JP3772525B2 - Printing apparatus and printing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a printing apparatus and a printing method for printing a multi-tone image by driving a head including a nozzle capable of forming dots continuously at intervals smaller than the pixel interval in the main scanning direction.
[0002]
[Prior art]
Conventionally, as an output device of a computer, an ink jet printer for recording an image by forming dots with several colors of ink ejected from a plurality of nozzles provided in a head has been proposed. Widely used for printing with multiple colors and multiple gradations. In recent years, in order to enrich gradation expression, an ink jet printer capable of expressing gradation of two or more values, on / off for each dot, a so-called multi-value printer has been proposed. For example, a printer that can express three or more types of density for each dot by changing the dot diameter and ink density, and a multi-gradation can be expressed by forming a plurality of dots overlapping each pixel. It is a printer.
[0003]
FIG. 8 is an explanatory diagram showing how dots with different diameters are formed by a multi-value printer. This printer includes a piezo element PE in the head, and ejects ink droplets according to a voltage applied to the piezo element. As shown in the upper stages W1, W2, and W3 of FIG. 8, if the voltage waveform applied to the piezo element, that is, the drive waveform is changed, the ink droplets IP1, IP2, and IP3 respectively correspondingly have small, medium, and large diameters. Dots (hereinafter referred to as small dots, medium dots, and large dots, respectively) can be formed. In the drive waveform shown in FIG. 8, the larger the ink droplet, the higher the amplitude of the drive waveform and the higher the flying speed of the ink.
[0004]
Consider a case where the carriage 31 incorporating the head forms dots while moving in the main scanning, that is, in the direction shown in the middle of FIG. FIG. 23 schematically shows how small dots and medium dots are formed first. In FIG. 23, dw1 and dw2 shown in the upper part of FIG. 23 are drive waveforms for forming small and medium dots, and IP1 and IP2 indicate ink droplets ejected by the respective drive waveforms. The squares labeled c1 to c4 indicate pixels on which dots are formed on the paper.
[0005]
As described above, since the flying speed varies depending on the dot diameter, the drive waveform dw1 for forming the small dot IP1 and the drive waveform dw2 for forming the medium dot IP2 as shown in the upper part of FIG. Can be formed in the same pixel c1 by adjusting the timing and continuously outputting them. When the drive waveform dw2 is being output, if a mask signal that prohibits ink ejection from the head is sent, only the small dot IP1 can be formed. Similarly, it is possible to form only the medium dot diameter. As a result, in the multi-value printer shown in FIG. 23, for each pixel, “no dot formation” “small dot formation” “large dot formation” “small diameter dot and large diameter dot” It is possible to express four values of “overlapping”.
[0006]
[Problems to be solved by the invention]
However, in such a multi-value printer, there is a limit in increasing the gradation values that can be expressed for each pixel by increasing the types of drive waveforms. FIG. 24 shows how dots are formed when the drive waveform dw3 is further increased in the multi-value printer shown in FIG. The ink droplet IP3 ejected by the drive waveform dw3 is larger than the ink droplet IP2, and the flying speed is fast. However, since the carriage moves in the main scanning direction while the drive waveforms dw1, dw2, and dw3 are output, the ink droplet IP3 is not formed in the pixel c1 when the movement speed of the carriage is high. 24, it may be formed at a position protruding in the main scanning direction. If the dots are formed so as to protrude from the pixels, the image quality of the printed image is greatly deteriorated. Originally, a multi-value printer aims at high-quality printing by increasing the number of gradations that can be expressed for each pixel, and such a decrease in image quality cannot be overlooked.
[0007]
Even if the ink droplet IP3 can be formed on the pixel c1 in FIG. 24, the same problem will occur if the number of types of drive waveforms is further increased. For this reason, in a multi-value printer that continuously outputs two or more types of drive waveforms to form dots having different diameters, there is a limit to the number of gradations that can be expressed for each pixel.
[0008]
Such a problem can also be solved by reducing the speed at which the carriage moves in the main scanning direction, but in this case, another problem of a decrease in printing speed occurs. Also, in FIG. 24, it is possible to treat a large pixel (a pixel indicated by a broken line in FIG. 24) that includes the position where the ink droplet IP3 is formed in the pixel as a unit. It means a reduction, which leads to a reduction in image quality.
[0009]
In the above description, a printer using a piezo element has been described as an example. However, a similar problem may occur in a printer that discharges ink droplets by energizing a heater to generate bubbles in ink. The same problem may occur not only in dots having different diameters but also in a multi-value printer that forms dots with inks having different densities and a printer that expresses multiple gradations by overlapping a single type of dot.
[0010]
The present invention has been made to solve the above-described problems, and in a multi-value printer, prevents dots from being formed protruding from the pixels, and increases the possibility of gradation expression of the multi-value printer. An object of the present invention is to provide a technique that can improve image quality.
[0011]
[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.
The printing apparatus of the present invention includes:
While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing apparatus that prints an image corresponding to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming two or more dots at an interval narrower than an interval between the pixels,
By controlling the driving of the head, a predetermined correspondence between two or more dots that can be formed at an interval narrower than the interval between the pixels and two or more pixels adjacent in the main scanning direction, The gist of the invention is that it includes head control means for forming dots corresponding to the image data.
[0012]
The printing method of the present invention includes:
While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing method for printing an image according to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming two or more dots at an interval narrower than the interval between the pixels,
By controlling the driving of the head, a predetermined correspondence between two or more dots that can be formed at an interval narrower than the interval between the pixels and two or more pixels adjacent in the main scanning direction, The gist is to form dots according to the image data.
[0013]
According to such a printing apparatus and printing method, two or more dots that can be formed at an interval narrower than the interval between the pixels are periodically changed in a predetermined correspondence relationship with two or more pixels adjacent in the main scanning direction. Can be formed. To explain based on the example shown in FIG. 24, three types of dots IP1, IP2, and IP3 are formed corresponding to two or more pixels adjacent in the main scanning direction. For example, the dots IP1 and IP2 are formed to correspond to the pixel c1, and the dot IP3 is formed to correspond to the pixel c2. Of course, the dot IP1 may correspond to the pixel c1, and the dots IP2 and IP3 may correspond to the pixel c2. Further, since it corresponds to two or more pixels, the dot IP1 can correspond to the pixel c1, the dot IP2 to the pixel c2, and the dot IP3 to the pixel c3.
[0014]
Various correspondences can be set in the same manner when the types of dots that can be formed further increase. Naturally, the types of dots that can be formed are not limited to the three types shown in FIG. 24, and there may be more types or fewer types. Further, not only dots having different diameters as shown in FIG. 24 but also correspondences can be set not only for dots having different ink densities, but also for a single type of dot. In the case of a single type of dot, for example, it is possible to set a correspondence relationship in which two dots are formed on the above-described pixel c1 and formed without overlapping dots on the pixel c2. In this way, the correspondence can be variously set according to the number of dots that can be formed by the head at an interval narrower than the interval between the pixels.
[0015]
If the correspondence relationship is set in advance such that the dots IP1 and IP2 correspond to the pixel c1 and the dot IP3 corresponds to the pixel c2, the printing apparatus and the printing method periodically set each dot based on this correspondence relationship. To form. That is, in the description of the example of FIG. 24, dots IP1 and IP2 are formed in the pixel c3, and dots IP3 are formed in the pixel c4. The same applies to the other correspondence relationships described above. According to the printing apparatus and the printing method described above, by forming dots in association with two or more pixels in this way, each dot can be formed without protruding from each pixel, and the image quality can be improved. .
[0016]
When one correspondence relationship between the dot and the pixel is set, there is a possibility that an arbitrary dot cannot be formed in each pixel constituting the raster that is a dot row in the main scanning direction. For example, in the above example, the dot IP3 cannot be formed in the pixel c1, and conversely, the dots IP1 and IP2 cannot be formed in the pixel c2.
[0017]
Therefore, in the printing apparatus,
The head control means includes
While forming the dots to be formed in the main scanning direction divided into a plurality of main scanning,
The correspondence relationship is preferably means for controlling driving of the head so as to form dots with different correspondence relationships for each of the plurality of main scans.
[0018]
By so doing, dots are formed by a plurality of main scans in which the correspondence between the dot type and the pixel is different, so that an arbitrary dot can be formed for each pixel. To explain the above example, in a printing apparatus that periodically forms dots IP1, IP2, and IP3, for example, in the first main scan, the dots c1 and IP2 correspond to the pixels c1 and the dots c2 correspond to the dots c2. Dots are formed corresponding to IP3. In the second main scan, the same raster is formed by associating the dot IP3 with the pixel c1 and the dots IP1, IP2 with the pixel c2. By doing so, all the pixels of the dots IP1, IP2, and IP3 can be formed on both the pixels c1 and c2. The same applies to the case where dots are formed by other correspondence relationships.
[0019]
Note that any dot can be formed in each pixel even if any one of the above-described dots is formed for each main scan. For example, only the dot IP1 is formed on all pixels in the first main scan, and only the dot IP2 is formed in the second main scan. The above-described printing apparatus is superior in image quality to a printing apparatus that performs such recording. Such characteristics are obtained by periodically forming a plurality of types of dots for each main scan.
[0020]
When a single type of dot is formed in each main scan, all the rasters are formed in one main scan when viewed for each type of dot. When such recording is performed, if a dot formation position shift occurs due to a mechanical manufacturing error of the nozzle, the entire raster is formed shifted, resulting in a deterioration in image quality. On the other hand, according to the printing apparatus, since each raster is formed by a plurality of main scans while periodically forming a plurality of types of dots, each raster is formed by a plurality of main scans even when viewed for each type of dots. It will be formed. As a result, the shift that can occur at the dot formation position can be averaged over the entire raster, and the image quality can be improved.
[0021]
In a printing apparatus that forms a raster by a plurality of main scans,
It is desirable that the plurality of main scans are the number of main scans corresponding to the number of pixels for which the correspondence relationship is determined.
[0022]
In this way, each raster can be configured with the minimum necessary main scanning. Therefore, the printing speed can be most improved in a printing apparatus that forms each raster by a plurality of main scans.
[0023]
In the printing apparatus of the present invention,
The two or more dots may be two or more types of dots having different diameters.
[0024]
In order to form two or more types of dots having different diameters in this way, it is necessary to periodically output signals corresponding to the respective diameters to the head. In this state, if the number of types of dots is increased, the dots are likely to be formed out of the pixels, so that the present invention can be used effectively.
[0025]
As an example,
The two or more types of dots are three types of dots each having a large diameter, a medium diameter, and a small diameter,
The correspondence relationship may be a relationship in which a small-diameter dot and a medium-diameter dot are associated with one pixel, and a large-diameter dot is associated with a pixel adjacent to the pixel.
[0026]
In such a case, the number of gradations that can be expressed for each pixel can be increased by forming dots with the above three diameters. Further, since the small-diameter and medium-diameter dots are formed so as to correspond to one pixel, it is possible to form every other type of dot in the main scanning direction every other main scanning. As a result, even if each raster is formed by one main scan, the recording rate of each type of dot can be sufficiently secured. Further, in order to form an arbitrary dot in each pixel, it is sufficient to form each raster by two main scans, so that the printing speed is not greatly reduced.
[0027]
Other aspects of the invention
In the above-described printing apparatus of the present invention, when each raster is formed by one main scan, the types of dots that can be formed for each pixel are limited. Image processing to create the image is required. Therefore, as described below, the present invention can also take the form of a printing apparatus provided with means for realizing such image processing.
[0028]
A printing apparatus as another aspect of the present invention includes:
While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing apparatus that prints an image corresponding to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming two or more dots at an interval narrower than an interval between the pixels,
Storage means for storing a predetermined correspondence between two or more dots that can be formed at an interval narrower than the interval between the pixels and two or more pixels adjacent in the main scanning direction;
Multi-value conversion means for converting the input image data into multi-value gradation values that the head can express for each pixel;
For pixels in which the multi-valued image data does not correspond to dots that can be formed based on the correspondence stored in the storage unit, the image data of the pixels are pixels that are close to each other, and , Dot rearrangement means for replacing the dot corresponding to the image data with a formable pixel;
This is an aspect of a printing apparatus comprising: a head control unit that controls the driving of the head based on the image data replaced by the rearrangement unit and forms dots with the correspondence relationship stored in the storage unit.
[0029]
In such a printing apparatus, the multi-value conversion means multi-values the image data into gradation values that can be expressed for each pixel. Here, multi-value conversion is performed without considering the correspondence between pixels and formed dots. Therefore, for example, a gradation value for forming a large dot may be assigned to a pixel that is not associated with a large dot. In the printing apparatus, when there is such a pixel, the data is replaced with the data of adjacent pixels capable of forming a large dot by the dot rearrangement unit. Since the pixels are replaced with adjacent pixels, if the pixel interval is sufficiently small, the replacement does not cause deterioration in image quality. As a result, according to the printing apparatus of this aspect, it is possible to appropriately form dots according to the multivalued image data.
[0030]
In the above description, the case of three types of dots having different diameters is taken as an example. However, even when the type of dots changes or the correspondence changes, dots can be appropriately formed by the same process. is there.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples.
(1) Device configuration:
FIG. 1 is a block diagram showing the configuration of a printing apparatus as an embodiment of the present invention. As shown in the figure, a scanner 90 and a color printer 22 are connected to a computer 90, and a predetermined program is loaded and executed on the computer 90, thereby functioning as a printing apparatus as a whole. The computer 90 includes the following units interconnected by a bus 80 with a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. The ROM 82 stores programs and data necessary for executing various arithmetic processes by the CPU 81 in advance, 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 data exchange with the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). The hard disk 16 stores various programs loaded in the RAM 83 and executed, various programs provided in the form of device drivers, and the like.
[0032]
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, and a program necessary for image processing can be downloaded to the hard disk 16 by connecting to a specific server SV. It is also possible to load a necessary program from the flexible disk FD or CD-ROM and cause the computer 90 to execute it.
[0033]
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 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 performing image retouching 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. Data ORG supplied from the scanner 12 is original color image data ORG that is read from a color original and includes three color components of red (R), green (G), and blue (B).
[0034]
When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives image information from the application program 95, and signals that can be processed by the printer 22 (here, cyan, magenta, yellow, and black colors). 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.
[0035]
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 thus converted in resolution is still image information consisting of three colors of RGB, the color correction module 98 refers to the color correction table LUT, and cyan (C) and magenta used by the printer 22 for each pixel. (M), yellow (Y), and black (K) data are converted into data. The color-corrected data in this way has gradation values with a width of, for example, 256 gradations. The halftone module executes halftone processing for expressing such gradation values by the printer 22 by forming dots in a dispersed manner. The processed image data is rearranged in the order of data to be transferred to the printer 22 by the rasterizer 100 and output as final image data FNL. In this embodiment, the printer 22 only serves to form dots according to the image data FNL and does not perform image processing. Of course, the above-described processing may be performed by the printer 22.
[0036]
Next, a schematic configuration of the printer 22 will be described with reference to FIG. As shown in the figure, the printer 22 includes a mechanism for transporting the paper P by the paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and a print head mounted on the carriage 31. And a control circuit 40 for exchanging signals with the paper feed motor 23, the carriage motor 24, the print head 28 and the operation panel 32. .
[0037]
The mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 is an endless drive belt between the carriage motor 24 and a slide shaft 34 that is installed in parallel with the axis of the platen 26 and slidably holds the carriage 31. 36, a pulley 38 for extending 36, a position detection sensor 39 for detecting the origin position of the carriage 31, and the like.
[0038]
The carriage 31 accommodates a black ink (Bk) cartridge 71 and inks of five colors, cyan (C1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y). The color ink cartridge 72 can be mounted. For two colors, cyan and magenta, two types of light and dark inks are provided. A total of six ink ejection heads 61 to 66 are formed on the print head 28 below the carriage 31. An inlet pipe 67 (which guides ink from the ink tank to the color heads) is provided at the bottom of the carriage 31. (See FIG. 4). When a black (Bk) ink cartridge 71 and a color ink cartridge 72 are mounted on the carriage 31 from above, an introduction tube 67 is inserted into a connection hole provided in each cartridge, and the ejection heads 61 to 66 are ejected from each ink cartridge. Ink can be supplied to the printer.
[0039]
A mechanism for ejecting ink and forming dots will be described. FIG. 4 is an explanatory diagram showing a schematic configuration inside the ink ejection head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 using the capillary phenomenon as shown in FIG. The print head 28 is guided to each color head 61 to 66. When the ink cartridge is first installed, an operation of sucking ink to the respective color heads 61 to 66 is performed by a dedicated pump. In this embodiment, a pump for sucking and a cap for covering the print head 28 at the time of sucking are performed. The illustration and description of such a configuration is omitted.
[0040]
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). Each nozzle is one of electrostrictive elements and is responsive. An excellent piezo element PE is arranged. FIG. 5 shows the structure of the piezo element PE and the nozzle Nz in detail. As illustrated 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 ink to the nozzle Nz. As is well known, the piezo element PE is an element that transforms electro-mechanical energy at a very high speed because the crystal structure is distorted by application of a voltage. 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 extends for the voltage application time as shown in the lower part of FIG. One side wall of 68 is deformed. As a result, the volume of the ink passage 68 contracts according to the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is ejected from the tip of the nozzle Nz at high speed. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.
[0041]
FIG. 6 is an explanatory diagram showing the arrangement of the inkjet nozzles Nz in the ink ejection heads 61-66. The arrangement of these nozzles consists 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, when arranged in a zigzag pattern as shown in FIG. 6, there is an advantage that the nozzle pitch k can be easily set small.
[0042]
The printer 22 of the present invention includes the nozzle Nz having a constant diameter as shown in FIG. 6, and three types of dots having different diameters can be formed using the nozzle Nz. This principle will be described. FIG. 7 is an explanatory diagram showing the relationship between the drive waveform of the nozzle Nz and the ejected ink Ip when the ink is ejected. A drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. Once a negative voltage is applied to the piezo element PE in the interval d2, the piezo element PE is deformed in the direction of increasing the cross-sectional area of the ink passage 68 as opposed to that described with reference to FIG. 7, the ink interface Me called meniscus is indented inside the nozzle Nz. On the other hand, when a negative voltage is suddenly applied as shown in the section d2 using the driving waveform shown by the solid line in FIG. 7, the meniscus is indented greatly inward as compared with the state A as shown in the state a. Next, when the voltage applied to the piezo element PE is positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, a large ink droplet is ejected from the state where the meniscus is not dented so much (state A), as shown in state B and state C, and from the state where the meniscus is greatly recessed (state a), state b and Small ink droplets are ejected as shown in state c.
[0043]
As described above, the dot diameter can be changed according to the rate of change when the drive voltage is made negative (sections d1 and d2). Further, it can be easily imagined that the dot diameter can be changed depending on the peak voltage of the drive waveform. In this embodiment, based on such a relationship between the drive waveform and the dot diameter, the drive waveform for forming the small dot IP1 having a small dot diameter and the medium dot IP2 having the second dot diameter are obtained. Three types of drive waveforms are prepared: a drive waveform for forming and a drive waveform for forming a large dot IP3 having the largest diameter. FIG. 8 shows drive waveforms used in this embodiment. The drive waveform W1 is a waveform that forms a small dot IP1, the drive waveform W2 is a waveform that forms a medium dot IP2, and the drive waveform W3 is a waveform that forms a large dot. As shown in FIG. 8, the flying speed increases as the dot diameter increases. By properly using these drive waveforms, three types of dots having small, medium and large dot diameters can be formed from the nozzle Nz having a constant nozzle diameter. Further, in the printer 22 of this embodiment, these drive waveforms are output continuously and periodically in the order of W1, W2, and W3 as the carriage 31 moves.
[0044]
The timing for outputting the drive waveforms W1, W2, and W3 will be described. As described above, since the flying speed of the medium dot IP2 formed by the driving waveform W2 is lower than the flying speed of the small dot IP1 formed by the driving waveform W1, it is possible to form dots in the same pixel. is there. Although the large dot IP3 has a higher flight speed than the medium dot IP2, the large dot IP3 cannot be formed in the same pixel as the small dot IP1 because of the relationship with the moving speed of the carriage 31. In this embodiment, the output timings of the drive waveforms W1, W2 are adjusted so that the small dots IP1 and the medium dots IP2 are formed in the same pixel. Further, the output timing of the drive waveform W3 is adjusted so that the large dot IP3 is formed in a pixel adjacent in the moving direction of the carriage 31 with respect to the pixel in which the small dot IP1 and the medium dot IP2 are formed.
[0045]
Next, an internal configuration of the control circuit 40 of the printer 22 will be described, and a method for driving the head 28 including the 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, the control circuit 40 includes a CPU 81, a PROM 42, a RAM 43, a PC interface 44 for exchanging data with the computer 90, a paper feed motor 23, a carriage motor 24, an operation panel 32, and the like. A peripheral input / output unit (PIO) 45 for exchanging signals with the timer, a timer 46 for timing, a driving buffer 47 for outputting dot on / off signals to the heads 61 to 66, and the like. These elements and circuits are connected to each other via a bus 48. The control circuit 40 is also provided with a transmitter 51 that outputs a drive waveform (see FIG. 8) 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 it in the RAM 43, and outputs it to the driving buffer 47 at a predetermined timing.
[0046]
A mode in which the control circuit 40 outputs signals to the heads 61 to 66 will be described. FIG. 10 is an explanatory diagram showing 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 having the drive buffer 47 as the source side and the distribution output device 55 as the sink side, and each piezo element PE constituting the nozzle row has its electrode. One of these is connected to each output terminal of the drive buffer 47, and the other is connected to the output terminal of the distribution output device 55 all together. As shown in FIG. 10, a drive waveform of the transmitter 51 is output from the distribution output device 55. When the CPU 81 determines ON / OFF for each nozzle and outputs a signal to each terminal of the drive buffer 47, only the piezo element PE that has received the ON signal from the drive buffer 47 side is driven according to the drive waveform. The As a result, the ink particles Ip are simultaneously ejected from the nozzles of the piezo element PE that has received the ON signal from the transfer buffer 47.
[0047]
As shown in FIG. 6, since the heads 61 to 66 are arranged along the transport direction of the carriage 31, the timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Therefore, the CPU 81 outputs a dot ON / OFF signal through the transfer buffer 47 at a necessary timing in consideration of the displacement of the nozzles of the heads 61 to 66, and sets the dots of the respective colors. Forming. Further, as shown in FIG. 6, the output of on / off signals is controlled in consideration of the fact that each of the heads 61 to 66 has nozzles formed in two rows.
[0048]
The printer 22 having the hardware configuration described above transports the paper P by the paper feed motor 23 (hereinafter referred to as sub-scanning), reciprocates the carriage 31 by the carriage motor 24 (hereinafter referred to as main scanning), and at the same time. The piezo elements PE of the color heads 61 to 66 of the print head 28 are driven to discharge the inks of the respective colors to form dots and form a multicolor image on the paper P.
[0049]
In this embodiment, as described above, the printer 22 having the head for ejecting ink using the piezo element PE is used. However, a printer for ejecting ink by other methods may be used. For example, the present invention may be applied to a printer of a type in which electricity is supplied to a heater arranged in the ink passage and ink is ejected by bubbles generated in the ink passage.
[0050]
(2) Dot formation control:
Next, a dot formation control process in the printing apparatus of this embodiment will be described. The flow of the dot formation control processing routine is shown in FIG. This is a process executed by the CPU 81 of the computer 90.
[0051]
When this process is started, the CPU 81 inputs image data (step S100). This image data is data delivered from the application program 95 shown in FIG. 2, and for each of the R, G, and B colors constituting the image, 256 levels of gradations of 0 to 255 are provided. Data having a value. The resolution of the image data changes according to the resolution of the original image data ORG.
[0052]
The CPU 81 converts the resolution of the input image data into a resolution for the printer 22 to print (step S105). When the image data is lower than the printing resolution, resolution conversion is performed by generating new data between adjacent original image data by linear interpolation. Conversely, when the image data is higher than the print resolution, resolution conversion is performed by thinning out the data at a constant rate. Note that the resolution conversion processing is not essential in the present embodiment, and printing may be executed without performing such processing.
[0053]
Next, the CPU 81 performs color correction processing (step S110). The color correction process is a process of converting image data composed of R, G, B gradation values into data of gradation values of C, M, Y, K colors used in the printer 22. This process is performed by using a color correction table LUT (see FIG. 2) that stores combinations of C, M, Y, and K for expressing colors composed of combinations of R, G, and B by the printer 22. . Various known techniques can be applied to the process of performing color correction using the color correction table LUT. For example, a process based on an interpolation operation (such as the technique described in Japanese Patent Laid-Open No. Hei 4-144482) can be applied.
[0054]
The CPU 81 performs multi-value processing on the image data that has been color corrected in this way (step S120). Multi-leveling means that the gradation value (256 gradations in the present embodiment) of the original image data is converted into gradation values that can be expressed by the printer 22 for each pixel. As will be described later, in the present embodiment, multi-value conversion to four gradations of “no dot formation”, “small dot formation”, “medium dot formation”, and “large dot formation” is performed. It is also possible to perform multi-value conversion to a larger number of gradations including the gradation value expressed by superimposing the images. The multivalue processing can be performed by various methods, but processing by an error diffusion method and processing by a dither method are representative. The error diffusion method is generally excellent in image quality, and the dither method has a characteristic that high-speed processing is possible. In the present embodiment, it is possible to selectively use both according to the user's selection.
[0055]
First, the multilevel processing by the error diffusion method will be described. FIG. 12 shows the flow of multi-value processing by the error diffusion method. When this process is started, the CPU 81 inputs the image data Cd (step S122). The image data Cd input here is data that has been subjected to color correction processing (step S110 in FIG. 11) and has 256 gradations for each color of C, M, Y, and K. Diffusion error correction data Cdx is generated for this data (step S124). In the error diffusion process, an error in gradation expression generated for a processed pixel is distributed in advance with a predetermined weight applied to pixels around the pixel, so that in step S124, the corresponding error is read and this error is now read. This is reflected in the pixel that is focused on to be processed. FIG. 13 exemplifies how much weight is distributed to which pixels around the pixel PP of interest by which weight. With respect to the pixel PP of interest, the density error is a predetermined weight (1/4, 1/8) for several pixels in the scanning direction of the carriage 31 and several adjacent pixels on the rear side in the transport direction of the paper P. , 1/16). The error diffusion process will be described in detail later.
[0056]
The size of the diffusion error correction data Cdx thus generated and the first threshold th1 is compared (step S126). If the data Cdx is smaller than the threshold th1, dots are added to the value Cdr representing the multi-value quantization result. A value 0, which means not forming, is substituted (step S128). The threshold value th1 is a value serving as a reference for determining whether or not to form dots in this way. The threshold th1 can be set to any value, but is set based on the following concept in the present embodiment.
[0057]
FIG. 14 shows the relationship between the recording rate of large, medium, and small dots in this embodiment and the gradation value of the image data. In this embodiment, as shown in FIG. 14, only small dots are formed at gradation values 0 to gr1, small dots and medium dots are formed at gr1 and gr2, and medium dots and large dots are formed at gr2 and above. Is set. With a gradation value greater than gr1, either large, medium, or small dots are formed, and pixels that do not form dots are hardly formed. The threshold th1 is set so that the formation or non-formation of small dots occurs as set in FIG. 14 in the range of gradation values 0 to gr1. In this embodiment, th1 = gr1 / 2 is set.
[0058]
If the correction data Cdx is equal to or greater than the first threshold th1, then 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, a value 1 meaning the formation of a small dot is substituted for the value Cdr representing the multi-value quantization result (step S132). Like the threshold th1, the threshold th2 is set based on the dot recording rate in FIG. 14, and in this embodiment, th2 = (gr1 + gr2) / 2.
[0059]
If the correction data Cdx is greater than or equal to the second threshold th2, then 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, a 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 of FIG. 14, and in this embodiment, th3 = (gr2 + 255) / 2. If the correction data Cdx is greater than or equal to the third threshold th3, a 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, quaternarization is performed by the above processing. However, when the number of dots that can be formed increases and it is necessary to perform more multi-values, the above threshold value is increased in the same manner. It can be processed.
[0060]
Next, the CPU 81 calculates an error caused by the multi-value conversion, and executes a process of diffusing the error to surrounding pixels (step S140). The error means a value obtained by subtracting the gradation value of the original image data from the evaluation value of the density expressed by each dot after multi-value conversion. For example, a pixel having a gradation value of 255 in the original image data is considered, and the evaluation value of density due to formation of a large dot is equivalent to gradation value 255, and the evaluation value of density due to formation of a medium dot is equivalent to gradation value gr2. When it is determined that a large dot is to be formed for this pixel (Cdr = 3), the density evaluation value expressed as the gradation value of the original image data is equal to the value 255, and no error occurs. . On the other hand, when it is determined that a medium dot is to be formed (Cdr = 2), an error corresponding to Err = gr2-255 is generated.
[0061]
The error thus calculated is diffused to surrounding pixels at the rate shown in FIG. For example, when an error corresponding to the gradation value 4 is calculated in the pixel PP of interest, an error corresponding to the gradation value 1 that is ¼ of the error is diffused to the adjacent pixel P1. It will be. Similarly, the error is diffused at the ratio shown in FIG. 13 for the other pixels. The diffused error is reflected in 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 repeating the above (step S142), the CPU 81 once terminates the multilevel processing by error diffusion and returns to the dot formation control processing routine (FIG. 11). Through the above processing, any one of values 0 to 3 is assigned to the result value Cdr for each pixel.
[0062]
Next, multi-value processing by the dither method will be described with reference to the flowchart shown in FIG. When this process is started, the CPU 81 inputs the image data Cd (step S152). The image data Cd input here is data that has been subjected to color correction processing (step S110 in FIG. 11). Next, the image data Cd is compared with the gradation value gr1 (step S154). As shown in FIG. 14, the gradation value gr1 is a gradation value that is a boundary between a low gradation region that forms only small dots and an intermediate gradation region that forms both small dots and medium dots. In step S154, it is determined whether or not the image data Cd has a low gradation.
[0063]
As described above, the printer 22 of this embodiment can express four values for each dot. Further, as shown in FIG. 14, the image data has a low gradation to be expressed by either “no dot formation” or “small dot formation” and “small dot formation” or “depending on the gradation value”. It is divided into an intermediate gradation to be expressed by either “medium dot formation” and a high gradation to be expressed by either “medium dot formation” or “large dot formation”. In this embodiment, before performing multi-value conversion by the dither method, it is determined to which region the image data belongs. By doing so, as described below, it is possible to perform quaternarization with one kind of dither matrix.
[0064]
When the gradation value Cd of the image data corresponds to a low gradation smaller than the value gr1, the CPU 81 compares the gradation value Cd with the threshold value TH1 (step S156). The threshold value TH1 is set to a different value for each pixel by the dither matrix. In this embodiment, a blue noise matrix in which values 0 to 255 appear in 16 × 16 square pixels is used. However, in step S156, the image data Cd can take only a value smaller than gr1. Therefore, the threshold value Th1 is set by multiplying each value of the dither matrix by gr1 / 255. The reason why the threshold value TH1 is set in this way is that the same dither matrix is used in the intermediate gradation and the high gradation. A total of three types of dither matrices dedicated to each gradation may be prepared.
[0065]
In the low gradation, either “no dot formation” or “small dot formation” is assumed. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH1, a value 0 meaning non-formation of dots is substituted for the value Cdr representing the multivalue conversion result (step S158). In the opposite case, a value 1 meaning the formation of a small dot is substituted for the value Cdr (step S160).
[0066]
FIG. 16 shows the concept of multivalued processing by the dither method. Here, as a general case, both the image data Cd and the dither table are shown as values that can take values from 0 to 255. As shown in FIG. 16, the size of each pixel of the image data Cd and the corresponding portion of the dither table is compared. When the method of the image data Cd is larger than the threshold value shown in the dither table, the dot is turned on, and when the method of the image data Cd is small, the dot is turned off. In FIG. 16, a hatched pixel means a pixel that turns on a dot.
[0067]
In step S154, if the gradation value Cd of the image data is greater than or equal to the value gr1, that is, if it corresponds to the intermediate gradation, then the image data Cd and the gradation value gr2 are compared (step S154). S162) It is determined whether the image data Cd belongs to an intermediate gradation or a high gradation. When the image data Cd is smaller than the value gr2, that is, when the image data Cd belongs to the intermediate gradation, after subtracting the value gr1 from the image data Cd (step S164), the magnitude is compared with the threshold value TH2 (step S164). Step S166). The reason why the value gr1 is subtracted in step S164 is to make it possible to apply the same dither matrix as in the case of low gradation. By doing this, the image data Cd becomes data that takes values from 0 to (gr2-gr1), and thus the threshold value TH2 can be set by multiplying each value of the dither matrix by (gr2-gr1) / 255.
[0068]
In the intermediate gradation, either “small dot formation” or “medium dot formation” is assumed. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH2, the value 1 indicating the formation of a small dot is substituted for the value Cdr representing the multivalue conversion result (step S168), and vice versa. Substitutes the value 2 which means the formation of medium dots (step S170).
[0069]
In step S162, if the gradation value Cd of the image data is greater than or equal to the value gr2, that is, corresponds to a high gradation, after subtracting the value gr2 from the image data Cd (step S172), the threshold value TH3 is greater or smaller. Are compared (step S176). The reason why the value gr2 is subtracted in step S172 is to make it possible to apply the same dither matrix as in the case of low gradation. By doing this, the image data Cd becomes data taking values from 0 to (255-gr2), and thus the threshold value TH3 can be set by multiplying each value of the dither matrix by (255-gr2) / 255.
[0070]
At high gradation, either “medium dot formation” or “large dot formation” is assumed. Therefore, when the gradation value Cd of the image data is smaller than the threshold value TH3, a value 2 meaning the formation of a medium dot is substituted for the value Cdr representing the multivalue conversion result (step S176). In the opposite case, a value 3 meaning the formation of a large dot is substituted for the value Cdr (step S178). Through the above processing, one pixel of the image data converted into the print resolution is converted into a four-valued format. When the gradation value further increases, multi-value can be obtained by repeatedly executing the processing corresponding to steps S162 to S170 according to the gradation value. The CPU 81 repeatedly executes the above processing, and when the processing for all the pixels is completed (step S180), the multi-value processing by the dither method is once ended and the processing returns to the dot formation control routine of FIG.
[0071]
Next, the CPU 81 performs rasterization (step S210). This means that data for one raster is rearranged in the order of transfer to the head of the printer 22. The contents of the rasterizing process in this embodiment are shown in FIG.
[0072]
When the rasterizing process is started, the CPU 81 inputs image data (step S202). Also, initialization is performed by substituting the value 0 into the variable DN and substituting the value 1 into the variable CN (step S202). A variable DN is a value indicating the order of data rasterized and transferred to the printer 22. The variable CN is a pixel number. The pixel number is a number assigned to the pixels constituting the raster in the main scanning direction, and corresponds to c1, c2, c3,... Shown in FIG. In FIG. 19, it is represented by variables such as c1 and c2 for convenience, but in reality, integers are given in the order of 1, 2,.
[0073]
Next, it is determined whether the raster to be processed is a raster that is to record an image in the first main scan or a raster that is to record an image in the second main scan (step S204). In this embodiment, since each raster is formed by two main scans, it is determined which data corresponding to which main scan should be prepared. If data to be used for the first main scan is to be prepared, the value 0 is substituted for the variable F (step S208). If data to be used for the second main scan is to be prepared, the value 1 is substituted for the variable F. (Step S206).
[0074]
Here, the meaning of the variable F will be described. In this embodiment, three types of large, medium, and small dots can be formed as described above, and each dot is formed in association with two adjacent pixels in each main scan. That is, as shown in FIG. 18, the small dot IP1 and the medium dot IP2 are formed in the pixel c1, and the large dot IP3 is formed in the pixel c2. FIG. 19 shows how dots are continuously formed according to this correspondence. Each square shown in FIG. 19 represents a pixel. A black circle represents a small dot IP1, a circle surrounding the small dot represents a medium dot IP2, and a circle with the largest diameter represents a large dot IP3. P1 in FIG. 19 shows a state of dots formed by the first main scanning. If the raster is formed with the correspondence shown in FIG. 18, small dots and medium dots are formed in the pixels c1, c3, and c5, and large dots are formed in the pixels c2 and c4, as indicated by P1 in FIG. .
[0075]
At this time, large dots cannot be formed in the pixels c1, c3, and c5. Therefore, in this embodiment, each raster is formed by two main scans, and the correspondence between dot types and pixels is different between the first main scan and the second main scan. Arbitrary dots can be formed on the pixels (see the bottom row in FIG. 19). In FIG. 19, the state of dots formed by the second main scan for the same raster as P1 is indicated by P2. This time, the correspondence is changed so that large dots are formed in the pixels c1, c3, and c5, and small dots and medium dots are formed in the pixels c2 and c4. The variable F set in steps 206 and 208 in FIG. 17 is a variable for controlling the appropriate use of this correspondence relationship. When the value 0 is set in the variable F, the correspondence relationship indicated by P1 in FIG. When a dot is formed and the value 1 is set in the variable F, it means that the dot is formed with the correspondence shown by P2 in FIG.
[0076]
After setting the variable F described above, the CPU 81 determines whether or not the remainder obtained by dividing the pixel number CN by 2 is equal to the variable F (step S210). Note that the processing of step S210 is indicated as “CN% 2 = F?” In the flowchart of FIG. Here, “%” is a remainder operator. This calculation determines whether the pixel number CN is an odd number or an even number. When the pixel number is an even number, the calculation result is 0, and when the pixel number is an odd number, the value is 1.
[0077]
As described above, the variable F is set to a value of 0 when the raster is formed in the first main scan P1, and is set to a value of 1 when the raster is formed in the second main scan P2. ing. In the main scanning P1, large dots are formed on even-numbered pixels (corresponding to P1 in FIG. 19), and in the main scanning P2, large dots are formed on odd-numbered pixels (corresponding to P2 in FIG. 19). Therefore, in other words, the variable F is set to a value of 0 for main scanning in which large dots are to be formed in even-numbered pixels, and is set to 1 for main scanning in which large dots are to be formed in odd-numbered pixels. Is set. Eventually, the variable F specifies the pixel in which the large dot is to be formed in the form of the calculation result “CN% 2”. Accordingly, when the calculation result of “CN% 2” matches the value of the variable F in step S210, the CPU 81 determines whether or not the pixel is a pixel for which a large dot should be turned on. This is performed (step S230). If the image data is to form a large dot, a value 1 meaning dot formation is substituted into the data PD [DN] transferred to the drive buffer 40 of the printer 22 (step S234), and the large dot is formed. If the data does not form dots, the value 0 as mask data is substituted (step S232).
[0078]
When the value 1 is set in the data PD [DN], ink is ejected from the nozzles by the input of the driving waveform as described above with reference to FIG. 10, and dots are formed. When the value 0 is set, a drive waveform is output from the distribution output device 55 (see FIG. 9), but since the circuit on the source side of the nozzle is turned off, no dots are formed. Note that the data PD [DN] stores only information indicating dot on / off, and does not store information regarding the dot type. In the printer 22 of this embodiment, the arrangement of the data PD and the drive waveform (see FIG. 18) that is periodically output correspond to each other on a one-to-one basis. The dots can be formed.
[0079]
In the previous step S210, when the result of the calculation “CN% 2” does not coincide with the value of the variable F, the CPU 81 determines that the pixel being processed is a pixel on which a small dot and a medium dot are to be formed. Accordingly, it is determined whether or not the image data is to form a small dot (step S212), and if it is to be formed, the value 1 is substituted into the data PD [DN] (step S216), and if it is not to be formed. Substitutes the value 0 for the data PD [DN] (step S214). Further, the data number DN is incremented by 1 (step S218), and the medium dot on / off is recorded in the data PD to be transferred immediately after the data PD on which the small dot on / off is recorded. That is, it is determined whether or not the image data is to form a medium dot (step S220), and if it is to be formed, the value 1 is substituted into the data PD [DN] (step S224), and if not formed. Substitutes the value 0 for the data PD [DN] (step S222).
[0080]
With the above processing, small dots and medium dots are turned on / off or large dots are turned on / off according to the pixel number CN. In preparation for the processing of the next pixel, the CPU 81 increments the data number DN and the pixel number CN by 1 (step S240), and the above processing (step S242) is completed until the processing of all the pixels constituting each raster is completed (step S242). Steps S204 to S240) are repeated. The rasterized data is output to the printer 22 in the dot formation control processing routine (FIG. 11) (step S250 in FIG. 11). In the above description, the flow of processing for one raster has been described. However, as shown in FIG. 6, the present embodiment includes 48 nozzles and can simultaneously form 48 rasters. Therefore, in practice, the entire process is repeatedly executed for the number of nozzles, and data is output to the printer 22.
[0081]
The large dot IP3 cannot be formed in the same pixel as the small dot IP1 and the medium dot IP2 in one main scan. If it is used for printing as it is, a dot is formed at a position shifted from the pixel, resulting in a decrease in image quality. On the other hand, according to the printing apparatus described above, small dots, medium dots, and large dots are formed in separate pixels in each main scan, and each raster is formed in two main scans. Thus, the large dot IP3 can be formed without causing the above-described deviation from the pixel. As a result, in the printing apparatus, the number of gradations that can be expressed for each pixel can be increased, and the image quality can be improved.
[0082]
In this embodiment, the small dots IP1, medium dots IP2, and large dots IP3 are printed according to the correspondence shown in FIG. 18, but various correspondences can be set. For example, as shown in FIG. 20, one dot may correspond to each pixel. That is, the small dot IP1 may be formed in the pixel c1, the medium dot IP2 may be formed in the pixel c2 adjacent to the pixel c1, and the large dot IP3 may be formed in the adjacent pixel c3. The intervals D1, D2 at which the drive waveforms dw1, dw2, dw3 are output are adjusted so as to realize such association. FIG. 21 shows how dots are formed in such a case. The meanings of symbols and the like are the same as in FIG. 19 described above. If each dot is formed periodically according to the above correspondence, the small dot IP1 is formed in the pixels c1 and c4 and the medium dot IP2 is formed in the pixels c2 and c5 in the first main scanning, as indicated by P1 in FIG. The large dot IP3 is formed in the pixel c3. In this case, as shown by P2 and P3 in FIG. 21, three main scans having different correspondences are performed to form arbitrary dots on each pixel (see the bottom row in FIG. 21). When it is difficult to form the small dot IP1 and the medium dot IP2 in the same pixel, it can be said that it is desirable in terms of image quality to form the dot with the above-described correspondence.
[0083]
In this embodiment, the printer 22 capable of forming three types of dots has been described as an example. However, the present invention can be similarly applied to cases where there are more or fewer types of dots that can be formed. The present invention can also be applied to a printer that forms a single type of dot. For example, assume that dots IP1, IP2, and IP3 are all the same type of dots in FIG. In the first main scan, printing is performed in a correspondence relationship in which two dots are formed on the pixel c1 so as to overlap without forming dots on the pixel c2, as indicated by P1 in FIG. In the second main scanning, as shown in P2, the correspondence relationship between pixels formed by overlapping dots and pixels that are not so is different from the first time. In this way, it is possible to overlap and form up to three dots for each pixel as shown in the lowermost stage of FIG. 19, and to increase the gradation expression. Of course, the present invention can also be applied to a case where a larger number of dots are superimposed.
[0084]
In the present embodiment, each raster is formed by two main scans as shown in FIG. 19, but the second main scan P2 in FIG. 19 may be omitted. If each raster is formed by one main scan, the printing speed can be increased. In the case where only the main scan P1 of FIG. 19 is performed, the large dot IP3 cannot be formed in the pixel c1. Therefore, when the image data is to form the large dot IP3 in the pixel c1, the printed image may be impaired in gradation expression. Therefore, in such a case, it is desirable to take measures to prevent the gradation expression from being impaired. Various countermeasures are possible. For example, in the dot formation control process, there is a method of performing a dot rearrangement process having the following contents immediately before rasterization (step S200 in FIG. 11).
[0085]
The dot rearrangement process will be specifically described with reference to FIG. For example, it is assumed that the multivalued image data represents the dot formation shown in the upper part of FIG. When dots are formed according to the correspondence relationship indicated by P1 in FIG. 19, it is possible to form small dots and medium dots set in the pixel c1 in the upper part of FIG. Since only large dots can be formed in the adjacent pixel c2, it is not possible to form small dots and medium dots set in the upper part of FIG. Similarly, a large dot cannot be formed in the pixel c3. Therefore, as the dot rearrangement process, as shown in the lower part of FIG. 22, both data are exchanged, a large dot is formed in the pixel c2, and a small dot and a medium dot are formed in the pixel c3. Since only large dots can be formed in the pixel c4, the data of the pixel c5 is replaced by the same concept. With this processing, the image data is corrected to the form shown in the lower part of FIG.
[0086]
In this way, all the dots can be formed in one main scan, so that gradation expression is not impaired. Strictly speaking, this is different from the original image data that was faithfully printed because the dot formation position is moved. However, in a printer that can print at a very high resolution, the gap between dots is narrow, so this shift is The impact on is very small. In the above example of dot rearrangement processing, replacement with pixels adjacent in the main scanning direction is performed. However, replacement with pixels adjacent in the sub scanning direction may be performed.
[0087]
In addition, as another means for preventing the gradation expression from being impaired, the density of each dot is set so that the density when the small dot and the medium dot are overlapped and the density when the large dot is formed independently are substantially the same. The amount of ink may be adjusted. By adopting such means, there is an advantage that the processing speed can be increased in that it is not necessary to perform complicated processing such as dot rearrangement.
[0088]
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 spirit of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing a configuration of software.
FIG. 3 is a schematic configuration diagram of a printer of the present invention.
FIG. 4 is an explanatory diagram showing a schematic configuration of a dot recording head of the printer of the present invention.
FIG. 5 is an explanatory diagram illustrating a principle of dot formation in the printer of the present invention.
FIG. 6 is an explanatory diagram showing an example of nozzle arrangement in the printer of the present invention.
FIG. 7 is an enlarged view of nozzle arrangement in the printer of the present invention and an explanatory diagram showing a relationship with dots to be formed.
FIG. 8 is an explanatory diagram for explaining the principle of forming dots having different diameters by the printer of the present invention.
FIG. 9 is an explanatory diagram illustrating an internal configuration of a printer control apparatus.
FIG. 10 is an explanatory diagram showing a nozzle driving waveform and a state of dots formed by the driving waveform in the printer of the present invention.
FIG. 11 is a flowchart showing the flow of a dot formation control routine.
FIG. 12 is a flowchart showing a flow of multilevel processing by error diffusion.
FIG. 13 is an explanatory diagram showing weights when diffusing errors.
FIG. 14 is an explanatory diagram showing a relationship between a recording rate of each large, medium, and small dot and a gradation value.
FIG. 15 is a flowchart showing a flow of multi-value processing by a dither method.
FIG. 16 is an explanatory diagram showing the concept of dot on / off determination by the dither method.
FIG. 17 is a flowchart showing a flow of rasterization processing.
FIG. 18 is an explanatory diagram showing how dots are formed in the present example.
FIG. 19 is an explanatory diagram showing correspondence between dot types and pixels in the present embodiment.
FIG. 20 is an explanatory diagram showing another state of dot formation in the present example.
FIG. 21 is an explanatory diagram showing other correspondence between dot types and pixels;
FIG. 22 is an explanatory diagram showing an example of dot rearrangement.
FIG. 23 is an explanatory diagram showing correspondence between dot types and pixels in a conventional printer.
FIG. 24 is an explanatory diagram showing how dots are formed when the number of types of dots is increased in a conventional printer.
[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 ... Control 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 ... Transfer buffer
48 ... Bus
51 ... Transmitter
55 ... Distribution output device
61, 62, 63, 64, 65, 66... Ink ejection head
67 ... Introducing 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 I / O interface (SIO)
90 ... Personal computer
91 ... Video driver
95 ... Application program
96 ... Printer driver
97 ... Resolution conversion module
98 ... Color correction module
99 ... Halftone module
100: Transfer buffer

Claims (6)

While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing apparatus that prints an image corresponding to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming three kinds of dots having a large diameter, a medium diameter, and a small diameter at intervals smaller than the interval between the pixels .
A head control means for forming a dot in accordance with the prior SL image data,
For an adjacent pixel composed of two pixels adjacent in the main scanning direction,
A first main scan that forms a small-diameter dot and a medium-diameter dot on one of the adjacent pixels, and forms a large-diameter dot on the other of the adjacent pixels;
A second main scan is performed in which a large-diameter dot is formed on one of the adjacent pixels and a small-diameter and medium-diameter dot is formed on the other of the adjacent pixels. A printing apparatus comprising head control means for controlling driving of the head so as to be formed in each pixel constituting the pixel . While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing apparatus that prints an image corresponding to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming two types of dots having a first diameter and a second diameter at an interval narrower than the interval between the pixels.
Head control means for forming dots corresponding to the image data,
For an adjacent pixel composed of two pixels adjacent in the main scanning direction,
A first main scan that forms dots of the first diameter on one of the adjacent pixels, and forms dots of the second diameter on the other of the adjacent pixels;
Performing the second main scanning in which a dot having the second diameter is formed on one of the adjacent pixels and a dot having the first diameter is formed on the other of the adjacent pixels; A printing apparatus comprising head control means for controlling the driving of the head so that all of the pixels can be formed in each pixel constituting the adjacent pixel . While performing the main scanning that reciprocally moves the head relative to the printing medium, the head is driven to form dots, thereby forming a raster that is a pixel array arranged at regular intervals in the main scanning direction. A printing apparatus that prints an image corresponding to the image data on the print medium,
The head is a head including a nozzle capable of continuously forming three kinds of dots having a large diameter, a medium diameter, and a small diameter at intervals smaller than the interval between the pixels.
Head control means for forming dots corresponding to the image data,
For an adjacent pixel constituted by three first to third pixels adjacent in the main scanning direction,
A first main scan for forming a small-diameter dot in the first pixel, a medium-diameter dot in the second pixel, and a large-diameter dot in the third pixel;
A second main scan for forming a medium diameter dot in the first pixel, a large diameter dot in the second pixel, and a small diameter dot in the third pixel;
A third main scan for forming a large-diameter dot in the first pixel, a small-diameter dot in the second pixel, and a medium-diameter dot in the third pixel, respectively. A printing apparatus comprising head control means for controlling driving of the head so that all dot diameters can be formed in each pixel constituting the adjacent pixel . While performing a main scan in which a head including a nozzle capable of continuously forming three types of dots having a large diameter, a medium diameter, and a small diameter at intervals smaller than the pixel interval is reciprocated relative to the print medium, A printing method for forming a raster, which is a pixel row arranged at regular intervals in the main scanning direction by driving a head to form dots, and printing an image according to input image data on the printing medium. ,
Driving the head,
For an adjacent pixel composed of two pixels adjacent in the main scanning direction,
Performing a first main scan that forms small and medium diameter dots on one of the adjacent pixels and forms a large diameter dot on the other of the adjacent pixels;
Performing a second main scan that forms a large diameter dot on one of the adjacent pixels and forms a small diameter medium dot on the other of the adjacent pixels;
The printing method , wherein all of the three types of dot diameters can be formed in each pixel constituting the adjacent pixel . While performing a main scan in which a head including a nozzle capable of continuously forming two types of dots having a first diameter and a second diameter at intervals smaller than the pixel interval is reciprocated relative to the print medium. In this printing method, a dot is formed by driving the head to form a raster, which is a pixel row arranged in the main scanning direction at a constant interval, and print an image corresponding to input image data on the print medium. There,
  Driving the head,
  For an adjacent pixel composed of two pixels adjacent in the main scanning direction,
  Performing a first main scan that forms dots of the first diameter on one of the adjacent pixels and forms dots of the second diameter on the other of the adjacent pixels;
  Performing a second main scan that forms dots of the second diameter on one of the adjacent pixels and forms dots of the first diameter on the other of the adjacent pixels;
  The printing method, wherein all of the two types of dot diameters can be formed in each pixel constituting the adjacent pixel. While performing a main scan in which a head including a nozzle capable of continuously forming three types of dots having a large diameter, a medium diameter, and a small diameter at intervals smaller than the pixel interval is reciprocated relative to the print medium, A printing method for forming a raster, which is a pixel row arranged at regular intervals in the main scanning direction by driving a head to form dots, and printing an image according to input image data on the printing medium. ,
  Driving the head,
  For an adjacent pixel constituted by three first to third pixels adjacent in the main scanning direction,
  Performing a first main scan for forming a small-diameter dot in the first pixel, a medium-diameter dot in the second pixel, and a large-diameter dot in the third pixel;
  Performing a second main scan to form a medium diameter dot in the first pixel, a large diameter dot in the second pixel, and a small diameter dot in the third pixel;
  Performing a third main scan for forming a large diameter dot in the first pixel, a small diameter dot in the second pixel, and a medium diameter dot in the third pixel, respectively.
  The printing method, wherein all of the three types of dot diameters can be formed in each pixel constituting the adjacent pixel.

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