JP2004104437A - Method for generating correction table and method for controlling generation device of correction table - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a gradation correction table without bending, which differs from a table to be requested, is obtained and that discontinuity occurs in a recording concentration characteristic after gradation correction when the table is generated by using the patch of sampled concentration in a multi-value printer using a discontinuous index pattern. <P>SOLUTION: Output gamma for measurement patch output is set and the recording characteristic of the printer is corrected into a linear shape (S102). The patch is outputted (S104) and patch concentration is measured (S105). The reverse consultation table of a "signal value-concentration" table is generated (S106). The reverse table is smoothed by a regression curve (S107). The reverse table is finely adjusted (S108) and an intermediate output gamma table is generated (S201). The generated table is corrected for an index (S202) and the gradation correction table is generated (S109). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for creating a correction table and a method for controlling the creation apparatus, for example, a recording characteristic of a recording apparatus having a non-linear characteristic between an input signal value and a recording signal value output according to the input signal value. The creation of a correction table for correcting the
[0002]
[Prior art]
A recording device such as a printer, a copying machine, and a facsimile records an image composed of a dot pattern on a recording medium such as paper or a plastic thin plate based on image information. Recording apparatuses can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and the like according to the recording method. Among them, an ink jet type (ink jet recording apparatus) records an image by ejecting ink (recording liquid) droplets from an ejection port of a recording head to fly and adhere to a recording medium.
[0003]
Hereinafter, as an example of the recording apparatus, a host (PC) receives a dot image transferred by developing a 300 dpi, 8-bit image data into a binary (multi-valued) dot image and records the image, and an output resolution of 600 dpi. The description will be made with an ink jet recording apparatus (ink jet printer) having the following in mind.
[0004]
The ink jet recording apparatus records an image by combining pixels (dot-on) where recording droplets land on a recording medium and pixels (dot-off) where recording droplets have not landed.
[0005]
In recent years, it has become possible to increase the density of ejection ports of a recording head, and accordingly, it has become possible to perform high-resolution printing with a relatively high resolution (for example, 600 dpi). Therefore, in order to obtain a high-definition print, if a host connected to the printer and serving as a source of image data attempts to process high-resolution (for example, 600 dpi) image data suitable for the printer and transfer it to the printer, The data amount is quadrupled as compared with the transfer of 300 dpi image data, and the data processing time and transfer time are greatly increased. Therefore, there is known a method described in Japanese Patent Application Laid-Open No. 9-46522, in which a binary dot matrix is treated as a multi-valued super pixel on the printer side, and the printer is processed as a 300 dpi multi-valued printer, for example.
[0006]
[Multi-level printer using index pattern]
Japanese Patent Application Laid-Open No. 9-46522 discloses a technique for reducing the load of data processing and transfer, in which an output resolution is 600 dpi, a binary inkjet printer has a resolution of 600 dpi, and a binary 2 × 2 pixel is treated as one set. It is disclosed that the printer is treated as a quinary printer with a resolution of 300 dpi.
[0007]
FIG. 1 is a diagram showing a method of arranging on dots when a set of 2 × 2 pixels of binary with a resolution of 600 dpi is used as one set. The set of 2 × 2 pixels is called a “super pixel”, and the arrangement of on dots is called an “index pattern”.
[0008]
As shown in FIG. 1, the superpixel has five index patterns of 0, 1, 2, 3, and 4 on dots. A printer which holds such an index pattern in advance expands 300 dpi, quinary image data input from the host into 600 dpi, binary image data with reference to the index pattern, and records an image.
[0009]
Next, pseudo halftone processing in a printer using an index pattern will be described.
[0010]
The binary printer with an output resolution of 600 dpi can be regarded as a quinary printer with an input resolution of 300 dpi from the host side by performing index pattern expansion processing on the printer body side. Accordingly, the host develops the 300 dpi, 8-bit input image data into a quinary dot image by a known pseudo halftone process such as a multi-value error diffusion process or a multi-value dither process, and supplies the image to the printer.
[0011]
FIG. 2 is a diagram showing the distribution of the average number of index patterns assigned per unit area (vertical axis) with respect to the signal value (horizontal axis) of an 8-bit input image signal. Here, "average" means that the error diffusion method and the dither method may have different numbers of local recording dots at the start of processing of the processing target image, and do not consider this local difference. Means that.
[0012]
As shown in FIG. 2, for example, when the signal value is "0", all pixels of 300 dpi are occupied by the index pattern of index number 0, and when the signal value is "64", all pixels of 300 dpi are index number 1 Indicates that it is occupied by an index pattern. FIG. 3 shows the correspondence between the signal values (center values) and the index numbers. It should be noted that in the area of 0 <signal value <64, pixels of index numbers 0 and 1 are mixed, and in the area of 64 <signal value <128, pixels of index numbers 1 and 2 are mixed.
[0013]
FIG. 4 is a diagram showing an average of 600 dpi per unit surface and the number of binary on dots (vertical axis) with respect to the signal value (horizontal axis) of an 8-bit input image signal.
[0014]
For example, in the area of 0 <signal value <64, the index pattern of index number 0 decreases and the index pattern of index number 1 increases. That is, in an area where 0 <signal value <64, the number of on-dots increases as the index pattern of index number 1 increases, as shown by the solid line in FIG.
[0015]
In the area of 64 <signal value <128, the index pattern of index number 1 decreases and the index pattern of index number 2 increases. Therefore, in the region of 64 <signal value <128, as shown by the broken line in FIG. 4, the number of on-dots by the index pattern of index number 1 (600 dpi, one on-dot per four pixels) decreases, and the index pattern of index number 2 ( Since the number of on-dots increases by 600 dpi (2 on-dots per four pixels), the total number of on-dots in the region of 64 <signal value <128 increases as shown by the solid line in FIG. Thus, the input resolution using the index pattern shown in FIG. 1 is 300 dpi, the output resolution of the quinary printer is 600 dpi, and the number of binary on-dots increases in proportion to the signal value of the input image signal.
[0016]
[Printing characteristics of a five-level printer with an input resolution of 300 dpi]
As described above, the signal value of the input image signal of the quinary printer with an input resolution of 300 dpi is proportional to the number of ON dots. As described above, when a linear relationship is established between the driving signal (input image signal) of the printer and the output of the recording material (ejection of ink), such output characteristics of the printer are referred to as “linear output characteristics”.
[0017]
However, due to mechanical and optical dot gain, recording density and the number of on-dots are not generally proportional. FIG. 5 is a diagram showing a recording density (vertical axis) when an 8-bit input signal value (horizontal axis) is binary-recorded at 600 dpi, and the recording density tends to peak.
[0018]
[Tone correction table corresponding to index pattern]
In order to compensate for the effect of the dot gain shown in FIG. 5 and to correct the relationship between the input signal value and the recording density to the proportional relationship shown in FIG. 6, a gradation correction table disclosed in Japanese Patent Publication No. Hei 8-2659 (FIG. In this publication, a "density characteristic correction table" is used.
[0019]
In the gradation correction table, a table as shown in FIG. 7 for correcting the relationship between the input signal value and the recording characteristic shown in FIG. The 300-dpi, 8-bit image signal is converted into a gradation-corrected image signal by a gradation correction table, pseudo-halftone-processed by multi-value error diffusion processing or the like, and developed into a 300-dpi, 5-valued dot image. Input to the printer. The printer develops the 300 dpi, quinary dot image into a 600 dpi, binary dot image with reference to the index pattern. Then, the nozzles of the recording head corresponding to the ON dots of the binary dot image are driven to eject the recording droplets.
[0020]
FIG. 8 is a flowchart illustrating the derivation of a gradation correction table for a five-level printer with an input resolution of 300 dpi.
[0021]
Derivation of the gradation correction table is performed by recording the input signal value by a printer, measuring the density of the recorded printed matter, and calculating a table for compensating the density characteristic.
[0022]
First, an output gamma for output of a measurement patch (a gradation correction table through which an input signal value shown in FIG. 9 is passed) is set (S102), and a measurement patch is set (S103). Then, a measurement patch is output (S104), and the density of the output patch is measured with a densitometer (S105).
[0023]
As the measurement patch, the patch shown in FIG. 10 is used in consideration of the reduction in the time required for recording and measurement and the reproducibility of recording by the inkjet printer. The numbers recorded above the respective patches shown in FIG. 10 indicate the signal values of the patches, and the CMYK characters at the upper end indicate the ink for recording the patch row below those characters.
[0024]
Next, a "signal value-density" table is created based on the patch density measurement results, and the signal value and the density value are normalized from 0 to 1, as shown in FIG. Create a table. In FIG. 11, for convenience of description, the horizontal axis represents the signal value and the vertical axis represents the density, but in the following description, both the vertical and horizontal axes are normalized from 0 to 1. Then, in order to obtain an inverse function of the normalization table, the normalization table is reversely searched to create a reverse lookup table of the "signal value-density" table (S106).
[0025]
As shown by the black circles in FIG. 11, errors due to reproducibility of the ink jet printer during printing and measurement errors are mixed in the actual measured values of the density. Therefore, smoothing of a reverse lookup table based on a regression curve is performed by performing a polynomial approximation as shown in Expression (1), and a table showing a smooth curve as shown by a solid line in FIG. 11 (S107). In the smoothing by polynomial approximation, a similar process using a spline curve is disclosed in detail in Japanese Patent Publication No. Hei 8-2659, and a detailed description thereof will be omitted.
y = c ₁ x + c ₂ x ² + C ₃ x ³ + C ₄ x ⁴ + C ₅ x ⁵ … (1)
[0026]
A deviation due to vibration due to the polynomial approximation and a deviation between the origin (0.0, 0.0) and the end point (1.0, 1.0) may occur. Adjustment is made (S108). Then, in the section from the origin to the end point, the range of the standardized and finely adjusted reverse lookup table is returned to, for example, a 12-bit integer table format to create a tone correction table (S109).
[0027]
By correcting the gradation using the gradation correction table obtained in this way, the linearity is established between the input image signal value and the output recording density of the printer, and the gradation is improved. Can be done.
[0028]
Note that the gradation correction table is a one-dimensional table for each ink color, has a smaller table size than the color conversion table which is a three-dimensional table, and uses a plurality of gradation correction tables. Technology is used.
Correction of print head ejection amount using gradation correction table
Driving amount correction using gradation correction table
[0029]
Hereinafter, an application technique using the gradation correction table will be described in detail.
[0030]
[Correction of ejection amount of print head using gradation correction table]
The output density characteristics of the ink jet printer vary depending on the amount of ink ejected from the nozzles of the recording head. The ejection amount of the mass-produced recording head has a variation of about ± 10% with respect to the standard due to the variation of characteristics occurring in the production.
[0031]
Generally, a color processing unit of a printer is designed so that an output result is desired based on a standard ejection amount of a recording head. In other words, if a print head whose ejection amount deviates from the standard ejection amount is used, an output result different from the standard output result expected at the time of design is obtained. That is, the variation in the ejection amount of the recording head causes deterioration in gradation, such as deterioration in color reproducibility and imbalance in density ink.
[0032]
In order to solve this problem, Japanese Patent Application Laid-Open No. 2-167755 discloses a color processing unit designed so that the output result is optimal when the ejection amount of the recording head is at a lower limit, and the recording unit having an ejection amount larger than that is designed. A method of correcting a discharge amount is disclosed in which when a head is used, a gradation correction table is used to make the discharge amount of a print head to be used equal to that of a print head having a lower limit discharge amount.
[0033]
FIG. 12 is a block diagram illustrating a configuration example of a printer driver 300 (color processing unit) and an inkjet printer 400 that operate on the host.
[0034]
The 300 dpi, 8-bit RGB image signal input to the printer driver 300 is converted into a 300 dpi, 8-bit CMYK signal by the three-dimensional lookup table (3DLUT) of the RGB / CMYK converter 301. In the following, a description will be given of a 300 dpi, 8-bit cyan (C) signal, but the processing for signals of other color components is the same.
[0035]
The 300-dpi, 8-bit (256-value) C signal is subjected to gradation correction by the gradation correction unit 302 and expanded to 12 bits (4081 values). At this time, the gradation correction table used by the gradation correction unit 302 is selected from the gradation correction table database 305 based on the separately input ejection amount information of the print head. The expanded 300-dpi, 12-bit C signal is subjected to pseudo-halftone processing by the multi-level error diffusion processor 303 into a 300-dpi, 3-bit (quinary) multi-level dot image.
[0036]
The 300 dpi, 3-bit multi-valued dot image is transferred (input) from the host to the printer 400. The 300 dpi, 3-bit multi-valued dot image input to the printer 400 is developed into a 600 dpi, binary dot image by the dot image development processing unit 401 which refers to the super pixel index pattern stored in the index pattern memory 402. Is done.
[0037]
The 600 dpi, binary dot image is stored in the dot image development buffer 403, sequentially sent to the recording unit 404, and associated with the nozzles arranged at 600 dpi intervals in the inkjet recording head. Then, the recording nozzle corresponding to the on-dot of the binary dot image of 600 dpi is driven, and the recording droplet is ejected.
[0038]
Next, a method of deriving and correcting a gradation correction table used by the gradation correction unit 302 for ejection amount correction will be described. A continuous index pattern is used. An example of a case of roughly classifying into three ranks will be described.
Lower limit value (small discharge amount): n [ng]
Central value (during discharge amount): 1.05 n [ng]
Upper limit (large discharge amount): 1.10 n [ng]
[0039]
A 12-bit gradation correction table is created using a print head of a small discharge amount rank, and the discharge amount when the maximum value 4080 of the gradation correction table is assigned to a print head of a small discharge amount is 4080 × n [ ng]. Therefore, the maximum value of the gradation correction table for the same ejection amount for the other ejection amount ranks is as follows.
Maximum value of gradation correction table during ejection amount = 4080 × n / (1.05 × n) ≒ 3886
Maximum value of gradation correction table for large ejection amount = 4080 × n / (1.1 × n) ≒ 3709
[0040]
By using the gradation correction table obtained for each discharge amount of the print head and controlling the discharge amount after gradation correction to be the same, a similar output result is obtained regardless of the discharge amount rank of the print head. be able to.
[0041]
In the above description, the maximum value of the gradation correction table has been described. Similarly, when a 12-bit gradation correction table is created using a print head having a medium discharge amount, gradation correction of another discharge amount rank is performed. By setting the center value of the table as follows, the ejection amount can be made the same for all input / output image signal values regardless of the ejection amount rank of the recording head.
Correction value of discharge amount large rank = Correction value of medium discharge amount rank x 3709/3886
Correction value of discharge amount small rank = Correction value of discharge amount middle rank × 4080/3886
[0042]
Hereinafter, a procedure for creating a gradation correction table (maximum value = 3886) for a print head with a middle discharge amount using a print head with a middle discharge amount will be described with reference to the flowchart in FIG. It should be noted that, for each processing shown in FIG. 8, a description of substantially the same processing is omitted, and different processing will be described.
[0043]
FIG. 13 is a diagram showing the input / output characteristics of a printer in which the maximum value of the 12-bit gradation correction table is set to "4080". The inverse function (broken line c) is the gradation correction table.
[0044]
In this case, since the gradation correction table of the maximum value = 3886 is obtained by using the print head of the middle rank of the ejection amount, the output density characteristic shown by the broken line b is converted into the characteristic shown by the solid line a, and its inverse function (solid line) Find d).
[0045]
In step S106 for creating a reverse lookup table, the following two methods are conceivable to obtain a tone correction table as shown by a solid line d.
[0046]
● First method (b → a → d)
The inverse function of the gradation correction table (solid line d) of the maximum value 3886 is indicated by a solid line a. The solid line a indicates a region in which the input signal value is 243 (≒ 3886/4080 × 255) or more in FIG. Sticking to the upper limit. Therefore, the range of the vertical axis y in FIG. 13 is set to 0 to 1, and the curves a and b shown in FIG. 13 are respectively represented by y = a (x) and y = b (x ) Gives the following relationship:
y = a (x) = b (x) / b (243/255)
However, 0 ≦ x ≦ 243/255
y = a (x) = 1
However, 243/255 <x ≦ 255/255
[0047]
Further, the gradation correction table becomes an inverse function y = d (x) of y = a (x).
[0048]
● Second method (b → c → d)
A tone correction table y = c (x) having a maximum value of 4080 is obtained, and a tone correction table y = d (x) is obtained based on the obtained value.
d (x) = c (3886/4080 × x)
[0049]
Next, in step S109 for creating a gradation correction table, x and y in Expression (1) obtained by polynomial approximation of the reverse lookup table y = d (x) become real numbers of 0 to 1, respectively. Therefore, in order to set the maximum value of the tone correction table to 3886, a result obtained by multiplying the calculation result of Expression (1) by 3886 and converting the result into an integer is used as the tone correction table.
[0050]
The gradation correction tables for the print heads of the large discharge amount rank and the small discharge amount rank can be calculated as follows based on the gradation correction tables for the print heads of the medium discharge amount rank obtained above.
Correction value for large discharge amount rank = Correction value for medium discharge amount rank x 3709/3886
Correction value for discharge amount small rank = Correction value for medium discharge amount rank × 4080/3886
[0051]
[Driving amount correction using gradation correction table]
Next, the correction of the driving amount using the gradation correction table will be described.
[0052]
An ink jet printer is a method of recording an image by directly spraying ink on a recording medium, and therefore, the ink ejection amount (application amount) is compared with the ink receiving amount (upper limit of the ink ejection amount) of the recording medium (recording paper). ), Beading (ink overflow, bleeding due to ink overflow) occurs.
[0053]
The upper limit of the ink ejection amount differs depending on the characteristics of the recording medium. Therefore, in order to perform color processing corresponding to recording media having different upper limit values of the driving amount, the gradation correction table is adjusted with respect to the color conversion table of the common RGB / CMYK conversion unit 301 to reduce the driving amount. May be adjusted.
[0054]
FIG. 14 is a block diagram showing a configuration example of a printer driver 300 (color processing unit) and an ink jet printer 400 operating on a host. A configuration in which the printer driver performs ejection amount correction of a recording head using a gradation correction table. An example is shown. FIG. 15 is a diagram for explaining the storage contents of the database 304 (see FIG. 14).
[0055]
When the color conversion table A and the gradation correction table A for the recording medium A having the ink receiving amount of 100% already exist, for example, the recording medium having the ink receiving amount of 80% is used in order to keep the size of the database 304 small. For B, color processing that satisfies the ink receiving amount of the recording medium B may be performed by diverting the color conversion table A for the recording medium A and recreating the gradation correction table.
[0056]
When the printer driver (color processing unit) 300 receives image data of 300 dpi and 8 bits each for RGB, the input image data is subjected to RGB → CMYK color conversion after color correction by the 3DLUT of the color conversion unit 301. To become CMYK data. The CMYK image data is subjected to gradation correction by the gradation correction unit 302, subjected to multi-value pseudo halftone processing by the multi-value error diffusion processing unit 303, and then output to the printer 400. At this time, the color processing table used by the color conversion processing unit 301 and the gradation correction unit 302 is based on, for example, information about the type of recording medium input by a user interface (not shown) provided by the printer driver 300. Selected from database 304. For example, when the type of the input recording medium corresponds to the recording medium B, the color conversion table A and the gradation correction table B shown in FIG.
[0057]
As shown in FIG. 15, between the recording media A and B having different ejection amounts, the color conversion table A is made common by using the gradation correction tables A and B having the function of adjusting the ejection amount. Color processing is performed. Hereinafter, the gradation correction table B having a function of adjusting the shot amount will be described.
[0058]
The ink receiving amount of the recording medium A is the same as the maximum ejection amount of the color processing table (a set of the color conversion table and the gradation correction table) created for the recording head of the middle ejection amount, and Assuming that the amount (ink receiving amount) is 100%, the recording medium B has an ink receiving amount of 80% of the recording medium A. When a color conversion table for the recording medium A is used as one of the color processing table sets for the recording medium B, a gradation correction table table that satisfies the ink receiving amount of the recording medium B is calculated by, for example, the following equation. be able to.
Gradation correction value for recording medium B = gradation correction value for recording medium A x 0.8
[0059]
The gradation correction table for the recording medium B has an ejection amount of 80% of the gradation correction table for the recording medium A everywhere. Therefore, when the color processing is performed by the “color conversion table for the recording medium A” + “the gradation correction table for the recording medium B” by performing the gradation correction using the calculated gradation correction table, the recording medium B Image data can be color-processed so as not to exceed the ink receiving amount of the image data.
[0060]
[Multi-valued printer using discontinuous index pattern]
As printers have become cheaper and more sophisticated, printers with higher resolution and a smaller amount of memory in the main body have been desired. To realize this, a discontinuous index pattern as shown in FIG. 16 is used as an index pattern of a super pixel of 2 × 2 pixels of 600 dpi with the same resolution, the index number is kept small, and the amount of memory is reduced. The reduced configuration has been adopted.
[0061]
As shown in FIG. 16, the superpixel has four types of index patterns of 0, 1, 2, and 4 on dots, which correspond to 300 dpi and four values. Similar to FIG. 3, FIG. 17 summarizes the correspondence between signal values (center values) and index numbers.
[0062]
When the index pattern shown in FIG. 16 is used under the conditions shown in FIG. 17, the number of on-dots with respect to the signal value at 600 dpi and binary is as shown in FIG. . This is because, in the region of 0 <signal value <170, the number of dots decreases by 1 dot and increases by 2 dots, whereas in the region of 170 <signal value <255, the number of dots decreases by 2 dots and increases by 4 dots. Note that the number of ON dots is equivalent to the amount of ink applied.
[0063]
Such a system in which the number of on-dots increases in a polygonal line is different from the recording density characteristic of a multi-value printer using a normal (continuous) index pattern shown by a broken line in FIG. The recording density is bent at a portion where the increase of the on-dot is bent (corresponding to the switching point of the index pattern). Therefore, in order to obtain a linear recording density by the correction, a gradation correction table as shown in FIG. 20 corresponding to a portion where the recording density is bent shown in FIG. 19 is required.
[0064]
[Patent Document 1]
Japanese Patent Publication No. 8-2659
[0065]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention is to solve the above-described problems individually or collectively. In a recording apparatus in which the output of a recording signal value with respect to an input signal value is discontinuous, a linear output characteristic is compensated for by compensating for the discontinuous output characteristic. It is an object of the present invention to create a gradation correction table having an arbitrary maximum value that can be set as follows.
[0066]
Further, in a recording apparatus in which the output of the recording signal value with respect to the input signal value is discontinuous, a gradation correction table having an arbitrary maximum value capable of compensating the discontinuous output characteristic and obtaining a linear output characteristic is provided. Another object of the present invention is to create a tone correction curve based on a gradation correction curve for compensating for discontinuous output characteristics.
[0067]
[Means for Solving the Problems]
The present invention has the following configuration as one means for achieving the above object.
[0068]
The creation method according to the present invention is a method for creating a correction table for correcting a recording characteristic of a recording apparatus having a non-linear characteristic between an input signal value and a recording signal value output according to the input signal value. A second tone correction table having a maximum value different from the first tone correction table is created based on the first tone correction table created in a state where the nonlinear characteristic is compensated. It is characterized by the following.
[0069]
The control method according to the present invention is directed to an apparatus for creating a correction table for correcting a recording characteristic of a recording apparatus having a non-linear characteristic between an input signal value and a recording signal value output according to the input signal value. In the control method, a first gradation correction table created in a state where the nonlinear characteristic is compensated is set, and the first gradation correction table is based on the first gradation correction table. A second tone correction table having a different maximum value is created.
[0070]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, creation of the gradation correction table according to the embodiment of the present invention will be described in detail with reference to the drawings.
[0071]
[Create gradation correction table]
First, creation of a gradation correction table of a system having input / output characteristics shown in FIG. 18 will be described.
[0072]
FIG. 21 is a flowchart illustrating an example of a procedure for creating (deriving) a tone correction table. The tone correction table is created by causing a host to execute software provided as a part of a printer driver or in connection therewith. be able to.
[0073]
Compared to the processing shown in FIG. 8, the processing shown in FIG. 21 includes the creation of an inverse index table (S200), the creation of an intermediate output gamma table (S201), and the correction of the index (described later). S202) has been added. The same processes as those in FIG. 8 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0074]
● Principle of creating gradation correction table
The gradation correction table can be considered as an inverse function of the “input signal value−output density” function. Therefore, an output gamma is created using a curve that cancels out the discontinuity of the index pattern, and the created output gamma is calculated and converted according to the curve to obtain the gradation corresponding to the discontinuous index pattern. Obtain a correction table.
[0075]
A method of creating a gradation correction table corresponding to a discontinuous index pattern will be schematically described using Expressions (2) to (6). For the sake of simplicity, a case will be described in which the input and output ranges of all functions are normalized to the range of 0 to 4080.
z = o (x) (2)
x = o ^-1 (Z) ... (3)
z = n (i (x)) (4)
n ^-1 (Z) l = i (x) (5)
x = i ^-1 (N ^-1 (Z)) ... (6)
Here, x: normalized input signal value [0, 4080]
z: Normalized output density [0, 4080]
i (•): Standardized index table (∝ ink ejection amount)
Input [0, 4080], Output [0, 4080]
o (·): normalized output density table for normalized input signal values
Input [0, 4080], Output [0, 4080]
n (•): Normalized output density table input [0, 4080] and output [0, 4080] with respect to the input of the normalized ejection amount
[0076]
Note that the normalized input signal value x corresponds to the image input signal value, and the normalized output density z corresponds to the output density of the printer. Further, the standardized index table i (•) represents the number of ON dots (ink ejection amount) with respect to the input signal value when the index pattern of the present embodiment is used. FIG. 18 shows a graph obtained by calculating i (x) for the entire range [0, 4080] of the normalized input signal value x.
[0077]
The standardized output density table o (·) for the standardized input signal value x does not perform gradation correction, that is, the standardized output density table o (·) is used when the output is performed with the number of on dots corresponding to the input signal value as shown in FIG. The output density with respect to the input signal value thus standardized is represented. The normalized output density table o (·) for the normalized input signal value x is as shown in FIG. 19 because of the bent portion (switching point of the inclination) shown in FIG.
[0078]
The normalized output density table n (•) for the normalized input signal value x indicates the output density for the normalized input signal value when the number of ON dots for the input signal value is in a proportional relationship as shown in FIG. It is standardized and represented. FIG. 5 shows a normalized output density table n (•) for the normalized input signal value x in this case.
[0079]
In the present embodiment, the output density characteristic when gradation correction is not performed is represented by Expression (2), and this is graphed as a solid line shown in FIG. Therefore, the tone correction table to be obtained in the present embodiment is Expression (3), which is the inverse function of Expression (2), and is represented by a thick solid line shown in FIG.
[0080]
The conventional method of creating a gradation correction table is for a system having continuous recording characteristics as shown in FIG. Therefore, the present invention is applicable to a system having output density characteristics as shown in FIG. This corresponds to equation (7).
z = n (x) (7)
[0081]
The output density characteristic (FIG. 5) of the system using a continuous index pattern corresponding to the equation (7) is a characteristic indicating the output density with respect to the input image signal value, and at the same time, the output density characteristic with respect to the number of 600 dpi on dots. It can be said that the characteristic indicates the output density. On the other hand, in the system according to the present embodiment, the number of on dots with respect to the input signal value can be represented by i (x), and has a characteristic as shown in FIG.
[0082]
As described above, the output density characteristic in the present embodiment is expressed by Expression (4) using the output density characteristic n (•) of a system using a continuous index pattern and the standardized index table i (•). Can be represented. Hereinafter, the tone correction table is derived by modifying equation (4).
[0083]
Using a conventional method of creating a gradation correction table, n as shown by a solid line in FIG. ^-1 (·) Is obtained and given to both sides of the equation (4) to obtain the equation (5). Inverse function i of i (•) ^-1 (·) Is obtained as shown by a solid line in FIG. 22, and is given to both sides of equation (5) to obtain equation (6).
[0084]
On the other hand, from Expression (3), which is a conventional tone correction table, it can be seen that the tone correction table can be defined as one that receives a normalized output density z as an input and outputs a normalized input signal value x. Looking at equation (6) based on this, it can be seen that i ^-1 (N ^-1 It can be seen that (•)) is the gradation correction table in the present embodiment.
[0085]
In a system using a discontinuous index pattern as in the present embodiment, in order to obtain the output density characteristic n (•) of a system using a continuous index pattern, an inverse function i (•) of i (•) is used. ^-1 A patch may be output using (•) instead of the gradation correction table, and the density of the output patch may be measured.
[0086]
Hereinafter, processing unique to the present embodiment, which is shown in the flowchart of FIG. 21, will be described in detail.
[0087]
● Reverse index table (S200)
The inverse index table shown by the solid line in FIG. 22 is an inverse function of the table of the number of on dots with respect to the input signal value when a discontinuous index pattern is used, shown by the broken line. As shown in FIG. 22, this table can be easily created, and a detailed description of the creation method is omitted. The inverted index table set here is used for setting the output gamma for outputting the measurement patch (S102), but is not used for correcting the index (S202).
[0088]
That is, in order to obtain the output density characteristic n (·) of a system using a continuous index pattern, an inverse index table is created (S200), and set as a gradation correction table for outputting a patch for measurement (S200). S102).
[0089]
By outputting a patch using the inverse index table, the number of on-dots is linear with respect to the input image signal value as shown in FIG. 6 after multi-value → binary conversion (expansion of an index pattern) by the printer 400. Can be obtained. In other words, by using the inverted index table, the number of ON dots for the input image signal value becomes linear, and even if a patch sampled at an appropriate interval shown in FIG. It is possible to prevent a point at which the density characteristic is switched from being missed.
[0090]
Also, if sampled patches can be used, even in systems where the density reproduction characteristics within the same paper surface or between paper surfaces are unstable, the effect of fluctuations in the ejection amount due to the temperature rise of the recording head due to recording is suppressed. As a result, a highly reliable recording density characteristic can be obtained. Of course, there is also an advantage that many processes in the conventional method of creating a tone correction table can be used to create a tone correction table in a system having a non-linear printing characteristic like the printer 400 of the present embodiment. Specifically, in steps S102 to S108 shown in FIG. 21, the same processing as the conventional method of creating a gradation correction table is executed.
[0091]
● Creating an intermediate output gamma table (S201)
By matching the input / output range [0, 1] of the reverse lookup table finely adjusted by the processing of step S108 to [0, 4080] for both input and output, the present embodiment calls this “intermediate output gamma table” n ^-1 (•) is requested.
[0092]
● Correction for index (S202)
As described above, the gradation correction table o to be obtained by comparing the expressions (3) and (6). ^-1 (•) indicates i ^-1 (N ^-1 It can be seen that it is equivalent to (•)). Then i ^-1 (•) and n ^-1 By combining (•), o ^-1 (•) is requested.
[0093]
That is, for all the input values in the input range [0, 255], n shown in FIG. ^-1 Check the output value by referring to (•). Then, the output value is stored in an inverse index table i shown by a solid line in FIG. ^-1 By inputting to (•), the composite output value i of the table ^-1 (N ^-1 (・)). In other words, in step S202, the gradation correction table n having no bending shown in FIG. ^-1 () Is converted into a numerical value, and a gradation correction table having a bend indicated by a thick solid line in FIG. 20 is obtained.
[0094]
By calculating the discontinuous bent portion of the gradation correction table by numerical conversion in this way, the color reproduction characteristics of the printer are not affected by instability and the density measurement error at the time of density measurement is not affected. Misalignment "can be prevented.
[0095]
The composite output value i for each input image signal value obtained by the above procedure ^-1 (N ^-1 (•)) is converted into a table, and a gradation correction table o ^-1 By substituting into the array for (•), a gradation correction table (output gamma table) as shown by a thick solid line in FIG. 20 is obtained (S109).
[0096]
[Problem of creating a gradation correction table by the above method]
However, if a gradation correction table is created by the above method for a multi-value printer using a discontinuous index pattern, the maximum value corresponds to the point P in FIG. Even if an attempt is made to create a gradation correction table less than 4080), a gradation correction table having a desired maximum value (point P in FIG. 24) and having a linear output density characteristic after gradation correction is obtained. Can not get.
[0097]
More specifically, for the full-range gradation correction table indicated by the broken line C1 in FIG. 25, the above-described method is used to derive a gradation correction table having an arbitrary maximum value for a printing apparatus having linear output characteristics. The tone correction table having the desired maximum value is represented by a two-dot chain line C0, and it is not possible to obtain a tone correction table that compensates for the nonlinearity of the printer and makes the output density characteristic linear.
[0098]
Further, based on the tone correction table corresponding to the non-linearity of the printer, when a tone correction table having a desired maximum value is created using the above-described method of converting the tone correction table by, for example, simple scaling, The gradation correction table as shown in FIG. 24 is obtained, and the originally required gradation correction table as shown in FIG. 26 cannot be obtained, and the gradation after the gradation correction is rather deteriorated.
[0099]
Specifically, based on the gradation correction table for the print head of the middle discharge amount shown in FIG. 24, the gradation correction tables for the large and small discharge amounts obtained by the above-described method are as shown in FIG. And the bent portion of the gradation correction table for compensating the output characteristics of the printer is located on the extension of the point Q on the x-axis. However, when performing output with a printer having output characteristics as shown in FIG. 18, in order to make the output density characteristics linear, the gradation correction table for the large and small ranks of the ejection amount is set as shown in FIG. The bent portion needs to be located on the extension of the point P on the y-axis.
[0100]
Further, in the method of creating a gradation correction table having a nonlinear output characteristic using the discontinuous index pattern, the maximum value is adjusted for the intermediate output gamma, and the correction for the index is performed. When the gradation correction table indicated by the two-dot chain line C0 in FIG. 25 is converted, the gradation correction table indicated by the solid line C2 is obtained. However, the gradation correction table C2 has a maximum value different from the desired maximum value.
[0101]
[solution]
The following three measures can be considered to solve the above problems.
(1) For each gradation correction table having a different maximum value, a gradation correction table is created based on the output density data of the printer.
(2) Tone correction tables having different maximum values based on one intermediate output gamma are obtained by analytical conversion.
(3) Conversion is performed based on one tone correction table to analytically determine a tone correction table having an arbitrary maximum value.
[0102]
Hereinafter, the above three solutions will be sequentially described as embodiments.
[0103]
[First Embodiment]
In the first embodiment, an inkjet printer that performs binary recording with an output resolution of 600 dpi uses a 300 dpi, quaternary index pattern as shown in FIG. However, an example in which gradation correction is performed as a four-valued multi-value printer with an input resolution of 300 dpi will be described.
[0104]
The configuration examples of the printer driver 300 (color processing unit) and the inkjet printer 400 running on the host are the same as those in FIG. 12, and detailed description thereof will be omitted. The relationship between the input image signal value of the printer 400 and the number of ON dots is a non-linear polygonal line as shown in FIG.
[0105]
Hereinafter, a method of creating a gradation correction table for a system having output characteristics as shown in FIG. 16 will be described.
[0106]
FIG. 27 is a flowchart illustrating an example of a procedure for creating (deriving) a tone correction table according to the first embodiment. The host executes software provided as a part of the printer driver or in connection with the tone correction table. A correction table can be created.
[0107]
Compared to the processing shown in FIG. 21, the processing shown in FIG. 27 is added with the setting of the maximum value of the gradation correction table (S301), which will be described in detail later. 8 and 21 are denoted by the same reference numerals, detailed description thereof will be omitted, and only characteristic portions will be described.
[0108]
Setting of maximum value of gradation correction table (S301)
The maximum value of the gradation correction table to be obtained is set. Since the gradation correction table of the print head having the middle ejection amount is obtained, “3886” (see FIG. 24) is set as the maximum value of the gradation table.
[0109]
● Setting of output gamma for output of measurement patch (S102)
In order to obtain an output density characteristic n (·) in a system using a continuous index pattern using equation (1), the inverse index table created in step S200 is set as a tone correction table for outputting a measurement patch. . By outputting the measurement patch using this inverted index table, after the multi-valued to binary conversion (expansion of the index pattern) of the printer 400, a linear ON with respect to the input image signal value as shown in FIG. An output of the number of dots can be obtained.
[0110]
By performing recording using the inverted index table in this manner, the number of on-dots relative to the input image signal value becomes linear, and thus, even if patches sampled at appropriate intervals shown in FIG. As shown in FIG. 23, it is possible to prevent the switching of the density characteristic from being missed. In addition, by enabling arbitrary sampling, it is possible to obtain highly reliable recording density characteristics even in systems where the density reproduction characteristics within the same paper surface or between paper surfaces are unstable, such as ink jet printers. Become. Further, the same processing as that of the related art can be used for many processing when creating a gradation correction table of a system having a non-linear recording characteristic.
[0111]
● Creating an intermediate output gamma table (S201)
The input / output range [0, 1] of the reverse lookup table fine-tuned by the processing in step S108 is converted into an input [0, 4080] and an output [0, 3886].
[0112]
● Correction for index (S202)
As described above, the work of adding the nonlinearity of the input / output characteristics of the printer to the intermediate output gamma table obtained by removing the influence of the nonlinearity of the input / output characteristics of the printer is performed. A table used for conversion of the gradation correction table in the correction for the index, which is characteristic of the first embodiment, will be described.
[0113]
First, it is conceivable that the intermediate output gamma shown by the solid line in FIG. 7 is converted by an inverted index table whose maximum value shown by the dashed line in FIG. 28 is 4080. More specifically, the conversion is performed by performing correction using the intermediate output gamma for all of the input values 0 to 255 and obtaining the output value of the inverse index table for the input of the obtained correction value. However, when the intermediate output gamma whose maximum value is not 4080 is converted in this way as in the first embodiment, a clear shift occurs at the maximum value portion. This is because, when the maximum value is 3886 as in the first embodiment, the correction values to be input to the reverse index table exist in the regions X and Y shown in FIG. .
[0114]
In the first embodiment, in view of the above, a table that is obtained based on the following conditions and that changes according to the maximum value of the gradation correction table as shown by a solid line in FIG. 28 is used as the inverse index table for correcting the index. I do.
(A) The bent portion between the regions X and Y caused by the input / output characteristics of the printer is not affected by the change of the maximum value of the gradation correction table.
(B) The maximum value of the intermediate output gamma table is stored by the conversion using the inverted index table, in other words, the same value is maintained before and after the conversion.
[0115]
Therefore, the correction value of the gradation correction table is obtained by calculating the correction value by the intermediate output gamma for each of the input values 0 to 255, and performing the correction by the reverse index table using the obtained correction value as an input. The correction value of the index table can be obtained.
[0116]
● Creation of gradation correction table (S109)
In step S202, the intermediate output gamma converted by the inverse index table is converted into a format that can be stored in the database 305 of the tone correction table shown in FIG. 12, thereby creating a tone correction table.
[0117]
As described above, the gradation correction table for the recording head of the middle ejection amount is obtained.
[0118]
In the above, the method of deriving the gradation correction table for the print head of the medium ejection amount used in the design has been described. Can be created. More specifically, the maximum value is set to 3709 when creating a gradation correction table for a print head with a large ejection amount rank, and set to the maximum value when creating a gradation correction table for a print head with a small ejection amount rank. By setting the values to 4080, a gradation correction table corresponding to the ejection amount correction can be obtained.
[0119]
[Second embodiment]
Hereinafter, creation of the gradation correction table according to the second embodiment of the present invention will be described. Note that, in the present embodiment, the same reference numerals are given to configurations substantially similar to those of the first embodiment, and detailed description thereof will be omitted.
[0120]
Hereinafter, a case where color processing is performed in a system using a printer 400 having a non-linear output characteristic having a discharge amount correction function similar to that of the first embodiment shown in FIG. 12 will be described.
[0121]
In the second embodiment, when the tone correction table of the printer 400 having a non-linear output characteristic is obtained, a state in which the non-linear output characteristic of the printer 400 is compensated using, for example, the method described in the first embodiment. Is used to determine the intermediate output gamma, and by using the obtained intermediate output gamma, a tone correction table having an arbitrary maximum value is determined. More specifically, for example, the intermediate output gamma having a maximum value of 3886 is converted to generate an intermediate output gamma having an arbitrary maximum value (for example, 4706), and thereafter, the intermediate output gamma having the generated maximum value 4706 is generated. Is converted into a gradation correction table in a format that takes into account the nonlinear output characteristics of the printer 400.
[0122]
FIG. 29 is a flowchart illustrating a method for creating a gradation correction table according to the second embodiment. Note that, by using the intermediate output gamma of the maximum value 3886 for the print head of the medium discharge amount, which is created by the same method as in the first embodiment, the floor of the maximum value 3709 for the print head of the large discharge amount is used. A case where a key correction table is created will be described.
[0123]
● Setting of intermediate output gamma (S501)
An intermediate output gamma of the maximum value 3886 created by the same method as in the first embodiment is set. Since the intermediate output gamma is obtained while compensating for the non-linear output characteristics of the printer, there is no bent portion as shown in C1 in FIG. 32 (the maximum value is different).
[0124]
● Setting of maximum value of output gamma (S502)
The maximum value of the gradation correction table to be obtained is set. In the second embodiment, a maximum value of 3709 is set for a print head with a large rank of discharge amount.
[0125]
● Creation of reverse index table (S200)
A table for converting the intermediate output gamma obtained while compensating for the non-linear output characteristics of the printer into a gradation correction table corresponding to the non-linear output characteristics of the printer is created. This processing is substantially the same as the “creation of the inverted index table (S200)” in the first embodiment, but the converted gradation correction table maximum value is 3709. Therefore, the table created here is obtained by replacing the input signal value “3886” in FIG. 28 with “3709”. Of course, the inverted index table created here is used for correction of the index (S202).
[0126]
● Output gamma thinning process (S503)
Conversion is performed based on the gradation correction table of an arbitrary maximum value (here, 3886) set in the setting of the intermediate output gamma (S501) to create an arbitrary (here, 3709) intermediate output gamma. . Any method can be used as a conversion method between the gradation correction tables having different maximum values. For example, if the output values of the gradation correction table having the set maximum value are simply scaled, Good. The gradation correction table after scaling in the case of performing simple scaling is as follows.
Output value after scaling = ROUND (3709/3886 x correction value before scaling)
Here, ROUND (·) is a function that takes a real number as an argument, rounds the input real number, and then converts it to an integer.
[0127]
● Correction for index (S202)
The same processing as in the first embodiment is performed using the inverted index table created in step S200.
[0128]
● Creation of gradation correction table (S109)
As in the first embodiment, the data is converted into a tone correction table format.
[0129]
In the above description, a method of creating a gradation correction table with a maximum value of 3709 for a print head with a large discharge amount rank has been described. Can be obtained by
[0130]
In the above description, a case has been described in which a gradation correction table for a print head of another discharge amount rank is obtained based on a gradation correction table for a print head of a middle discharge amount that has already been created. The gradation correction table may be a table for a print head of any discharge amount rank.
[0131]
[Third embodiment]
Hereinafter, creation of the gradation correction table according to the third embodiment of the present invention will be described. Note that, in the present embodiment, the same reference numerals are given to configurations substantially similar to those of the first embodiment, and detailed description thereof will be omitted.
[0132]
The third embodiment is a system shown in FIG. 12 using a printer having a non-linear output characteristic having the same ejection amount correction function as that of the first embodiment. An example will be described in which a gradation correction table having a maximum value of 3709 is derived for a print head having a large ejection amount rank based on the correction table.
[0133]
FIG. 30 is a flowchart illustrating a method for creating a gradation correction table according to the third embodiment.
[0134]
● Output gamma setting (S600)
A gradation correction table of the maximum value 3886 created by the same method as in the first embodiment is set.
[0135]
● Setting of maximum value of output gamma (S502)
The maximum value of the gradation correction table is set to 3709 for a print head with a large discharge amount rank.
[0136]
● Creation of index table (S601)
A table shown by a solid line, which is an inverse function of the number of on dots with respect to an input signal value when a discontinuous index pattern is used, which is shown by a broken line in FIG. 31, is created. Since this table can be easily created, a description of the creation method is omitted.
[0137]
● Creation of reverse index table (S200)
A table for converting the intermediate output gamma obtained while compensating for the non-linear output characteristics of the printer into a gradation correction table corresponding to the non-linear output characteristics of the printer is created. This processing is substantially the same as the “creation of the inverted index table (S200)” in the first embodiment, but the converted gradation correction table maximum value is 3709. Therefore, the table created here is obtained by replacing the input signal value “3886” in FIG. 28 with “3709”.
[0138]
● Creation of intermediate output gamma (S201)
The output gamma of the maximum value 3886 corresponding to the non-linear output characteristic of the printer set in step S600 is converted using the index table created in step S601, and the same as the intermediate output gamma of the first embodiment. The table is converted to a table obtained with the printer non-linearity compensated. More specifically, output gamma correction values are obtained for all input values, conversion is performed using an index table using the correction values as input, and the output value is set as an intermediate output gamma (see the following expression). .
Intermediate Opg [i] = index table [Opg [i]]
Here, Opg is an abbreviation for “output gamma”.
i is an integer from 0 to 255
[0139]
● Output gamma thinning process (S503)
As in the second embodiment, a thinning process is performed on the obtained intermediate output gamma.
[0140]
● Correction for index (S202)
The same processing as in the second embodiment is performed using the inverted index table created in step S200.
[0141]
● Creation of gradation correction table (S109)
As in the first embodiment, the data is converted into a tone correction table format.
[0142]
By the way, in the present embodiment, unlike Japanese Patent Publication No. 8-2659, a method is employed in which an inverse table of the input signal value-output density table is obtained, and then the data is smoothed using a regression curve. However, similarly to Japanese Patent Publication No. Hei 8-2659, a gradation correction table may be obtained by using a method of obtaining an inverse table after smoothing the data of the input signal value-output density table.
[0143]
Further, in the above, an example in which a combination of dots corresponding to the same size and the same ink type is used as an index pattern has been described. In the case of a printer using two types of inks, a light ink and a dark ink, a combination of a light dot and a dark dot can be used for an index pattern, respectively. The method can be applied.
[0144]
Furthermore, in the above, the example where the bent portion of the recording density caused by the switching of the index pattern is one is described, but the number of the bent portion is not limited to one, and even in a system having two or more bent portions, The method for creating a gradation correction table according to the embodiment can be applied.
[0145]
Of course, the method of creating the correction table according to the embodiment is not limited to an ink jet printer using a discontinuous index pattern, but is widely applied to all recording devices having a discontinuous output characteristic with respect to input, for example, a hard copy device of a CRT. Can be used.
[0146]
[Modification]
In the second and third embodiments, an example has been described in which a table in which a desired maximum value is stored as shown in FIG. 28 is used as an inverse index table used for correction of an index. However, the inverted index table in which the maximum value 4080 is stored shown in FIG. 31 is used instead of the table in which the desired maximum value is stored, and the gradation corresponding to the index is corrected using the inverted index table. The end of the correction table (curve C1 shown in FIG. 32) may be interpolated with a straight line to obtain a curve C2 shown in FIG.
[0147]
This reduces the accuracy, but makes it possible to use one fixed table as the reverse index table, reducing the memory for storing the reverse index table and reducing the processing time required for recalculating the reverse index table. For example, a simpler system configuration can be achieved.
[0148]
● Other methods of thinning output gamma
In the above description, a method of creating a gradation correction table having a different maximum value is to simply scale the gradation correction value of an intermediate output gamma created in a state where the nonlinear output characteristics are compensated, thereby obtaining the maximum value. A method for obtaining a different gradation correction table has been described. By performing simple scaling on all the tone correction tables for each color, the color balance after the output gamma thinning process is maintained even if tone correction tables with different maximum values are used. As the thinning processing, for example, a method that maintains the linearity of the output density characteristic may be used. In this case, the color processing can be performed using the tone correction tables having different maximum values, and the density characteristics of the output image can be preserved.
[0149]
● System configuration using gradation correction table
The gradation correction table created in each of the above embodiments is used in a system for correcting the ejection amount of the print head. However, the created gradation correction table can also be used for a system for performing the injection amount correction as shown in FIG.
[0150]
The gradation correction table corresponding to each discharge amount rank of the print head is as shown in FIG. 26, and the gradation correction table of each discharge amount rank is simply multiplied by a constant for the entire defined area. Not be. That is, even if the maximum value of the gradation correction table is converted by the ratio of the driving amount, the target driving amount may not be achieved.
[0151]
Therefore, when the created tone correction table is used for the ejection amount correction, in consideration of the above points, for example, while gradually decreasing the maximum value of the tone correction table, the tone correction table that satisfies the ejection amount is used. It is necessary to take measures such as finding the maximum value of.
[0152]
[Other embodiments]
The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but can be applied to a device including one device (for example, a copier, a facsimile machine, etc.). May be applied.
[0153]
Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (or a CPU or a CPU) of the system or the apparatus. Needless to say, the present invention can also be achieved by an MPU) reading and executing a program code stored in a storage medium. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0154]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is executed based on the instruction of the program code. It goes without saying that the CPU included in the expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0155]
When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.
[0156]
【The invention's effect】
As described above, according to the present invention, in a recording apparatus in which the output of the recording signal value with respect to the input signal value is discontinuous, it is possible to compensate for the discontinuous output characteristic and obtain a linear output characteristic. Can be created.
[0157]
Further, in a recording apparatus in which the output of the recording signal value with respect to the input signal value is discontinuous, a gradation correction table having an arbitrary maximum value capable of compensating the discontinuous output characteristic and obtaining a linear output characteristic is provided. Can be created based on a gradation correction curve for compensating for discontinuous output characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing a method of arranging on dots when a resolution of 600 dpi and a set of binary 2 × 2 pixels are used.
FIG. 2 is a diagram showing an average distribution of the number of index patterns allocated per unit area with respect to signal values of an 8-bit input image signal;
FIG. 3 is a diagram summarizing the correspondence between signal values and index numbers;
FIG. 4 is a diagram showing an average of 600 dpi per unit surface and the number of binary on-dots with respect to a signal value of an 8-bit input image signal;
FIG. 5 is a diagram showing a recording density when an 8-bit input signal value is recorded at 600 dpi and binary.
FIG. 6 is a diagram showing a relationship between an input signal value and a recording density;
FIG. 7 is a diagram showing a table that is the inverse function of FIG. 5;
FIG. 8 is a flowchart illustrating derivation of a gradation correction table for a five-level printer with an input resolution of 300 dpi;
FIG. 9 is a diagram showing a gradation correction table for passing input signal values;
FIG. 10 is a diagram illustrating an example of a measurement patch.
FIG. 11 is a diagram showing a signal value-density table.
FIG. 12 is a block diagram illustrating a configuration example of a printer driver (color processing unit) and an inkjet printer that operate on a host.
FIG. 13 is a diagram illustrating input / output characteristics of a printer in which the maximum value of a 12-bit gradation correction table is “4080”;
FIG. 14 is a block diagram illustrating a configuration example of a printer driver (color processing unit) and an inkjet printer that operate on a host.
FIG. 15 is a view for explaining storage contents of a database;
FIG. 16 is a view for explaining an index pattern by super pixels;
FIG. 17 is a diagram summarizing the correspondence between signal values and index numbers;
FIG. 18 is a diagram showing the number of ON dots with respect to a signal value;
FIG. 19 is a diagram showing a recording density characteristic of a multi-value printer using a continuous index pattern.
FIG. 20 is a diagram showing a gradation correction table;
FIG. 21 is a flowchart showing an example of a procedure for creating a gradation correction table;
FIG. 22 is a diagram illustrating a method of creating a gradation correction table.
FIG. 23 is a view for explaining a method of creating a gradation correction table.
FIG. 24 is a diagram for explaining a method of creating a gradation correction table.
FIG. 25 is a view for explaining a method of creating a gradation correction table.
FIG. 26 is a diagram showing a necessary gradation correction table;
FIG. 27 is a flowchart illustrating an example of a procedure for creating a gradation correction table according to the first embodiment;
FIG. 28 is a diagram showing a table used for conversion of a gradation correction table in correction for an index;
FIG. 29 is a flowchart showing a method for creating a gradation correction table according to the second embodiment;
FIG. 30 is a flowchart showing a method for creating a gradation correction table according to the third embodiment;
FIG. 31 is a view for explaining a method of creating a gradation correction table.
FIG. 32 is a diagram illustrating a method of creating a gradation correction table.

Claims (8)

A method for creating a correction table for correcting a recording characteristic of a recording apparatus having a non-linear characteristic between an input signal value and a recording signal value output according to the input signal value,
A second tone correction table having a maximum value different from the first tone correction table based on the first tone correction table created in a state where the non-linear characteristic is compensated. And how to create. 2. The method according to claim 1, wherein the second tone correction table is created based on an image signal value input to the printing apparatus and a print density characteristic of the printing apparatus. The second gradation correction table is created based on a table in which the non-linear characteristic is compensated, which is generated from a table corresponding to the non-linear characteristic with the first gradation correction table as an input. The method according to claim 1, wherein: 4. The apparatus according to claim 1, wherein the second gradation correction table is created based on a table obtained by scaling a gradation correction value of the first gradation correction table. 5. Creation method. 4. The recording medium according to claim 1, wherein the second gradation correction table is used for correcting a recording material hit amount in consideration of a receiving amount of a recording material of a recording medium. 5. How to make. A control method of an apparatus for creating a correction table for correcting a recording characteristic of a recording apparatus having a non-linear characteristic between an input signal value and a recording signal value output according to the input signal value,
Set a first gradation correction table created in a state where the nonlinear characteristics are compensated,
A control method comprising: creating a second tone correction table having a maximum value different from that of the first tone correction table based on the first tone correction table. A non-transitory computer-readable storage medium storing a program for controlling an information processing apparatus to execute creation of a gradation correction table according to any one of claims 1 to 6. A recording medium on which the program according to claim 7 is recorded.

Images