JP2007145022A - Image forming apparatus and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record high quality image with a jaggy inconspicuous in an inkjet recording system. <P>SOLUTION: An inkjet recording apparatus 100 ejects an ink droplet on a plain paper or the like to form an image, wherein the inkjet recording apparatus uses a pigment type ink which includes at least a pigment, a wetting agent, polyol or glycol ether having a carbon number of ≥8, an anionic or nonionic surfactant, a water-soluble organic solvent and water, and preferably has a pigment concentration of not less than 6 wt.% and a viscosity of not less than 8 cp (25°C). In order to make a jaggy of a character or the like inconspicuous, a jaggy correction process for recording a small dot for correction of a jaggy on the contoured part of a binary image such as a character is performed, for example, in a host computer 102. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an image forming apparatus that forms an image by recording dots on an image recording medium, and more particularly to a jaggy correction processing technique for improving the recording quality of binary images such as characters in the image forming apparatus. In this specification, an inkjet printer is taken up as an image forming apparatus.

Inkjet printers have many advantages such as high-speed recording, recording on so-called plain paper without requiring a special fixing process, and generation of noise during recording is small enough to be ignored . An ink jet printer uses an ink jet head in which an ink liquid chamber and nozzles communicating with the ink liquid chamber are formed. By applying pressure to the ink in the ink liquid chamber according to image information, ink droplets are ejected from the nozzle, and paper or paper An image is formed on a recording medium such as a film.

Such an ink jet printer is classified into a serial type and a line type. The serial type ink jet printer forms an image while scanning the ink jet head in the width direction of the paper (main scan), and after one or more scans are completed, the paper is conveyed to form the next recording line. It is going. In the line type serial printer, the nozzles are formed almost all over the width direction of the paper, and printing is performed while transporting the paper without performing scanning in the width direction.

  Line-type inkjet printers have the advantage of high recording speed because they form one line in the width direction at a time, but the size of the entire printer increases because of the large head, and high-resolution recording In order to perform the above, it is necessary to make the arrangement of the nozzles high in density, and there is a problem that the manufacturing cost of the head becomes high. The serial type ink jet printer forms an image with a relatively small head, and therefore has an advantage that the apparatus cost is low. Currently, many serial type ink jet printers are put into practical use.

  In the case of a serial type ink jet printer, the printing speed is determined by the image resolution, nozzle density, dot forming drive frequency, sub-scanning speed, and the like. Among these, the nozzle density is limited by the processing accuracy of the nozzle, liquid chamber, flow path, and actuator. In particular, in the case of inkjet using a piezo element, in order to divide and form into channels corresponding to nozzles, there is only mechanical processing such as dicing or formation of thin film PZT by printing, so-called bubble jet method formed by semiconductor process Compared to (or thermal ink jet method), the nozzle density is low. The upper limit of the nozzle density of an ink jet head using a piezo element is currently about 360 dpi.

  By the way, in order to improve the printing speed, it is preferable to form the printing area by one main scanning. For example, when an image having a nozzle density of 300 dpi and a resolution of 300 dpi in the sub-scanning direction is created, it is possible to create the image in a single scan in the head movement direction (main scanning direction). On the other hand, when an image of 600 dpi is created, it is necessary to fill the image by a so-called interlace method in which two main scans and one sub-scan (paper conveyance) are performed. The non-interlace method) creates images quickly. Also in the main scanning direction, as a method of forming one line in the main scanning direction, a method of forming by one main scanning (one pass printing) and a method of forming by a plurality of main scanning (so-called multi-scanning). Of course, the printing speed is faster with 1-pass printing that can be formed in one main scan.

  However, in the case of an ink jet printer using a piezo element, as described above, the nozzle density itself is low, so in order to increase the recording speed, an image is inevitably created when using a one-pass non-interlace method. The resolution of the image will be low. When the image density is a low resolution, a method of multi-leveling one pixel is effective for improving the image quality. Examples of the multivalued method include a method of changing the size of one dot itself, a method of forming one pixel by discharging a plurality of small dots, or a method of changing the density of the ink itself. However, high image quality by multi-value is effective for images such as photographs, but is hardly effective for graphics and characters. This is because, in the case of characters and graphics, a dot size larger than that of the background portion is necessary, and when a small-sized dot is used, a low-density character or graphics image is obtained. Therefore, in binary images such as character graphics, a problem peculiar to low resolution occurs, and particularly in the case of characters, character quality deteriorates and characters are difficult to read. The problem specific to this low resolution will be described in detail.

  The recorded image of the ink jet printer is represented by dots formed in a matrix in the scanning direction of the head and the transport direction of the recording paper, which is a direction perpendicular thereto. Here, when a character is printed as a dot image, the quality of the character varies greatly depending on the resolution of the image to be printed. For example, when a character of the same size is printed at 300 dpi and when printed at 600 dpi, the number of dots that make up the character differs by a factor of four, so that when printed at 600 dpi, it can be expressed in more detail. Of course, the character quality is good. In particular, in the shaded portion of the character, dots increase (or decrease) in a staircase pattern according to the resolution, so that when printed at 300 dpi, it becomes easier to be recognized as jagged (jaggy).

  As a method of reducing this jaggy, there is an image output method described in Patent Document 1. This compares the bit pattern of the sample window in the bitmap image of the character with a predetermined bit pattern and corrects the central pixel in the sample window to a small dot if they match. It is. As a similar method, there is an image forming apparatus described in Patent Document 2. This discriminates the outline portion of the image from the black dot data and reduces the size of the print dots other than the edge dots and the black dots.

  However, these techniques work effectively for LED printers and laser printers, as exemplified by the examples in the specification. This is because LED printers and laser printers use toner having a particle size of 10 μm or less, so that there is almost no spread on plain paper and small dots as specified can be obtained. Furthermore, in a laser printer, it is possible to form a dot of a specified size at an optimum position by slightly changing the light emission position and length of the laser. However, in the ink jet recording apparatus, the ink spread is larger than that of the laser printer. Also, since it takes time to form dots compared to LED printers and laser printers, it is difficult to change the dot size that changes depending on the number and length of drive pulses during the drive cycle, and at most several types of dot sizes are changed. The dot size changes. For the same reason, dot formation positions can be formed only at almost fixed positions within one pixel, and it is difficult to change the position within one pixel relatively freely like LED printers and laser printers. .

  There is also a smoothing method conventionally called anti-aliasing. However, this method changes the dot with a very large number of gradations, so that high-precision smoothing can be achieved, but the processing is very complicated and requires processing time. Thus, it is not suitable when high throughput is required.

Inkjet printers also have problems associated with ink. When printing on plain paper with an inkjet printer, inkjet printing such as image color reproducibility, durability, light resistance, ink drying, character bleeding (feathering), color boundary bleeding (color bleed), duplex printing, etc. The image quality degradation problem peculiar to the device is apparent. Furthermore, when trying to perform high-speed printing on plain paper, it is an extremely difficult task to satisfy all these characteristics for printing.

  In general, an ink used for ink jet recording generally contains water as a main component and contains a colorant and a wetting agent such as glycerin for the purpose of preventing clogging. As the colorant, there are a dye and a pigment, and a dye-based ink is often used for the color portion from the point that excellent color developability and stability can be obtained. However, fastness such as light resistance and water resistance of an image obtained using a dye-based ink is inferior to that using a pigment as a colorant, and in particular, the water resistance has an ink absorption layer. If ink jet recording paper is used, a certain degree of improvement can be achieved, but satisfaction is not obtained when plain paper is used.

  Therefore, in recent years, the use of pigment-based inks that use organic pigments, carbon black, etc. as colorants has been studied or practically used to improve the problems associated with dye-based inks when using plain paper. Has been changed. Since pigments are not soluble in water unlike dyes, they are usually used as water-based inks in a state where pigments are mixed with a dispersing agent, dispersed and stably dispersed in water. Although the use of pigments can improve light resistance and water resistance, it is difficult to satisfy other image quality characteristics at the same time. It is difficult to obtain color developability, color reproducibility, etc., and character bleeding, color boundary bleeding, double-sided printing property, ink drying property (fixing property), etc. are not yet satisfactory. .

Therefore, Patent Documents 3 and 4 disclose techniques for solving the problems in the case where printing is performed on plain paper using the pigment-based ink. In Patent Document 3 , by using an ink containing a pigment, a polymer dispersant, and a resin emulsion, and adjusting the solid content adhesion amount per unit area on the recording paper at the time of 100% duty printing, it is unique to the pigment ink. An ink jet recording method is disclosed in which printing unevenness due to pigment aggregation is reduced regardless of the paper type, and there is no printing blur and an image quality with high printing density can be obtained. Further, in Patent Document 4 , an ink composition containing a pigment having a dispersing group on the pigment surface and surface-treated so as to be dispersible in an aqueous solvent, and an ink containing a penetrating agent are used. By adjusting the amount of ink composition discharged per unit area, irregular bleeding of the printed image can be suppressed, and the discharged ink composition can be quickly dried on the recording medium to ensure a high print density. An ink jet recording method capable of obtaining a good printed image is disclosed.

In the ink jet recording method of Patent Document 3 , the contact angle of the ink used is very high at 70 ° or more with respect to paper sized like plain paper, so that the print density is improved and the character bleeding is reduced. An improvement is seen. However, when printing on recording paper at 100% Duty, the solid content adhesion amount per unit area is required to be about several tens ng / m2, which causes a problem in terms of ink fixability (drying property). . In particular, when high-speed printing is performed with a plurality of sheets stacked, high-speed printing is not suitable because a paper smearing problem due to ink transfer occurs between papers. Also, depending on the type of paper, there is a problem that white streaks or the like of the background of the paper occur in the solid portion or the character portion due to the high contact angle during 100% duty printing. Furthermore, at the color boundary part, the problem of color bleeding is likely to occur between the dots printed adjacent to each other due to the high contact angle.

Further, the ink jet recording method of Patent Document 4 is advantageous in terms of image quality in terms of ink drying property (fixability) because a penetrating agent is used, and when printing a plurality of papers at a high speed, paper is used. This is suitable for high-speed printing because there is no paper smearing problem due to ink transfer. However, since a penetrant is used in the ink composition, character bleeding phenomenon occurs when printing on plain paper, especially in the case of plain paper. Since the ink penetrates, the double-sided printability on plain paper is unsuitable due to the ink see-through phenomenon.

Japanese Patent No. 2886192 Japanese Patent No. 3029533 JP-A-6-171072 JP 2000-355159 A

An object of the present invention is to provide an image forming apparatus and a program that can greatly improve the recording quality of binary images such as characters as well as high-speed printing .

The main feature of the present invention for achieving the above object is that the processed font data is held in the image forming apparatus for forming an image by recording dots on the image recording medium as described in claim 1. A font data memory, a means for performing jaggy correction processing for recording dots for jaggy correction on the contour of an image, and font data of a specified size of a character to be subjected to the jaggy correction processing is the font data memory And a means for performing expansion processing on the font data when it does not exist above, and performing the jaggy correction processing on the expanded font data.

Another feature of the present invention is that, as described in claim 2, in the image forming apparatus according to claim 1, the dots for jaggy correction form a stepped shape of a dot row that forms a contour portion of a binary image. It is to be recorded only in one of the blank portion or the image portion around the change point.

Another feature of the present invention, as described in claim 3, in the image forming apparatus according to claim 1, wherein, dots, step changes in the dot rows forming the contour of the images for the jaggy correction It is to be recorded in both the blank portion and the image portion around the point.

Another feature of the present invention is that, as described in claim 4, in the image forming apparatus according to claim 1, a plurality of types of dots having different sizes are used as dots for jaggy correction.

According to another aspect of the present invention, as described in claim 5, in the image forming apparatus according to claim 1, the dots for the jaggy correction form a step-like change in a dot row that forms an outline portion of the image. In addition to being added to the blank portion around the point, the dots in the image portion around the step-like change point can be replaced with smaller dots.

According to another feature of the present invention, as described in claim 6 , in the image forming apparatus according to claim 1, the means for performing the jaggy correction processing includes an image using an m × n size window and a predetermined size. This is to recognize a pixel position where a dot for jaggy correction is to be recorded by pattern matching with the reference pattern.

According to another feature of the present invention, as described in claim 7 , in the image forming apparatus according to claim 1, the means for performing the jaggy correction processing includes an image using a window of m × n size and a predetermined size. This is to recognize the pixel position where the dot for jaggy correction should be recorded and the size of the dot to be recorded there by pattern matching with the reference pattern.

Another feature of the present invention is that, as described in claim 8 , in the image forming apparatus according to claim 6 or 7 , m or n of the size of the window is selected in the range of 3 or more and 7 or less. It is in.

According to another feature of the present invention, as described in claim 9 , in the image forming apparatus according to claim 6 or 7 , the pattern matching is performed by paying attention to one pixel of the blank portion or the image portion. It is in.

Another feature of the present invention is that, as described in claim 10 , in the image forming apparatus according to claim 1, the means for performing the jaggy correction processing corrects only a character image having a size equal to or smaller than a predetermined font size. It is to be a target of processing.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, the image forming apparatus ejects ink droplets onto an image recording medium. An ink jet recording apparatus for recording an image, and at the time of jetting, at least a pigment, a wetting agent, a polyol or glycol ether having 8 or more carbon atoms, an anionic or nonionic surfactant, a water-soluble organic solvent, water, The object is to use a pigment-based ink having a pigment concentration of 6% by weight or more and an ink viscosity of 8 cp (25 ° C.) or more.

Further, the present invention is characterized in that, as described in claim 12, a program for causing a computer to execute the function of each unit of the image forming apparatus described in claim 1 is provided.

  The characteristics of the present invention described above and other characteristics will be specifically described below in connection with the embodiment.

According to the image forming apparatus of the present invention, the following effects can be obtained.
(1) Processing time for jaggy correction can be reduced. (2) It is possible to effectively perform jaggy correction on the shaded portion of the character. (3) A dot for jaggy correction can be recorded at an appropriate position, and a dot of an appropriate size for jaggy correction can be recorded at an appropriate position to perform an appropriate jaggy correction. (4) A sufficient jaggy correction effect can be obtained without unnecessarily increasing the processing time for the jaggy correction. (5) It is possible to suppress a decrease in recording speed due to jaggy correction processing for a large character image that takes time to process. (6) Even when plain paper is used as the image recording medium, jaggies are not noticeable, feathering and color bleeding are suppressed, and high-quality images with good color tone and density can be recorded. Since jaggy is not noticeable even at low resolution, high-speed and high-quality image recording is possible with one pass and non-interlace.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of an embodiment of an image forming apparatus according to the present invention. In FIG. 1, 100 is an ink jet recording apparatus, and 101 is a host computer such as a personal computer.

  In the example shown here, raster data is sent from the host computer 101 to the inkjet recording apparatus 100, and jaggy correction for binary images such as characters is performed on the host computer 101 side. That is, a means for jaggy correction processing is provided on the host computer side. However, a configuration in which means for jaggy correction processing is provided on the inkjet recording apparatus 100 side is also possible. Further, the inkjet recording apparatus 100 may be configured to receive a print command from application software executed by the host computer 101 and develop it into raster data. In this case, the inkjet recording apparatus 100 performs jaggy correction processing. It will be equipped with means for.

  The ink jet recording apparatus 100 is of a serial type, and a carriage 4 is movably mounted on guide rails 2 and 3 laid horizontally on the frame 1. A recording head 5 is mounted on the carriage 4, and a motor or the like (not shown) is used. The carriage 4 can be moved in the direction of arrow A by the drive source. A sheet 7, which is a printing medium set on the guide plate 6, is taken in by a platen 10 that is rotated via a drive gear 8 and a sprocket gear 9 by a drive source (not shown), and is pressed against the peripheral surface of the platen 10. The pressure roller 11 can be conveyed in the direction indicated by the arrow B. The platen 10 can also be manually rotated by the feed knob 10a. Then, while moving and scanning the print head 5 (carriage 4) in the main scanning direction (arrow A direction), the paper 7 is transported in the sub-scanning direction (arrow B direction) and ink droplets are ejected from the print head 5. The image is printed on the paper 7.

  The carriage 4, the print head 5, and the ink supply system will be described in more detail.

  The recording head 5 is an inkjet head that discharges ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk), and crosses a plurality of ink discharge ports with the main scanning direction. The ink droplets are mounted with their ink droplets discharged in a downward direction. In addition, each ink cartridge for supplying ink of each color to the recording head 5 is replaceably mounted on the carriage 4. The ink cartridge 15 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Thus, the ink supplied to the ink jet head is maintained at a slight negative pressure. The recording head 5 can also be configured using a single inkjet head that ejects ink droplets of a plurality of colors. Further, as an ink jet head, a piezoelectric type that pressurizes the ink liquid chamber through a vibration plate by a piezoelectric element, or an ink liquid chamber by displacing the vibration plate by an electrostatic force between the vibration plate and an electrode opposed thereto. An electrostatic type or the like that pressurizes can be used, but here, it is assumed that a piezoelectric ink jet head is used.

  Here, the ink jet head constituting the print head 5 will be described with reference to FIGS. FIG. 2 is a cross-sectional view of the main part of the ink jet head, and FIG. 3 is an explanatory diagram of the nozzle arrangement of the ink jet head.

As shown in FIG. 2, the inkjet head is provided with a nozzle plate 17 in which a plurality of nozzles 16 are formed on the front surface of a liquid chamber forming member 15 that forms the ink liquid chamber 14. Since this is a piezoelectric type ink jet, the ink in the ink liquid chamber 14 is ejected from the nozzle 16 by applying pressure to the ink in the ink liquid chamber 14 by a piezoelectric element (not shown) via a vibration plate (not shown). The ink droplets 18 fly and adhere to the paper 7 to form dots.
In the ink jet head shown here, as shown in FIG. 3, nozzles 16 are arranged in a staggered manner in two rows on the nozzle plate 17. In each dot row, dots 16 are arranged at a pitch of 2 × Pn. The interval between the dot rows is L. The nozzles 16 of one nozzle row and the nozzles 16 of the other nozzle row are shifted by a half Pn of the nozzle pitch in the vertical direction, that is, the sub-scanning direction in the figure. Due to such a nozzle arrangement, a dot image with a pitch Pn can be recorded by one main scanning and sub-scanning.

  Although not shown in FIG. 1, in order to move and scan the carriage 4 in the main scanning direction, a timing belt stretched between a driving pulley driven by a main scanning motor and a driven pulley is attached to the carriage 4. The carriage 4 is configured to be reciprocated in accordance with forward and reverse rotations of the main scanning motor. In order to transport the sheet 7 set on the guide plate 6 to a recording position by the recording head 5, a sheet feeding roller and a friction pad for feeding the sheet from the guide plate 6, a guide member for guiding the sheet, and a sheet are fed. A conveyance roller that conveys the sheet, a conveyance roller that is pressed against the circumferential surface of the conveyance roller, and a leading end roller that defines a sheet feeding angle from the conveyance roller are provided. The transport roller is rotationally driven through a gear train by a sub-scanning motor. Further, a platen roller is provided to guide the sheet fed from the transport roller to the recording unit. Further, on the downstream side in the paper transport direction, a transport roller and a spur that are rotationally driven to send the paper in the paper discharge direction, and a paper discharge roller and spur for sending the paper to the paper discharge tray, and a paper discharge path are secured. A guide member or the like is provided. During printing, the piezoelectric element of the inkjet head of the recording head 5 is driven in accordance with the image signal while moving the carriage 4 in the main scanning direction, and ink droplets are ejected onto the stopped paper 7 to record an image for one line. . Then, after the paper 7 is sub-scanned by a predetermined amount, the next line image is recorded. When the image recording for one page is completed, the paper 7 is discharged.

  Although not shown in FIG. 1, a recovery processing device for recovering ejection failure of the inkjet head is provided at a position outside the image recording area on the right end side in the moving direction of the carriage 4. This recovery processing apparatus has capping means, suction means and cleaning means. The carriage 4 is moved to the recovery processing apparatus side during recording standby, and the ejection surface of the inkjet head is capped by the capping means and kept in a wet state, thereby preventing ink ejection failure due to drying of the ink. Further, by performing ink ejection not related to recording during recording or the like, the ink viscosity in all the nozzles becomes constant, and stable ejection performance is maintained. When a discharge failure occurs, the discharge surface of the inkjet head is sealed by the capping unit, bubbles and the like are sucked out of the nozzle together with the ink by the suction unit through the tube, and ink or dust attached to the nozzle is removed by the cleaning unit. By removing, the ejection failure is recovered.

  As shown in a simplified manner in FIG. 4, the inkjet recording apparatus 100 includes a head drive unit 14 that drives a piezoelectric element of an inkjet head of the recording head 5, a carriage drive control unit 15 that drives the carriage 4, a platen 10, and a sheet. A line feed drive control unit 16 that drives a motor related to conveyance, a recording control unit 13 that controls each of the units 14 to 15, a data processing unit 17 that exchanges data and commands with the host computer 101, interprets commands, and the like. Is provided.

  The raster data sent from the host computer 101 is temporarily stored in a memory (not shown) of the data processing unit 17 and then transferred to the recording control unit 13 in synchronization with the recording operation. The drive data according to the raster data Is sent from the recording control unit 13 to the head driving unit 14. According to this drive data, the head drive unit 14 drives the piezoelectric element of the ink jet head of the recording head 5 to eject ink droplets and perform image recording. Further, under the control of the recording control unit 13, main scanning and sub-scanning are controlled by the carriage drive control unit 15 and the line feed drive control unit 16.

  As described above, in the example shown here, jaggy correction for binary images such as characters is performed on the host computer side. However, if jaggy correction is performed on the ink jet recording apparatus side, the processing is performed by the data processing unit 17. Will be done. When receiving a print command instead of raster data from the host computer side, the data processing unit 17 also performs raster data development processing.

  The configuration of the head drive unit 14 will be described with reference to FIGS. FIG. 5 is a block diagram illustrating an example of the internal configuration of the head driving unit 14. FIG. 6 is a block diagram showing an example of the internal configuration of the driver circuit 110 in FIG. FIG. 7 is a signal waveform diagram related to head driving.

  As shown in FIG. 5, the head drive unit 14 includes a drive waveform generation unit 106 and a driver circuit 110. Digital data DD having a continuous drive waveform as shown in FIG. 7A is supplied from the recording control unit 13 to the drive waveform generating unit 106. In the drive waveform generation unit 106, the D / A converter 107 converts the digital data DD into an analog signal, which is amplified by the amplifier 108 and the current amplifier 109, thereby generating a drive waveform Vp as shown in FIG. This is supplied to the driver circuit 110.

  In addition to the drive data S2 corresponding to the raster data given from the host computer side, the recording control unit 13 receives the latch signal S1, the clock signal S3, and the drive waveform selection signals M1, M2, and M3 (logic signals) from the driver circuit 110. Given to. In the example shown here, the size of ink droplets ejected from the inkjet head can be controlled to large droplets, medium droplets, and small droplets. Therefore, the drive data S2 represents four values including non-printing, and is, for example, 2-bit data per pixel, that is, per channel of the inkjet head.

  The driver circuit 110 drives the piezoelectric elements 111_1 to 111_n of each channel of the inkjet head according to the drive data S2, and as shown in FIG. 6, the shift register 112, the latch circuit 113, the data selector 114, the level shifter 115, It is composed of transmission gates 116_1 to 116_n which are switching means corresponding to the piezoelectric elements of the ink jet and head channels.

  The drive data S2 is shifted into the shift register 112 by the clock S3. When drive data corresponding to the number of channels of the inkjet head is accumulated in the shift register 112, the drive data is latched in the latch circuit 113 by the latch signal S1 and is supplied to the data selector 114. The data selector 114 selects and outputs a drive waveform selection signal M3 that is active only for five cycles of the drive waveform for a channel whose drive data indicates a large droplet, and a drive waveform M2 for a channel whose drive data indicates a medium droplet. Is selected and output, the drive waveform selection signal M1 is selected and output for a channel whose drive data indicates a droplet, and any of the drive selection signals M1 to M3 is selected for a channel whose drive data indicates non-printing. A signal corresponding to non-printing is output without selection. An output signal (logic signal) of the data selector 114 is converted by the level shifter 115 and applied to the transmission gates 116_1 to 116_n corresponding to the channels. The transmission gate 116 of the channel for which the drive waveform selection signal M3 is selected conducts during the active period of the same signal and applies the drive waveform as shown in FIG. 7D to the piezoelectric element 111 of the same channel. In the channel, a large drop of ink is ejected and a large dot is shot. The transmission gate 116 of the channel for which the drive waveform selection signal M2 is selected conducts during the active period of the signal and applies the drive waveform as shown in FIG. 7C to the piezoelectric element of the same channel. A medium dot is ejected by ejecting a medium drop of ink. A drive waveform as shown in FIG. 7B is applied to the piezoelectric element of the channel for which the drive waveform selection signal M1 is selected, and a small dot is ejected by ejecting a small droplet of ink in that channel. . Since the transmission gate 116 of the channel in which none of the drive voltage selection signals M1 to M3 is selected is non-conductive, no drive waveform is applied to the piezoelectric element of the channel, and therefore no ink droplet is ejected from the channel. , Dot is not hit (becomes blank).

  For recording binary images such as characters, large dots are basically used, and small dots and medium dots are used only for jaggy correction. Large, medium, and small dots are used for recording a multi-valued image.

  The ink used in the inkjet recording apparatus 100 is preferably a pigment-based ink containing at least a pigment, a wetting agent, a polyol or glycol ether having 8 or more carbon atoms, an anionic or nonionic surfactant, a water-soluble organic solvent, and water. More preferably, an ink having a pigment concentration of 6% by weight or more and an ink viscosity of 8 cp (25 ° C.) or more is used. Using such ink, even when recording on plain paper, good color tone (sufficient color developability, color reproducibility), high image density, clear image quality without feathering and color bleeding, and duplex printing Can be tolerated, and can exhibit high fastness such as high ink drying property (fixing property), light resistance and water resistance suitable for high-speed printing.

Here, the ink will be described more specifically. As described below, the ink used in the present invention comprises a pigment as a colorant and a solvent for decomposing and dispersing it as essential components, and further includes additives such as wetting agents, surfactants, emulsions, antiseptics. Agent and pH adjuster. The reason why the humectant 1 and the humectant 2 are mixed is to make use of the characteristics of the humectant and to easily adjust the viscosity.
(1) Pigment (self-dispersing pigment) 6% by weight or more (2) Wetting agent 1
(3) Wetting agent 2
(4) Water-soluble organic solvent (5) Anion or nonionic surfactant (6) Polyol or glycol ether having 8 or more carbon atoms (7) Emulsion (8) Preservative (9) pH adjuster (10) Pure water

  Regarding the pigment of (1), an inorganic pigment or an organic pigment can be used. As the inorganic pigment, in addition to titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (eg, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments). , Dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (for example, basic dye type chelates, acidic dye type chelates), nitro pigments, nitroso pigments, aniline black, and the like. Of these pigments, those having good affinity for water are preferably used. The particle diameter of the pigment is preferably 0.05 μm to 10 μm, more preferably 1 μm or less, and most preferably 0.16 μm or less. The amount of the pigment added is preferably about 6 to 20% by weight, more preferably about 8 to 12% by weight.

  Specific examples of preferable pigments include the following.

  For black, carbon black (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, channel black, or metals such as copper, iron (CI Pigment Black 11), titanium oxide, aniline black (CI And organic pigments such as CI Pigment Black 1).

  For color use, CI pigment yellow 1 (fast yellow G), 3, 12 (disazo yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 81 , 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 408, 109, 110, 117, 120, 138, 153, CI Pigment Orange 5, 13, 16, 17, 36, 43, 51 CI Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant First Scarlet), 23, 31, 38, 48: 2 (Permanent Red 2B (Ba)), 48: 2 (Permanent Red 2B (Ca) ), 48: 3 (Permanent Red 2B (Sr)), 48: 4 (Permanent Red 2B (Mn)), 49: 1, 52: 2, 53: 1, 57: 1 (Buri Antcarmin 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81 (Rhodamine 6G rake), 83, 88, 101 (Bengara), 104, 105, 106, 108 (Cadmium red), 112 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, CI pigment violet 1 (rhodamine lake), 3, 5: 1, 16, 19, 23, 38, CI pigment blue 1, 2, 15 (phthalocyanine blue R), 15: 1, 15: 2, 15: 3 (phthalocyanine blue E), 16, 17: 1, 56 , 60, 63, CI pigment green 1, 4, 7, 8, 10, 17, 18, 36, and the like.

  Other pigment pigments (eg carbon) treated with resin, etc., can be dispersed in water, and pigments (eg carbon) can be dispersed in water by adding functional groups such as sulfone groups and carboxyl groups to the surface. Processed pigments and the like can also be used. Further, the pigment may be included in the microcapsule so that the pigment can be dispersed in water.

  Preferably, the pigment for black ink is preferably added to the ink as a pigment dispersion obtained by dispersing the pigment in an aqueous medium with a dispersant. As a preferable dispersant, a known dispersion used for preparing a known pigment dispersion can be used.

  Specific dispersions include, for example, polyacrylic acid, polymethacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic. Acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer Polymer, styrene-α-methylstyrene-acrylic acid copolymer-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, vinylnaphthalene-maleic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate -Fatty acid vinyl ethylene copolymer, vinyl acetate-malein Examples include acid ester copolymers, vinyl acetate-crotonic acid copolymers, vinyl acetate-acrylic acid copolymers, and the like.

  Preferably, these copolymers have a weight average molecular weight of 3,000 to 50,000, more preferably 5,000 to 30,000, and most preferably 7,000 to 15,000. The amount of the dispersant added can be appropriately selected within the range in which the pigment is stably dispersed, but is preferably in the range of 1: 0.06 to 1: 3, more preferably 1: 0.125 to 1: 3. It is a range.

  The pigment used as the colorant is a particle having a particle size of 0.05 μm to 0.16 μm or less with respect to the total weight of the recording ink, and is dispersed in water by the dispersant. The dispersant is a polymer dispersant having a molecular weight of 5,000 to 100,000. When at least one water-soluble organic solvent is a pyrrolidone derivative, particularly 2-pyrrolidone, the image quality is improved.

  The lubricant 2 in (2), the wetting agent 2 in (3), and the water-soluble organic solvent in (4) are those in which water is used as a liquid medium in the ink. For example, the following water-soluble organic solvents are used for the purpose of preventing the drying and for improving the dissolution stability. A plurality of these water-soluble organic solvents may be used in combination.

  Ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, Polyhydric alcohols such as 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether Polyhydric alcohol alkyl ethers such as propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxy Nitrogen-containing heterocyclic compounds such as ethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam, γ-butyrolactone; amides such as formamide, N-methylformamide, N, N-dimethylformamide; Amines such as ethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine; sulfur-containing compounds such as dimethylsulfoxide, sulfolane, thiodiethanol; Emissions carbonate, ethylene carbonate.

  Among these organic solvents, diethylene glycol, thiodiethanol, polyethylene glycol 200 to 600, triethylene glycol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, petriol, 1,5-pentanediol 2-pyrrolidone and N-methyl-2-pyrrolidone are preferred. These are excellent in solubility and prevention of poor jetting characteristics due to water evaporation.

  The other wetting agent preferably contains sugar. Examples of saccharides include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides) and polysaccharides, preferably glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, Examples include lactose, sucrose, trehalose and maltotriose. Here, the polysaccharide means a saccharide in a broad sense, and is used to include a substance that exists widely in nature such as α-cyclodextrin and cellulose.

  Examples of derivatives of these saccharides include reducing sugars of the aforementioned saccharides (for example, sugar alcohols (represented by the general formula HOCH2 (CHOH) nCH2OH (where n is an integer of 2 to 5)), oxidized sugars (for example, , Aldonic acid, uronic acid, etc.), amino acids, thioic acids, etc. Particularly preferred are sugar alcohols, and specific examples thereof include maltitol, sorbit and the like.

  The content of these saccharides is suitably 0.1 to 40% by weight, preferably 0.5 to 30% by weight of the ink composition.

  The surfactant of (5) is not particularly limited, but examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, polyoxyethylene alkyl ether sulfate salt, and the like. Is mentioned. Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides, and the like. Can be mentioned. The surfactants can be used alone or in combination of two or more.

  The surface tension of the ink is an index indicating the permeability to paper. The surface tension referred to here is a dynamic surface tension in a short time of 1 second or less after the surface is formed, and is different from the static surface tension measured at the saturation time. As a measuring method, a method capable of measuring a dynamic surface tension of 1 second or less by a known method described in JP-A-63-131237 can be used. Here, a Wilhelmy type suspension plate type surface tension meter is used. The measured value shall be used. The surface tension value is preferably 40 mJ / m 2 or less, and more preferably 35 mJ / m 2 or less, whereby excellent fixing properties and drying properties can be obtained.

  A partially water-soluble polyol and / or glycol which is a polyol or glycol ether having 6 or more carbon atoms of (6) but having a solubility of less than 0.1 to 4.5% by weight in water at 25 ° C. By adding 0.1 to 10.0% by weight of ether with respect to the total weight of the recording ink, the wettability of the ink to the heat element is improved. It turns out that it is obtained. For example, (ii) 2-ethyl-1,3-hexanediol, solubility 4.2% (20 ° C.), (b) 2,2,4-trimethyl-1,3-pentanediol, solubility: 2 0.0% (25 ° C).

  A penetrant having a solubility of less than 0.1-4.5% by weight in water at 25 ° C. has the advantage of very high permeability instead of low solubility. Therefore, the combination of a penetrant having a solubility of less than 0.1 to 4.5% by weight in water at 25 ° C. and a combination of other solvents and other surfactants is very highly permeable. Ink can be obtained.

  It is preferable that a resin emulsion is added as the emulsion of (7). The resin emulsion means an emulsion in which the continuous phase is water and the dispersed phase is a resin component. Examples of the resin component in the dispersed phase include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, and styrene resins. This resin is preferably a polymer having both a hydrophilic part and a hydrophobic part. The particle size of these resin components is not particularly limited as long as an emulsion is formed, but is preferably about 150 nm or less, more preferably about 5 to 100 nm.

  These resin emulsions can be obtained by mixing resin particles in water, optionally with a surfactant. For example, an acrylic resin or styrene-acrylic resin emulsion can be obtained by adding (meth) acrylic acid ester or styrene, (meth) acrylic acid ester, and optionally (meth) acrylic acid ester, and a surfactant to water. It can be obtained by mixing. The mixing ratio of the resin component and the surfactant is usually preferably about 10: 1 to 5: 1. When the amount of the surfactant used is less than the above range, it is difficult to form an emulsion, and when it exceeds the above range, the water resistance of the ink tends to be lowered or the penetrability tends to deteriorate.

  The ratio of the resin as the dispersed phase component of the emulsion and water is 60 to 400 parts by weight, preferably 100 to 200 parts by weight with respect to 100 parts by weight of the resin.

  Commercially available resin emulsions include Microgel E-1002, E-5002 (styrene-acrylic resin emulsion, manufactured by Nippon Paint Co., Ltd.), Boncoat 4001 (acrylic resin emulsion, manufactured by Dainippon Ink & Chemicals, Inc.), Boncoat 5454 (styrene-acrylic resin emulsion, manufactured by Dainippon Ink & Chemicals, Inc.), SAE-1014 (styrene-acrylic resin emulsion, manufactured by Nippon Zeon Co., Ltd.), Cybinol SK-200 (acrylic resin emulsion, Seiden Chemical Co., Ltd.) Etc.).

The ink used in this embodiment preferably contains a resin emulsion such that the resin component is 0.1 to 40% by weight of the ink, more preferably 1 to 25% by weight.

  The resin emulsion has the property of thickening and aggregating, has the effect of suppressing the penetration of the coloring components, and further promoting the fixing to the recording material. Further, depending on the type of resin emulsion, a film is formed on the recording material, and the printed material has an effect of improving the abrasion resistance.

  Although it is a preservative of (8), for example, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol and the like can be used as antiseptic and antifungal agents. Examples of the rust inhibitor include acidic sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

  As the pH adjuster of (9), any substance can be used as long as the pH can be adjusted to 7 or more without adversely affecting the prepared ink. Examples thereof include amines such as diethanolamine and triethanolamine, hydroxides of alkali metal elements such as lithium hydroxide, sodium hydroxide and potassium hydroxide, ammonium hydroxide, quaternary ammonium hydroxide, and quaternary phosphonium. Examples thereof include carbonates of alkali metals such as hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the chelating reagent include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uramil diacetate, and the like.

  Jagged correction is performed on a binary image such as a character on the host computer 101 side. An example of a processing system related to this is shown in FIG.

  In FIG. 8, image and character print commands issued from the application software 200 (for example, the position / thickness / shape of the line of the image, the typeface / size / position of the character, etc.) are temporarily stored in the drawing data memory 201. . The rasterizer 202 reads and interprets the print command stored in the drawing data memory 201 and converts it into a dot pattern according to the designated position and thickness if it is a line drawing command. For example, the corresponding font data is fetched from the font data memory 207 and raster data that can be recorded by the inkjet recording apparatus 100 is generated. This raster data is temporarily stored in the raster data memory 203 and output to the ink jet recording apparatus 100 via an interface unit (not shown).

  In the example of the processing system shown here, development of characters into a dot pattern is performed by the font processor 204 independent of the rasterizer 202. However, the font processor 204 and the rasterizer 202 can be integrated. The rasterizer 202 and the font processor 204 are generally realized as software such as a printer driver, but one or both of them can be realized as hardware. Further, the font data memory 207 may be the same physical memory as the drawing data memory 201 or an independent physical memory.

The font processor 204 includes jaggy correction means 206 for performing jaggy correction processing for recording dots for jaggy correction on the character outline portion in addition to the dot development means 205 for developing characters into font data (bitmap data). Including. That is, in the example shown here, jaggy correction is performed only on the font data. However, although a specific example is not shown, an embodiment in which similar jaggy correction is performed not only on characters but also on other binary images, for example, diagonal lines of graphics images, is also included in the present invention. Such jaggy correction is executed by the rasterizer 202 or by a separately provided jaggy correction means. The font data memory 207 holds processed font data (including jaggy correction processing).

  An example of a processing flow for one character in the font processor 204 will be described with reference to FIG. It is checked whether or not the font data of the designated size of the character to be processed exists in the font data memory 207 (step S1). Only when it does not exist, the dot expansion means 205 expands the font data. Processing is executed (step S2). The generated font data is stored in the font data memory 207. The font data is subjected to jaggy correction processing (step S4) by the jaggy correction means 206. However, this jaggy correction processing is executed in step S3 when it is determined that the condition that “the designated font size is equal to or smaller than the predetermined size and the resolution of the output inkjet recording apparatus 100 is equal to or smaller than the predetermined resolution” is satisfied. This is only the case. The reason for providing such conditions will be described later.

  Prior to the description of the processing procedure of the jaggy correction process (step S4), a specific example of jaggy correction will be described.

  FIG. 10 shows an example of a character in which jaggy has occurred, and FIG. 11 shows an example of the dot arrangement of the hatched portion. As can be seen in FIG. 11, the dot line forming the outline is stepped in the shaded area, so that the outline of the line becomes discontinuous at the joint (change point), and so-called jaggy occurs. The example shown here is an example in which the number of dots forming a straight line between change points is four diagonal lines (this is called a diagonal line with a slope of 1/4).

  FIG. 12 shows an example of jaggy correction for making such a slanted jagged line with a slope of ¼ inconspicuous. The example shown here shows jaggies by adding a small dot to a blank portion of a character line formed by large dots (replacement with a blank small dot) and / or replacing a large dot with a small dot in an image portion. It is an example which correct | amends. It is possible to use medium dots in addition to small dots for jaggy correction, an example of which will be described later.

  12, (a) and (b) are examples in which the change point blank portion is replaced with small dots, (c) is an example in which the large dots in the change point image portion are replaced with small dots, and (d) And (e) are examples in which the change point blank portion is replaced with a small dot and the large dot in the change point image portion is replaced with a small dot. More specifically, in the example of (a), one pixel (positions 46 and 51) in the change point blank portion is replaced with a small dot. In the example of (b), two pixels (positions 45 and 46 and positions 51 and 52) in the change point blank portion are replaced with small dots. In the example of (c), two pixels (positions 47 and 48 and positions 49 and 50) in the change point image portion are replaced from large dots to small dots. In the example of (d), two pixels in the change point blank portion are replaced with small dots as in the example of (b), and one pixel (positions 47 and 50) of the change point image is changed from a large dot to a small dot. Has been replaced. In the example of (e), in addition to the same conversion as in the example of (d), the large dots at positions 48 and 49 are also replaced with small dots.

  By such correction, the stepped step at the change point of the oblique line becomes inconspicuous, and a relatively smooth contour is formed. The ink jet recording method has a characteristic that ink droplets spread after landing on paper, so that the contour becomes smoother. In addition, when recording on plain paper using dye-based ink, even if the above-mentioned jaggy correction is performed, the contour is uneven due to whisker-like blur called feathering, so the effect of the jaggy correction is fully exhibited. I can't. On the other hand, in the present invention, since the pigment-based ink as described above is used, such whisker-like blur is unlikely to occur, and the overall blur occurs to some extent, so that the effect of the jaggy correction is sufficient. It is demonstrated and a smooth outline is expressed.

  Here, the oblique line with the inclination of 1/4 is described, but the oblique line with the inclination of 1/3, the oblique line with the inclination of 1/5 or less, the mirror inversion oblique line, the 90 degree rotation oblique line, the 180 degree rotation oblique line, and the 270 degree rotation oblique line. The same jaggy correction effect can be obtained for this.

  An example of jaggy correction for an oblique line having an inclination of 1/2 will be described with reference to FIG. In FIG. 13, (a) shows the dot arrangement before the jaggy correction. When two pixels (for example, positions 70 and 71) in the blank portion of the staircase change point (F, G) are replaced with small dots with respect to this diagonal line, the small dots are arranged up to the adjacent change point as shown in (b). It becomes a shape and the effect of smoothing the outline cannot be obtained. Therefore, according to the present invention, in such a case, the replacement range of the blank portion with the small dots, that is, the addition range of the small dots is set to one pixel before the change point, that is, the straight line between the step change points. The number of pixels is limited to one less than the number of dots forming the. The result of performing the jaggy correction according to such a restriction is as shown in (c). Thus, jaggies can be improved even with diagonal lines having a slope of 1/2.

  By providing such a restriction, the dot replacement is not performed for the oblique line with the inclination 1/1 as shown in FIG. If one pixel in the blank portion at the change point of the oblique line is replaced with a small dot, the dot arrangement as shown in (b) is obtained, which is not only ineffective but also harmful.

  Next, an example of jaggy correction using small dots and medium dots as dots for jaggy correction will be described with reference to FIG. The object to be processed here is a diagonal line with a slope of ¼. FIG. 15A shows an example in which one pixel in the change point blank portion is replaced (added) with a small dot, and the dot arrangement is the same as that in FIG. (B) is an example in which two pixels in the change point blank portion are replaced with small dots and medium dots. (C) is an example in which two pixels in the change point image portion are replaced with small dots and medium dots. (D) is an example in which two pixels in the change point blank portion are replaced with small dots and one pixel in the change point image portion is replaced with medium dots. (E) is an example in which two pixels in the change point blank portion are replaced with small dots and two pixels in the change point image portion are replaced with medium dots.

  Next, the procedure of the jaggy correction process (step S4 in FIG. 9) will be described.

  FIG. 16 is a flowchart illustrating an example of a processing procedure for jaggy correction using only small dots. In this process, pattern matching is used for recognizing a pixel position to be replaced with a small dot. A window of size m × n is used for this pattern matching. Here, description will be made assuming that a window of m = n = 5 as shown in FIG. 17 is used.

  First, the first pixel of the font data is set as a target pixel (step S101). Font data (bitmap data) corresponding to a 5 × 5 window centered on the target pixel is acquired (step S102), and pattern matching with a reference pattern of 5 × 5 size prepared in advance is performed (step S102). S103). The reference pattern represents a dot arrangement in which the target pixel should be replaced with a small dot, and examples thereof are shown in FIGS. 18 (a) and 19 (a). If there is a match by this pattern matching (step S104, Yes), the target pixel is replaced with a small dot (step S105), the target pixel is moved to another pixel position (step S106), and the processing is repeated from step S102. . If the pattern matching does not match (No at Step S104), Step S105 is skipped and the process proceeds to Step S106. Such a process is repeated until all the pixels of the font data have been processed (step S107, Yes).

  For example, as shown in FIG. 18B, when the pixel at the position 46 in the blank portion becomes the target pixel, the pixel matches with the reference pattern shown in FIG. The pixel at the position is replaced (added) with a small dot. Further, as shown in FIG. 19B, when the pixel at the position 47 in the image portion becomes a target pixel, it matches the reference pattern shown in FIG. The pixel at the position is replaced from a large dot to a small dot.

  A data format representing replacement with small dots will be described. When the font data is data representing each pixel with a plurality of bits, for example, when the data is 1 byte / 1 pixel data representing a blank with a value of 0 and a large dot with a value of 255, the data of the pixel replaced with a small dot For example, a method of rewriting to 85 can be used. In this case, the result of jaggy correction is directly reflected in the font data. In addition, when the font data is 1 bit / 1 pixel data, a 1 bit / 1 pixel small dot memory is prepared separately from the memory for storing the font data itself, for example, replaced with small dots. A method can be used in which 1 is written in the pixel bit and the bit of the pixel not to be replaced is set to 0. In this case, the rasterizer 202 reads the contents of the small dot memory together with the font data, and generates raster data in which the small dots are recorded in the pixels replaced with the small dots.

  By using a window of 5 × 5 size and a reference pattern, it is possible to determine whether or not to replace the two pixels before and after the change point with small dots. For example, by using the reference pattern in FIG. 20A, the pixel at the position 45 in FIG. 18B can be replaced with a small dot. Further, by using the reference pattern in FIG. 20B, the large dot at the position 48 in FIG. 19B can be replaced with a small dot. In this window size, only two pixels before and after the change point can be replaced with small dots. For example, when the position 44 in FIG. 18 or FIG. 19 is the target pixel, the change point is outside the window. It is clear from this. In order to make it possible to replace the position of 44 with small dots, the size of the window and the reference pattern may be enlarged to 7 × 7.

  In this way, by increasing the size of the window and the reference pattern, the change point of the diagonal line near horizontal or vertical is detected, and small dots are added (replaced) according to the inclination, thereby improving the quality of the diagonal line. It can be further improved.

  Now, the size of the matching window and the reference pattern is determined in consideration of the range that needs to be replaced with small dots and whether the processing time is in time for the recording speed. The Furthermore, since the amount of data used for pattern matching increases as the size increases, the time required for pattern matching also increases. Therefore, from the viewpoint of processing time, the size should be as small as possible. On the other hand, how many dots before and after the change point should be replaced with small dots is determined by the required character quality. Therefore, it is necessary to determine an optimum size from the processing speed and character quality. According to experiments, when ink as described above is used, the unevenness of adjacent dots due to spreading of ink is reduced, so that small dot replacement of 7 dots or less achieves sufficient character quality improvement and throughput of 10 PPM or more. I knew it was possible. Therefore, the window size is suitably m ≦ 7 or n ≦ 7. The lower limit of the window size is m ≧ 3 and n ≧ 3.

  Even when windows of the same size are used, the processing time varies depending on the content of small dot replacement. In the example of FIG. 12, the processing time increases in the order of (a), (b), (c), (d), and (e).

  One of the causes is that pattern matching may be executed when the target pixel is a blank part in (a) and (b), and when the target pixel is an image part in (c), whereas (d) This is because in (e) and (e), it is necessary to perform pattern matching for both the case where the target pixel is a blank portion and the case of an image portion (that is, all pixels). Another reason is that the number of reference patterns increases in the order of (a), (b) = (c), (d), (e). That is, in order to implement (b), a reference pattern for determining the second pixel of the blank part is further required in the reference pattern of (a), and reference for determining the first pixel of the image part is further used in (d). A pattern is required, and in (e), a reference pattern for determining the second pixel of the image portion is further required.

  FIG. 21 shows an example of a jaggy correction processing procedure based on only small dot replacement in the blank portion. Step S111 in this flowchart is added, and other steps are the same as the procedure shown in FIG. That is, only when it is determined in step S111 that the pixel of interest is a blank portion pixel, the processing after step S102 for pattern matching is executed, and when it is determined that the target pixel is not a blank portion pixel, steps S102 to S102 are performed. Step S105 is skipped. According to this processing procedure, the jaggy correction shown in FIGS. 12A and 12B is possible.

  FIG. 22 shows an example of a jaggy correction processing procedure based only on small dot replacement in the image area. Step S112 in this flowchart is added, and the other steps are the same as the procedure shown in FIG. That is, only when it is determined in step S112 that the pixel of interest is a pixel in the image portion, the processing subsequent to step S102 for pattern matching is executed, and when it is determined that it is not a pixel in the image portion, steps S102 to S102 are performed. Step S105 is skipped. According to this processing procedure, it is possible to perform jaggy correction as shown in FIG.

  FIG. 23 shows an example of a jaggy correction processing procedure using small dots and medium dots as shown in FIG. In step 103A, pattern matching is performed using a reference pattern that also considers replacement with medium dots, and if there is a match, the pixel of interest is replaced with small dots or medium dots according to the reference pattern matched in step S105A. Is the same as the processing procedure shown in FIG. That is, in this example, the position for recording the dot for jaggy correction is recognized by pattern matching, and the size of the dot (small dot, medium dot) to be recorded at that position is recognized.

  A data format representing replacement with small dots or medium dots will be described. When the font data is data representing each pixel with a plurality of bits, for example, when the data is 1 byte / 1 pixel data representing a blank with a value of 0 and a large dot with a value of 255, it is replaced with a small dot or a medium dot. For example, a method of rewriting pixel data to a value 85 or a value 170 can be employed. In this case, the result of jaggy correction is directly reflected in the font data. When the font data is 1 bit / 1 pixel data, a 1 bit / 1 pixel small dot memory and a medium dot memory are prepared separately from the memory for storing the font data itself. A method can be used in which 1 is written in the bit of the pixel replaced with the medium dot and 0 is set in the bit of the pixel not to be replaced. In this case, the rasterizer 202 reads the contents of the small dot memory and the medium dot memory together with the font data, and generates raster data in which small dots or medium dots for jaggy correction are recorded. Become.

In an inkjet printer , the quality of characters recorded on plain paper was evaluated by applying the jaggy correction method shown in FIGS. The result is shown in FIG. The ink used contains at least the above-mentioned pigment, wetting agent, polyol or glycol ether having 8 or more carbon atoms, an anionic or nonionic surfactant, a water-soluble organic solvent, water, a pigment concentration of 6% by weight or more, and a viscosity. 8 cp (25 ° C.) or more. Other conditions are as follows.

Head: 384 nozzles / color
Nozzle pitch = 84 μm (equivalent to 300 dpi)
Image resolution: 300dpi
Dot size: Large dots have a diameter of 120 μm, small dots have a diameter of 40 μm
Character: MS Mincho Font size = 6, 10, 12, 20, 30, 50, 80 points Number of reference patterns: 16 patterns for Fig. 12 (a)
56 patterns for FIG.
56 patterns for FIG.
72 patterns for FIG. 12 (d)
104 patterns for FIG. 12 (e) Printing method: Number of passes (number of scans for forming one line) = 1
Interlace = none Paper: MyPaper TA manufactured by Ricoh Co., Ltd.

  As seen in FIG. 24, when jaggy correction is not performed, that is, when printing is performed using only large dots, jaggy is conspicuous at 30 points or less and the character quality is poor. When the jaggy correction was applied, the jaggy was not noticeable, there was no feathering, the density was sufficient, and the character quality was greatly improved. For comparison, when the same ink was corrected by changing the used ink to the dye ink, many feathering (character blurring) occurred, and the jagged feeling due to the feathering was conspicuous.

  Regarding the relationship between the jaggy correction method and the character quality, the methods (d) and (e) in FIG. 12 have the best character quality, then (b) and (c), and then (a) in that order. there were. In other words, the method of recording dots for jaggy correction on both the blank portion and the image portion has the highest jaggy improvement effect. This is because even if the same reference pattern is used, the step becomes smoother by forming the periphery of the change point with many small dots.

  Also, as can be seen from FIG. 24, the character quality is better for a larger size than for a smaller size. However, the jaggy improvement effect was obtained even with a small size. Furthermore, in the methods of (d) and (e) in FIG. 12, the effect of jaggy correction is great regardless of the font size. Therefore, from the viewpoint of character quality, it is preferable to apply the jaggy correction process regardless of the font size. However, as the font size increases, the number of dots forming the font increases and the processing time increases, so in order to improve the throughput (for example, to achieve a throughput exceeding 20 PPM), FIG. In step S3, it is effective to perform the condition determination regarding the font size so that the jaggy correction is applied only to a font of a predetermined size or less (for example, 50 points or less).

  In addition, this evaluation was performed for a case where recording was performed at 300 dpi. However, in the case of a lower resolution (for example, 200 dpi, 150 dpi, etc.), the diameter of the dots constituting the character is increased, and the stepped steps are more conspicuous. Therefore, the effect of jaggy correction is even greater. On the other hand, in the case of a high resolution such as 600 dpi, 1200 dpi, and 2400 dpi, the number of dots constituting the font is large and the dot size is small, so that jaggy is not conspicuous from the beginning. Therefore, in the case of an ink jet recording apparatus capable of recording at different resolutions, it is preferable from the viewpoint of improving the throughput that the condition determination regarding resolution is performed in step S3 of FIG. 9 and the jaggy correction processing is not executed depending on the resolution. For example, it is possible to execute the jaggy correction process only when it is 360 dpi or less and not to execute it when the resolution is 450 dpi or higher.

  Although the case of recording on plain paper has been described, the same effect can be obtained by jaggy correction when recording on coated paper, glossy paper, OHP film, and the like.

1 is a diagram illustrating a configuration example of an inkjet recording system that is an embodiment of an image forming apparatus according to the present invention. It is principal part sectional drawing of an inkjet head. It is a figure for demonstrating the nozzle arrangement | sequence of an inkjet head. It is a block diagram which shows the structural example of the control system of an inkjet recording device. FIG. 2 is a block diagram illustrating an example of a head driving unit of an ink jet recording apparatus. It is a block diagram showing an example of a driver circuit of a head drive unit. It is a signal waveform diagram for explanation of a driver circuit. It is a block diagram for demonstrating an example of the processing system relevant to jaggy correction in a host computer. It is a flowchart which shows an example of the processing flow of a font processor. It is a figure which shows an example of a character image with which jaggy is conspicuous. It is a figure which shows the dot arrangement | positioning of the oblique line of inclination 1/4. It is a figure which shows the example of jaggy correction | amendment with respect to the oblique line of inclination 1/4. It is a figure which shows the example of jaggy correction | amendment with respect to the oblique line of inclination 1/2. It is a figure for demonstrating the jaggy correction | amendment with respect to the oblique line of inclination 1/1. It is a figure which shows the example of the jaggy correction using a small dot and a medium dot. It is a flowchart which shows an example of the jaggy correction process sequence which uses a small dot for jaggy correction. It is a figure which shows an example of the window for matching. It is a figure which shows the example of a reference pattern and pattern matching. It is a figure which shows the example of a reference pattern and pattern matching. It is a figure which shows the example of a reference pattern. It is a flowchart which shows an example of the jaggy correction process procedure which pays attention only to the pixel of a blank part. It is a flowchart which shows an example of the jaggy correction process procedure which pays attention only to the pixel of an image part. It is a flowchart which shows an example of the jaggy correction process sequence which uses a small dot and a medium dot for jaggy correction. It is a figure which shows the evaluation result of recording quality.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Inkjet recording apparatus 101 Host computer 202 Rasterizer 204 Font processor 205 Dot development means 206 Jaggy correction means

Claims (9)

In an inkjet recording system for forming an image by ejecting ink droplets from an inkjet head onto an image recording medium and recording dots on the image recording medium.
The inkjet head ejects droplets of pigment-based ink containing at least a pigment, a wetting agent, a polyol or glycol ether having 8 or more carbon atoms, an anionic or nonionic surfactant, a water-soluble organic solvent, and water,
An ink jet recording system comprising means for jaggy correction processing for recording dots for jaggy correction on a contour portion of a binary image.   2. The ink jet recording system according to claim 1, wherein the dots for the jaggy correction are recorded only in one of a blank portion or an image portion around a step change point of a dot row forming a contour portion of a binary image. An ink jet recording system.   2. The ink jet recording system according to claim 1, wherein the jaggy correction dots are recorded in both a blank portion and an image portion around a step change point of a dot row forming a contour portion of a binary image. An ink jet recording system.   2. The ink jet recording system according to claim 1, wherein a plurality of types of dots having different sizes are used as the dots for the jaggy correction.   2. The inkjet recording system according to claim 1, wherein the means for the jaggy correction processing includes dots for jaggy correction by pattern matching between a binary image using a window of size m × n and a predetermined reference pattern. An ink jet recording system characterized by recognizing a pixel position to record.   2. The inkjet recording system according to claim 1, wherein the means for the jaggy correction processing includes dots for jaggy correction by pattern matching between a binary image using a window of size m × n and a predetermined reference pattern. An ink jet recording system for recognizing a pixel position to be recorded and a dot size to be recorded there.   7. The ink jet recording system according to claim 5, wherein m or n of the window size is selected in a range of 3 or more and 7 or less.   7. The ink jet recording system according to claim 5, wherein the pattern matching is performed by paying attention to one pixel of a blank portion or an image portion.   2. The ink jet recording system according to claim 1, wherein the jaggy correction means targets only a character image having a size equal to or smaller than a predetermined font size for jaggy correction processing.

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