JP2005145018A - Inkjet recording method and inkjet recording system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain stable gradation and color reproducibility by preventing degradation of a density reproducibility to be caused by the fact that a plurality of dots are mutually drawn on a recording medium in an inkjet recording apparatus which applies an area tone system by halftone dots. <P>SOLUTION: Dots of a halftone dot outline part among a dot arrangement determined by the area tone system by halftone dots are recorded precedently, and dots inside a halftone dot are recorded after a predetermined time difference. Since the dots inside the halftone dot are drawn in a state in which the dots of the halftone dot outline part are not absorbed yet, a shape and a density of the whole halftone dot become stable. Image processing of a high reliability in density and color reproduction can be carried out accordingly. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording method and a recording system for recording on a recording medium using an ink containing a coloring material, and in particular, recording using an ink jet recording head configured by integrating a plurality of discharge ports at a high density. It is about the method.

  2. Description of the Related Art With the development of information processing devices such as copying machines, word processors, computers, and communication devices, ink-jet recording devices that employ an ink-jet method as means for recording digital images of these devices have recently become widespread. In an ink jet recording apparatus, as a recording head, a recording head (nozzle) composed of a plurality of recording elements (nozzles) including an ejection port for ejecting ink and a liquid path for supplying ink to the recording head is used. Recording is performed by ejecting ink, which is a recording liquid, as flying droplets from the head and landing the ink on a recording medium such as paper. Therefore, since it is a non-contact system, it has an advantage of low noise. In addition, high-resolution recording can be realized relatively easily by increasing the density of the recording elements, and even for low-priced recording media such as plain paper, there is no need for special processing such as development and fixing. It is possible to obtain a quality image. In particular, the on-demand type ink jet recording apparatus is promising for future demand because it can be easily colored and the apparatus itself can be miniaturized and simplified.

  By the way, such an ink jet recording apparatus can be roughly divided into a serial type and a line type. In the serial type recording apparatus, a recording main scan that performs recording while moving and scanning a recording head including a plurality of recording elements arranged in the conveyance direction of the recording medium in a direction crossing the conveyance direction of the recording medium; An image is sequentially formed while alternately repeating sub-scanning for transporting the recording medium by a predetermined amount corresponding to the area recorded by the recording main scanning. Therefore, the serial type ink jet recording apparatus is characterized by being relatively small and inexpensive.

  On the other hand, in a line type recording apparatus, a long recording head (line type long recording head) in which recording elements are arranged larger than the width of an image to be recorded is used in a direction intersecting with the arrangement direction of the recording elements. An image is formed by moving and transporting the recording medium relatively once. Therefore, the line type recording apparatus can form an image at a remarkably high speed as compared with the serial type recording apparatus that performs recording scanning many times. Inkjet recording devices have been required to have higher speed as well as higher image quality, and at the same time, the technology of integrated arrangement of nozzles has been promoted in the recording head. There is great expectation for a recording device equipped with a head.

  However, new problems also arise in the ink jet recording apparatus capable of recording high-density images at high speed.

  In a line type recording apparatus or a system that forms an image on a recording medium by one or a few recording scans as in the case of serial type recording at high speed, the recording medium is connected to each recording head. It is desired to absorb and fix a predetermined amount of ejected ink in a relatively short time. However, some types of recording media cannot completely absorb a predetermined amount of ink within a predetermined time. If ink that cannot be absorbed instantaneously is present on the recording medium, the ink droplets recorded at adjacent positions come into contact with each other and coalesce with each other, and the surface of the recording medium attracts and mixes colors, thereby degrading the image quality. Sometimes.

  For such a problem, it may be possible to provide a fixing device such as a heating and drying means. However, this is rather a large-scale and high-priced apparatus, and an inkjet recording apparatus characterized by being able to be provided at a low price is not a very practical means. In addition, there is a method of speeding up ink fixing by reducing the amount of ink used for recording, but in this case, a new problem arises that only an image having a low density or recording density can be obtained.

  In the following, various image problems that appear when the ink absorption speed is low, and some examples of methods for solving the problems will be described. (See Patent Document 1 and Patent Document 2.)

  For example, Patent Document 1 discloses a recording method for preventing a connecting stripe appearing every recording scan in a serial type ink jet recording apparatus. When the ink absorption speed is slow, the ink recorded in the end area of the recording head in each recording scan is affected by the recording position by contacting the ink recorded in the previous recording scan, and each recording scan There are cases where white stripes or black stripes called connecting stripes stand out at the boundary. In Patent Document 1, the above-mentioned problem of the connecting stripe is solved by making the recording timing in the boundary portion different from that in other areas.

  Patent Document 2 discloses a device for obtaining a high-contrast image without blurring, particularly for solid images forming characters and graphs. When the ink absorption speed is slow, in an image where ink is concentrated locally, such as characters and graphs, the ink overflows from the contour to the non-recording area, and the boundary is blurred and blurred. It may end up. To solve this problem, Patent Document 2 discloses a technique for extracting a solid area recorded at 100%, classifying the solid area into boundary pixels and skeleton pixels, and recording a relatively large amount of ink in the skeleton pixels. ing. According to this, while increasing the density of the whole solid area by the skeleton pixel, the outline pixels surrounding it absorb ink overflow from the skeleton pixel, so that more ink than necessary overflows to the outer non-recording area. This makes it possible to obtain a clear image with a strong contrast.

JP-A-6-40046 JP 2000-118007 A U.S. Pat. No. 4,723,129 US Pat. No. 4,740,796 US Pat. No. 4,463,359 U.S. Pat. No. 4,345,262 US Pat. No. 4,313,124 US Pat. No. 4,558,333 US Pat. No. 4,459,600 JP 59-123670 A JP 59-138461 A Japanese Patent No. 3,427,026

  By the way, when trying to record an image with higher gradation and resolution as in recent years, image processing until the original image signal is converted into a binary signal value that can be recorded by the recording apparatus is important. And it comes to play a complex role. In the image processing, image data processing for the purpose of expressing a desired density is performed in consideration of the ink landing state on the recording medium. Therefore, it is preferable that the behavior of the ink on the recording medium is stable enough to be predicted to some extent. On the contrary, the more stable the behavior of the ink on the recording medium, the easier it is to express the desired density, so the reliability of the image processing increases.

  However, as described above, when recording on a recording medium with slow ink absorption, adjacent dots are merged due to the relationship between the presence or absence of adjacent dots, the difference in landing time, and the slight deviation in the landing position of dots. The shape of the large dots that are formed is greatly affected. Therefore, even when recording is performed according to the same image signal, there is a problem that the dot shape on the recording medium is not stable and only a gradation with low reproducibility can be obtained. Furthermore, the coalescence of dots may cause artifacts having density discontinuity. In other words, even when trying to record a smooth gradation image, local density levels appear at a certain gradation, resulting in streaking, and visually creating line artifacts such as white or black lines that degrade image quality. To make it happen.

  In the future, what is required of an ink jet recording apparatus is to simultaneously realize higher speed and lower cost in addition to higher image quality. Therefore, it can be said that one of the most important issues is to solve the above-mentioned problems relating to image processing and to realize reliable and stable gradation and color reproduction. However, including the above-disclosed patent documents, problems that have been noticed in the prior art, i.e., connecting stripes and character quality that occur when ink absorption is slow, and problems related to objects formed by solid recording are solved. Was possible, but could not be actively solved for other problems. That is, a recording method that can realize reliable and stable gradation and color reproduction irrespective of the ink absorption speed of the recording medium has not yet been proposed.

  The present invention has been made in view of the above problems, and an object of the present invention is to randomly draw a plurality of dots on a recording medium in an inkjet recording apparatus to which an area gradation method using a halftone dot is applied. Deterioration of the density reproducibility caused is reduced, and stable gradation and color reproducibility are obtained.

  To this end, in the present invention, an ink jet that forms an image on the recording medium by ejecting ink from the plurality of recording elements while moving and scanning a recording head in which a plurality of recording elements are arranged relative to the recording medium. In the recording method, in order to express a predetermined gradation, a step of determining a dot arrangement to be recorded by a halftone dot method, and all dots of the arrangement determined in the step are converted to dots constituting the outline of the dot A classification step for classifying into one or more contour dot groups and an internal dot group including one or more dots constituting the inside of a halftone dot, and the contour dot group and the internal dot group are recorded at different timings. A recording step, wherein the outline dot group is recorded prior to the internal dot group.

  Further, in an inkjet recording system for forming an image on the recording medium by ejecting ink from the plurality of recording elements while moving and scanning a recording head in which a plurality of recording elements are arranged relative to the recording medium, In order to express a predetermined gradation, means for determining an arrangement of dots to be recorded by a halftone dot method, and all dots of the arrangement determined by the means include at least one dot constituting the outline of the halftone dot Classifying means for classifying the outline dot group into an internal dot group including one or more dots constituting the inside of a halftone dot, and recording means for recording the outline dot group ahead of the internal dot group. It is characterized by comprising.

  According to the present invention, a good contour is formed by recording dots in the halftone dot contour in advance, and the subsequent halftone dot internal dots are recorded when the contour dot is not completely absorbed. Therefore, the shape and density of the entire halftone dot are stabilized, and highly reliable image processing can be performed in density and color reproduction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a front view for explaining the outline of a serial type ink jet recording apparatus applicable to the present embodiment. A plurality of inkjet recording heads 21 are mounted on the carriage 20, and 21-1 to 21-4 respectively receive black (K), cyan (C), magenta (M), and yellow (Y) ink. It is a recording head for discharging. Each recording head 21 has a plurality of ink ejection openings for ejecting ink. An ink cartridge is integrally formed by a plurality of recording heads 21-1 to 21-4 and ink tanks 22-1 to 22-4 that can be attached to and detached from these and supply ink.

  Control signals and the like to the recording head 21 are sent via the flexible cable 23. A recording medium 24 such as plain paper, high-quality exclusive paper, OHP sheet, glossy paper, glossy film, postcard or the like is sandwiched by a paper discharge roller 25 through a conveyance roller (not shown), and the direction of the arrow is driven by the conveyance motor 26 being driven. (Sub-scanning direction). The carriage 20 can be reciprocated in the main scanning direction via the drive belt 29 by driving the carriage motor 30, and the movement path is guided and supported by the guide shaft 27 and the linear encoder 28.

  A heating element (electrothermal converter) that generates thermal energy for discharging ink is provided further inside (liquid path) of the ink discharge port of the recording head 21. The heating element is driven based on the reading timing of the linear encoder 28 and the recording signal. As a result, ink is ejected from each ejection port of the recording head and landed on the recording medium 24, whereby images are sequentially formed.

  A recovery unit 32 is installed at the home position of the carriage 20 set outside the recording area, and a plurality of cap portions 31 corresponding to the recording heads 21 are provided. When recording is not performed, the carriage 20 is moved to the home position, and the caps 31-1 to 31-4 of the cap unit 31 seal the ink discharge port surface of the corresponding recording head 21. Thus, evaporation of the ink solvent from the ejection port and adhesion of foreign matters such as dust are suppressed, and ink sticking and clogging at the ejection port are prevented. Further, the cap unit 31 is used for so-called idle ejection that eliminates clogging and clogging of an ink ejection port having a low recording frequency by receiving ink droplets in a state of being separated from the ink ejection port, or capped. By operating a pump (not shown) in the state, ink is sucked from the ejection port, and may be used for recovery of the ejection port that has caused ejection failure.

  Reference numeral 33 denotes an ink receiving portion. When the recording heads 21-1 to 21-4 pass the upper part of the ink receiving portion 33 immediately before the recording scan, the recording heads 21-1 to 21-4 perform preliminary ejection. Furthermore, a blade, a wiping member, or the like (not shown) is disposed at a position adjacent to the cap portion 31 so that the discharge port surface of the recording head 21 can be cleaned.

  FIG. 2 is a configuration diagram for explaining a part of the structure of the recording head 21. In FIG. 2, the recording head 151 is mainly composed of a heater board 153 and a top plate 154 placed on the heater board 153. The heater board 153 is formed with a plurality of heaters 152 which are electrothermal converters for heating ink, while the top plate 154 has a plurality of discharge ports 155 and a tunnel communicating with the discharge ports 155. A liquid channel 156 is formed. Although not shown, each liquid path 156 is commonly connected to one ink liquid chamber at the rear thereof, and the ink liquid chamber is further connected to an ink tank via an ink supply port. The ink stored in the ink tank is supplied to the ink liquid chamber via the ink supply port, and then supplied to the vicinity of the discharge port by the capillary force of each liquid path. The heater board 153 and the top plate 154 are assembled by being aligned so that the liquid paths 156 and the heaters 152 correspond to each other one to one. In FIG. 2, only four heaters 152 are shown, but actually, a larger number of recording elements are formed by more heaters 152 and liquid paths 156.

  When a predetermined drive pulse is supplied to the heater 152 in the assembled state as shown in FIG. 2, film boiling occurs in the ink on the heater 152 and bubbles are generated. In addition, due to the volume expansion of the bubbles, the ink is pushed out from the ejection port 155 and ejected. However, the ink jet recording method applicable to the present invention is not limited to a method using a heating element (heater) as shown in FIGS. 1 and 2, and for example, ink droplets are continuously ejected to form particles. In the case of the continuous type, the charge control type, the divergence control type, etc., and in the case of the on-demand type that ejects ink droplets as needed, the ink droplets are ejected from the orifice by the mechanical vibration of the piezoelectric vibration element. It can also be applied to a pressure control method or the like.

  FIG. 3 is a block diagram for explaining the configuration of the control system in the ink jet recording apparatus applicable to the present invention. In FIG. 3, reference numeral 111 denotes an image input unit which inputs multi-value image data from an image input device such as a scanner or a digital camera, multi-value image data stored in a hard disk of a personal computer, or the like to the recording apparatus main body. To play a role. An operation unit 112 includes various keys for instructing various parameter settings and recording start. A CPU 113 controls the entire recording apparatus according to a control program 114b stored in the storage medium 114. The control program 114b also stores a program for operating the recording apparatus when an error occurs, such as an error processing program. Reference numeral 114a denotes a storage medium for storing various data, which stores landing position information, information mainly about the type of the recording medium, information about ink, information about environment such as temperature and humidity, and the like. The storage medium 114 may be a ROM, FD, CD-ROM, HD, memory card, magneto-optical disk, or the like. Reference numeral 115 denotes a RAM, which can temporarily store various tables in the storage medium 114, change the contents of the table, and advance image processing while referring to the contents. It can also be used as a work area for various programs in the storage medium 114, a temporary save area for error processing, and a work area for image processing.

  Reference numeral 116 denotes an image data processing unit. The image data processing unit 116 according to the present embodiment quantizes the input multi-value image data into lower-level image data, and further performs the final 2 corresponding to the quantized gradation value “K”. An ejection pattern that becomes a value signal can be created. In addition, as a process unique to the present invention, the binarized print data also serves to distribute the print data to different print elements and different print scans.

  Reference numeral 117 denotes an image recording unit that outputs an image. The image recording unit 117 ejects ink based on the ejection pattern created by the image data processing unit 116 to form dots on the recording medium. Reference numeral 118 denotes a bus line for transmitting various data such as address signals, data, and control signals in the recording apparatus.

  FIG. 4 is a flowchart for briefly explaining each step of data processing that the CPU 113 of the present embodiment causes the image data processing unit 116 to perform. In the recording apparatus of the present embodiment, it is assumed that 8-bit multi-value data that can represent 256 levels of gradation is input to the image input unit 111. The CPU 113 transfers the multi-value data to the image processing unit 116, and quantizes the 256 levels of gradation into values that can be expressed in 64 levels (step S41). For the quantization performed here, a multi-value error diffusion method is applied, but another arbitrary halftone processing method such as an average density preservation method, a dither matrix method, or the like can also be applied. After the quantization process is completed, the image processing unit 116 further develops the image data up to binary data for determining whether or not to record dots in all the recording pixels. At this time, it is first determined whether or not the value K quantized in step S41 is 24 or less (step S42).

  In step S42, if K ≦ 24, the process proceeds to step S43, and the density K of the pixel is represented by halftone dots in an area of 8 areas × 8 areas.

  FIG. 5 shows an example of a dot pattern after binarization corresponding to the value K. In the figure, each grid indicates one area where recording / non-recording is to be determined by one dot, and each area is configured with a density of 1200 dpi (dot / inch; reference value). For one pixel, a density value K is expressed by recording / non-recording of dots in a matrix composed of 8 areas × 8 areas. In FIG. 5, black portions indicate areas where dots are recorded, and white portions indicate areas where dots are not recorded. For example, when K = 1, dots are recorded only in one area in the center of 8 areas × 8 areas. In the case of K = 4, dots are recorded in four areas that are in contact with the area recorded when K = 1. Thus, in the present embodiment, gradation expression up to K ≦ 24 is performed by binarization processing according to the dot concentration type gradation method (hereinafter referred to as halftone method).

  Further, the process proceeds to step S45, and a distribution process of halftone dot area is performed. By this process, it is determined at which timing and at which nozzle the dots recorded in each area are recorded. The halftone dot area distribution process will be described in detail later.

  On the other hand, if it is determined in step S42 that K> 24, the process proceeds to step S44, and further binarization processing for K is performed by a normal error diffusion method.

  When the image data is completely binarized in step 45 or step S44 and it is determined at which timing and by which nozzle the data is transferred, the data is transferred to the image recording unit 117, and an image using a predetermined recording head is used. Is recorded (step S46).

As described above, in the present embodiment, the subsequent binarization method differs depending on the value of K after quantization. However, this method does not limit the present invention and this embodiment. For example, binarization processing may be performed with halftone dots in the same way as K ≦ 24 even at high gradations. Furthermore, the halftone dots may be arranged periodically or a screening method in which the halftone dots are arranged aperiodically (see Patent Document 12).
In the present embodiment, the effect of the present invention can be obtained particularly from a low gradation area to a halftone. On the other hand, in a high gradation area, the gradation and color caused by dot bleeding to be improved by the present invention. Since almost no variation in reproducibility is observed, such a configuration is adopted.

  Next, the distribution process to the preceding landing area in the halftone dot and the subsequent landing area, which is the most characteristic part of the present invention, will be described.

  FIG. 6 is a diagram for explaining the area of the halftone dot region to be recorded and the recording order. Here, a case where K = 24 will be described as an example. When K = 24, the dot recording area is as shown in FIG. In the present embodiment, the entire area shown in FIG. 5 (d) is divided into an area for forming the outline in FIG. 6 (a) and an area for forming the interior of the halftone dot in FIG. 6 (b). Are recorded at different times. FIG. 6C is a diagram in which perfect circle dots are recorded in the area shown in FIG. 6A in a state where no blur occurs, and FIG. 6D is the area shown in FIG. 6B. Fig. 2 shows a diagram in which a perfect circle dot is recorded without blurring at all.

  As described above, if the dots are not attracted at all, or if all the dots are recorded with sufficient time intervals, the landing state close to FIG. 6C or 6D can be obtained. I can do it. In general, however, the dots that have landed almost simultaneously attract each other due to their surface tension, and are merged together. Therefore, when recording is simultaneously performed in the area of FIG. 6B, a large dot as shown in FIG. One circular dot is formed. Also, as shown in FIG. 6A, even when dots are simultaneously recorded in an area that is almost circular, a smooth circle is formed as shown in FIG. The above phenomenon can be said to be remarkable when a recording medium having a low ink absorption speed is applied, such as glossy paper. However, it is generally considered that if the landing time difference between dots recorded at adjacent positions is within about 100 msec, they can attract each other.

  FIG. 7 is an image diagram for explaining the dot recording order on the recording medium. According to the figure, as time T elapses, dots in the halftone dot outline are recorded in advance, and subsequently dots in the halftone dot are recorded. By controlling the dot recording order in this way, in the present invention, the shape of the large coalesced dots formed on the recording medium after being recorded in all 24 areas can be kept good.

  The dots in the halftone dot outline portion recorded as the preceding dots are not greatly affected by each minute landing position deviation by recording adjacent dots almost simultaneously, as shown in FIG. A stable-shaped circle can be formed at a substantially stable position. Also, since the dots inside the halftone dots recorded as subsequent dots are not easily absorbed yet and are easily attracted to the preceding dots remaining on the surface of the recording medium, as a result, as shown in FIG. Dots can be formed.

  FIG. 9 and FIG. 10 are different from the method described in FIG. 6 in comparison with the method of separating the outline and the interior as in the present embodiment, and the entire recording area is divided into two uniformly and different from each other. An example in which dots are recorded at timing is schematically shown. 9 (a) and 9 (b) show areas for recording preceding dots and succeeding dots. FIGS. 9 (c) and 9 (d) are the same as FIGS. 6 (c) and 6 (d). Similarly, an image when a perfect circle dot is recorded on the paper surface is shown. Further, FIG. 10 compares the shape of a large dot obtained by recording the subsequent dot in the area of FIG. 9B immediately after recording the preceding dot in the area of FIG. 9A with FIG. It is shown.

  According to this comparative example, since the preceding dots shown in FIG. 9C are not recorded at positions adjacent to each other, variations in the respective landing positions are not corrected, and distorted dots are formed. The In addition, the subsequent dots are not attracted to a well-defined outline circle, but are recorded on the preceding dots with variations in landing positions. As a result, large dots having a distorted shape as shown in FIG. Will be formed.

  FIGS. 11A and 11B are diagrams showing the state of large dots when a halftone dot image of K = 24 is formed on six consecutive pixels, for the present embodiment and a comparative example. According to the figure, in the present embodiment shown in FIG. 11A, when the preceding dots recorded in the halftone dot outline portion touch each other, the respective landing positions are corrected, and a substantially smooth circle is used as the outline. First formed. Therefore, even after the succeeding dots are recorded, the shape of the large dots in the 8 × 8 area does not collapse, and smaller dots are formed compared to the comparative example. Therefore, there are many remaining blank paper portions as compared with FIG. As described above, in the gradation region where the number of dots in 8 × 8 is large to some extent, the state where the area of the large dots to be formed is small and an adequate amount of blank region remains is added next. It is easy to ensure density improvement by dots. Therefore, it can be said that the present embodiment is superior to the comparative example in terms of gradation.

  According to the present embodiment, by intentionally using such ink draw, dots in a halftone dot image recorded at any position on the recording medium have little variation in dot shape, and are well-formed dots. Can be formed stably. Therefore, the image density obtained with respect to the signal value K can also obtain a stable value on the same type of recording medium, so that highly reliable image processing can be performed and the desired density and color can be reproduced. It becomes possible to obtain with.

  In the present embodiment, among all the recording areas shown in FIG. 5D, for example, the area shown in FIG. 6B ′ is extracted as the area forming the inside of the halftone dot, and FIG. The same effect can be obtained when the area shown in FIG. 6 is recorded with the subsequent dots and the outline in FIG. 6A and the further four inner areas in FIG. 6B ′ are recorded with the preceding dots. The effect of the present invention is obtained by setting at least the contour dot as the preceding dot, and it is not always necessary to distinguish the preceding dot and the succeeding dot according to the method shown in FIG. Further, it is not necessary to simultaneously record dots inside the halftone dots. However, it can be said that it is ideal that 25% or more, more preferably 50% or more of all the dots constituting the halftone dot are recorded as subsequent dots. Therefore, also in each embodiment disclosed below, “inside the halftone dot” and “contour part” are not limited to the classifications shown in FIGS. 6A and 6B, but “at least the contour part” "Area including a part of" and "area contacting the inside of the contour part".

  Hereinafter, several examples will be described as a form of a recording head for realizing the present embodiment.

  FIG. 12 is a diagram showing an arrangement state of the ejection ports of the recording head 10 applicable to the ink jet recording apparatus of the present embodiment. In the figure, reference numerals 11 to 14 denote discharge port arrays in which a plurality of discharge ports are arranged in the Y direction at a density of 600 dpi. It is assumed that an average of 2.5 pl ink droplets are ejected from each ejection port. The ejection port array 11 and the ejection port array 12 are arranged in a state shifted by a half pitch in the Y direction, and by discharging ink while moving in the X direction, an image is formed at a recording density of 1200 dpi in the Y direction. It is possible to do. The relationship between the ejection port arrays 13 and 14 is the same as the relationship between the ejection port arrays 11 and 12, and all the ejection port arrays 11 to 14 are configured to eject the same color ink. The ejection port arrays 11 and 13 and the ejection port arrays 12 and 14 are arranged at a distance of 2 mm from each other, and the ejection ports 11 and 12 record subsequent dots and the ejection ports 13 and 14 record preceding dots, respectively. It has become. Furthermore, while the recording head 10 moves and scans in the X direction at a predetermined speed, ink is ejected from each ejection port at a predetermined frequency, so that the preceding dot and the succeeding dot are changed with a time difference within 100 msec on the recording medium. Each parameter is adjusted so that recording is performed by the same recording scan of the recording head 10.

  For example, as a modification of the present embodiment, all the nozzle arrays 11 to 14 are arranged so as to be shifted from each other by ¼ pitch in the Y direction, and an image of 2400 dpi is formed on the recording medium in the Y direction. It is good. In this case, for example, in the high image quality mode in which high resolution is required, recording is performed at a recording resolution of 2400 dpi by using multipass recording, while in the high speed mode in which a higher speed is required, the ejection port array 11 and 12 may record the subsequent dots, and the ejection openings 13 and 14 may record the preceding dots, respectively, in one recording scan. At this time, the dot group recorded with the preceding dot and the dot group recorded with the succeeding dot have a positional relationship that is relatively shifted by about 10 μm. If the attracting is performed normally, the effect of the present invention can be obtained.

  By the way, in order to more effectively implement the present invention, the subsequent dots are landed before the preceding dots are completely absorbed by the recording medium, in other words, the preceding dots exist in a liquid state on the surface of the recording medium. One of the important conditions is that the succeeding dot is brought into contact with the preceding dot during this time. In other words, this is a condition for forming a large circular dot with a well-defined outline by drawing the dots inside the halftone dot to the dots in the outline. As described above, the landing time difference is generally about 100 msec. However, even if the subsequent dots are recorded when the absorption time is exceeded, the effect of the present invention is not lost. For example, even when the preceding dot and the succeeding dot are recorded by two recording scans having a time difference far exceeding 100 msec, such as multi-pass recording and reciprocal recording, the degree of difference is not limited. The effect of the invention can be obtained.

  Therefore, as a modification of the present embodiment, the dot inside the halftone dot shown in FIG. 6A is recorded in the preceding forward recording scan, and the halftone dot shown in FIG. 6B in the subsequent backward recording scan. The effect of the present invention can also be obtained by adopting a method of recording point outline dots.

  Further, in the two-pass multi-pass printing in which the paper is transported by a half amount of the print head width during each printing scan, the dot in the halftone dot contour shown in FIG. 6A is printed in the preceding first printing scan. Even if the dots in the halftone dots shown in FIG. 6B are recorded in the subsequent second recording scan, the effect of the present invention can be obtained. The inventors of the present invention recorded the divided dots as shown in FIGS. 9A and 9B by two printing scans, and the divided dots as shown in FIGS. 6A and 6B. When the output image was compared with the case of recording by the recording scan of the number of times, it was confirmed that the better image with sharpness was obtained in the latter.

  Further, even in 4-pass multi-pass printing in which paper is conveyed by a quarter of the print head width during each printing scan, the dots in the halftone dot contour are printed in the preceding printing scan, and the dots in the subsequent printing scan. It was confirmed that better image quality was obtained by recording the inner side.

  In the multipass recording and the reciprocal recording described above, since the dots to be recorded are originally divided by each recording scan, it is possible to record little by little while drying the ink on the recording medium. Therefore, it can be said that problems such as blurring, random pulling of dots and spread of halftone dots, which the present invention is trying to solve, are less likely to occur than when all dots are printed in one printing scan. However, such a printing method has a drawback in that the throughput decreases due to the large number of printing scans. Also from this point, the effects of the present invention and the present embodiment can be obtained by multi-pass recording and reciprocal recording. However, when recording with fewer recording scans, particularly when recording at high speed with one recording scan. In addition, it can be said that it is further demonstrated.

  FIG. 13 is a diagram for explaining the configuration of a line-type recording head applied in this embodiment. Since this embodiment uses a line type recording apparatus, unlike the serial type shown in FIG. 1, the recording medium is transported in the X direction at a predetermined speed to the recording head 120 that is fixed. ing. In FIG. 13, a plurality of recording heads having the same configuration as the recording head shown in FIG. 12 are arranged as shown in the figure (in this case, six parts from 121 to 126). In the Y direction, dots corresponding to the width of the recording medium can be recorded at a recording density of 1200 dpi. Furthermore, by arranging the recording heads 127 for one color configured in this way for four colors in the X direction, it is possible to form a full color image with four colors of black, cyan, magenta and yellow. ing.

The verification conditions and results actually performed in order to confirm the effect of this example are reported below. In the recording head 120, ink droplets were adjusted to be ejected at 2.5 ± 0.5 pl. As ink, four colors (cyan, magenta, yellow, black) for commercially available BJF900 (manufactured by Canon Inc.) are used, and as a recording medium, photo glossy paper dedicated to inkjet (Pro Photo Paper, PR101: manufactured by Canon Inc.) ) Was prepared. The drive frequency of the recording head was 16 kHz, and an image of K = 24 was recorded on all pixels with a recording resolution of 1200 × 1200 dpi. In the recording medium and ink components to be applied, the ink absorption time required by the Brist method was 14 msec per 10 ml / m ^2. Therefore, when recording is performed by the recording head used in this embodiment, the preceding dot and the succeeding dot are recorded. The dots are recorded within a time sufficiently shorter than 100 msec.

  Thus, both can be landed so that the subsequent dot contacts before the preceding dot is absorbed, and the preceding dot and the subsequent dot are combined to form a dot as shown in FIG. It was observed that That is, it is possible to suitably leave a blank paper portion that is not covered with halftone dots and to obtain a good gradation expression.

  FIG. 14 is a diagram illustrating an arrangement state of ejection openings for ejecting a certain color in a recording head applicable to the ink jet recording apparatus of the present embodiment. In the figure, reference numerals 131 to 134 denote discharge port arrays in which a plurality of discharge ports are arranged in the Y direction at a density of 600 dpi. It is assumed that an average of 0.8 pl ink droplets are ejected from the ejection ports 131 and 132, and an average of 2.5 pl ink droplets are ejected from 133 and 134. The ejection port array 131 and the ejection port array 132 are arranged in a state shifted by a half pitch in the Y direction. By ejecting ink while moving in the X direction, an image of 1200 dpi in the Y direction is recorded on the recording medium. It is possible to form. Further, the relationship between the ejection port arrays 133 and 134 is the same as the relationship between the ejection port arrays 131 and 132. Further, the ejection port arrays 131 and 133 and the ejection port arrays 132 and 134 are arranged at a distance of 2 mm from each other, and the ejection ports 131 and 132 are preceded by small dots, and the ejection ports 133 and 144 are preceded. A large dot that becomes a dot is recorded.

  FIG. 15 shows a recording head 140 for ejecting ink of four colors applied in this embodiment. In the figure, reference numerals 131 to 134 and 141 to 144 denote the discharge port arrangements described with reference to FIG. 14, wherein 131 to 134 discharge cyan ink and 141 to 144 discharge magenta ink. Further, reference numerals 145 to 148 are the same as the ejection port arrangement described in FIG. 12 of the first embodiment. In this embodiment, 145 and 146 are 2.5 pl yellow ink, and 147 and 148 are 2.5 pl. Each of the black inks is ejected. Further, ink is ejected in the order of black, yellow, magenta, and cyan on the recording medium by ejecting ink at a predetermined frequency from each ejection port while the recording head 140 moves and scans in the X direction at a predetermined speed. Thus, cyan and magenta preceding dots and succeeding dots are recorded in the same recording scan with a time difference within 100 msec.

  As in this embodiment, the outline of a halftone dot is first recorded with a smaller preceding dot, and then the inside of the halftone dot is recorded with a larger subsequent dot, while maintaining the density of the halftone dot, the contour shape Can be controlled more finely. That is, in the image processing, the gradation can be controlled in a more preferable state.

  In the present embodiment, as in the first embodiment, it is more effective to record the preceding dots and the subsequent dots with a sufficiently short landing time difference. Even if the subsequent dot is recorded after the preceding dot is almost fixed, the effect of the present invention can be obtained. In this case, even better image quality can be obtained at the same time due to the effect of multipass.

  As described above, according to the present embodiment, density characteristics and color reproduction are performed by performing control divided into the preceding dot and the subsequent dot as described above for cyan and magenta in which gradation is particularly important. An image having excellent properties can be obtained. Of course, it is also effective to adopt such a configuration for yellow and black.

  FIG. 16 is a diagram for explaining the configuration of a line-type recording head 150 applied in this embodiment. In this embodiment, the recording medium is transported in the X direction at a predetermined speed with respect to the recording head 150 that is fixed. In FIG. 16, a plurality of the recording heads having the same configuration as the recording head shown in FIG. 14 are arranged as shown in the figure (here, six pieces from 151 to 156), whereby both large dots and small dots are arranged. In the Y direction, dots corresponding to the width of the recording medium can be recorded at a recording density of 1200 dpi. Furthermore, by arranging the recording heads 157 for one color configured in this way for four colors in the X direction, it is possible to form a full color image with four colors of black, cyan, magenta and yellow. It has become.

  According to the present embodiment, as in the second embodiment, the effect of recording the preceding dot and the succeeding dot with a very short time difference can be obtained by the line type ink jet recording apparatus capable of high-speed recording. In addition, as in Example 3, after recording the halftone dot contour portion with small dots in advance, the halftone dot inside is recorded with large dots, so that the shape of the halftone dots is maintained in a favorable state. It is also possible to control the gradation.

  In the third and fourth embodiments, the method of forming a halftone dot outline by using smaller dots has been described. For example, the preceding dot and the succeeding dot are recorded by two types of inks having the same color but different densities. You may comprise. Further, the subsequent dots may be recorded with higher density and smaller dots. In this case, it can be expected that the shape of the outline of the halftone dot is formed more precisely and clearly.

  As described above, the present invention is also applicable to an ink jet recording apparatus that records dots having a plurality of densities and sizes for each color. In either case, the recording area for forming halftone dots is appropriately classified into the contour and the inside of the halftone dot according to the configuration of the recording head to be applied, ink type, recording medium type, recording speed, etc. If it can be recorded, the effect of the present invention can be obtained.

  Furthermore, in the above-described embodiment, the pseudo halftone process using halftone dots is performed for K = 0 to 24 out of 64 gradations, and the error diffusion method is applied for K = 25 to 64. The present invention is not limited to this. Conversely, the effect of the present invention is sufficiently confirmed even if the low density portion is subjected to pseudo halftone processing by the error diffusion method and the high density portion is subjected to pseudo halftone processing using halftone dots and then the processing of the present invention. It can be done. In this case, the granularity of the dots in the low density portion is reduced, and the gray level becomes more favorable as the white paper portion is efficiently left in the high density portion.

  In the above embodiment, as described with reference to FIG. 2, an ink jet recording method is applied in which flying droplets are formed using thermal energy and recording is performed. The effect of the present invention is not obtained only by this configuration, but the above method can be said to be a very effective recording method in that it can be realized relatively simply and at low cost. As for the typical configuration and principle, for example, those performed using the basic principle disclosed in Patent Document 3 or Patent Document 4 are preferable. This method can be applied to both the so-called on-demand type and continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding nucleate boiling to the electrothermal transducer, the thermal energy is generated in the electrothermal transducer, and the recording head This is effective because film boiling occurs on the heat acting surface, and as a result, bubbles in the liquid (ink) corresponding to the drive signal can be formed. By the growth and contraction of the bubbles, liquid (ink) is ejected through the ejection opening to form at least one droplet. It is more preferable that the drive signal has a pulse shape, since the bubble growth and contraction is performed immediately and appropriately, and thus it is possible to achieve discharge of a liquid (ink) having particularly excellent responsiveness. As this pulse-shaped drive signal, those described in Patent Document 5 and Patent Document 6 are suitable. Note that further excellent recording can be performed by employing the conditions described in Patent Document 7 of the invention relating to the temperature increase rate of the heat acting surface. As the configuration of the recording head, in addition to the combination configuration (straight liquid channel or right-angle liquid channel) of the discharge port, the liquid channel, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, the heat acting part A configuration using Patent Document 8 or Patent Document 9 that discloses a configuration arranged in a region in which the lens is bent is also included in the present invention.

  In addition, with respect to a plurality of electrothermal transducers, Patent Document 10 that discloses a configuration in which a common slit is used as a discharge portion of the electrothermal transducer or an opening that absorbs a pressure wave of thermal energy is associated with the discharge portion. The effect of the present invention is also effective as a configuration based on Patent Document 11 that discloses the configuration. That is, whatever the form of the recording head is, according to the present invention, recording can be performed reliably and efficiently.

  In addition, even a serial type recording device can be connected to the device body or supplied with ink from the device body by being attached to the recording head fixed to the device body. The present invention is also effective when a replaceable chip type recording head or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself is used.

  In addition, it is preferable to add a recording head ejection recovery means, a preliminary auxiliary means, and the like as the configuration of the recording apparatus of the present invention, since the effects of the present invention can be further stabilized. Specifically, heating is performed using a capping unit, a cleaning unit, a pressurizing or suction unit, an electrothermal transducer, a heating element different from this, or a combination thereof. Examples thereof include a preliminary heating unit for performing the discharge and a preliminary discharge unit for performing discharge different from the recording.

  The present invention can be applied to all ink jet recording apparatuses that perform recording by attaching ink to a recording medium such as paper, cloth, leather, nonwoven fabric, OHP paper, and metal. Specific application equipment can be used for office equipment such as printers, copiers, and facsimile machines, industrial production equipment, and the like.

1 is a front view for explaining an outline of a serial type inkjet recording apparatus applicable to the present embodiment. It is a block diagram for explaining a part of the structure of the recording head. FIG. 2 is a block diagram for explaining a configuration of a control system in an ink jet recording apparatus applicable to the present invention. It is a flowchart for demonstrating each process of the data processing which CPU applied in embodiment of this invention performs. (A)-(d) is the figure which showed the dot pattern example after binarization corresponding to a gradation value. (A)-(f) is a figure for demonstrating the area and recording order of the dot area | region recorded. It is an image figure for demonstrating the recording order of the dot with respect to a recording medium. FIG. 6 is a diagram showing a state of large dots gathered at the center of a halftone dot obtained by the recording method of the present invention. It is a schematic diagram for demonstrating the comparative example with respect to embodiment of this invention. It is a schematic diagram for demonstrating the comparative example with respect to embodiment of this invention. (A) And (b) is the figure which showed the recording state at the time of forming a halftone dot continuously about this embodiment and a comparative example. FIG. 3 is a diagram illustrating an arrangement state of ejection ports of a recording head applicable to Embodiment 1 of the present invention. FIG. 6 is a diagram illustrating an arrangement state of ejection openings of a recording head applicable to Embodiment 2 of the present invention. FIG. 9 is a diagram illustrating an arrangement state of ejection openings of a recording head applicable to Embodiment 3 of the present invention. FIG. 9 is a diagram illustrating an arrangement state of ejection openings of a recording head applicable to Embodiment 3 of the present invention. FIG. 10 is a diagram illustrating an arrangement state of ejection ports of a recording head applicable to Example 4 of the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording head 11-14 Ejection port array 20 Carriage 21 Recording head 22 Ink tank 23 Flexible cable 24 Recording medium 25 Discharge roller 26 Conveyance motor 27 Guide shaft 28 Linear encoder 29 Drive belt 30 Carriage motor 31 Cap part 32 Recovery unit 33 Ink Receiving unit 111 Image input unit 112 Operation unit 113 CPU
114 Storage medium 115 RAM
116 Image Processing Unit 117 Image Recording Unit 121-127 Recording Head 131-134 Discharge Port Array 140 Recording Head 141-148 Discharge Port Array 151-157 Recording Head

Claims (7)

In an inkjet recording method for forming an image on the recording medium by ejecting ink from the plurality of recording elements while moving and scanning a recording head in which a plurality of recording elements are arranged relative to the recording medium,
A step of determining a dot arrangement to be recorded by a halftone dot method in order to express a predetermined gradation;
All the dots in the array determined in this step are classified into a contour dot group including one or more dots constituting the outline of a halftone dot and an internal dot group including one or more dots constituting the inside of the halftone dot. A classification process;
A recording step of recording the outline dot group and the internal dot group at different timings, wherein the outline dot group is recorded prior to the internal dot group in the recording step. Inkjet recording method.   The inkjet recording method according to claim 1, wherein in the recording step, the recording element that records the outline dot group is different from the recording element that records the internal dot group.   In the recording step, the moving scan of the recording head for recording the outline dot group with respect to the recording medium is different from the moving scan of the recording head for recording the internal dot group with respect to the recording medium. The inkjet recording method according to claim 1.   The inkjet recording method includes a main recording scan for ejecting ink from the plurality of recording elements while moving the recording head relative to the recording medium, and the recording medium in a direction crossing the main recording scan. 4. The ink jet recording method according to claim 1, wherein an image is formed on the recording medium by alternately repeating sub-scanning in which a predetermined amount of moving scanning is performed relative to the recording head. .   The recording head is a long recording head having a recording element group arranged over a recording width of a recording medium, and the ink jet recording method performs the recording while discharging ink at a predetermined frequency by the recording head. 4. An image is formed on the recording medium by moving and scanning the recording medium at a predetermined speed relative to the recording head in a direction intersecting an arrangement direction of element groups. The inkjet recording method according to any one of the above.   6. The ink jet recording method according to claim 1, wherein in the recording step, the internal dot group is recorded as a larger dot than the outline dot group. In an inkjet recording system for forming an image on the recording medium by ejecting ink from the plurality of recording elements while moving and scanning a recording head in which a plurality of recording elements are arranged relative to the recording medium,
Means for determining the arrangement of dots to be recorded by a halftone dot method in order to express a predetermined gradation;
All the dots of the arrangement determined by the means are classified into a contour dot group including one or more dots constituting the outline of the halftone dot and an internal dot group including one or more dots constituting the inside of the halftone dot. Classification means;
An ink jet recording system comprising: recording means for recording the outline dot group in advance of the internal dot group.

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