JP4240057B2 - Printing apparatus, printing method, and recording medium - Google Patents

Description

  The present invention relates to a printing apparatus, a printing method, and a recording medium that include a head capable of forming two or more types of dots having different ink densities and dot diameters, and that can print a multi-tone image using ink ejected from the head.

  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. With regard to such a printing apparatus, a printing apparatus and a printing method using dark and light inks have been proposed for the purpose of further improving printing quality in a low image density region, that is, a so-called highlight portion (for example, Japanese Patent Application No. 8- 209232). This is intended to realize printing with excellent gradation expression by preparing inks with high density and low density for the same color and controlling the ejection of both inks.

  In addition, as another means for expressing multi-gradation, there is also a printing apparatus capable of printing by changing the density per unit area in multiple stages by forming two types of dots having different ink densities and dot diameters. It has been proposed (for example, JP-A-59-201864). In this case, one pixel is composed of 4 dots, and by changing the appearance frequency of pixels with high and low density, it is possible to print an image with multiple levels of density.

  On the other hand, in a printer that records an image using dots, a dot that is called banding in the direction in which the head reciprocates, that is, the main scanning direction, is caused by a mechanical manufacturing error of the head that forms ink by ejecting ink. Uneven formation may occur. Although banding occurs at any gradation, the image quality is impaired, but the effect is particularly noticeable in halftones where the number of dots is relatively small. In printers that record images using dots, it is also important to prevent such banding from occurring in order to improve image quality. In the past, banding was eliminated by various methods in addition to high image quality by multi-gradation. As a technique for this purpose, for example, one raster is formed by multiple main scans of the head. A wrapping method has been proposed.

  However, in a printing apparatus capable of forming two types of dots having different ink densities and dot diameters, no consideration has been given to improving the image quality by eliminating banding. In the first place, in such a printing apparatus, both are formed in a predetermined pattern according to the gradation of the input pixel, and in dot units according to various conditions at the time of recording an image with dots. It has not been determined which of the two types of dots should be formed.

  Also, in conventional printing devices, dots with a large diameter of light ink have a lower density per unit area than dots with a small diameter of dark ink, thereby achieving high image quality with multiple gradations. It was. For this reason, although the density that can be expressed by the combination of both is in multiple stages, the degree of freedom in using two types of dots with different ink densities and dot diameters is limited for input image data. In general, since a dot having a smaller dot diameter is more likely to cause banding, banding may occur due to the limitation of the degree of freedom in use. In addition, an unfavorable state may occur in light of other conditions for recording dots, such as an allowable amount of ink per unit area of paper.

  The present invention has been made in view of the above problems, and in a printing apparatus, for various purposes including prevention of banding, for effectively utilizing two or more types of dots having different ink densities and dot diameters. The purpose is to provide technology.

A printing apparatus according to an aspect of the present invention includes:
A printing device for printing an image,
A head capable of forming a plurality of types of dots in which at least one of density and dot diameter is different from each other using dark ink and light ink;
By determining the density and the dot diameter of the dots to be formed for each pixel according to the gradation value of each pixel of the input image data, the types of dots to be formed are the plurality of types. Determining means for determining any one of the dots;
Head drive control means for driving the head to form the determined type of dots;
With
The plurality of types of dots are a first type of dot formed using the light ink and having a first dot diameter, and a second dot formed using the dark ink and smaller than the first dot diameter. A unit density that is a density per unit area of the first type dots and the unit density of the second type dots are substantially the same.
The determining means determines whether or not dots are formed by the dark ink, and then determines whether or not dots are formed by the light ink when the dots are not formed by the dark ink and consumes more dark ink. If so, the ratio between the first type dots and the second type dots is changed so that more first type dots are formed than half the second type dots .
A printing apparatus according to another aspect of the present invention includes:
A printing apparatus capable of printing an image by forming a plurality of dots on a print medium based on input image data,
For at least one color, a head capable of forming two or more types of the same density dots in which the unit density, which is the density per unit area, is substantially the same by combining different densities and different dot diameters;
Means for setting which unit density dot should be formed for each pixel, including the presence or absence of dot formation, according to the gradation of each pixel of the input image data;
For the pixels on which the same density dots are to be formed, dot form selection means for selecting which of the same density dots should be formed based on a predetermined condition;
The gist of the present invention is to provide a head drive control means for driving the head to form the set dots.

A printing method according to another aspect of the present invention includes:
For at least one color, an image input using a head capable of forming two or more types of the same density dots in which the unit density, which is the density per unit area, is substantially the same by combining different densities and different dot diameters. A printing method for printing an image by forming a plurality of dots on a print medium based on data,
According to the gradation of each pixel of the input image data, for each pixel, including the presence or absence of dot formation, set which unit density dot should be formed,
For pixels where the same density dots are to be formed, select which of the same density dots should be formed based on a predetermined condition,
The gist is to drive the head to form the set dots.

  According to such a printing apparatus and printing method, two or more types of dots having different ink densities and dot diameters can be formed, and the various dots that can be formed in this way have the same density per unit area. There are two or more types of density dots. According to the gradation of each pixel of the input image data, the printing apparatus and the printing method of the present invention should form a dot having a unit density for each pixel, including whether or not a dot is formed. In addition, for the pixels to be formed by the same density dots, it is selected which of the dots should be formed based on a predetermined condition. From the viewpoint of increasing the number of gradations, a head capable of forming many types of dots having different densities per unit area can be provided, but a head capable of forming at least two types of dots having substantially the same density per unit area. By providing, the degree of freedom of use of these dots increases. As a result, the image quality can be improved or the convenience of the user can be improved in accordance with the conditions for selecting dots with the same density per unit area.

In the printing apparatus, the predetermined condition in the dot form selection unit may be a condition related to an improvement in printed image quality.

  In this way, it is possible to improve the image quality by properly using the same density dots. The improvement in image quality here means various image quality improvements such as elimination of banding and multi-gradation.

  Here, the condition related to the image quality in the dot form selection means is that each of the dots of the same density so as to eliminate dot formation unevenness by the printing apparatus in the gradation corresponding to the dots of the same density. It is desirable to use a dot arrangement condition in which dots are mixed at a predetermined ratio.

  According to such a printing apparatus, it is possible to eliminate dot formation unevenness caused by a mechanical manufacturing error of the recording head and other causes, and it is possible to improve printed image quality. Note that the predetermined ratio in the printing apparatus does not necessarily require that the dots formed by the combination of the two or more are mixed at the same ratio, and the dot formation unevenness is felt according to human visual sensitivity. Any ratio may be used. In some cases, only one of the dots may be formed. The predetermined ratio may be set based only on conditions for eliminating dot formation unevenness, or may be set in consideration of other conditions.

  As such a dot arrangement condition, each dot of the same density dots is arranged according to a predetermined arrangement so as to eliminate dot formation unevenness by the printing apparatus in the gradation corresponding to the same density dots. It can also be set as a condition, or can be set as a condition for randomly selecting each dot of the same density dots.

  Various arrangements can be considered as the predetermined arrangement, but when there are only two types of dots having the same density per unit area, for example, a checkered arrangement may be considered.

On the other hand, in the printing apparatus,
The predetermined condition may be a condition related to an allowable amount of ink that the print medium can absorb per unit area.

  Generally, when printing an image by forming dots with ink, there is a limit to the allowable amount of ink that can be absorbed per unit area by the printing medium. If dots are formed exceeding this limit, the print medium is easily broken and the image quality is also deteriorated due to blurring or the like. According to the printing apparatus, it is possible to select dots to be formed in consideration of the ink allowance, and thus the best image quality can be obtained according to the printing medium.

In the printing apparatus,
The printing apparatus is a printing apparatus including an integrally formed ink cartridge that accumulates inks having different densities.
The predetermined condition may be a printing apparatus which is a condition related to consumption of ink having different densities.

  In a printing apparatus that accumulates ink having different densities for each color in an integrally formed ink cartridge, it is most desirable from the viewpoint of cost to use these plural inks evenly. According to the printing apparatus, since dots to be formed can be selected under the conditions related to the consumption of ink having different densities, for example, when a large amount of light ink having a low density is consumed, Instead of dots to be formed with light ink, by forming dots with a small dot diameter using ink with a high density, both can be used evenly, and the cost of using the printing apparatus can be reduced. it can.

  Since the printing apparatus of the present invention described above can also be configured by realizing some of the functions by a computer, the present invention can also take the form of a recording medium recording such a program. .

The computer-readable recording medium of the present invention is
A recording medium in which a program for printing an image by forming a plurality of dots on a printing medium based on input image data is recorded in a computer-readable manner,
Depending on the gradation of each pixel in the input image data, for each pixel, set which dot should be formed, including the presence or absence of dot formation, based on the unit density, which is the density per unit area Function to
A function for selecting which of the same density dots should be formed based on a predetermined condition when there are a plurality of the same density dots having substantially the same unit density; and
A recording medium recording a program for realizing a function of forming dots on the printing medium with the set dot diameter and density by a computer.

  The above-described printing apparatus of the present invention can be realized by executing the program recorded on the recording medium by the computer.

  Storage media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed materials printed with codes such as bar codes, and computer internal storage devices (memory such as RAM and ROM). ) And external storage devices can be used. Moreover, the aspect as a program supply apparatus which supplies the computer program which implement | achieves the function of each process or each means of said invention to a computer via a communication path is also included.

Hereinafter, embodiments of the present invention will be described based on examples.
(1) Apparatus Configuration FIG. 2 shows a schematic structure of the printer 22 of the present invention, and FIG. 1 shows a configuration of a color image processing system as an example system using the printer 22 of the present invention. In order to clarify the function of the printer 22, first, an outline of the color image processing system will be described with reference to FIG. This color image processing system includes a scanner 12, a personal computer 90, and a color printer 22. The personal computer 90 includes an input unit 92 including a color display 21, a keyboard, a mouse, and the like. The scanner 12 reads color image data from a color original, and supplies original color image data ORG composed of three color components of red (R), green (G), and blue (B) to the computer 90.

  The computer 90 includes a CPU, RAM, ROM, etc. (not shown), and an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and the final color image data FNL is output from the application program 95 via these drivers. An application program 95 that performs image retouching or the like reads an image from the scanner 12 and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image. When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives image information from the application program 95, and signals that can be printed by the printer 22 (here, cyan, magenta, yellow, and black colors). Is converted into a binary signal). In the example shown in FIG. 1, the printer driver 96 includes a rasterizer 97 that converts color image data handled by the application program 95 into image data in units of dots, and a printer 22 for the image data in units of dots. The color correction module 98 that performs color correction according to the ink color to be used and the characteristics of color development, the color correction table CT that the color correction module 98 refers to, and the presence or absence of ink in dot units from the image information after color correction And a halftone module 99 for generating so-called halftone image information expressing the density in a certain area. The printer 22 receives the printable signal and records image information on a recording sheet.

  Next, a schematic configuration of the printer 22 will be described with reference to FIG. As shown in the figure, the printer 22 includes a mechanism for transporting the paper P by the paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and a print head mounted on the carriage 31. And a control circuit 40 that controls the exchange of signals with the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32. Yes.

  The carriage 31 of the printer 22 is supplied with black ink (Bk) cartridge 71 and inks of six colors, cyan (C1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y). The stored color ink cartridge 72 can be mounted. For two colors, cyan and magenta, two types of light and dark inks are provided. The density of these inks will be described later. A total of six ink ejection heads 61 to 66 are formed on the print head 28 below the carriage 31. An inlet pipe 67 (which guides ink from the ink tank to the color heads) is provided at the bottom of the carriage 31. (See FIG. 3). When a black (Bk) ink cartridge 71 and a color ink cartridge 72 are mounted on the carriage 31 from above, an introduction tube 67 is inserted into a connection hole provided in each cartridge, and the ejection heads 61 to 66 are ejected from each ink cartridge. Ink can be supplied to the printer.

  A mechanism for ejecting ink will be briefly described. FIG. 3 is an explanatory diagram showing a schematic configuration inside the ink ejection head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out via the introduction pipe 67 using the capillary phenomenon as shown in FIG. The print head 28 is guided to each color head 61 to 66. When the ink cartridge is first installed, an operation of sucking ink to the respective color heads 61 to 66 is performed by a dedicated pump. In this embodiment, a pump for sucking and a cap for covering the print head 28 at the time of sucking are performed. The illustration and description of such a configuration is omitted.

  As will be described later, the heads 61 to 66 for each color are provided with 32 nozzles Nz for each color (see FIG. 6), and each of the nozzles is one of electrostrictive elements and is responsive. An excellent piezo element PE is arranged. FIG. 4 shows the structure of the piezo element PE and the nozzle Nz 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 Nz. As is well known, the piezo element PE is an element that transforms electro-mechanical energy at a very high speed because the crystal structure is distorted by application of a voltage. In the present embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE extends for the voltage application time as shown in the lower part of FIG. One side wall of 68 is deformed. As a result, the volume of the ink passage 68 contracts according to the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is ejected from the tip of the nozzle Nz at high speed. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.

  The printer 22 having the hardware configuration described above rotates the platen 26 and other rollers by the paper feed motor 23 to convey the paper P (hereinafter referred to as sub-scanning), and reciprocates the carriage 31 by the carriage motor 24. Simultaneously (hereinafter referred to as main scanning), the piezo elements PE of the color heads 61 to 66 of the print head 28 are driven to discharge the inks of the respective colors to form dots and form a multicolor image on the paper P. .

  The mechanism for transporting the paper P includes a gear train (not shown) that transmits the rotation of the paper feed motor 23 not only to the platen 26 but also to the paper transport rollers. Further, the mechanism for reciprocating the carriage 31 has an endless drive belt 36 stretched between the carriage motor 24 and a slide shaft 34 that is mounted in parallel with the axis of the platen 26 and slidably holds the carriage 31. And a position detection sensor 39 for detecting the origin position of the carriage 31.

  5 and 6 are explanatory views showing the arrangement of the inkjet nozzles Nz in the ink ejection heads 61 to 66. FIG. The printer 22 of this embodiment can form dots having two types of dot diameters for each color. In order to form dots with different dot diameters, for example, as shown in FIG. 5, a method of providing nozzles with different diameters for each color is also conceivable, but in this embodiment, all have the same diameter as shown in FIG. Using nozzles, dots having different dot diameters are formed by the control described later. The arrangement of these nozzles consists of six sets of nozzle arrays that eject ink for each color, and 32 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. Note that the 32 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, and may be arranged on a straight line. However, when arranged in a zigzag pattern as shown in FIG. 6, there is an advantage that the nozzle pitch k can be easily set small.

  Here, the principle of forming two types of dots having different dot diameters using a head having a fixed nozzle diameter will be described. FIG. 7 is an explanatory diagram showing the relationship between the drive waveform of the nozzle Nz and the ejected ink Ip when the ink is ejected. A drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. Once a negative voltage is applied to the piezo element PE in the interval d2, the piezo element PE is deformed in the direction in which the cross-sectional area of the ink passage 68 is increased, contrary to the case described with reference to FIG. 7, the ink interface Me called meniscus is indented inside the nozzle Nz. On the other hand, when a negative voltage is suddenly applied as shown in the section d2 using the driving waveform shown by the solid line in FIG. 7, the meniscus is indented greatly inward as compared with the state A as shown in the state a. Next, when the voltage applied to the piezo element PE is positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, a large ink droplet is ejected from the state where the meniscus is not dented so much (state A), as shown in state B and state C, and from the state where the meniscus is greatly recessed (state a), state b and Small ink droplets are ejected as shown in state c.

  As described above, the dot diameter can be changed according to the rate of change when the drive voltage is made negative (sections d1 and d2). Further, it can be easily imagined that the dot diameter can be changed depending on the peak voltage of the drive waveform. In the present embodiment, based on such a relationship between the drive waveform and the dot diameter, a drive waveform for forming a dot with a small dot diameter and a drive waveform for forming a dot with a large dot diameter are two. There are different types. By properly using the both, it is possible to form two types of dots having large and small dot diameters from the nozzle Nz having a constant nozzle diameter. FIG. 8 shows drive waveforms used in this embodiment. The drive waveform W1 is a waveform for forming a dot having a small dot diameter, and the drive waveform W2 is a waveform for forming a dot having a large dot diameter.

  The internal configuration of the control circuit 40 of the printer 22 will be described, and a method for driving the head 28 including the plurality of nozzles Nz shown in FIG. 6 using the above-described drive waveform will be described. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, the control circuit 40 includes a CPU 41, a PROM 42, a RAM 43, a PC interface 44 for exchanging data with the computer 90, a paper feed motor 23, a carriage motor 24, an operation panel 32, and the like. A peripheral input / output unit (PIO) 45 for exchanging signals with the timer, a timer 46 for measuring time, a transfer buffer 47 for outputting dot on / off signals to the heads 61 to 66, and the like. These elements and circuits are connected to each other via a bus 48. The control circuit 40 includes a transmitter (OSC1) 51 that outputs a drive waveform (w1 in FIG. 8) for forming a small dot at a predetermined frequency, and a drive waveform (FIG. 8) for forming a large dot. transmitter (OSC2) 52 that outputs w2), selector 54 that selectively outputs the outputs of both transmitters 51 and 52, and a distributor that distributes the output from selector 54 to heads 61-66 at a predetermined timing. 55 is also provided. The control circuit 40 receives the dot data processed by the computer 90, temporarily stores it in the RAM 43, and outputs it to the transfer buffer 47 at a predetermined timing. Therefore, image processing for forming a multi-tone image is not performed on the printer 22 side. The control circuit 40 simply controls on / off in units of dots, that is, whether or not to form dots.

  A mode in which the control circuit 40 outputs signals to the heads 61 to 66 will be described. FIG. 10 is an explanatory diagram showing connection of one nozzle row of the heads 61 to 66 as an example. As shown in the figure, one nozzle row of the heads 61 to 66 is interposed in a circuit having the transfer buffer 47 as the source side and the distribution output device 55 as the sink side. Each of the piezo elements PE constituting the nozzle array has one electrode connected to each output terminal of the transfer buffer 47 and the other connected to the output terminal of the distribution output unit 55 all at once. Since either one of the drive waveforms of the first or second transmitters 51 and 52 is output from the distribution output device 55, the CPU 41 determines ON / OFF for each nozzle, and each terminal of the transfer buffer 47. When the signal is output, only the piezo element PE that has received the ON signal from the transfer buffer 47 side is driven according to the drive waveform of the selected side of the first or second transmitter 51 or 52. As a result, the ink particles Ip are simultaneously ejected from the nozzles of the piezo element PE that has received the ON signal from the transfer buffer 47. Therefore, in the printer 22 of this embodiment, the dot diameter formed at one time by each nozzle array is limited to one type. The timing at which the transfer buffer 47 outputs data is synchronized with the drive waveform output from the distribution output unit 55 side in accordance with the signal output from the selector 54.

  As shown in FIG. 6, since the heads 61 to 66 are arranged along the transport direction of the carriage 31, the timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Accordingly, the CPU 41 outputs the dot ON / OFF signal via the transfer buffer 47 at a necessary timing after taking into account the positional deviation of the nozzles of the heads 61 to 66, and sets the dots of the respective colors. Forming. Further, as shown in FIG. 6, the output of on / off signals is controlled in consideration of the fact that each of the heads 61 to 66 has nozzles formed in two rows.

  Next, the ink composition provided in the printer 22 of this embodiment will be described. As described above, the printer 22 of this embodiment includes the heads 63 and 65 for the light cyan ink and the light magenta ink in addition to the so-called four colors of CMYK. The components of these inks are shown in FIG. The normal density cyan ink (indicated by C1 in FIG. 11) has 3.6% by weight of the direct blue 99 dye, and the light cyan ink (indicated by C2 in FIG. 11) has the direct blue 99 dye in the cyan ink. It is 0.9 weight percent which is 1/4 of C1. In addition, magenta ink having a normal density (indicated by M1 in FIG. 11) has 2.8 weight percent of acid red 289 as a dye, and light magenta ink (indicated by M2 in FIG. 11) has acid red as a dye. , 0.7 weight percent, which is 1/4 of the magenta ink M1. The yellow ink Y is 1.8% by weight of direct yellow 86 as a dye, and the black ink Bk is 4.8% by weight of hood black 2. The density of yellow ink and black ink is only one type. Each ink has a viscosity adjusted to about 3 [mPa · s], and the surface tension is also adjusted in addition to the viscosity of each color ink. Therefore, control of the piezo element PE for each color head It can be made the same regardless of the ink to be formed. In this embodiment, among these inks, black ink is stored in a single cartridge 71, and color ink is stored in an integrated ink cartridge 72 shown in FIG.

  As described above, the printer 22 of this embodiment can form dots having two types of dot diameters. In this embodiment, dots with a small dot diameter (hereinafter referred to as small dots) are formed with an ink weight of 5 ng (nanogram), and dots with a large dot diameter (hereinafter referred to as large dots) are formed with an ink weight of 20 ng. The brightness of each dot is approximately represented by the product of the dye weight and the ink weight. The brightness of the dots represented in this way is also shown in FIG. As shown in FIG. 11, the lightness (lightness 18.0) of small dots formed with cyan ink C1 is equal to the lightness (lightness 18.0) of large dots formed with light cyan ink C2, and formed with magenta ink M1. It can be seen that the brightness of the small dots (lightness 14.0) and the brightness of the large dots (lightness 14.0) formed with the light magenta ink M2 are equal.

  If you want to prepare dots with different densities and different dot diameters for the purpose of expressing multiple gradations, you can use small dots formed with light ink with low density (hereinafter referred to as “light small dots”) to form with dark ink with high density. However, in this embodiment, a large dot (hereinafter referred to as a light large dot) formed with light ink having a low density can be set. And small dots (hereinafter referred to as dark and small dots) formed with high density dark ink were set at the same brightness. By doing so, the degree of freedom in selecting both dots can be increased, and various effects described later can be obtained. In the present embodiment, the two types of dots are set to have the same lightness, but the lightness of the two does not need to be exactly the same, and may be approximately the same lightness.

(2) Dot Generation Processing Routine According to the First Embodiment Next, the dot generation processing routine in the embodiment according to the present invention will be described. In the following, for the sake of simplicity, the generation process of four types of dots (dark small dots, dark large dots, light small dots, light large dots) formed for one cyan color will be described. Similarly, the same processing as that described below is applied to magenta that can form four types of dots. For yellow and black that are not provided with dark and light inks, a process in which a portion corresponding to the selective use of dark and light dots is omitted from the following process is applied.

  FIG. 13 shows a flow of a dot generation processing routine according to the first embodiment. This routine is a part of the processing in the halftone module 99 of the printer driver 96, and is a routine executed by the CPU of the computer 90 in this embodiment.

  When the dot generation processing routine is executed, the CPU inputs pixel gradation data (step S100). The data input here is data obtained by converting a color image into image data in dot units and then performing color correction according to the ink color CMY used by the printer 22 and the color development characteristics of the RGB image data. It is. In this embodiment, the gradation data is given by 8 bits and takes a range of gradation values from 0 to 255.

  Next, the CPU creates correction data Data reflecting diffusion errors from neighboring pixels that have already been processed for the input data (step S200). In this embodiment, error diffusion processing is adopted as described later as processing for bringing the gradation expression of the entire printed image closer to the original color image. In the error diffusion process, the shading error generated for the processed pixel is distributed in advance with a predetermined weight applied to the pixels around the pixel, so that in step S200, the corresponding error is read and this is now read. This is reflected in the pixel to be printed. FIG. 14 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). The error diffusion process will be described in detail later.

  The CPU compares the corrected image data Data with a predetermined threshold value Th1 to Th3 (step S300). The predetermined threshold has a relationship of Th1 <Th2 <Th3, and the thresholds Th1 to Th3 change according to the gradation value. When the image data Data is equal to or greater than the threshold Th3, that is, when the gradation value of the image data Data corresponds to the darkest region, a process for forming a dark dot having the darkest density per unit area is performed ( Step S350). This process is a process of setting dot formation data for input to the nozzles Nz that eject ink (see FIG. 9) and selecting a drive waveform (see FIG. 8). When the processed image data Data is between the predetermined threshold values Th2 and Th3, that is, when Th2 <Data <Th3, this corresponds to a so-called halftone. Since there are two types of dots representing such gradations, light dots and dark dots, they are used separately (step S400).

  In the present embodiment, both are used properly according to a predetermined pattern, and a pattern (see FIG. 23) in which dark and light dots are formed in a checkered pattern is adopted as a relatively simple pattern. When such a pattern is adopted, based on the dot position data, for example, when the sum of the position data in the main scanning direction and the position data in the sub-scanning direction is an even number, a dark dot is formed and the number is an odd number. In such a case, light dots should be formed. Similarly, when using both dots according to other patterns, they can be used separately based on dot position data.

  In addition, the proper use of both may be performed using a dither table. The dither table is a table that gives a threshold value for forming dark dots in a 4 × 4 matrix as shown in FIG. 15, for example. In FIG. 15, for example, among the gradation values 0 to 255, the data corresponding to the halftone is shown as having 50 to 100 gradations, that is, Th2 = 50 and Th3 = 100. FIG. 15 compares the magnitude relationship between the halftone image data Data and the threshold value stored in the dither table, and shows how dark dots are formed in a portion where the image data Data is larger than the threshold value. . In FIG. 15, light large dots are formed in portions where dark dots are not formed. Since the halftone image data Data always exists between the threshold values Th2 and Th3, by forming the dither table by distributing these threshold values Th2 and Th3, in the halftone, dark dots and dark dots are formed in a pattern intended in advance. Light large dots can be formed. Such a pattern may be set experimentally so that banding can be eliminated in consideration of an ink permissible amount per unit area (hereinafter referred to as ink duty limit).

  If a value other than the threshold values Th2 and Th3 is used for the dither table, the appearance pattern of dark and light dots in halftone changes according to the image data. Although FIG. 15 shows a 4 × 4 dither table, a larger dither table may be used.

  In this way, in the halftone, it is assigned whether to form a dark dot or a light large dot for each dot (step S400). When a light large dot is to be formed (step S420), the light large dot is formed. Processing for forming dots is executed (step S440). In other cases, processing for forming dark dots is executed (step S430).

  When the image data Data is between the predetermined threshold values Th2 and Th1, that is, when Th1 ≦ Data <Th2, a process for forming light small dots having a low density per unit area is performed (step S450). Further, when the image data Data is smaller than the predetermined threshold Th1, that is, when Data <Th1, it corresponds to a so-called highlight portion, and processing for not forming dots is performed (step S500).

  As described above, it is set what kind of dots should be formed including the case where dots are not formed. Next, the CPU executes error calculation and error diffusion processing based on such settings (step S700). The error here means an error in brightness between the image data Data corrected in step S200 and the actually formed dots. This error is caused by the fact that the gradation value of the image data Data can take a value of, for example, 0 to 255 continuously, whereas the lightness that can be expressed by the formation of dots can only take a certain discrete value. It is an error. For example, assuming that the evaluation value of the brightness of the dark dot is 255, if a dark dot is formed even though the number of gradations of the image data Data is 199, 255-199 = A lightness error of 56 has occurred. This means that the density of the formed dots is too high compared to the density to be expressed. That is, assuming that the brightness evaluation value RV is determined according to the dots to be formed, the error ERR is obtained by ERR = Data−RV.

  The error diffusion refers to a process of diffusing the error thus obtained with a predetermined weight (see FIG. 14) applied to pixels around the pixel PP currently being processed. Since the error should be diffused to the unprocessed pixels, as shown in FIG. 14, the error is diffused only to the pixels arranged in the carriage scanning direction and the paper conveyance direction. Based on the above example, if the error is 56, 14 corresponding to 1/4 of the error 56 is diffused to the pixel P1 adjacent to the currently processed pixel PP. This error is reflected in step S200 when the pixel P1 is processed next. For example, if the data of the pixel P1 is the gradation value 214, the error 14 diffused therefrom is subtracted and the correction data is set to the value 200. By repeatedly executing this process, an image having a gradation corresponding to the input image data is printed as the entire image, although each pixel includes a brightness error. Note that the weight values shown in FIG. 14 are merely examples, and other weight values may be used.

  Based on the result of the dot generation processing routine described above, the CPU executes processing for the printer 22 to form each dot. Since various processes are known for this process depending on the configuration of the printer 22, the description based on the flowchart is omitted here. However, as described above with reference to FIG. 11, in the printer 22 of this embodiment, the dot diameter that can be formed at a time by a set of nozzle arrays is constant, and dots with different dot diameters are mixedly formed. For this purpose, a slightly special scan is required. Various aspects of such scanning will be described below. The following method is an application of a well-known overlap-type dot recording method.

  FIG. 16 schematically shows a first scanning mode in the case where large and small dots are mixed in a 6 × 6 area using a head with six nozzles. In FIG. 16, the state of ink ejection corresponding to the number of head scans is shown on the left side, and the state of dots formed on the right side is shown. The number given to each dot corresponds to the scanning order of the head. As shown in FIG. 16, in the first main scanning, large dots are formed every other dot in the main scanning direction using the lower half nozzles of the head. Next, after the sheet is conveyed by 3 dots in the sub-scanning direction, small dots are formed every other dot in the main scanning direction using all the nozzles. Then, after the sheet is further conveyed in the sub-scanning direction by 3 dots, large dots are formed using the upper half nozzle. According to such an aspect, by printing each raster in two scans, it is possible to print by mixing large and small dots at the same ratio.

  FIG. 17 shows the second mode. As long as the dot diameter is constant, the location where dots are formed in one main scan can be freely controlled, and as shown in FIG. 17, large and small dots can be mixed in a checkered pattern.

  FIG. 18 shows the third aspect. Here, the point that the number of nozzles is six is the same as in the first and second aspects, but differs in that the nozzle pitch is twice the dot recording density in the sub-scanning direction. In this embodiment, first, large dots are formed using the lower two nozzles. In this case, all dots of each raster are formed by one main scan. Next, the paper for 5 dots is conveyed in the sub-scanning direction, and small dots are formed using the three middle nozzles. Further, the paper is conveyed by 5 dots in the sub-scanning direction, and large dots are formed using the uppermost nozzle. As a result, it is possible to print by mixing the large and small dots at the same ratio while printing the rasters uniformly with either large or small dots.

  FIG. 19 shows the fourth aspect. The nozzle interval is the same as in FIG. In this case, by forming the dots while conveying the paper by 3 dots in the sub-scanning direction, large and small dots can be mixed in a checkered pattern as shown in FIG.

  FIG. 20 shows the fifth aspect. The nozzle interval is the same as in FIG. The relationship between the head scanning order and the nozzles that eject ink is the same as in FIG. However, FIG. 19 is different in that small dots are formed in the third scanning, whereas large dots are formed in the third scanning in the mode of FIG. As a result, it is possible to change the formation ratio of large and small dots to form large dots: small dots = 3: 1. Of course, if dots that are opposite in size to those in FIG. 20 are formed in each scan, the formation ratio of both can be reversed and a large number of small dots can be formed.

  As described above, if each raster is recorded in two or more scans, dots can be formed by freely changing the existence ratio of large and small dots and the existence pattern thereof. Here, a method using six nozzles is illustrated, but the same applies to the case where there are 32 nozzles. However, in this embodiment, since there is a condition that the diameter of dots that can be formed by each nozzle in a single scan is limited to one type, it is necessary to perform dot formation by applying the above-described overlap. If there is no restriction condition and a head capable of freely forming large and small dots from each nozzle is used, recording may be performed by one scan while mixing large and small dots in each raster.

  According to the printing apparatus described above, since dark dots and light large dots can be formed in a mixed tone, dot formation unevenness, that is, banding due to a mechanical manufacturing error of the head is prevented. be able to. FIGS. 21 and 22 show a state in which a certain area is recorded with only small dots. FIG. 21 shows a state where there is no mechanical manufacturing error in the head. In such a case, dot formation unevenness does not occur. On the other hand, FIG. 22 shows a state where a mechanical manufacturing error exists in the head. As shown in FIG. 22, when there is a mechanical manufacturing error in the head, as a result of variations in the ink ejection direction, dots are not uniformly formed and banding occurs. FIG. 22 shows a case where dot formation unevenness occurs only in the sub-scanning direction, but such unevenness can also occur in the main scanning direction.

  On the other hand, FIG. 23 and FIG. 24 show the state of dots formed by the printing apparatus of this embodiment. In these drawings, light large dots are indicated by large circles and dark dots are indicated by small circles. FIG. 23 shows a state where there is no mechanical manufacturing error in the head, and FIG. 24 shows a case where there is an error. As is clear from FIG. 24, it can be seen that the dot formation unevenness is very inconspicuous compared to FIG. This is not an effect that occurs only in the specific pattern shown in FIG. 24, but is an effect that generally occurs by recording a mixture of light large dots and dark dots.

  This effect occurs for the following reason. First, since the ink is different between the light dots and the dark dots, it may be formed by different heads. That is, since the machine manufacturing error varies from head to head, dot formation unevenness occurs in multiple directions, and as a result, formation unevenness is eliminated in the entire image. In addition, large dots overlap with adjacent dots, and dot formation unevenness is less noticeable.

    On the other hand, if the purpose is only to prevent banding, a method in which all dots are formed with large dots can be considered. However, if recording is always performed using only large dots, problems such as blurring may occur if the allowable amount of ink per unit area, that is, the ink duty limit is exceeded. In the printing apparatus according to the present embodiment, such a problem does not occur because the light large dots and the dark dots are selectively used in consideration of the ink duty. In the printing apparatus of the present embodiment, since the mixing ratio of the light large dots and the dark dots can be freely set, a mode in which only the light large dots are used for the recording paper allowed by the ink duty. It can also be taken.

(3) Dot Generation Processing Routine According to Second Embodiment Next, a printing apparatus according to the second embodiment of the present invention will be described. This printing apparatus is the same in hardware configuration as the printing apparatus shown in the first embodiment, and the contents of the dot generation processing routine are different. FIG. 25 is a flowchart showing the flow of a dot generation processing routine in the second embodiment.

  In the dot generation processing routine in the second embodiment, only the processing for sorting the dark and light dots in so-called halftone (step S400 in FIG. 13) is different, and the other processing is the same as in the first embodiment (FIG. 13), the description is omitted here. Only the processing in the halftone that is different from the first embodiment will be described.

  In this embodiment, a random number is generated for halftone, ie, Th2 <Data <Th3 image data Data, and it is determined whether to form a dark dot or a light large dot (step S410). For example, when the random number generated in the range of 0 to 1 is larger than the threshold value 0.5, dark dots are generated, and in other cases, light large dots are generated. When the dot thus determined is a light large dot (step S420), a process for forming a light large dot is executed (step S460), and when it is a dark dot, a dark dot is formed. The process for performing is performed (step S440). If the relationship between the random number and the threshold value is changed, the ratio of dark dots to light dots can be changed, so the ratio of occurrence of both, in other words, the banding can be eliminated while considering the ink duty limit. For example, the threshold value may be set. Further, the threshold value may be changed according to the recording paper or the like.

  According to such a printing apparatus, similarly to the printing apparatus of the first embodiment, banding can be prevented as a result of being able to form a mixture of large and small dots. The state of dots formed by the printing apparatus is shown in FIG. It can be seen that the banding is less noticeable than the dot recording state shown in FIG. In general, irregular formation of dots with regularity is conspicuous, but in this embodiment, since random numbers are used, there is an advantage that dot formation is not regular, and such irregularity is not noticeable.

  The number of dots generated in this example is shown in FIG. FIG. 27 is a graph showing the relationship between the number of gradations of image data and the incidence of each type of dot. The dot generation rate refers to the proportion of each dot in a certain area. For example, when the incidence of light small dots is 60%, it means that 60 light small dots are recorded in 10 × 10 100 dots. As shown in FIG. 27, in the halftone, light large dots and dark dots are used for recording, and in the present embodiment, random numbers are used for the distribution of both, and therefore both exist with substantially the same occurrence rate. In this embodiment, it is confirmed that the ink duty limit is also satisfied at such a ratio.

(4) Dot Generation Processing Routine According to Third Embodiment Next, a printing apparatus according to the third embodiment of the present invention will be described. The configuration of this printing apparatus is the same as that of the printing apparatus shown in the first embodiment, and the contents of the dot generation processing routine are different. FIG. 28 is a flowchart showing the flow of a dot generation processing routine in the third embodiment. This routine is part of the processing in the halftone module 99 of the printer driver 96. In this embodiment, the routine is executed by the CPU of the computer 90, and is the same as the first embodiment.

  When the dot generation processing routine in the third embodiment is started, the CPU inputs pixel gradation data (step S100), and adds correction errors from neighboring pixels that have already been processed to create correction data Data. (Step S200). These processes are the same as those in the first embodiment (FIG. 13).

  Next, the CPU performs processing for determining on / off of dark dots based on the image data Data (step S600). Details of the processing for determining whether the dark dots are on or off are shown in the dark dot formation determination processing routine of FIG. In this processing routine, first, processing for generating dark level data Dth is performed with reference to the table of FIG. 30 based on the image data Data (step S602). FIG. 30 is a graph for setting the recording ratio of light ink and dark ink with respect to the gradation data of the original image. In practice, the graph of FIG. 30 is stored as a table on the ROM. The image data Data takes values from 0 to 255 for each color (8 bits for each color). The table of FIG. 30 shows the ratio of dark ink to light ink in the finally obtained printed matter. When given gradation data, the dot of the currently processed pixel is dark ink or light ink. It does not directly determine on / off.

  Based on the gradation value of the input image data, dark level data Dth corresponding to a predetermined dark ink recording rate is obtained by referring to the table in FIG. 30 (right vertical axis in FIG. 30). For example, when printing a solid area with an input cyan gradation value of 63, the recording rate of the cyan ink C1, which is dark ink, is 0 percent, and the dark level data Dth is also 0. When printing a solid area with a gradation value of 191, the recording rate of the cyan ink C1 is 75%, and the dark level data is the value 191.

  Next, it is determined whether or not the dark level data Dth thus obtained is larger than the threshold value Dref1 (step S604). This threshold value Dref1 is a determination value as to whether or not to form a dot with dark ink on the pixel of interest, and may be a fixed value in the entire region. In this embodiment, a threshold matrix of distributed dither is used for setting the threshold. The concept of the threshold in the dither method has been described with reference to FIG. In this example, a systematic dither method was applied using a global matrix (blue noise matrix) of about 64 × 64 in particular. In this dither matrix, the threshold value is determined so that there is no bias in the appearance of the threshold value (0 to 255) in any 16 × 16 region within the 64 × 64 matrix. 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 a distributed dither is used, dark dots are generated in a discrete manner, so that the distribution of dark and light dots is not biased and the image quality is improved. It should be noted that other methods such as a density pattern method or a pixel distribution method may be employed to determine whether dark dots are turned on or off.

  If the dark dot data Dth is larger than the threshold value Dref1, it is determined that the dark dot of the pixel is to be turned on (step S606). If the dark dot data Dth is smaller than the threshold value Dref1, the dark dot of the pixel is selected. It is determined to be turned off (step S608).

  Next, when it is determined by this determination that dark dots are to be turned on, it is determined whether or not to form dark dots with reference to the table shown in FIG. 31 (step S610 in FIG. 29). The determination method using the table is the same as the dark dot on / off determination method described above (FIG. 29). In this case, the ON / OFF state of the dark dots is determined using the table indicated by the white square symbol “□” in FIG. 31 and the 64 × 64 dither matrix described above. In this way, when it is determined that the dark dot should be turned on, processing for that is executed (step S615). If the dark dot is turned off, the dark dot is turned on / off by the same method (step S620). In this case, the table indicated by the white circle symbol “◯” in FIG. 31 is used. If it is determined that dark dots should be turned on, processing for that is executed (step S625).

  If dark dots are not formed as a result of the above processing (step S600), it is determined whether or not to form light dots (step S630). This determination uses the same method as the determination of dark dot on / off (see FIG. 29). That is, on / off of light dots is determined based on the table and dither matrix of FIG.

  If it is determined that a light dot should be formed, it is determined whether the light large dot is on or off using the table of FIG. 31 (step S635). In this case, the table indicated by the black square symbol “■” in FIG. 31 is used. If it is determined that the light dot should be turned on, processing for that is executed (step S640). If the light large dot is turned off, it is determined whether the light small dot is on or off by the same method (step S645). In this case, the table indicated by the black circle symbol “●” in FIG. 31 is used. If it is determined that the light dot should be turned on, processing for that is executed (step S650).

  Through the above processing, it is determined which of the four types of dots (dark dot, dark dot, light large dot, light small dot) should be formed according to the corrected image data Data. In some cases, neither dot is formed. However, a plurality of types of dots are not overlapped on the same pixel.

  In the above processing, based on the table shown in FIG. 30, the dot on / off state is first determined according to the ink density, and then the dot on / off state according to the dot diameter is determined using the table of FIG. Judging off. On the other hand, on / off determination according to ink density may be omitted, and on / off determination may be performed for each dot type using a table corresponding to FIG. 31 from the beginning.

  When the dots to be formed are determined in this way, the CPU next executes error calculation and error diffusion processing (step S700). Since this process is the same as the process in the first embodiment (step S700 in FIG. 13), description thereof is omitted.

  According to the printing apparatus, dark dots and light large dots can be mixed and formed in a halftone, and thus banding in such gradation can be avoided. Here, the table of FIG. 30 and the table of FIG. 31 are experimentally determined so as to obtain the effect of avoiding banding. At this time, the allowable ink amount per unit area of the printing paper is not exceeded. If the dot occurrence rate in FIG. 31 is set, the best image free from bleeding or the like can be obtained in consideration of such restrictions.

  In each printing apparatus described above, the use of dark dots and light large dots may be used in consideration of the use of dark ink and light ink. For example, when a large amount of dark ink is consumed, a large number of light large dots may be formed in the halftone. As the ink consumption, for example, a means for sensing the consumption of each ink by applying light to the cartridge 72 may be adopted, or by storing the accumulated number of dots formed, the ink consumption can be reduced. It is good also as what calculates. In this way, if the dots are selectively used in consideration of the ink consumption, the cost for using the printing apparatus can be reduced. In particular, when a plurality of color inks are stored in the integrated cartridge 72 (see FIG. 12) as in the printing apparatus according to the present embodiment, it is possible to use all of the inks uniformly. Reduction effect is high.

  Further, the printing apparatus in the above description can change the ink density and the dot diameter by two types, respectively, but the ink density or the dot diameter may be further increased. In the above-described printing apparatus, two types of dots are selectively used only in halftones. However, if dots can be selectively used in other gradations by increasing the types of ink density and dot diameter. In addition, the image quality can be improved in consideration of banding and ink duty, and the uniform use of ink can be performed more effectively.

  Furthermore, since the printing apparatus includes processing by a computer, it is possible to adopt an embodiment as a recording medium in which a program for realizing each function described above is recorded. Such storage media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter printed with codes such as bar codes, computer internal storage devices (such as RAM and ROM). A variety of computer-readable media can be used, such as memory) and external storage devices. Moreover, the aspect as a program supply apparatus which supplies the computer program which implement | achieves the function of each process or each means of said invention to a computer via a communication path is also possible.

  In the various printing apparatuses described above, dots having different diameters are formed by selecting the drive waveforms output from the two transmitters 51 and 52. From a single transmitter, FIG. Alternatively, two types of drive waveforms may be alternately output, and either one may be masked according to the dot diameter to be formed.

  Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various embodiments can be implemented without departing from the scope of the present invention. For example, although the various processes described above are executed by the computer 90, the printer 22 may be provided with a function for executing such processes and executed on the printer 22 side. Further, the present invention may be applied to a printer of a type in which electricity is supplied to a heater arranged in the ink passage and ink is ejected by bubbles generated in the ink passage. In such a printer, since the dots having different dot diameters can be formed by changing the energization time and the energization area to the heater, the present invention can be applied.

1 is a schematic configuration diagram of an image processing system using a printer of the present invention. 1 is a schematic configuration diagram of a printer of the present invention. It is explanatory drawing which shows schematic structure of the dot recording head of the printer of this invention. It is explanatory drawing which shows the dot formation principle in the printer of this invention. It is explanatory drawing which shows the example of nozzle arrangement | positioning in the printer of this invention. It is explanatory drawing which shows nozzle arrangement | positioning in the printer of this invention. It is explanatory drawing which shows the principle which forms the dot from which a dot diameter differs by this invention. It is explanatory drawing which shows the drive waveform of the nozzle in the printer 22 of this invention. 2 is an explanatory diagram showing an internal configuration of a printer 22; FIG. It is explanatory drawing which shows the drive circuit structure of a head. It is explanatory drawing which shows an ink composition and a characteristic. It is explanatory drawing which shows the ink cartridge in the printer of this invention. It is a flowchart which shows the flow of the dot generation process routine in 1st Example. It is explanatory drawing which shows the weighting coefficient in an error diffusion process. It is explanatory drawing which shows the method of the dot ON / OFF determination using a dither matrix. It is explanatory drawing which shows the 1st aspect which records by mixing the large and small dots with the printer of this invention. It is explanatory drawing which shows the 2nd aspect which records by mixing the large and small dots with the printer of this invention. It is explanatory drawing which shows the 3rd aspect which records by mixing the large and small dots with the printer of this invention. It is explanatory drawing which shows the 4th aspect which records by mixing the large and small dots with the printer of this invention. It is explanatory drawing which shows the 5th aspect recorded with a large and small dot mixed by the printer of this invention. It is explanatory drawing which shows the state recorded only by the small dot and there is no dot formation nonuniformity. It is explanatory drawing which shows the state recorded only with a small dot and there exists a dot formation nonuniformity. It is explanatory drawing which shows the state recorded by mixing large and small dots, and there is no dot formation nonuniformity. It is explanatory drawing which shows the state recorded by mixing large and small dots and having dot formation unevenness. It is a flowchart which shows the flow of the dot generation process routine in 2nd Example. It is explanatory drawing which shows the state in which the large and small dots generated at random are mixed and there is dot formation unevenness. It is explanatory drawing which shows the dot incidence in 2nd Example. It is a flowchart which shows the flow of the dot generation process routine in 3rd Example. It is a flowchart which shows the flow of a dark dot formation judgment processing routine. It is a graph which shows the relationship between an input data gradation value and a shading dot recording rate. It is a graph which shows the relationship between an input data gradation value and each dot recording rate of darkness, darkness, lightness, and lightness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Scanner 21 ... Color display 22 ... Color printer 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Print head 31 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive belt 38 ... Pulley 39 ... Position detection Sensor 40 ... Control circuit 41 ... CPU
42 ... Programmable ROM (PROM)
43 ... RAM
44 ... PC interface 45 ... PIO
46 ... Timer 47 ... Transfer buffer 51, 52 ... Transmitter 54 ... Selector 55 ... Distribution output device 61, 62, 63, 64, 65, 66 ... Ink ejection head 67 ... Introducing pipe 68 ... Ink passage 71 ... Black Ink cartridge 72 ... Color ink cartridge 90 ... Personal computer 91 ... Video driver 92 ... Input unit 95 ... Application program 96 ... Printer driver 97 ... Rasterizer 98 ... Color correction module 99 ... Halftone module

Claims (5)

A printing device for printing an image,
A head capable of forming a plurality of types of dots in which at least one of density and dot diameter is different from each other using dark ink and light ink;
By determining the density and the dot diameter of the dots to be formed for each pixel according to the gradation value of each pixel of the input image data, the types of dots to be formed are the plurality of types. Determining means for determining any one of the dots;
Head drive control means for driving the head to form the determined type of dots;
With
The plurality of types of dots are a first type of dot formed using the light ink and having a first dot diameter, and a second dot formed using the dark ink and smaller than the first dot diameter. A unit density that is a density per unit area of the first type dots and the unit density of the second type dots are substantially the same.
The determining means determines whether or not dots are formed by the dark ink, and then determines whether or not dots are formed by the light ink when the dots are not formed by the dark ink and consumes more dark ink. The ratio between the first type dots and the second type dots is changed so as to form more of the first type dots than the second type dots in a halftone. apparatus. The printing apparatus according to claim 1,
The plurality of types of dots include dark dots and dark dots formed with the dark ink, and light large dots and light small dots formed with the light ink,
The printing apparatus, wherein the first type dot is the light large dot, and the second type dot is a dark dot. The printing apparatus according to claim 2,
The determining means includes
A first table showing dot recording rates of the dark dots and dark dots according to the gradation values of the input image data; and the light large dots according to the gradation values of the input image data And a second table indicating the dot recording rate of light small dots,
After determining whether or not the dark dots and dark dots are formed with reference to the first table, refer to the second table when neither the dark dots nor the dark dots are formed. Determining the presence or absence of the formation of the light large dots and light small dots;
Printing device. A printing method for printing an image using a head capable of forming a plurality of types of dots using dark ink and light ink and at least one of density and dot diameter being different from each other,
(A) The type of dot to be formed is determined by determining the density and dot diameter of the dot to be formed for each pixel according to the gradation value of each pixel of the input image data. Determining any one of the plurality of types of dots;
(B) driving the head to form the determined type of dots;
The plurality of types of dots have a first density having a first density and a first dot diameter, and a first density having a second density higher than the first density. A second type of dot having a second dot diameter smaller than that of the first dot, and a unit density that is a density per unit area of the first type of dot and the unit density of the second type of dot Is almost the same,
Wherein the step (a) After determining the presence or absence of formation of dots by the dark ink, the addition to determining the presence or absence of formation of dots by the light ink when dots by deep ink is not formed, the dark ink is more When a large amount is consumed, the ratio between the first type dots and the second type dots is changed so that more first type dots are formed than half the second type dots. , Printing method. A recording medium in which a program for printing an image is recorded on a printing apparatus using a dark ink and a light ink and having a head capable of forming a plurality of types of dots having different densities and / or dot diameters. And
By determining the density and the dot diameter of the dots to be formed for each pixel according to the gradation value of each pixel of the input image data, the types of dots to be formed are the plurality of types. A decision function to determine one of the dots,
A function of causing the head to form the determined type of dots;
Is a recording medium that records a program for causing a printing apparatus to realize
The plurality of types of dots include a first type of dot having a first density and a first dot diameter, and a first density having a second density higher than the first density. A second type dot having a second dot diameter smaller than the diameter, and a unit density that is a density per unit area of the first type dot and the unit density of the second type dot Almost identical,
The determining function determines whether or not dots are formed by the dark ink, and then determines whether or not dots are formed by the light ink when the dots are not formed by the dark ink and consumes more dark ink. The ratio between the first type dots and the second type dots is changed so that more first type dots are formed than half the second type dots in a halftone. Medium.

Images