JP3541668B2 - Printing apparatus, printing method, and recording medium - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a printing apparatus and a printing method for printing an image by discharging ink, and a recording medium on which a program for the printing is recorded, and more particularly to a printing apparatus and the like in a case where dots to be formed have a diameter that allows mutual contact. .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an output device of a computer, dots are formed by several colors of ink ejected from a plurality of nozzles provided on a head while relatively reciprocating a head and a sheet (hereinafter, referred to as main scanning). Inkjet printers that record images using a computer have been proposed, and are widely used for printing images processed by a computer or the like in multiple colors and multiple gradations. In an ink jet printer, when forming a solid area, it is necessary to set a dot diameter so that no gap is generated between dots. The setting of the diameter will be described with reference to FIG.
[0003]
FIG. 24 shows a state in which dots are recorded on printing paper by an inkjet printer. The squares indicated by broken lines in these figures indicate locations where dots should be formed. In the ideal case, the center of each dot is located approximately at the center of these squares. In order to be able to form a so-called solid area, it is necessary to make no gap between adjacent dots. Therefore, at least the dot diameter must be at least d0 shown in FIG. Since d0 corresponds to a diagonal line of a square with one side a, d0 = √2 × a. On the other hand, deviations occur in dot formation positions due to various factors such as mechanical manufacturing errors of the nozzles. In order to form a solid area even when such a deviation occurs, it is necessary to allow a margin for the dot diameter with respect to the above value (△ d in FIG. 24). As described above, the dot diameter dl is set to d0 + 2 × △ d as a value that can form a solid area while preventing banding. FIG. 25 shows how dots having such a diameter are formed. By partially overlapping the adjacent dots in this way, it is possible to prevent a gap from being generated. In recent years, an ink jet printer capable of forming dots with two or more types of different diameters has been proposed, but at least one type usually has dots corresponding to the above-described diameters.
[0004]
[Problems to be solved by the invention]
On the other hand, in an ink jet printer, dots are formed by ejecting ink onto paper, so that it takes a certain amount of time for the dots to dry. In FIG. 25, after the dot Dot1 is formed, if the adjacent dot Dot2 is formed before the dot is dried, the ink may bleed at the overlapping portion (the hatched portion in FIG. 25). Was. Also, due to such bleeding, the two may be united to form large elliptical dots as shown in FIG. 26 in some cases. The occurrence of such bleeding or large oval dots makes the graininess of the image conspicuous, and is one of the causes of lowering the image quality. In order to avoid such a phenomenon, it is possible to increase the time interval at which dots are formed, but another problem of lowering the printing speed is caused.
[0005]
Dot bleeding or the like occurs when the dots come into contact with each other. Although FIG. 25 illustrates a case where adjacent dots contact each other, depending on the dot diameter, there is a case where adjacent dots contact each other with one space therebetween. In addition, similar problems have occurred with dots having a relatively small diameter. In general, a dot having a small diameter tends to have an elliptical shape as shown in FIG. 27, and adjacent dots easily come into contact with each other as shown in FIG. Dots of small diameter are used when printing relatively bright areas. In such an area, dots are sparsely formed, and each dot is easily recognized. Therefore, generation of large dots as described above with reference to FIG. 26 is considered to degrade image quality.
[0006]
Such a problem can occur not only in an ink jet printer that forms dots while performing main scanning, but also in an ink jet printer that forms a raster without main scanning by providing a plurality of nozzles in the raster direction. In FIGS. 25 and 26, the problem has been described by taking the main scanning direction as an example, but the same applies to the relative movement (hereinafter referred to as sub-scanning) direction of the head and the printing paper in the direction intersecting with the main scanning. Problems can arise. Further, a similar problem may occur even when each raster is formed by two or more main scans by the so-called overlap recording.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in the related art, and is a technology that can prevent bleeding or the like due to contact between adjacent dots and improve image quality in an ink jet printer. The purpose is to provide.
[0008]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the problems described above, the printing apparatus of the present invention employs the following configuration.
A first printing apparatus according to the present invention includes:
Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing device that prints an image corresponding to the input image data on the print medium,
For each pixel corresponding to the image data, a pixel determination unit that determines whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
Suppressing means that acts on the pixel determining means, and suppresses the determination of a peripheral pixel of the forming pixel as a forming pixel on which a dot having a diameter that can be in contact with a dot formed on the forming pixel should be formed.
A dot forming means for driving the head to form dots in accordance with the result determined by the pixel determining means is provided.
[0009]
The first printing method according to the present invention includes:
Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing method for printing an image corresponding to the input image data on the print medium,
(A) determining, for each pixel corresponding to the image data, whether to be a pixel to be formed with a dot or a blank pixel as a pixel not to form a dot;
(B) in the step (a), a step of suppressing a pixel around the formation pixel from being a formation pixel in which a dot having a diameter capable of contacting a dot formed in the formation pixel is to be formed;
(C) a step of driving the head to form dots in accordance with the result determined in the step (a).
[0010]
According to the printing apparatus and the printing method, for each pixel corresponding to the image data, it is determined whether the pixel is a pixel to be formed or a blank pixel is a pixel not forming a dot. In the process of forming dots accordingly, it is possible to suppress the determination of pixels around the formation pixel as formation pixels to form dots having a diameter that can be in contact with the dots formed in the formation pixel. As a result, the occurrence of dots that are in contact with each other is suppressed, so that bleeding or the like in the contact portion between the dots can be prevented, and the image quality can be improved.
[0011]
In the above invention, when the dots formed in the pixels around one formation pixel are dots having a diameter that cannot be in contact with the dots formed in this formation pixel, it does not matter whether the formation is suppressed or not. is there. Note that the diameter that can be contacted means a pixel that may be contacted in consideration of a shift in the dot formation position.
[0012]
Here, the “peripheral pixels” include not only pixels located in a direction in which a raster is formed, but also pixels located in a direction intersecting with the raster (hereinafter, referred to as a sub-scanning direction). However, whether or not bleeding occurs between the contacted dots is related to whether or not both are formed within the time for drying the ink. Therefore, when adjacent dots cannot be formed in the sub-scanning direction within a short time until the dots dry due to the mechanism of the printing apparatus or the type of paper, a raster is formed from the peripheral pixels. It may be specified to a pixel located in the direction. The above-described invention is applicable to both a printing apparatus that performs main scanning and a printing apparatus that does not perform main scanning.
[0013]
In the above printing apparatus,
The pixel determination unit is a unit that determines the pixel as the formation pixel when the image data of each pixel is larger than a predetermined threshold,
The suppression unit may be a unit that increases the threshold value for a suppression pixel that is a pixel that should suppress the formation of a dot having a contactable diameter than a pixel that does not.
[0014]
According to such a printing apparatus, for the suppression pixel, the threshold value that determines whether or not each pixel should be a formation pixel is increased, so that dot formation at the pixel can be suppressed. When the printing apparatus is capable of forming dots having a plurality of diameters, only the threshold value related to the formation of dots having a diameter that can contact the dots formed on the formed pixels may be increased.
[0015]
In the above printing apparatus,
The deviation amount that increases the threshold value may be a value that decreases as the distance between the formation pixel and the suppression pixel increases.
[0016]
According to such a printing apparatus, it is possible to increase the certainty that the formation of a dot having a diameter that allows contact with the formation pixel is suppressed as the pixel is closer to the formation pixel. Since the area of the portion where the dots contact each other increases as the distance between them decreases, formation of a dot having a diameter that can be touched can be more reliably suppressed for a pixel with a shorter distance. Can be further reduced, and the image quality can be improved. As a result, the printing apparatus has a relatively high dot recording density, and can improve image quality even when contact between dots becomes unavoidable.
[0017]
In the above printing apparatus,
The pixel determination unit is a unit that determines whether each pixel is the formation pixel by an error diffusion method,
The suppression means may be a means for suppressing the formation of a dot having a contactable diameter by allocating a large diffusion error in error diffusion to the peripheral pixels.
[0018]
The first printing device is
When the raster is formed by main scanning in which the head reciprocates relatively in the raster direction with respect to a print medium,
The peripheral pixels may be pixels located in the main scanning direction with respect to the formed pixels, and may be pixels formed continuously with the formed pixels in the main scanning.
[0019]
In a printing apparatus that forms a raster by main scanning, when pixels formed continuously during the main scanning come into contact with each other, bleeding or the like easily occurs. In the above-described printing apparatus, since contact of dots with such pixels is suppressed, bleeding and the like can be suppressed, and image quality can be improved.
[0020]
The pixels that are continuously formed are, for example, adjacent pixels when all the dots of the raster are formed by one main scan. When a raster is formed by two main scans by performing recording by a so-called overlap method, for example, the next pixel adjacent to a pixel to be formed is separated by one in the main scanning direction according to the recording method. And so on correspond to pixels formed continuously. This may be extended to a more general number.
[0021]
That is, in the printing device,
The peripheral pixels in which the formation of the dots is suppressed are determined according to the relative number of movements of the head and the print medium in a direction intersecting the raster performed while all the dots forming the raster are formed. The pixel may be a pixel separated from the formation pixel by a distance.
[0022]
In the case of a printing apparatus with a main scan, each time the number of main scans required to form a raster increases, one form pixel and a pixel formed continuously with the form pixel, that is, a dot having a contactable diameter The distance from the pixel where the formation of the pixel should be suppressed increases. This relationship is the same even in a printing apparatus capable of forming a raster without main scanning. The number of series of recordings required to form a raster can be counted in units of sub-scanning performed for each recording. In the printing apparatus, the distance between the morphological pixel and the pixel having a diameter that can be contacted is increased in accordance with the number of movements, so that dot bleeding and the like can be appropriately suppressed, and image quality can be improved. it can.
[0023]
further,
The suppression unit may be a unit that suppresses the formation of the dots in a region where the dot recording rate is 50% or less.
[0024]
The blurring of dots is conspicuous in an area where dots are formed relatively sparsely. In the printing apparatus, the contact of dots can be suppressed in such an area, so that the image quality can be improved. Note that the area where the recording rate is 50% or less is a guideline and not a strict one. Therefore, in consideration of the effect on image quality, it is assumed that the formation of the dots is suppressed in a wider range than this. No problem.
[0025]
A second printing apparatus according to the present invention includes:
Forming a raster as a dot row arranged at a predetermined recording pitch in one direction by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing device that prints an image corresponding to the input image data on the print medium,
For each pixel corresponding to the image data, a pixel determination unit that determines whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
For each formed pixel, means for determining the number of contact pixels, which are pixels that are formed pixels of a dot having a diameter that can contact a dot to be formed in the formed pixel,
A dot forming unit that divides by a division number set based on the maximum value of the number of the contact pixels to form dots of each raster is provided.
[0026]
A second printing method according to the present invention includes:
Forming a raster as a dot row arranged at a predetermined recording pitch in one direction by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing method for printing an image corresponding to the input image data on the print medium,
(A) determining, for each pixel corresponding to the image data, whether to form a pixel to be formed with a dot or a blank pixel as a pixel not forming a dot;
(B) for each formation pixel, a step of calculating the number of contact pixels, which are pixels forming dots having a diameter that allows contact with the dots to be formed in the formation pixel;
(C) forming a dot of each raster by dividing by a division number set based on the maximum value of the number of contact pixels.
[0027]
According to the printing apparatus and the printing method, when a dot that can be contacted is formed, the raster is divided and recorded, so that occurrence of bleeding or the like between the two can be suppressed. This is because, by recording in a divided manner, there is a margin for drying the previously formed dots. For example, when a dot having a diameter that allows contact with an adjacent pixel is formed for a certain formed pixel, the raster is formed twice. In addition, in the case where an adjacent pixel and a dot formed on the adjacent pixel can be in contact with a certain form pixel, the raster is formed in three times. As described above, in the above-described printing apparatus and the like, the number of times of forming the raster is set according to the maximum value of the number of pixels in which the dots that can be formed on the pixels can be contacted. By taking such a measure, it is possible to appropriately suppress bleeding or the like due to contact of dots.
[0028]
Note that the second printing apparatus and printing method of the present invention are applicable not only to a printing apparatus that forms a raster with main scanning but also to a printing apparatus that forms a raster without main scanning. Further, the printing apparatus and the like of the present invention described above can be applied to a printing apparatus capable of forming not only dots having one kind of diameter but also dots having a plurality of different diameters.
[0029]
The printing apparatus of the present invention described above can also be configured by realizing the determination of dot formation and the like by a computer, and therefore, the present invention can also take an aspect as a recording medium on which such a program is recorded. it can.
[0030]
The first recording medium of the present invention comprises:
A computer-readable recording medium for recording a program for setting data in common with a printing apparatus that prints an image corresponding to input image data by ejecting ink on a print medium, at least,
For each pixel corresponding to the image data, a function of determining whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
In the above-described function, a program for realizing a function of suppressing a determination that a pixel around the formation pixel is a formation pixel in which a dot having a diameter that can be in contact with a dot formed in the formation pixel is to be formed is recorded. This is a recording medium.
[0031]
The second recording medium of the present invention comprises:
A method for printing a program for setting data common to a printing apparatus that prints an image corresponding to input image data by ejecting ink on a print medium, comprising:
For each pixel corresponding to the image data, a function of determining whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
For each formed pixel, a function of calculating the number of contact pixels that are pixels that are formed pixels of a dot having a diameter capable of contacting a dot to be formed in the formed pixel,
And a function of setting a series of recording times required for forming each raster based on the maximum value of the number of the contact pixels.
[0032]
The above-described printing apparatus and printing method of the present invention described above can be realized by executing the program recorded on each of the above-described recording media by the computer. Examples of the 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, and an internal storage device of a computer (a memory such as a RAM or a ROM). ) And external storage devices, such as various computer readable media. The present invention also includes an aspect as a program supply device that supplies a computer program for realizing the control function of the printing apparatus to a computer via a communication path.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples.
(1) Device configuration
FIG. 1 is a block diagram illustrating a configuration of a printing apparatus as one embodiment of the present invention. As shown in the figure, the scanner 12 and the color printer 22 are connected to a computer 90, and a predetermined program is loaded and executed on the computer 90 to function as a printing apparatus as a whole. The computer 90 includes the following units interconnected by a bus 80, centering on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. The ROM 82 previously stores programs and data necessary for the CPU 81 to execute various arithmetic processes, and the RAM 83 temporarily reads and writes various programs and data necessary for the CPU 81 to execute various arithmetic processes. Memory. The input interface 84 controls input of signals from the scanner 12 and the keyboard 14, and the output interface 85 controls output of data to the printer 22. The CRTC 86 controls signal output to the CRT 21 capable of color display, and the disk controller (DDC) 87 controls transmission and reception of data with the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). The hard disk 16 stores various programs loaded and executed in the RAM 83 and various programs provided in the form of device drivers. In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. The SIO 88 is connected to the modem 18, and is connected to the public telephone line PNT via the modem 18. The computer 90 is connected to an external network via the SIO 88 and the modem 18. By connecting to a specific server SV, it is also possible to download a program required for image processing to the hard disk 16. In addition, it is also possible to load a necessary program from a flexible disk FD or a CD-ROM and cause the computer 90 to execute the program.
[0034]
FIG. 2 is a block diagram illustrating a software configuration of the printing apparatus. In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and the final image data FNL to be transferred to the printer 22 is output from the application program 95 via these drivers. . 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. The data ORG supplied from the scanner 12 is original color image data ORG read from a color original and composed of three color components of red (R), green (G), and blue (B).
[0035]
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 the printer 22 in a printable signal (here, each color of cyan, magenta, yellow, and black). Into a multi-valued signal). In the example shown in FIG. 2, the printer driver 96 includes a resolution conversion module 97, a color correction module 98, a color correction table LUT, a halftone module 99, and a rasterizer 100.
[0036]
The resolution conversion module 97 serves to convert the resolution of the color image data handled by the application program 95, that is, the number of pixels per unit length into a resolution that can be handled by the printer driver 96. Since the image data whose resolution has been converted in this way is still image information of three colors of RGB, the color correction module 98 refers to the color correction table LUT and uses the cyan (C) and magenta colors used by the printer 22 for each pixel. (M), yellow (Y) and black (K). The color-corrected data has a gradation value in a width of, for example, 256 gradations. The halftone module 99 executes a halftone process for expressing such gradation values by dispersing and forming dots by the printer 22. The image data processed in this manner is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 22, and output as final image data FNL. Note that the halftone module 99 corresponds to a pixel determination unit in the present invention.
[0037]
In this embodiment, the printer 22 only plays a role of forming dots in accordance with the image data FNL, and does not perform image processing. However, the above-described modules may be provided in the printer 22 and the processing may be performed by the printer 22.
[0038]
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, a mechanism for reciprocating a carriage 31 in the axial direction of a platen 26 by a carriage motor 24, and a print head mounted on the carriage 31. The control circuit 40 controls the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32 to exchange signals with each other. .
[0039]
The mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes an endless drive belt between a carriage shaft 24 and a slide shaft 34 laid parallel to the platen 26 and holding the carriage 31 in a slidable manner. A pulley 38 on which the carriage 36 is extended and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.
[0040]
The carriage 31 contains a cartridge 71 for black ink (Bk) and five color inks of cyan (C1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y). The color ink cartridge 72 can be mounted. For two colors of cyan and magenta, two types of inks are provided. A total of six ink discharge heads 61 to 66 are formed on the print head 28 below the carriage 31. At the bottom of the carriage 31, an introduction pipe 67 (which guides ink from the ink tank to each color head). (See FIG. 4). When the cartridge 71 for black (Bk) ink and the cartridge 72 for color ink are mounted on the carriage 31 from above, the introduction pipe 67 is inserted into the connection hole provided in each cartridge, and the ejection heads 61 to 66 from each ink cartridge. Can be supplied to the printer.
[0041]
A mechanism for discharging ink and forming dots will be described. FIG. 4 is an explanatory diagram showing a schematic configuration inside the ink discharge head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 by utilizing the capillary phenomenon as shown in FIG. The print head 28 is guided to each color head 61 to 66 of the print head 28. When the ink cartridge is first mounted, the operation of sucking ink into the heads 61 to 66 of the respective colors is performed by a dedicated pump. 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.
[0042]
As will be described later, the heads 61 to 66 for each color are provided with 48 nozzles Nz for each color (see FIG. 6). An excellent piezo element PE is arranged. FIG. 5 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the upper part of FIG. 5, the piezo element PE is installed at a position in contact with the ink passage 68 that guides the 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 expansion of the piezo element PE, and the ink corresponding to the contraction is discharged as particles Ip at a high speed from the tip of the nozzle Nz. Printing is performed by the permeation of the ink particles Ip into the paper P mounted on the platen 26.
[0043]
FIG. 6 is an explanatory diagram showing the arrangement of the inkjet nozzles Nz in the ink ejection heads 61 to 66. The arrangement of these nozzles is composed of six sets of nozzle arrays that eject ink for each color, and 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. Note that the 48 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, and may be arranged on a straight line. However, the arrangement in a staggered manner as shown in FIG. 6 has the advantage that the nozzle pitch k can be easily set small in manufacturing.
[0044]
Although the printer 22 of the present invention includes the nozzles Nz having a constant diameter as shown in FIG. 6, three types of dots having different diameters can be formed using the nozzles Nz. This principle will be described. FIG. 7 is an explanatory diagram showing the relationship between the driving waveform of the nozzle Nz when ink is ejected and the ink Ip ejected. The drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. In the section d2, once a negative voltage is applied to the piezo element PE, the piezo element PE is deformed in a direction in which the cross-sectional area of the ink passage 68 is increased, contrary to the above description with reference to FIG. As shown in the state A of FIG. 7, the ink interface Me called the meniscus is in a state in which it is depressed inside the nozzle Nz. On the other hand, when a negative voltage is suddenly applied as shown in a section d2 using the drive waveform shown by the solid line in FIG. 7, the meniscus is greatly depressed inward compared to the state A as shown in the state a. Next, when the voltage applied to the piezo element PE is made positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, large ink droplets are ejected as shown in states B and C from the state where the meniscus is not much depressed inward (state A). As shown in state c, a small ink droplet is ejected.
[0045]
As described above, the dot diameter can be changed in accordance with the change rate when the drive voltage is made negative (section d1, d2). It is easy to imagine that the dot diameter can be changed depending on the magnitude of the peak voltage of the driving waveform. In this embodiment, based on such a relationship between the drive waveform and the dot diameter, a drive waveform for forming a small dot having a small dot diameter and a medium dot having the second dot diameter are formed. There are prepared two types of drive waveforms for this purpose. FIG. 8 shows a driving waveform used in this embodiment. The drive waveform W1 is a waveform for forming small dots, and the drive waveform W2 is a waveform for forming medium dots. By selectively using the two types, two types of small and medium dots can be formed from the nozzle Nz having a fixed nozzle diameter.
[0046]
In addition, a large dot can be formed by forming a dot using both the drive waveforms W1 and W2 in FIG. This situation is shown in the lower part of FIG. The lower part of FIG. 8 shows a state from the ejection of the small and medium dot ink droplets IPs and IPm ejected from the nozzles to the paper P. When two types of small and medium dots are formed using the driving 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 is thus formed from the driving waveforms in the two types shown in FIG.
[0047]
Finally, the internal configuration of the control circuit 40 of the printer 22 will be described, and a method of driving the head 28 including a plurality of nozzles Nz shown in FIG. 6 will be described. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, inside the control circuit 40, in addition to the CPU 41, the PROM 42, and the RAM 43, a PC interface 44 for exchanging data with the computer 90, the paper feed motor 23, the carriage motor 24, the operation panel 32, and the like. A peripheral input / output unit (PIO) 45 for exchanging signals with the controller, a timer 46 for measuring time, and a driving buffer 47 for outputting dot on / off signals to the heads 61 to 66 are provided. Are interconnected by a bus 48. The control circuit 40 is also provided with a transmitter 51 that outputs a drive waveform (see FIG. 9) at a predetermined frequency, and a distributor 55 that distributes the output from the transmitter 51 to the heads 61 to 66 at a predetermined timing. ing. The control circuit 40 receives the dot data processed by the computer 90, temporarily stores the dot data in the RAM 43, and outputs the dot data to the driving buffer 47 at a predetermined timing.
[0048]
A mode in which the control circuit 40 outputs a signal to the heads 61 to 66 will be described. FIG. 10 is an explanatory diagram showing the connection of one nozzle row of the heads 61 to 66 as an example. One nozzle row of the heads 61 to 66 is interposed in a circuit in which the driving buffer 47 is on the source side and the distribution output unit 55 is on the sink side, and each piezo element PE constituting the nozzle row has its electrode Is connected to each output terminal of the driving buffer 47, and the other is connected to the output terminal of the distribution output device 55 collectively. As shown in FIG. 8, the drive waveform of the transmitter 51 is output from the distribution output unit 55. When ON / OFF is determined for each nozzle from the CPU 41 and a signal is output to each terminal of the driving buffer 47, only the piezo element PE that has received the ON signal from the driving buffer 47 side is driven according to the driving waveform. You. 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 driving buffer 47.
[0049]
As shown in FIG. 6, the heads 61 to 66 are arranged along the transport direction of the carriage 31, so that the timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Therefore, the CPU 41 outputs the ON / OFF signal of each dot at a necessary timing via the driving buffer 47 in consideration of the displacement of each nozzle of the heads 61 to 66, and outputs the dot of each color. Has formed. Also, as shown in FIG. 6, the output of the on / off signal is controlled in consideration of the fact that each of the heads 61 to 66 also has two rows of nozzles.
[0050]
In the present embodiment, it is possible to form dots having different diameters by continuously outputting the driving waveforms W1 and W2 shown in FIG. 8 from a single transmitter 51. Each of them may be prepared, and dots having different diameters may be formed depending on their use.
[0051]
In the printer 22 having the hardware configuration described above, the carriage 31 is reciprocated by the carriage motor 24 (hereinafter, referred to as main scanning) while the paper P is transported by the paper feed motor 23 (hereinafter, referred to as sub-scanning). The piezo elements PE of the respective color heads 61 to 66 of the print head 28 are driven to discharge the respective color inks, thereby forming dots to form multi-color images on the paper P.
[0052]
In the present embodiment, as described above, the printer 22 having the head that discharges ink using the piezo element PE is used, but a printer that discharges 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 arranged in an ink passage is energized and ink is ejected by bubbles generated in the ink passage.
[0053]
(2) Dot formation control
Next, control processing of dot formation in the printing apparatus of the present embodiment will be described. FIG. 11 shows the flow of the dot formation control processing routine. This is a process executed by the CPU 81 of the computer 90.
[0054]
When this process is started, the CPU 81 inputs image data (step S100). This image data is data passed from the application program 95 shown in FIG. 2 and includes 256 gradations of values 0 to 255 for each color of R, G, and B for each pixel constituting the image. This is data having a value. The resolution of this image data changes according to the resolution of the original image data ORG and the like.
[0055]
The CPU 81 converts the resolution of the input image data into a resolution for printing by the printer 22 (hereinafter, referred to as a printing resolution) (step S105). If the image data is lower than the print resolution, resolution conversion is performed by generating new data between adjacent original image data by linear interpolation. Conversely, if the image data is higher than the print resolution, resolution conversion is performed by thinning out the data at a fixed rate. Note that the resolution conversion processing is not essential in the present embodiment, and printing may be executed without performing such processing.
[0056]
Next, the CPU 81 performs a color correction process (step S110). The color correction process is a process of converting image data consisting of R, G, and B tone values into tone value data of each of the C, M, Y, and K colors used by the printer 22. This processing is performed by using a color correction table LUT (see FIG. 2) storing combinations of C, M, Y, and K for expressing colors composed of respective combinations of R, G, and B on the printer 22. . Various well-known techniques can be applied to the processing itself for color correction using the color correction table LUT, and for example, processing by interpolation calculation (for example, the technique described in JP-A-4-144481) can be applied.
[0057]
The CPU 81 performs a multi-value processing on the image data color-corrected in this manner (step S120). In other words, the halftone module 99 shown in FIG. 2 executes the processing. Multi-value conversion means that the gradation value (256 gradations in this embodiment) of the original image data can be expressed by the printer 22 for each dot (in this embodiment, “no dot formation”, “small dots” (4 values of dot formation), “medium dot formation” and “large dot formation”. The multi-value processing can be performed by various methods. In this embodiment, an error diffusion method which is excellent in image quality is applied.
[0058]
The multilevel processing by the error diffusion method will be described. FIG. 12 shows a flow of the multi-value processing by the error diffusion method. When this process is started, the CPU 81 inputs the image data Cd (Step S122). The input image data Cd is subjected to color correction processing (step S110 in FIG. 11), The data has 256 gradations for each of M, Y, and K colors. Diffusion error correction data Cdx is generated for this data (step S124). In the error diffusion process, an error of the gradation expression generated for the processed pixel is allocated in advance by assigning a predetermined weight to pixels around the pixel. Therefore, in step S124, the corresponding error is read out and this is read out. From the pixel to be processed.
[0059]
A description will be given of the setting of how much weight is assigned to the peripheral pixels and the weight of the error with respect to the target pixel PP with reference to FIGS. FIG. 13 shows an error distribution setting that is often used. The density error is given a predetermined weight (１ ／, ８) for several pixels in the scanning direction of the carriage 31 with respect to the target pixel PP, and for several adjacent pixels behind the paper P in the conveyance direction. , 1/16). FIG. 14 shows settings in this embodiment. The weight of the error allocated to the pixel P1 adjacent to the pixel PP of interest in the carriage scanning direction is a value of 1/4 in the example shown in FIG. 13, whereas in the present embodiment (FIG. 14) The weight is set large with a value of 1/2. The significance of this setting will be described later. The distribution shown in FIG. 14 corresponds to one of the suppression means in the present invention.
[0060]
The diffusion error correction data Cdx generated in this way is compared with the first threshold th1 (step S126). If the data Cdx is smaller than the threshold th1, a dot is added to the value Cdr representing the multi-level quantization result. A value of 0, which means not to be formed, is substituted (step S128). The threshold value th1 is a value serving as a reference for determining whether or not to form a dot as described above. This threshold th1 can be set to any value, but in this embodiment, it is set based on the following concept.
[0061]
FIG. 15 shows the relationship between the recording ratio of each of the large, medium, and small dots and the gradation value of the image data in this embodiment. In this embodiment, as shown in FIG. 15, only small dots are formed at gradation values 0 to gr1, small dots and medium dots are formed at gr1 to gr2, and medium dots and large dots are formed at gr2 and higher. Is set to At a tone value of gr1 or more, a dot of any of large, medium, and small is formed, and a pixel that does not form a dot does not occur. The threshold value th1 is set so that formation or non-formation of small dots occurs as shown in FIG. 18 in the range of gradation values 0 to gr1. In this embodiment, th1 is set to gr1 / 2.
[0062]
If the correction data Cdx is equal to or greater than the first threshold th1, the magnitude of the correction data Cdx is compared with the second threshold th2 (step S130), and the correction data Cdx is smaller than the second threshold th2. In this case, the value 1 meaning the formation of a small dot is substituted for the value Cdr representing the multi-value quantization result (step S132). The threshold value th2 is set based on the dot recording rate in FIG. 18 similarly to the threshold value th1, and is set to th2 = (gr1 + gr2) / 2 in the present embodiment.
[0063]
If the correction data Cdx is greater than or equal to the second threshold th2, the magnitude of the correction data Cdx is compared with the third threshold th3 (step S134), and the correction data Cdx is smaller than the third threshold th3. In this case, the value 2 meaning the formation of a medium dot is substituted for the value Cdr representing the multi-value quantization result (step S136). Similarly to the threshold th1, the threshold th3 is set based on the dot recording rate in FIG. 18, and is set to th3 = (gr2 + 255) / 2 in the present embodiment. If the correction data Cdx is equal to or greater than the third threshold th3, the value 3 meaning the formation of a large dot is substituted for the value Cdr representing the multi-value quantization result (step S138). In the present embodiment, quaternary conversion is performed by the above processing. However, when the number of types of dots that can be formed increases and it is necessary to perform more multi-level conversion, the above-described threshold value is increased to increase the threshold. Can be processed.
[0064]
Next, the CPU 81 executes a process of calculating an error caused by the multi-value conversion and diffusing the error to peripheral pixels (step S140). The error refers to a value obtained by subtracting the tone value of the original image data from the evaluation value of the density represented by each dot after multi-value conversion. For example, considering a pixel having a gradation value of 255 in the original image data, the evaluation value of the density by forming a large dot is equivalent to the gradation value of 255, and the evaluation value of the density by forming a medium dot is equivalent to the gradation value of gr2. If it is determined that a large dot is to be formed for this pixel, no error occurs because the tone value of the original image data and the density evaluation value expressed are both equal to 255. On the other hand, if it is determined that a medium dot is to be formed, an error corresponding to Err = gr2-255 will occur.
[0065]
The error calculated in this way is diffused to peripheral pixels at the rate shown in FIG. For example, when an error corresponding to the gradation value 4 is calculated in the pixel PP of interest, an error corresponding to the gradation value 2 which is の of the error is diffused to the adjacent pixel P1. Will be. Similarly, errors are diffused for the other pixels at the ratio shown in FIG. The error diffused in this manner is reflected on the image data Cdx in step S124 described above, and diffusion error correction data Cdx is generated. When the processing for all the pixels is completed by the repetition of the above (step S142), the CPU 81 once ends the multi-value processing by error diffusion and returns to the dot formation control processing routine (FIG. 11).
[0066]
Through the above processing, any one of values 0 to 3 is assigned to the result value Cdr for each pixel. Based on this data, the printer 22 turns on / off each nozzle in accordance with the timing of the drive waveform to form dots having respective diameters.
[0067]
Here, the significance of setting the weight of the error distribution shown in FIG. 14 will be specifically described with reference to FIGS. For ease of explanation, consider a low gradation area recorded only with small dots, and set this area to gradation values 0 to 85 (gr1 = 85 in FIG. 15). Further, a threshold value (th1 in FIG. 12) for judging on / off of small dots and a density evaluation value of small dots are set to a value of 85.
[0068]
First, a case where a solid area having a constant gradation value 55 is formed will be considered. FIG. 16A shows a part of the image data. Since the tone value 55 of the target pixel PP is larger than the threshold value 42, a small dot is formed (Step S132 in FIG. 12). As a result, the target pixel is in a state (density evaluation value 85) darker than the density to be originally expressed, and therefore, an error Err having a value of 85−55 = 30 occurs in the target pixel PP. If this error is diffused to the surrounding pixels by the distribution shown in FIG. 13 (see FIG. 16A), for example, the error distributed to the adjacent pixel P1 becomes the value 8, and further distributed to the adjacent pixel P2. The error has a value of 4. If these errors are reflected, the gradation value of the pixel P1 is 55-8 = 47, and the gradation value of the pixel P2 is 55-4 = 51. Since the pixel P1 has a value larger than the threshold value 42, a small dot is formed. In FIG. 16B, pixels where dots are to be formed are hatched. The pixel P2 is not hatched in FIG. 16B because the dot generation is determined in consideration of the error from the pixel P1.
[0069]
On the other hand, FIG. 17 shows a state in which the error is diffused by the distribution of FIG. As in FIG. 16, an error Err having a value of 30 occurs in the target pixel PP. If this error is diffused to peripheral pixels by the distribution shown in FIG. 14 (see FIG. 17A), for example, the error distributed to the adjacent pixel P1 becomes the value 15, and further distributed to the adjacent pixel P2. The error has a value of 4. If these errors are reflected, the gradation value of the pixel P1 is 55−15 = 40, and the gradation value of the pixel P2 is 55−4 = 51. Since the pixel P1 is smaller than the threshold value 42, no dot is formed.
[0070]
As described above, if the error distribution to the pixel P1 adjacent to the pixel PP of interest is set to be large by the error distribution as shown in FIG. 14, it is determined that a dot should be formed for the pixel PP of interest. In this case, the formation of dots on the adjacent pixel P1 is suppressed. In this sense, it can be said that the setting of the error distribution shown in FIG. 14 functions as one of the means for suppressing the occurrence of dots in the pixel P1 adjacent to the pixel PP of interest. As described above, the error distribution for suppressing the occurrence of dots is not limited to the distribution shown in FIG. 14, but can be variously set according to the above-described threshold th1 and the dot density evaluation value.
[0071]
Next, the CPU 81 performs rasterization (step S210). This means that the data for one raster is rearranged in the order in which the data is transferred to the head of the printer 22. There are various modes in a recording method in which the printer 22 forms a raster. The simplest mode is one in which all dots of each raster are formed by one forward movement of the head. In this case, data for one raster may be output to the head in the processing order. Another mode is so-called overlap. For example, this is a recording method in which dots of each raster are formed every other dot in the first main scan, and the remaining dots are formed in the second main scan. In this case, each raster is formed by two main scans. When such a recording method is adopted, it is necessary to transfer data obtained by picking up every other dot of each raster to the head. There is a so-called bidirectional recording as another recording mode. This is to form dots not only during the forward movement of the head but also during the backward movement. When such a recording mode is adopted, it is necessary to reverse the transfer order of the data for the forward movement and the data for the backward movement. The process in step S210 creates data to be transferred to the head in accordance with the recording method performed by the printer 22. When the data that can be printed by the printer 22 is thus generated, the CPU 81 outputs the data and transfers the data to the printer 22 (step S215).
[0072]
According to the printing apparatus described above, as described with reference to FIGS. 16 and 17, when a dot is formed for a certain pixel, formation of a dot is suppressed for a pixel adjacent in the main scanning direction. Can be multivalued. As a result, according to the printing apparatus, it is possible to prevent the adjacent dots from coming into contact with each other and to prevent bleeding or the like, thereby improving the image quality.
[0073]
In the above-described embodiment, since the distribution shown in FIG. 14 is used in the error diffusion process (step S140 in FIG. 12), the same distribution is used for all the large, medium, and small dots. As described above, the setting of the error distribution shown in FIG. 14 is a setting for suppressing the formation of dots in the pixel P1 adjacent to the pixel of interest PP from the viewpoint of suppressing bleeding or the like due to contact between dots. . Considering factors that affect image quality other than bleeding, such as the occurrence of so-called false contours, the distribution shown in FIG. 13 may be more preferable. Even if dots are small in diameter such that there is no possibility that the dots will contact each other even when the dots are formed in the adjacent pixel P1, or even if the dots contact each other in a high density area where the dots are densely formed, bleeding may occur. For a dot that does not affect the image quality, a normal error distribution (for example, the distribution shown in FIG. 13) can be used. In such a case, a plurality of tables (for example, FIGS. 13 and 14) indicating the error distribution may be prepared, and the tables may be selectively used according to the types of dots determined to be formed. This makes it possible to suppress the contact between dots while utilizing the characteristics of the table shown in FIG.
[0074]
In FIG. 14, the error distribution is set so as to suppress the occurrence of dots in the pixel P1 adjacent to the target pixel PP. For example, if the diameter of the dot is so large that a dot formed on the pixel P2 (FIG. 14) adjacent to the pixel of interest with a gap therebetween may also be in contact with the pixel of interest, the distribution to the pixel P2 The dot formation can also be suppressed by increasing the error. As described above, the setting of the error distribution in FIG. 14 can be variously set in accordance with the dot diameter and the pitch at which the dots are recorded.
[0075]
Further, the setting of the error distribution may be changed according to the number of main scans required to form each raster. In FIG. 14, the formation of dots on the pixel P1 adjacent to the pixel of interest PP is suppressed. This is because, when all the dots of the raster are formed in one main scan, the adjacent pixels are the pixels which are most likely to cause bleeding or the like.
[0076]
On the other hand, when rasters are formed by the so-called overlap method, the necessity of suppressing the formation of dots for the adjacent pixel P1 decreases. For example, consider an overlap method in which a raster is completed by two main scans. At this time, every other dot of the raster is formed in the first main scan, and the remaining dots are formed in the second main scan. Therefore, it takes time from the formation of the target pixel PP to the formation of the adjacent pixel P1. In such a case, it is desirable to suppress the formation of dots in the pixel P2, which is a pixel formed in the same main scan as the target pixel PP, rather than the pixel P1 adjacent to the target pixel PP. FIG. 18 shows an example of error distribution set from such a viewpoint. The weight of the error distributed to the pixel P2 has a value of 1/4, and is set to be larger than the value 1/8 shown in FIGS. It should be noted that this value was not set to be as large as the weight (value ２) allocated to the pixel P1 in FIG. 14 because the error resulting from the multi-level conversion of the pixel P1 for the pixel P2 is further increased. This is in consideration of distribution. The distribution in FIG. 18 can also be variously set according to the necessity of suppressing the generation of dots.
[0077]
With the same concept, even when a raster is constituted by three or more main scans, various distributions of errors can be set. Alternatively, a plurality of error distribution tables set according to the number of main scans may be prepared, and each table may be used properly according to the designation of the print mode.
[0078]
In the above-described embodiment, the multi-value conversion is performed so as to suppress the contact between the dots in the entire area of the image data. However, this may be performed only in a part of the image. For example, it is also possible to perform multi-valued processing that suppresses contact between dots only in a region where the recording density of dots is low, that is, in a region where large dots formed by contact between dots are easily visible and image quality is easily impaired. Good. An example of such an area is an area where the recording rate is 50% or less. For example, the following method can be considered as means for realizing such multi-value processing.
[0079]
According to the relationship between the recording rate and the gradation value shown in FIG. 15, in the case of the present embodiment, the region where the dot recording density is low corresponds to the region where the gradation value is low. Of course, the range can be changed in accordance with the setting of the dot recording rate, but the correspondence between the recording rate and the gradation value can be obtained. For example, it is assumed that an area where the dot recording rate is low has a tone value grl or less. In this case, when the image data Cd is input in the multi-value conversion in FIG. 12, the magnitude of each image data Cd is compared with the gradation value grl, and the formation of the contacting dots is suppressed only when Cd <grl. What should I do?
[0080]
(3) Second embodiment
Next, a printing apparatus according to a second embodiment of the present invention will be described. The printing apparatus according to the second embodiment has the same hardware configuration as the printing apparatus according to the first embodiment (FIGS. 1 to 10) described above. The same applies to the flow of the dot formation control processing routine (FIG. 11). In the present embodiment, the contents of the multi-value processing are different from those of the first embodiment. A description will be given of multi-value conversion in the second embodiment.
[0081]
FIG. 19 is a flowchart showing the flow of the multi-value processing in the second embodiment. The basic processing contents are the same as those of the multi-value conversion in the first embodiment (see FIG. 12). In the first embodiment, the formation / non-formation of each dot is determined by comparing the magnitude of the diffusion error correction data Cdx with the thresholds th1, th2, and th3 (steps S126, S130, and S134 in FIG. 12). In contrast, in the second embodiment, the value obtained by adding the threshold noise Ns to each threshold value is compared with the diffusion error correction data Cdx (steps S125, S131, and S135 in FIG. 19), and each dot is turned on. -The difference is that it is determined to be off. This threshold noise Ns is set according to the result of turning on / off each dot (step S141 in FIG. 19). The second embodiment also differs from the first embodiment in that a commonly used distribution (FIG. 13) is used as the distribution of the diffusion error. In the present embodiment, the threshold noise Ns corresponds to a part of the suppression unit in the present invention.
[0082]
The setting of the threshold noise Ns will be described. When the threshold noise Ns is a positive value, it means that the threshold value involved in turning on / off each dot becomes large. Therefore, as is clear from the flowchart of FIG. 19, formation of each dot is suppressed. Will be done. In the second embodiment, a positive predetermined value is set as the threshold noise Ns when it is determined to turn on the dot for a certain pixel, and the threshold noise Ns is set to a value 0 when the determination is made to turn off the dot. I do. With this setting, dot formation is suppressed at a pixel adjacent to a pixel where a dot is to be formed, and contact between dots can be suppressed. In the second embodiment, the threshold noise Ns is used as one means for suppressing the contact of dots.
[0083]
The value set as the threshold noise Ns can be determined based on the diameter of the dot and the recording pitch in response to a request for suppressing the contact of the dot. Further, a threshold noise Ns that is reflected in multi-level conversion for a plurality of pixels may be set. FIG. 20 shows an example of the threshold noise Ns. FIG. 20 is an explanatory diagram illustrating threshold noise Ns set for pixels P1, P2, and P3 that are sequentially adjacent to the pixel of interest PP in the main scanning direction. In such a setting, when performing multi-valued processing for the pixel P1, dot on / off is determined based on a value obtained by adding the threshold noise Ns1 to the threshold th1, and the threshold noise is set to the threshold th1 for the pixel P2. On / off of the dot is determined based on the value obtained by adding Ns2. Depending on whether the dot of the pixel P1 is on or off, the threshold noise Ns1 may be further added to the pixel P2. If the threshold noise Ns is set in this manner, for example, there is a case where the dot diameter is so large that there is a possibility that a dot contact may occur even in a pixel P2 adjacent to the pixel PP of interest with a gap therebetween. Also, the occurrence of dots in the pixel P2 can be suppressed.
[0084]
The threshold noise Ns is a value that can be variously set according to a request to suppress the contact of dots. For example, when setting the threshold noise Ns affecting a plurality of pixels as shown in FIG. The threshold noise Ns can be set to be smaller in accordance with the distance from. In general, the closer to the pixel PP of interest, the higher the necessity of avoiding contact with the dots. Therefore, if the setting is made as shown in FIG. Can be suppressed.
[0085]
The threshold noise Ns can also be set according to the number of main scans for forming a raster. FIG. 21 is an explanatory diagram showing the setting of the threshold noise Ns in the case of performing the overlap type recording in which the raster is formed by two main scans. As described in the first embodiment, when performing the overlap recording, it is desired to suppress the occurrence of dots in the pixel P2 adjacent to the pixel PP of interest more than the pixel P1 adjacent to the pixel PP of interest. . If the threshold noise Ns shown in FIG. 21 is used, the threshold noise Ns is increased at the pixel P2 adjacent to one pixel PP of interest, so that the generation of dots at the pixel PP is suppressed. Can be. The threshold value noise Ns can be set by changing various pixels in accordance with the number of main scans for forming a raster. A plurality of threshold noises may be prepared and selectively used according to the number of main scans for forming a raster. Further, in the second embodiment, as in the first embodiment, for example, dot formation may be suppressed only in an image area having a low dot recording rate.
[0086]
In the second embodiment, the error diffusion method is used as the multi-level conversion means, but a dither method, which is another typical method, may be used. Although the specific processing of the dither method is not described, it is a multivalued method of forming dots when the tone value of each pixel is larger than a threshold value given by a so-called dither matrix. If the threshold noise Ns set in the second embodiment is added to the threshold given by the dither matrix, it is possible to suppress the occurrence of dots. However, since the dither matrix is not a method that can naturally eliminate the brightness error caused by adding such threshold noise Ns, when the threshold noise Ns is added to any pixel, the threshold noise Ns is added to another pixel. It is desirable to minimize the brightness error by subtracting.
[0087]
(4) Third embodiment
Next, a printing apparatus according to a third embodiment of the present invention will be described. The printing apparatus of the third embodiment has the same hardware configuration as that of the first embodiment (FIGS. 1 to 10). In the third embodiment, the flow of the dot formation control processing routine is different from that of the first embodiment (FIG. 11). The routine will be described.
[0088]
FIG. 22 is a flowchart showing the flow of the dot formation control processing routine of the third embodiment. This routine is the same as the dot formation control processing routine in the first embodiment up to the input of image data, resolution conversion, color correction processing, and multi-value processing (steps S100, S105, S110, S120). The content of the multi-value processing is the same as the processing in the first embodiment (FIG. 12). In this embodiment, a distribution (FIG. 13) that is generally used as a distribution for diffusing an error is used.
[0089]
After the multi-value conversion is completed, the number of contact pixels is counted in the dot formation control processing routine of the third embodiment (step S208). The number of contact pixels refers to the number of pixels in which dots that can be contacted with the dots formed in the pixels are formed. The contact pixel count will be specifically described with reference to FIG. FIG. 23 is an explanatory diagram showing a state in which dots to be formed in each pixel are determined by multileveling. For convenience of illustration, 10 pixels each in the vertical and horizontal directions are shown. In the following description, each pixel is represented by using the numbers L1 to L10 and C1 to C10 shown in FIG. 23, for example, as (L1, C1).
[0090]
Now, focus on the pixel (L2, C2). This pixel is a pixel on which a dot is to be formed. However, a dot that can contact this dot is not formed in any pixel. Therefore, the number of touching pixels for the pixel (L2, C2) has a value of 0.
[0091]
Next, attention is paid to the pixels (L1, C4) that are the pixels on which dots are to be formed. The dot formed in the pixel (L2, C5) is in contact with the dot formed in this pixel. As described above, in the printer 22 of the present embodiment, the carriage performs the main scanning to form the raster. Then, due to the mechanism, rasters adjacent in the sub-scanning direction cannot be formed by one main scanning. Therefore, for the printer 22 of the present embodiment, the contact of dots that occurs in the sub-scanning direction cannot cause bleeding or the like and does not affect the image quality. Therefore, in the present embodiment, when the contact of dots occurs in the sub-scanning direction, it is ignored. Since the pixels (L2, C5) do not touch any dots when viewed in the main scanning direction, the number of touching pixels is 0. Of course, in the case of a printer in which contact in the sub-scanning direction affects image quality, the number of contact pixels of the pixels (L2, C5) may be set to a value of one.
[0092]
Next, paying attention to the pixel (L2, C5), since the dot formed in the pixel (L2, C6) adjacent in the main scanning direction is in contact with the dot of this pixel, the number of contact pixels is 1 It becomes. As for the pixel (L2, C6), since the dots formed on both the pixels (L2, C5) and (L2, C7) adjacent in the main scanning direction are in contact with each other, the number of contact pixels is 2 Become.
[0093]
Pixels adjacent in the main scanning direction do not always correspond to contact pixels. For example, focusing on the pixels (L5, C1), (L5, C2), and (L5, C3) arranged in the main scanning direction, since small dots are formed in these pixels, none of the dots are in contact with each other. It is. Therefore, the number of contact pixels for these pixels is all zero.
[0094]
In addition, there may be cases where a pixel other than a pixel adjacent in the main scanning direction is a contact pixel. For example, focusing on the pixels (L6, C5), (L6, C7), and (L6, C9) on which the large dots are formed, these pixels are not pixels adjacent to each other in the main scanning direction. In contact. Therefore, the number of touching pixels becomes value 1 or value 2, respectively. Furthermore, paying attention to the pixel (L8, C1), since the dots formed in both the pixels (L8, C2) and (L8, C3) are in contact, the value of the number of contacted pixels is 2.
[0095]
As described above based on the specific example, the number of contact pixels can be determined according to the dot diameter and the dot recording position. In the case of the present embodiment, if a large dot is formed between adjacent pixels with one space therebetween in the main scanning direction, they can make contact with each other, but no dot contact can occur with a pixel further away. Therefore, the number of touching pixels can be obtained by examining the types of dots formed in two pixels on the left and right in the main scanning direction for each pixel on which dots are formed. In step S208 in FIG. 22, the number of contact pixels for each pixel is obtained in this manner, and the maximum value is obtained.
[0096]
Next, the CPU 81 sets the number of main scans (hereinafter referred to as the number of passes) required to form each raster according to the maximum value of the number of contact pixels. For example, if the number of touching pixels is 0, it means that none of the dots are touching, so the number of passes is set to 1. In this case, even if each raster is formed by one main scan, bleeding or the like due to contact between dots does not occur.
[0097]
If the number of touching pixels is 1, it means that two dots are touching at any point. Therefore, in this case, the number of passes is set to the value 2. This is because, if the dots that are in contact with each other are formed in two main scans, bleeding or the like does not occur even if the dots are in contact with each other. From the above example, the number of passes can be set by “the maximum value of the number of contact pixels + 1”. Of course, the value may be set to a value larger than this, or may be set to a value smaller than this as long as the number of passes that can appropriately avoid bleeding due to contact between dots can be set.
[0098]
After setting the number of passes in this way, the CPU 81 performs rasterization and outputs data (steps S210 and S215). These processes are the same as in the first embodiment. However, in the rasterization, it is desirable to appropriately assign a contacting dot to each main scan. For example, consider the case where the number of passes is the value 2. In this case, the odd-numbered dots of the raster are formed in the first main scan (C1, C3, C5, etc. in FIG. 73), and the even-numbered dots (C2, C4, C4) of the raster are formed in the second main scan. C6, etc.) is a simple method. However, in this case, the pixels (L6, C5), (L6, C7), and (L6, C9) in FIG. 73 are formed in the first main scan, and bleeding occurs at the contact portion. Therefore, in the rasterization, for example, the data is set such that the pixels (L6, C5) and the pixels (L6, C9) are formed in the first main scan, and the pixels (L6, C7) are formed in the second main scan. It is desirable to set. In the present embodiment, the above assignment is realized by storing the position of the contact pixel for each pixel when detecting the contact state of the dots for all the pixels when counting the number of contact pixels.
[0099]
According to the printing apparatus of the third embodiment, by forming the dots that are in contact with each other in a plurality of main scans, it is possible to avoid the occurrence of bleeding or the like in the contact and to improve the image quality. Since the setting of the number of passes is usually closely related to the feed amount in the sub-scanning direction, the third embodiment has been described on the assumption that the entire image is formed with a fixed number of passes. The number may be changed. For example, an image may be formed only in a region near a pixel having a large number of contact pixels with a larger number of passes than in other regions. In this way, it is possible to minimize a decrease in printing speed due to an increase in the number of passes. Further, as in the first embodiment, the number of contact pixels can be counted only in an area where the dot recording rate is low to determine the number of passes.
[0100]
In the third embodiment, the error diffusion method is used as a method of multi-value conversion, but multi-value conversion may be performed using a dither method, which is another typical method.
[0101]
The CPU 81 of the computer 90 performs the dot formation control processing in each embodiment described above. Therefore, the above-described embodiment can also take an aspect as a computer-readable recording medium that records a part or all of the respective dot formation control processes. Examples of such a storage medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, and a computer internal storage device (such as a RAM or a ROM). Various computer readable media are available, such as memory and external storage. Further, an embodiment as a program supply device for supplying a computer program for performing the above-described multi-value conversion to a computer via a communication path is also possible.
[0102]
Although the embodiments described above are directed to the printer 22 with main scanning, the present invention has a plurality of nozzles in the raster direction and can be applied to a printer capable of forming a raster without main scanning. It is. Further, a part of each dot formation control processing routine described above can be used in combination.
[0103]
Further, in each of the above-described embodiments, a description has been made as to avoid contact between dots formed with each color ink in a printer equipped with multi-color inks. However, the present invention is also applicable to a printer equipped with a single color ink. It is possible, and it is possible to avoid contact with dots formed with different inks (eg, other colors or densities of ink).
[0104]
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 implemented without departing from the gist of the present invention. For example, various control processes described in the above embodiments may be partially or entirely realized by hardware.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present invention.
FIG. 2 is an explanatory diagram illustrating a configuration of software.
FIG. 3 is a schematic configuration diagram of a printer of the present invention.
FIG. 4 is an explanatory diagram showing a schematic configuration of a dot recording head of the printer of the present invention.
FIG. 5 is an explanatory diagram showing a dot formation principle in the printer of the present invention.
FIG. 6 is an explanatory diagram showing an example of a nozzle arrangement in the printer of the present invention.
FIG. 7 is an enlarged view of a nozzle arrangement in the printer of the present invention and an explanatory diagram showing a relationship with a formed dot.
FIG. 8 is an explanatory diagram illustrating the principle of forming dots having different diameters by the printer of the present invention.
FIG. 9 is an explanatory diagram showing an internal configuration of a control device of the printer.
FIG. 10 is an explanatory diagram showing a nozzle driving waveform and a dot formed by the driving waveform in the printer of the present invention.
FIG. 11 is a flowchart illustrating a flow of a dot formation control routine according to the first embodiment.
FIG. 12 is a flowchart showing a flow of a multi-value processing by error diffusion in the first embodiment.
FIG. 13 is an explanatory diagram showing an error distribution normally used in error diffusion.
FIG. 14 is an explanatory diagram showing error distribution used in error diffusion in the first embodiment.
FIG. 15 is an explanatory diagram showing a dot recording rate in the first embodiment.
FIG. 16 is an explanatory diagram showing a relationship between error distribution and dot formation in a normal error diffusion method.
FIG. 17 is an explanatory diagram showing a relationship between error distribution and dot formation in the error diffusion method in the first embodiment.
FIG. 18 is an explanatory diagram showing a second error distribution used in error diffusion in the first embodiment.
FIG. 19 is a flowchart showing a flow of a multi-value processing by the error diffusion method in the second embodiment.
FIG. 20 is an explanatory diagram showing setting of threshold noise.
FIG. 21 is an explanatory diagram showing a second setting of threshold noise.
FIG. 22 is a flowchart illustrating a flow of a dot formation control processing routine according to the third embodiment.
FIG. 23 is an explanatory diagram illustrating counting of the number of contact pixels.
FIG. 24 is an explanatory diagram showing setting of a dot diameter.
FIG. 25 is an explanatory diagram showing a state where dots are formed in adjacent pixels.
FIG. 26 is an explanatory diagram showing a state of a dot when dot bleeding occurs.
FIG. 27 is an explanatory diagram showing a state of a dot when the dot is elliptical.
[Explanation of symbols]
12 ... Scanner
14 ... Keyboard
15… Flexible drive
16 ... Hard disk
18… Modem
21 ... Color display
22 ... Color printer
23 ... Paper feed motor
24 ... Carriage motor
26 ... Platen
28 ... Print head
31 ... carriage
32 Operation panel
34 ... 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: Peripheral input / output unit (PIO)
46 ... Timer
47 ... Drive buffer
48… Bus
51… Transmitter
55 ... distribution output device
61, 62, 63, 64, 65, 66 ... head for ink ejection
67… Introduction pipe
68 ... Ink passage
71: Cartridge for black ink
72 ... Color ink cartridge
80 ... Bus
81 ... CPU
82 ROM
83 ... RAM
84 input interface
85 Output interface
86 ... CRTC
87 ... Disk controller (DDC)
88: Serial input / output interface (SIO)
90 ... Personal computer
91 ... Video driver
95 ... Application program
96 ... Printer driver
97 ... Resolution conversion module
98 ... Color correction module
99 ... Halftone module
100 ... rasterizer

Claims (10)

Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing device that prints an image corresponding to the input image data on the print medium,
For each pixel corresponding to the image data, when the image data for each pixel is larger than a predetermined threshold, the pixel is determined to be the formation pixel, thereby determining whether the pixel is a formation pixel as a pixel to be formed. Pixel determination means for determining whether to be a blank pixel as a pixel not forming
The pixel determining means is operated so as to switch the determination method according to the determination result, and a dot having a diameter such that pixels around the formation pixel can contact the dots formed in the formation pixel should be formed. Suppression means for suppressing the determination of forming pixels;
Dot forming means for driving the head to form dots in accordance with the result determined by the pixel determining means ,
The printing apparatus, wherein the suppression unit is a unit that switches the determination method by setting the threshold value larger for a suppression pixel that is a pixel that should suppress formation of a dot having a contactable diameter than for a pixel that does not. The printing device according to claim 1 ,
The printing apparatus, wherein the deviation amount that increases the threshold value is a value that decreases as the distance between the formation pixel and the suppression pixel increases. The raster is formed by main scanning that reciprocates the head relatively to the print medium in the raster direction,
2. The printing apparatus according to claim 1, wherein the peripheral pixels are pixels located in the main scanning direction with respect to the formation pixels, and are pixels formed continuously with the formation pixels in the main scanning. 3. The printing device according to claim 1,
The peripheral pixels in which the formation of the dots is suppressed are determined according to the relative number of movements of the head and the print medium in a direction intersecting the raster performed while all the dots forming the raster are formed. A printing device which is a pixel separated from the formation pixel by a distance. The printing device according to claim 1,
The printing apparatus, wherein the suppression unit is a unit that suppresses the formation of the dots in an area where the dot recording rate is 50% or less. Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing device that prints an image corresponding to the input image data on the print medium,
For each pixel corresponding to the image data, a pixel determination unit that determines whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
For each formed pixel, means for determining the number of contact pixels, which are pixels that are formed pixels of a dot having a diameter that can contact a dot to be formed in the formed pixel,
A dot forming unit that divides by a division number set based on a maximum value of the number of contact pixels to form dots of each raster. Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing method for printing an image corresponding to the input image data on the print medium,
(A) For each pixel corresponding to the image data, when the image data for each pixel is larger than a predetermined threshold, the pixel is determined to be the formation pixel, and a pixel to be formed as a dot is determined as a formation pixel. Determining whether to perform a blank pixel as a pixel that does not form a dot,
(B) In the step (a), by switching the determination method according to the determination result, a dot having a diameter that allows pixels around the formation pixel to come into contact with dots formed in the formation pixel is formed. Suppressing the determination of the formation pixel to be formed;
(C) driving the head according to the result determined in the step (a) to form dots .
The step (b) is a step of switching the method of the determination by setting the threshold value larger for the suppressed pixels, which are the pixels to be suppressed in forming the dots having the contactable diameters, than for the pixels that are not. Method. Forming a raster as a dot row arranged in one direction at a predetermined recording pitch by discharging ink from the head, and moving the print medium relative to the head in a direction intersecting the raster, A printing method for printing an image corresponding to the input image data on the print medium,
(A) determining, for each pixel corresponding to the image data, whether to form a pixel to be formed with a dot or a blank pixel as a pixel not forming a dot;
(B) for each formation pixel, a step of calculating the number of contact pixels, which are pixels forming dots having a diameter that allows contact with the dots to be formed in the formation pixel;
(C) forming a dot of each raster by dividing by a division number set based on the maximum value of the number of contact pixels. A computer-readable recording medium for recording a program for setting data common to a printing apparatus that prints an image corresponding to input image data on a print medium by ejecting ink, wherein at least the image data For each corresponding pixel, when the image data for each pixel is larger than a predetermined threshold, the pixel is determined to be the formation pixel, so that the pixel to be formed as a pixel to be formed or a pixel not to form a dot A function to determine whether to be a blank pixel,
In the determining function, for the suppression pixel, which is a pixel that should suppress the formation of a dot having a contactable diameter, the determination method is performed according to the determination result by increasing the threshold value as compared with a pixel that does not have the diameter. By switching, a function of suppressing the determination of a pixel around the formation pixel to be a formation pixel on which a dot having a diameter that can be in contact with the dot formed on the formation pixel should be formed is recorded. Medium. A computer-readable recording medium for recording a program for setting data in common with a printing apparatus that prints an image corresponding to input image data on a print medium by ejecting ink,
For each pixel corresponding to the image data, a function of determining whether to be a formation pixel as a pixel to form a dot or a blank pixel as a pixel not forming a dot,
For each formed pixel, a function of calculating the number of contact pixels that are pixels that are formed pixels of a dot having a diameter capable of contacting a dot to be formed in the formed pixel,
A recording medium on which a program for realizing a function of setting a series of recording times required for forming each raster based on the maximum value of the number of contact pixels is recorded.

Images