according to claim 1, wherein the first dot pattern has a lower density of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value. A computer program for causing a computer to generate print data to be supplied to the printing unit in order to perform printing using a printing unit capable of forming ink dots on a print medium,
The computer program comprises:
A function of separating an image represented by the image data into an outline area and an image area other than the outline area;
A function of converting the image data into multi-gradation data representing gradation values of ink colors available in the printing unit;
The printing unit can reproduce the multi-tone data by selecting one of a plurality of ink dot patterns prepared in advance according to the tone value of the multi-tone data. Function to reduce the number of gradations
Including a program that causes the computer to implement,
The color reduction function includes a function of using a first dot pattern for at least a part of the outline area and using a second dot pattern for an image area other than the outline area. ,
The computer program according to claim 1, wherein the first dot pattern has a lower density of ink dots in a peripheral portion of the first dot pattern than the second dot pattern corresponding to the same gradation value.

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