JP2000272171A - Printing apparatus, printing method, and recording medium - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize high-quality and high-speed printing in a printer. SOLUTION: In an ink jet printer, recording is performed by an overlap method in the following manner. In the odd-numbered main scanning, dots are formed in pixels in odd-numbered columns, and in the even-numbered main scanning, dots are formed in pixels in even-numbered columns. When print data to be provided to the printer is generated by halftone processing, dots are preferentially formed in pixels in odd columns. This processing is realized by using a dither matrix in which a small threshold value is set for odd columns.
According to this processing, in the low gradation area, dots are generated only in odd rows. The printer executes high-speed printing by omitting the even-numbered main scanning in an area where it is not necessary to form dots in even-numbered columns.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a printing apparatus, a printing method, and a recording medium on which a program for realizing such printing is recorded. About.

[0002]

2. Description of the Related Art Various printers are used as output devices of computers and digital cameras. As such a printer, there is an ink jet printer that forms dots by discharging ink and prints an image in multiple colors and multiple gradations. Ink jet printers can only express binary values of dot on / off for each pixel. Therefore, in an ink jet printer, halftone processing for expressing a gradation value of an image by a distribution of dots is performed, and ON / OFF of dots for each pixel is determined.

In recent years, there has been proposed a printer capable of expressing three or more levels of density for each pixel by using dots having different ink densities and ink weights. Even in such a multi-value printer, the tone values that can be expressed for each pixel are very limited as compared with the tone values of the image to be printed. Therefore, even in the multi-value printer, the printing is executed after similarly performing the halftone processing.

The dots are formed by repeatedly executing a main scan in which the head reciprocates in one direction with respect to the printing paper and a sub-scanning in which the printing paper is conveyed in a direction intersecting with the main scanning. General. When printing is performed by such a method, in an inkjet printer, a streak-like density unevenness called banding occurs due to a shift in a dot formation position due to a mechanical manufacturing error of a dot forming element that ejects ink, and image quality deteriorates. Sometimes. As a technique for reducing the deviation and improving the image quality, recording using a so-called overlap method has been proposed.

[0005] Recording by the overlap method refers to a method in which each raster is formed by two or more dot forming elements.
FIG. 20 is an explanatory diagram showing the state of dots formed by the overlap method. The positions of the dot forming elements in each main scan are shown on the left side of the figure. Each numbered symbol means a dot forming element. Here, the case where a head in which four dot forming elements are arranged at a dot forming element pitch of 3 dots in the sub-scanning direction is used is illustrated.
Each number indicates a dot forming element number.

As shown in the figure, each time a main scan is performed, a sub-scan is performed with a feed amount corresponding to two dots. Dots can be formed on each raster within the range shown as a printable area in the figure, and an image can be printed. As is apparent from the drawing, in the printable area, two dot forming elements pass through each raster in two main scans. For example, the uppermost raster r1 of the printable area is the fourth dot forming element and the second raster r1.
And the dot forming element of the number. That is, 1
In the fourth main scan, the fourth dot forming element forms dots at odd-numbered pixels of the raster r1. In the fourth main scan, the second dot forming element forms dots at even-numbered pixels of the raster r1. The state of the dots formed on the right side of the figure is shown. "O" and "□" indicate dots. The shape of each symbol corresponds to the symbol of a dot forming element that forms a dot. As shown, it can be seen that each raster of the printable area is formed by two dot forming elements.

[0007] Such a storage method of forming each raster by a plurality of dot forming elements is called an overlap method. FIG.
In the case of 0, the case where each raster is formed by two dot forming elements is illustrated, but there is also a case where the raster is formed by using more dot forming elements. By forming each raster with a plurality of dot forming elements in this way, there is an advantage that the shift of the forming position caused by the characteristics of each dot forming element can be dispersed. For example, let us consider a case where the fourth dot forming element has a characteristic that the dot forming position is shifted in the sub-scanning direction. If a raster is formed using only the fourth dot forming element, the position of the entire raster is shifted in the sub-scanning direction. As a result, the interval between adjacent rasters becomes non-uniform, and a stripe-like shading unevenness called banding occurs. On the other hand, if the raster is formed by a plurality of dot forming elements, the entire raster can be prevented from shifting in the sub-scanning direction, and the occurrence of banding can be suppressed. Therefore,
By performing the recording by the overlap method, the image quality can be improved.

[0008]

However, recording by the overlap method has a problem that the printing speed is reduced. In the overlap method, since each dot forming element is driven intermittently and each raster is formed by a plurality of dot forming elements, the driving rate of each dot forming element decreases. When each raster is formed by a plurality of dot forming elements, compared to the case of forming a single dot forming element,
The sub-scan feed amount also decreases, and the number of sub-scans required to print the entire image increases. Conventionally, in the recording method using the overlap method, the printing speed has been reduced due to these causes.

In general, the convenience of a printer is affected by the image quality and printing speed. It is desirable to execute high-quality printing at high speed. In recent years, in order to improve the image quality of a printer, higher resolution has been achieved, and the number of pixels tends to increase. For this reason, the time required for printing an image tends to increase. Under such a tendency, a reduction in printing speed due to the application of the overlap method cannot be overlooked. On the other hand, a decrease in image quality due to banding that occurs when the overlap method is not applied is not allowed.

This problem is not limited to the ink jet printer, but is a problem common to printing apparatuses that form dots and print an image while performing main scanning. The present invention has been made to solve such a problem, and an object of the present invention is to provide a technique for improving a printing speed without lowering image quality due to banding in a printing apparatus that performs printing by forming dots. And

[0011]

Means for Solving the Problems and Their Functions and Effects In order to solve at least a part of the above problems, the present invention employs the following means. The printing apparatus of the present invention performs a main scan that reciprocates a head relative to a print medium and a sub-scan that conveys the print medium relatively to the head in a direction that intersects the main scan direction. A printing apparatus that prints an image by forming dots on each pixel on the print medium, wherein the head is a head including a plurality of dot forming elements for forming dots in the sub-scanning direction; An input unit for inputting image data of an image, a halftone unit for performing a halftone process on the image data, and a main scan while driving the head, and a subscan with a predetermined feed amount to perform the main scan. Dot forming control means for forming a raster as each dot row in the direction by a plurality of dot forming elements, wherein the halftone means includes a plurality of dot forming elements forming the raster. And summarized in that a specific pixel corresponding to the dot-forming elements of the parts is a half-tone processing means under conditions preferentially dots are formed.

Such a printing apparatus prints an image by an overlap method in which each raster is formed by a plurality of dot forming elements. The halftone unit performs a halftone process so that a dot is formed prior to the specific pixel. Therefore, in a gradation range where the dot formation density is relatively low, dots are formed only in specific pixels. The specific pixel is a pixel formed by some dot forming elements. Therefore, in such a gradation range, it is possible to form each raster by using only a part of the dot forming elements necessary for forming each raster in printing in the overlap mode. In general, banding is remarkable in a region where the recording density is high, and therefore, in a gradation range where the recording density is relatively low such that dots are formed only in specific pixels, each raster is formed using some dot forming elements. No significant banding occurs when formed. The printing apparatus of the present invention can improve the efficiency of forming an image in the above gradation range by the above-described operation, and can realize high-quality printing at high speed.

The operation of the present invention will be described more specifically with reference to the recording of the overlap system shown in FIG. In the overlap type printing shown in FIG. 20, each raster is formed by two dot forming elements, and the first dot forming element forms odd-numbered pixels, and the second dot forming element forms even-numbered pixels. I do. In such a case, an odd-numbered pixel formed by the first dot forming element is defined as a specific pixel. The halftone means sets on / off of the dots of each pixel so that the dots are formed in preference to the odd-numbered pixels. In a relatively low gradation area, dots are formed only in odd-numbered pixels. Therefore, in such a gradation, a raster can be formed only by the main scanning by the first dot forming element, and the printing speed can be improved. As described above, in such a gradation, remarkable banding does not occur even if the raster is formed only by the main scanning by the first dot forming element.

In the present invention, some dot forming elements do not necessarily have to be a single dot forming element. In the case of performing the overlap method in which each raster is formed by three or more dot forming elements, some nozzles may be formed by two or more dot forming elements. In such a case, the priority at which dots are formed may be set in a stepwise manner. For example, when each raster is formed by three dot forming elements, the priority at which dots are formed in the order of a pixel formed by the first dot forming element and a pixel formed by the second dot forming element is determined. May be lower. In this way, in the low gradation area, dots can be formed only by the first dot forming element, and in the intermediate gradation area, the first dot forming element and the second dot forming element can be formed.
The dots can be formed using only the dot forming elements of.

Referring to the example of FIG. 20, when halftone processing is executed with odd-numbered pixels as specific pixels, pixels formed by the third and fourth dot forming elements correspond to the specific pixels. The pixels formed by the first and second dot forming elements correspond to the other pixels. That is,
In one main scan, a dot forming element forming a specific pixel and a dot forming element forming another pixel are mixed in the head. In such a case, by forming dots with priority on a specific pixel, the amount of data transferred to the head as a halftone result can be reduced, and the printing speed can be improved. In recent years, the number of dot forming elements provided in the head has increased, and the number of pixels constituting each raster has tended to increase. Therefore, the effect of improving the printing speed by partially omitting the data transfer in this way is great. .

In the printing apparatus according to the present invention, the halftone means includes a storage means for storing a correspondence between each main scan and a raster according to the feed amount, and a plurality of rasters formed by each main scan. It is preferable that the setting means is provided with setting means for setting the specific pixels so that the priority of the pixels formed in the main scanning is common.

In this way, the priority of each pixel can be unified for each main scan. That is, the pixels to be formed in one main scan can be unified to specific pixels or other pixels. As a result, control for improving dot formation efficiency can be performed for each main scan, and printing speed can be further improved. The storage means is not limited to a means for directly storing the correspondence between each main scan and the raster, and may be any means for storing information capable of specifying the correspondence.

As such control, for example, the dot formation control means determines whether or not there is a pixel on which a dot should be formed for each main scan, and determines whether there is no pixel on which a dot should be formed. If it is determined that the main scanning is not performed, the main scanning may be omitted.

This makes it possible to reduce the number of main scans in the gradation range in which dots are formed only in specific pixels. That is, in the main scanning corresponding to the formation of a specific pixel, dots are formed in each pixel, and the execution of the main scanning corresponding to other pixels can be omitted. As a result, if the above control is executed, the printing speed can be further improved.

In the present invention, the halftone means may be means for performing halftone by a dither method.

The dither method is a halftone process for determining whether a dot of a pixel to be written is on or off according to a magnitude relationship between a threshold value given for each pixel and a gradation value of image data by a preset dither matrix. Is the way. In the dither method, by setting the threshold of the dither matrix,
Pixels that are likely to turn on dots can be controlled relatively easily. Therefore, the halftone process giving priority to a specific pixel can be relatively easily realized.

In the present invention, the halftone means is not necessarily limited to the dither method. Other halftone means, for example, an error diffusion method may be applied. In the error diffusion method, for example, by using different values for a specific pixel and other pixels as a threshold value that is used as a criterion for determining whether a dot is on or off, it is possible to realize halftone processing in which a specific pixel has priority. it can.

The present invention can be applied to a printing apparatus having a head capable of forming a single type of dot, but the head is capable of forming a plurality of dots having different density evaluation values. The halftone means is a means for storing a recording rate set in advance for each dot, and the halftone means is lower than a gradation value expressed when a dot having a maximum density is formed in the specific pixel. At a predetermined gradation value, a recording rate storage means for storing a recording rate set within a range in which the sum of the recording rates of the respective dots is equal to or less than the density of a specific pixel, and a halftone based on the stored recording rate. And means for performing a tone process.

When a plurality of dots having different density evaluation values are used, a smooth gradation expression can be realized by changing the recording density of each dot according to the gradation of the image data. In such a case, it is possible to variously set the relationship between the recording rate of each dot and the gradation value. In the printing apparatus having the above configuration, in a predetermined low gradation area, each recording rate is set such that the sum of the dot recording rates is equal to or less than the density of the specific pixel. Therefore, in such a low gradation area, gradation can be expressed by forming dots only in specific pixels. Therefore, according to the printing apparatus, the effect of improving the printing speed based on the above-described operation can be obtained in the low gradation region. As a result, the printing apparatus can realize high-quality printing with smooth gradation expression at high speed.

The predetermined tone value can be set arbitrarily within a range not more than the tone value expressed when the dot having the highest density evaluation value is formed in the specific pixel. The gradation value expressed when the dot having the highest density evaluation value is formed in the specific pixel is a gradation value corresponding to the maximum density that can be expressed by forming a dot only in the specific pixel. It is desirable to set the dot recording rate so as not to exceed the density of the specific pixel in all ranges below the gradation value, since the effect of improving the printing speed can be obtained in a wide range.

The present invention can be configured as a printing method described below. That is, the printing method of the present invention includes a main scan in which a head including a plurality of dot forming elements for forming dots is reciprocated relative to a print medium, and the head is moved in a direction intersecting the main scan direction with the print medium. A printing method for printing an image by forming dots in each pixel on the print medium by performing sub-scanning that is relatively conveyed to the printing medium, and (a) inputting image data of the image And (b) determining a relationship between each raster and the plurality of dot-forming elements based on a sub-scan feed amount set in advance so that the plurality of dot-forming elements correspond to each raster as a dot row in the main scanning direction. (C) specifying a correspondence between the image data under the condition that dots are preferentially formed in specific pixels corresponding to some of the dot forming elements among a plurality of dot forming elements forming each raster. Half of And performing over emissions treatment, a method of printing and forming dots by performing it, the main scanning and sub-scanning based in (d) of the half-tone processed results.

According to this printing method, high-quality printing can be performed at high speed by the same operation as that described above for the printing apparatus. Note that it goes without saying that the invention of the printing method can also include the various additional elements described above for the printing apparatus.

The present invention can also be constituted as the following recording medium. That is, the first recording medium of the present invention is a computer-readable program for driving a printing apparatus that prints an image by repeatedly performing main scanning and sub-scanning of a head including a plurality of dot forming elements for forming dots. A recording medium capable of recording, wherein a function of specifying a correspondence between each raster and a plurality of dot forming elements corresponding to the formation of the raster based on a preset sub-scan feed amount; Out of a plurality of dot forming elements that form a halftone process of the image data under the condition that dots are preferentially formed in specific pixels corresponding to some of the dot forming elements. It is a recording medium on which recording is performed.

The second recording medium of the present invention is a recording medium in which a program for driving a printing apparatus that prints an image by repeatedly performing main scanning and sub-scanning of a head is recorded in a computer-readable manner, A function of determining whether or not there is a pixel for forming a dot for each main scan, and a function of omitting the execution of the main scan when it is determined that there is no pixel for forming a dot. This is a recording medium on which a program to be realized is recorded.

When the program recorded on the recording medium is executed by a computer, high-quality printing can be performed at a high speed, as described above for the printing apparatus. The above program may be configured as a single program for realizing the above functions, or may be configured as a part of a program for driving a printing apparatus. Further, it may be configured as a program for realizing the various additional elements described above in the printing apparatus.

As the above-mentioned storage medium, a flexible disk, CD-ROM, magneto-optical disk, IC card,
Various media that can be read by a computer, such as a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, an internal storage device (a memory such as a RAM or a ROM), and an external storage device of the computer can be used. The present invention also includes a mode as a program supply device for supplying a program for realizing the above functions via a communication path.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. (1) Configuration of Apparatus: Hereinafter, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory diagram illustrating a schematic configuration of a printing apparatus as an embodiment. The printing apparatus of this embodiment is configured by connecting a printer PRT to a computer PC by a cable CB. The computer PC plays a role of transferring data for printing to the printer PRT and controlling operations of the printer PRT. These processes are performed based on a program called a printer driver.

The computer PC can load and execute a program from a recording medium such as a flexible disk or a CD-ROM via a flexible disk drive FDD or a CD-ROM drive CDD. The computer PC is connected to an external network TN, and can access a specific server SV to download a program. As a matter of course, these programs may adopt a mode in which the entire program necessary for printing is loaded collectively, or a mode in which only some modules are loaded.

FIG. 2 is an explanatory diagram showing functional blocks of the printing apparatus. In the computer PC, an application program 95 is executed under a predetermined operating system.
Is working. A printer driver 96 is incorporated in the operating system. The application program 95 performs processing such as generation of image data. The printer driver 96 is provided with functional units such as an input unit 100, a color correction processing unit 101 and a color correction table LUT, a halftone processing unit 102 and a recording rate table RT, a rasterizing unit 103, and an output unit 104.

When a print command is issued from the application program 95, the input unit 100 receives image data. The color correction processing unit 101 performs a color correction process for correcting a color component of the image data into a color component corresponding to the ink of the printer PRT. The color correction process is performed with reference to a color correction table LUT that stores in advance the correspondence between the color components of the image data and the color components that can be expressed by the ink of the printer PRT. The halftone processing unit 102 performs a halftone process on the data that has been subjected to the color correction process in order to express the tone value of each pixel in the dot recording density. As described later, the printer PRT can form three types of dots having different density evaluation values. The relationship between the gradation value and the recording rate of each dot is set in advance as a recording rate table RT. The halftone processing unit 102 outputs the recording rate table RT
The halftone process is executed according to the recording rate stored in. The rasterizing unit 103 arranges the halftone-processed data in the order in which the data is transferred to the printer PRT.
The print data thus generated is output to the printer PRT by the output unit 104.

The printer PRT has a printer driver 96.
The input unit 110 receives the print data transferred from
The data is temporarily stored in the buffer 115. And buffer 11
5, the main scanning unit 111 and the sub-scanning unit 112 perform main scanning of the head and transport the printing paper, and the head driving unit 113 drives the head to print an image.

FIG. 3 is an explanatory diagram showing a schematic configuration of the printer PRT. As shown in the drawing, the printer PRT includes a circuit for transporting the paper P by a paper feed motor 23, and
A circuit for reciprocating in the axial direction, a circuit for driving a print head 28 mounted on a carriage 31 to eject ink and form dots, a paper feed motor 23, a carriage motor 24, a print head 28, The control circuit 40 controls the exchange of signals with the panel 32.

A circuit for reciprocating the carriage 31 in the axial direction of the platen 26 includes a sliding shaft 34 laid parallel to the axis of the platen 26 and holding the carriage 31 slidably.
A pulley 38 for extending an endless drive belt 36 between the carriage motor 24 and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.

The carriage 31 of the printer PRT has a cartridge 71 for black ink (K) and five colors of cyan (C), light cyan (LC), magenta (M), light magenta (LM), and yellow (Y). Can be mounted. A total of six ink ejection heads 61 to 66 are formed on the print head 28 below the carriage 31.

FIG. 4 is an explanatory diagram showing the arrangement of the nozzles Nz in the ink discharge heads 61 to 66. The arrangement of these nozzles consists of six nozzle arrays that eject ink for each color. In each nozzle array, 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k.

FIG. 5 is an explanatory diagram showing the principle of ejecting ink in the head 28. For convenience of illustration, K, C, L
The internal structure of the head C is shown. As shown
Each nozzle is provided with an ink passage 68 for supplying ink from the ink cartridges 71 and 72. The piezo element P is located adjacent to the ink passage 68.
E is provided. When the control circuit 40 applies a predetermined drive voltage to the piezo element PE, the ink path 68 is deformed in the direction shown by the arrow in the figure due to the distortion of the piezo element PE, and the ink droplet Ip is ejected.

The printer PRT has three different ink weights.
Different types of dots can be formed. A dot with the maximum amount of ink is called a large dot, a dot with an intermediate amount of ink is called a medium dot, and a dot with the minimum amount of ink is called a small dot. The principle of forming these three types of dots will be described. FIG. 6 is an explanatory diagram showing the relationship between the driving waveform of the nozzle Nz when the ink is ejected and the ejected ink Ip.
The drive waveform indicated by a broken line in FIG. 6 is a waveform when a normal dot is ejected. In the section d2, once the potential of the piezo element PE is set to a low potential, the piezo element PE is deformed in a direction to increase the sectional area of the ink passage 68. Since this deformation is performed at a higher speed than the ink supply speed from the ink passage 68, an ink interface M called a meniscus is formed.
e is a state in which it is dented inside the nozzle Nz as shown in the state A of FIG. Using the driving waveform shown by the solid line in FIG.
When the potential is rapidly decreased as shown in the section d1, the deformation speed of the ink passage 68 is further increased, so that the meniscus is largely inwardly depressed as compared with the state A (state a). Next, when the voltage applied to the piezo element PE is made positive (section d3), ink is ejected. At this time,
Large ink droplets are ejected from the state in which the meniscus is not much depressed inward (state A) as shown in states B and C, and from the state in which the meniscus is largely dented inward (state a) to state b and state c. As shown, small ink droplets are ejected.

Based on this principle, the weight of the ejected ink can be changed in accordance with the rate of change when the potential of the piezo element PE is lowered (sections d1 and d2), that is, the driving waveform for driving the nozzles. . In this embodiment, the driving waveform for forming the small dot IPs and the medium dot IPm
Are prepared. FIG. 7 shows a driving waveform used in this embodiment. Drive waveform W
1 is a waveform for forming small dots IPs, and a drive waveform W2 is a waveform for forming medium dots IPm. As shown in FIG. 7, as the ink weight increases, the flying speed increases. By properly using these drive waveforms, it is possible to form two types of small and medium dots from the nozzle Nz having a constant nozzle diameter. In the printer PRT of this embodiment, these drive waveforms are output continuously and periodically in the order of W1 and W2 as the carriage 31 moves.

Further, a large dot can be formed by forming a dot using both the drive waveforms W1 and W2 of FIG. This situation is shown in the lower part of FIG. FIG.
The lower part of the drawing shows the sheet P after the ink droplets IPs and IPm of small dots and medium dots ejected from the nozzles are ejected.
Up to. When two types of small and medium dots are formed using the driving waveform of FIG. 7, the medium dots eject the ink droplet IPm more vigorously. By adjusting the timing at which the small dot ink droplets IPs and the medium dot ink droplets IPm are continuously ejected in accordance with the flying speed difference of the ink and the moving speed of the carriage 31 in the main scanning direction, both inks can be adjusted. The droplet can reach the paper P at substantially the same timing. In this embodiment, a large dot is formed from the two types of driving waveforms shown in the upper part of FIG.

The control circuit 40 for controlling each function of the printer PRT is configured as a microcomputer having a CPU, a PROM, and a RAM. The control circuit 40 is provided with a transmitter for outputting a driving waveform for driving the piezoelectric element to each of the heads 61 to 66 and a distribution output unit for distributing and outputting the driving waveform to each nozzle. I have. When the control circuit 40 outputs a driving waveform based on the data for specifying the dot on / off for each nozzle of the heads 61 to 66, ink is emitted from the nozzles set to on based on the principle described above. Discharged.

The printer PRT having the above-described hardware configuration includes a sub-scan for transporting the paper P by the paper feed motor 23 and a carriage motor 24 for moving the carriage 31.
The main scanning for driving the piezo element PE of each of the heads 61 to 66 to form a dot while reciprocating is repeated to form an image on the paper P.

In this embodiment, as described above, the printer PRT having the head for discharging ink using the piezo element PE is used, but a printer for discharging ink by another method may be used. . For example, the present invention may be applied to a printer of a type in which a heater disposed in an ink passage is energized and ink is ejected by bubbles generated in the ink passage. In addition, not only printers that eject ink, but also so-called thermal transfer types,
It is also possible to apply to a sublimation type printer or the like.

(2) Dot formation control processing routine: Next, the dot formation control processing routine in this embodiment will be described. FIG. 8 is a flowchart of the dot formation control processing routine. This routine is a process performed by the printer driver 96, and is a routine executed by the CPU of the computer PC in this embodiment.

When this process is started, the CPU inputs image data (step S100). This image data is data passed from the application program 95 shown in FIG. 2 and includes 256 gradation values of 0 to 255 for each of the R, G, and B colors for each pixel constituting the image. Is data having

The CPU converts the resolution of the input image data into a resolution for printing by the printer PRT (step S105). Further, the CPU performs a color correction process (step S110). The color correction process is a process of converting image data composed of R, G, and B tone values into tone values of C, LC, M, LM, Y, and K colors used in the printer PRT. This processing is performed by using a color correction table LUT in which data for representing a color composed of each combination of R, G, and B with each color combination used in the printer PRT is stored in advance. Various well-known techniques can be applied to the processing itself for performing color correction using the color correction table LUT. For example, processing by interpolation calculation can be applied. By this processing, the image data becomes C, LC, M,
The data is converted into data having 256 gradations for each of the colors LM, Y, and K. This processing is performed by the color correction processing unit 1 in FIG.
01 processing.

The CPU performs multi-value processing on the color-corrected image data (step S200).
Multi-value conversion means the gradation value of the original image data (25 in this embodiment).
(6 gradations) is converted to a gradation value that can be expressed by the printer PRT for each pixel. In the present embodiment, multi-leveling to four gradations of “no dot formation”, “small dot formation”, “medium dot formation”, and “large dot formation” is performed. Needless to say, multi-value conversion into more gradations may be performed according to the types of dots that can be formed by the printer PRT. This processing corresponds to the processing of the halftone processing unit 102 in FIG.

FIG. 9 is a flowchart of a multi-value processing routine. The multi-value processing can be performed by various methods such as a so-called error diffusion method. In this embodiment, the multi-value processing is performed by the dither method. In addition, a multi-value processing is performed based on a preset recording ratio of large dots, medium dots, and small dots. FIG. 10 is an explanatory diagram showing a table for giving recording rates of large dots, medium dots, and small dots.

As shown, the recording rate of small dots gradually increases as the gradation value increases from 0. After the recording rate of small dots reaches 50%, the recording rate of medium dots gradually increases while the recording rate of small dots decreases.
After the recording rate of the medium dot reaches 50%, the recording rate of the medium dot decreases and gradually increases until the recording rate of the large dot reaches 50%. In the area D1 on the lower gradation side than the gradation value at which the recording rate of the large dot reaches 50%, the sum of the recording rates of the respective dots is set to 50% or less.

After the recording rate of large dots reaches 50%, the recording rate of small dots gradually increases while maintaining the recording rate of large dots. The recording rate of small dots reaches 50%,
After the recording rate combined with large dots reaches 100%,
The recording rate of medium dots is increased while the recording rate of small dots is reduced. The recording rate of large dots is maintained at 50%. Therefore, the total of the recording rates of each dot remains at 100%.
After the recording rate of medium dots reaches 50%, the recording rate of large dots increases to 100% while the recording rate of medium dots decreases. The recording rate set in this way is stored in the table as level data for each gradation value. The level data is, as shown on the right side of FIG.
This means data represented by data of ~ 255 (8 bits).

Returning to FIG. 9, the contents of the multi-value processing routine will be described. When this processing is started, the CPU reads the large dot level data LD (step S20).
2). Then, based on the magnitude relationship between the level data LD and the threshold th, it is determined whether the large dot is on or off (step S204).

As the threshold value th, a different value is set for each pixel by a so-called dither matrix. FIG. 11 is an explanatory diagram showing the concept of dot on / off determination by the dither method. For convenience of illustration, only some pixels are shown. As shown in FIG. 11A, the level of the large dot level data LD and the threshold stored in the corresponding pixel of the dither matrix are compared for each pixel. Level data L
When D is larger than the threshold value indicated in the dither table, the dot is turned on, and when the level data LD is smaller, the dot is turned off. In FIG. 11, the hatched pixels indicate the pixels that turn on the dots. FIG. 11A is an explanatory diagram showing the concept,
The level data and the threshold value of the dither matrix do not always correspond to actual data.

FIG. 12 is an explanatory diagram showing an example of a dither matrix in this embodiment. For convenience of illustration, 4
The dither matrix in which the threshold values 1 to 16 correspond to the size corresponding to the pixels of × 4 is shown. In the actual processing, a dither matrix having a size corresponding to 64 × 64 pixels is used. The dither matrix of this embodiment is
The setting is such that dots can be generated prior to the odd-numbered pixels in the main scanning direction. As illustrated, pixels included in odd columns c1 and c3 in the main scanning direction (hatched portions in the drawing) have smaller thresholds than pixels included in even columns c2 and c4. The eight pixels in the odd columns c1 and c3 have the value 1
Threshold values up to 〜8 correspond. Eight pixels in the even-numbered columns c2 and c4 correspond to thresholds of values 9 to 16. A small threshold value means that a dot is easily generated.
The dither matrix of the embodiment is set so that dots are dispersed and generated under such conditions. here,
Although a 4 × 4 matrix has been exemplified, each threshold value is similarly set in a 64 × 64 matrix so that dots are preferentially formed in odd columns. The reason for using such a setting matrix will be described later.

In step S204, when the level data LD is equal to or larger than the threshold value th, it is determined that the large dot should be turned on, and the data of binary "11" is added to the result value Rd indicating the formation of the large dot. substitute. Each bit of the result value Rd corresponds to ON / OFF of the drive waveforms W1 and W2 shown in FIG. When the value 11 of the result value RE is transferred to the driving buffer, a large dot is formed because ink is ejected by both the driving waveforms W1 and W2. In this case, ON / OFF determination of medium dots and small dots is not performed.

In step S204, when the level data LD is smaller than the threshold value, it is determined that the large dot should not be turned on, and the process proceeds to the determination of the medium dot on / off. The CPU reads medium dot level data Ldm based on the table shown in FIG. 10 (step S208). Then, the level data LD is corrected by adding this level data to the large level data LD (step S210). The level data L thus corrected
D is compared with the threshold th (step S21).
2). The threshold th is given by the same dither matrix as the large dot. The corrected level data LD is equal to the threshold value t.
h, it is determined that the dark medium dot should be turned on, and the binary value “01”, which means that, is set to the result value R.
Substitute for d. When the result value Rd is sent to the printer PRT, only the drive waveform W2 for forming a medium dot becomes valid, and a medium dot is formed. If it is determined that a medium dot should be formed, the determination of ON / OFF of the small dot is not performed.

FIG. 11B shows how to determine the ON / OFF state of the medium dot in this embodiment. FIG. 11B
The lower part in the middle is the level data Ldm of the middle dot. In the present embodiment, the sum of this level data and the previously read large dot level data LD is taken as corrected level data LD. Figure 11 shows the corrected level data.
This is shown in the upper part of (b). Level data LD after this correction
It is determined that the medium dot should be turned on for pixels equal to or larger than the threshold given by the dither table. Pixels indicated by hatching in FIG. 11B are pixels determined to be on. In comparison with FIG. 11A, it can be seen that the medium dot is turned on at a pixel that does not overlap with the large dot.

The reason why the on / off state of the medium dot is determined using the level data LD thus corrected will be described. As an extreme example, among the preset recording rate settings, consider an area where the gradation data is near the value 255, that is, an area where the level data of the medium dot is smaller than the level data of the large dot. For such an area, not the corrected level data LD but the medium dot level data Ld
When the on / off of the dot is determined using m itself, the pixel where the large dot is turned off (the level data LD of the large dot)
<Th), the middle dot level data Ld
Since m <th, the medium dot is also turned off.
As a result, the recording rate of the medium dot becomes 0%, and the preset recording rate cannot be realized. Even in a region where the level data of the medium dot is larger than the level data of the large dot, the recording rate of the medium dot is lower than the preset recording rate due to the same reason. In the present embodiment, the on / off state of the medium dot is determined based on the sum of the level data Ldm of the medium dot and the level data LD of the large dot, thereby forming the large dot and the medium dot in different pixels. , A predetermined recording rate is secured.

In step S212, if the level data LD is smaller than the threshold th, it is determined that the medium dot should not be turned on, and the process proceeds to the determination of the small dot on / off. The CPU reads the small dot level data Lds (step S216). The level data Lds is corrected by adding it to the level data LD (step S218). Since the sum of the level data of the large dot and the level data of the medium dot is stored in the level data LD before the correction, at this point, the total sum of the level data of the large dot, the medium dot, and the small dot is obtained after the correction. Is stored in the level data LD. Then, the magnitude of the corrected level data LD is compared with the threshold th (step S22).
0). The reason why the corrected level data LD is used to determine the on / off state of the small dot is based on the same reason as in the case of the medium dot. By judging on / off of dots using such data, it is possible to form small dots at a preset recording rate while avoiding overlapping of large dots and medium dots.

The threshold th is given by the same dither matrix as the large dot. If the corrected level data LD is equal to or larger than the threshold th, it is determined that the small dot should be turned on, and a binary value "10" indicating that is turned on is substituted for the result value Rd (step S222). . When the result value Rd is sent to the printer PRT, only the drive waveform W1 for forming a small dot becomes valid, and a small dot is formed. If the level data LD is smaller than the threshold th, it is determined that a small dot should not be formed, and the result value Rd
Is substituted for “00” in binary (step S224).
Thus, the CPU ends the multi-value processing routine.

With the above processing, it has been determined which dot should be formed for one pixel. CPU
Means that the processing is completed for all pixels (step S2
26), the above processing is repeated. When the processing is completed for all the pixels, the multi-value processing routine ends, and the process returns to the dot formation control processing routine.

Next, the CPU rasterizes the multi-valued data (step S300). This means that the data for one raster is rearranged in the order in which the data is transferred to the head of the printer PRT. In this embodiment, the overlap recording is performed. In the first main scan, dots are formed in odd-numbered pixels of each raster, and in the second main scan, dots are formed in even-numbered pixels. That is, each raster is 2
It will be formed by main scanning twice. The CPU transfers, to the head, data obtained by picking up every other dot of each raster as rasterization. Thus the printer P
When the data that can be printed by the RT is generated, the CPU transfers the data to the printer PRT (step S31).
0).

The printer PRT receives this data and executes printing. A process for the printer PRT to execute printing will be described. FIG. 13 is a flowchart of the dot formation routine. This routine is executed by the printer P
This is a process executed by the CPU in the control circuit 40 of the RT.

When the dot forming routine is started, CP
U inputs print data (step S402). The print data is data received from the computer PC,
This data specifies on / off of large dots, medium dots, and small dots for each pixel. Since the head of the printer PRT has 48 nozzles for each ink, in step S402, data for 48 rasters is input. Based on the data thus input, the CPU
Determines whether there is a pixel whose dot should be turned on in the next main scan (step S404). If only the value “00” indicating dot non-formation is input as raster print data corresponding to the next main scan, it is determined that there are no pixels to be turned on. The value "0
If any pixel other than “0” exists, it is determined that there is a pixel to be turned on.

If it is determined that there is a pixel to be turned on, the CPU sets data for main scanning (step S404). In order to drive each nozzle, print data is output to a drive circuit. When the main scanning data is set in this way, the CPU executes main scanning (step S406). Ink is ejected from each nozzle according to the print data, and dots are formed in each pixel. Since the printer PRT performs printing by the overlap method in which each raster is formed by two main scans,
In each main scan, a dot is formed on either the odd-numbered pixel or the even-numbered pixel of each raster.

When the main scanning is completed, the CPU conveys the paper as a sub-scan (step S410). The sub-scan feed amount is set in advance. On the other hand, step S
If it is determined in 404 that there is no pixel to be turned on, the CPU skips the execution of the main scan and executes the sub-scan.

The CPU repeatedly executes the above processing until the printing of the image is completed (step S412). Depending on the print data, main scanning may be performed, or main scanning may be omitted.

FIG. 14 is an explanatory diagram showing an example of dot recording. Here, the position of the head in the sub-scanning direction in each main scan is shown on the left side of the drawing, and the state of dots to be formed is shown on the right side of the drawing. The number in each symbol means the nozzle number. For convenience of illustration, a head having four nozzles at a three-dot pitch is illustrated here.

In FIG. 14, “○” indicates nozzles and dots corresponding to odd-numbered main scans, and “□” indicates nozzles and dots corresponding to even-numbered main scans. As shown in the drawing, if the sub-scan is executed with a feed amount equivalent to 2 dots, rasters r1, r2,... Can be formed in the range shown as the printable area in the figure, and an image can be printed. The reason why printing is not performed by the first to third nozzles in the first main scan is that an adjacent raster cannot be formed in subsequent main scans. For the same reason, there are nozzles that do not form dots in the second and subsequent main scans.

FIG. 15 is an explanatory diagram showing the state of dots formed in the low gradation area. Here, taking a 4 × 4 pixel as an example, the state of dots formed according to a change in gradation value is shown. The case where the multi-value conversion is performed using the dither matrix shown in FIG. 12 is illustrated. The figure shows a case where the gradation value gradually increases from the left side to the right side in the figure. As shown in FIG. 10, small dots are mainly formed in the low gradation area. Therefore, the number of small dots formed increases as the gradation value increases. The dots are formed in the dither matrix of FIG. As described above, the dither matrix is set so that dots are formed in preference to odd columns in the main scanning direction. Therefore, as shown in FIG. 15, the dots are formed prior to the odd-numbered rows.

The small dot recording rate is 50 on the right side of FIG.
%. This corresponds to the gradation value T1 in FIG. In the range below this tone value, dots are formed only on odd-numbered columns. As shown in FIG. 14, in the present embodiment, overlap recording is performed in which dots are formed in odd-numbered pixels in odd-numbered main scans and dots are formed in even-numbered pixels in even-numbered main scans. Do. In the gradation range shown in FIG. 15, dots are formed only in odd-numbered pixels, so that even-numbered main scanning is omitted (see step S404 in FIG. 13).

FIG. 16 is an explanatory diagram showing the state of dots formed in the intermediate gradation. As in FIG. 15, the state of the dots formed according to the change in the gradation value is shown. FIG.
This corresponds to a range of the middle gradation value T1 or more. At this gradation value, printing of medium dots is started. As shown in the flowchart of FIG. 13, the medium dot is turned on before the small dot.
An off determination is performed. Therefore, medium dots are generated in ascending order of pixels in the dither matrix having a smaller threshold. Since the sum of the recording rates of medium dots and small dots is set to 50%, small dots are sequentially replaced with medium dots. The right side of the figure shows the case where the recording rate of the medium dot becomes 50%. This corresponds to the gradation value T2 in FIG. In the range below this tone value, dots are formed only in odd-numbered pixels as shown. Therefore, as described with reference to FIG. 15, the even-numbered main scanning is omitted.

At the gradation values equal to or larger than the value T2, the medium dots are sequentially replaced with the large dots in the same manner as shown in FIG. In a region of a gradation lower than the gradation value at which the recording ratio of the large dot is 50%, that is, in the region D1 in FIG. 10, the overall recording ratio is maintained at 50% or less. Therefore, in such a range, the even-numbered main scanning is omitted.

FIG. 17 is an explanatory diagram showing the state of dots formed in the high gradation area. The state of the dots formed according to the change in the gradation value is shown. Area D1 in FIG.
At higher gradation values, 50% of large dots are recorded, and then small dots are formed in even-numbered pixels. The number of small dots increases with the gradation value. The recording rate of the entire dot gradually increases beyond 50%. The right side of FIG. 17 shows a case where a large dot is recorded at a recording rate of 50% and a small dot is recorded at a recording rate of 50%. This corresponds to the gradation value T3 in FIG.

As shown in FIG. 17, the overall recording rate is 50
When the value exceeds%, dots are formed in even-numbered pixels. Therefore, the even-numbered main scan is not necessarily omitted. However, for example, in a case where dots are formed in even-numbered pixels only in the upper-end raster as in the state shown on the left end in FIG. Only those corresponding to are executed. Other main scanning can be omitted. As the recording rate of the entire dot increases, the number of main scans that can be omitted gradually decreases. When the state shown at the right end of FIG. 17, that is, when the recording rate reaches 100%, it is necessary to execute all the main scans.

FIG. 18 is an explanatory view showing the state of dots formed in a higher gradation area. The value T in FIG.
At the gradation value of 3, medium dots are formed as the gradation value increases. The recording rate of large dots is maintained at 50%, and the overall recording rate is maintained at 100%. As shown, small dots are sequentially replaced with medium dots.
On the right side of FIG. 18, 50% of large dots and 50% of medium dots
The case where it was formed at the recording rate of

In these gradation ranges, the recording rate is 100%
Therefore, all main scanning is executed regardless of the gradation value. For tone values greater than the range shown in FIG. 18, medium dots are sequentially replaced with large dots in a similar manner. Since the recording rate is 100% even at these gradation values, all main scanning is performed regardless of the gradation values.

As described above, according to the printing apparatus of the present embodiment, high-quality printing in which banding due to a shift in the dot formation position is suppressed is realized by performing recording by the overlap method. At this time, printing can be performed in a relatively low gradation area included in the area D1 in FIG. 10 by omitting the even-numbered main scanning. For this reason, the number of main scans can be reduced, and the printing speed can be improved. As described above, according to the printing apparatus of the present embodiment, high-quality printing can be performed at high speed.

In the present embodiment, the multi-value processing is executed based on the recording rate shown in FIG. By performing multi-leveling using a table set so that the total sum of recording rates is 50% or less in a low gradation area, the number of main scans in a wide gradation range can be reduced. it can. FIG. 10B shows a recording rate as a comparative example. In the table of FIG. 10B, small dots are set to gradually increase until the recording rate reaches 100%. With the recording rate set in this way, after the recording rate of small dots reaches 100%, the recording rate is always maintained at 100%. When a table with such a setting is used, dots are formed only in pixels in odd columns only in the gradation range of the section D2 in the drawing.
Accordingly, the range in which the effect of improving the printing speed by reducing the number of main scans is narrowed.

Of course, the dot recording rate can be arbitrarily set within a range in which the gradation value can be appropriately expressed, and the present invention can be applied to any recording rate. However, FIG.
It is preferable to set the total recording rate in a wide range as shown in (a) from the viewpoint of improving the printing speed. In this embodiment, the case where each raster is formed by two main scans has been described as an example. Therefore, a recording rate set to be suppressed to 50% or less was applied. On the other hand, each raster can be formed by three or more main scans. In such a case, it is preferable to suppress the recording rate of each dot to a value equal to or less than the value corresponding to the ratio between the pixels formed in each main scan and the pixels constituting each raster.

In the above embodiment, the case where the dots are formed prior to the odd-numbered rows has been described as an example. Various modifications are conceivable for setting a pixel (hereinafter, referred to as a specific pixel) for forming a dot with priority. A first modification will be described. FIG. 19 is an example of a dither matrix in the first modification. As in the embodiment, a matrix corresponding to 4 × 4 pixels has been exemplified. In this matrix, dots are formed preferentially for hatched pixels. In the upper half, dots are preferentially formed in even-numbered pixels, and in the lower half, dots are preferentially formed in odd-numbered pixels.

FIG. 20 is an explanatory diagram showing how dots are formed in the first modification. The meanings of the symbols are the same as in FIG. In the embodiment, the dots are formed in the odd-numbered rows of pixels in the odd-numbered main scan, and the dots are formed in the even-numbered rows of pixels in the even-numbered main scan. On the other hand, in the modified example, the main scanning is performed by changing the pixels formed by the upper half and the lower half of the nozzle. That is, the first and second nozzles form pixels in even rows, and the third and fourth nozzles form pixels in odd rows.

When dots are recorded by such a method,
As shown, dots formed in odd-numbered main scans (dots represented by “○” in the figure) and dots formed in even-numbered main scans (dots represented by “□” in the figure) Dots) are arranged in a checkered pattern in units of two rasters. On the other hand, as is apparent from the dither matrix shown in FIG. 19, pixels in which dots occur preferentially are also arranged in a checkered pattern. Therefore, according to the modification, the odd-numbered main scanning can be omitted in the low gradation area.

In the embodiment, dots are formed side by side in the sub-scanning direction at a gradation value at which the dot recording rate is 50% (see FIG. 15). On the other hand, in the modified example, at the gradation value at which the recording rate becomes 50%, the pixels indicated by “□” in FIG. 20 are formed in a checkered pattern. Therefore, it is possible to suppress the occurrence of a so-called pseudo contour at such a recording rate.

As described above, the present invention is not applied only when the pixels in a predetermined column are set as specific pixels, and various pixels can be set as specific pixels according to the mode of main scanning and sub-scanning. it can. In such a case, it is desirable that the pixels to be formed in each main scan are unified with specific pixels or non-specific pixels. In this embodiment,
Pixels formed by odd-numbered main scans correspond to specific pixels, and pixels formed by even-numbered main scans correspond to non-specific pixels. In the modification, on the other hand, pixels formed in even-numbered main scans correspond to specific pixels, and pixels formed in odd-numbered main scans correspond to non-specific pixels. With this setting, the number of main scans can be reduced in a low gradation area, and the printing speed can be improved.

However, the present invention is not limited to the case where the pixels to be formed in each main scan are specified pixels or unspecified pixels. For example, the main scanning and the sub-scanning of the modified example (FIG. 20) and the multi-value processing using the dither matrix of FIG. 12 may be applied in combination. As already described, when the dither matrix of FIG. 12 is used, in the low gradation area, dots are formed in preference to the pixels in the odd columns. If the main scanning and the sub-scanning are performed in the mode shown in FIG. 20, dots are formed using only the third nozzle and the fourth nozzle in such an area.

In this case, since it is necessary to form dots in each main scan, the number of main scans cannot be reduced. However, in the low gradation area, it is not necessary to set data for the first nozzle and the second nozzle in each main scan, and the printing speed can be improved accordingly. In recent years, the number of nozzles provided in the head tends to increase, and the number of pixels forming each raster tends to increase. Therefore, since the data to be transferred to some of the nozzles becomes unnecessary, the processing load at the time of printing is greatly reduced.

In this embodiment, it has been described that the printer PRT determines whether or not to perform the main scanning (step S404 in FIG. 13). This determination may be made on the computer PC side. Rasterizing the dot formation control processing routine (FIG. 8) (step S30)
In (0), data arrangement is performed in consideration of the correspondence between each raster and the nozzle. At this time, it may be determined at the same time whether or not there is a dot formed in each main scan. It is assumed that the feed amount of the sub-scan is transferred to the printer PRT together with the print data in each main scan, and the feed amount of the sub-scan is changed according to the determination result of whether or not to perform the main scan. It is possible to realize the same control as shown in FIG.

A description will be given in accordance with the main scanning and sub-scanning modes shown in FIG. When the computer PC determines that the main scanning should be performed, the print data is output together with the data for performing the feed of two dots. Printer PR
T receives this data, executes a sub-scan corresponding to 2 dots, and then executes a main scan. If it is determined on the computer PC side that main scanning should be omitted, a value corresponding to two sub-scans, that is, data indicating that a feed of four dots is to be performed, and the next data that has been determined to be omitted should be performed. The print data corresponding to the main scan is output. The printer PRT receives this data, executes a sub-scan corresponding to 4 dots, and then executes a main scan. As a result, the same operation as that of omitting the main scanning once is realized. By controlling in this manner, the number of main scans can be reduced, the amount of data transferred from the computer PC to the printer PRT can be reduced, and the printing speed can be further improved.

In the embodiment and the modification described above, 4
The case where each raster is formed by two main scans with two nozzles has been exemplified. The present invention can be similarly applied to a case in which more nozzles are provided and a case where each raster is formed by many main scans. In the above explanation,
Although a printer capable of forming three types of dots, large, medium, and small, has been described as an example, the invention can be applied to a binary printer that can form only a single type of dot.

As a second modified example, a case where each raster is formed by three main scans will be described. FIG. 21 is an explanatory diagram showing the correspondence between pixels and main scanning in the second modification. Each square in the figure represents a pixel. Here, nine columns of pixels c1 to c9 are shown in the main scanning direction. In FIG. 21, the pixels in the hatched columns are 3n + 1
(N = 0 or an integer greater than or equal to) the number of main scans, that is,
.. Means pixels formed in the first, fourth,... Main scans. Blank pixels mean pixels formed by the main scanning of the number of times represented by 3n + 2 (n is an integer equal to or greater than 0), that is, the second main scanning, the fifth main scanning,. The filled pixel is 3
n means a pixel formed by the main scanning of the number of times represented by n (n = 1 or an integer), that is, the third, sixth,... main scanning.

FIG. 22 shows an example of a dither matrix in the second modification. Here, an example of a 6 × 6 dither matrix is shown. In the second modification, it is assumed that pixels are generated preferentially in the hatched columns in FIG. Therefore, as shown in FIG. 22, a small threshold value of 1 to 12 is set for the pixels corresponding to columns c1 and c4.
In this way, a raster can be formed only in the (3n + 1) th main scanning in the low gradation area.

In the second modified example, it is assumed that a dot is generated by giving priority to a blank pixel next to a hatched pixel. Therefore, in the dither matrix shown in FIG.
An intermediate threshold between values 13 to 24 is set for the pixels corresponding to columns c2 and c5. In this way, a raster can be formed only in the 3n + 1th and 3n + 2 main scans in an intermediate gradation region that cannot be expressed only by hatched pixels. Further, in a high gradation area, a raster is formed in all main scans.

When forming each raster in three main scans as in the second modification, halftone processing can be performed by changing the priority of pixels corresponding to each main scan stepwise. In this case, the main scanning can be efficiently omitted according to the gradation range, and the printing speed can be improved.
However, it is not always necessary to change the priority stepwise. A dot may be formed by giving priority only to the hatched pixels in FIG. 21, and blank pixels and solid pixels may be treated with the same priority. Conversely, dots may be preferentially formed in hatched pixels and blank pixels.

When three types of dots, large, medium and small, are used in the second modification, it is preferable to change the setting of the recording rate. FIG. 10A shows an example in which the recording rate of each dot is set while suppressing the total recording rate of the dots to 50% or less in the low gradation area. When each main scan is formed by three rasters, for example, the density of hatched pixels is 1
/ 3. Therefore, it is preferable to set the recording rate of each dot while suppressing the total recording rate of the dots in the low gradation area to 1/3 or less, for example, about 30%. In this way, an image can be printed only in the 3n + 1-th main scan in a wide gradation area. Similarly, in the gradation area where the recording rate exceeds 1/3, it is desirable to set the recording rate of each dot while suppressing the total recording rate of the dots to 2/3, for example, about 65%.

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 gist of the present invention. For example, the various processes described above may be executed by either the computer PC or the printer PRT. Further, it may be realized by any of software and hardware.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a schematic configuration of a printing apparatus as an embodiment.

FIG. 2 is an explanatory diagram illustrating functional blocks of the printing apparatus.

FIG. 3 is an explanatory diagram illustrating a schematic configuration of a printer PRT.

FIG. 4 is an explanatory diagram showing an arrangement of nozzles Nz in the ink ejection heads 61 to 66.

FIG. 5 is an explanatory diagram showing the principle of discharging ink in a head.

FIG. 6 is an explanatory diagram showing a relationship between a driving waveform of a nozzle Nz when ink is ejected and an ink Ip ejected.

FIG. 7 is an explanatory diagram showing drive waveforms and dot formation timings used in this embodiment.

FIG. 8 is a flowchart of a dot formation control processing routine.

FIG. 9 is a flowchart of a multi-value processing routine.

FIG. 10 is an explanatory diagram showing a table for giving recording rates of large dots, medium dots, and small dots.

FIG. 11 is an explanatory diagram showing a concept of dot on / off determination by a dither method.

FIG. 12 is an explanatory diagram illustrating an example of a dither matrix in the present embodiment.

FIG. 13 is a flowchart of a dot formation routine.

FIG. 14 is an explanatory diagram illustrating a dot recording example.

FIG. 15 is an explanatory diagram showing a state of dots formed in a low gradation area.

FIG. 16 is an explanatory diagram showing a state of dots formed in the intermediate gradation.

FIG. 17 is an explanatory diagram showing a state of dots formed in a high gradation area.

FIG. 18 is an explanatory diagram showing a state of a dot formed in an even higher gradation area.

FIG. 19 is an explanatory diagram of a dither matrix in a first modified example.

FIG. 20 is an explanatory diagram showing a state of dots formed by the overlap method.

FIG. 21 is an explanatory diagram showing the correspondence between pixels and main scanning in a second modified example.

FIG. 22 is an explanatory diagram of a dither matrix according to a second modification.

[Explanation of symbols]

 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 61 ... Ink ejection head 68 ink path 71, 72 ink cartridge 95 application program 96 printer driver 100 input unit 101 color correction processing unit 102 halftone processing unit 103 rasterizing unit 104 output unit 110 input unit 111 main scanning Unit 112 Sub-scanning unit 113 Head driving unit 115 Buffer

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C262 AA02 AA24 AB19 BB10 BB14 BB19 BB22 5C072 AA03 BA03 BA15 FA06 FA16 FB27 KA01 QA14 UA11 UA17 XA04 5C074 AA09 AA12 BB06 BB16 CC04 CC26 DD04 DD05 EE DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD DD LL18 MP01 MP08 NN04 NN10 PP20 PP33 PP62 PP68 PQ08 PQ20 PQ23 RR04 RR06 RR09 RR14 TT05

Claims (8)

[Claims] A main scanning unit that reciprocates a head relative to a printing medium; and a sub-scanning unit that conveys the printing medium relative to the head in a direction that intersects the main scanning direction. A printing apparatus that prints an image by forming dots on each pixel on the print medium, wherein the head is a head that includes a plurality of dot forming elements that form dots in the sub-scanning direction. An input unit for inputting image data, a halftone unit for performing halftone processing on the image data, and performing a main scan while driving the head, and performing a sub-scan with a predetermined feed amount to perform the main scan in the main scan direction. Dot forming control means for forming a raster as each dot row by a plurality of dot forming elements, wherein the halftone means is a part of a plurality of dot forming elements forming the raster. Printer to the particular pixels corresponding to the dot-forming elements is a half-tone processing means under conditions preferentially dots are formed. 2. The printing apparatus according to claim 1, wherein the halftone unit is formed by a storage unit that stores a correspondence relationship between each main scan and a raster according to the feed amount, and is formed by each main scan. And a setting unit for setting the specific pixel so that a plurality of rasters have a common priority in pixels formed in the main scanning. 3. The printing apparatus according to claim 2, wherein the dot formation control unit determines whether or not there is a pixel for which a dot is to be formed for each main scan, and a dot formation unit. A main scanning omitting unit that omits execution of the main scanning when it is determined that there is no pixel to be printed; 4. The printing apparatus according to claim 1, wherein said halftone means is a means for performing halftone by a dither method. 5. The printing apparatus according to claim 1, wherein the head is a head capable of forming a plurality of dots having different density evaluation values, and the halftone unit is configured to perform recording set in advance for each dot. Means for storing a rate, wherein at a predetermined tone value lower than a tone value expressed when a dot having a maximum density evaluation value is formed at the specific pixel, the recording rate of each dot is A printing apparatus, comprising: a recording rate storage unit that stores a recording rate set within a range where the total sum is equal to or less than a specific pixel density; and a unit that performs a halftone process based on the stored recording rate. 6. A main scan for reciprocating a head having a plurality of dot forming elements for forming dots relative to a print medium, and moving the print medium relative to the head in a direction intersecting the main scan direction. (A) inputting image data of the image, the method comprising: performing image-conveying sub-scanning to form a dot at each pixel on the print medium to print an image; b) Based on a sub-scan feed amount set in advance such that a plurality of dot forming elements correspond to each raster as a dot row in the main scanning direction.
(C) specifying a correspondence relationship between each raster and a plurality of dot forming elements; and (c) preferentially assigning dots to specific pixels corresponding to some dot forming elements among a plurality of dot forming elements forming each raster And (d) forming dots by performing the main scanning and the sub-scanning based on the result of the halftone processing under the condition where is formed. Printing method. 7. A computer-readable recording medium for recording a program for driving a printing apparatus for printing an image by repeatedly executing main scanning and sub-scanning of a head having a plurality of dot forming elements for forming dots. A function of specifying a correspondence relationship between each raster and a plurality of dot forming elements corresponding to the formation of the raster based on a preset sub-scan feed amount; and forming a plurality of dots forming each raster. A recording medium on which a program for realizing a function of performing halftone processing of the image data under a condition that dots are preferentially formed in specific pixels corresponding to some dot forming elements among the elements is recorded. 8. A recording medium in which a program for driving a printing apparatus that prints an image by repeatedly executing main scanning and sub-scanning of a head is recorded in a computer-readable manner, wherein dots are formed for each main scanning. A recording medium that records a program for realizing a function of determining whether or not a pixel to be formed exists and a function of omitting the execution of the main scanning when it is determined that there is no pixel to be formed. .