JP2020196152A - Ink discharge amount correction method and printing method - Google Patents

Abstract

To reduce differences in color values caused by differences in impact shape between ink droplets by arranging a correction table for correcting differences of coverage factor.SOLUTION: An ink discharge amount correction method, in which discharge amounts of ink droplets discharged from a printing device that performs printing by discharging the ink droplets to a printing medium is corrected, includes: a first correction table generating step of generating a first correction table for performing a correction based on information on differences of color values caused by differences in discharge amounts between ink droplets; a second correction table generating step of generating a second correction table for performing a correction based on information on differences in color values caused by differences of shapes in which the ink droplets impact on the printing medium; and a discharge amount control table correction step of correcting a discharge amount control table that controls discharge amounts of the ink droplets, on the basis of the first correction table and the second correction table.SELECTED DRAWING: Figure 8

Description

The present invention relates to an ink ejection amount correction method and a printing method.

Conventionally, for example, as described in Patent Document 1, when the amount of ink droplets ejected differs depending on the printing apparatus, a correction table based on the information of the difference data of the color value according to the ejection weight of the ink droplets is created. , A method and a printing apparatus for performing halftone processing and printing data conversion in a state where the ejection amount is controlled after the color conversion processing of image data using the ejection amount control table to which the correction is applied have been known.

JP-A-2009-143135

However, there is a problem that the correction may not be completed only by the correction table based on the information of the difference data of the color values according to the ejection weight of the ink droplet described in Patent Document 1. For example, the difference in color value caused by the difference in coverage caused by the different landing states of the ejected ink droplets cannot be completely corrected from the color value data generated from the ejected weight. Here, the coverage is the ratio of the area covered by the ink on the surface of the print medium for each pixel.

The ink ejection amount correction method of the present application is a method of correcting the ejection amount of the ink droplets ejected by a printing apparatus that prints by ejecting ink droplets onto a printing medium, and the color value due to the difference in the ejection amount The first correction table generation step of generating the first correction table for making corrections based on the difference information, and the second correction based on the information of the difference in color value due to the difference in the shape of the ink droplets landing on the print medium. Includes a second correction table generation step of generating a correction table, and a discharge amount control table correction step of correcting the discharge amount control table that controls the discharge amount based on the first correction table and the second correction table. It is characterized by.

In the above ink ejection amount correction method, the first correction table generation step and the second correction table generation step generate the first correction table and the second correction table for each of a plurality of types of ink droplet sizes. Is preferable.

In the above ink ejection amount correction method, it is preferable that the second correction table generation step uses the difference in the spectral reflectance of the image printed on the print medium as an alternative parameter for the difference in shape.

In the above ink ejection amount correction method, it is preferable that the second correction table generation step uses the difference in the binarized image data of the image printed on the print medium as an alternative parameter for the difference in shape.

In the above ink ejection amount correction method, the second correction table generation step uses the difference in the coverage of the surface of the print medium due to the ink droplets landing on the print medium as an alternative parameter for the difference in shape. Is preferable.

In the above ink ejection amount correction method, it is preferable that the second correction table generation step uses the presence or absence of separation of the ink droplets that have landed on the print medium as an alternative parameter for the difference in shape.

In the above ink ejection amount correction method, the second correction table is a table in which the gradation value of the printed image and the correction value for correcting the ejection amount of the ink droplet corresponding to the gradation value correspond to each other. It is preferable that the correction value in the middle gradation region of the gradation value is larger than the correction value in the low gradation region of the gradation value and the high gradation region of the gradation value.

The printing method of the present application is characterized in that printing is performed using a discharge amount control table corrected by the ink discharge amount correction method described in any of the above.

It is a front view which shows the structure of the printing apparatus which concerns on Embodiment 1. FIG. It is a block diagram which shows the structure of the printing apparatus which concerns on Embodiment 1. FIG. It is explanatory drawing of the basic function of a printer driver. It is explanatory drawing of the discharge amount control table. It is a graph which shows the relationship between the input gradation value and the coverage rate that the surface of a print medium is covered with ink. It is a schematic diagram which shows the example of the landing state in which the ink droplet is landed at a predetermined position without breaking. It is a schematic diagram which shows the example of the landing state in which an ink drop is cracked and landed. It is a flowchart which shows the flow of the 1st correction table calculation and the 2nd correction table calculation. It is explanatory drawing of the correction pattern. It is a schematic diagram which shows the example of the 1st correction reference table. It is a schematic diagram which shows the calculation example of the correction factor of the 1st correction table in which the relationship between the weight change of the ejection amount of ink droplets per dot, and the correction factor has a downward-sloping relationship. It is a schematic diagram which showed the example of the discrete gradation value, the spectral reflectance obtained from the gradation value, and the spectral reflectance in the approximation function by interpolation. It is a graph which shows the example of the 2nd correction reference table. It is a graph which shows the ejection control value of the ink drop before and after applying the correction in Embodiment 1. In the first embodiment, the ejection control value of ink droplets before and after the correction is applied when only the first correction table is applied when the ejection control of four gradations of no dot, small dot, medium dot, and large dot is performed. It is a graph which shows. Ink droplets before and after the correction application when the first correction table and the second correction table are applied when the ejection control of four gradations of no dot, small dot, medium dot, and large dot in the first embodiment is performed. It is a graph which shows the discharge control value.

Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. The following is an embodiment of the present invention and does not limit the present invention. In addition, in each of the following figures, in order to make the explanation easy to understand, it may be described on a scale different from the actual one. In addition, in the coordinates added to the drawing, the Z-axis direction is the vertical direction, the + Z direction is the upward direction, the X-axis direction is the front-back direction, the −X direction is the front direction, the Y-axis direction is the left-right direction, and the + Y direction is the left direction. The XY plane is the horizontal plane.

(Embodiment 1)
FIG. 1 is a front view showing the configuration of a printing system 1 as a printing device according to the first embodiment, and FIG. 2 is a block diagram of the same.
The printing system 1 is composed of a printer 100 and an image processing device 110 connected to the printer 100. The printer 100 is an inkjet serial printer that prints a desired image on a long print medium 5 supplied in a rolled state based on print data received from the image processing device 110.
As the print medium 5, for example, high-quality paper, cast paper, art paper, coated paper, synthetic paper, and the like can be used. Further, the print medium 5 is not limited to such paper, and for example, a cloth, a film made of PET (Polyethylene terephthalate), PP (polypropylene), or the like can be used.

<Basic configuration of image processing device>
The image processing device 110 includes a print control unit 111, an input unit 112, a display unit 113, a storage device 114, and the like, and controls a print job that causes the printer 100 to print. The image processing device 110 is configured by using a personal computer as a preferable example.
The software on which the image processing device 110 operates includes general image processing application software (hereinafter referred to as an application) that handles image data to be printed, control of the printer 100, and print data for causing the printer 100 to execute printing. The printer driver software to be generated (hereinafter referred to as the printer driver) is included.
Here, the image data is text data or full-color image data constituting a printed image, and refers to, for example, general RGB digital image information. Hereinafter, the printed image will be described as image data.

The print control unit 111 includes a CPU (Central Processing Unit) 115, an ASIC (Application Specific Integrated Circuit) 116, a DSP (Digital Signal Processor) 117, a memory 118, a printer interface (I / F) unit 119, and the like, and is a printing system. 1 Centrally manage the entire system.
The input unit 112 is an information input means as a human interface. Specifically, for example, a keyboard, a mouse pointer, or a port to which an information input device is connected.
The display unit 113 is an information display means (display) as a human interface, and is related to information input from the input unit 112, an image to be printed on the printer 100, and a print job under the control of the print control unit 111. Information etc. are displayed.
The storage device 114 is a rewritable storage medium such as a hard disk drive (HDD) or a memory card, and is used for software (a program operated by the print control unit 111) for operating the image processing device 110, images to be printed, and a print job. Related information etc. are stored.
The memory 118 is a storage medium that secures an area for storing a program in which the CPU 115 operates, a work area in which the CPU 115 operates, and the like, and is composed of storage elements such as RAM and EEPROM.

<Basic configuration of printer 100>
The printer 100 includes a printing unit 10, a moving unit 20, a printer control unit 30, and the like. The printer 100, which has received the print data from the image processing device 110, controls the print unit 10 and the moving unit 20 by the printer control unit 30 based on the print data, and prints the image on the print medium 5.
The print data is data for image formation obtained by converting general image data obtained by, for example, a digital camera or the like so that the printer 100 can print it by an application provided in the image processing device 110 and a printer driver. It contains commands to control 100.

The printing unit 10 is composed of a head unit 11, an ink supply unit 12, and the like.
The moving unit 20 is composed of a main scanning unit 40, a sub scanning unit 50, and the like. The main scanning unit 40 includes a carriage 41, a guide shaft 42, a carriage motor (not shown), and the like. The sub-scanning unit 50 includes a supply unit 51, a storage unit 52, a transport roller 53, a platen 55, and the like.

The head unit 11 includes a print head 13 and a head control unit 14 having a plurality of nozzles (nozzle rows) for ejecting printing ink (hereinafter referred to as ink) as ink droplets. The head unit 11 is mounted on the carriage 41 and reciprocates in the main scanning direction along with the carriage 41 moving in the main scanning direction (X-axis direction shown in FIG. 1). While the head unit 11 (print head 13) moves in the main scanning direction, ink droplets are ejected onto the print medium 5 supported by the platen 55 under the control of the printer control unit 30 to follow the main scanning direction. A plurality of dot sequences (raster lines) are formed on the print medium 5.
In the following description, the operation of ejecting ink from the nozzle row to form dots while moving in the main scanning direction is referred to as a pass operation or simply a pass. One pass operation means dot formation associated with one movement in the main scanning direction. A desired image based on image data by combining a partial image printed by dot formation accompanying one movement in the main scanning direction in a sub-scanning direction (Y-axis direction shown in FIG. 1) that intersects the main scanning direction. Is printed.

The ink supply unit 12 includes an ink tank and an ink supply path (not shown) for supplying ink from the ink tank to the print head 13.
The ink includes, for example, a four-color ink set in which black (K) is added to a three-color ink set of cyan (C), magenta (M), and yellow (Y) as an ink set composed of a dark ink composition. There is. Further, for example, eight colors including ink sets such as light cyan (Lc), light magenta (Lm), light yellow (Ly), and light black (Lk), which are composed of a light ink composition in which the density of each color material is lightened. There is an ink set etc. The ink tank, the ink supply path, and the ink supply path to the nozzle for ejecting the same ink are provided independently for each ink.

The piezo method is used as the inkjet method for ejecting ink droplets. In the piezo method, pressure is applied to the ink stored in the pressure generating chamber by an actuator using a piezoelectric element (piezo element) according to the print information signal, and ink droplets are ejected (discharged) from a nozzle communicating with the pressure generating chamber. This is a printing method.
The method of ejecting ink droplets is not limited to this, and may be another printing method in which ink is ejected in the form of droplets to form a dot group on a printing medium. For example, a method in which ink is continuously ejected in droplet form from a nozzle by a strong electric field between a nozzle and an acceleration electrode placed in front of the nozzle, and a print information signal is given from a deflection electrode while the ink droplets fly to perform printing. Alternatively, the electrostatic suction method, which is a method of ejecting ink droplets in response to a print information signal without deflecting the ink droplets, is forced by applying pressure to the ink with a small pump and mechanically vibrating the nozzle with a crystal transducer or the like. A method of injecting ink droplets, a thermal jet method in which ink is heated and foamed by a microelectrode according to a print information signal, and ink droplets are ejected for printing may be used.

The moving unit 20 moves the print medium 5 relative to the printing unit 10 under the control of the printer control unit 30.
The guide shaft 42 extends in the main scanning direction and supports the carriage 41 in a slidable state, and the carriage motor serves as a drive source for reciprocating the carriage 41 along the guide shaft 42. That is, the main scanning unit 40 moves the carriage 41 (that is, the print head 13) along the guide shaft 42 in the main scanning direction under the control of the printer control unit 30.

The supply unit 51 rotatably supports the reel in which the print medium 5 is wound in a roll shape, and sends the print medium 5 to the transport path. The storage unit 52 rotatably supports a reel for winding the print medium 5, and winds the printed medium 5 for which printing has been completed from the transport path.
The transport roller 53 includes a drive roller that moves the print medium 5 in the sub-scanning direction on the upper surface of the platen 55, a driven roller that rotates with the movement of the print medium 5, and the like, and supplies the print medium 5 from the supply section 51 to the print section 10. A transport path is configured to be transported to the storage unit 52 via the print area (the area on the upper surface of the platen 55 where the print head 13 mainly scans and moves).

The printer control unit 30 includes an interface unit 31, a CPU 32, a memory 33, a drive control unit 34, and the like, and controls the printer 100.
The interface unit 31 is connected to the printer interface unit 119 of the image processing device 110, and transmits / receives data between the image processing device 110 and the printer 100.
The CPU 32 is an arithmetic processing unit for controlling the entire printer 100.
The memory 33 is a storage medium for securing an area for storing a program in which the CPU 32 operates, a working area for operating the CPU 32, and the like, and is composed of storage elements such as RAM and EEPROM.
The CPU 32 controls the printing unit 10 and the moving unit 20 via the drive control unit 34 according to the program stored in the memory 33 and the print data received from the image processing device 110.

The drive control unit 34 includes firmware that operates based on the control of the CPU 32, and controls the drive of the printing unit 10 and the moving unit 20. The drive control unit 34 includes a drive control circuit including a movement control signal generation circuit 35, a discharge control signal generation circuit 36, a drive signal generation circuit 37, and the like, and a ROM or flash memory (not shown) containing firmware for controlling these drive control circuits. ) And so on.

The movement control signal generation circuit 35 is a circuit that generates a signal for controlling the movement unit 20 according to an instruction from the CPU 32 based on the print data.
The ejection control signal generation circuit 36 is a circuit that generates a head control signal for selecting a nozzle for ejecting ink, selecting an ejection amount, controlling the ejection timing, and the like according to an instruction from the CPU 32 based on print data. Is.
The drive signal generation circuit 37 is a circuit that generates a drive waveform that drives the pressure generating unit included in the print head 13.

With the above configuration, the printer control unit 30 sets the carriage 41 that supports the print head 13 along the guide shaft 42 in the main scanning direction (X-axis direction) with respect to the printing medium 5 supplied to the printing area by the sub-scanning unit 50. ) By repeating the operation of ejecting ink droplets from the print head 13 while moving and the operation of moving the print medium 5 in the sub-scanning direction (+ Y direction) intersecting the main scanning direction by the sub-scanning unit 50, the print medium A desired image is formed (printed) in 5.

<Basic functions of printer driver>
FIG. 3 is an explanatory diagram of the basic functions of the printer driver.
Printing on the print medium 5 is started by transmitting print data from the image processing device 110 to the printer 100. The print data is generated by the printer driver.
Hereinafter, the process of generating print data will be described with reference to FIG.

The printer driver receives image data from the application, converts it into print data in a format that can be interpreted by the printer 100, and outputs the print data to the printer 100. When converting image data from an application into print data, the printer driver performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, command addition processing, and the like.

The resolution conversion process is a process of converting the image data output from the application into the resolution (printing resolution) at the time of printing on the print medium 5. For example, when the print resolution is specified as 720 × 720 dpi, the vector format image data received from the application is converted into the bitmap format image data having a resolution of 720 × 720 dpi. Each pixel data of the image data after the resolution conversion process is composed of pixels arranged in a matrix. Each pixel has, for example, 256 gradation values in the RGB color space. That is, the pixel data after the resolution conversion indicates the gradation value of the corresponding pixel.
Pixel data corresponding to one row of pixels arranged in a predetermined direction among the pixels arranged in a matrix is called raster data. The predetermined direction in which the pixels corresponding to the raster data are lined up corresponds to the moving direction (main scanning direction) of the print head 13 when printing an image.

The color conversion process is a process of converting RGB data into data in the CMYK color system space. The CMYK colors are cyan (C), magenta (M), yellow (Y), and black (K), and the image data in the CMYK color system space is data corresponding to the color of the ink possessed by the printer 100. Therefore, for example, when the printer 100 uses eight types of inks of the CMYK color system, the printer driver generates image data of the eight-dimensional space of the CMYK color system based on the RGB data.
This color conversion process is performed based on a LUT (color conversion look-up table). The pixel data after the color conversion process is, for example, 256 gradations of CMYK color data represented by the CMYK color space.

The LUT is a table in which the gradation value of RGB data and the gradation value of CMYK color system data are associated with each other, and the color conversion process is performed based on this LUT.

The halftone process is a process of converting 256 gradation data into data having a number of gradations that can be formed by the printer 100. By this halftone processing, the data showing 256 gradations is, for example, 1-bit data showing 2 gradations with dots and without dots, or 2 gradations showing no dots, small dots, medium dots, and large dots. Converted to bit data. Specifically, the ink droplet ejection amount corresponding to the gradation value is obtained from the ink droplet ejection amount control table corresponding to the gradation value of 0 to 255 and the ink droplet ejection amount, and the obtained ejection amount is used. , The pixel data is created so that the dots are dispersed and formed by using the dither method, the error diffusion method, or the like.

The ejection amount control table is a table in which data indicating 256 gradations in the CMYK color system space is associated with the ejection amount of ink droplets. For example, the gradation value of 0 to 255 is obtained from the ejection amount control table to obtain the ejection amount of ink droplets corresponding to the gradation value. For example, in the case of 2 gradations, there are no dots, with dots, and in the case of 4 gradations, the generation rates of no dots, small dots, medium dots, and large dots are obtained.

The dither mask is a partial processing method of halftone processing that distributes pixels to the amount of ink droplets ejected (the generation rate of each dot).

FIG. 4 is an explanatory diagram showing an example of an ink droplet ejection amount control table at four gradations.
The ejection amount control table includes a gradation value for each pixel included in the image data (hereinafter referred to as an input gradation value in the description of the embodiment) and an ink droplet for each dot size of dots formed on the print medium 5 by the printer 100. It is a table for associating the ejection amount (or the number of dots generated) with the ink, and is stored in the memory 33 in the printer 100 for each ink color.

The rasterization process is a process of rearranging pixel data arranged in a matrix (for example, 1-bit or 2-bit data as described above) according to the dot formation order at the time of printing. The rasterization process includes a path allocation process of allocating image data composed of pixel data after halftone processing to each path for ejecting ink droplets while the print head 13 (nozzle row) mainly scans and moves. When the path allocation is complete, the actual nozzles that form each raster line that makes up the printed image are allocated.

The command addition process is a process of adding command data according to the printing method to the rasterized data. The command data includes, for example, sub-scanning data related to the amount of movement in the sub-scanning direction and the speed on the upper surface of the platen 55 of the medium.
The series of processes by the printer driver is performed by the ASIC 116 and the DSP 117 under the control of the CPU 115, and in the print data transmission process, the print data generated by the series of processes is transmitted to the printer 100 via the printer interface unit 119. Will be sent.

<Covering rate according to each gradation due to the impact shape of ink droplets>
FIG. 5 is a graph showing the relationship between the input gradation value and the coverage ratio in which the surface of the print medium 5 is covered with the ink by the landed ink droplets.
As the gradation value of the printed image increases, the proportion of the ejected ink droplets covering the print medium 5 also increases, and the proportion of the surface of the print medium 5 exposed without being covered by the ink droplets decreases. When the ink droplets land on the print medium 5, the surface of the print medium 5 is covered with the ink droplets, and the coverage of the surface of the print medium 5 increases. When there is a difference in the landing shape of the ink droplets, the method of changing the coverage in the print medium 5 may be different. For example, the coverage may be different depending on whether the landing shape of the ink droplet is broken or not, even if the ejection amount is the same. The characteristic shown by the solid line in FIG. 5 is an example when the landing shape of the ink droplet is not broken, and the characteristic shown by the broken line is an example when the landing shape of the ink droplet is broken.

FIG. 6 is a schematic view showing an example of a landing state in which the ink droplets have landed at a predetermined position without breaking. FIG. 7 is a schematic view showing an example of a landing state in which ink droplets are broken and landed.
Although the gradations have the same ejection amount, the appearance when the ejected ink droplets cover the print medium 5 differs due to the difference in the landing shape, resulting in a difference in coverage. In the low gradation region and the high gradation region, the ratio of the ejected ink droplets covering the print medium 5 and the ratio of the surface of the print medium 5 being exposed without being covered by the ink droplets are extremely biased. Therefore, there is little difference in coverage due to the difference in landing shape. However, in the medium gradation region, the ratio of the ejected ink droplets covering the print medium 5 and the ratio of the surface of the print medium 5 being exposed without being covered with the ink droplets are relatively close regions, and thus are covered. The color value also fluctuates due to the influence of the rate.
For example, when the degree of penetration of the ink in the plane direction with respect to the print medium 5 is relatively small, as shown in FIGS. 6 and 7, when the ink droplets are broken and landed, the coverage is determined. It tends to be higher than when it lands without breaking. As a result, when the ink droplets are broken and landed, as shown by the broken line in FIG. 5, the covering ratio is increased in the middle gradation region.

Therefore, the ink ejection amount correction method of the present embodiment includes a first correction table generation step of generating a first correction table that performs correction based on information on a gradation difference due to a difference in ejection amount, and an ink droplet is a print medium 5. A second correction table generation process that generates a second correction table that makes corrections based on information on gradation differences due to differences in the shape of landing on the ink, and discharge that controls the discharge amount based on the first correction table and the second correction table. It is characterized by including a discharge amount control table correction step for correcting the amount control table.
This will be described in detail below.

<Flow of 1st correction table calculation, 2nd correction table calculation and correction value application>
FIG. 8 is a flowchart showing the flow of the first correction table calculation and the second correction table calculation.
In the flow of calculating the first correction table and calculating the second correction table, first, in step S1, the correction pattern 201 is printed. The correction pattern 201 is composed of, for example, as shown in FIG. 9, a color value acquisition pattern composed of one predetermined gradation value and a spectral reflectance acquisition pattern composed of nine predetermined gradation values.
The predetermined gradation value of the color value acquisition pattern is not limited, but a gradation value that can detect a change in the color value according to a weight change in the amount of ink droplets ejected per dot is preferable. Further, although the predetermined gradation value and the number of patterns of the spectral reflectance acquisition pattern are not limited, the gradation value is such that a change in the spectral reflectance can be detected, and the expansion processing performed when the second correction table is created. On the other hand, the number of gradations such that the difference in the correction values is small is preferable.
Here, the extended processing is to perform interpolation calculation based on the discrete information obtained from the spectral reflectance acquisition patterns of a plurality of discrete gradation values (for example, nine discrete gradation values in the example shown in FIG. 9). This refers to the process of associating data with the number of gradations that the printer 100 can form.

Next, in step S2, the printed correction pattern 201 is color-measured by the colorimeter, and the color value 202 of the colorimetric acquisition pattern and the spectral reflectance 203 of each gradation value of the spectral reflectance acquisition pattern are acquired. To do.

Next, in step S3, the first correction table 206 is generated from the color value 202.
The first correction table 206 is generated from the color value 202 and the first correction reference table 204 described below. Step S3 is a first correction table generation step.
The first correction reference table 204 is a table that associates the weight change rate of the amount of ink droplets ejected per dot with the correction factor α that corrects the change in the color value due to the weight change, as shown in FIG. Yes, prepare it after sufficient evaluation in advance. The color value can be corrected by correcting the amount of ink droplets ejected based on the first correction reference table 204. Specifically, in the first correction reference table 204, the weight of ink droplets per dot is set at the time of color design, and the color value acquired from the standard design machine adjusted to eject with this weight is used as the reference color value. As a result, the relationship between the weight change of the ink droplet ejection amount per dot and the color value change is converted into the weight change of the ink droplet ejection amount per dot and the correction factor α to form a linear relationship. In FIG. 10, ◯ indicates the coordinates of the standard design airframe. If the color value decreases as the weight of the ink droplet ejection amount per dot increases, the relationship between the weight change of the ink droplet ejection amount per dot and the correction factor α is a downward-sloping relationship. is there. If the color value increases as the weight of the ink droplet ejection amount per dot increases, the relationship between the weight change of the ink droplet ejection amount per dot and the correction factor α is an upward-sloping relationship. is there. FIG. 10 is a schematic view showing an example of a first correction reference table in which the relationship between the weight change of the amount of ink droplets ejected per dot and the correction factor α is a downward-sloping relationship.

Based on the above color value 202, the correction factor α is calculated from the first correction reference table 204. For example, when the relationship of the first correction reference table 204 is a downward-sloping relationship, if the color value 202 is the same as the color value of the correction pattern 201 printed by the standard design machine, the correction factor α = 1.0. If the color value 202 is smaller than the color value of the correction pattern 201 printed by the standard design machine, for example, the correction factor α = 1.1. If the color value 202 is larger than the color value of the correction pattern 201 printed by the standard design machine, for example, the correction factor α = 0.9.
FIG. 11 is a schematic diagram showing a calculation example of the correction factor α of the first correction table, in which the relationship between the weight change of the ejection amount of ink droplets per dot and the correction factor α is a downward-sloping relationship. In FIG. 11, the circle mark indicates the coordinates of the standard design aircraft, and the ◆ mark indicates the coordinate example of the correction target aircraft. Further, the arrow indicates the correction factor α of the correction target aircraft.
This correction factor α is multiplied by all the data of the number of gradations that can be formed by the printer 100 in the ejection amount control table 208 in order to correct the weight change of the ejection amount of ink droplets per dot. As described above, the ejection amount control table 208 is a table that associates the input gradation value with the ejection amount (or the number of dots generated) of ink droplets for each dot size of dots formed on the print medium 5 by the printer 100. Yes, pre-designed.

Next, in step S4, the second correction table 207 is generated from the spectral reflectance 203.
The second correction table 207 is generated from the spectral reflectance 203 and the second correction reference table 205 described below. Step S4 is a second correction table generation step.
The second correction reference table 205 is a table that associates the input gradation value with the spectral reflectance of the printed image of the input gradation value printed by the standard design machine, and is prepared after sufficient evaluation in advance. I will do it. Specifically, the second correction reference table 205 performs interpolation calculation based on the discrete information of the spectral reflectance obtained from the spectral reflectance acquisition patterns of nine discrete gradation values, for example, as shown in FIG. By doing so, it is generated by performing an expansion process corresponding to the data of the number of gradations that the printer 100 can form. In FIG. 12, ◯ indicates the spectral reflectance information obtained from the nine spectral reflectance acquisition patterns in the standard design aircraft, and the dotted line indicates the characteristics obtained by the interpolation calculation.
More specifically, for example, the landing shape of the standard design aircraft is in a perfect circular state, and discrete gradation values X = 0, 32, 64, 96, 128, 160, 192, 224, 255 are set. When this is done, the spectral reflectance obtained from each gradation value is used as the reference reflectance. By performing interpolation calculation on this reference reflectance, an approximate function is created, and by performing extended processing corresponding to the data of the number of gradations that can be formed by the printer 100, the second correction reference table 205 is obtained.

On the other hand, in the correction target aircraft, when the impact shape in which the ink droplets are broken and the reflectance when the ink droplets cover the print medium 5 changes, nine discrete prints printed on the correction target aircraft are performed. The value of the spectral reflectance 203 obtained from the spectral reflectance acquisition pattern of the gradation value is deviated from the value of the spectral reflectance referred to in the second correction reference table 205. Since the spectral reflectance 203 is also composed of the spectral reflectances at discrete gradation values, the same processing as described above is performed to convert the data into data having a number of gradations that can be formed by the printer 100. A ratio is calculated as a difference between the converted data and the second correction reference table 205, and the second correction table 207 is generated with this ratio as the correction factor β. The correction factor β = spectral reflectance 203 / reference reflectance. FIG. 13 is a graph of an example of the second correction table 207.
Since this correction factor β is different for each input gradation value, it is multiplied for each gradation value associated with the input gradation value of the discharge amount control table 208.
That is, the spectral reflectance 203 is an alternative parameter representing the difference in the shape of the ink droplets landing on the print medium 5.

Next, in step S5, the correction applied discharge amount control table 210 is generated by multiplying the pre-designed discharge amount control table 208 by the first correction table 206 and the second correction table 207. Step S5 is a discharge amount control table correction step of correcting the discharge amount control table 208 that controls the discharge amount based on the first correction table 206 and the second correction table 207 and generating the correction applied discharge amount control table 210.
FIG. 14 is a graph of the discharge amount control table 208 before and after applying the correction when showing two gradations with and without dots in the first embodiment. In FIG. 14, the solid line shows the input gradation value before correction and the ink droplet ejection amount control value corresponding thereto. Further, the broken line indicates the case where the correction is performed by the first correction table 206, and the dotted line indicates the case where the correction is performed by the first correction table 206 and the second correction table 207. In the correction to which only the first correction table 206 is applied, a certain amount of correction is made according to the input gradation value, that is, the gradation value of the printed image, and in the correction to which the first correction table 206 and the second correction table 207 are applied, the printed image is corrected. The correction value in the middle gradation region is corrected so as to be larger than the correction in the low gradation region and the high gradation region of the gradation value according to the gradation value of.

FIG. 15 shows the discharge amount control table 208 before and after the correction is applied when only the first correction table 206 is applied when the four gradations of no dot, small dot, medium dot, and large dot are shown in the first embodiment. Is a graph.
On the other hand, FIG. 16 shows the case where the first correction table 206 and the second correction table 207 are applied to show the four gradations of no dot, small dot, medium dot, and large dot in the first embodiment. It is a graph of the discharge amount control table 208 before and after applying the correction of. When showing 4 gradations of no dot, small dot, medium dot, and large dot, it is the same as when showing 2 gradations with and without dots, and the first correction table 206 and the first correction table 206 according to the size of the ink droplet are shown. The second correction table 207 is applied to the correction for each size of ink droplets. Therefore, the change in the ejection amount of ink droplets or the change in the generation rate according to the gradation value of the printed image is larger than the correction in the low gradation region and the high gradation region of the gradation value in the middle gradation region. Become. In other words, the first correction table 206 and the second correction table 207 are generated for each of a plurality of types of ink droplet sizes, and the amount of ink droplets ejected or the plurality of types of ink droplets for each of a plurality of types of ink droplet sizes. Obtain each generation rate for each size.

Next, in step S6, halftone processing is performed using the correction application discharge amount control table 210 and the dither mask 209.
That is, as described above, the ink ejection amount correction method in the present embodiment is a method of correcting the ejection amount of ink droplets by correcting the ejection amount control table 208 to generate the correction applied ejection amount control table 210. is there.

Further, in the printing method in the present embodiment, the ejection amount control table corrected by the ink ejection amount correction method described above, that is, the correction applied ejection amount control table 210 generated by correcting the ejection amount control table 208 is used. Perform halftone processing. In the print data generation process described with reference to FIG. 3, printing is performed using the print data generated including this halftone process.

As described above, the following effects can be obtained according to the ink ejection amount correction method and the printing method according to the present embodiment.
Even if the color value differs depending on the state of the ink droplets ejected by the printing system 1 with respect to the same type of printing system 1, the color value generated by the difference in the weight of the ink droplets ejected by the printing system 1 In addition to applying the first correction table 206 for correcting the difference, by applying the second correction table 207 for correcting the difference in the landing shape of the ink droplets ejected by the printing system 1, on the print medium 5, It is possible to reduce the difference in color value that changes due to the influence of ink droplet ejection. As a result, deterioration of quality due to the difference in color value in each printing system 1 can be suppressed.

Further, by generating the first correction table 206 and the second correction table 207 for each of a plurality of types of ink droplet sizes, the printing method has not only a single dot size but also a plurality of dot sizes. The correction can also be applied to the printing method used.

Further, as an alternative parameter of the difference in the shape in which the ink droplets land on the print medium 5, the difference in the spectral reflectance of the image printed on the print medium 5, that is, the spectral reflectance in the standard design aircraft and the spectral reflection in the correction target aircraft By using the difference from the rate 203, it is possible to relatively calculate the ratio of ink droplets on the print medium 5 per unit area, which are ejected on the print medium 5 for each gradation.

Further, on the surface of the print medium 5, as the gradation value of the printed image increases, the proportion occupied by the ink increases, and the proportion of the print medium 5 exposed decreases. Further, in the middle gradation region, the ratio of the ejected ink droplets covering the print medium 5 and the ratio of the surface of the print medium 5 being exposed without being covered with the ink droplets are relatively close regions, so that they are covered. The color value also fluctuates due to the influence of the rate. According to the ink ejection amount correction method of the present embodiment, the relationship between the ratio occupied by the ink and the ratio occupied by the print medium 5 is such that the correction value in the middle gradation region is lower depending on the gradation value of the printed image. Since the correction factor is changed so as to be larger than the correction of the toning region and the high gradation region of the gradation value, the correction can be performed under more appropriate conditions.

(Modification example 1)
In the first embodiment, when the second correction reference table is created and the second correction table 207 is generated, the input gradation value and the spectral reflectance of the printed image of the input gradation value printed by the standard design machine correspond to each other. It was explained that it is desirable to create and generate a table by attaching it, but it is not limited to this configuration. Specifically, the print image of the correction pattern 201 is subjected to the binarized image conversion process, and the ratio of the ejected ink droplets covering the print medium 5 per unit area and the surface of the print medium 5 are the ink droplets. It is also possible to use a method of calculating the coverage ratio for each gradation value by obtaining the ratio of exposure without being covered with ink. For example, the surface image of the printed image of the correction pattern 201 is captured by an device capable of optically capturing the print image, and the binarized image conversion process of the printed image data is performed. An arbitrary threshold value is set, and the coverage ratio is calculated by calculating the ratio of the ejected ink droplets covering the print medium 5 and the ratio of the surface of the print medium 5 being exposed without being covered with the ink droplets. That is, as an alternative parameter for the difference in shape in which the ink droplets land on the print medium 5, the difference in the binarized image data of the image printed on the print medium 5 is used. Further, here, the difference in the binarized image data means the difference in the coverage ratio in which the surface of the print medium 5 is covered with the ink.

According to the ink ejection amount correction method of the present modification, the ratio of ink droplets ejected on the printing medium 5 for each gradation and occupying the printing medium 5 per unit area can be relatively calculated. As a result, it is possible to reduce the difference in color value that changes under the influence of ink droplet ejection on the print medium.

(Modification 2)
In the first embodiment, it is explained that when calculating the second correction table 207, it is desirable to calculate by the second correction reference table 205 and the spectral reflectance 203 acquired from the correction pattern 201 printed by the correction target aircraft. However, it is not limited to this configuration. Specifically, when it is considered that the impact shape of the ink droplets is limited to several types after sufficient evaluation in advance, for example, the printing device A, which is a printing device having the same model number as the standard design machine. , B, C, and D, the impact shape of the ink droplets is such as a perfect circle shape, an elliptical shape, two different size round shapes due to separation, and three different size round shapes due to separation, respectively. When four types are confirmed, the settings are changed to the above four types of landing states on the standard design aircraft, and the input gradation values in the above four types of landing states and the printed ones printed by the standard design aircraft. Tables 205A, 205B, 205C, and 205D that associate the input gradation value with the spectral reflectance of the printed image are created. The table calculated from the landing state at the time of color design is used as a reference table, the ratio between this reference table and the above four types of tables is calculated, and the second correction tables 207A, 207B, 207C, and 207D are set with this ratio as the correction factor β. Generate. That is, it is a table / reference table that associates the spectral reflectance of the printed image of the input gradation value printed in the landing shape of the known ink droplet. For example, when the landing shape of the ink droplets of the standard design machine at the time of color design is a perfect circle, the input gradation value in the reference table = perfect circle state and the printed image of the input gradation value printed by the standard design machine. It is a table for associating with the spectral reflectance of the above four types, and four types of second correction tables with the above four types are generated. By incorporating it into a printing device having a function of selecting one of the four types of the second correction table, it is possible to select and set the correction according to the landing shape of the ink droplet possessed by each printer.

Further, for example, instead of four types such as a perfect circle shape, an elliptical shape, two perfect circle shapes due to separation, and three perfect circle shapes due to separation, two second types corresponding to two types with or without separation of ink droplets. Correction tables 207F and 207G may be generated. That is, as an alternative parameter for the difference in shape in which the ink droplets land on the print medium 5, the presence or absence of separation of the ink droplets that land on the print medium 5 may be used.

According to this method, when the difference in shape can be predicted as the presence or absence of ink droplet separation, by preparing a plurality of second correction tables according to the presence or absence of ink droplet separation, the ink droplets can be printed on the print medium. It is possible to reduce the difference in color values that changes depending on the presence or absence of separation.

The contents derived from the embodiment are described below.

The ink ejection amount correction method of the present application is a method of correcting the ejection amount of the ink droplets ejected by a printing apparatus that prints by ejecting ink droplets onto a printing medium, and the color value due to the difference in the ejection amount The first correction table generation step of generating the first correction table for making corrections based on the difference information, and the second correction based on the information of the difference in color value due to the difference in the shape of the ink droplets landing on the print medium. Includes a second correction table generation step of generating a correction table, and a discharge amount control table correction step of correcting the discharge amount control table that controls the discharge amount based on the first correction table and the second correction table. It is characterized by.

According to this method, even if the color value differs depending on the state of the ink droplets ejected by the printing apparatus for the same type of printing apparatus, it is caused by the difference in the weight of the ink droplets ejected by the printing apparatus. In addition to applying the first correction table that corrects the difference in color values, by applying the second correction table that corrects the difference in the impact shape of the ink droplets ejected by the printing device, the ink is printed on the print medium. It is possible to reduce the difference in color value that changes under the influence of droplet ejection. As a result, it is possible to suppress deterioration in quality due to differences in color values between printing devices.

In the above ink ejection amount correction method, it is preferable to generate the first correction table and the second correction table for each of a plurality of types of ink droplet sizes.

According to this method, the correction can be applied not only to a printing method in which the printing method consists of a single dot size but also in a printing method having a plurality of dot sizes.

In the above ink ejection amount correction method, the first correction table generation step and the second correction table generation step use the difference in spectral reflectance of the image printed on the print medium as an alternative parameter for the difference in shape. It is preferable to use it.

According to this method, it is possible to relatively calculate the ratio of ink droplets on the print medium per unit area, which are ejected on the print medium for each gradation.

In the above ink ejection amount correction method, it is preferable that the second correction table generation step uses the difference in the binarized image data of the image printed on the print medium as an alternative parameter for the difference in shape.

According to this method, it is possible to relatively calculate the ratio of ink droplets on the print medium per unit area, which are ejected on the print medium for each gradation.

In the above ink ejection amount correction method, the second correction table generation step uses the difference in the coverage of the surface of the print medium due to the ink droplets landing on the print medium as an alternative parameter for the difference in shape. Is preferable.

According to this method, it is possible to relatively calculate the ratio of ink droplets on the print medium per unit area, which are ejected on the print medium for each gradation.

In the above ink ejection amount correction method, it is preferable that the second correction table generation step uses the presence or absence of separation of the ink droplets that have landed on the print medium as an alternative parameter for the difference in shape.

According to this method, when the difference in shape can be predicted as the presence or absence of ink droplet separation, by preparing a plurality of second correction tables according to the presence or absence of ink droplet separation, the ink droplets can be printed on the print medium. It is possible to reduce the difference in color values that changes depending on the presence or absence of separation.

In the above ink ejection amount correction method, the second correction table is a table in which the gradation value of the printed image and the correction value for correcting the ejection amount of the ink droplet corresponding to the gradation value correspond to each other. It is preferable that the correction value in the middle gradation region of the gradation value is larger than the correction value in the low gradation region of the gradation value and the high gradation region of the gradation value.

On the surface of the print medium, as the gradation value of the printed image increases, the proportion occupied by the ink increases and the proportion of the print medium exposed decreases. Further, in the medium gradation region, the ratio of the ejected ink droplets covering the print medium and the ratio of the surface of the print medium exposed without being covered with the ink droplets are relatively close regions, so that the coverage ratio is high. Affected, the color value also fluctuates. According to the ink ejection amount correction method of the present embodiment, the relationship between the ratio occupied by the ink and the ratio occupied by the print medium is such that the correction value in the middle gradation region is low gradation according to the gradation value of the printed image. Since the correction factor is changed so as to be larger than the correction of the region and the high gradation region of the gradation value, the correction can be performed under more appropriate conditions.

The printing method of the present application is characterized in that printing is performed using a discharge amount control table corrected by the ink discharge amount correction method described in any of the above.

According to this method, even if the color value differs depending on the state of the ink droplets ejected by the printing apparatus for the same type of printing apparatus, it is caused by the difference in the weight of the ink droplets ejected by the printing apparatus. By applying the ejection amount control table that corrects the difference in color value and the difference in the impact shape of the ink droplets ejected by the printing device, it is possible to reduce the difference in color value between individuals in each printing device. it can.

1 ... printing system, 5 ... printing medium, 10 ... printing unit, 11 ... head unit, 12 ... ink supply unit, 13 ... printing head, 14 ... head control unit, 20 ... moving unit, 30 ... printer control unit, 31 ... Interface unit, 32 ... CPU, 33 ... Memory, 34 ... Drive control unit, 35 ... Movement control signal generation circuit, 36 ... Discharge control signal generation circuit, 37 ... Drive signal generation circuit, 40 ... Main scanning unit, 41 ... Carriage, 42 ... Guide shaft, 50 ... Sub-scanning unit, 51 ... Supply unit, 52 ... Storage unit, 53 ... Conveying roller, 55 ... Platen, 100 ... Printer, 110 ... Image processing device, 111 ... Print control unit, 112 ... Input unit , 113 ... Display unit, 114 ... Storage device, 115 ... CPU, 116 ... ASIC, 117 ... DSP, 118 ... Memory, 119 ... Printer interface unit, 201 ... Correction pattern, 202 ... Color value, 203 ... Spectral reflectance, 204 ... 1st correction reference table, 205 ... 2nd correction reference table, 206 ... 1st correction table, 207 ... 2nd correction table, 208 ... Discharge amount control table, 209 ... Disamask, 210 ... Correction applicable discharge amount table, S1 ... Correction pattern printing step, S2 ... Color measurement step, S3 ... First correction table generation step, S4 ... Second correction table generation step, S5 ... Correction application discharge amount table generation step, S6 ... Halftone processing step.

Claims (8)

A method of correcting the amount of ink droplets ejected by a printing apparatus that prints by ejecting ink droplets onto a printing medium.
A first correction table generation step of generating a first correction table that performs correction based on information on a difference in color value due to the difference in discharge amount, and
A second correction table generation step of generating a second correction table that makes corrections based on information on a difference in color value due to a difference in shape of the ink droplets landing on the print medium.
An ink ejection amount correction method comprising a ejection amount control table correction step of correcting an ejection amount control table that controls the ejection amount based on the first correction table and the second correction table. According to claim 1, the first correction table generation step and the second correction table generation step generate the first correction table and the second correction table for each of a plurality of types of ink droplet sizes. The described ink ejection amount correction method. The ink according to claim 1 or 2, wherein the second correction table generation step uses a difference in spectral reflectance of an image printed on the print medium as an alternative parameter for the difference in shape. Discharge amount correction method. The second correction table generation step according to claim 1 or 2, wherein the difference in the binarized image data of the image printed on the print medium is used as an alternative parameter for the difference in shape. Ink ejection amount correction method. Claim 1 or claim, wherein the second correction table generation step uses a difference in the coverage of the surface of the print medium due to the ink droplets landing on the print medium as an alternative parameter for the difference in shape. Item 2. The ink ejection amount correction method according to item 2. The ink ejection according to claim 1 or 2, wherein the second correction table generation step uses the presence or absence of separation of the ink droplets that have landed on the print medium as an alternative parameter for the difference in shape. Amount correction method. The second correction table is a table in which the gradation value of the printed image and the correction value for correcting the ejection amount of the ink droplet corresponding to the gradation value are associated with each other.
The ink according to claim 6, wherein the correction value in the middle gradation region of the gradation value is larger than the correction value in the low gradation region of the gradation value and the high gradation region of the gradation value. Discharge amount correction method. A printing method characterized in that printing is performed using a discharge amount control table corrected by the ink discharge amount correction method according to any one of claims 1 to 7.

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