JP7190935B2 - Image processing device - Google Patents

Description

The present invention relates to a technique for correcting image data to be printed.

Generally, an inkjet printing apparatus stores ink in an ink chamber of an inkjet head, applies a voltage (driving voltage) to a piezoelectric element in the ink chamber to give minute vibrations, and ejects ink from a plurality of nozzles formed on the bottom surface of the inkjet head. An image to be printed is printed on a print medium by ejecting ink.

As described above, since the inkjet printing apparatus prints by ejecting ink by applying a driving voltage, there is a problem that the amount of ink ejected varies depending on the frequency of the driving voltage (driving frequency). This problem is caused by the vibration during ink ejection and the residual vibration remaining in the ink chamber after ink ejection affects the surrounding ink chamber and the next ink ejection process. are the same, the amount of ink ejected varies according to changes in the drive frequency.

Further, the frequency fluctuation characteristics of the ink ejection amount differ from ink jet head to ink jet head due to slight differences in the configuration of the ink chambers for each ink jet head. For this reason, for example, in the case of a line-type inkjet printing device in which a plurality of inkjet heads are arranged in the print width direction perpendicular to the transport direction of the print medium, differences in the position, size, amount of material components, etc. of the inkjet heads can affect ink ejection. The amount is different for each inkjet head, and the density unevenness of the ink per inkjet head width occurs in the conveying direction of the print medium.

Furthermore, the frequency variation characteristic of the ink ejection amount varies depending on the input control of the driving voltage, that is, the driving pattern of the inkjet head. For example, it varies depending on the number of ink ejection drops and the ink ejection pattern (for example, nozzle single drive/thinning drive for halftone dot printing, continuous nozzle drive for solid printing, etc.).

In other words, conventional inkjet printers have the problem that the amount of ink ejected fluctuates due to differences in the driving frequency of the inkjet head, the inkjet head (housing), and the driving pattern of the inkjet head. could have declined. Therefore, in Patent Document 1, the driving frequency of the inkjet head is corrected by correcting the driving voltage according to the change in the driving frequency, and in Patent Document 2, by changing the waveform of the driving voltage according to the change in the driving frequency. A uniform ink discharge amount is obtained even when the amount changes.

JP-A-2006-239861 JP 2017-13392 A

However, even if the driving voltage or the driving voltage waveform of the inkjet head is corrected as in Patent Documents 1 and 2, the vibration during ink ejection and the residual vibration after ink ejection affect other ink chambers and the next ink ejection process. It is difficult to sufficiently suppress fluctuations in the amount of ink ejected due to this, and there is a possibility that the amount of ink ejected may be excessive or insufficient depending on the number of ink droplets ejected or the ejection pattern.

In general, the driving frequency of the inkjet head is uniquely determined for each printing process according to the type of printing medium, etc., and the same process (control) is performed for a plurality of inkjet heads. Even if the driving voltage or the driving voltage waveform of the inkjet head is corrected in accordance with the change in the driving frequency as described above, it is difficult to eliminate the variation in the amount of ink ejected from each inkjet head.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate variations in the amount of ink ejected that depend on the drive frequency, and to improve the quality of printed images.

In order to solve the above-described problems, an image processing apparatus according to the present invention controls the amount of variation in the amount of ink ejected that occurs when the ink ejecting unit ejects ink and then ejects ink. a storage unit for storing each drive frequency and each ink ejection unit; A determination unit that determines an ejection unit, and a variation amount of the ink ejection amount corresponding to the predetermined drive frequency and the predetermined ink ejection unit are specified from the storage unit, and if the variation amount is equal to or greater than a threshold value, the variation. and a correcting unit that identifies an image area corresponding to the ink ejection unit in which the amount of ink is generated from the image data and corrects the density of the image area.

According to the present invention, it is possible to eliminate variations in the amount of ink ejected that depend on the drive frequency, and improve the quality of printed images.

It is a figure which shows the structural example of an inkjet printing apparatus and an image processing apparatus. FIG. 5 is a diagram showing an example of variation in drive frequency and ink discharge amount; FIG. 10 is a diagram showing an example of managing the amount of variation in the amount of ink ejected; It is a figure which shows the processing flow of an image processing apparatus. FIG. 10 is a diagram showing an example of determination of a solid image; 4A and 4B are diagrams showing a printing example and a correction example of image data; FIG. FIG. 10 is a diagram showing another example of correction of image data;

In this embodiment, instead of the method of correcting the driving voltage or driving voltage waveform of the inkjet head as in Patent Documents 1 and 2, it is assumed that the inkjet head has frequency fluctuation characteristics of the amount of ink to be printed. A method of correcting the image data is adopted.

Specifically, the degree of influence of residual vibration is analyzed from the image data to be printed and the driving frequency during printing, and the image density in the image data is corrected in advance according to the degree of influence. to make the ink discharge amount consistent. This eliminates variations in the amount of ink ejected due to changes in factors such as the drive frequency of the inkjet head, the inkjet head (housing), and the drive pattern of the inkjet head (the number of ink droplets ejected, the ink ejection pattern, etc.). We aim to improve quality.

An embodiment for carrying out the present invention will be described below with reference to the drawings. In the present embodiment, a line-type inkjet printing apparatus is used in which a plurality of inkjet heads are arranged in the print width direction perpendicular to the transport direction of the print medium.

FIG. 1 is a diagram showing a configuration example of an inkjet printing apparatus 1 according to this embodiment. In this embodiment, the image processing apparatus 100 that operates inside the inkjet printing apparatus 1 has the features of the present invention. The print processing will be explained first.

As shown in FIG. 1, the inkjet printing apparatus 1 includes a print job storage unit 11 and the like. For example, the inkjet printing apparatus 1 is connected to a terminal device 3 via a communication network, and after receiving a print job output from the terminal device 3 that requested printing, stores the print job in the print job storage unit 11. Remember.

Then, the printing condition management unit 12 acquires printing condition data included in the print job from the print job storage unit 11, and drives a plurality of inkjet heads (ink ejection units) 17 based on the acquired printing condition data. In addition to determining the voltage, driving frequency, etc., temperature data of each color ink is acquired from each temperature sensor 18 attached to each inkjet head 17 and managed.

Further, the image data analysis unit 13 acquires image data to be printed included in the print job from the print job storage unit 11, and performs RIP (Raster Image Processor) processing for converting the acquired image data into raster data, and image data processing. In order to reproduce the colors included in the color, a color conversion process or the like is performed to determine the usage rate of each color ink for each pixel.

After that, the print control unit 14 takes out the printing paper P from the paper tray, feeds it to the transport belt 15, drives the driving roller 16 to move the printing paper P to the lower side of the inkjet head 17, and Based on the usage rate of each color ink for each ink jet head 17, the plurality of inkjet heads 17 are driven with the drive voltage at the determined drive frequency, and cyan (C) and black (K ), magenta (M), and yellow (Y).

The inkjet printing apparatus 1 according to the present embodiment further includes an image processing apparatus 100 as shown in FIG. 1 in addition to the existing components described above. The image processing apparatus 100 is an apparatus for correcting image data to be printed. Such an image processing apparatus 100 can be realized by a computer having a memory, a CPU, an input/output interface, and the like.

First, functions of the image processing apparatus 100 will be described. The image processing apparatus 100 mainly includes a data storage unit 101, a printing condition determination unit 102, and an image data correction unit 103, as shown in FIG.

Here, the frequency variation characteristics of the ink ejection amount described in the background art will be described. FIG. 2(a) is a diagram showing an example of variation in the drive frequency and the ink discharge amount measured by a certain inkjet head 17. FIG. The horizontal axis indicates the driving frequency (high frequency on the right side), and the vertical axis indicates the variable discharge amount [%]. As shown in FIG. 2A, in the inkjet head 17, the amount of ink ejected increases or decreases as the driving frequency differs. It can be seen that there is a tendency to

FIG. 2B is a diagram showing an example of fluctuations in the drive frequency and the ink discharge amount for each inkjet head measured with two different inkjet heads 17 . Here, the variation in the high frequency region is enlarged and shown. From FIG. 2B, it can be seen that the amount of ink ejected differs depending on the inkjet head, and that there is a difference in the magnitude and phase of the frequency variation.

FIG. 2(c) is a diagram showing an example of variation in the driving frequency and ink ejection amount for each number of ejection drops measured by a certain inkjet head 17. In FIG. A case where the number of ejection drops within a predetermined drive period is 6 drops and 3 drops is shown. As can be seen from FIG. 2C, with the inkjet head 17, fluctuations in the amount of ink ejected tend to be greater when the number of ejected drops is larger than when the number of ejected drops is small. Further, although not shown, with regard to the ink ejection pattern, there is a tendency that continuous nozzle driving for solid printing causes greater variation in the amount of ink ejected than nozzle single driving/thinning driving for halftone dot printing. be.

Therefore, the administrator of the inkjet printing apparatus 1 determines the amount of variation in the amount of ink ejected from each of the inkjet heads 17 that make up the inkjet printing apparatus 1 each time the inkjet head 17 ejects ink. Measure in advance by changing the drive frequency or the like.

Then, as shown in FIG. 3, the fluctuation amount of the ink ejection amount is stored in the data storage unit 101 for each driving frequency for driving the inkjet head 17, for each inkjet head 17, and for each driving pattern of the inkjet head 17. Keep In addition, since the amount of variation in the amount of ink ejected also depends on the viscosity of the colored ink, the amount of variation in the amount of ink ejected is measured by changing the temperature of the colored ink, and the amount of variation in the amount of ink ejected is stored as data for each temperature of the colored ink. It is stored in the storage unit 101 .

Therefore, the data storage unit 101 stores the fluctuation amount of the ink ejection amount for each driving frequency for driving the inkjet head 17, for each inkjet head 17, for each driving pattern of the inkjet head 17, and for each color ink in the inkjet head 17. Equipped with a function to store data for each temperature.

Based on the print job stored in the print job storage unit 11, the print condition determination unit 102 selects a driving frequency for driving the inkjet head 17 and an inkjet head for printing image data to be printed at the driving frequency. , and a drive pattern for printing image data to be printed.

The image data correction unit 103 obtains from the data storage unit 101 all fluctuation amounts of the ink discharge amount corresponding to the determined driving frequency, inkjet head, and driving pattern, and also corresponding to the temperature of the color ink in the inkjet head 17. If there is a variation amount equal to or greater than the threshold value X [%] among all the variation amounts, an image area corresponding to the inkjet head 17 in which the variation amount equals or exceeds the threshold value is specified from the image data to be printed, and It has a function to correct the density of the image area.

Further, the image data correction unit 103 determines whether or not there is a solid image of a predetermined size or larger in which dots are aggregated in the image area. If not, it has a function not to perform the above correction. In other words, even when the image data correction unit 103 specifies an image region in which the amount of variation equal to or greater than the threshold value X occurs, the image data correction unit 103 determines that the solid image is included in the image region and the solid image is equal to or larger than the predetermined size. Only when there is, the above correction is made.

Further, the image data correction unit 103 determines whether or not the printing medium on which the image data to be printed is printed is a predetermined type of printing paper. If it is not the printing paper, it has a function not to perform the above correction. In other words, the image data correction unit 103 performs the above correction only when the print medium on which the image data to be printed is printed is a predetermined type of print paper.

Next, a method for correcting image data performed by the image processing apparatus 100 will be described. A method of correcting image data will be described below with reference to FIG. FIG. 4 is a diagram showing the processing flow of the image processing apparatus 100. As shown in FIG.

Step S1;
First, the print condition determining unit 102 acquires a print job from the print job storage unit 11. FIG. A print job includes image data to be printed and printing condition data. The printing condition data includes double-sided or single-sided printing, paper size, paper type, etc. specified by the printing user.

Step S2;
Next, the printing condition determining unit 102 determines the drive frequency for driving the inkjet head 17 based on the paper type specified by the printing user. Further, the printing condition determination unit 102 determines the inkjet head and drive pattern for printing the image data to be printed, based on the image data to be printed. An existing method is used for determining the driving frequency and the driving pattern. Regarding the method of determining the inkjet head, for example, the printing condition determining unit 102 refers to the position information of each inkjet head 17, and selects the inkjet head 17 corresponding to the position where the dot exists in the image data as the inkjet head 17 to be used for printing. decide.

Step S3;
Next, the image data correction unit 103 acquires the temperature of the color ink related to the inkjet head 17 determined in step S2 from the printing condition management unit 12 . Then, the image data correction unit 103 determines the amount of ink ejected corresponding to the driving frequency determined in step S2 for all the inkjet heads 17 that meet all the conditions of the inkjet head and drive pattern determined in step S2, and the temperature. is specified from the data storage unit 101 . Then, if there is a variation amount equal to or greater than the threshold value X among all the variation amounts, the image data correction unit 103 selects an image area corresponding to the inkjet head 17 in which the variation amount equal to or greater than the threshold value X is generated from the image data to be printed. Identify.

Step S4;
Next, the image data correction unit 103 identifies a solid image in which dots are aggregated from the image area identified in step S3, and determines whether or not the solid image has a predetermined area or more. For example, the image data correction unit 103 identifies a solid image in which dots of the same number of drops are gathered in the print width direction in the print medium conveyance direction, and determines whether or not the size is M×N pixels or more.

Specifically, as shown in FIG. 5, the image data correction unit 103 identifies the solid image A from the image area, and the solid image A is dropped from each of the five nozzles on the bottom of the inkjet head 17 five times. If it is a solid image of 5×5 dots, it is determined to be larger than the threshold image B of 4×4 dots defined in advance, and is taken as a solid image to be corrected.

The solid image A and the threshold image B are not limited to a square, but may be a rectangle such as 3×4 dots or 2×4 dots, a circle, an ellipse, a sector, a rhombus, a star, or the like. In addition, a set of dots includes a state in which a plurality of dots are arranged in a predetermined image area, for example, evenly arranged, unevenly distributed, etc. In the present embodiment, the density (for example, average density) in a predetermined area is a predetermined value. If the above is the case, even if the density is uneven within the predetermined area, it is treated as a solid image.

Then, if the specified solid image is a solid image having a predetermined area or more, the process proceeds to step S5. On the other hand, if there is no solid image, or if the specified solid image is a solid image with an area less than the predetermined area, the process ends without correction.

Step S5;
Next, the image data correction unit 103 determines whether or not the print medium specified by the print user is a predetermined type of print paper. The predetermined type of printing paper is, for example, high-quality paper such as matte paper. If matte paper is specified, the process proceeds to step S6. On the other hand, if matte paper is not specified, the process ends without correction.

Step S6;
Finally, the image data correction unit 103 corrects (density adjustment) the density of the image area based on the variation amount of the ink ejection amount specified in step S3, and stores the corrected image data in the print job 11. FIG. Note that whether or not to execute steps S4 and S5 may be selectable. For example, when steps S4 and S5 are not executed, the image data correction unit 103 sets the entire image region specified in step S3 as a correction target.

FIG. 6 is a diagram showing an example of printing and an example of correction of image data. If the image data D to be corrected included in the print job is solidly printed with a driving voltage in a low-frequency range in which the fluctuation of the ink ejection amount is small, it is printed with approximately the same density as the image data D, but the driving voltage in the high-frequency range is printed. If solid printing is performed with , the density is higher than that of the image data D.

Therefore, when a solid image is printed with a drive voltage in the high-frequency range, that is, when the variation in the ink ejection amount is greater than or equal to the threshold value X, the variation in the ink ejection amount specified in step S3 is referred to, and step If the drive frequency determined in S2 has a tendency to increase the amount of ink ejected, correction is made so that the number of ejected drops in the inkjet head 17 becomes, for example, -1 (6 drops become 5 drops). Reduce the image density of the image area. For example, as shown in FIG. 6, the image data D' is corrected to an error diffusion pattern in which about 5% of pixels having a density lower than the image density of the image data D (zero density is possible) are mixed. On the other hand, if the number of ejection drops in the image data to be printed is small, the variation in ink ejection is small, so correction may not be performed.

According to the present embodiment, in the image processing apparatus 100, the data storage unit 101 stores the fluctuation amount of the ink ejection amount for each driving frequency for driving the inkjet head 17, for each inkjet head 17, and for each inkjet head 17 driving frequency. It is stored for each pattern and for each temperature of color ink in the inkjet head 17 . Based on the print job, the print condition determination unit 102 determines a predetermined drive frequency, a predetermined inkjet head 17, and a predetermined drive pattern to be used for print processing. After that, the image data correction unit 103 specifies from the data storage unit 101 the amount of variation in ink discharge amount corresponding to the predetermined driving frequency, the predetermined inkjet head 17, the predetermined driving pattern, and the current temperature of the color ink. If the amount of variation is equal to or greater than the threshold, the image area corresponding to the ink jet head 17 in which the amount of variation occurs is specified from the image data of the print job, and the density of the image area is corrected. Therefore, it is possible to reduce variations in the amount of ink discharged due to driving frequency, inkjet head, etc., and to improve the phenomenon that image density varies due to differences in driving frequency, inkjet head, etc. FIG. As a result, the quality of printed images can be improved.

Further, according to the present embodiment, the image data correction unit 103 determines whether or not there is a solid image having a predetermined area or more in which dots are aggregated in the image area. If there is no solid image, the above correction is not performed. Therefore, only the solid image having a size that greatly affects the appearance is corrected, so that the time required for image correction can be shortened.

Further, according to the present embodiment, the image data correction unit 103 determines whether or not the print medium on which the image data is to be printed is matte paper. Since the above correction is not performed, correction is performed only for matte paper on which ink ejection failure is likely to be conspicuous. For example, since correction is not performed for plain paper, the time required for image correction can be greatly reduced.

(Modification 1)
In the present embodiment, the case where the image data correction unit 103 sets the whole or part of the image area corresponding to the inkjet head 17 as the correction target has been described. On the other hand, the image data correction unit 103 may correct only the image area corresponding to the joint of the adjacent inkjet heads 17 .

Generally, as shown in FIG. 7, the plurality of inkjet heads 17 are arranged side by side in the print width direction and alternately shifted in position in the transport direction. In this case, there is a possibility that the density unevenness of the ink per line, which is the transport direction of the print medium, becomes conspicuous at the boundary of each image area corresponding to each of the inkjet heads 17a, 17b, . . . . When the image in the boundary area is not corrected, the image in the boundary area becomes the place where the density unevenness is most conspicuous in the entire image.

Therefore, as shown in FIG. 7, only the image area corresponding to the joint of the adjacent inkjet heads 17 is corrected as in the image data D'', and the image area other than the image area corresponding to the joint is corrected. is image data D as it is. As a result, unevenness in ink density between lines can be suppressed more reliably, and the time required for image correction can be shortened.

(Modification 2)
In the present embodiment, cyan, black, magenta, and yellow have been described as correction targets. On the other hand, the image data correcting unit 103 may correct only colors that are highly visible with respect to the color of the printing paper or colors specified by the user. For example, if the printing paper is white, only the image density of black, which has the largest lightness difference with respect to the white color, is changed. Accordingly, since the image density of only the specific color is corrected, the time required for image correction can be shortened.

(Modification 3)
In this embodiment, the case where the image processing apparatus 100 operates inside the inkjet printing apparatus 1 has been described. On the other hand, since the image processing apparatus 100 is characterized by correcting image data to be printed, it may operate inside the terminal apparatus 3 shown in FIG. In this case, the image processing apparatus 100 acquires the print job from the inkjet printing apparatus 1, corrects the image data to be printed, and transmits the print job including the image data after the image correction to the inkjet printing apparatus 1. .

Note that the inkjet printing apparatus 1 described in the present embodiment is an example of a printing apparatus and an image forming apparatus, and an enclosing and sealing apparatus attached to the inkjet printing apparatus 1 can also be included in the target apparatus.

<Appendix>
This application discloses the following inventions.

(Appendix 1)
a storage unit that stores, for each drive frequency for driving the ink ejection unit and for each ink ejection unit, the amount of variation in ink ejection amount that occurs when the ink ejection unit ejects ink and then ejects ink; ,
a determination unit that determines a predetermined drive frequency based on a print job and determines a predetermined ink ejection unit that prints image data of the print job at the predetermined drive frequency;
A variation in the amount of ink ejection corresponding to the predetermined drive frequency and the predetermined ink ejection unit is specified from the storage unit, and when the amount of variation is equal to or greater than a threshold value, the ink ejection unit in which the amount of variation occurs is determined. a correction unit that identifies an image area from the image data and corrects the density of the image area;
An image processing device comprising:

(Appendix 2)
The correction unit is
It is characterized in that it is determined whether or not there is a solid image of a predetermined size or more in the image area, and if the solid image exists, the correction is performed, and if the solid image does not exist, the correction is not performed. The image processing device according to appendix 1.

(Appendix 3)
The correction unit is
3. The image according to appendix 1 or 2, wherein the correction is performed when the printing medium on which the image data is printed is a predetermined type of printing paper, and the correction is not performed when the printing medium is not the predetermined type of printing paper. processing equipment.

DESCRIPTION OF SYMBOLS 1... Inkjet printing apparatus 11... Print job storage part 12... Printing condition management part 13... Image data analysis part 14... Print control part 15... Conveyor belt 16... Drive roller 17... Inkjet head 18... Temperature sensor 3... Terminal device 100... Image processing apparatus 101 data storage unit 102 print condition determination unit 103 image data correction unit

Claims (3)

a storage unit that stores, for each drive frequency for driving the ink ejection unit and for each ink ejection unit, the amount of variation in ink ejection amount that occurs when the ink ejection unit ejects ink and then ejects ink; ,
a determination unit that determines a predetermined drive frequency based on a print job and determines a predetermined ink ejection unit that prints image data of the print job at the predetermined drive frequency;
A variation in the amount of ink ejection corresponding to the predetermined drive frequency and the predetermined ink ejection unit is specified from the storage unit, and when the amount of variation is equal to or greater than a threshold value, the ink ejection unit in which the amount of variation occurs is determined. a correction unit that identifies an image area from the image data and corrects the density of the image area;
An image processing device comprising: The correction unit is
It is characterized in that it is determined whether or not there is a solid image of a predetermined size or more in the image area, and if the solid image exists, the correction is performed, and if the solid image does not exist, the correction is not performed. The image processing apparatus according to claim 1. The correction unit is
determining whether or not a printing medium on which the image data is to be printed is a predetermined type of printing paper; if it is the predetermined type of printing paper, the correction is performed; if it is not the predetermined type of printing paper, the correction is performed; 3. The image processing apparatus according to claim 1, wherein no processing is performed.

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