JP3785775B2 - Printing apparatus, image processing method, and recording medium storing program for realizing the method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a black ink dot and a plurality of hue inks by a printing apparatus including a head capable of forming a plurality of hue ink dots capable of expressing black on a print medium in combination with black ink dots. The present invention relates to a technology for recording a multi-tone image by controlling the formation of dots.
[0002]
[Prior art]
2. Description of the Related Art In recent years, color printers that eject several colors of ink from a head have become widespread as computer output devices, and are widely used for printing images processed by a computer or the like in multiple colors and multiple gradations. When a multicolor image is printed with three colors of ink of cyan, magenta, and yellow (CMY), several methods are conceivable for forming a multi-tone image. One is a method adopted by conventional printers, and the density of dots printed on the paper is determined by the dot density (unit: constant size of the dots formed on the paper by the ink ejected at a time. (Appearance frequency per area). Another method is to vary the density per unit area by adjusting the dot diameter formed on the paper. Recently, fine processing of a head for forming ink particles has progressed, and the density of dots that can be formed per predetermined length and the variable range of the dot diameter have improved year by year. However, in the case of a printer, the print density ( The resolution is still about 300 to 720 dpi and the particle size is only a few tens of microns, and the gap between the expressive power of silver salt photography (called resolution of several thousand dpi on the film) is still large.
[0003]
In particular, in a region having a low image density, that is, a region in which the printed dot density is low, dots are sparsely formed (so-called graining), and this is noticeable. Therefore, in order to suppress the dot variation as much as possible and form dots that faithfully reflect the gradation of the original image, an error distribution method that distributes density errors that occur during multi-value conversion to surrounding pixels. Since black dots are very conspicuous, the black density is divided into cyan, magenta, and yellow ink densities, and so-called composite black is used to express black color by mixing three ink dots. Proposals have been made.
[0004]
[Problems to be solved by the invention]
However, conventional printers that record images using black ink and color inks such as cyan, magenta, and yellow have the following problems.
{Circle around (1)} Since black ink has a large weight per dot, the quantization error is large when multi-value processing such as halftoning is performed. Therefore, it is necessary to use error diffusion, an average error minimum method, and the like, and a long time is required for the calculation. However, if the dither method is used, the quantization error is large and the image quality is deteriorated.
[0005]
{Circle around (2)} Since black ink has low brightness, it is difficult to eliminate graininess even in the low density region even if error diffusion or the average error minimum method is used. However, if all black areas are expressed in composite black, three colors of ink are ejected, and in the case of an ink jet printer, excessive ink is ejected from the viewpoint of water absorption of the paper. Therefore, it is possible that the paper will be lost. If the ink duty is strictly limited, dark black cannot be expressed. In addition, when black is expressed by composite black, black is obtained by additive color mixing, so it is inevitably a grayish image compared to black by the original black ink, especially in the high density area. There was also a problem that became sweet.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems related to black expression, to shorten the calculation time in printing a multi-tone image and to suppress graininess.
[0007]
[Means for solving the problems and their functions and effects]
In order to achieve this object, the present invention employs the following configuration. First, the printing apparatus of the present invention is
A black ink dot capable of expressing black alone and a plurality of hue ink dots capable of expressing black by combination are provided on a print medium, and the black ink dot and the plurality of hues are provided. A printing apparatus that records a multi-tone image with dots of ink,
Input means for inputting gradation data of an image to be printed for each pixel;
Storage means for storing a relationship between the gradation data when expressing black based on the input gradation data and the density to be realized by the black ink and inks of a plurality of hues;
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. First dot formation determination means for determining whether or not to form the black ink dot at a position corresponding to the pixel;
For the plurality of hue inks, a second determination is made by error diffusion or a minimum average error method to determine whether or not to form dots of inks of other hues different from the black at positions corresponding to the pixels. Dot formation determination means;
Head driving means for driving the head based on the determination results of the first and second dot formation determining means to form the black ink dots and the other color ink dots;
With
The storage means stores the relationship as follows:
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And is defined as
b) The density to be realized by the inks of the plurality of hues is stored as a relationship in which the gradation data is defined from 0 to a range larger than the predetermined value and lower than the maximum gradation value.
Is the gist.
[0008]
On the other hand, the image recording method of the present invention corresponding to this printing apparatus is
By using a printing apparatus having a head capable of forming, on a print medium, dots of black ink that can express black alone and ink dots of a plurality of hues that can express black by combination, the dots of black ink And a method of recording a multi-tone image by controlling the formation of dots of the plurality of hue inks,
Input the gradation data of the image to be printed for each pixel,
The relationship between the gradation data when expressing black based on the input gradation data, and the density to be realized by the black ink and inks of a plurality of hues,
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And is defined as
b) The density to be realized by the plurality of hue inks is stored as a relationship in which the gradation data is determined from 0 to a range larger than the predetermined value and lower than the maximum gradation value;
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. Determining whether or not to form the black ink dot at a position corresponding to the pixel;
For the plurality of hue inks, whether or not to form dots of inks of other hues different from the black at positions corresponding to the pixels is determined by error diffusion or an average error minimum method,
Based on the determination results, the head is driven to form the black ink dots and the other color ink dots.
Is the gist.
[0009]
In this printing apparatus and image recording method, first, for each pixel, an assumed image density on the print medium is obtained based on the input gradation data. If this density is equal to or higher than the predetermined density, whether or not the black ink dot is formed at the position corresponding to the pixel is compared with a threshold matrix corresponding to the dither pattern prepared in advance. Judging. Separately from this determination, it is determined whether or not to form a dot of ink having a different hue from black at a position corresponding to the pixel, and the head is driven based on the results of both determinations. Black ink dots and / or other hue ink dots are formed.
[0010]
That is, according to the present invention, when the image density on the printing medium is high, dots are formed using a dither pattern with black ink, but at least in the area where the image density is low, at least the dither pattern is used. No black dots are formed. The formation of ink dots of hues other than black is performed separately from the formation of black ink dots. Since the dot density per unit area is high in the region where the density of black is high, even if the black ink dots are formed using a dither pattern, the deterioration in image quality is not noticeable. On the other hand, since the formation of black dots using a dither pattern is not performed in the low density region, the graininess can be suppressed. As a result, the black ink can achieve a high-speed processing by adopting the dither method, and has an excellent effect that the image quality is not deteriorated.
[0011]
Note that the density of the image on the print medium assumed based on the gradation data may be a density converted to the density of the black ink, but a predetermined calculation is performed from the density of each primary color separated into the three primary colors. It is good also as what is calculated | required by a type | formula. Also, instead of determining the formation of black ink dots after determining the density of the image on the print medium, prepare a table that directly converts the gradation data to the density of black ink and ink of other hues, In this table, the data may be set so that the density of the black ink is low in the region where the overall density is high. In this case, it is not necessary to determine whether the density is equal to or higher than a predetermined value.
[0012]
Further, since dots are formed with black ink in a region where black density is high, in the case of an ink jet printer, excessive ink is not ejected from the viewpoint of water absorption of paper. Therefore, dark black can be expressed even on paper with a strict ink duty. Further, since dots are formed with black ink in a region where the black density is high, the black in the high density region is tightened and the image quality is not sweetened compared to the case where black is expressed with composite black.
[0013]
The invention of a recording medium recording a program for realizing such an image recording method on a computer is as follows:
It is determined whether or not a black ink dot capable of expressing black alone and a plurality of hue ink dots capable of expressing black by combination are formed on a print medium, and the black ink dot and the dot A recording medium on which a program for controlling the formation of dots of ink of a plurality of hues and recording a multi-tone image is recorded in a computer-readable manner,
The relationship between the gradation data when expressing black based on the input gradation data, and the density to be realized by the black ink and inks of a plurality of hues,
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And is defined as
b) A function of storing the density to be realized by the plurality of hue inks as a relationship in which the gradation data is defined as a range from 0 to a range larger than the predetermined value and lower than the maximum gradation value;
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. A function for determining whether or not to form the black ink dot at a position corresponding to the pixel;
A function of determining whether or not to form dots of inks of other hues different from black at positions corresponding to the pixels with respect to the plurality of hue inks by an error diffusion or a minimum average error method,
A function of forming the black ink dots and the other hue ink dots on the print medium based on the both determination results.
The gist is that a program realized by a computer is recorded.
[0014]
A program recorded on such a recording medium is read by a machine and executed by a computer. The computer executes the program, determines the dot formation, and then forms the dot on the print medium, thereby realizing the image recording method described above.
[0015]
In such a printing apparatus and image recording method, the threshold matrix used for determining the formation of dots with black ink can be a distributed threshold matrix. When a distributed threshold matrix is used, the dispersibility of dot formation can be improved, and the appearance of roughness can be reduced.
[0016]
In addition, when determining the dot formation of a plurality of hue inks, the recording rate of inks of other hues is obtained based on the density of black, and the error diffusion method or the average error minimum is determined based on the recording rate of each color ink. It may be determined whether or not to form dots of each color ink by a method. In this case, since the error diffusion or the average error minimum method is used, the black expression by the ink dots of other hues can be seen on average by diffusing the quantization error in each pixel to a certain area. Therefore, it is possible to form an image with almost no error and good reproducibility.
[0017]
Furthermore, when determining the dot formation of inks of other hues, the recording rates of the inks of other hues are obtained based on the black density, and the systematic dither method is used based on the recording rates of the inks of each color. Further, it may be determined whether or not to form dots of each color ink. In this case, since the systematic dither method is used, the multi-value processing can be speeded up in combination with the use of the dither pattern for determining the black ink dots.
[0018]
In such a printing apparatus, various types of heads for recording ink on a print medium can be used. For example, a mechanism that ejects ink particles by pressure applied to ink by applying voltage to an electrostrictive element provided in the ink passage may be used. It is also easy to employ a mechanism that ejects ink particles by the pressure applied to the ink in the ink passage by bubbles generated by energization of the heating element provided in the ink passage. In addition, it is possible to employ a head that forms dots by a thermal transfer or thermal sublimation type mechanism.
[0019]
Furthermore, as a head for recording an image, one capable of forming dots of cyan, magenta, and yellow inks can be used as inks of a plurality of hues that can express black by combination. Cyan, magenta, and yellow are one of the basic three primary color combinations in image recording using ink, and the original colors can be reproduced over a wide range.
[0020]
As such a head, it is possible to use at least cyan and magenta inks capable of two or more types of dots having different densities per unit area, and whether or not to form a plurality of ink dots having different hues. This determination may be made for the ink dots on the lower density side. If low density ink is used in the low density region, an image that does not give a more granular feeling can be formed.
[0021]
Other aspects of the invention
The present invention includes other aspects as follows. In the first aspect, one of the input means, the first dot formation determination means, and the second dot formation determination means of the printing apparatus or some related means is not inside the casing of the printing apparatus. This configuration is placed on the side of an apparatus that outputs an image to be printed. The first and second dot formation determining means can be realized by a discrete circuit, but can also be realized by software in an arithmetic logic circuit centering on the CPU. In the latter case, the side that outputs the image to be printed, for example, the computer side, performs processing related to dot generation, and the generated dots are ejected from the head into the casing of the printing apparatus. It is also possible to consider a form in which only the mechanism that is controlled and formed on the paper is stored. Of course, it is possible to divide these means into two groups at appropriate locations, one of which is realized in the casing of the printing apparatus and the other is realized on the image output side.
[0022]
The second form is a form as a supply apparatus that supplies a program for realizing the image processing of the present invention on a computer via a communication line.
[0023]
The third form is an aspect as a printed matter recorded by the image recording method. That is, a black ink dot and a plurality of hue inks are used using a printing apparatus having a head capable of forming a plurality of hue ink dots capable of expressing black in combination with black ink dots on a print medium. Printed matter recorded by a method of controlling the formation of dots and recording a multi-tone image,
Input the gradation data of the image to be printed for each pixel,
When the density of the image on the print medium assumed based on the input gradation data is equal to or higher than a predetermined density, the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. Determining whether to form the black ink dot at a position corresponding to the pixel;
Determining whether or not to form a dot of ink of a different hue from the black at a position corresponding to the pixel;
Based on both the determination results, the form of a printed matter obtained as a result of driving the head to form the black ink dots and the other color ink dots can be considered.
[0024]
In the printed matter formed in this manner, dots are formed with black ink in a region where the black density is high, and black color is expressed by a combination of a plurality of inks having different hues in a region where the black density is low. Accordingly, in the case of an ink jet printer, excessive ink is not ejected from the viewpoint of water absorption of the paper, and when the printed matter is paper, the paper does not swell. Even when the ink duty is severe, a printed matter expressing dark black can be obtained. If the distribution of the dots of the printed matter on which dots are formed by such an image recording method is analyzed, the distribution of the black dots is different between the area where the black density is high and the area where the black density is low, and the image is recorded by the above image recording method. I can recognize that.
[0025]
Similarly, a printed matter printed by the above-described printing apparatus of the present invention can be considered as an embodiment of the invention.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a printing apparatus as an embodiment of the present invention. As shown in the figure, a scanner 90 and a color printer 20 are connected to a computer 90, and a predetermined program is loaded and executed on the computer 90, thereby functioning as a printing apparatus as a whole. As shown in the figure, the computer 90 includes the following units connected to each other by a bus 80 with a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. The ROM 82 stores programs and data necessary for executing various arithmetic processes by the CPU 81 in advance, and the RAM 83 temporarily reads and writes various programs and data necessary for the CPU 81 to execute various arithmetic processes. Memory. The input interface 84 controls input of signals from the scanner 12 and the keyboard 14, and the output interface 85 controls output of data to the printer 20. The CRTC 86 controls signal output to the CRT 21 capable of color display, and the disk controller (DDC) 87 controls data exchange with the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). The hard disk 16 stores various programs loaded in the RAM 83 and executed, various programs provided in the form of device drivers, and the like. In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. The SIO 88 is connected to the modem 18 and is connected to the public telephone line PNT via the modem 48. The computer 90 is connected to an external network via the SIO 88 and the modem 18, and a program necessary for image processing can be downloaded to the hard disk 76 by connecting to a specific server SV. It is also possible to load a necessary program from the flexible disk FD or CD-ROM and cause the computer 90 to execute it.
[0027]
FIG. 2 is a schematic configuration diagram of the printer 20. As shown in the figure, the printer 20 includes a mechanism for transporting paper P by a paper feed motor 22, a mechanism for reciprocating a carriage 30 in the axial direction of a platen 26 by a carriage motor 24, and a print head mounted on the carriage 30. And a control circuit 40 that controls the exchange of signals with these paper feed motor 22, carriage motor 24, print head 28, and operation panel 32. Yes.
[0028]
The mechanism for transporting the paper P includes a gear train that transmits the rotation of the paper feed motor 22 not only to the platen 26 but also to a paper transport roller (not shown). In addition, the mechanism for reciprocating the carriage 30 includes an endless drive belt 36 that is stretched between the carriage motor 24 and a slide shaft 34 that is laid in parallel with the platen 26 shaft and slidably holds the carriage 30. And a position detection sensor 39 for detecting the origin position of the carriage 30.
[0029]
FIG. 3 shows the configuration of the printer 20 with the control circuit 40 as the center. As shown in the figure, this control circuit 40 is configured as an arithmetic and logic circuit centered on a known CPU 41, a P-ROM 43 storing a program, a RAM 44, a character generator (CG) 45 storing a dot matrix of characters, and the like. In addition, an I / F dedicated circuit 50 dedicated to interface with an external motor or the like, a head drive circuit 52 connected to the I / F dedicated circuit 50 to drive the head 28, and also the paper feed motor 22 And a motor drive circuit 54 for driving the carriage motor 24. The I / F dedicated circuit 50 has a built-in parallel interface circuit, and is connected to the computer via the connector 56 and can receive a printing signal output from the computer. The output of the image signal from the computer will be described later.
[0030]
Next, a specific configuration of the carriage 30 and the principle of ink ejection by the print head 28 mounted on the carriage 30 will be described. FIG. 4 is a perspective view showing the shape of the carriage 30. FIG. 5 is a plan view showing nozzle portions that discharge ink of each color in the print head 28 arranged in the lower portion of the carriage 30. As shown in FIG. 4, the carriage 30 is substantially L-shaped, and can mount a black ink cartridge (not shown) and a color ink cartridge 70 (see FIG. 6), and both cartridges can be mounted. A partition plate 31 is provided. A total of six ink discharge heads 61 to 66 are formed on the print head 28 below the carriage 30, and the introduction pipes 71 to 71 lead ink from the ink tanks to the heads for the respective colors at the bottom of the carriage 30. 76 is erected. When the black ink cartridge and the color ink cartridge 70 are mounted on the carriage 30 from above, the introduction pipes 71 to 76 are inserted into the connection holes provided in the cartridges.
[0031]
A mechanism for ejecting ink will be briefly described. As shown in FIG. 7, when the ink cartridge 70 is mounted on the carriage 30, the ink in the ink cartridge is sucked out via the introduction pipes 71 to 76 using the capillary phenomenon, and is provided at the lower part of the carriage 30. The print head 28 is guided to the respective color heads 61 to 66. When the ink cartridge is mounted for the first time, an operation of sucking ink to each of the color heads 61 to 66 is performed by a dedicated pump. In this embodiment, a pump for suction, a cap that covers the print head 28 at the time of suction, etc. The illustration and description of this configuration are omitted.
[0032]
As shown in FIGS. 5 and 7, each of the color heads 61 to 66 is provided with 32 nozzles n for each color, and is one of the electrostrictive elements for each nozzle and has excellent responsiveness. A piezo element PE is arranged. FIG. 8 shows the structure of the piezo element PE and the nozzle n in detail. As shown in the drawing, the piezo element PE is installed at a position in contact with the ink passage 68 that guides ink to the nozzle n. As is well known, the piezo element PE is an element that transforms electro-mechanical energy at a very high speed because the crystal structure is distorted by application of a voltage. In this embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE expands for the voltage application time as shown in the lower part of FIG. One side wall of 68 is deformed. As a result, the volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is ejected from the tip of the nozzle n at high speed. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.
[0033]
The arrangement of the color heads 61 to 66 in the print head 28 is divided into three groups, with two heads as one set, as shown in FIG. 5, in view of the arrangement of the piezo elements PE described above. . A black ink head 61 is disposed at an end on the side close to the black ink cartridge, and a cyan ink head 62 is adjacent to the black ink head 61. Adjacent to this set are a head 63 for ink (hereinafter referred to as light cyan ink) having a lower density than the cyan ink supplied to the cyan ink head 62 and a magenta ink head 64. In the next set, a head 65 for ink having a lower density than normal magenta ink (hereinafter referred to as light magenta ink) and a yellow head 66 are arranged. The composition and concentration of each ink will be described later.
[0034]
The printer 20 of the present embodiment having the hardware configuration described above rotates the platen 26 and other rollers by the paper feed motor 22 and conveys the paper P, while the carriage 30 is reciprocated by the carriage motor 24 and simultaneously prints. The piezo elements PE of the respective color heads 61 to 66 of the head 28 are driven to discharge the respective color inks, thereby forming a multicolor image on the paper P. As shown in FIG. 9, the printer 20 forms a multicolor image based on a signal received from an image forming apparatus such as a computer 90 via the connector 56. In this example, the application program operating inside the computer 90 displays an image on the CRT display 93 via the video driver 91 while processing the image. When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives image information from the application program and converts it into a signal that the printer 20 can print. In the example shown in FIG. 9, the printer driver 96 includes a rasterizer 97 that converts image information handled by the application program 95 into color information in dot units, and image information (floor level) converted into color information in dot units. Color correction module 98 that performs color correction in accordance with the color development characteristics of the image output apparatus (here, printer 20) with reference to color correction table CT with respect to tone data), and dot units from the image information after color correction There is provided a halftone module 99 for generating so-called halftone image information representing the density in a certain area depending on the presence or absence of ink. Since the operation of each of these modules is well known, the description thereof will be omitted in principle, and the contents of the color correction module 98 and the halftone module 99 related to the present invention will be described later.
[0035]
As described above, the printer 20 of this embodiment includes the heads 63 and 65 for light cyan ink and light magenta ink in addition to the so-called CMYK four color inks. These inks are obtained by reducing the dye concentrations of ordinary cyan ink and magenta ink as shown in FIG. As shown, the normal density cyan ink (indicated by C1 in FIG. 10) is 3.6% by weight of direct dye 99, 30% by weight of diethylene glycol, 1% by weight of Surfinol 465, 65.4% of water. In contrast to the weight percent, light cyan ink (indicated by C2 in FIG. 10) and direct blue 99 as a dye are set to 0.9 weight percent, which is 1/4 of cyan ink C1, to adjust the viscosity. Therefore, diethylene glycol is changed to 35 weight percent and water is changed to 63.1 weight percent. Further, the normal concentration of magenta ink (indicated by M1 in FIG. 10) is 2.8% by weight of acid red 289, 20% by weight of diethylene glycol, 1% by weight of Surfinol 465, and 79% by weight of water. On the other hand, light magenta ink (indicated by M2 in FIG. 10), acid red, which is a dye, is 0.7% by weight that is 1/4 of magenta ink M1, 25% by weight of diethylene glycol, and 74% by weight of water. Changed to percent.
[0036]
As shown in FIG. 10, the yellow ink Y and the black ink K use direct yellow 86 and hood black 2 as dyes and are 1.8 weight percent and 4.8 weight percent, respectively. . In any ink, the viscosity is adjusted to about 3 [mPa · s]. In this embodiment, since the surface tension is adjusted to be the same in addition to the viscosity of each color ink, the control of the piezo element PE for each color head can be made the same regardless of the ink forming the dots.
[0037]
FIG. 11 shows the measured brightness of each color ink. The horizontal axis of FIG. 11 is the recording rate with respect to the recording resolution of the printer, and indicates the ratio of dots recorded on the white paper P by the ink particles Ip ejected from the nozzles n. That is, the recording rate 100 indicates a state where the entire surface of the paper P is covered with the ink particles Ip. In this embodiment, the density of the dye of the light cyan ink C2 is about 1/4 by weight percent with respect to the cyan ink C1, and the lightness of both inks at this time is when the recording rate of the light cyan ink C2 is 100%. Is equal to the lightness when the recording rate of the cyan ink C1 is about 35%. This relationship is the same for the magenta ink M1 and the light magenta ink M2. The ratio of the recording rate at which inks with different densities have the same brightness is determined from the point of view of the beauty of color mixing when both inks are mixed, but in practice it is in the range of 20 to 50 percent. It is desirable to adjust. When this relationship is expressed as a percentage by weight of the dye in both inks, the low density ink (light cyan ink C2 and light magenta) with respect to the weight percentage of dye in the high density ink (cyan ink C1 and magenta ink M1). The relationship of the weight percentage of the dye in the ink M2) is almost equivalent to the latter being adjusted to about 1/5 to 1/3 of the former.
[0038]
Next, the state of printing using multicolor ink in the printer 20 of this embodiment will be described along the processing in the color correction module 98 and the halftone module 99 of the printer driver 96. FIG. 12 is a flowchart showing an outline of color correction processing and halftone processing performed by the printer driver 96 of this embodiment. As shown in the figure, when the printing process is started, each pixel is scanned in turn with the upper left corner of one image as the origin, and the color of one pixel is firstly scanned from the rasterizer 97 in the order along the scanning direction of the carriage 30. Image data (RGB each 8 bits) is input (step S100). Next, based on the RGB color image data, the color correction table CT is referred to, and gradation data DS for the three colors of CMY is obtained (step S105). This process corresponds to the process of the color correction module 98. In FIG. 12, the process of referring to the color correction table CT is shown as a function f (). The color correction table CT may obtain data of four colors of CMYK directly from RGB. However, in this embodiment, the black expression is divided into real black and composite black. In this case, gradation data of three colors from RGB to CMY is obtained.
[0039]
The printer 20 actually records images in a total of six colors using light cyan ink C2 and light magenta ink M2, which are low-density inks. Although it is possible to obtain gradation data of six colors C1, C2, M1, M2, Y, and K directly from the image data, for convenience of explanation, here, from the color image data of RGB, the color correction module 98 A description will be given assuming that the CMY three-color gradation data is once obtained.
[0040]
Next, based on the inputted gradation data DS of each color of CMY, the recording ratios Rk, Rcom of real black (that is, black by black ink K) dots and composite black (that is, black by three colors of CMY) dots. Is determined with reference to FIG. 13 (step S110). If the recording rate of each CMY hue is not zero for one pixel, it can be considered that a black component exists. For example, if (C, M, Y) = (100, 110, 120), it can be replaced with (C, M, Y, K) = (0, 10, 20, 100). However, if the CMY component is simply replaced with black K, the black dots are very conspicuous, and the quality of the image may deteriorate when printing a natural image or the like. Therefore, for a certain density or less, even if it is a black component, the image quality is improved by using composite black instead of real black. In this embodiment, based on the gradation data DS obtained by referring to the color correction table CT, the recording rate Rk of the real black dots using the black ink K and the composite black using the CMY inks are used. It is set in advance how the dot recording rate Rcom is distributed. This is the graph shown in FIG.
[0041]
That is, first, the maximum gradation data DS of the black component is obtained from the CMY data obtained by referring to the color correction table CT (step S110). The maximum value Kmx that can replace each color of CMY with black K is obtained. Then, referring to the graph of FIG. 13, the real black dot recording rate Rk and the composite black dot recording rate Rcom are obtained, and further, the recording rates Rc, Rm, and Ry of the CMY colors are obtained (step). S115). For example, in the case of (C, M, Y) = (100, 110, 120), the maximum value Kmx to be replaced with black is a value 100, and based on this, referring to FIG. The value 34 is obtained as Rk, and the value 66 is obtained as the composite black recording rate Rcom. As a result, the ratios of the recording rates (Rc, Rm, Ry, Rk) of CMYK 4 colors are (66, 76, 86, 34). In the example shown in FIG. 13, since the gamma correction and the like have been completed when the color correction data is obtained with reference to the color correction table CT, the ratio of each color is simply set to the black recording rate Rk. However, each correction such as gamma correction may be performed at the time of referring to FIG.
[0042]
In FIG. 11, the recording rate is shown as a percentage, but in FIG. 13, 100 percent is shown as an absolute value of 255 so that the value used in the halftone processing routine can be directly referred to. The composite black recording rate Rcom is actually represented by a collection of dots of cyan, magenta, and yellow color inks, and some of them are light cyan ink C2 and light magenta ink with low density. It is further converted into each recording rate Rcc2, Rcm2, Rcy of M2 and yellow ink Y. These methods will be described later.
[0043]
After obtaining the real black dot recording rate Rk, and further determining the composite black dot recording rate Rcom and the CMY recording rates Rc, Rm, and Ry based on the composite black dot recording rate Rk, halftone processing by the dither method is performed on the real black dots. A process for referring to the threshold matrix TM is performed (step S120). That is, the threshold value Dref for determining on / off of the real black dot is read. This threshold value Dref is a determination value as to whether or not to form a dot of real black ink K on the pixel of interest, and can be simply fixed to about 127. In this embodiment, a threshold matrix of a distributed dither is adopted for setting the threshold, and a systematic dither method is applied particularly using a global matrix (blue noise matrix) of about 64 × 64. Therefore, the threshold value Dref for determining on / off of the dots of the real black ink K is different for each pixel of interest. FIG. 14 shows the concept of threshold values in the systematic dither method. In FIG. 14, the size of the matrix is 4 × 4 for convenience of illustration, but in the embodiment, a matrix of 64 × 64 is used.
[0044]
FIG. 15 shows a part of a 64 × 64 global matrix (blue noise matrix) used in this embodiment. In this matrix, the threshold value is determined so that there is no bias in the appearance of the threshold value (1 to 255) in any 16 × 16 region in the matrix. The method for determining the threshold is as follows.
{Circle around (1)} First, numerical values from 1 to 4096 are arranged separately in a grid of 64 × 64 = 4096.
(2) Next, the numerical value of each cell is divided by 4096/255 = 16.06.
(3) Finally, add 1 to the result of division and round off the decimals.
As a result, numerical values from 1 to 255 are arranged in each cell. In addition, the appearance frequency of each numerical value from 1 to 255 is 16 times or 17 times. When such a global matrix is used, the occurrence of pseudo contours is suppressed. The distributed dither is a type in which the dot spatial frequency determined by the threshold matrix is high, and the dots are generated in a disjoint manner in the region. Specifically, a Beyer-type threshold matrix is known. When the distributed dither is employed, dots are generated by the real black ink K in a discrete manner, so that the distribution of dots by the real black ink K is not biased and the image quality is improved.
[0045]
After reading the threshold value Dref of the pixel with reference to the threshold value matrix TM in this way, a process of comparing the recording rate Rk of the real black ink dot of the pixel with the threshold value Dref is performed (step S130). As a result of the comparison, if it is determined that the real black dot recording rate Rk is equal to or greater than the threshold value Dref, a process of forming dots with the real black ink K at a position corresponding to this pixel is performed (step S140). Thereafter, the process proceeds to halftone processing (step S200) for cyan, magenta, and yellow inks. By this halftone process, a process of actually expressing composite black is also performed. Note that the order of forming the real black dots and the CMY dots may be reversed.
[0046]
As a result of the above processing, the dots of the real black ink K are sequentially formed according to a dither pattern prepared in advance. This situation is shown in FIG. In FIG. 16, a 4 × 4 dither pattern is illustrated, but in fact, the global pattern shown in FIG. 15 is used as already described. If the dither pattern illustrated in FIG. 16A is used, as shown in FIG. 16B and FIG. 16C, if the regions have the same density, the pixels in the locations corresponding to the locations with the smaller threshold values are sequentially installed. Thus, dots of real black ink K are formed.
[0047]
Next, cyan, magenta, and yellow halftone processing will be described. In this process, printing is performed in consideration of the presence of dark and light inks based on the cyan, magenta, and yellow recording rates Rc, Rm, and Ry obtained in step S115. Specifically, as shown in FIG. 11, for cyan C and magenta M, dots of light cyan ink C2 and light magenta ink M2 (hereinafter referred to as light ink) with low density can be formed. Depending on the density, these light ink dots are used to form dots. In practice, the on / off of the dots of the normal inks C1 and M1 (hereinafter referred to as dark ink) having a high density is first determined, and the quantization error caused by the on / off of the dark ink dots is included. In order to eliminate the quantization error, ON / OFF of the light ink dots is determined. That is, on / off of dark ink dots is determined by dithering, and on / off of light ink dots is determined by error diffusion. Hereinafter, processing for determining ON / OFF of each dot by associating two dots having different densities will be described.
[0048]
An example of processing of cyan ink C1 and light cyan ink C2 having different densities is shown in the flowchart of FIG. As shown in the figure, when this process is started, a process of inputting a recording rate for the ink to be processed (here, a recording rate Rc for cyan ink C) is performed (step S210). The recording rate of each color was obtained in step S115 of the color correction and halftone processing routine (FIG. 12).
[0049]
In the following description, it is assumed that printing is performed only with cyan ink. However, in practice, multicolor printing is performed, and for magenta, magenta ink M1 having a high density and light magenta ink having a low density are used. With M2, dark and light dots are formed. For yellow, dots are formed by the yellow ink Y. Also, when dots of different color inks are formed in a predetermined area, control necessary to improve color reproducibility by color mixing, for example, do not print different color dots at the same location The intended control is performed. Actually, in this embodiment, the formation of the real black dots and the formation of the yellow ink Y dots are handled by using the same dither pattern so that the two dots do not overlap. A description of the processing is omitted.
[0050]
Next, based on the input recording rate Rc, processing for determining ON / OFF of the dots of the cyan ink C1 is performed (step S220). The process for determining ON / OFF of the dots of the cyan ink C1 is the same as the process for determining ON / OFF of the real black dots described above. That is, first, based on the recording rate Rc of the entire cyan, the processing shown in FIG. 18 is referred to determine the recording rate Rcc1 to be realized with dark ink. FIG. 18 shows a table for setting the recording ratios of light ink and dark ink with respect to the overall recording ratio of each color. This table shows the ratio of dark ink and light ink in the finally obtained printed matter, and gives the dark ink recording rate and the light ink recording rate uniquely, so that the dark ink or It does not determine whether dots are turned on or off with light ink. To briefly explain this relationship, in this technique, as shown in FIG. 17, first, on / off of dark ink dots is determined using this table (step S220), and the result is referred to as light. Whether the dot is on or off is determined (step S240). Accordingly, the reason why the recording rate of the light ink dots matches the table shown in FIG. 18 is as follows.
[0051]
The density of the image per unit area can be expressed by the number of dark ink dots and light ink dots formed there. According to FIG. 18, the number of dark dots formed per unit area is considered as a ratio with respect to a value having a maximum density of 255, and this is Ks. Similarly, the number of light ink dots is Us. At this time, if an attempt is made to make the density of the formed image equal to the recording rate Rc of the input image,
Rc = Ks × (Dark dot evaluation value) / 255
+ Us × (light dot evaluation value) / 255
It becomes. Since the evaluation value (darkness of the formed dots) of the dark ink dot can be regarded as 255, the evaluation value of the dark ink dot table and the evaluation value of the light ink dot are shown in FIG. The table of light ink dots is determined. In the example shown in FIG. 18, for example, the data of the point where the recording rate of the light ink dot is maximum (gradation data is 95, dark ink dot data is 18 and light ink dot data is 122) is expressed by the above equation. When entered, the light dot evaluation value is Z
95 = 18 × 255/255 + 122 × Z / 255
Thus, the dot evaluation value of light ink is 160. The dark dot evaluation value and the light dot evaluation value are the same as those treated as the result value RV in the flowchart of the dark / light dot on / off determination method described later.
[0052]
Based on the input recording rate Rc of each color, the dark dot recording rate Rcc1 corresponding to a predetermined dark ink recording rate is obtained by referring to the table of FIG. It is determined whether or not the dark dot recording rate Rcc1 thus obtained is larger than the threshold value Dref1. This threshold value Dref1 is obtained from the same distributed dither matrix used when the on / off state of the real black dots is determined (see FIGS. 14 and 15).
[0053]
If the dark dot recording rate Rcc1 is larger than the threshold value Dref1, it is determined that the dark ink dot of the pixel is to be turned on, and a process for calculating the result value RV is performed. The result value RV is a value (dark dot evaluation value) corresponding to the density of the pixel. When it is determined that the dark dot is on, that is, a dot with high density ink is formed on the pixel, the density of the pixel is determined. A corresponding value (for example, value 255) is set.
[0054]
On the other hand, if the recording rate Rcc1 of the dark ink dots is less than or equal to the threshold value Dref1, it is determined that the dark dots are off, that is, not formed. At this time, the value 0 is substituted into the result value RV. Since the white background of the paper remains in a portion where dots with high density ink are not formed, the result value RV is set to 0.
[0055]
After the dark ink dots are turned on / off and the result value RV is calculated (step S220 in FIG. 17), the recording rate Rc of the next pixel of interest is determined based on the processed pixels nearby. The correction data DC to which the diffusion error ΔDu is added is processed (step S225). This is because error diffusion processing is performed using light ink dots. When printing by error diffusion, the shading error generated for a processed pixel is distributed in advance with a predetermined weight assigned to pixels around that pixel. This is reflected in the pixels to be printed. FIG. 19 exemplifies how much weight is distributed to which pixels in the periphery with respect to the pixel PP of interest. With respect to the pixel PP of interest, the density error is a predetermined weight (1/4, 1/8) for several pixels in the scanning direction of the carriage 30 and several adjacent pixels on the rear side in the transport direction of the paper P. , 1/16).
[0056]
After obtaining the correction data DC, it is determined whether or not the dark dot is turned on (the dot is formed by the cyan ink C1) (step S230). If the dark dot is not formed, the low density ink is determined. , That is, a process for determining on / off of the dot (hereinafter referred to as a light dot) by the light cyan ink C2 (step S240). Processing for determining whether to turn on / off light dots will be described based on the light dot formation determination processing routine shown in FIG. In the process of determining on / off of the light dot, in this example, the dot formation by the light cyan ink C2 is performed by applying the error diffusion method, and the gradation data DC corrected by the concept of error diffusion is the threshold Dref2 for the light dot. It is determined whether or not it is larger (step S244). This threshold value Dref2 is a determination value as to whether or not to form dots of light ink with low density on the pixel of interest, and is simply a fixed value here.
[0057]
If the correction data DC is larger than the threshold value Dref2, it is determined that the light dot is turned on, and a result value RV (light dot evaluation value) is calculated (step S246). Here, the result value RV is a value that is corrected by the correction data DC using the value 122 as a reference value, but may be a fixed value. On the other hand, when it is determined that the correction data DC is equal to or less than the threshold value Dref2, it is determined that the light dot is to be turned off, and a process of adding the value 0 to the result value RV is performed (step S248).
[0058]
After light dots are turned on / off and the result value RV is calculated in this way (step S240 in FIG. 17), error calculation is performed (step S250). The error calculation is obtained by subtracting the result value RV from the correction data DC. When neither dark nor light dots are formed, the result value RV is set to 0, so that the correction value DC is included in the error ERR. That is, since the density to be realized in the pixel is not obtained at all, the density is calculated as an error. On the other hand, when dark dots or light dots are formed, since the result value RV corresponding to each dot is substituted, the difference from the data DC from which the determination is made becomes an error ERR.
[0059]
Next, error diffusion processing is performed (step S260). With respect to the error obtained in step S250, a predetermined weight (see FIG. 19) is assigned to the peripheral pixels of the pixel of interest, and this error is diffused. After the above processing, the process moves to the next pixel, and the processing from step S210 described above is repeated.
[0060]
According to the present embodiment described above, when the black density is high, dots are formed by the real black ink K, and when the black density is low, black is expressed by the composite black by the combination of CMY. . Since the formation of real black dots is performed using a dither pattern, the processing can be performed in a short time. Determining dot formation using a dither pattern is an area where the density of black is high, that is, an area where the dot density per unit area is high, so even if the dither pattern is used, image quality degradation is not noticeable. . On the other hand, since the black color is expressed by the combination of CMY inks in the low density region, the graininess can be suppressed. As a result, as a whole, a high-quality image can be formed in a short time.
[0061]
In addition, since dots are formed with real black ink in a region where black density is high, in the case of the ink jet printer 20 as in the embodiment, excessive ink is ejected from the viewpoint of water absorption of the paper. There is also the advantage that there is no. Therefore, even if the paper has a strict ink duty, the paper does not scatter and can express dark black. Further, since dots are formed with real black ink in the region where the black density is high, the black in the high density region is tightened and the image quality is not sweetened as compared with the case where black is expressed with composite black.
[0062]
In this embodiment, dots are formed with real black ink in the high density area, and dots are formed with composite black ink in the low density area. However, as shown in FIG. There is a region where the recording rate Rk and the composite black recording rate Rcom coexist. That is, real black and composite black are not clearly separated at the predetermined density, but when black density increases beyond the initial position, the formation of dots by real black gradually increases, and composite black The rate of dot formation is decreasing. For this reason, even when the real black dots are formed by the black ink K, the graininess hardly occurs. Further, even if real black dots are formed from the dither pattern, they are buried in the composite black dots, and the image quality is not deteriorated.
[0063]
Furthermore, in the region where the density of black is low, black is expressed only by composite black, and dots are formed by error diffusion, so the image quality in the low density region is extremely high. In this embodiment, since dots are formed by error diffusion for cyan and magenta including composite black, the quantization error can be suppressed to a predetermined value or less when viewed in a certain area. Further improvements are being made. In addition, the printer 20 of the embodiment prepares dark and light inks for cyan and magenta, determines the on / off state of each dot by dithering for dark ink dots and error diffusion for light ink dots. Therefore, the quality of the printed image is extremely high. As for black expression, black is expressed by a combination of light inks in the low density region. In addition to eliminating graininess in low-density areas using light ink, the color mixing at the joint from recording with light ink dots to recording with dark ink dots is extremely smooth, and the print quality is extremely high. Can also be obtained.
[0064]
Next, another embodiment of the present invention will be described. In the above embodiment, as shown in FIG. 13, the recording rates Rk and Rcom for real black and composite black are allocated in advance based on the gradation data DS, and the composite black recording rate Rcom is further set for each color. Processing to distribute to light ink was performed. On the other hand, in the example shown in FIG. 21, gradation data (RGB) for each pixel is input (step S300), and a color conversion table CT prepared in advance is referred to based on the gradation data (step S300). S305), the respective densities of the six color components of black ink K, cyan ink C1, light cyan ink C2, magenta ink M1, light magenta ink M2, and yellow ink Y corresponding directly to real black are obtained (step S310). Thereafter, binarization is performed for each color using the density (step S330), and the heads 61 to 66 are driven using the result to print six colors (step S400). The binarization process for each color is performed by the dither method for the black ink K, the cyan ink C1, the magenta ink M1, and the yellow ink Y, and the error diffusion method for the light cyan ink C2 and the light magenta ink M2. Yes.
[0065]
Here, in the color conversion table, when the density of the image formed on the paper P is high from the RGB format gradation data DS, the black ink K recording rate is set high, and the image density is low. In this case, the recording rate of the black ink K is set to be substantially zero. Therefore, by using this color conversion table CT, as in the first embodiment, the dots of the black ink K are formed in the high density region, and the on / off of the dots is the cyan ink C1, magenta. It is calculated at high speed by the dither method together with the ink M1. On the other hand, in the low density region, the black ink K dots are hardly formed. For this reason, although the dots are formed by the dither method for the black ink K, the image quality of the entire image does not deteriorate. In the color conversion table CT, it is sufficient that the black ink component is substantially 0 in the region where the output density is low, and the region where the output density is low may be determined experimentally.
[0066]
In this example, in the color conversion table CT, when the density of the image formed on the paper P is high, the dot recording rate of the black ink K is set high. Alternatively, a black density corresponding to so-called skeleton black may be used. Naturally, the density perceived by the human eye is not determined only by the black density when replaced with composite black, and can therefore be set according to the density of each color forming the image. For example, a color in which a slight black component is added to blue B has a high density, so that the dots of black ink K can be formed even if the size of the black component is not so high. Considering RGB, for example, the lightness L is
L = (3 · R + 6 · G + B) / 10
Can be asking. Accordingly, the brightness is calculated from the RGB gradation data, and if the brightness is equal to or greater than a predetermined value, the black ink K is not used and, in the first embodiment, the maximum value Rmax of the real black component to be replaced. In the case of the second embodiment, a color conversion table is created based on this equation. Note that the coefficient of the formula for obtaining the brightness is an approximate value, and may be appropriately determined depending on how to take RGB as a reference.
[0067]
Although one embodiment of the present invention has been described above, it is needless to say that the present invention can be implemented in various modes within the scope not changing the gist thereof. For example, it is easy to adopt a configuration applied to a normal CMYK four-color printer that does not have light ink. Further, as long as black can be expressed by combination, the present invention may be applied to a printer using ink other than CMY. The black ink is called real black in this embodiment, but it is not necessary to be completely black, and any ink that can express black or an approximate color alone can be used.
[0068]
Moreover, it is also possible to use three or more types of inks having different densities instead of using two types of inks having different densities. In this case, the density ratio of the dye density of the ink may be geometric series (1: n: 2 × n ··) or a power relationship (1: n). ² : N ^Four ・ ・） Here, n = 2, 3,... (A positive integer of 2 or more). In this embodiment, the systematic dither method is used for the determination of dot formation. However, the present invention is not limited to these methods, and various known dither methods can be applied to the determination of dark dots and light dots. Can do.
[0069]
In this embodiment, two types of ink having different densities are prepared only for cyan and magenta, but it is also possible to use a combination of inks having different densities for yellow and black. Instead of using dark and light inks, it is also possible to use large and small dots having different diameters.
[0070]
In the present embodiment described above, a program for controlling the formation of dark and light dots and dots having different diameters or a program for determining the formation of dots having different hues is prepared not on the printer 20 side but on the printer driver 96 side of the computer 90. However, it can also be prepared in the printer 20. For example, when image information to be printed is sent from the computer 90 in a language such as Postscript, the printer 20 has a halftone module 99 or the like. In this embodiment, a software program that realizes these functions is stored in a hard disk or the like in the computer 90, and is incorporated into the operating system in the form of a printer driver when the computer 90 starts up. Or a portable storage medium (portable storage medium) such as a CD-ROM, and transferred from the portable storage medium to the main memory of the computer system or an external storage device. It is also possible to transfer the information from the computer 90 to the inside of the printer 20 for use. It is also possible to provide a device that provides the software program via a communication line, and transfer the processing contents of the halftone module to the computer or printer 20 via the communication line. it can.
[0071]
Further, in the above-described embodiment, both the dark and light inks are ejected by using the piezo element PE and applying a voltage having a predetermined time width to the piezo element PE. However, other ink ejection methods are employed. It is also easy. Ink discharge methods that have been put into practical use are roughly divided into a method that separates and discharges ink particles from a continuous ink jet, and an on-demand method that is also used in the above-described embodiments. The The former includes a charge modulation method in which droplets are split from an ink jet by charge modulation, and a microdot method in which minute satellite particles generated when large diameter particles are split from an ink jet are used for printing. Yes. These methods are also applicable to the printing apparatus of the present invention using a plurality of types of ink concentrations.
[0072]
The on-demand method generates ink particles when ink particles are required in units of dots. In addition to the method using the piezo element employed in the above-described embodiments, the on-demand method is also illustrated in FIGS. As shown in (E), a method is known in which a heating element HT is provided in the vicinity of the ink nozzle NZ, the bubble BU is generated by heating the ink, and the ink particles IQ are ejected by the pressure. These on-demand ink ejection methods are also applicable to the printing apparatus of the present invention that uses a plurality of types of density ink or a plurality of dots having different diameters.
[0073]
In the above-described embodiment, a printer that can operate independently has been described as the printing apparatus. However, it is needless to say that the present invention can be applied to printing apparatuses incorporated in various devices. For example, the present invention can be applied to a digital copying machine or a facsimile. In the embodiments, an ink jet type printing apparatus is taken up. However, as long as an image is recorded by dots, it can be applied to a thermal transfer, thermal sublimation type printer, a color laser printer, or the like.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example in which a printing apparatus according to an embodiment is configured around a computer.
FIG. 2 is a schematic configuration diagram of a printer 20 in the embodiment.
3 is a block diagram illustrating a configuration of a control circuit 40 in the printer 20. FIG.
4 is a perspective view showing a configuration of a carriage 30. FIG.
FIG. 5 is an explanatory diagram showing the arrangement of the color heads 61 to 66 in the print head 28;
6 is a perspective view showing the shape of a color ink cartridge 70. FIG.
FIG. 7 is an explanatory diagram illustrating a configuration for ejecting ink in each of the color heads 61 to 66;
FIG. 8 is an explanatory diagram showing a state in which ink particles Ip are ejected by extension of a piezo element PE.
FIG. 9 is a block diagram illustrating an example of processing from image information handled by a computer 90 to printing.
FIG. 10 is an explanatory diagram showing components of each color ink.
FIG. 11 is a graph illustrating the relationship between the recording rate and brightness of each color ink.
12 is a flowchart illustrating processing in the color correction module 98 and the halftone module 99. FIG.
FIG. 13 is a graph for determining a real black recording rate Rk and a composite black recording rate Rcom in this example.
FIG. 14 is an explanatory diagram showing a dark dot determination method using a systematic dither method.
FIG. 15 is an explanatory diagram showing a part of a 64 × 64 global matrix;
FIG. 16 is an explanatory view exemplifying the formation of dots of real black ink K;
FIG. 17 is a flowchart showing a halftone processing routine for each color in the embodiment.
FIG. 18 is a graph for setting the recording rate of each color.
FIG. 19 is an explanatory diagram showing weighting in error diffusion.
FIG. 20 is a flowchart showing a light dot formation determination processing routine.
FIG. 21 is a flowchart showing a color correction and halftone processing routine in the second embodiment.
FIG. 22 is an explanatory diagram illustrating another configuration example of the ink particle ejection mechanism.
[Explanation of symbols]
20 ... Printer
22 ... Paper feed motor
24 ... Carriage motor
26 ... Platen
28 ... Print head
30 ... carriage
31 ... Partition plate
32 ... Control panel
34 ... Sliding shaft
36 ... Drive belt
38 ... pulley
39 ... Position detection sensor
40 ... Control circuit
41 ... CPU
43 ... ROM
44 ... RAM
50 ... I / F dedicated circuit
52. Head drive circuit
54 ... Motor drive circuit
56 ... Connector
61-66 ... Ink discharge head
68 ... Ink passage
70 ... cartridge for color ink
71 ... introduction pipe
90 ... Computer
91 ... Video driver
93 ... CRT display
95 ... Application program
96 ... Printer driver
97 ... Rasterizer
98 ... Color correction module
99 ... Halftone module
P ... paper
PE ... piezo element
n ... Nozzle

Claims (12)

A black ink dot capable of expressing black alone and a plurality of hue ink dots capable of expressing black by combination are provided on a print medium, and the black ink dot and the plurality of hues are provided. A printing apparatus that records a multi-tone image with dots of ink,
Input means for inputting gradation data of an image to be printed for each pixel;
Storage means for storing a relationship between the gradation data when expressing black based on the input gradation data and the density to be realized by the black ink and inks of a plurality of hues;
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. First dot formation determination means for determining whether or not to form the black ink dot at a position corresponding to the pixel;
For the plurality of hue inks, a second determination is made by error diffusion or a minimum average error method to determine whether or not to form dots of inks of other hues different from the black at positions corresponding to the pixels. Dot formation determination means;
Head driving means for driving the head based on the determination results of the first and second dot formation determining means to form the black ink dots and the other hue ink dots; and
The storage means stores the relationship as follows:
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And b) the density to be realized by the inks of the plurality of hues is a relationship in which the gradation data is defined as a range from 0 to a range larger than the predetermined value and lower than the maximum gradation value. Remembered as a printing device. The printing apparatus according to claim 1,
The input means is means for inputting the gradation data as data for a plurality of colors that can constitute the image to be printed,
The storage means
A conversion table for converting the input gradation data for a plurality of colors into a density to be realized by the black and the plurality of hue inks, wherein an image density to be realized by the printing apparatus is determined. in less than a predetermined value, the concentration should be realized by the black ink is storing a conversion table set in advance to be less than a predetermined value,
The first dot formation determining means is
A density determining unit that refers to the conversion table based on the input gradation data for a plurality of hues and obtains a density to be realized by the black and the plurality of hue inks;
A determination unit configured to determine whether or not to form the dots of the black ink using a density to be realized by the black ink.   The printing apparatus according to claim 1, wherein the threshold matrix used by the first dot formation determination unit is a distributed threshold matrix. The printing apparatus according to claim 1,
The head is an ink of a hue different from the black, at least cyan or printing apparatus dots is possible the formation of a magenta ink. The printing apparatus according to claim 1,
The second dot formation determining means is
Taking into account the under color removal by the concentration which is realized by the ink of the referenced black were determined with the stored relationship, a recording rate determination hand stage for determining the respective recording rates of a plurality of ink the different hues Printing device.   The printing apparatus according to claim 5, wherein the plurality of inks include cyan and magenta inks. The printing apparatus according to claim 1, wherein the head includes a mechanism that ejects ink particles by pressure applied to the ink by applying a voltage to an electrostrictive element provided in the ink passage. The printing apparatus according to claim 1, wherein the head includes a mechanism for ejecting ink particles by pressure applied to ink in the ink passage by air bubbles generated by energization of a heating element provided in the ink passage. The printing apparatus according to claim 1, wherein the head is capable of forming dots of cyan, magenta, and yellow ink as inks of a plurality of hues that can express black by combination. The printing apparatus according to claim 1 ,
The head can have two or more types of dots having different densities per unit area, at least for cyan and magenta inks,
The printing apparatus, wherein the second dot formation determination unit determines whether or not to form a plurality of ink dots having different hues with respect to the low density dot. By using a printing apparatus having a head capable of forming, on a print medium, dots of black ink that can express black alone and ink dots of a plurality of hues that can express black by combination, the dots of black ink And a method of recording a multi-tone image by controlling the formation of dots of the plurality of hue inks,
Input the gradation data of the image to be printed for each pixel,
The relationship between the gradation data when expressing black based on the input gradation data, and the density to be realized by the black ink and inks of a plurality of hues,
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And b) the density to be realized by the inks of the plurality of hues is a relationship in which the gradation data is defined as a range from 0 to a range larger than the predetermined value and lower than the maximum gradation value. Remember as
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. Determining whether or not to form the black ink dot at a position corresponding to the pixel;
For the plurality of hue inks, whether or not to form dots of inks of other hues different from the black at positions corresponding to the pixels is determined by error diffusion or an average error minimum method,
An image recording method for driving the head based on both the determination results to form the black ink dots and the other hue ink dots. It is determined whether or not a black ink dot capable of expressing black alone and a plurality of hue ink dots capable of expressing black by combination are formed on a print medium, and the black ink dot and the dot A recording medium on which a program for controlling the formation of dots of ink of a plurality of hues and recording a multi-tone image is recorded in a computer-readable manner,
The relationship between the gradation data when expressing black based on the input gradation data, and the density to be realized by the black ink and inks of a plurality of hues,
a) The density to be realized by the black ink is a range in which the gradation data is equal to or greater than a predetermined value near the gradation value at which the use amount of inks of a plurality of hues that can express black by the combination is maximized. And b) the density to be realized by the inks of the plurality of hues is a relationship in which the gradation data is defined as a range from 0 to a range larger than the predetermined value and lower than the maximum gradation value. Function to remember as,
For the black ink, the density to be realized by the black ink is determined with reference to the stored relationship, and the density to be realized by the black ink is compared with a threshold matrix corresponding to a dither pattern prepared in advance. A function for determining whether or not to form the black ink dot at a position corresponding to the pixel;
A function of determining whether or not to form dots of inks of other hues different from black at positions corresponding to the pixels with respect to the plurality of hue inks by an error diffusion or a minimum average error method,
A recording medium on which a program for realizing by a computer a function of forming the black ink dots and the ink dots of the other hues on the print medium based on the both determination results is recorded.

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