JP2005186378A - Printing with dot recording rate changed in accordance with printing environment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique to improve the reproducibility of colors by compensating a discharge error of the quantity of ink while suppressing adhesion of the ink to a printing device in printing to record as far as the end of a printing medium by using a plurality of kinds of dots different in size. <P>SOLUTION: The printing control device generates printing data to be supplied to a printing section for forming dots by discharging ink onto a printing medium. The printing control device receives error information showing an error in the quantity of ink of an ink drop to form a specific dot of at least one kind from among relatively small dots of a plurality of kinds of dots and compensates the error in the quantity of the ink in accordance with an area to which the pixel belongs and error information. The recording rate of a specific dot is adjusted to become low in a pixel belonging to the peripheral area of a printing paper than in a pixel belonging to the central area. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for printing an image on a printing medium by ejecting ink droplets, and more particularly to a printing technique capable of recording one pixel with dots of a plurality of types of sizes.

  In recent years, printers that eject a plurality of types of ink droplets of different sizes from the nozzles of a print head have become widespread as computer output devices. For example, as disclosed in Patent Document 1, an image is printed up to the end of a print sheet. Has also been realized. As one method for realizing such borderless printing, a method has been proposed in which ink ejected to the outside of the printing paper is absorbed by an ink absorbing material provided in a groove portion of the platen. On the other hand, as disclosed in Patent Document 2, high image quality is also achieved by compensating for errors in the ejection amount due to manufacturing variations of the print head.

Japanese Patent Laid-Open No. 2002-103586 Japanese Patent Laid-Open No. 11-99672 JP 2002-210945 A

  However, ink droplets of small size have the property of rapidly decelerating, so if they are ejected to areas other than printing paper, ink will mist and adhere to the printer before reaching the ink absorber. Problems may arise. On the other hand, if the dot distribution is performed so as to suppress the ejection of ink droplets of a size that tends to mist, there is a problem that the compensation of the error of the ink ejection amount does not function properly due to the variation in the distribution.

  The present invention has been made to solve the above-described problems in the prior art. In printing in which printing is performed up to the edge of a print medium using a plurality of types of dots having different sizes, the ink adheres to the printing apparatus. It is an object of the present invention to provide a technique for improving color reproducibility by compensating for an ink amount ejection error while suppressing the ink amount.

The present invention is a print control device that generates print data to be supplied to a printing unit in order to perform printing using a printing unit that forms dots by ejecting ink onto a printing medium,
The printing unit includes a print head having a plurality of nozzles and a plurality of ejection driving elements for ejecting ink droplets from the plurality of nozzles, respectively. Any of N types of dots having different sizes (N is an integer of 2 or more) can be selectively formed.
The print control device includes:
An error information receiving unit that receives error information indicating an error in the ink amount of an ink droplet for forming at least one kind of specific dot among relatively small dots among the N kinds of dots;
The given image data is divided into a peripheral area on the edge side of the print medium and a central area on the center side of the print medium, and each pixel according to the gradation value of each pixel of the image data A dot data generation unit for generating dot data representing the dot formation state in
With
The dot data generation unit
(A) a function of adjusting the recording rate of the specific dots for the same pixel value of the image data so that the pixels belonging to the peripheral region are lower than the pixels belonging to the central region;
(B) a function of generating dot data in which an error in the ink amount is compensated according to an area to which the pixel belongs and the error information;
It is characterized by having.

  According to the printing control apparatus of the present invention, error information indicating an error in the ink amount of an ink droplet for forming at least one type of specific dot among a plurality of types of dots having different sizes. Therefore, the error of the ink amount can be compensated for each specific dot even in printing in which the recording rate of the specific dot for the same pixel value of the image data is different between the peripheral portion and the central portion. it can. Thereby, in printing that reduces the recording rate of relatively small dots at the peripheral portion, it is possible to suppress a gradation difference between the central portion and the peripheral portion due to an ink amount error.

In the print control apparatus, the dot data generation unit includes:
A color conversion unit that converts the color system of the image data to generate multi-gradation data represented by a plurality of color components that can be used by the printing unit;
A color reduction processing unit that performs color reduction processing by converting the gradation value of the multi-gradation data into any of (N + 1) gradation values for each pixel;
With
The color conversion unit performs color conversion using the corrected color conversion table for the central region for the pixels belonging to the central region, and uses the corrected color conversion table for the peripheral region for the pixels belonging to the peripheral region. Color conversion,
The color reduction processing unit performs a color reduction process using the central area dot recording rate table for pixels belonging to the central area, and performs a color reduction process using the peripheral area dot recording rate table for pixels belonging to the peripheral area. Done
The peripheral region dot recording rate table is configured such that the recording rate of the specific dots for the same pixel value of the image data is lower than the central region dot recording rate table,
The corrected color conversion table for the central region is a reference color conversion table set on the assumption that there is no error in the ink amount, and the ink amount using the error information and the dot recording rate table for the central region. Is a table generated by adjusting to compensate for the error of
The peripheral area corrected color conversion table is generated by adjusting the reference color conversion table so as to compensate for the ink amount error using the error information and the peripheral area dot recording rate table. You may make it a table.

  In this way, since the dot distribution rate does not vary depending on the error information, it is possible to maintain an appropriate dot profile optimized from the viewpoint of suppressing graininess and banding.

In the print control apparatus, the dot data generation unit includes:
A color conversion unit that converts the color system of the image data to generate multi-gradation data represented by a plurality of color components that can be used by the printing unit;
A color reduction processing unit that performs color reduction processing by converting the gradation value of the multi-gradation data into any of (N + 1) gradation values for each pixel;
With
The color reduction processing unit performs a color reduction process using the corrected dot recording rate table for the central region for the pixels belonging to the central region, and uses the corrected dot recording rate table for the peripheral region for the pixels belonging to the peripheral region. To reduce the color
The corrected dot recording rate table for the central region is adjusted so that the error is compensated for the reference dot recording rate table for the central region set on the assumption that there is no error in the ink amount. Is a table generated by
The corrected dot recording rate table for the peripheral area is adjusted so that the error is compensated for the reference dot recording ratio table for the peripheral area set on the assumption that there is no error in the ink amount. Is a table generated by
The peripheral region reference dot recording rate table may be configured such that the specific dot recording rate for the same pixel value of the image data is lower than the central region reference dot recording rate table. .

  In this way, the present invention can be applied simply by adjusting the dot recording rate table.

  In the print control apparatus, when the print medium is roll paper, it is preferable that the peripheral area is set only on an end side parallel to the sub-scanning direction of the roll paper.

  The present invention relates to a printing apparatus, a computer program for causing a computer to implement the functions of the method or apparatus, a recording medium storing the computer program, a data signal including the computer program and embodied in a carrier wave, It can implement | achieve in various forms, such as.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Device configuration:
B. Print data generation processing in an embodiment of the present invention:
C. Compensation for ink drop ejection errors in embodiments of the present invention:
D. Variation:

A. Device configuration:
FIG. 1 is a block diagram showing the configuration of a printing system as an embodiment of the present invention. This printing system includes a computer 90 as a printing control device and a color printer 20 as a printing unit. The combination of the color printer 20 and the computer 90 can be called a “printing apparatus” in a broad sense.

  In the computer 90, 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 print data PD to be transferred to the color printer 20 is output from the application program 95 via these drivers. The application program 95 performs desired processing on the image to be processed, and displays the image on the CRT 21 via the video driver 91.

  The printer driver 96 includes a resolution conversion module 97, a color conversion module 98, a color reduction module 99, a print data generation module 100, a color conversion table LUT, an ink amount compensation unit 101, and an error information reception unit 102. And are provided. These functions will be described later. The color reduction module 99 has a recording rate table DT.

  The printer driver 96 corresponds to a program for realizing a function for generating print data PD. A program for realizing the function of the printer driver 96 is supplied in a form recorded on a computer-readable recording medium. Such recording media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter on which codes such as bar codes are printed, computer internal storage devices (such as RAM and ROM). A variety of computer-readable media such as a memory) and an external storage device can be used.

  FIG. 2 is a schematic configuration diagram of the color printer 20. The color printer 20 includes a sub-scanning drive unit that transports the printing paper P in the sub-scanning direction by the paper feed motor 22 and a main unit that reciprocates the carriage 30 in the axial direction (main scanning direction) of the paper feed roller 25 by the carriage motor 24. A scanning drive unit, a head drive mechanism that drives a print head unit 60 (also referred to as “print head assembly”) mounted on the carriage 30 to control ink ejection and dot formation, and these paper feed motors 22, A control circuit 40 that controls the exchange of signals with the carriage motor 24, the print head unit 60, and the operation panel 32 is provided. The control circuit 40 is connected to the computer 90 via the connector 56.

  The print head unit 60 has a memory (not shown) that stores error information indicating an error in ink discharge amount. The control circuit 40 reads out error information from this memory and transmits it to the computer 90 via the connector 56. The transmitted error information is received by the error information receiving unit 102 (FIG. 1) in the computer 90.

  Error information is stored for each large, medium, and small dot. An error in the ink ejection amount is caused by a change in the size of the ink droplet Ip. This variation is caused by an ink passage manufacturing error described later and individual differences of piezoelectric elements PE described later.

  The sub-scanning drive unit that transports the printing paper P includes a gear train (not shown) that transmits the rotation of the paper feed motor 22 to the paper feed roller 25. The main scanning drive unit that reciprocates the carriage 30 is an endless drive between the carriage motor 24 and a slide shaft 34 that is installed in parallel with the axis of the paper feed roller 25 and slidably holds the carriage 30. A pulley 38 that stretches the belt 36 and a position sensor 39 that detects the origin position of the carriage 30 are provided.

  FIG. 3 is an explanatory diagram illustrating a state in which the end portion of the printing paper P is printed. Two nozzles # 1 and # 2 of the print head 28 are disposed on the opening of the downstream groove 126r, and two nozzles # 7 are disposed on the opening of the upstream groove 126f and on the platen frame 125. , # 8 and other nozzles # 3, # 4, # 5, and # 6 are respectively arranged. Further, as shown in FIG. 3B, the side end portion Ps of the printing paper P is disposed on the opening of the side groove portion 126s. The groove portions such as the downstream groove portion 126r, the upstream groove portion 126f, and the side groove portion 126s are respectively provided with ink absorbing materials 127r, 127f, and 127s for absorbing ink.

  Since the four nozzles # 1, # 2, # 7, and # 8 are arranged on the openings of the downstream groove 126r and the upstream groove 126f, the printing paper P is sub-sided unless the discharged ink becomes mist. Even if ink is ejected before reaching by scanning feed, the platen frame 125 and the roller 25d are not stained with ink.

  The color printer 20 performs printing while feeding the printing paper P in the sub-scanning direction by at least one of the upstream paper feed rollers 25a and 25b and the downstream paper feed rollers 25c and 25d. The upstream paper feed rollers 25a and 25b and the downstream paper feed rollers 25c and 25d correspond to the paper feed roller 25 described above.

  FIG. 3A shows a state in which printing is performed on the leading end portion Pf of the printing paper P. The two nozzles # 1 and # 2 start ink ejection slightly before the leading end portion Pf of the printing paper P is sent to a position where these nozzles can record. As a result, even if there is a paper feed error, printing can be performed without creating a margin up to the front end portion Pf of the printing paper P without staining the platen frame 125 and the roller 25d with ink.

  FIG. 3B shows a state where printing is performed on the side end portion Ps of the printing paper P. Since the side end portion Ps of the printing paper P is disposed on the opening of the side groove portion 126s, similarly, printing can be performed without creating a margin up to the side end portion Ps of the printing paper P.

  FIG. 3C shows a state where printing is performed on the rear end portion Pr of the printing paper P. The two nozzles # 7 and # 8 stop ejecting ink after the trailing edge Pr of the printing paper P passes through a position where these nozzles can record. Thus, even if there is a paper feed error, printing can be performed without creating a margin up to the rear end portion Pr of the printing paper P without staining the platen frame 125 and the like with ink.

  However, when the size of the ink droplet is too small, the ejected ink droplet is not absorbed by the ink absorbents 127r, 127f, and 127s, and there is a problem that the ink droplet may float in the color printer 20. In the present invention, this problem is solved by prohibiting the ejection of small dots at the edge of the printing paper P.

  FIG. 4 is an explanatory diagram showing the nozzle arrangement on the lower surface of the print head 28. On the lower surface of the print head 28, a black ink nozzle row K for discharging black ink, a cyan ink nozzle row C for discharging cyan ink, a magenta ink nozzle row M for discharging magenta ink, A yellow ink nozzle row Y for discharging yellow ink is formed.

  Each nozzle is provided with a piezo element, which will be described later, as an ejection driving element for driving each nozzle to eject ink droplets. During printing, ink droplets are ejected from each nozzle while the print head 28 moves in the main scanning direction.

  FIG. 5 is an explanatory diagram showing the structure of the nozzle Nz and the piezo element PE. The piezo element PE is installed at a position in contact with the ink passage 68 that guides ink to the nozzle Nz. In the present embodiment, by applying a voltage between the electrodes provided at both ends of the piezo element PE, one of the side walls of the ink passage 68 is deformed to eject the ink droplet Ip from the tip of the nozzle Nz at a high speed. .

  FIG. 6 is an explanatory diagram showing the relationship between the two types of drive waveforms of the nozzle Nz when ink is ejected and the two ink droplets IPs and IPm ejected. FIG. 6A shows a driving waveform for ejecting small ink droplets IPs capable of forming small dots by itself, and FIG. 6B shows a medium ink droplet IPm capable of forming medium dots by itself. The drive waveform for discharging is shown. In this embodiment, the small dots correspond to “specific dots” in the claims.

The small ink droplet IPs can be ejected from the nozzle Nz through two processes, an ink absorption process and an ink ejection process, as described below.
(1) Ink supply process (d1s): In this process, the ink passage 68 (FIG. 5) is expanded and ink is supplied from an ink tank (not shown) to the ink passage 68. Expansion of the ink passage 68 is performed by lowering the potential applied to the piezo element PE and contracting it.
(1) Ink ejection process (d2): In this process, the ink passage 68 is compressed and ink is ejected from the nozzles Nz. The ink passage 68 is compressed by increasing the potential applied to the piezo element PE and expanding it.

  The middle ink droplet IPm can be ejected in the same manner as the small ink droplet IPs by lowering the potential relatively slowly as shown in FIG. 6B during the ink absorption process. This is because more ink can be supplied from an ink tank (not shown) if the ink passage 68 is slowly expanded by slowly lowering the potential.

  As described above, when the rate of decreasing the potential is increased, the ink interface Me shifts to the inner side of the nozzle Nz as shown in FIG. Ink droplets become smaller. On the other hand, when the potential decrease rate is slowed down, the ink interface Me shifts to the inside of the nozzle Nz as shown in FIG. Becomes larger. In this embodiment, the size of the ink droplet is changed by changing the potential change rate in the ink supply process in this way.

  FIG. 7 is an explanatory diagram showing a state in which dots of three sizes of large, medium, and small are formed at the same position using the small ink droplet IPs and the medium ink droplet IPm. The drive waveform W1 is a waveform for ejecting small ink droplets IPs, and the drive waveform W2 is a waveform for ejecting medium ink droplets IPm. As can be seen from FIG. 7, in this embodiment, after the drive waveform W1 for ejecting the small ink droplet IPs is output, the drive waveform W2 for ejecting the middle ink droplet IPm is output after a predetermined time has elapsed. Yes.

  The reason why the two drive waveforms W1 and W2 are output to the piezo element PE at such timing is to make the landing positions of the small ink droplet IPs and the medium ink droplet IPm coincide. That is, as can be seen from FIG. 7, when the small ink droplet IPs having a relatively low average flying speed is ejected first, and the medium ink droplet IPm having a relatively high average flying speed is ejected after a certain period of time, the landing position is reached. Can be matched. The average flying speed means an average value of the flying speed from ejection to landing, and decreases when the deceleration rate is large.

  The color printer 20 having the hardware configuration described above moves the carriage 30 back and forth by the carriage motor 24 while transporting the printing paper P by the paper feed motor 22 and simultaneously drives the piezo elements of the print head 28 so that each color. Ink droplets are ejected to form large, medium, and small ink dots to form a multi-color, multi-tone image on the printing paper P.

B. Print data generation processing in an embodiment of the present invention:
FIG. 8 is a flowchart showing a routine of print data generation processing in the embodiment of the present invention. The print data generation process is a process performed by the computer 90 to generate print data PD to be supplied to the color printer 20. It is assumed that the printing mode is set so that printing is performed up to the edge of the printing paper P.

  In step S100, the printer driver 96 (FIG. 1) inputs image data from the application program 95. This input process is performed in response to a print command from the application program 95. Here, the image data is assumed to be RGB data.

  In step S110, the resolution conversion module 97 converts the resolution of the input RGB image data (that is, the number of pixels per unit length) to a predetermined print resolution. The predetermined printing resolution is a resolution having an area where printing can be performed up to the end of the printing paper P.

  FIG. 9 is a plan view showing the relationship between the image data area subjected to resolution conversion and the printing paper P. As can be seen from FIG. 9, the image data area is wider than the area of the printing paper P. As a result, regardless of the sub-scan feed error of the printing paper P or the landing error of the middle ink droplet IPm, the middle ink droplet IPm can be landed to the end of the printing paper P.

  However, the area of the image data is within a range in which the medium ink droplet IPm that has not landed on the printing paper P does not land outside the groove (FIG. 3) such as the upstream groove 126f, the downstream groove 126r, and the side groove 126s. Limited. The reason for this limitation is to prevent the medium ink droplet IPm from landing on the platen frame 125 of the color printer 20.

  On the other hand, the prevention of landing of the small ink droplets IPs on the platen frame 125 is realized by controlling so that the small ink droplets IPs are ejected only in the central region and the small ink droplets IPs are not ejected outside the central region. . The central region is a region set so that the small ink droplets IPs do not land outside the printing paper P regardless of errors such as the sub-scan feed error of the printing paper P and the landing errors of the small ink droplets IPs.

  The central region is set because when the small ink droplets IPs land on the outside of the printing paper P, they may float due to deceleration or be repelled by the ink absorbers 127r, 127f, 127s and become mist. . The reason why the small ink droplets IPs are repelled by the ink absorbers 127r, 127f, and 127s is that the small ink droplets IPs are small, so that the surface tension becomes the main factor governing the physical behavior of the small ink droplets IPs.

  In this embodiment, an area excluding an area corresponding to the outside of the printing paper P and an area corresponding to an error range such as a sub-scan feed error and an ink droplet landing error inside the printing paper P is referred to as a central area. Call. In the present embodiment, an area other than the central area in the image data area and surrounding the central area is referred to as a peripheral area.

  However, for example, when it is assumed that there is no error, an area corresponding to the inside of the printing paper P may be set as the central area, or more widely corresponding to the outside of the printing paper P when it is assumed that there is no error. A region that slightly protrudes from the region to be performed may be set as the central region.

  In step S120, the color conversion module 98 refers to the color conversion table LUT, and converts the RGB image data for each pixel into multiple gradations of the plurality of ink colors (FIG. 4) that can be used by the color printer 20. Convert to data. The color conversion table LUT includes a central area table and a peripheral area table.

  The color conversion module 98 performs color conversion for the pixels belonging to the central area using the table for the central area, and performs color conversion for the pixels belonging to the peripheral area using the table for the peripheral area. The reason for switching the table according to the region to which the pixel belongs will be described later. The multi-gradation data generated in this way has, for example, 256 gradation values.

  In step S200, the color reduction module 99 performs color reduction processing. The color reduction process is a process of reducing 256 gradations, which is the number of gradations of multi-gradation data, to 4 gradations, which is the number of gradations that the color printer 20 can express with each pixel. In the present embodiment, these four gradations are expressed by “no dot formation”, “small dot formation”, “medium dot formation”, and “large dot formation”.

  FIG. 10 is a flowchart showing the flow of color reduction processing in the embodiment of the present invention. In step S210, the color reduction module 99 selects the recording rate table DT used in the color reduction processing. This selection is performed depending on whether the pixel subject to color reduction belongs to the central region (FIG. 9) or the peripheral region.

  FIG. 11 is an explanatory diagram showing a dot recording rate table used for determining level data for three sizes of large, medium, and small dots. FIG. 11A shows a dot recording rate table DTmid for the central region of the printing paper and a dot recording rate table DTend for the peripheral region of the printing paper.

  The recording rate table DTmid for the central area shown in FIG. 11A is configured to express gradation values of multi-gradation data using dots of three sizes, large, medium and small. The recording rate table DTend for the peripheral area shown in FIG. 11B is configured to express gradation values of multi-gradation data using only two large and medium size dots. However, by replacing small dots with medium dots corresponding to substantially the same ink amount, the ink discharge amount per unit area corresponding to each gradation value is made substantially the same.

  FIG. 11B shows details of the dot recording rate table DTmid for the central area. The horizontal axis represents the gradation value (0 to 255), the left vertical axis represents the dot recording rate (%), and the right vertical axis represents the level data (0 to 255). Here, the “dot recording rate” means a ratio of pixels in which dots are formed among pixels in the region when a uniform region is reproduced according to a certain gradation value. In FIG. 11B, the curve SD indicates the small dot recording rate, the curve MD indicates the medium dot recording rate, and the curve LD indicates the large dot recording rate.

  FIG. 12 is an explanatory diagram showing the dot recording rate table DTmid for the central region and the ink discharge amount. FIG. 12A is a diagram showing the relationship between the gradation value of multi-gradation data and the dot recording rate of each size dot, and the curves SD, MD, and LD are dotted lines in FIG. 11B. Same as SD, MD, LD. FIG. 12B is an explanatory diagram showing the relationship between the gradation value and the weight of ink ejected to a predetermined area. The ink weight is generated using the design value of the ink drop weight. Here, the design values of the ink droplet weights of the small, medium, and large sizes are 10 ng, 20 ng, and 30 ng.

  As can be seen from FIG. 12B, when the gradation value increases from 0 to 255, the ink discharge amount increases from 0 ng to 7650 ng along the straight line Wi. As described above, in this embodiment, in order to make the explanation easy to understand, it is assumed that the ink weight ejected to a predetermined region and the gradation value have a linear relationship.

As can be seen from FIGS. 12A and 12B, the weight of the ink ejected to the predetermined area increases as follows according to the increase in the gradation value.
(1) In the region from the gradation value 0 to the gradation value G1, the ink weight increases linearly as the dot recording rate of small dots increases.
(2) In the area from the gradation value G1 to the gradation value G2, the dot recording rate of small dots is constant, and the ink weight increases linearly as the dot recording rate of medium dots increases.
(3) In the area from the gradation value G2 to the gradation value G3, the dot recording rate of small dots and medium dots is constant, and the ink weight increases linearly as the dot recording rate of large dots increases.
(4) In the area from the gradation value G3 to the maximum gradation value, the dot recording rate of small dots and medium dots starts to decrease, and the ink weight is linearly replaced by replacing the small dots and medium dots with large dots. Will increase.

In the present embodiment, such a profile is generated as a result of the following trade-off.
(1) In order to suppress graininess (image roughness), it is preferable to increase the dot recording rate of relatively small dots. Such characteristics are remarkable in a low gradation region.
(2) In order to reduce banding (striped image quality degradation), it is preferable to reduce the dot recording rate of relatively small dots by replacing relatively small dots with relatively large dots. Such characteristics are remarkable in a high gradation region.
For this reason, in this embodiment, the upper limit of the dot recording rate for small dots is set to 25%, and the upper limit of the dot recording rate for medium dots is set to 50%.

  In step S220 (FIG. 10), the color reduction module 99 sets the large dot level data LVL as follows. The level data refers to data obtained by converting the dot recording rate into 256 levels from 0 to 255. The level data LVL is data obtained by converting the dot recording rate of large dots, the level data LVM is data obtained by converting the dot recording rate of medium dots, and the level data LVS is data obtained by converting the dot recording rate of small dots. It is. For example, in the example shown in FIG. 11B, if the gradation value of multi-gradation data is gr1, the large dot level data LVL is obtained as zero using the curve LD, and the medium dot level data is obtained. The LVM is obtained as Lm1 using the curve MD, and the small dot level data LVS is obtained as Ls1 using the curve SD.

  In step S230, the level data LVL thus set and the threshold value THL are compared. Here, for example, dot on / off determination is performed by a systematic dither method. The dither threshold THL used in the systematic dither method is set to a different value for each pixel by a so-called dither matrix. In this embodiment, a matrix in which values 0 to 254 appear in a 16 × 16 square pixel block is used.

  FIG. 13 is an explanatory diagram showing the concept of dot formation by the systematic dither method. For the sake of illustration, only some pixels are shown. As shown in FIG. 13, each pixel of the level data LVL is compared with the size of the corresponding portion of the dither table. If the level data LVL is larger than the threshold value THL shown in the dither table, a dot is formed, and if the level data LVL is smaller, no dot is formed. The hatched pixels in FIG. 13 mean pixels that form dots.

  In step S230, when the level data LVL is larger than the threshold value THL, it is determined that a large dot should be formed (step S281). On the other hand, if the level data LVL is smaller than the threshold value THL in step S230, it is determined that a large dot should not be formed, and the process proceeds to step S240.

  In step S240, medium dot level data LVM is set. The setting method is the same as that for setting the large dot level data LVL. If the level data LVM is larger than the threshold value THM in step S250, it is determined that a medium dot should be formed (step S282). On the other hand, if the level data LVM is smaller than the threshold value THM in step S250, it is determined that medium dots should not be formed, and the process proceeds to step S260.

  In step S260, small dot level data LVS is set. The setting method is the same as the setting of the level data LVL and LVM for large dots and medium dots. If the level data LVS is larger than the threshold value THS in step S270, it is determined that a small dot should be formed (step S283). On the other hand, if the level data LVS is smaller than the threshold value THS in step S270, it is determined that no dot should be formed (step S284).

  When the above process is performed for all pixels (step S290), the process proceeds to step S300 (FIG. 8).

  In step S300, the print data generation module 100 rearranges the dot data representing the dot formation state in each pixel in the order of data to be transferred to the color printer 20, and outputs the data as final print data PD. The print data PD includes raster data indicating the dot recording state during each main scan and data indicating the sub-scan feed amount.

  As described above, the present embodiment is configured such that the pixels belonging to the peripheral region and the pixels belonging to the central region have different recording rates for small dots and medium dots for the same pixel value. In such a configuration, in order to appropriately compensate the ink amount error, the following compensation process is performed in the present embodiment.

C. Compensation for ink drop ejection errors in embodiments of the present invention:
FIG. 14 is an explanatory diagram showing a compensation method for an error in the ink amount in the central region. The dotted line Wi is a line indicating the relationship between the gradation value and the ink ejection amount (design value) when there is no error, and is the same as the straight line Wi in FIG. A solid line We is a line indicating a relationship between the gradation value and the predicted ink discharge amount when an ink amount error is taken into consideration. The solid line We is a diagram generated based on the dot recording rate table DTmid using the predicted ink droplet weight values in the table shown in FIG. The solid line We deviates from the dotted line Wi by an error in the ink amount of each size included in the predicted value.

  In this embodiment, the gradation value of the multi-gradation data is adjusted as follows. For example, when the gradation value is G, the ink ejection amount (design value) on the assumption that there is no ink amount error is Rt on the dotted line Wi. However, since the ink amount error is actually predicted, it is predicted. The ink discharge amount is Re. As a result, at the gradation value G, it is predicted that a difference will occur between the ink discharge amount (design value) Rt and the predicted ink discharge amount Re. This difference becomes an error in the ink amount to be compensated.

  This difference is compensated by converting the gradation value as follows. For example, when the input gradation value is G, the ink discharge amount (design value) is the ink discharge amount Rt corresponding to the Pt point on the dotted line Wi. The Pc point is determined by searching on the solid line We for a gradation value that can eject the ink amount closest to the ink ejection amount Rt. The gradation value Gc corresponding to this Pc point becomes the adjusted output gradation value. In this way, the input gradation value G is converted to the output gradation value Gc.

  FIG. 15 is an explanatory diagram showing the dot recording rate table DTmid for the central region and the ink discharge amount. FIG. 15A is a table generated using the ink amount design value. For example, when the input gradation value is 106, 64 small dots are formed and 128 medium dots are formed, but no large dots are formed. On the other hand, the design value of the ink drop weight is 10 ng for small dots and 20 ng for medium dots. As a result, as shown in the figure, it is assumed in the color reduction process that 640 ng of ink is formed to form small dots, 2560 ng of ink is formed to form medium dots, and a total of 3200 ng of ink is ejected. I understand.

  FIG. 15B is a dot recording rate table DT generated using the predicted ink amount. It is known from the error information that the weight of the ink droplet is 11 ng for the small dot and 17 ng for the medium dot. As a result, if the gradation is not adjusted, 704 ng (= 11 ng × 64) of ink is formed to form a small dot, 2176 ng (= 17 ng × 128) of ink is formed to form a medium dot, and a total of 2880 ng of ink is obtained. Expected to be discharged. Since this value is smaller than the amount of ink desired for accurate color reproduction, it can be seen that if it is not compensated, a color having a lower gradation than the color desired to be reproduced is reproduced.

  FIG. 16 is a conversion table for the central region used for adjusting the gradation value in the pixels belonging to the central region. This conversion table is a table for adjusting the gradation value so that the ink amount predicted to be ejected is close to the ink amount desired to be ejected. For example, when the input gradation value that is the gradation to be expressed is 106, 115 corresponds to the output gradation value. As a result, it can be seen that the ink amount predicted to be ejected is changed from 2880 ng to 3204 ng, and approaches 3200 ng, which is the ink amount desired to be ejected.

  FIG. 17 is an explanatory diagram illustrating a method of compensating for an ink amount error in the peripheral region. The dotted line Wi is a line indicating the relationship between the gradation value and the ink ejection amount (design value) when there is no error, and is the same as the straight line Wi in FIG. A solid line We ′ is a line indicating the relationship between the gradation value and the predicted ink ejection amount when an ink amount error is taken into consideration. The solid line We ′ is a diagram generated based on the dot recording rate table DTend using the predicted ink droplet weight values in the table shown in FIG. The solid line We 'is different from the solid line We in FIG. This is because the solid line We 'is formed with the weight of ink droplets for forming two sizes of medium dots and large dots, unlike the solid line We.

  FIG. 18 is an explanatory diagram showing the dot recording rate table DTend for the peripheral area and the ink ejection amount. FIG. 18A is a table generated using the ink amount design value. For example, when the input gradation value is 106, 160 medium dots are formed, but small dots and large dots are not formed. On the other hand, since the design value of the ink drop weight is 20 ng for the medium dot, it can be understood that 3200 ng of ink is ejected by only the medium dot in the color reduction process.

  FIG. 18B is a dot recording rate table DT generated using the predicted ink amount. Since the weight of the ink droplet for forming the medium dot is 17 ng, it is predicted that 2703 ng of ink will be ejected if the gradation is not adjusted.

  FIG. 19 is a peripheral area conversion table used for adjustment of gradation values in pixels belonging to the peripheral area. In this conversion table, an output gradation value of “119” corresponds to an input gradation value of “106”. On the other hand, in the central area conversion table, an output gradation value of “115” corresponds to an input gradation value of “106”. Thus, it can be seen that the conversion contents are different between the central area and the peripheral area. This is because the distribution ratios of small dots and medium dots are different.

  These conversion tables are used for adjusting the color conversion table. Specifically, the central area conversion table is used for adjusting the color conversion table for the central area, and the peripheral area conversion table is used for adjusting the color conversion table for the peripheral area.

Adjustment of each color conversion table is executed according to installation of the printer driver 96 or replacement of the print head unit 60. This adjustment is performed in the following sequence.
(1) The computer 90 reads error information from the memory of the print head unit 60 via the control circuit 40 of the printer 20. The read error information is received by the error information receiving unit 102 in the computer 88 and sent to the ink amount compensating unit 101.
(2) The ink amount compensation unit 101 generates a conversion table for each of the central region and the peripheral region, and adjusts the output value of the color conversion table for each region using this conversion table.
(3) The computer 90 is set to execute color conversion using the two tables adjusted in this way.

  As a result, the color conversion module 98 performs color conversion using the table in which the ink amount error is compensated for the central region for the pixels belonging to the central region, and the ink for the peripheral region for the pixels belonging to the peripheral region. The color conversion is performed using a table in which the amount error is compensated.

  As described above, in this embodiment, in printing in which printing is performed up to the edge of the printing medium using a plurality of types of dots having different sizes, the ejection error of the ink amount is set as the central region while suppressing adhesion of ink to the printing apparatus. The color reproducibility can be improved by compensating for each of the peripheral areas.

D. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D-1. In the above-described embodiment, the ink amount ejection error is compensated by adjusting the color conversion table. However, for example, it may be configured to compensate by adjusting the dot recording rate table. The ink amount error compensation performed in the present invention may be configured to be performed according to the region to which the pixel belongs and the error information. However, the former has an advantage that an ink amount error can be compensated while maintaining an optimized dot profile from the viewpoint of suppressing graininess and banding, and the latter has each advantage stored in the dot recording rate table. There is an advantage that the present invention can be easily applied by simply multiplying the recording rate of the size dots by the reciprocal of the error information.

D-2. In the above-described embodiment, the dot recording rate is changed stepwise in the central region and the peripheral region. For example, the dot recording rate is the same at the boundary between the central region and the peripheral region, and the edge of the printing paper is changed. The recording rate may be changed toward the part. This has the advantage that the gradation difference at the boundary between the central region and the peripheral region can be further reduced.

D-3. In the above-described embodiment, the specific dot is only the small dot. However, for example, the small dot and the medium dot may be configured as the specific dot. In this case, it is preferable to set the dot recording rate so that these specific dots are replaced with large dots in the peripheral region and the central region. In general, the specific dot of the present invention may be at least one kind of relatively small dots among a plurality of kinds of dots having different sizes. Further, it is not always necessary to prohibit the formation of specific dots as in the above embodiment, and the recording rate of specific dots may be suppressed.

D-4. In the above-described embodiment, the printing paper P, which is a rectangular cut paper, is used as the printing medium, but the present invention can also be applied to printing on roll paper that is long in the sub-scanning direction. However, when printing on roll paper, it is preferable to set a peripheral region or a transition region only on the end side parallel to the sub-scanning direction of the print medium in the image data region as shown in FIG. . In this way, for example, when printing a plurality of images on roll paper, it is possible to reduce the burden of data processing on the end side parallel to the main scanning direction of the print medium in the image data area, and to record specific dots. There is an advantage that it is possible to prevent deterioration in image quality due to a decrease in rate.

D-5. In the above-described embodiment, an ink jet printer including a piezo element has been described as an example. However, various types of printers such as a printer that discharges ink with bubbles generated in ink by energizing a heater provided in a so-called nozzle are used. Applicable to printing devices.

D-6. In the above-described embodiment, a printer that can selectively form any one of three types of dots having different sizes in a pixel area on a print medium using each nozzle is used. Or a printer capable of selectively forming four or more types of dots. The printer used in the present invention can selectively form any of N types of dots (N is an integer of 2 or more) of different sizes in a pixel area on the print medium using each nozzle. It ’s fine.

D-7. In the above-described embodiment, the gradation value is reduced using systematic dither. However, the gradation value may be reduced using another color reduction processing method such as error diffusion or a density pattern method. Note that the pixels in the image data and the pixels on the print medium do not necessarily have a one-to-one correspondence, and a plurality of pixels on the print medium may correspond to one pixel in the image data.

D-8. The present invention can be applied not only to color printing but also to monochrome printing. Further, the present invention can be applied to printing that expresses multiple gradations by expressing one pixel with a plurality of dots.

D-9. In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced by hardware. For example, part or all of the functions of the printer driver 96 shown in FIG. 1 can be executed by the control circuit 40 in the printer 20. In this case, part or all of the functions of the computer 90 serving as a print control apparatus for creating print data are realized by the control circuit 40 of the printer 20.

  When some or all of the functions of the present invention are realized by software, the software (computer program) can be provided in a form stored in a computer-readable recording medium. In the present invention, the “computer-readable recording medium” is not limited to a portable recording medium such as a flexible disk or a CD-ROM, but an internal storage device in a computer such as various RAMs and ROMs, a hard disk, and the like. An external storage device fixed to the computer is also included.

1 is a block diagram showing a configuration of a printing system as an embodiment of the present invention. 1 is a schematic configuration diagram of a color printer 20. FIG. FIG. 3 is an explanatory diagram illustrating a state in which an end portion of the printing paper P is printed. FIG. 3 is an explanatory diagram showing a nozzle arrangement on the lower surface of the print head. Explanatory drawing which shows the structure of the nozzle Nz and the piezo element PE. Explanatory drawing which showed the relationship between the two types of drive waveforms of the nozzle Nz when ink is ejected, and the two ink droplets IPs and IPm ejected. Explanatory drawing which shows a mode that the dot of three sizes of large, medium, and small is formed in the same position using small ink drop IPs and medium ink drop IPm. 6 is a flowchart illustrating a routine of print data generation processing according to the embodiment of the present invention. FIG. 4 is a plan view showing a relationship between a region of image data subjected to resolution conversion and a printing paper P. 6 is a flowchart showing a flow of color reduction processing in the embodiment of the present invention. Explanatory drawing which shows the dot recording rate table utilized for the determination of the level data of three sizes of large, medium, and small. FIG. 6 is an explanatory diagram showing a dot recording rate table DTmid for the central region and ink discharge amount. Explanatory drawing which shows the idea of the presence or absence of the dot formation by an organized dither method. FIG. 5 is an explanatory diagram illustrating a method for compensating for an ink amount error in a central region. FIG. 6 is an explanatory diagram showing a dot recording rate table DTmid for the central region and ink discharge amount. The conversion table for center areas used for adjustment of a gradation value in the pixel which belongs to a center area. FIG. 5 is an explanatory diagram illustrating a method for compensating for an ink amount error in a peripheral region. Explanatory drawing which shows the dot recording rate table DTend for peripheral areas, and the ink discharge amount. 6 is a peripheral area conversion table used for adjusting gradation values in pixels belonging to the peripheral area. The top view which shows the relationship between the area | region of the image data in the modification, and the printing paper R which is roll paper.

Explanation of symbols

20 ... Color printer 21 ... CRT
DESCRIPTION OF SYMBOLS 22 ... Paper feed motor 24 ... Carriage motor 25 ... Paper feed roller 25a ... Upstream paper feed roller 25c ... Downstream paper feed roller 25d ... Roller 28 ... Print head 30 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive Belt 38 ... Pulley 39 ... Position sensor 40 ... Control circuit 56 ... Connector 60 ... Print head unit 68 ... Ink passage 90 ... Computer 91 ... Video driver 95 ... Application program 96 ... Printer driver 97 ... Resolution conversion module 98 ... Color conversion module 99 Color reduction module 100 Print data generation module 101 Ink amount compensation unit 102 Error information receiving unit 125 Platen frame 126f Upstream groove 126r Downstream groove 126s Side groove 127r Ink absorber

Claims (7)

A printing control device that generates print data to be supplied to the printing unit in order to perform printing using a printing unit that forms dots by ejecting ink onto a printing medium,
The printing unit includes a print head having a plurality of nozzles and a plurality of ejection driving elements for ejecting ink droplets from the plurality of nozzles, respectively. Any of N types of dots having different sizes (N is an integer of 2 or more) can be selectively formed.
The print control device includes:
An error information receiving unit that receives error information indicating an error in the ink amount of an ink droplet for forming at least one kind of specific dot among relatively small dots among the N kinds of dots;
The given image data is divided into a peripheral area on the edge side of the print medium and a central area on the center side of the print medium, and each pixel according to the gradation value of each pixel of the image data A dot data generation unit for generating dot data representing the dot formation state in
With
The dot data generation unit
(A) a function of adjusting the recording rate of the specific dots for the same pixel value of the image data so that the pixels belonging to the peripheral region are lower than the pixels belonging to the central region;
(B) a function of generating dot data in which an error in the ink amount is compensated according to an area to which the pixel belongs and the error information;
A printing control apparatus comprising: The print control apparatus according to claim 1,
The dot data generation unit
A color conversion unit that converts the color system of the image data to generate multi-gradation data represented by a plurality of color components that can be used by the printing unit;
A color reduction processing unit that performs color reduction processing by converting the gradation value of the multi-gradation data into any of (N + 1) gradation values for each pixel;
With
The color conversion unit performs color conversion using the corrected color conversion table for the central region for the pixels belonging to the central region, and uses the corrected color conversion table for the peripheral region for the pixels belonging to the peripheral region. Color conversion,
The color reduction processing unit performs color reduction processing using the central region dot recording rate table for pixels belonging to the central region, and performs color reduction processing using the peripheral region dot recording rate table for pixels belonging to the peripheral region. Done
The peripheral area dot recording rate table is configured such that the recording rate of the specific dots for the same pixel value of the image data is lower than the central area dot recording rate table,
The corrected color conversion table for the central region is a reference color conversion table set on the assumption that there is no error in the ink amount, and the ink amount using the error information and the dot recording rate table for the central region. Is a table generated by adjusting to compensate for the error of
The peripheral area corrected color conversion table is generated by adjusting the reference color conversion table so as to compensate for the ink amount error using the error information and the peripheral area dot recording rate table. Printing control device, which is a table. The print control apparatus according to claim 1,
The dot data generation unit
A color conversion unit that converts the color system of the image data to generate multi-gradation data represented by a plurality of color components that can be used by the printing unit;
A color reduction processing unit that performs color reduction processing by converting the gradation value of the multi-gradation data into any of (N + 1) gradation values for each pixel;
With
The color reduction processing unit performs a color reduction process using the corrected dot recording rate table for the central region for the pixels belonging to the central region, and uses the corrected dot recording rate table for the peripheral region for the pixels belonging to the peripheral region. To reduce the color
The corrected dot recording rate table for the central region is adjusted so that the error is compensated for the reference dot recording rate table for the central region set on the assumption that there is no error in the ink amount. Is a table generated by
The corrected dot recording rate table for the peripheral area is adjusted so that the error is compensated for the reference dot recording ratio table for the peripheral area set on the assumption that there is no error in the ink amount. Is a table generated by
The printing control apparatus, wherein the peripheral region reference dot recording rate table is configured such that the specific dot recording rate for the same pixel value of the image data is lower than the central region reference dot recording rate table. The print control apparatus according to any one of claims 1 to 3,
The print medium is roll paper,
The print control apparatus, wherein the peripheral area is set only on an end side parallel to the sub-scanning direction of the roll paper. A printing apparatus that performs printing by forming dots on a print medium,
A print head having a plurality of nozzles and a plurality of ejection drive elements for ejecting ink droplets from the plurality of nozzles, respectively, and using each nozzle, N types having different sizes in one pixel area on the print medium A printing section capable of selectively forming any one of the dots (N is an integer of 2 or more);
A print control apparatus according to any one of claims 1 to 4,
A printing apparatus comprising: A printing control method for generating print data to be supplied to the printing unit in order to perform printing using a printing unit that forms dots by ejecting ink onto a printing medium,
(A) A print head having a plurality of nozzles and a plurality of ejection drive elements for ejecting ink droplets from the plurality of nozzles, respectively, and having a size in a pixel area on the print medium using each nozzle. Preparing a printing unit capable of selectively forming any one of different N types (N is an integer of 2 or more);
(B) receiving error information indicating an error in the ink amount of an ink droplet for forming at least one kind of specific dot among relatively small dots among the N kinds of dots;
(C) The given image data is divided into a peripheral region on the end side of the print medium and a central region on the center side of the print medium, and according to the gradation value of each pixel of the image data Generating dot data representing a dot formation state in each pixel;
With
The step (c)
(C-1) adjusting the recording rate of the specific dots for the same pixel value of the image data so that the pixels belonging to the peripheral region are lower than the pixels belonging to the central region;
(C-2) generating dot data in which the error of the ink amount is compensated according to the area to which the pixel belongs and the error information;
A printing control method comprising: A computer program for causing a computer to execute processing for generating print data to be supplied to the printing unit in order to perform printing using a printing unit that forms dots by ejecting ink onto a printing medium. There,
The printing unit includes a print head having a plurality of nozzles and a plurality of ejection driving elements for ejecting ink droplets from the plurality of nozzles, respectively. Any of N types of dots having different sizes (N is an integer of 2 or more) can be selectively formed.
The computer program is
(A) a function of receiving error information indicating an error in the ink amount of an ink droplet for forming at least one kind of specific dot among relatively small dots among the N kinds of dots;
(B) The given image data is divided into a peripheral area on the edge side of the print medium and a central area on the center side of the print medium, and according to the gradation value of each pixel of the image data A function of generating dot data representing a dot formation state in each pixel;
Having a program for causing the computer to realize
The function (b) is
(B-1) a function of adjusting the recording rate of the specific dots for the same pixel value of the image data so that the pixels belonging to the peripheral region are lower than the pixels belonging to the central region;
(B-2) a function of generating dot data in which an error in the ink amount is compensated according to an area to which the pixel belongs and the error information;
A computer program comprising:

Images