JP2007320118A - Inkjet recording device, and recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a bidirectional difference of an area factor by a satellite, a dot gap or the like from occurring at the time of a bidirectional printing, and to reduce unevenness in the bidirectional density. <P>SOLUTION: The switching from a black ink to a color ink is performed in response to the characteristics of image data. An area factor is increased by the variety of the color inks, and the bidirectional difference can be reduced. (Example) The color inks are mainly used for an image of a bit map main body, and the black ink is mainly used in the case of character data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a color image forming method for an ink jet printer.

  Conversion from CMY ink to black ink has been conventionally performed as UCR technology such as JP-A-57-173838, JP-A-49-85912 and JP-B-62-57144. Japanese Patent Publication No. 8-5221 shows a method of switching between 100% UCR and skeleton black (less than 100% UCR) in order to prevent scumming due to black ink in a highlight portion and to improve character quality. The Japanese Patent Publication No. 8-5221 detects the CMY signal and performs the switching described above, and is basically one of UCR technologies.

Furthermore, nothing is shown regarding the ink coverage on the recording medium due to the ink penetration difference, and there is no description regarding the objects and effects of the present invention.
JP-A-57-173838 JP 49-85912 A Japanese Patent Publication No.62-57144 Japanese Patent Publication No. 8-5221

  In bi-directional printing used as a means for high-speed recording, the ink dot shape difference between the forward scan and the backward scan appears as a density difference, resulting in density unevenness between the forward scan portion and the backward scan print portion. However, the image quality was degraded.

  Black ink is switched to CMY ink depending on the continuity of the image data or the characteristics of the image data. Alternatively, the lookup table describing how to use ink is switched.

  As described above, the black ink is switched to the CMY ink depending on the continuity of the image data or the characteristics of the image data. Alternatively, in bidirectional printing used as a means for high-speed recording by increasing the coverage on the recording medium by using a larger amount of CMY ink than black ink by switching a look-up table describing how to use ink, forward scanning and A recording apparatus capable of reducing image deterioration due to density unevenness between the forward scanning portion and the backward scanning portion where the shape difference of the ink dots on the recording medium in the backward scanning appears as a density difference has been realized.

  Further, the present invention is effective by a vertically aligned head system in which different color ink discharge portions are arranged in the recording medium conveyance direction.

(First Example)
Description of recording apparatus Fig. 5 shows a conventional inkjet color printer.

  The print head 1 is a device that has a plurality of nozzle rows and performs image recording by forming dots on a recording medium by ejecting ink droplets. Different color inks are ejected from different print heads, and a color image is formed on the recording medium by mixing these ink droplets.

  The print data is transmitted from the electric circuit of the printer main body to the print head via the cable 9. The print head arrays 1K (dark black), 1C (dark cyan), 1LC (light cyan), 1M (dark magenta), 1LM (light magenta), and 1Y (dark yellow) are mounted on the carriage 201. In this example, the apparatus has a six-color ink.

  The above-described print heads are generally called a side-by-side system, and the print heads are arranged corresponding to a plurality of ink colors in the main scanning direction of the carriage. Aside from this method, a case where print head portions that eject a plurality of ink colors are arranged perpendicular to the main scanning direction of the carriage, that is, in the recording medium conveyance direction, is called a vertical arrangement method. The vertical arrangement method has an advantage that the apparatus can be reduced in size because a plurality of ink colors can be arranged in a smaller space than the horizontal arrangement method. In addition, since the order of ink placement for each color does not change even when printing in both directions, the color unevenness in both directions is less than in the horizontal arrangement method.

  The carriage 201 performs movement control in the main scanning direction by detecting the carriage scanning speed and the printing position by the speed detecting means 5. The power source is a carriage drive motor 8 that is transmitted by belts 6 and 7 and moves on a sliding shaft. Printing is performed during the operation in the main scanning direction.

  The recovery unit 400 has a function to keep the print head in a good state at all times. In the non-printing state, the cap row 420 closes the ejection surface of the print head to prevent drying and the like. A position where the carriage 201 faces the recovery unit 400 is referred to as a home position (hereinafter referred to as HP). The function of the recovery unit during the printing operation will be described. The actual printing operation does not always use all the nozzles in one head. In addition, there is a non-use head in which print data is not transferred even if the print head has a plurality of colors. In this way, if ink is not ejected for a certain period of time during carriage scanning (when the print head is not capped), the ink ejection performance deteriorates due to sticking or drying of the print head surface and image deterioration. May occur. In order to prevent this phenomenon, the print head discharges using nozzles in the head in addition to the print data at a certain time interval, so that the state of the print head surface is always kept optimal. This operation is called preliminary discharge. The ink ejected by the preliminary ejection is ejected toward the cap 420 in the recovery unit 400 so as not to be scattered and contaminated inside the recording medium or the printer, sucked by a recovery pump (not shown), and stored in a waste ink tank. . Therefore, when the preliminary ejection operation during printing is performed, the carriage 201 needs to return to HP in both one-way and two-way printing and face the cap row 420.

  For feeding in the sub-scanning direction, the recording medium is fed by a paper feed member (rubber roller or the like) driven by a paper feed motor (not shown). When paper is fed from the direction of arrow A in FIG. 6 and reaches the printing position, the printing operation is performed by the print head row. Thereafter, the paper is discharged in the direction of arrow B by the paper discharge mechanisms 2 and 3.

  Ink is supplied for each color from the ink cassettes 10K, 10C, 10LC, 10M, 10LM, and 10Y to the print head. In this example, dark cyan ink and light cyan ink, dark magenta ink and light magenta ink are stored in the same ink cassette.

  FIG. 6 is a block diagram illustrating a control configuration of the recording apparatus.

  A control unit 301 controls the operation of the entire apparatus, and is used as a work area when various processes are executed by the CPU 310 such as a microprocessor, a ROM 311 storing a control program executed by the CPU 310 and various data, and the CPU 310. A RAM 312 for temporarily storing data is provided. The RAM 312 has a receiving buffer for recording the recording data received from the host 100, and recording heads 1K (dark black) and 1C (dark cyan) for discharging and recording ink of each color of C, M, Y, K, LC, and LM. ) And 1LC (light cyan), 1M (dark magenta), 1LM (light magenta), and 1Y (dark yellow) corresponding to each color component of C, M, Y, Bk, LC, and LM storing print data A print buffer is provided.

  In FIG. 6, these print buffers are described as a C print buffer, an M print buffer, a Y print buffer, a Bk print buffer, an LC print buffer, and an LM print buffer.

  A head driver 302 is a dark cyan ink recording head 1C, a dark magenta ink recording head 1M, a dark yellow ink recording head 1Y, and a dark black ink recording in accordance with print data of each color output from the control unit 301. The head 1K, the light cyan ink recording head 1LC, and the light magenta ink recording head 1LM are driven. Each of 303 and 304 is a motor driver that drives a corresponding carriage drive motor 8 or a paper feed motor (not shown).

  An interface unit 306 controls an interface between the recording apparatus and the host.

  An operation unit 307 includes various keys operated by the user and a display such as an LCD.

Block diagram FIG. 2 is a block diagram showing a general image signal processing portion in the above-described ink jet recording apparatus. There are cases where a part or all of FIG. 2 is performed by the recording apparatus main body or processing on the host computer and transmission to the recording apparatus, and either of them may be used in this case. When processing is performed on the host computer, the processing in FIG. 2 is performed by the host computer 100 in FIG. 6 and transmitted to the interface unit 306 as print data.

  R, G, and B original image signals obtained by reading with a scanner or by computer processing or the like are converted into R ′, G ′, and B ′ by the color conversion unit A40. This processing is conversion from an original image signal to an image signal adapted to the recording apparatus.

  Next, R ′, G ′, and B ′ are converted into signal values corresponding to each color ink by the color processing unit B41. In this example, since the ink composition has six colors, the signal values are dark cyan, dark magenta, dark yellow, dark black, light cyan, and light magenta density signals C1, M1, Y1, K1, LC1, and LM1.

  Next, the gamma (γ) correction unit 42 performs gamma correction using the gamma correction table, and the corrected image density signals C2, M2, Y2, K2, LC2, and LM2 are binarized by the quantization unit 43, respectively. To generate image signals C3, M3, Y3, K3, LC3, and LM3 to be transferred to the print heads 1C, 1M, 1Y, 1K, 1LC, and 1LM. As a binarization method used in the quantization unit 43, for example, a dither method can be used. The dither method is a method of performing binarization using a predetermined dither pattern in which threshold values for the density signal of each pixel are made different.

○ Satellite for bidirectional printing Fig. 3 shows the ink droplet landing state for bidirectional printing. As described above, serial printers use bidirectional printing to achieve high-speed printing. In this method, recording is performed by reciprocating the carriage 201 in FIG.

  At this time, ink droplets are ejected from the print head 1, but there may be a difference in the landing shape on the recording medium during forward scanning and sub-scanning. This occurs when the structure of the ink discharge portion of the print head 1 is asymmetrical or when the ink droplet discharge direction is not perpendicular to the print head but is slightly angled. When a small-volume ink droplet called a satellite lands on a large-volume ink droplet called a main droplet, the dot shape as shown in the forward scanning of FIG. 3 is obtained. However, when the satellite lands on a position different from the main droplet for the above reason, the dot shape as shown in the backward scanning of FIG. 3 is obtained. Thus, the area of the ink droplet after landing = the difference in coverage appears as a difference in density. This density difference becomes a band-like unevenness having a printing width and is called banding. Further, when the recording medium swells due to moisture in the ink and becomes a wavy state (hereinafter referred to as cockling), the landing position at the time of reciprocation changes, so that the same state occurs.

Ink characteristics In the case of a printer that emphasizes the quality of black characters, an ink composition is used in which black ink is relatively hard to permeate and spread. This is to prevent deterioration of the quality caused by the penetration of the ink along the fibers of the recording medium and the generation of beveled jagged edges (called feathering) around the characters. Such an ink composition is referred to as a superposition ink. In the case of overlay ink, good character quality with good cutting quality can be obtained. FIG. 7A schematically shows the dot shape of the added ink. It can be seen that the reproducibility of the straight lines and curves of the characters is high because the edges stand out and have a clear shape. However, since the ink is relatively difficult to permeate, the area covering the recording medium on the recording medium is relatively small. For this reason, if the ink droplet landing accuracy is not high to some extent, the surface of the recording medium cannot be covered by dot misalignment or the like, and the density may be lowered or the color (white) of the recording medium may appear, resulting in image deterioration.

  Conversely, ink having a relatively high penetration rate is mainly used for printing color images. In the case of a color image, since a plurality of color inks are ejected in a short time, mixing of different color ink boundaries on the surface of the recording medium can be prevented by increasing the penetration speed of the ink into the recording medium. This type of ink is called penetrating ink and has a high margin of ink droplet landing accuracy compared to the above-described overlay ink because it penetrates the recording medium and has a high coverage. FIG. 7B schematically shows the dot shape of the penetrating ink. Since the ink permeates along the fibers of the recording medium, it has a jagged shape. Therefore, the outer perimeter length of the ink droplet is large and the coverage is high. Generally, the penetrability is improved by adding a small amount of a surfactant or the like to the ink.

  The bleeding rate is defined as a scale indicating the degree of bleeding of this ink.

Bleeding rate = (diameter of ink dots landed on recording medium) / (diameter when ejected ink droplets are spheres)
It is represented by Even if the ejected ink droplets have the same size, the spreading rate increases as the ink spreads on the recording medium.

Ink replacement In the first embodiment of the present invention, the ink used is switched from black ink to CMY ink due to the continuity of black data in the image data. An image that needs to be cut off, such as a black character, is printed in two directions using black ink as it is. However, black data in an image in which various colors such as a photographic image are mixed uses CMY ink instead of black ink. Use at a fixed ratio. This makes it possible to improve the coverage on the recording medium by using a larger amount of CMY ink than black ink, and to prevent density unevenness during bidirectional printing due to the satellite and dot displacement described above.

  FIG. 1 shows an example of the conversion ratio between black ink and CMY ink. In this example, only the black ink that does not use the LC ink and the LM ink, which are light inks, is used. However, when the light ink is used, the method of the present embodiment is not changed but only the dark ink is used.

Multivalued data for each ink color is obtained in the gamma correction unit of FIG. Each CMY ink is converted as shown in the figure in response to the black ink changing from 0 to 255 using the multi-value data as an input value. When using CMY inks corresponding to black ink, the color and density must be close to those of black ink before conversion. In the case of the ink jet method, the color development differs depending on the order of ink ejection and the printing speed, and therefore the ratio of CMY inks used instead of black ink is not generally determined. Here, the conversion ratio of CMY is not C = M = Y but C>M> Y. As an example, as described above, the size of the ink droplet (unit of discharge amount = p1 is 10 ⁻¹² liter) is relatively large and is about 40 pl due to the ink composition in which black ink hardly penetrates. In contrast, CMY ink has a dot diameter of about 15 pl even with a small discharge amount. Assuming that C>M> Y, the ink droplets in total are 15 pl × 3 = 45 pl. That is, the black ink is 40 pl, the converted CMY ink is 45 pl, and the ink droplet volume recorded on the recording medium is almost the same before and after the conversion.

  Although this ratio varies depending on the characteristics of the recording medium, ink, or printing method, the gist of the present invention that CMY ink is used instead of black ink can be commonly applied.

  Next, a black data extraction method will be described with reference to FIG. This method is processing performed before RGB input in FIG. When a certain number of black data continues in the image, it is determined as character data and only black ink is used. In this example, black data is defined as R = G = B = 0. Although the figure shows a case where black data continues in the main scanning direction and the sub-scanning direction, it may be continuous only in the main scanning direction, only in the sub-scanning direction, or both.

  When black data does not continue for a certain number, that is, when isolated points of black data or continuous black data less than the predetermined number, the amount printed with black ink is replaced with CMY ink for printing. The replacement method is as described above.

  The data replacement may be performed by the control unit 301 in FIG. Data sent from the host computer 100 is stored in the print buffer, but it is determined whether or not the predetermined number of black ink data in the print buffer is continuous, and the black ink data is converted into CMY ink data according to the conversion ratio. In place of this, the head driver 302 is driven to record on the recording medium. In this way, the conversion from black ink to CMY ink can be realized in the printer body.

(Second embodiment)
In this embodiment, the processing result of the color processing unit B41 in FIG. 2 is changed according to the continuous result of the black data. The color processing unit B41 is a part for converting R′G′B ′ data converted into a desired color space into an ink color unique to the printing apparatus. When a certain number of black data continues, it is determined that black ink such as black characters is preferentially used, and each ink color is recorded through a color processing section B (similar to the prior art) using black ink. On the other hand, if the black data does not continue for a certain number, it is determined that CMY ink is preferentially used, and each ink color is recorded through the color processing unit B ′ using CMY ink.

  Usually, the color processing units A and B as described above are stored in a look-up table format. In this embodiment, a plurality of look-up tables called color processing units B and B 'are held in advance and are used properly depending on the continuity of the black data. An example is shown in FIG. This figure shows the output state of each ink color corresponding to the image data from white (R = G = B = 255) to black (R = G = B = 0). Although only the ink switching between white and black is shown in the same figure, all the conditions for conversion from RGB to CMYKLcLm are actually described in the above lookup table. In this embodiment, the combination of black ink and CMY ink is described. The range to be changed is the entire range of the lookup table. When a certain number of black data continues, a lookup table using black ink is used as shown in FIG. When the image data is black (R = G = B = 0), only black ink is used, but black ink is also used in other cases. When a certain number of black data does not continue, a lookup table that does not use black ink at all is used as shown in FIG. In some cases, as shown in FIG. 8C, a lookup table in which black ink is set to a small number may be used. This is because the use of CMY ink instead of black ink has the same effect as the first embodiment in that the ink droplet ejection amount increases and the ink coverage on the recording medium increases.

(Third embodiment)
In this embodiment, the characteristics of the image data are analyzed, and the color processing section B is changed according to the result, and the look-up table is switched.

  There are several types of image data such as bitmap data, text data, and graphics data. FIG. 9 shows an example in which two types of image data exist on the recording medium. The portion indicated by the gray portion is bitmap data assuming a photographic-like natural image. The portion indicated by a horizontal line indicates character data. In this embodiment, it is divided into a case of bitmap data and a data format other than that where there are few black characters in a certain area on the recording medium. In the case of bitmap data, a photographic-like natural image is mainly handled. Unlike a character image, such an image has a small blank area on the image and a large amount of ink. Therefore, the lookup table of the color processing unit B41 that mainly uses CMY ink rather than black ink is used. On the other hand, since it is assumed that there are many cases of characters and graphs other than bitmap data, the lookup table of the color processing unit B41 using mainly black ink is used. This data format analysis is performed by the RGB input processing routine shown in FIG. In response to this result, the lookup table of the color processing unit B41 is switched. An example of the lookup table may be that shown in the second embodiment. Since the analysis of the data format is performed for each area on the recording medium, a certain area can be a lookup table using black ink, and a certain area can be a lookup table using CMY ink. In this way, the ink usage method can be set for each area on the recording medium. In particular, in the case of bitmap data, the combination of black ink and CMY ink can be set over the entire color space of the printer, so that natural ink switching can be realized, which is advantageous for the tone reproducibility required for bitmap data. For example, in the case of bitmap data, a lookup table that does not use black ink is used, and in a case other than bitmap data, a lookup table that uses black ink is used. Also, by dividing the usage of black ink and CMY ink by area, the black color is the same in the area.

  In this way, it is possible to use CMY ink in which density unevenness does not occur due to a difference in ink droplet coverage in a photographic-like natural image, and black ink in a character image.

  Further, since it is only necessary to be able to identify the data for each area, it may be determined whether the data is text data or any other data. A specific image file format (Tiff, JPEG, etc.) may be determined as a natural image. As described above, the present invention is effective even with other methods capable of determining whether the data is character data or a natural (photo) image.

The figure which shows switching of color ink and black ink. The block diagram which shows an image signal processing part. The figure which shows the dot shape at the time of bidirectional printing. The figure which shows the case of black data arrangement | positioning in image data. 1 is a diagram illustrating an ink jet recording apparatus. The block diagram which shows a control structure. The figure which shows the dot shape difference by the difference in how to spread. The figure which shows the color processing look-up table of a 2nd Example. The figure which shows the arrangement | sequence of image data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Print head 5 Speed detection means 6,7 Belt 8 Carriage drive motor 10 Ink cassette 40 Color conversion part A
41 Color conversion part B
42 Gamma Correction Unit 43 Quantization Unit 100 Host 201 Carriage 301 Control Unit 302 Head Driver 303, 304 Motor Driver 306 Interface Unit 307 Operation Unit 310 CPU
311 ROM
312 RAM
400 recovery unit 420 cap row

Claims (10)

  A first printing method for printing black data using both black ink and color ink according to an analysis result of the image data analyzing means, and a color ink that uses less black ink than the first printing method. An ink jet recording apparatus that performs printing by switching to a second printing method in which the amount of ink used is increased.   According to the analysis result of the image data analysis means, the black data is a first color processing look-up table using both black ink and color ink, and only color ink is used without using black ink. An inkjet recording apparatus, wherein the second color processing lookup table is switched to perform printing.   According to the analysis result of the image data analysis means, the black data is more than the first color processing lookup table using both black ink and color ink, and the first color processing lookup table. An ink jet recording apparatus, wherein printing is performed by switching to a second color processing lookup table in which the amount of black ink used is reduced and the amount of color ink used is increased.   4. An ink jet recording apparatus according to claim 1, wherein said image data analyzing means judges whether or not a certain number of black data continues.   4. An ink jet recording apparatus according to claim 1, wherein said image data analyzing means judges whether or not the image data is bitmap data.   4. An ink jet recording apparatus according to claim 1, wherein said image data analyzing means judges whether or not the image data is text data.   4. The ink jet recording apparatus according to claim 1, wherein the switching from the black ink to the color ink is such that the total volume of the switching color ink is equal to or larger than the ink volume of the black ink.   4. The ink jet recording apparatus according to claim 1, wherein switching from the black ink to the color ink is performed at the time of bidirectional printing.   4. The ink jet recording according to claim 1, wherein a plurality of nozzle groups from which ink droplets are ejected are arranged in a recording medium transport direction so that different color inks can be ejected. apparatus.   4. The ink jet recording apparatus according to claim 1, wherein the color ink has a bleeding rate on a recording medium larger than that of the black ink.

Images