JP2005178164A - Generation of dot recording rate data in a printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for improving color misregistration of reproduced colors by a method other than a method of directly calibrating an RGB-CMYK color conversion table.
Calibration of dot recording rate data for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks is performed. First, a dot recording rate table for outputting recording rate data for a plurality of sizes of ink dots in response to an ink amount input is prepared. The dot recording rate table is calibrated for each dot size. This calibration is preferably performed for each ink, and a dot recording rate table is preferably generated for each ink.
[Selection] Figure 2

Description

  The present invention relates to a technique for generating dot recording rate data for a color printer capable of recording ink dots of a plurality of sizes.

  Among color printers, there are printers that can record a plurality of ink dots of different sizes (hereinafter also referred to as “multi-size dot printers”).

  FIG. 8A is an explanatory diagram showing an overview of print data generation processing for a multi-size dot printer. The color conversion unit 130 converts the color image data RGB into ink amount data CMYK. The ink amount data CMYK is converted into dot recording rate data LDc, MDc, SDc... For a plurality of sizes of ink dots by the dot recording rate table 140. FIG. 8B shows an example of the dot recording rate table 140. The horizontal axis is the ink amount data, and the vertical axis is the dot recording rate. In this printer, three types of dots, a small dot SD, a medium dot MD, and a large dot LD, can be used, and changes in the dot recording rate for these three types of dots are shown. Here, the “dot recording rate” means a dot formation ratio in an arbitrary plurality of pixels. When dots of a certain size are formed on all the pixels in an arbitrary area, the recording rate of dots of that size is 100%. Further, when dots of a certain size are formed in half of the pixels in an arbitrary area, the recording rate of dots of that size is 50%. This dot recording rate table 140 is commonly applied to all inks.

  The halftone processing unit 150 performs halftone processing using dot recording rate data LDc, MDc, SDc... Of multiple sizes of each ink, and generates dot formation data PD indicating the recording state of each dot in each pixel. In this example, since three types of large, medium, and small dots can be formed for each ink, 2 for representing four dot formation states (no dot, small dot formation, medium dot formation, large dot formation) for each ink. Bit dot formation data Dc, Dm, Dy, and Dk are generated.

  The color conversion lookup table 130 is created so as to output ink amount data for faithfully reproducing the input color image data. An arbitrary color is reproduced by a combination of a plurality of inks, but gray (achromatic color) may be reproduced by so-called composite black (also referred to as “composite gray”) using CMY inks. When composite black is used, since the number of dots per unit area increases, there is an advantage that individual dots are less noticeable and the graininess of the image is improved.

  By the way, the ink ejection amount tends to vary considerably from printer to printer due to manufacturing errors. When reproducing gray using composite black, if there is an error in the ink amount of the color ink, this error may cause the tint (tint) or brightness to change. Gray color shift).

  Therefore, conventionally, the color conversion lookup table 130 has been calibrated in order to prevent color misalignment when gray is reproduced with composite black (for example, Patent Document 1).

JP-A-10-278287

  In this technology, first, a color conversion lookup table for converting RGB data to CMYK data is prepared, and various color patches are changed by slightly changing the RGB value from a value that reproduces gray (R = G = B). Print. Then, the color shift of gray is improved by calibrating the color conversion lookup table according to this result. However, such a calibration may not sufficiently improve the gray color shift.

  FIG. 9 shows an example of a shift in gray colorimetric values reproduced with composite black. Here, the horizontal axis is the b * axis of the L * a * b * color system, and the vertical axis is the L * axis. The solid line shows the colorimetric values obtained by measuring the color patch (also called “gray patch”) that reproduces gray (achromatic color represented by R = G = B) using composite black. ing. A dotted line indicates a color shift caused by an error in the ink discharge amount of the color ink. If the discharge amounts of some of the three types of CMY inks deviate from the design values, a color misalignment such as a broken line may occur with respect to gray. Since normal ink deviates from ideal ink, the amount of CMY ink when reproducing gray is often not equal to each other. In such a case, even when the CMY ink amounts are all shifted by the same amount, color misregistration occurs.

  As shown by a solid line in FIG. 9, a color patch due to various factors other than an error in ink ejection amount occurs in the gray patch that is actually printed. For example, in order to suppress the memory capacity of the color conversion lookup table, the number of bits of the input of the color conversion lookup table is limited to a certain value (for example, 6 bits), and an interpolation operation is performed on the output of the color conversion lookup table The method of obtaining the final ink amount data by performing is often used. In this case, a color shift occurs in gray due to a rounding error caused by limiting the number of input bits, an output interpolation calculation error, and the like. If a color misalignment such as the solid line in FIG. 9 has occurred, it is difficult to obtain an appropriate calibration amount, and calibration that sufficiently improves the gray color misalignment may not be possible. It was.

  Such a problem of color misregistration is a problem that is common to other reproduction colors as well as gray. However, the gray color misregistration is easily noticeable with the naked eye, and thus has a feature that the influence on the image quality is great.

  An object of the present invention is to provide a technique for improving the color misregistration of reproduced colors by a method other than a method of directly calibrating an RGB-CMYK color conversion table.

In order to achieve the above object, a first method according to the present invention is a dot recording rate data calibration method for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks. And
(A) preparing a dot recording rate table for outputting recording rate data of ink dots of a plurality of sizes in response to an ink amount input;
(B) calibrating the dot recording rate table for each dot size;
Is provided.

  According to this method, the ink discharge amount can be compensated by calibrating the dot recording rate table. Therefore, it is not necessary to directly calibrate the RGB-CMYK color conversion table, and it is possible to improve color misregistration by calibrating the dot recording rate table. In addition, since the dot recording rate table is calibrated for each dot size, it is possible to improve color misregistration in different brightness areas.

  It is preferable that the calibration is performed so that gray reproduced with the plurality of types of color inks approaches an achromatic color.

  According to this configuration, it is possible to improve gray color shift that is particularly conspicuous.

  The calibration may be performed for each dot size of each ink, and the dot recording rate table for each ink may be generated.

  According to this configuration, since the dot recording rate table is calibrated for each ink, color misregistration can be improved even when the ejection amount error differs for each ink.

The step (b)
For each dot size, printing a test patch sheet including a reference gray color reproduced using an achromatic color ink and a plurality of color bias patches reproduced using the plurality of types of color inks;
Determining a calibration amount for each dot according to a printing result of the plurality of color deviation patches;
Calibrating the dot recording rate table according to the calibration amount;
Including
The plurality of color bias patches are color patches that reproduce colors close to the reference gray color using only one type of size dot, and at least part of the dot recording rate of the plurality of types of color inks is The color patches may be different from each other.

  According to this configuration, it is possible to easily determine the calibration amount for each size dot.

The plurality of types of color inks include cyan ink, magenta ink, and yellow ink,
The test patch sheet is
A plurality of first color bias patches obtained by fixing the dot recording rate of cyan ink and changing the dot recording rates of yellow ink and magenta ink are used as the yellow ink dot recording rate and the magenta ink dot recording rate. A first type of sheet arranged two-dimensionally according to
A plurality of second color bias patches obtained by fixing the dot recording rate of magenta ink and changing the dot recording rate of yellow ink and cyan ink are used as the yellow ink dot recording rate and the cyan ink dot recording rate. A second type of sheet arranged two-dimensionally according to
May be included.

  The calibration amount of the chromatic color ink can be easily determined by searching for the color bias patch having an appropriate hue in the first and second type sheets.

The step (b)
Printing the first and second type test patch sheets;
Determining a primary calibration amount of cyan ink, magenta ink, and yellow ink by selecting a color-biased patch whose hue substantially matches the reference gray color in the first-type and second-type test patch sheets; When,
A plurality of test patch sheets printed at the dot recording rate after readjustment of the dot recording rates of cyan ink, magenta ink, and yellow ink calibrated using the primary calibration amount, respectively, by equal amounts. Printing a third type of test patch sheet including a color-biased patch;
Determining a secondary calibration amount of cyan ink, magenta ink, and yellow ink by selecting a color bias patch whose brightness substantially matches the reference gray color in the third type test patch sheet;
May be included.

  According to this configuration, it is possible to obtain a calibration amount that substantially matches both the hue and the brightness with the reference gray color.

A second method according to the present invention is a method of generating dot recording rate data for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks,
(A) preparing a dot recording rate table for outputting recording rate data of ink dots of a plurality of sizes in response to an ink amount input for each ink;
(B) using the dot recording rate table, outputting recording rate data of ink dots of each size of each ink according to the ink amount of each ink;
Is provided.

  According to this method, the color misregistration caused by the error in the ejection amount of each ink can be improved by the dot recording rate table for each ink. Therefore, it is not necessary to directly calibrate the RGB-CMYK color conversion table, and the color misregistration can be improved by the dot recording rate table for each ink.

A printer driver according to the present invention is a printer driver for generating print data for a printer that can record ink dots of a plurality of sizes for each of a plurality of types of color inks,
A color conversion unit that outputs ink amounts of the plurality of types of color inks in response to predetermined color image data input;
A plurality of dot recording rate tables provided for each ink and outputting recording rate data of a plurality of sizes of ink dots in accordance with the ink amount of each ink;
Is provided.

  Also in this printer driver, the color misregistration caused by the error in the ejection amount of each ink can be improved by the dot recording rate table for each ink. Therefore, it is not necessary to directly calibrate the RGB-CMYK color conversion table, and the color misregistration can be improved by the dot recording rate table for each ink.

  The present invention can be realized in various forms, for example, dot recording rate data calibration method and device, dot recording rate data creation method and device, print data creation method and device, and printer driver. And its installation method, printing method and printing apparatus, computer program for realizing the functions of the method or apparatus, a recording medium recording the computer program, a data signal including the computer program and embodied in a carrier wave, Or the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Modified example

A. First embodiment:
FIG. 1 is an explanatory diagram showing a dot recording rate table calibration system 100 as a first embodiment of the present invention. The system 100 includes a computer 200 and a color printer 300 for color calibration. The computer 200 includes a calibration processing unit 210 that executes various processes for calibrating the dot recording rate table.

  The color printer 300 for color calibration is a printer equipped with a print head (not shown) to be color calibrated. This print head is the same as the print head used in an actual printer. The color calibration described below is preferably performed for each individual printer in the actual machine. However, the print head may be classified into several groups according to the deviation of the ink discharge amount, and color calibration may be performed for each group.

  The calibration processing unit 210 includes an input receiving unit 220, a test patch sheet printing unit 230, a dot recording rate table correction unit 240, and a table storage unit 250. The input receiving unit 220 has a function of receiving an instruction from an operator (operator) of the system 100. The test patch sheet printing unit 230 has a function of outputting print data TPD for printing a test patch sheet, which will be described later, to the color calibration printer 300 and printing the test patch sheet. The table storage unit 250 is a memory that stores a dot recording rate table, and is provided in the hard disk of the computer 200, for example.

  2A to 2C are explanatory views showing the contents of the calibration process of the dot recording rate table in the first embodiment. FIG. 2A shows a dot recording rate table before calibration, which is the same as that shown in FIG. 8B described above. This dot recording rate table is a look-up table that outputs the dot recording rate for three types of dots, small dots SD, medium dots MD, and large dots LD, with ink amount data as input. The dot recording rate table before calibration can be the same for all inks. However, when the dot size varies depending on the ink type, a dot recording rate table is prepared for each group of inks using different dot sizes. As will be described below, in the first embodiment, one dot recording rate table common to all inks is calibrated for each color ink, thereby creating a dot recording rate table for each ink.

  FIG. 2B shows a test patch sheet printed by the test patch sheet printing unit 230. The test patch sheets include three first type test patch sheets TP1L, TP1M, and TP1S for confirming magenta / yellow, and three second type test patch sheets TP2L, TP2M, and TP2S for confirming cyan / yellow. Is included. The first type of test patch sheets TP1L, TP1M, and TP1S are for large dots, medium dots, and small dots. The second type test patch sheets TP2L, TP2M, and TP2S are also for large dots, medium dots, and small dots.

  FIG. 3 is an explanatory diagram showing the large dot test patch sheet TP1L. In the center of the test patch sheet TP1L, a central patch CP printed in standard composite gray is disposed. Also, two ink axes (magenta axis M and yellow axis Y) intersecting through the central hatch CP are drawn on the sheet. Further, a plurality of color deviation patches CSP are respectively arranged in four areas separated by these two ink axes M and Y. The ink axes M and Y indicate the increasing / decreasing direction of the magenta dot recording rate and the increasing / decreasing direction of the yellow dot recording rate, respectively.

  The central patch CP is reproduced using the dot recording rate of CMY three colors when gray is reproduced using a standard printer with no error in the ink ejection amount. If the CMY ink is an ideal ink, the dot recording rates of the CMY ink for the central patch CP are equal to each other. Since the actual ink deviates from the ideal ink, the dot recording rate of each ink for the central patch CP is usually not equal.

  The color deviation patch CSP is printed using a dot recording rate shifted from the central patch CP by the values indicated by the two ink axes M and Y. However, in the test patch sheet for checking magenta / yellow, the dot recording rate of cyan ink is the same constant value as the central patch CP. In the example of FIG. 3A, the color deviation patch CSP is not arranged on the M axis or the Y axis, but the color deviation patch may be arranged on these axes. For example, the color-biased patch arranged on the M-axis is a color patch in which the dot recording rate of yellow ink is equal to the central patch CP and the dot recording rate of magenta ink is different from the central patch CP.

  The background BG of the color patches CP and CSP is printed so as to reproduce the same gray color as that of the central patch CP using only black ink (achromatic ink). Therefore, when this test patch sheet is printed using a standard printer with no error in the ink ejection amount, the color of the central patch CP matches the color of the background BG. Actually, since the ink discharge amount of the printer deviates from the standard value (design value), the color of the central patch CP does not match the color of the background BG. However, at this time, among the plurality of color deviation patches CSP, there are those that match the color of the background BG.

  In the second type test patch sheets TP2L, TP2M, and TP2S (FIG. 2B) for cyan / yellow confirmation, color-biased patches are arranged along the cyan axis C and the yellow axis Y. The bias patch has the same dot recording rate of magenta ink.

  FIG. 3B shows an example of dot arrangement in a certain color deviation patch CSP. The color deviation patch CSP is printed using only the large dots LDm of magenta ink, the large dots LDc of cyan ink, and the large dots LDy of yellow ink. As described above, only the large dots are used for printing the color deviation patch CSP in the test patch sheet TP1L for large dots, and the difference between the plurality of color deviation patches CSP included in the same sheet is that of the large dots. It is only a number (ie, large dot recording rate).

  The color deviation CSP is preferably printed so that the three colors of ink hardly overlap each other as in the example of FIG. The first reason is that when the inks overlap each other, the relationship between the ink amount (that is, the dot recording rate) and the color of the patch deviates from a linear relationship, so that it is difficult to determine an appropriate calibration amount at the time of calibration. is there. The second reason is that since the color shift of gray tends to be noticeable in a relatively light gray, it is preferable to determine the calibration amount in a light gray. In order to print gray so that the three color inks hardly overlap, it is preferable to set the dot recording rate of each ink to a value in the range of 5% to 30%. Further, this range is more preferably 5% to 20%, and most preferably 5% to 15%.

  In the test patch sheets TP1M and TP2M for medium dots (FIG. 2B), the center patch and the color deviation patch are printed using only medium dots. Further, in the test patch sheets TP1S and TP2S for small dots, the center patch and the color deviation patch are printed using only small dots.

  When printing the six test patch sheets shown in FIG. 2B, the test patch sheet printing unit 230 (FIG. 1) displays dot formation data indicating the dot formation state of each ink (CMYK) in each print pixel. Print data TPD including Dc, Dm, Dy, and Dk is supplied to the printer 300. Dot formation data Dc, Dm, Dy, Dk for printing each test patch sheet is prepared in advance and stored in the hard disk of the computer 200. The test patch sheet printing unit 230 reads out the dot formation data Dc, Dm, Dy, Dk and outputs them to the printer 300 in accordance with an output instruction from the operator, and prints the test patch sheet.

  The operator determines the calibration amounts for large dots, medium dots, and small dots as follows. First, when determining the calibration amount of large dots, the two test patch sheets TP1L and TP2L for large dots are observed. Then, on each of the sheets TP1L and TP2L, a gray patch having the same hue as the background BG is selected from the center patch CP and the color deviation patch CSP.

  As a first example, consider a case where the hue of a color-biased patch with M = + 2% and Y = + 1% in the sheet TP1L is the same as that of the background BG. In this case, the calibration amount of the large dot recording rate LD is 0% for cyan C, + 2% for magenta, and + 1% for yellow. As a second example, consider a case where the hue of a color-biased patch with C = −1% and Y = + 1% in the sheet TP2L is the same as that of the background BG. In this case, the calibration amount of the large dot recording rate LD is -1% for cyan C, 0% for magenta, and + 1.5% for yellow.

  Strictly speaking, if the ideal calibration amounts of cyan and magenta are not 0%, the color-biased patch that is the same color as the background BG in both of the two test patch sheets TP1L and TP2L not exist. However, also in this case, the chromatic ink calibration amount can be obtained by ignoring a slight difference in color and selecting a gray patch whose hue is almost the same as that of the background BG.

  In this embodiment, the reason for using the first type test patch sheet for confirming magenta / yellow and the second type test patch sheet for confirming cyan / yellow is as follows. Of the three primary colors of CMY, when the yellow ink amount or recording rate changes, the change in saturation is large, but the change in lightness is small. On the other hand, when the ink amount or recording rate of cyan or magenta changes, the change in brightness is large. Therefore, if a test patch sheet for checking cyan / magenta is printed and used, both the cyan and magenta dot recording rates change between a plurality of color bias patches. The change is great. If the difference in brightness is large, it may be difficult to select a color bias patch whose hue matches the background BG that is the reference gray color. On the other hand, in the first and second type test patch sheets as described above, the brightness does not change much even if the yellow dot recording rate changes, so a color bias patch whose hue matches the background BG is used. Easy to find. As a result, there is an advantage that it is easy to visually determine a calibration amount (a correction amount of the dot recording rate) for compensating an error in the discharge amount of cyan or magenta.

  For medium dots and small dots, similarly to the large dots, two types of test patch sheets are observed to determine the CMY calibration amounts. When the operator inputs a calibration amount relating to large, medium, and small dots of CMY inks to the computer 200, the dot recording rate table correction unit 240 corrects the dot recording rate table for each CMY ink.

  FIG. 2C shows a method for correcting the dot recording rate table in the first embodiment. In this example, only the dot recording rate MD of medium dots is corrected. For example, when the calibration amount of medium dots is + 5%, the dot recording rate MD1 after calibration can be obtained by multiplying the original dot recording rate MD of medium dots by 1.05. The same applies to small dots and large dots. The dot recording rate table is calibrated for each ink. In the first embodiment, since calibration is performed for cyan, magenta, and yellow, a different dot recording rate table is obtained for each of these inks. For black ink, the dot recording rate table before calibration is applied as it is. The dot recording rate table thus calibrated is mounted on a commercially available printer driver for a printer.

  FIG. 4 is a block diagram illustrating the configuration of the printer driver in the embodiment. This printer driver includes a resolution conversion unit 20, a color conversion unit 30, dot recording rate tables 40, 42, 44, 46, a halftone processing unit 50, and a data array unit 60. The resolution conversion unit 20 has a function of converting the resolution of the input color image data RGB data into a resolution suitable for processing after the color conversion unit 30. The color conversion unit 30 performs color conversion using a color conversion look-up table that receives color image data R′G′B ′ after resolution conversion and outputs ink amount data CMYK. The dot recording rate tables 40, 42, 44, and 46 are calibrated for each ink by the above-described method. The ink amount data CMYK representing the ink amount of each ink is used as an input, and the dot of each size of each ink. Dot recording rate data LDc, MDc, SDc... The halftone processing unit 50 executes the halftone process using the three types of dot recording rate data for each ink, thereby forming dot formation data Dc, Dm, Dy, Dk is generated. The data arrangement unit 60 arranges these dot formation data Dc, Dm, Dy, Dk and outputs them as print data PD.

  Normally, the printer driver is implemented as a program stored in a storage unit such as a hard disk in the computer. In this case, the print data PD created by the printer driver is supplied to an external printer. Alternatively, a printer driver may be installed in the printer. In this case, the print data PD created by the printer driver is supplied to a print execution unit (printing mechanism) inside the printer. Even in the case of a printer driver installed in a computer, an external printer can be referred to as a “print execution unit”. Accordingly, the printer driver generally has a function of generating print data to be supplied to the print execution unit based on the color image data. Note that the resolution conversion unit 20 and the data arrangement unit 60 may be omitted from the printer driver.

  In this printer driver, even when the error of the ink discharge amount of each size differs for each ink, the dot recording rate tables 40, 42, 44, and 46 for each ink are independently set so as to compensate for these errors. It can be calibrated. Therefore, it is possible to reduce the color reproduction shift due to the variation in the ink discharge amount. In particular, if the deviation of gray color reproduction is reduced by using a test sheet as shown in FIGS. 2 and 3, there is an advantage that color reproduction in the vicinity of gray can be remarkably improved as compared with the prior art.

  Further, in this embodiment, since the dot recording rate can be calibrated independently for each of large dots, medium dots, and small dots, there is also an advantage that color misregistration in different brightness ranges can be improved. That is, large dots are mainly used in the relatively dark lightness range (shadow region), small dots are used in the relatively light lightness range (highlight region), and medium dots are the lightness range between them (halftone). Mainly used in the region). Therefore, according to the method of this embodiment, it is possible to improve color misregistration in each of the three brightness ranges of the shadow area, the halftone area, and the highlight area.

  Note that the ink discharge amount error is not different for each ink, but may be common to all inks. For example, when the error in the ink discharge amount is caused by the error in the drive waveform for ink discharge, the error in the ink discharge amount is common to all inks. In such a case, the same calibration may be performed for all inks to create a common dot recording rate table.

As a method for mounting the dot recording rate tables 40, 42, 44, and 46 after calibration in the printer driver, various methods as described below can be employed.
(1) The dot recording rate tables 40, 42, 44, and 46 after calibration are prepared in advance by a printer manufacturer, and the dot recording rate tables 40, 42, 44, and 46 after calibration are provided to the user together with the printer driver installation program. provide.
(2) The dot recording rate table before calibration and the calibration amount for each ink are provided to the user together with the printer driver installation program, and after calibration using the dot recording rate table correction unit 240 (FIG. 1) when installing the printer driver. Dot recording rate tables 40, 42, 44, and 46 are created. In this case, the dot recording rate table correction unit 240 is provided as a part (module) of the installation program.
(3) The dot recording rate table before calibration is provided to the user together with the printer driver installation program, and the dot recording rate table correction unit 240 acquires the calibration amount for each ink from a specific location at the time of installation. Recording rate tables 40, 42, 44, and 46 are created. The calibration amount for each ink can be stored in the memory of the printer main body, for example.

  In the method (2) or (3) described above, a single table common to all inks may be supplied as a dot recording rate table before calibration, or a table may be supplied for each ink. . If only one dot recording rate table common to all inks is supplied, the capacity of the installation program can be reduced.

B. Second embodiment:
FIG. 5 is an explanatory diagram showing a method of calibrating the dot recording rate table in the second embodiment. The second embodiment is different from the first embodiment (the method shown in FIG. 2C) only in the dot recording rate table correction method, and the other configurations and processing procedures are the same as those in the first embodiment. .

  FIG. 5A shows the contents of the dot recording rate table before correction, which is the same as FIG. 2A. In the second embodiment, it is assumed that the medium dot recording rate MD is corrected by + 5% and the large dot recording rate LD is corrected by + 3%. At this time, the medium dot recording rate MD is corrected so that the slope α of the first rising portion of the recording rate MD (the range of ink amounts d0 to d1) is increased by 5%. Similarly, the correction of the large dot recording rate LD increases the slope β of the rising portion in the range of the ink amounts d1 to d2 by 3%.

  The dot recording rate is corrected in order from the smallest dot. In the example of FIG. 5, there is no correction of the small dot recording rate, and only the recording rate of medium dots and large dots is to be corrected, so the medium dot recording rate MD is first corrected. When correcting the medium dot recording rate MD, first, the end ink amount d1 'of the rising portion after correction obtained by multiplying the inclination α by 1.05 is calculated. This terminal ink amount d1 'can be obtained by solving (d1-d0) / (d1'-d0) = 1.05. Next, the dot recording rate in the range R1 ′ (d1 ′ to 255) between the corrected final ink amount d1 ′ and the maximum ink amount value (= 255) is changed to the original range R1 (d1 to 255). ). This mapping is executed by simply mapping each coordinate value in the range R1 before correction of the axis (horizontal axis) of the ink amount data to each coordinate value in the range R1 'after correction. In this embodiment, linear mapping is performed, but predetermined nonlinear mapping may be performed.

  FIG. 5B shows the contents of the dot recording rate table after changing the slope α of the medium dot recording rate MD. In the mapping from the range R1 to the range R1 ', all dot recording rates after the ink amount d1 in FIG. 5A are affected. Accordingly, in FIG. 5B, the three types of dot recording rates SD1, MD1, and LD1 after the ink amount d1 'are corrected from the original dot recording rates SD, MD, and LD.

  After correcting the slope α of the medium dot recording rate MD in this way, the slope β of the large dot recording rate LD is corrected. At this time, similarly to the case of the medium dot recording rate MD, first, the corrected end ink amount d2 ″ after the inclination β is multiplied by 1.03 is calculated. This terminal ink amount d2 ″ is obtained by solving (d2′−d1 ′) / (d2 ″ −d1 ′) = 1.03. Here, d1 'and d2' mean the ink amount after the medium dot recording rate MD is corrected. Next, the dot recording rate in the range R2 ″ (d ″ to 255) between the corrected final ink amount d2 ″ and the maximum ink amount value (= 255) is corrected to the range R2 before correction. Mapping is performed from a dot recording rate of '(d' to 255). FIG. 5C shows the contents of the dot recording rate table after changing the slope β of the large dot recording rate LD. In the mapping from the range R2 ′ to the range R2 ″, three types of dot recording rates SD2, MD2, and LD2 in the range after the ink amount d2 ′ in FIG. It has been modified from LD1.

  As described above, in the second embodiment, the ink discharge amount error is compensated by adjusting the slope of the first rising portion (ramp portion) of the dot recording rate of each size. Also by this method, it is possible to calibrate the error of the ink discharge amount of each size of each ink.

C. Third embodiment:
FIG. 6 is a flowchart showing a calibration processing procedure in the third embodiment. In the third embodiment, the processing procedure for obtaining the calibration amount is different from that in the first and second embodiments, but the dot recording rate table calibration method using the apparatus configuration and the calibration amount is different from that in the first and second embodiments. The same can be applied. Note that the procedure of FIG. 6 is executed for each dot size.

  In step S1, an initial dot recording rate table (FIG. 2A) is prepared, and in step S2, first and second type test patch sheets (FIG. 2B) are printed. Then, using the first type and second type test patch sheets, the first calibration amount is determined by selecting a color-biased patch whose hue substantially matches the background gray. The procedure so far is the same as in the first embodiment. For example, in the first type test patch sheet TP1L for confirming magenta / yellow, the hue of the color-biased patch whose calibration amount is M = + 4% and Y = −1% substantially matches the background gray. The primary calibration amounts are determined as C = 0%, M = + 4%, and Y = −1%.

  In step S4, a third type test patch sheet is printed. FIG. 7 is an example of a third type test patch sheet TP3L for large dots. The background BG of the third type test patch sheet TP3l is printed in the same gray as the first type and second type test patch sheets. That is, the background BG has a standard gray color reproduced using only achromatic ink. A plurality of color deviation patches CSP are printed on the background BG. The center color bias patch is a color patch printed according to the dot recording rate calibrated with the primary calibration amount. In this central color deviation patch, the dot recording rates of cyan, magenta, and yellow are C1, M1, and Y1. The other color deviation patches are printed with a dot recording rate in which each ink is readjusted by the same amount by the secondary calibration amount k (%). The dot recording rate of each ink after this readjustment is given by C1 × (1 + k), M1 × (1 + k), Y1 × (1 + k) in this example. Alternatively, the dot recording rate of each ink may be C1 + k, M1 + k, Y1 + k. These color bias patches are color patches in which the dot recording rates of the respective chromatic color inks are readjusted by an equal amount, and are color patches having substantially constant hue and different brightness. In the readjustment of the dot recording rate, it is preferable to maintain the dot recording rate ratio of each chromatic color ink as in the example of FIG.

  In step S5, the secondary calibration amount k is determined by selecting the color bias patch of the third type test patch sheet that has a lightness substantially the same as that of the background BG. As a result, the calibration amount of each chromatic color ink can be determined so that the hue and brightness match the reference gray color of the background BG.

  As described above, in the third embodiment, the primary calibration amount relating to the hue is determined using the first type or the second type test patch sheet, and then the secondary level relating to the lightness using the third type test patch sheet. Since the calibration amount is determined, it is possible to obtain a calibration amount that matches both the hue and brightness with the reference gray color.

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.

D1. Modification 1:
In the above embodiment, four types of CMYK inks are used. However, any other types of inks other than these can be used. For example, in addition to cyan ink and magenta ink, light cyan ink (relatively low density cyan ink) and light magenta ink (relatively low density magenta ink) may be used. In this case, it is also possible to reproduce an achromatic color using a composite gray of yellow ink, light cyan ink, and light magenta ink. In this case, the color patches in the test patch sheet shown in FIG. 2B are also printed using the composite gray of yellow ink, light cyan ink, and light magenta ink.

D2. Modification 2:
In the above-described embodiment, as a test patch sheet for hue adjustment, a first type sheet having a two-dimensional arrangement along the M axis and the Y axis, and a second type having a two-dimensional arrangement along the M axis and the C axis. However, various other configurations can be used as the test patch sheet. For example, prints of test sheets each having a two-dimensional arrangement of the M axis and the C axis may be used for each different value of the yellow ink amount. In this case, the number of test patch sheets increases, but there is an advantage that the constituent amounts of the three CMY inks can be determined at a time.

  In the test patch sheet of the above embodiment, the background BG is printed in the standard gray color. Instead, a color patch having a standard gray color printed separately is prepared, and each of the test patch sheets is prepared. You may make it compare with a color patch.

D3. Modification 3:
In the above-described embodiment, three different sizes of large, medium, and small ink dots can be used. However, the present invention is generally applicable when a plurality of ink dots having different sizes can be used.

D4. Modification 4:
In the above embodiment, the inkjet printer is targeted. However, the present invention is not limited to the inkjet printer, but can be applied to other types of printers such as a laser printer and a thermal sublimation printer. The present invention can also be applied to a copying machine, a facsimile, and the like. In this specification, “printer” has a broad meaning including a copying machine, a facsimile, and the like. “Ink” is used as a synonym for “coloring material” and has a broad meaning including toner.

1 is an explanatory diagram showing a dot recording rate table calibration system 100 as an embodiment of the present invention. FIG. Explanatory drawing which shows the content of the calibration process of the dot recording rate table in 1st Example. Explanatory drawing which shows test patch sheet TP1L for large dots. FIG. 2 is a block diagram illustrating a configuration of a printer driver in the embodiment. Explanatory drawing which shows the calibration method of the dot recording rate table in 2nd Example. The flowchart which shows the process sequence of 3rd Example. Explanatory drawing which shows 3rd type test patch sheet TP1L. Explanatory drawing which shows the outline | summary of the print data generation process for multi-size dot printers. The graph which shows an example of the shift | offset | difference of the gray colorimetric value reproduced by composite black.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Resolution conversion part 30 ... Color conversion part 40, 42, 44, 46 ... Dot recording rate table 50 ... Halftone processing part 60 ... Data arrangement part 100 ... Dot recording rate table calibration system 130 ... Color conversion part (color conversion look) Up table)
140 ... dot recording rate table 150 ... halftone processing unit 200 ... computer 210 ... calibration processing unit 220 ... input receiving unit 230 ... test patch sheet printing unit 240 ... dot recording rate table correction unit 250 ... table storage unit 300 ... for color calibration Color printer

Claims (8)

A method of calibrating dot recording rate data for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks,
(A) preparing a dot recording rate table for outputting recording rate data of ink dots of a plurality of sizes in response to an ink amount input;
(B) calibrating the dot recording rate table for each dot size;
A method comprising: The method of claim 1, comprising:
The calibration is performed such that gray reproduced by the plurality of types of color inks approaches an achromatic color. The method according to claim 1 or 2, comprising:
The calibration is performed for each dot size of each ink, and the dot recording rate table for each ink is generated. A method according to any one of claims 1 to 3,
The step (b)
For each dot size, printing a test patch sheet including a reference gray color reproduced using an achromatic color ink and a plurality of color bias patches reproduced using the plurality of types of color inks;
Determining a calibration amount for each dot according to a printing result of the plurality of color deviation patches;
Calibrating the dot recording rate table according to the calibration amount;
Including
The plurality of color bias patches are color patches that reproduce colors close to the reference gray color using only one type of size dot, and at least part of the dot recording rate of the plurality of types of color inks is A method that is different color patches. The method of claim 4, comprising:
The plurality of types of color inks include cyan ink, magenta ink, and yellow ink,
The test patch sheet is
A plurality of first color bias patches obtained by fixing the dot recording rate of cyan ink and changing the dot recording rates of yellow ink and magenta ink are used as the yellow ink dot recording rate and the magenta ink dot recording rate. A first type of sheet arranged two-dimensionally according to
A plurality of second color bias patches obtained by fixing the dot recording rate of magenta ink and changing the dot recording rate of yellow ink and cyan ink are used as the yellow ink dot recording rate and the cyan ink dot recording rate. A second type of sheet arranged two-dimensionally according to
Including a method. The method of claim 5, comprising:
The step (b)
Printing the first and second type test patch sheets;
Determining a primary calibration amount of cyan ink, magenta ink, and yellow ink by selecting a color-biased patch whose hue substantially matches the reference gray color in the first-type and second-type test patch sheets; When,
A plurality of test patch sheets printed at the dot recording rate after readjustment of the dot recording rates of cyan ink, magenta ink, and yellow ink calibrated using the primary calibration amount, respectively, by equal amounts. Printing a third type of test patch sheet including a color-biased patch;
Determining a secondary calibration amount of cyan ink, magenta ink, and yellow ink by selecting a color bias patch whose brightness substantially matches the reference gray color in the third type test patch sheet;
Including a method. A method for generating dot recording rate data for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks,
(A) preparing a dot recording rate table for outputting recording rate data of ink dots of a plurality of sizes in response to an ink amount input for each ink;
(B) using the dot recording rate table, outputting recording rate data of ink dots of each size of each ink according to the ink amount of each ink;
A method for generating dot recording rate data. A printer driver for generating print data for a printer capable of recording ink dots of a plurality of sizes for each of a plurality of types of color inks,
A color conversion unit that outputs ink amounts of the plurality of types of color inks in response to predetermined color image data input;
A plurality of dot recording rate tables provided for each ink and outputting recording rate data of a plurality of sizes of ink dots in accordance with the ink amount of each ink;
A printer driver.

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