JP2005028611A - Discharging control of improvement ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for shortening the time required for a printing process in the case of printing using an improvement ink for improving the quality of printed matter. <P>SOLUTION: A printing control device generates printing data to be supplied to a printing part capable of forming dots by discharging a colored ink and the improvement ink for improving the quality of printed matter onto a printing medium. The printing control device is equipped with a table selecting part and a dot data generating part. The table selecting part selects a colored dot recording ratio table in the case of determining a colored dot recording ratio, while it selects a transparent dot recording ratio table in the case of determining a transparent dot recording ratio. The dot data generating part generates dot data of colored dots and transparent dots on the basis of the selected dot recording ratio table. The transparent dot recording ratio table is characterised in that the recording ratio of a specific dot is set to zero with respect to all values that pixel values can take. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a printing technique for printing an image by ejecting ink onto a printing medium.
[0002]
[Prior art]
2. Description of the Related Art In recent years, color printers that eject several colors of ink from a print head have become widespread as computer output devices, and are widely used for printing images processed by a computer in multiple colors and multiple gradations. Such gradation expression is also performed by a method of selectively forming any one of a plurality of types of dots having different sizes in one pixel area on the print medium.
[0003]
In such a gradation expression method, each gradation value is expressed by recording dots of each size at an appropriate recording rate. This dot recording rate takes into account the size of each dot, and is a value that allocates dots of each size so as to reduce image quality degradation such as graininess (roughness of the image) and banding (striped image quality degradation). Is set in advance.
[0004]
On the other hand, in such a printer, for example, improvement ink for improving the quality of printed matter as disclosed in Patent Document 1 is used, thereby improving color development, water resistance, light resistance, and uneven gloss. The quality of printed matter such as suppression is being improved. Since such improved ink is almost transparent, it is strongly desired to shorten the time required for the dot data generation process rather than suppressing image quality degradation by appropriately allocating dots of each size.
[0005]
Japanese Patent Publication No. 2002-144551
[0006]
[Problems to be solved by the invention]
However, conventionally, setting the recording rate of dots formed with improved ink has not been considered from the viewpoint of shortening the time required for dot data generation processing.
[0007]
The present invention has been made to solve the above-described problems in the prior art, and provides a technique for shortening the time required for printing processing in printing using improved ink for improving the quality of printed matter. With the goal.
[0008]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of the above-described problems, the present invention is directed to ejecting dots by ejecting at least one kind of colored ink containing a colorant and an improved ink for improving the quality of printed matter onto a print medium. A print control device that generates print data to be supplied to the printing unit in order to perform printing using a printing unit that can be formed,
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:
In determining the colored dot recording rate, which is the recording rate of the colored dots formed with the colored ink, a colored dot recording rate table for storing the colored dot recording rate is selected, while the transparent dot formed with the improved ink is selected. In the determination of the transparent dot recording rate that is the dot recording rate, a table selection unit that selects a transparent dot recording rate table for storing the transparent dot recording rate;
Based on the selected dot recording rate table, dot data generation that generates dot data representing the formation state of the colored dots and the transparent dots in each pixel according to the pixel value of each pixel of given image data And
With
In the transparent dot recording rate table, the recording rate of a specific dot that is at least one type of dots among the N types of dots is set to zero for all possible values of the pixel value. It is characterized by.
[0009]
In the transparent dot recording rate table of the printing control apparatus of the present invention, since the recording rate of at least one type of specific dot is set to zero for all possible values of pixel values, at least one type of specific dot is set. The dots are not used at all for gradation expression. On the other hand, for the types of dots that are not used for gradation expression, the processing required for generating dot data can be simplified, so the time required for printing processing can be increased by increasing the number of types of dots that are not used for gradation expression. It can be shortened.
[0010]
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. The “printed product” refers to a product generated by discharging colored ink and improvement ink onto a print medium. “Improved ink” means ink for improving the quality of printed matter such as color development, water resistance, light resistance, and suppression of uneven gloss. The “transparent dot” means a dot formed with the improved ink, and does not mean that it is completely transparent.
[0011]
In the print control apparatus, the dot data generation unit includes:
In order to express a pixel value representing a color of each pixel of the given image data using at least a part of the colored ink available in the printing unit and the improvement ink. A color conversion unit that converts the gradation value of each of the inks,
In accordance with the gradation value of each ink generated by the color conversion, dot data representing the formation state of the colored dots formed with the colored ink and the transparent dots formed with the improvement ink in each pixel is generated. A subtractive color section,
With
The color reduction unit uniformly determines that the specific dot of the N types of transparent dots is not formed, and the specific dot of the N types of transparent dots according to a gradation value of the improvement ink. It may be configured to determine whether or not other transparent dots are formed.
[0012]
In this way, the process itself for determining whether or not at least some types of dots are formed can be deleted, and the time required for the printing process can be further shortened.
[0013]
In the printing control apparatus, the transparent dot recording rate table may be configured such that the number of gradations in which the dot recording rate is stored is smaller than that of the colored dot recording rate table.
[0014]
In this way, the consumption of the cache memory can be reduced, so that the cache hit rate can be increased and the color reduction processing can be accelerated. Note that the reduction in the number of gradations can be realized, for example, by storing the dot recording rate for only a part of the gradation values or by increasing the quantization width.
[0015]
In the print control apparatus, the transparent dot recording rate table includes a plurality of tables prepared for each type of the print medium,
The table selection unit may select one of the plurality of tables according to the type of the print medium.
[0016]
By so doing, the present invention can be applied even when the amount of improved ink to be ejected differs for each type of print medium.
[0017]
In the printing control apparatus, the transparent dot recording rate table includes a plurality of tables prepared for each type of the improved ink,
The table selection unit may select one of the plurality of tables according to the improvement ink.
[0018]
By so doing, the present invention can be applied even when the amount of improved ink to be ejected differs for each type of improved ink.
[0019]
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.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
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 the first embodiment of the present invention:
C. Print data generation processing in the second embodiment of the present invention:
D. Print data generation processing in the third embodiment of the present invention:
E. Variation:
[0021]
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.
[0022]
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.
[0023]
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, and a dot recording rate table DT. . These functions will be described later.
[0024]
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.
[0025]
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.
[0026]
FIG. 3 is an explanatory diagram showing the arrangement of the nozzles Nz on the lower surface of the print head 28. On the lower surface of the print head 28, nozzle arrays for discharging colored ink containing a coloring material and transparent improvement ink CL are formed. In this embodiment, black ink K, cyan ink C, light cyan ink LC, magenta ink M, light magenta ink LM, and yellow ink Y are used as colored inks.
[0027]
The colored ink is not limited to the six inks K, C, LC, M, LM, and Y, and can be arbitrarily set according to the preference of the image quality of the print image. For example, four inks K, C, M, and Y may be used, or only the black ink K may be used. Further, a combination of dark yellow ink having a lightness lower than that of the yellow ink Y, gray ink having a lightness higher than that of the black ink K, a blue ink, a red ink, and a green ink may be used. .
[0028]
As the improvement ink CL, a colorless and transparent ink having the same gloss as other inks and improving the color developability of the other inks may be used. As such an improvement ink, for example, the ink described in JP-A-8-60059 can be used. By using such an improvement ink, it is possible to improve the quality of the printed image, such as suppressing gloss unevenness and improving color developability. Further, by using an ink that improves water resistance and light resistance as the improved ink CL, it is possible to improve the water resistance and light resistance of the printed image.
[0029]
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.
[0030]
FIG. 4 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 high speed. .
[0031]
FIG. 5 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. 5A shows a driving waveform for ejecting small ink droplets IPs capable of forming small dots by itself, and FIG. 5B shows a medium ink droplet IPm capable of forming medium dots by itself. The drive waveform for discharging is shown. In this embodiment, small dots and medium dots correspond to “specific dots” in the claims.
[0032]
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. 4) is expanded and ink is supplied from an ink tank (not shown) to the ink passage 68. Expansion of the ink path 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.
[0033]
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. 5B during the ink absorption process. This is because if the ink passage 68 is slowly expanded by slowly decreasing the potential, more ink can be supplied from an ink tank (not shown).
[0034]
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.
[0035]
FIG. 6 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. 6, 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 certain time has elapsed. Yes.
[0036]
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. 6, when the small ink droplet IPs having a relatively slow average flying speed is ejected first, and the medium ink droplet IPm having a relatively fast average flying speed is ejected after a certain period of time, the landing position 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.
[0037]
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.
[0038]
B. Print data generation processing in the first embodiment:
FIG. 7 is a flowchart showing a routine of print data generation processing in the first embodiment. 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.
[0039]
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.
[0040]
In step S200, 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 resolution.
[0041]
In step S300, the color conversion module 98 refers to the color conversion table LUT (FIG. 1) and converts the RGB image data for each pixel into the above-described colored ink colors and improvement inks that can be used by the color printer 20. Convert to gradation data.
[0042]
In step S400, 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”.
[0043]
FIG. 8 is a flowchart showing the flow of colored dot color reduction processing in the first embodiment of the present invention. In step S410, the color reduction module 99 selects the colored dot recording rate table DTc from among a plurality of tables included in the dot recording rate table DT. The plurality of tables include a colored dot recording rate table DTc and a transparent dot recording rate table DTt, both of which will be described later. The details of the transparent dot color reduction processing will be described later.
[0044]
The colored dot recording rate table DTc and the transparent dot recording rate table DTt are respectively a colored dot recording rate which is a recording rate of colored dots formed with colored ink and a transparent dot which is a recording rate of transparent dots formed with improved ink. Stores the recording rate. The “transparent dot” simply means a dot formed with the improved ink, and does not mean that it is completely transparent.
[0045]
In step S411, the color reduction module 99 sets the large dot level data LVL while referring to the colored dot recording rate table DTc. The level data refers to data obtained by converting the dot recording rate into 256 levels from 0 to 255.
[0046]
FIG. 9 is an explanatory diagram showing a dot recording rate table DT used to determine level data for three sizes of large, medium, and small dots. The dot recording rate table DT includes the colored dot recording rate table DTc and the transparent dot recording rate table DTt as described above. FIG. 9 also shows the contents of the colored dot recording rate table DTc. The colored dot recording rate table DTc may be provided for each colored ink in accordance with the characteristics of each colored ink.
[0047]
The horizontal axis of the colored dot recording rate table DTc has gradation values (0 to 255), the left vertical axis shows dot recording rate (%), and the right vertical axis shows level data (0 to 255). It is shown. 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. 9, 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.
[0048]
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. 9, if the gradation value of the 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 LVM is Lm1 is obtained using the curve MD, and the level data LVS of the small dots is obtained as Ls1 using the curve SD.
[0049]
In step S412, the color reduction module 99 first determines whether or not the large dot level data LVL is zero. When the large dot level data LVL is zero, a comparison process (step S413) described later is bypassed, and the process proceeds to step S421. On the other hand, if the large dot level data LVL is not zero, the process proceeds to step S413.
[0050]
This determination process is performed because, when the level data LVL is zero, it can be determined that a large dot should not be formed without performing the comparison process (step S413). This is to reduce the time required for the comparison process by bypassing and to speed up the process.
[0051]
In step S413, the level data LVL set in step S411 is compared with the threshold value THL. Here, for example, dot on / off determination is performed by a systematic dither method. The threshold value 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 dither matrix in which values 0 to 254 appear in a 16 × 16 square pixel block is used.
[0052]
FIG. 10 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. 10, each pixel of the level data LVL is compared with 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. In FIG. 10, hatched pixels mean pixels that form dots.
[0053]
In step S413, when the level data LVL is larger than the threshold value THL, it is determined that a large dot should be formed (step S414). On the other hand, if the level data LVL is smaller than the threshold value THL in step S413, it is determined that a large dot should not be formed, and the process proceeds to step S421.
[0054]
In step S421, medium dot level data LVM is set. The setting method is the same as that for setting the large dot level data LVL. When the medium dot level data LVM is set, it is determined whether or not the medium dot level data LVM is zero (step S422), as in step S412. As a result of this determination, the comparison process (step S423) is performed only when the medium dot level data LVM is not zero, and whether or not medium dots are formed is determined (step S424).
[0055]
In steps S431 to S434, processing similar to that for large dots and medium dots is performed for small dots. When the above processing is performed for all the pixels for the colored ink (step S440), the color reduction processing for the transparent ink described later is performed. When these processes are completed, the process proceeds to step S500 (FIG. 7).
[0056]
In step S500, 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.
[0057]
Thus, it can be seen that in the color reduction processing of this embodiment, the processing speed increases as the level data of zero increases. This is because the number of times that comparison processing with the dither matrix can be bypassed increases as the level data of zero increases. Focusing on this point, the transparent dot recording rate table DTt is configured to adjust the ink ejection amount using only two sizes of dots. On the other hand, the colored dot recording rate table DTc is configured to adjust the ink ejection amount using three sizes of dots from the viewpoint of improving image quality such as granularity and suppression of banding.
[0058]
FIG. 11 is an explanatory diagram showing the relationship between the dot recording rate table and the ink discharge amount. FIG. 11A is a diagram showing a relationship between gradation values of multi-gradation data and dot recording rates of dots of each size, and is the same as the colored dot recording rate table DTc shown in FIG. is there. FIG. 11B is an explanatory diagram showing the relationship between the gradation value and the weight of ink ejected to a predetermined area. The predetermined area is assumed to be an area composed of 255 pixels. The ink weight is assumed to be 10 ng for small dots, 20 ng for medium dots, and 30 ng for large dots.
[0059]
FIG. 11B is a plot of the following product for each gradation value.
(1) The recording rate of dots of each size (for example, in the gradation value G2, small dots are 25% and medium dots are 50%)
(2) Ink weight (10 ng for small dots, 20 ng for medium dots, 30 ng for large dots)
(3) Number of pixels in a predetermined area (255 pixels)
For example, when the gradation value is 255 (maximum gradation value), the above product is 7650 ng (= 100% × 30 ng × 255 pixels).
[0060]
As can be seen from FIG. 11B, 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.
[0061]
As can be seen from FIGS. 11A and 11B, the weight of the ink ejected to the predetermined area increases as follows according to the increase of 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.
[0062]
In the present embodiment, such a dot recording rate profile is generated as a result of the following trade-off.
(1) In order to suppress graininess (roughness of the image), it is preferable to increase the dot recording rate of relatively small dots by decreasing the recording rate of relatively large dots that are easily visible. Such characteristics are particularly 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 particularly remarkable in a high gradation region.
As a result of such a trade-off, in this embodiment, the profile is set such that the upper limit value of the dot recording rate for small dots is 25% and the upper limit value of the dot recording rate for medium dots is 50%.
[0063]
FIG. 12 is an explanatory diagram showing the colored dot recording rate table DTc and the transparent dot recording rate table DTt in the first embodiment of the present invention. FIG. 12A shows a colored dot recording rate table DTc, and FIG. 12B shows a transparent dot recording rate table DTt.
[0064]
As can be seen from FIG. 12A, in the colored dot recording rate table DTc, the recording rates of the dots of each size are stored so that each gradation is expressed using three large, medium, and small dots. On the other hand, in the transparent dot recording rate table DTt, the recording rate of dots of each size is stored so that each gradation is expressed using only two sizes of dots, large dots and medium dots. For this reason, in the transparent dot recording rate table DTt, the recording rate of small dots is set to zero for all gradation values.
[0065]
As a result, in the colored dot recording rate table DTc, the area where gradation can be expressed by one dot is limited to only 21 gradations from 0 to 20, but in the transparent dot recording rate table DTt. The gradation value spreads to 170 gradations from 0 to 169.
[0066]
Thus, it can be seen that the transparent dot recording rate table DTt is configured such that the ratio of the number of gradations expressed by only medium dots to the total number of gradations is larger than that of the colored dot recording rate table. The fact that it is possible to represent with relatively few types of dots means that there are many types of dots that are not used for gradation expression.
[0067]
FIG. 13 is an explanatory diagram showing the relationship between the dot recording rate table and the ink discharge amount in the first embodiment. FIG. 13A is a diagram showing the relationship between gradation values of multi-tone data and dot recording rates of dots of various sizes, and the colored dot recording rate table DTc shown in FIG. 12B. Is the same. FIG. 13B is an explanatory diagram showing the relationship between the gradation value and the weight of ink ejected to a predetermined area.
[0068]
As can be seen from FIGS. 13A and 13B, the weight of ink ejected to a 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 169, the ink weight increases linearly as the dot recording rate of medium dots increases.
(2) In the area from the gradation value 170 to the maximum gradation value, the dot recording rate of medium dots starts to decrease, and the ink weight increases linearly by replacing the medium dots with large dots.
As described above, the ink amount can be adjusted using only the medium dots and the large dots as in the case of using three dots.
[0069]
FIG. 14 is a flowchart showing the flow of transparent dot color reduction processing in the first embodiment of the present invention. The transparent dot color reduction process is different from the colored dot color reduction process (FIG. 8) in that the process for determining whether or not a small dot is formed (steps S431 to S434) is deleted. The determination of whether or not a small dot is formed is deleted because it is known in advance that a small dot is not formed regardless of the gradation value.
[0070]
As described above, in the present embodiment, by using the transparent dot recording rate table DTt that uses only medium dots and large dots for the color reduction processing of the improved ink, processing that increases the ratio of zero level data is performed. Is called. Thereby, the probability of bypassing the comparison process with the dither matrix in the color reduction process (FIG. 8) can be increased. As a result, the number of comparison processes with the dither matrix that requires a relatively long time is reduced, and the time required for the printing process is shortened.
[0071]
In this embodiment, the processing for determining whether or not a small dot is formed has been deleted, so that the processing time can be further shortened. In this embodiment, the small dots correspond to “specific dots” in the claims.
[0072]
C. Print data generation processing in the second embodiment:
FIG. 15 is an explanatory diagram showing a transparent dot recording rate table DTta in the second embodiment of the present invention. As can be seen from this figure, in the transparent dot recording rate table DTta of the second embodiment, the recording rates of dots of each size are stored so that each gradation is expressed using only large dots. As a result, in the transparent dot recording rate table DTta, the recording rates of both small dots and medium dots are set to zero for all gradation values.
[0073]
As a result, in this embodiment, an area that can be expressed with a single dot spreads over all gradations. Further, in the transparent dot color reduction process, the transparent dot of the first embodiment is further deleted in that the process for determining whether or not medium dots are formed (steps S421 to S424) is deleted as shown in FIG. This is different from the color reduction process. As a result, it is only necessary to determine whether or not large dots are formed by comparison with a dither matrix.
[0074]
As described above, in this embodiment, by using the transparent dot recording rate table DTta that uses only large dots for the color reduction processing of the improved ink, processing that further increases the ratio of zero level data is performed. As a result, the time required for the printing process is further shortened. However, the first embodiment that uses medium dots also has the advantage that the improved ink can be discharged onto the print medium more finely than the second embodiment that uses only large dots. In this embodiment, small dots and medium dots correspond to “specific dots” in the claims.
[0075]
D. Print data generation processing in the third embodiment:
FIG. 17 is an explanatory diagram showing a transparent dot recording rate table DTtb in the third embodiment of the present invention. In the recording rate table of FIG. 17A, the dot recording rate is stored only in a relatively low region of 0 to 84, and the dot recording rate is not stored in other regions. On the other hand, in the recording rate table of FIG. 17B, the dot recording rate is stored only in a relatively high region of 170 to 255, and the dot recording rate is not stored in other regions.
[0076]
The recording rate tables in FIGS. 17A and 17B are used for improved ink in which ink ejection is performed only in a region where the gradation value is a predetermined low level and improved ink that is performed only in a predetermined high region. It is a table. These tables are set by paying attention to the fact that the improvement ink may be ejected only in a region where the gradation value is partly.
[0077]
Thus, since the transparent dot recording rate table of this embodiment stores the dot recording rate for only a part of the gradation values, the data amount of the dot recording rate table can be reduced. As a result, the consumption of a cache memory (not shown) can be reduced, so that the hit rate of the cache memory can be increased and the color reduction process can be accelerated.
[0078]
As a dot recording rate table for storing dot recording rates for only a part of gradation values, a table for storing dot recording rates only in an intermediate area as shown in FIG. 18 can be configured. Such a dot recording rate table may be configured to allow fine adjustment of the ink discharge amount using, for example, small dots and medium dots (FIG. 18A), or processing using only large dots. You may comprise so that speed may be made fast (FIG.18 (b)).
[0079]
The reduction in data amount can also be realized by increasing the quantization width and reducing the number of gradations. When the quantization width is increased, the quantization error also increases. Generally, the error in the improved ink ejection amount does not affect the quality of the printed matter as much as the error in the colored ink ejection amount.
[0080]
The transparent dot recording rate table having such various characteristics is preferably configured to be selected in accordance with the printing environment such as the type of improved ink and the type of printing medium.
[0081]
E. 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.
[0082]
E-1. In each of the above-described embodiments, 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. A printer that can selectively form types of dots or a printer that can selectively form four or more types of dots may be used. 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.
[0083]
E-2. In each of the above-described embodiments, the gradation value is reduced using systematic dither, but the effect of the present invention is also achieved when the gradation value is reduced using another color reduction processing method such as error diffusion. Is obtained.
[0084]
This is also because, in error diffusion, if the probability that zero level data is generated is increased as in the above embodiment, the processing speed is increased. This is because, even in error diffusion, it can be determined that a dot should not be formed when the level data is zero, and an error to be diffused does not occur if there is no level data and no dot, so the amount of calculation is reduced.
[0085]
Furthermore, when the present invention is applied, the number of types of dots formed with the improved ink tends to decrease, so that it is generally understood that the amount of information for controlling the ejection of the improved ink is reduced. Such a reduction in the amount of information for discharge control means a reduction in the amount of information to be generated, so that it is generally understood that a configuration that increases the processing speed by various methods in the color reduction processing can be realized.
[0086]
E-3. 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.
[0087]
E-4. 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.
[0088]
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.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a printing system as an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a color printer 20;
FIG. 3 is an explanatory diagram showing a nozzle arrangement on the lower surface of the print head.
FIG. 4 is an explanatory diagram showing structures of a nozzle Nz and a piezo element PE.
FIG. 5 is an explanatory diagram showing a relationship between two types of drive waveforms of the nozzle Nz when ink is ejected and two sizes of ink droplets IPs and IPm to be ejected.
FIG. 6 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 a small ink droplet IPs and a medium ink droplet IPm.
FIG. 7 is a flowchart illustrating a routine of print data generation processing in the first embodiment.
FIG. 8 is a flowchart showing the flow of colored dot color reduction processing in the first embodiment of the present invention.
FIG. 9 is an explanatory diagram showing a dot recording rate table used for determining level data of three sizes of large, medium, and small sizes.
FIG. 10 is an explanatory diagram showing the concept of dot formation by a systematic dither method.
FIG. 11 is an explanatory diagram showing a relationship between a dot recording rate table and an ink discharge amount.
FIG. 12 is an explanatory view showing a colored dot recording rate table and a transparent dot recording rate table in the first embodiment of the present invention.
FIG. 13 is an explanatory diagram showing a relationship between a transparent dot recording rate table and an ink discharge amount in the first embodiment of the present invention.
FIG. 14 is a flowchart showing the flow of transparent dot color reduction processing in the first embodiment of the present invention;
FIG. 15 is an explanatory diagram showing a relationship between a transparent dot recording rate table and an ink discharge amount in the second embodiment of the present invention.
FIG. 16 is a flowchart showing a flow of transparent dot color reduction processing in the second embodiment of the present invention;
FIG. 17 is an explanatory diagram showing a transparent dot recording rate table in the third embodiment of the present invention.
FIG. 18 is an explanatory diagram showing a transparent dot recording rate table in the third embodiment of the present invention.
[Explanation of symbols]
20 Color printer
21 ... CRT
22 ... Paper feed motor
24 ... Carriage motor
25. Paper feed roller
28 ... Print head
30 ... carriage
32 ... Control panel
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

Claims (8)

To perform printing using a printing unit capable of forming dots by discharging at least one kind of colored ink containing a colorant and an improvement ink for improving the quality of printed matter onto a print medium A print control device for generating print data to be supplied to the printing unit,
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:
In determining the colored dot recording rate, which is the recording rate of the colored dots formed with the colored ink, a colored dot recording rate table for storing the colored dot recording rate is selected, while the transparent dot formed with the improved ink is selected. In the determination of the transparent dot recording rate that is the dot recording rate, a table selection unit that selects a transparent dot recording rate table for storing the transparent dot recording rate;
Based on the selected dot recording rate table, dot data generation that generates dot data representing the formation state of the colored dots and the transparent dots in each pixel according to the pixel value of each pixel of given image data And
With
In the transparent dot recording rate table, the recording rate of a specific dot that is at least one type of dots among the N types of dots is set to zero for all possible values of the pixel value. A print control apparatus characterized by the above. The print control apparatus according to claim 1,
The dot data generation unit
In order to express a pixel value representing a color of each pixel of the given image data using at least a part of the colored ink available in the printing unit and the improvement ink. A color conversion unit that converts the gradation value of each of the inks,
In accordance with the gradation value of each ink generated by the color conversion, dot data representing the formation state of the colored dots formed with the colored ink and the transparent dots formed with the improvement ink in each pixel is generated. A subtractive color section,
With
The color reduction unit uniformly determines that the specific dot of the N types of transparent dots is not formed, and the specific dot of the N types of transparent dots according to a gradation value of the improvement ink. A printing control apparatus for determining whether or not to form other transparent dots. The print control apparatus according to claim 1 or 2,
The transparent dot recording rate table is a printing control apparatus in which the number of gradations in which dot recording rates are stored is smaller than that of the colored dot recording rate table. The print control apparatus according to any one of claims 1 to 3,
The transparent dot recording rate table includes a plurality of tables prepared for each type of the print medium,
The table selection unit is a print control apparatus that selects one of the plurality of tables according to a type of the print medium. The print control apparatus according to any one of claims 1 to 4,
The transparent dot recording rate table includes a plurality of tables prepared for each type of the improved ink,
The table selection unit is a print control device that selects one of the plurality of tables according to the improvement ink. A printing apparatus that performs printing by forming dots on a print medium,
A printing unit capable of forming dots by ejecting at least one kind of colored ink containing a colorant and an improvement ink for improving the quality of printed matter onto a print medium;
A printing control apparatus according to any one of claims 1 to 5;
A printing apparatus comprising: To perform printing using a printing unit capable of forming dots by discharging at least one kind of colored ink containing a colorant and an improvement ink for improving the quality of printed matter onto a print medium A print control method for generating print data to be supplied to the printing unit,
(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) In determining the colored dot recording rate, which is the recording rate of the colored dots formed with the colored ink, a colored dot recording rate table for storing the colored dot recording rate is selected, while forming with the improved ink In determining the transparent dot recording rate, which is the recording rate of the transparent dots, a step of selecting a transparent dot recording rate table storing the transparent dot recording rate;
(C) Based on the selected dot recording rate table, dot data representing the formation state of the colored dot and the transparent dot in each pixel is generated according to the pixel value of each pixel of the given image data. Process,
With
In the transparent dot recording rate table, the recording rate of a specific dot that is at least one type of dots among the N types of dots is set to zero for all possible values of the pixel value. A printing control method characterized by the above. To perform printing using a printing unit capable of forming dots by discharging at least one kind of colored ink containing a colorant and an improvement ink for improving the quality of printed matter onto a print medium A computer program for causing a computer to execute processing for generating print data to be supplied to the printing unit,
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.
(A) In determining the colored dot recording rate, which is the recording rate of the colored dots formed with the colored ink, a colored dot recording rate table for storing the colored dot recording rate is selected, while forming with the improved ink In determining the transparent dot recording rate, which is the recording rate of the transparent dots, a function of selecting a transparent dot recording rate table that stores the transparent dot recording rate;
(B) Based on the selected dot recording rate table, dot data representing the formation state of the colored dots and the transparent dots in each pixel is generated according to the pixel value of each pixel of the given image data. Function and
Having a program for causing the computer to realize
In the transparent dot recording rate table, the recording rate of a specific dot that is at least one type of dots among the N types of dots is set to zero for all possible values of the pixel value. A computer program characterized by the above.

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