JP2011218576A - Density correction method and printer - Google Patents

Abstract

When printing is performed by ejecting transparent ink, a variation in ink ejection characteristics is corrected for each nozzle, and a uniform image is printed.
A first ink ejection amount that is a standard ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and a third ink that is smaller than the first ink ejection amount. A test pattern having a multi-gradation patch is printed by ejecting transparent ink from the nozzle at each ejection amount of the ejection amount to form a dot, and with respect to the gradation value of the patch for each ejection amount of ink. The gloss level is measured, and the tone values of the patches when the gloss levels are the same are obtained for the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount, and the obtained first A correction table is created from the gradation value in the second ink ejection amount and the gradation value in the third ink ejection amount with respect to the gradation value of the ink ejection amount, and the amount of dots formed is corrected.
[Selection] Figure 8

Description

  The present invention relates to a density correction method and a printing apparatus.

2. Description of the Related Art Printing apparatuses that perform recording by ejecting liquid from nozzles and landing ink droplets (dots) on a medium are known. In such a printing apparatus, variations in ink ejection characteristics (for example, ink ejection amount) may occur in each of the plurality of nozzles due to manufacturing errors or the like. When printing is performed using nozzles having different ejection characteristics, the size of the formed dots also varies, and a clean image cannot be printed.

On the other hand, by using a plurality of types of ink, two or more types of ink droplets having different ink amounts are selectively ejected onto the medium to form a plurality of dots having different sizes in one pixel region. A method for correcting the variation for each nozzle is proposed. (For example, patent document 1).

JP 2006-88531 A

In recent years, printing is often performed using transparent ink. For example, when it is desired to give gloss to the printed surface, it is common to form a glossy surface by spraying transparent ink on the formed image and coating it. On the other hand, with the conventional method, it is not possible to correct the ejection amount for each nozzle for transparent ink, and bleeding may occur in a portion where the ink ejection amount is large, and conversely, gloss is sufficient in a portion where the ink ejection amount is small. There were problems such as being unable to obtain.

An object of the present invention is to print a uniform image by correcting variations in ink ejection characteristics for each nozzle when printing is performed by ejecting transparent ink with an inkjet printer.

The main invention for achieving the above object is: (A) a first ink ejection amount that is a standard ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and the first ink ejection amount. A plurality of gradation patches are provided by forming dots by ejecting transparent ink from a nozzle onto a medium with a third ink ejection amount that is smaller than an ink ejection amount and a third ink ejection amount. Printing a test pattern; (B) measuring the glossiness of each tone value of the patch for each ink ejection amount; and (C) the tone value of the patch when the glossiness is the same. Obtained for each case of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount, and for the gradation value of the obtained first ink ejection amount,
A correction coefficient is calculated from the gradation value at the second ink ejection amount and the gradation value at the third ink ejection amount, and (D) a correction table is created from the relationship between the ink ejection amount and the correction coefficient. (E) A density correction method that corrects the amount of dots to be formed by applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on the correction table.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram illustrating a configuration of a printer. FIG. 2 is a diagram illustrating a configuration of a printer according to an embodiment. It is sectional drawing for demonstrating the structure of a head. It is a figure which shows arrangement | positioning of the nozzle in a head unit. It is a figure which shows the example of the drive signal COM which defines operation | movement of the piezo element PZT. FIG. 6A is a diagram illustrating an example of the drive signal COM when the maximum potential difference Vh of the drive pulse is increased (Vhl). FIG. 6B is a diagram illustrating an example of the drive signal COM when the maximum potential difference Vh of the drive pulse is reduced (Vhs). FIG. 4 is a diagram illustrating a flow of print control performed by a printer driver. It is a figure showing the flow for producing a correction table in 1st Embodiment. It is a figure which shows the example of the test pattern printed by this embodiment. It is a figure which shows the relationship between the gradation value measured from the test pattern, and glossiness. It is a figure explaining the method for calculating the correction coefficient for every ink ejection amount. It is a figure which shows the example of the correction table produced in this embodiment. It is a figure showing the degree (color difference) of the discoloration of the dot by UV irradiation amount at the time of using a metal halide lamp and a mercury lamp. It is a figure showing the flow for producing a correction table in 2nd Embodiment. It is a figure which shows the relationship between the gradation value measured from the test pattern, and color difference ((DELTA) E).

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) The first ink ejection amount that is a standard ink ejection amount, the second ink ejection amount that is larger than the first ink ejection amount, and the ink ejection amount that is smaller than the first ink ejection amount. A test pattern having patches of a plurality of gradations is printed by ejecting transparent ink from a nozzle onto a medium at each ink ejection amount of the third ink ejection amount to form a dot, and (B) the ink For each ejection amount, measure the glossiness for each tone value of the patch, (
C) The tone value of the patch when the glossiness is the same is obtained and obtained for each case of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount. A correction coefficient is calculated from the gradation value at the second ink ejection amount and the gradation value at the third ink ejection amount with respect to the gradation value of the first ink ejection amount, and (D) the ink ejection amount. A correction table is created from the relationship between the correction coefficient and the correction coefficient, and (E) the amount of dots formed is corrected by applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on the correction table. A density correction method characterized by that.
According to such a density correction method, when printing is performed by ejecting transparent ink with an ink jet printer, it is possible to correct a variation in ink ejection characteristics for each nozzle and print a uniform image.

Further, (A) a first ink ejection amount that is a standard ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and an ink ejection amount that is larger than the first ink ejection amount. A test pattern having a plurality of gradation patches is printed by ejecting a transparent ink from a nozzle onto a medium to form dots at a third ink ejection amount with a small third ink ejection amount, and (B) The test pattern is irradiated with light, (C) the color difference before and after light irradiation is measured for each gradation value of the patch for each ink ejection amount, and (D) the patch level when the color difference is the same. A tone value is obtained for each case of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount, and the gradation value for the obtained gradation value of the first ink ejection amount is obtained. 2 inks A correction coefficient is calculated from the gradation value in the ejection amount and the gradation value in the third ink ejection amount, respectively, (E) a correction table is created from the relationship between the ink ejection amount and the correction coefficient, and (F) The density correction method is characterized by correcting the amount of dots to be formed by applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on the correction table.
According to such a density correction method, when printing is performed by ejecting transparent ink with an ink jet printer, it is possible to correct a variation in ink ejection characteristics for each nozzle and print a uniform image.

In this correction value acquisition method, the light applied to the test pattern is ultraviolet light,
It is desirable to irradiate with a dose of 100 mJ / cm ² or less.
In normal printing, ultraviolet rays are irradiated under irradiation conditions that do not cause yellowing. To irradiate UV under such irradiation conditions, yellowing of clear ink dots is likely to occur, and a correction table is created. The color difference (ΔE) can be clearly measured.

In this correction value acquisition method, the three-point data of the correction coefficient for the first ejection amount, the correction coefficient for the second ejection amount, and the correction coefficient for the third ejection amount are approximated by least squares. It is desirable to create the correction table by obtaining a straight line.
According to such a density correction method, it is possible to create a table of correction coefficients for all ink ejection amounts simply by examining three ink ejection amount data (reference, large, and small).

(A) a head portion having a plurality of nozzles for ejecting ink to form dots;
B) A control unit that controls the amount of ink ejected from the head unit, wherein the control unit has a first ink ejection amount, which is a standard ink ejection amount, and a larger amount of ink ejection than the first ink ejection amount. A plurality of inks printed by ejecting transparent ink from the nozzle at each of the second ink ejection amount and the third ink ejection amount, which is smaller than the first ink ejection amount. As for the glossiness for each tone value of the patch, measured for each ink ejection amount from the test pattern having the patch, the tone value of the patch when the glossiness is the same is the first ink. The second ink ejection amount for each of the ejection amount, the second ink ejection amount, and the third ink ejection amount, and the gradation value of the obtained first ink ejection amount. The correction coefficient is calculated from the gradation value in the third ink ejection amount and the gradation value in the third ink ejection amount, and the ink for each nozzle is based on the correction table created from the relationship between the ink ejection amount and the correction coefficient. By applying a correction coefficient corresponding to the ejection amount, a printing apparatus including a control unit that corrects the amount of dots formed is clarified.
According to such a printing apparatus, when printing is performed by ejecting transparent ink, it is possible to correct a variation in ink ejection characteristics for each nozzle and print a uniform image.

(A) a head portion having a plurality of nozzles for ejecting ink to form dots;
B) an irradiation unit that irradiates light to the dots, and (C) a control unit that controls the amount of ink ejected from the head unit and the amount of light emitted from the irradiation unit, wherein the control unit is a standard ink ejection A first ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and a third ink ejection amount that is smaller than the first ink ejection amount. The test pattern having a plurality of patches printed by ejecting transparent ink from the nozzles at each ink ejection amount is irradiated with light from the irradiation unit to the test pattern, and the test pattern before and after the light irradiation. The tone value of the patch when the color difference is the same for the color difference before and after the light irradiation with respect to each tone value of the patch measured for each ink ejection amount from the first ink The gradation value in the second ink ejection amount with respect to the obtained gradation value of the first ink ejection amount, obtained for each case of the ejection amount, the second ink ejection amount, and the third ink ejection amount. And from the gradation value in the third ink ejection amount,
A dot formed by calculating a correction coefficient and applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on a correction table created from the relationship between the ink ejection amount and the correction coefficient. And a control unit characterized by correcting the amount of the printing apparatus.
According to such a printing apparatus, when printing is performed by ejecting transparent ink, it is possible to correct a variation in ink ejection characteristics for each nozzle and print a uniform image.

=== Basic Configuration of Recording System ===
As a form of a printing apparatus for carrying out the invention, an ink jet printer (printer 1) will be described as an example. The printer 1 is a color inkjet printer that forms ink dots by ejecting ink toward a medium such as paper, cloth, and the like and prints an image on the medium. Here, as an ink used for printing, ultraviolet rays (hereinafter also referred to as UV)
It is possible to use an ultraviolet curable ink (hereinafter also referred to as a UV ink) that is cured by the irradiation. In the first embodiment, a general solvent-based ink (for example, water-based dye / pigment ink) that is fixed to a medium by drying or evaporation can also be used.

The UV ink is an ink containing an ultraviolet curable resin, and is cured by undergoing a photopolymerization reaction in the ultraviolet curable resin when irradiated with UV. Note that the printer 1 of the present embodiment
Are four colors of yellow (Y), magenta (M), cyan (C) and black (K) and transparent (
CL) UV ink is used for printing.
Hereinafter, an example of printing using UV ink will be described.

<Printer configuration>
FIG. 1 is a block diagram illustrating the overall configuration of the printer 1.
The printer 1 is communicably connected to a computer 110 that is an external control device. A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on the display device of the computer 110 and converting image data output from the application program into print data. This printer driver is a flexible disk FD or CD.
-It is recorded on a recording medium such as a ROM (computer-readable recording medium). Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

In order for the computer 110 to print an image on the printer 1, the print data converted from the image data according to the image to be printed is transmitted to the printer 1. The print data is data in a format that can be interpreted by the printer 1 and includes various command data and pixel data. The command data is data for instructing the printer 1 to execute a specific operation. The command data includes, for example, command data for instructing paper feed, command data for indicating the carry amount, and command data for instructing paper discharge. The pixel data is data related to pixels of an image to be printed.

Here, a pixel is a unit element constituting an image, and an image is formed by arranging these pixels two-dimensionally. Pixel data in the print data is data (for example, gradation values) related to dots formed on a medium (for example, paper S).

The printer 1 includes a transport unit 20, a head unit 30, an irradiation unit 40,
A detector group 50 and a controller 60 are included. The controller 60 controls each unit such as the transport unit 20 and the head unit 30 based on print data received from the computer 110 that is an external device, and prints an image on a medium. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

<Transport unit 20>
FIG. 2 is a side view illustrating the configuration of the printer 1 of the present embodiment.
The transport unit 20 is for transporting the paper S, which is a medium, in a predetermined direction (hereinafter also referred to as a transport direction). The transport unit 20 includes an upstream transport roller 23 </ b> A, a downstream transport roller 23 </ b> B, and a belt 24.

When a transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B rotate, and the belt 24 rotates. The medium fed by a feed roller (not shown) is conveyed to a printable area (area facing the head) by the belt 24. The paper S that has passed through the printable area is discharged to the outside by the belt 24. The paper S being conveyed is electrostatically attracted or vacuum attracted to the belt 24.

<Head unit 30>
The head unit 30 is for ejecting ink onto the paper S to form an image. The head unit 30 includes a head 31 and a head controller HC. A plurality of nozzles that are ink ejecting portions are provided on the lower surface of the head 31, and an ink chamber containing ink is provided in each nozzle.

The head unit 30 forms dots by ejecting each ink to the medium being transported, and prints an image on the medium. The printer 1 of this embodiment is a line printer,
Each head of the head unit 30 can form dots corresponding to the medium width at a time. In this embodiment, as shown in FIG. 2, the yellow ink head Y that discharges yellow UV ink, the magenta ink head M that discharges magenta UV ink, and the cyan UV ink are discharged in order from the upstream side in the transport direction. Cyan ink head C, black ink head K ejecting black UV ink, and transparent ink head C ejecting transparent UV ink
L heads are provided.

FIG. 3 is a cross-sectional view showing the structure of the head 31. The head 31 includes a case 311, a flow path unit 312, and a piezo element group PZT. Case 311 is a piezo element group PZ.
T is accommodated, and the flow path unit 312 is joined to the lower surface of the case 311. The flow path unit 312 includes a flow path forming plate 312a, an elastic plate 312b, and a nozzle plate 312c. The flow path forming plate 312a is formed with a groove that becomes the pressure chamber 312d, a through hole that becomes the nozzle communication port 312e, a through hole that becomes the common ink chamber 312f, and a groove that becomes the ink supply path 312g. The elastic plate 312b is an island portion 312h where the tip of the piezo element PZT is joined.
Have An elastic region is formed by an elastic film 312i around the island portion 312h. The ink stored in the ink cartridge is supplied to the pressure chamber 312d corresponding to each nozzle Nz via the common ink chamber 312f. The nozzle plate 312c is a plate on which the nozzles Nz are formed.

The piezo element group includes a plurality of comb-like piezo elements PZT (drive elements), and is provided in a number corresponding to the nozzles Nz. When the drive signal COM is applied to the piezo element PZT,
The piezoelectric element expands and contracts in the vertical direction according to the potential of the drive signal COM. When the piezo element PZT expands and contracts, the island 312h shown in FIG. 3 is pushed toward the pressure chamber 312d or pulled in the opposite direction. At this time, the elastic film 312i around the island portion 312h is deformed, and the pressure in the pressure chamber 312d rises and falls, thereby ejecting ink droplets from the nozzles.

FIG. 4 is an explanatory diagram of the nozzle Nz provided in the head 31. As shown in FIG. 4, each nozzle row is configured by nozzles Nz serving as ejection ports for ejecting ink of each color being arranged at a predetermined interval D in the transport direction. In each nozzle row, # 1 to # 36
360 nozzles Nz of 0 are provided.

<Irradiation unit 40>
The irradiation unit 40 is directed toward the UV ink dots (ink dots) landed on the medium.
V is irradiated. The dots formed on the medium by each head of the head unit 30 are cured by receiving UV irradiation from the irradiation unit 40. The irradiation unit 40 of this embodiment includes a provisional curing irradiation unit 41 and a main curing irradiation unit 42.

The pre-curing irradiation unit 41 irradiates UV for pre-curing the formed dots. Temporary curing refers to curing performed to prevent the formed dots from coming into contact with each other and bleeding. In the present embodiment, the provisional curing irradiation unit 41 includes a light emitting diode (LED) as a light source for UV irradiation. The LED can easily change the irradiation energy by controlling the magnitude of the input current.

The provisional curing irradiation unit 41 is provided on each downstream side of the YMCK color ink head and the clear ink head in the transport direction of the head unit 30 (see FIG. 2). Dots formed by the color ink heads of each color are preliminarily cured by receiving UV irradiation from the pre-curing irradiation unit 41, and are prevented from being mixed with dots of other colors and bleeding.

The length in the medium width direction of the pre-curing irradiation unit 41 is equal to or greater than the medium width, and the dots corresponding to the medium width can be pre-cured by one irradiation.

The main curing irradiation unit 42 irradiates UV for main curing dots formed on the medium. In the present embodiment, the main curing is curing performed to completely solidify the dots. The main curing irradiation section 42 is a lamp (metal halide lamp,
Equipped with mercury lamps).

Note that in the present embodiment, the main curing irradiation unit 42 has a function of completely curing the clear ink dots and further yellowing the clear ink dots when creating the correction table of the second embodiment. Details of yellowing will be described later.

The main curing irradiation section 42 is provided further downstream of the temporary curing irradiation section 41 located on the most downstream side in the medium transport direction (see FIG. 2). This is because the color ink dots temporarily cured by the pre-curing irradiation unit 41 are completely solidified. The length of the main curing irradiation unit 42 in the medium width direction is also equal to or greater than the medium width.

<Detector group 50>
The detector group 50 includes a rotary encoder, a paper detection sensor (both not shown), and the like. The rotary encoder detects the rotation amounts of the upstream-side transport roller 23A and the downstream-side transport roller 23B, and detects the transport amount of the medium based on the detection result. The paper detection sensor detects the position of the leading edge of the medium being fed.

<Controller 60>
The controller 60 is a control unit (control unit) for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63,
And a unit control circuit 64.

The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing device for performing overall control of the printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and is configured by a storage element such as a RAM or an EEPROM.
Then, the CPU 62 controls each unit such as the transport unit 20 via the unit control circuit 64 in accordance with a program stored in the memory 63. In addition, the CPU 62
A head control signal for controlling the operation of the head 31 is output to the head unit 30.

<About the drive signal COM>
FIG. 5 shows an example of the drive signal COM that determines the operation (deformed shape) of the piezo element PZT. The drive signal COM is composed of drive pulses as shown in FIG. The drive pulse corresponds to a waveform portion for operating the piezo element PZT, and the waveform is determined based on the operation performed by the piezo element PZT. In the repetition period T, the expansion and contraction of the piezo element PZT can be controlled by changing the maximum potential difference Vh of the drive pulses or combining drive pulses having different shapes.

FIG. 6A shows an example of the drive signal COM when the maximum potential difference Vh of the drive pulse in FIG. 5 is increased (Vhl). FIG. 6B shows a case where the maximum potential difference Vh of the drive pulse in FIG.
An example of the drive signal COM of hs) is shown. The drive pulse indicated by the broken line in the figure indicates the maximum potential difference Vh.
Is a waveform (corresponding to FIG. 5).

For example, when the drive pulse shown in FIG. 5 is applied to the piezo element PZT within the repetition period T, the piezo element PZT vibrates to the extent that it ejects an amount of ink that forms a medium dot. On the other hand, when a driving pulse having a maximum potential difference as shown in FIG. 6A within the repetition period T is applied to the piezo element PZT, the piezo element PZT ejects an amount of ink that forms a large dot. Vibrate. Further, when a driving pulse having a maximum potential difference as shown in FIG. 6B within the repetition period T is applied to the piezo element PZT, the piezo element PZT.
Vibrates to the extent that it ejects an amount of ink that forms a small dot.

As described above, the drive signal COM is generated for each piezo element PZT provided in each nozzle Nz, and defines the amount of ink ejected from each nozzle Nz.

<About printing operation>
When the printer 1 receives print data from the computer 110, the controller 6
0 is first an upstream side transport roller 23A and a downstream side transport roller 23 of the transport unit 20.
Rotate B to feed the medium to be printed in the transport direction. The medium is conveyed without stopping at a constant speed, and passes through the head unit 30 and the irradiation unit 40. During this time, ink is intermittently ejected from the head 31 based on the print data. When the ejected ink droplets land on the medium, dots are formed, and a dot line composed of a plurality of dots along the transport direction is formed on the medium. By irradiating the formed dots with UV from the pre-curing / pre-curing irradiation section 41 of the irradiation unit 40, a semi-cured dot is formed. After all the dots for each color ink have been temporarily cured, the main curing irradiation unit 42 provided in the transport downstream area.
Then, each color ink dot is completely cured by irradiating with UV. Thus, an image is printed on the medium.

The controller 60 performs such transport processing and dot formation processing until there is no more data to be printed, and gradually prints an image composed of dot lines on the medium. When there is no more data to be printed, the paper discharge roller is rotated to discharge the medium. The determination of whether or not to discharge paper may be based on a paper discharge command included in the print data.
The same process is repeated when the next printing is performed, and the printing operation is terminated when the next printing is not performed.

=== About print control processing by the printer driver ===
FIG. 7 shows a flowchart of print control performed by the printer driver in this embodiment.
The printer driver receives image data from the application program, converts it into print data in a format that can be interpreted by the printer 1, and outputs the print data to the printer. When converting image data from an application program into print data, the printer driver performs resolution conversion processing (S101), color conversion processing (S102), halftone processing (S103), rasterization processing (S104), and command addition processing (S105). )I do.

Hereinafter, various processes performed by the printer driver for printing characters and the like from image data will be described.

<S101: Resolution Conversion Process>
The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution (print resolution) for printing on a medium. For example, when the print resolution is specified as 720 × 720 dpi, the image data in the vector format received from the application program is 720 × 720 dpi.
Is converted to bitmap format image data.
Each pixel data of the image data after the resolution conversion process is RGB data of each gradation (for example, 256 gradations) represented by the RGB color space.

<S102: Color Conversion Process>
The color conversion process is a process for converting RGB data into YMCK color space data. YMC
The image data in the K color space is data corresponding to the ink color of the printer. This color conversion processing is performed based on a table (color conversion lookup table LUT) in which the gradation values of RGB data and the gradation values of YMCK data are associated with each other.
The pixel data after the color conversion process is 256-bit 8-bit YMCK data represented by the YMCK color space.

<S103: Halftone processing>
The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. For example, data indicating 256 gradations is 2 by halftone processing.
It is converted into 1-bit data indicating gradation and 2-bit data indicating 4 gradations. In the halftone process, a dither method, a γ correction, an error diffusion method, or the like is used. The data subjected to the halftone process has a resolution equivalent to the print resolution (for example, 720 × 720 dpi). The image data after halftone processing corresponds to 1-bit or 2-bit pixel data for each pixel, and this pixel data is data indicating the dot formation status (presence / absence of dot, dot size) in each pixel. Become.

<S104: Rasterization processing>
The rasterizing process rearranges the pixel data arranged in a matrix for each pixel data in the order of data to be transferred to the printer 1. For example, the pixel data is rearranged according to the arrangement order of the nozzles in each nozzle row.

<S105: Command addition processing>
The command addition process is a process for adding command data corresponding to the printing method to the rasterized data. The command data includes, for example, conveyance data indicating the medium conveyance speed.
The print data generated through these processes is transmitted to the printer 1 by the printer driver.

=== First Embodiment ===
In the first embodiment, a correction table is created in advance for each nozzle provided in the clear ink head, and an ink ejection amount is obtained by applying a correction value obtained from the correction table according to the ink ejection amount of each nozzle. By correcting this, an image with little density unevenness is formed even when printing is performed using clear ink.

The correction table is used by using a printer as a reference for creating a correction table in the development stage of the printer. Thereafter, in the printer manufacturing stage, the density is corrected for each nozzle of the manufactured printer based on the created correction table.

In the present embodiment, the gloss strength (glossiness) of the printed surface printed with clear ink is measured, and correction is made from the relationship between the amount of clear ink dots formed on the medium and the glossiness. Create a table. First, the characteristics of clear ink will be described.

<Glossiness of clear ink>
When printing is performed using clear ink, the printed surface has “gloss” due to light reflected by the clear ink dots formed on the medium. Gloss means that the smooth surface of a substance receives light and shines. Usually, the smoother the surface state of the substance, the stronger the gloss.
The intensity of gloss in printed materials depends on the state of the surface (printed surface) on which the image is printed,
The smoother the printed surface, the stronger the reflected light.

In order to make the printing surface smooth, it is necessary that the ink dots are uniformly formed on the printing surface. If the amount of clear ink ejected is small, dots are scattered sparsely on the printing surface, and the reflected light is scattered (diffuse reflection), so that the gloss does not become strong. Conversely, when the clear ink ejection amount is so large that the entire printing surface is covered with the clear ink dots, the reflected light becomes specular reflection light (regular reflection) reflected at the same angle as the incident light, and strong gloss is obtained. Therefore, the amount of clear ink dots formed on the medium can be known by examining the intensity of gloss.

The degree of glossiness is expressed as “glossiness”. The glossiness can be measured using a glossiness meter as an amount indicating the proportion of regularly reflected light in the reflected light. In a general gloss meter, a light receiving unit that irradiates light from a light source toward a surface to be measured at a predetermined angle (incident angle) and reflects light (reflected light) reflected from the surface to be measured in a regular reflection direction. Glossiness is measured by detecting with.

In the present embodiment, a gloss timepiece is used in the glossiness measurement described later. There are methods for measuring the light angle at 20 degrees, 45 degrees, 60 degrees, 75 degrees, and 85 degrees, but in this embodiment, the measurement is performed at an incident angle / reflection angle of 60 degrees. In addition, since glossiness shows a value proportional to the magnitude | size of an angle, even if it does not measure all angles, the glossiness of another angle can be measured by measuring about 60 degree light. .

<Density correction method>
FIG. 8 shows a flowchart for creating the correction table.
First, a test pattern is printed using clear ink while changing the amount of ink ejected from the nozzle (S201), and the glossiness of the test pattern is measured (S202). Then, a correction coefficient for a predetermined ink ejection amount is obtained from the relationship between the gradation value in the print data for forming dots and the measured glossiness (S203 and S204), and a correction table is created (S
205). Details of each step will be described below.

<S201: Test pattern printing>
First, a test pattern is printed using clear ink.
FIG. 9 shows an example of a test pattern printed in the present embodiment. The test pattern has a plurality of rectangular patches formed of clear ink on a white medium. Each patch is formed with a plurality of gradations of gradation value 0 to gradation value 255. The numbers in the patches in FIG. 9 indicate the gradation values. The medium on which the test pattern is printed may be black or the like, but it is better not to use a transparent medium. Since the transparent medium itself reflects light strongly, it does not know whether the reflected light that is measured is reflected by the clear ink dot or by the medium, and each accurate glossiness cannot be measured. Because.
The test pattern is printed with a plurality of types of patterns while changing the ink ejection amount.

The ink ejection amount includes a reference ejection amount (condition 1), a large ejection amount (condition 2) in which the amount of ink ejected per unit time is larger than the reference ejection amount, and an ink amount ejected per unit time is a reference ejection amount. Printing is performed under a condition of smaller ejection amount (condition 3) than the above, and three types of test patterns are formed. Here, the reference ejection amount is the amount of ink ejected by the drive signal COM shown in FIG. 5 during normal printing. Further, the large ejection amount is the drive signal COM represented in FIG. 6A, and the small ejection amount is the ink amount ejected by the drive signal COM represented in FIG. 6B.

<S202: Glossiness measurement>
Glossiness is measured for each patch of gradation values of the three types of printed test patterns using a glossmeter.
As described above, the glossiness is represented by the ratio of specular reflection light to incident light, and a different value is measured depending on the amount of clear ink dots formed on the patch. That is, the glossiness changes depending on the ink ejection amount and the gradation value. The unit of glossiness is expressed in%.

<S203: Tone value calculation>
The relationship between the calculated glossiness and the gradation value is checked for each ink ejection amount, and the gradation value at the same glossiness is obtained for each of the cases where the ink ejection amount is large and small.

FIG. 10 shows the relationship between the gradation value and the gloss level of a test pattern printed using clear ink. The horizontal axis in FIG. 10 indicates the gradation value, and the vertical axis indicates the glossiness. The gradation value (dot formation amount) and the gloss level are proportional. In the figure, a test pattern (condition 1) printed with the reference ink ejection amount is shown.
A straight line representing the relationship between the measured gradation value and the glossiness is displayed as a reference straight line. A straight line representing the relationship between the gradation value and the glossiness for each of the second ink ejection amount (condition 2) and the third ink ejection amount (condition 3) is displayed.

Even when printing is performed with the same gradation value using the clear ink of the same density, since the size of the dots formed is different depending on the difference of the ink ejection amount, the glossiness is also determined to be a different value depending on the ink ejection amount. For example, assume that 100 dots are formed with the reference ink ejection amount (condition 1) in order to form a patch having a gradation value of 150 in FIG. When printing is performed using ink of the same density and with an increased amount of ink ejection (Condition 2), the number of dots for forming a patch having the same gradation value 150 is larger than 100 because the number of dots formed is large. Less. In addition, when printing is performed using ink of the same density with less ink ejection (condition 3), the number of dots for forming a patch with the same gradation value 150 is 1 because the number of dots formed is small.
More than 00. Thereby, the measured glossiness becomes a different value.

In other words, in order to obtain the same glossiness, it is necessary to lower the gradation value when the ink ejection amount is large, and it is necessary to increase the gradation value when the ink ejection amount is small. For example, in FIG. 10, when the glossiness value with respect to the gradation value a of the reference condition (condition 1) is A, the gradation value when the glossiness is A under the condition 2 where the ink ejection amount is large is from a. B is low, and the tone value when the glossiness is A under condition 3 where the ink ejection amount is small is higher than c.
It is.

<S204: Correction coefficient calculation>
Create a graph plotting the gradation value for each ink ejection amount when the glossiness becomes the same value,
A straight line is obtained for each ink ejection amount, and a correction coefficient for each ink ejection amount is calculated from the slope of the straight line.

FIG. 11 is a diagram illustrating a method for calculating a correction coefficient for each ink ejection amount. The horizontal axis indicates the gradation value under the reference condition (condition 1), and the vertical axis indicates the gradation value at each ejection amount (conditions 2 and 3) when the glossiness is the same as the glossiness at each gradation value on the horizontal axis. Is shown.

In FIG. 11, what is indicated by ● is a plot of gradation values in the case of condition 1.
Under condition 1, since the gradation value on the horizontal axis is equal to the gradation value on the vertical axis, ● are arranged on a straight line with an inclination of 1 as shown in FIG.

In FIG. 11, Δ represents a plot of gradation values when the ink ejection amount is large (condition 2). As described in S203, when the ink ejection amount is large, the same glossiness as the reference condition is displayed when the gradation value is low. For example, in FIG. 10, when the ink ejection amount is large (condition 2), the gradation value at which the glossiness is A is b with respect to the glossiness A when the gradation value is a in the reference condition (condition 1). (A> b). Accordingly, as shown in FIG. 11, Δ in Condition 2 indicates a gradation value relatively lower than ● in Condition 1 with respect to the reference gradation value on the horizontal axis.

Similarly, the circled values in FIG. 11 are plotted when the ink ejection amount is small (condition 3). When the ink ejection amount is small (condition 3) with respect to the glossiness A when the gradation value is a in the reference condition (condition 1), the gradation value at which the glossiness is A is c (c
> A). Therefore, with respect to the reference gradation value on the horizontal axis, ○ in condition 3 indicates a relatively higher gradation value than ● in condition 1.

Next, for the plot Δ of condition 2 and the plot ◯ of condition 3, straight lines are obtained by least square approximation, respectively. As shown in FIG. 11, when the ink ejection amount is large (condition 2), the straight line has a smaller slope than the reference condition (condition 1) (slope β), and when the ink ejection amount is small (condition 3). A straight line with a larger slope than the reference condition (condition 1) (slope γ)
It becomes.

The inclination of these straight lines is used as a correction coefficient for each ink ejection amount. That is, the correction coefficient for the reference ink ejection amount is 1, the correction coefficient when the ink ejection amount is large is β, and the correction coefficient when the ink ejection amount is small is γ.

Depending on the ink ejection characteristics for each nozzle, the correction coefficient β for nozzles with a large amount of ink ejection
By multiplying by (1> β), the amount of dots formed on the medium is reduced, and correction is performed so as to obtain the same print density as that in the case of printing in the reference state. Conversely, for nozzles with a small ink ejection amount, the same print density as when printing in the standard state with the amount of dots formed on the medium increased by multiplying the correction coefficient γ (γ> 1). It is corrected to become.

<S205: Creation of Correction Table>
A correction table is created from the correction coefficients for the three types of ink ejection amounts calculated in S204.
FIG. 12 shows an example of the correction table created in this embodiment. The horizontal axis in FIG. 12 indicates the ink ejection amount, and the vertical axis indicates the correction coefficient. A straight line obtained by least square approximation is obtained for three points obtained by plotting the correction coefficients (1, α, β) obtained by the above-described method with respect to each ink ejection amount. As a result, a correction table representing the relationship between the ink ejection amount and the correction coefficient is created.

<Density correction>
The created correction table is stored in the memory 63 of each printer being manufactured in the manufacturing process of the printer 1.
At the time of printing, the printer driver requests the printer 1 to transmit the correction table stored in the memory 63 to the computer 110. The printer driver stores the correction table transmitted from the printer 1 in a memory in the computer 110. Based on the correction table, a correction coefficient corresponding to the ink ejection amount is calculated from the information on the ink ejection amount for each nozzle of the printer. By applying the calculated correction coefficient to the correction target nozzle, the amount of ink ejected from the nozzle is adjusted.

The correction at the time of printing is performed between the color conversion process (S102) and the halftone process (S103) of the print control by the printer driver. 25 after color conversion
By applying the correction coefficient to pixel data of 6 gradations, the amount of dots formed is adjusted by increasing or decreasing the ink ejection amount or changing the gradation value. This
Variations in ink ejection characteristics due to nozzle manufacturing errors and the like can be reduced, and uniform density printing can be performed.

=== Second Embodiment ===
In the second embodiment, as in the first embodiment, a correction table is created in advance,
By correcting the ink ejection amount for each nozzle provided in the clear ink head, an image with less density unevenness is formed.

In the first embodiment, the correction table is created by measuring the gloss level of the print surface of the test pattern printed using the clear ink, but in this embodiment, the degree of color change of the clear ink is measured. Create a correction table.

<About yellowing of clear ink>
A printed surface printed using clear ink may turn yellow as time passes (hereinafter also referred to as yellowing). In particular, when printing is performed using UV ink as in this embodiment, UV irradiation causes yellowing. Therefore, during normal printing, yellowing is prevented from occurring by controlling the UV irradiation amount.

FIG. 13 is a diagram showing the degree of dot discoloration due to UV irradiation when a metal halide lamp and a mercury lamp are used. Here, the degree of color change is expressed as a color difference (ΔE) that quantitatively represents a perceptual difference in color.

In FIG. 13, the gradient of the color difference (ΔE) is gentle in the region where the UV irradiation energy is 100 mJ / cm ² or more, and conversely, the gradient of the color difference (ΔE) is steep in the region of 100 mJ / cm ² or less. This indicates that discoloration (yellowing) is likely to occur when the UV irradiation energy is 100 mJ / cm ² or less. For example, when a metal halide lamp or a mercury lamp is used as the main curing irradiation section 42 of the printer 1, the UV irradiation energy is set to 100 mJ / cm ^2.
By setting it as these conditions, it can make it hard to produce yellowing. On the contrary, when the UV irradiation energy is 100 mJ / cm ² or less, it can be said that the color difference (ΔE) of the printed surface before and after the UV irradiation increases and yellowing is likely to occur.

The color difference (ΔE) can be generated from the color component values measured using a colorimeter.
The colorimeter is a spectrocolorimeter for measuring a colorimetric value in a predetermined range of an image and obtaining a colorimetric value in the predetermined range. For example, each color component value in an L * a * b * color space (L ₁ *, a ₁ *, b ₁
*) Etc. are measured.

The color difference ΔE is a colorimetric value (L ₁ *, a ₁ *, b ₁ *) before and after yellowing and (L ₂ *, a ₂ *, b ₂ *).
)Using,
ΔE = {(ΔL *) ² + (Δa *) ² + (Δb *) ² )} ^1/2 (Expression 1)
ΔL = (L ₁ * −L ₂ *), Δa = (a ₁ * −a ₂ *), Δb = (b ₁ * −b ₂ *)
It can be expressed by the following formula.

When the UV irradiation energy irradiated from the main curing irradiation unit 42 is constant, the color difference (ΔE
) Depends on the amount of clear ink dots formed on the medium. Therefore, similarly to the glossiness in the first embodiment, the amount of clear ink dots formed on the medium can be known by examining the color difference (ΔE) before and after yellowing of the printing surface.

<Density correction method>
FIG. 14 is a flowchart for creating a correction table in the second embodiment.
The basic flow is the same as S201 to S205 of the first embodiment, but S302 to S30.
The color component value measurement step before and after yellowing 4 is different from the color difference (ΔE) calculation step in S305. Details of each step will be described below.

<S301: Test pattern printing>
A test pattern similar to that of the first embodiment is printed using clear ink (see FIG. 9).

Also in the present embodiment, the reference ejection amount (condition 1), the large ejection amount (condition 2) in which the amount of ink ejected per unit time is larger than the reference ejection amount, and the ink amount ejected per unit time are the reference ejection. Printing is performed under three types of conditions of a small ejection amount (condition 3) smaller than the amount.

<S302: Color Component Value Measurement 1>
The color component values (L ₁ *, a ₁ *, b ₁ *) before yellowing are measured using a colorimeter for the patches of the gradation values of the three types of printed test patterns. Since the patch is transparent, in this step, the color component value for the medium color (white) is measured.

<S303: UV irradiation>
By irradiating UV to each patch formed in the test pattern, yellowing is forcibly generated. As described above, 100 using the metal halide lamp of the main curing irradiation unit 42 or the like.
The test pattern is yellowed by irradiating UV so as to be mJ / cm ² or less. Also, as a UV ink reaction initiator, SUBSTITUTED HOSPHINE OXIDE or PHENYL BI
When using S (2,4,6-TRIMETHYLBENZOIL) -PHOSPHINE OXIDE, yellowing tends to occur.
It is effective.

In step S301, UV irradiation is performed to cure the dots formed on the medium. At this time, a strong energy is applied so that the energy becomes 100 mJ / cm ² or more so as not to cause yellowing. UV is irradiated. On the other hand, since the purpose of this step is to yellow the clear ink dots, the UV irradiation energy is strictly controlled so as to be an energy of 100 mJ / cm ² or less.

<S304: Color Component Value Measurement 2>
The color component values (L ₂ *, a ₂ *, b ₂ *) are measured by using a colorimeter for each tone value patch after yellowing in step S303. One step of measuring color component values before yellowing (S302
), The same color component value (L ₁ *, a ₁ *, b ₁ *) is measured for all patches.
In this step, since the degree of yellowing changes depending on the amount of dots formed in each patch, a different value is measured for each patch having a different gradation value.

<S305: Color difference (ΔE) calculation>
<S306: Tone value calculation>
The measured value of S304 (L ₁ *, a ₁ *, b ₁ *) and the measured value of S302 (L ₂ *, a ₂ *,
b ₂ *) is substituted into the above-described (Equation 1), and the color difference (ΔE) is calculated for the patch of each gradation value (S305). Then, the relationship between the calculated color difference (ΔE) and the gradation value is checked for each ink ejection amount (S306).

FIG. 15 shows the relationship between the gloss level and the tone value of a test pattern printed using clear ink. The horizontal axis in FIG. 15 represents the gradation value, and the vertical axis represents the color difference (ΔE). In the figure, a curve representing the relationship between the gradation value measured for the test pattern (condition 1) printed with the reference ink ejection amount and the glossiness is displayed as a reference straight line. A curve representing the relationship between the gradation value and the color difference (ΔE) for each of the second ink ejection amount (condition 2) and the third ink ejection amount (condition 3) is displayed.

As described in the first embodiment, in order to obtain the same color difference (ΔE), it is necessary to lower the gradation value when the ink ejection amount is large, and the gradation value when the ink ejection amount is small. It is understood that it is necessary to increase the value. For example, in FIG. 15, when the color difference value with respect to the gradation value a of the reference condition (condition 1) is S, the gradation value when the color difference is S under the condition 2 where the ink ejection amount is large is lower than a. b, and the gradation value when the color difference is S under condition 3 where the ink ejection amount is small is c higher than a.

<S307: Correction coefficient calculation>
<S308: Creation of correction table>
Similar to the first embodiment, a graph is created by plotting gradation values for each ink ejection amount when the glossiness becomes the same value, a straight line is obtained for each ink ejection amount, and ink ejection is performed from the inclination of the straight line. A correction coefficient for each amount is calculated (S307). And 3 calculated in S307
A correction table is created from the correction coefficients for the types of ink ejection amounts (S308).

<Density correction>
Density correction is also performed in the same manner as in the first embodiment. The created correction table is stored in the memory 63 of each printer being manufactured in the manufacturing process of the printer 1. At the time of printing, a correction coefficient corresponding to the ink ejection amount is calculated from information on the ink ejection amount for each nozzle based on the created correction table. By applying the calculated correction coefficient to the correction target nozzle, the amount of ink ejected from the nozzle is adjusted.
By applying an appropriate correction coefficient for each nozzle in accordance with the ink ejection amount, variations in ink ejection characteristics due to nozzle manufacturing errors and the like can be reduced, and printing with a uniform density can be performed.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention
Needless to say, the present invention includes equivalents thereof without departing from the spirit of the invention. In particular, the embodiments described below are also included in the present invention.

<About printing devices>
In the above-described embodiment, the line printer having the head fixed as the printer 1 has been described as an example. However, a so-called serial printer of the type that moves the head 31 together with the carriage may be used.

<About UV ink>
In the above-described embodiment, ink that is cured by being irradiated with ultraviolet rays (UV) (U
V ink) was discharged from the nozzles. However, the liquid to be ejected is not limited to such an ink, and may be cured by receiving irradiation of electromagnetic waves other than UV. In this case, an electromagnetic wave for curing the liquid may be irradiated from the temporary curing irradiation unit and the main curing irradiation unit.

In the first embodiment, a general solvent-based ink (for example, water-based dye / pigment ink) that is fixed to a medium by drying or evaporation can be used instead of ink that is cured by electromagnetic waves.

<About ink colors to be used>
In the above-described embodiment, an example in which printing is performed using five colors of YMCK and CL has been described, but the present invention is not limited to this. For example, recording may be performed using ink of a color other than YMCKCL, such as light cyan, light magenta, and white.

<About head placement>
The arrangement of the ink color heads in the head unit is arranged in the order of YMCK arrangement from the upstream side in the transport direction, but is not limited to this. For example, the order of colors may be changed, or there may be a configuration in which there are two rows of K heads.

<About piezo elements>
In each of the above-described embodiments, the piezo element PZ is used as an element that performs an operation for ejecting the liquid.
Although T is illustrated, other elements may be used. For example, a heating element or an electrostatic actuator may be used.

<About the printer driver>
The printer driver processing may be performed on the printer side. In that case, a recording apparatus is configured by the printer and the PC on which the driver is installed.

1 printer, 20 transport unit,
23A upstream conveyance roller, 23B downstream conveyance roller,
24 belts, 30 head units,
31 heads, 311 case, 312 flow path unit,
312a flow path forming plate, 312b elastic plate, 312c nozzle plate,
312d Pressure chamber, 312e Nozzle communication port, 312f Common ink chamber,
312g Ink supply path, 312h island part, 312i elastic film,
40 irradiation unit, 41 pre-curing irradiation unit, 42 main curing irradiation unit,
50 detector groups, 60 controllers, 61 interface units,
62 CPU, 63 memory, 64 unit control circuit,
110 computer

Claims (6)

(A) The first ink ejection amount that is a standard ink ejection amount, the second ink ejection amount that is larger than the first ink ejection amount, and the ink ejection amount that is smaller than the first ink ejection amount. With each ink ejection amount of the third ink ejection amount,
A test pattern having a multi-tone patch is printed by ejecting transparent ink from a nozzle onto a medium to form dots,
(B) For each ink ejection amount, the glossiness for each gradation value of the patch is measured,
(C) The gradation value of the patch when the glossiness is the same, the first ink ejection amount,
Obtained for each of the second ink ejection amount and the third ink ejection amount,
A correction coefficient is calculated from the gradation value of the second ink ejection amount and the gradation value of the third ink ejection amount with respect to the obtained gradation value of the first ink ejection amount,
(D) A correction table is created from the relationship between the ink ejection amount and the correction coefficient,
(E) correcting the amount of dots to be formed by applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on the correction table;
A density correction method characterized by the above. (A) The first ink ejection amount that is a standard ink ejection amount, the second ink ejection amount that is larger than the first ink ejection amount, and the ink ejection amount that is smaller than the first ink ejection amount. With each ink ejection amount of the third ink ejection amount,
A test pattern having a multi-tone patch is printed by ejecting transparent ink from a nozzle onto a medium to form dots,
(B) irradiating the test pattern with light;
(C) measuring the color difference before and after light irradiation for each gradation value of the patch for each ink ejection amount;
(D) A gradation value of the patch when the color difference is the same is obtained for each of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount.
A correction coefficient is calculated from the gradation value of the second ink ejection amount and the gradation value of the third ink ejection amount with respect to the obtained gradation value of the first ink ejection amount,
(E) A correction table is created from the relationship between the ink ejection amount and the correction coefficient,
(F) correcting the amount of dots to be formed by applying a correction coefficient corresponding to the ink ejection amount for each nozzle based on the correction table;
A density correction method characterized by the above. The density correction method according to claim 2,
The light applied to the test pattern is ultraviolet light,
A density correction method characterized by irradiating with an irradiation dose of 100 mJ / cm ² or less. The density correction method according to any one of claims 1 to 3,
A correction coefficient for the first ejection amount, a correction coefficient for the second ejection amount, a correction coefficient for the third ejection amount,
A density correction method characterized in that the correction table is created by obtaining a straight line by least-square approximation of the three data points. (A) a head portion having a plurality of nozzles for ejecting ink to form dots;
(B) a control unit for controlling the amount of ink ejected from the head unit,
The controller is
A first ink ejection amount that is a standard ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and a third ink that is smaller than the first ink ejection amount. From a test pattern having a plurality of patches printed by ejecting transparent ink from the nozzles at each ink ejection amount,
About the glossiness for each gradation value of the patch measured for each ink ejection amount,
The tone value of the patch when the glossiness is the same is obtained for each of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount,
A correction coefficient is calculated from the gradation value of the second ink ejection amount and the gradation value of the third ink ejection amount with respect to the obtained gradation value of the first ink ejection amount,
Based on a correction table created from the relationship between the ink ejection amount and the correction coefficient, a correction coefficient corresponding to the ink ejection amount for each nozzle is applied to correct the amount of dots formed.
A control unit characterized by:
A printing apparatus comprising: (A) a head portion having a plurality of nozzles for ejecting ink to form dots;
(B) an irradiation unit for irradiating the dots with light;
(C) a control unit that controls the ink ejection amount from the head unit and the light irradiation amount from the irradiation unit;
The controller is
A first ink ejection amount that is a standard ink ejection amount, a second ink ejection amount that is larger than the first ink ejection amount, and a third ink that is smaller than the first ink ejection amount. A test pattern having a plurality of patches printed by ejecting transparent ink from the nozzles at each ink ejection amount.
Irradiate the test pattern from the irradiation unit,
About the color difference before and after the light irradiation for each gradation value of the patch measured for each ink ejection amount from the test pattern before and after the light irradiation,
The tone value of the patch when the color difference is the same is determined for each of the first ink ejection amount, the second ink ejection amount, and the third ink ejection amount.
A correction coefficient is calculated from the gradation value of the second ink ejection amount and the gradation value of the third ink ejection amount with respect to the obtained gradation value of the first ink ejection amount,
Based on a correction table created from the relationship between the ink ejection amount and the correction coefficient, a correction coefficient corresponding to the ink ejection amount for each nozzle is applied to correct the amount of dots formed.
A control unit characterized by:
A printing apparatus comprising:

Images