JP2002160353A - Image recording apparatus, print system, and method of correcting nonuniformities in density of ink-jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make correction of nonuniformities in density possible with high precision, in the case of using as an image recording object a recording medium that is difficult to correct the nonuniformities in density when producing data for correcting the nonuniformities in density by recording a pattern for correcting the nonuniformities in density. SOLUTION: The correction method includes the steps of recording a predetermined gradation image as a test pattern on an object recording medium for the image to be printed and on a recording medium for correction of the nonuniformities in density respectively; producing data reflecting the correlation from the results of read images on both of the mediums; and producing a correction table for the nonuniformities in density based on the data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus using an ink jet head having a plurality of nozzles.

[0002] The present invention relates to an image recording apparatus for correcting density unevenness of an ink jet head having a plurality of nozzles.

[0003]

2. Description of the Related Art An image recording apparatus (hereinafter also referred to as an ink jet recording apparatus) for recording an image by discharging ink onto a recording medium using an ink jet head which is a recording means having a plurality of nozzles for discharging ink. ) Is conventionally known.

[0004] Such an ink-jet recording apparatus has an output from an application program or the like installed in a computer serving as a host apparatus, for reasons such as low noise, low running cost, and easy downsizing of the apparatus. Printers that perform printing based on instructions, scanners that read original images, copiers that print copied images of originals, facsimile machines that transmit and receive original images via signal lines such as telephone lines, etc. Widely used.

[0005] As described above, when an image is formed on a recording medium, due to the influence of the nozzle shape of the ink jet head and the like,
It is known that the size and shape of the ejected ink droplets vary, and the dots formed on the recording medium that land on the recording medium vary from nozzle to nozzle, resulting in uneven density in the result of the recorded image. .

As a technique for correcting such density unevenness, a technique called head shading is known.
This head shading (hereinafter, also simply referred to as “HS”) uses a test pattern recorded using an ink jet head, reads the test pattern, determines the recording density corresponding to each nozzle, and determines a plurality of recording densities based on the recording density. The correction data corresponding to each of the nozzles is obtained, and the correction data is used to correct the image data corresponding to each of the nozzles, thereby eliminating image density unevenness caused by a plurality of nozzles.

In the correction by head shading, data relating to the correction amount for each nozzle is stored in an HS table, and image data is corrected using the HS table. In general, the correction is performed by adjusting the gradation value indicated by the multi-valued image data. In the case of an ink jet head that can control the ink discharge amount by this correction, the ink discharge amount is controlled. By controlling each nozzle, the density of each nozzle can be made uniform,
As a result, it is possible to suppress uneven streaks caused by variations among nozzles, and to record an even and smooth image.

A configuration for correcting density unevenness by conventional head shading will be described with reference to FIG.

FIG. 2 is a schematic diagram of a system including a printer 13 and a computer (hereinafter, referred to as a host PC) 1 which is a host device connected to the printer 13 and transferring image data for recording to the printer 13. FIG. 3 is a block diagram illustrating a configuration.

In FIG. 2, an HS medium 2 which is a recording medium for head shading (hereinafter, also referred to as a print medium) is displayed on the basis of an HS gradation image prepared in the host PC 1.
1 is printed. The HS gradation image to be printed is a gradation pattern to be used for correction. The printed gradation pattern is read into an optical reading device 1 such as a scanner.
1, the image average value of each gradation for each nozzle is obtained, and a correction value that matches the target density value of each gradation is obtained from this and a target table adapted to the recording medium. Obtained by interpolation. By performing this process for all nozzles, an HS table, which is data for correction, is created.

When recording an image, the correction for each nozzle is performed using the correction data stored in the HS table, thereby eliminating nozzle unevenness and reproducibility of print density gradation.・ I realize stability.

[0012]

However, according to the above-mentioned conventional method, a recording medium for recording a gradation pattern for correction to create an HS table has low elasticity like paper, and There is no problem in the case of a medium in which the density does not change greatly between the time of printing and the time of use, but it is difficult to create an HS table with the same work for other special media.

As an example, a cloth may be used as a recording medium. The fabric is easy to deform due to its elasticity,
Since there is a color change due to post-processing such as a coloring step performed after image recording, the positioning accuracy of the image portion corresponding to the nozzle position of the image read by the optical reading device 11 is low.
It was difficult to print the gradation pattern as the S correction image on the cloth as it was to correct the density unevenness.

Further, since the density saturation characteristics differ depending on the type of recording medium due to the difference between ink penetration and fixing on the medium, the density gradation characteristics are not linear characteristics proportional to image values, but individual density saturation curve characteristics. Therefore, if the target value is adjusted to that of a conventional HS medium, a problem occurs in gradation expression. In addition, in the case of a transfer sheet that performs transfer to another medium after image recording, the density is determined only after the chemical reaction or the dye is stabilized by the post-printing process. Correction is also needed.

Further, the density measurement also needs to be performed by another measuring device suitable for each medium, and the conventional method requires much labor and time to satisfy all of them, and is not practical.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in consideration of the problem described above, when a pattern for correcting uneven density is recorded and data for correcting uneven density is created. Provided is a print system, an image recording apparatus, and a method for correcting density unevenness of an inkjet head, which can accurately correct density unevenness when a recording medium that is difficult to perform is targeted for image recording. With the goal.

According to another aspect of the present invention, there is provided an image recording apparatus that performs recording in accordance with image data using an ink jet head having a plurality of nozzles, and a host apparatus that supplies the image data to the image recording apparatus. In the print system, the image recording device is configured to store an image on an image print target medium and a correction medium different from the image print target medium based on image data corresponding to a predetermined gradation image received from the host device. Control means for recording an image recorded on each of the image printing target medium and the correction medium, and a target of image data corresponding to the gradation image. Correction data for correcting density unevenness due to a plurality of nozzles of the inkjet head from target data as values. Correction data creating means for creating the correction data, wherein the correction data creating means creates the correction data in accordance with a characteristic correlation between the print target medium and the correction medium in creating the correction data. .

According to another aspect of the present invention, there is provided an image recording apparatus that performs recording on a recording medium in accordance with image data using an ink jet head having a plurality of nozzles, and a host apparatus that supplies the image data to the image recording apparatus. In a printing system, a correction unit corresponding to each of the plurality of nozzles, for correcting density unevenness caused by the plurality of nozzles, a correction unit configured to correct the image data based on the correction data, and a correction medium. Storage means for cutting out and holding data corresponding to each of the plurality of nozzles from data obtained by optically reading a result of recording a predetermined gradation image, and medium change information from means for instructing switching of the recording medium Detecting means for detecting the presence of correction data corresponding to the switched recording medium, and the determining means Therefore, if it is determined that there is correction data corresponding to the switched recording medium, the correction data is changed to correction data corresponding to the recording medium, and then an image is recorded, and the image corresponding to the switched recording medium is recorded. When it is determined that there is no correction data to perform, the correction data corresponding to the switched recording medium is created, and then the image is recorded.

According to the present invention, there is provided an image recording apparatus which performs recording in accordance with image data using an ink jet head having a plurality of nozzles, wherein a recording target medium used for image recording and a correction recording medium are specified. Gradation image recording means for recording a gradation image of gradation, the gradation image recorded on the recording medium, and a result of optically reading the gradation image recorded on the correction recording medium. Correction data creating means for creating correction data corresponding to each of the plurality of nozzles of the inkjet head based on the data.

Further, the present invention provides a method for correcting uneven density of an ink jet head in an image recording apparatus for performing recording in accordance with image data using an ink jet head having a plurality of nozzles, comprising: A gradation image recording step of recording a gradation image having a predetermined gradation on a correction recording medium; and the gradation image recorded on the recording medium; and the gradation image recorded on the correction recording medium. And a correction data generating step of generating correction data corresponding to each of the plurality of nozzles of the inkjet head based on a result of optically reading the toned image corresponding to each of the plurality of nozzles. Features.

<Operation> According to the present invention, when it is difficult to perform HS on a medium to be printed with an image, and when it is necessary to use another HS printing medium, data that takes into account their correlation is used. By creating an HS table using this, an HS table suitable for each image printing medium can be created.
An HS table for performing correction can be created. In addition, since printing on the HS print medium can be commonly used irrespective of the print target medium, it can be performed without having to increase the printing and reading work load.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a system including an ink jet printer 13 as an image recording apparatus to which the present invention can be applied, and a host PC 1 as a host device connected to the printer 13 for image data. The schematic configuration of is shown.

Here, the head used in the printer 13 is an ink jet head in which a plurality of nozzles are arranged, and an image is recorded by discharging ink from each nozzle. Further, as a configuration of the head 20 in the present embodiment, a configuration that employs an ejection method using an electrothermal converter that applies thermal energy to ink is applied as a configuration for ejecting ink.

In FIG. 1, the host PC 1 transfers tone image data 2 indicating a test pattern for HS correction and print setting data 3 such as a print mode to the printer body 13, and prints the tone image on the printer 13. .

In the printer 13, a host PC
Recording of an image by the head 20 based on the image data 14 received from 1 is performed under the control of a control unit (not shown). The control means includes a CPU, a ROM for storing a program executed by the CPU, a RAM used as a work area, and the like.

The image data 14 received by the printer 13
The print data for each head is generated through the image processing unit 17 using the setting data 15. The print data is subjected to non-uniformity correction for each nozzle by table conversion using an HS table 16 as correction data by an HS correction unit 18 for performing head shading.
9 to perform a binarization process,
1 and 22 are printed.

In the print setting at this time, as the HS table 16 for storing data used for correction, printing is performed linearly without HS correction, and a gradation image reflecting the nozzle state of the head 20 is printed. To do.

The recording medium on which the above-mentioned gradation image is printed is firstly a medium 22 on which an image is to be printed. If special processing is required for the medium following printing, the density measurement is performed. Each tone is measured at several points by the detector 12, an average value is calculated for each tone, and these are stored as measured value data of the tone.

Second, the same gradation image is printed on an HS medium 21 which is a recording medium for correcting head shading, the printed image is read by an optical reading device 12, and an image cut-out section 9 on the host PC 1 side. The image is cut out by several dots for each gradation and for each nozzle, and an average value 7 is obtained.

In this case, among the RGB channels, channels having a wide dynamic range and capable of sufficiently expressing the density linear characteristic in gradation are determined for each ink color.

The respective data from the images printed on the two types of media are created by a correlation graph (FIG. 6) based on a scatter diagram by interpolation such as the least square method.

The graph shown in FIG. 6 shows the density on the recording medium on which the gradation image is to be recorded and the image obtained when the corresponding density is printed on the HS medium by the optical reading device. Is a relationship graph.

The optical reading device 1 is configured such that the HS target data at the time of creating the HS table is linear in density on the print medium.
6, the set of values obtained by equally dividing the dynamic range on the density axis from the correlation graph shown in FIG. 6 becomes a set of linear density points. Is an HS target table having a linear density on the print medium.

However, there is a limit to the correction of the highest density portion due to the variation of the head 20, so that the highest density portion HS taking into account the head margin and the variation of the optical reader is taken into account.
The target limit is determined separately. This is an optical reading value of the highest density portion in consideration of the variation in the HS medium.

The difference between the maximum density portion of the HS target and the limit value of the HS target is set to 10 in the maximum density portion.
Calculation is performed so that the ratio becomes 0%, and the lowest density portion becomes 0%.

The HS target can be created in advance and can be created only once for each new medium, so that it can be created in advance.

Next, by using the HS target 4 and the nozzle cutout data 7 of the gradation pattern, the density at the time of printing is HS
The HS creating unit 8 creates an HS table by converting the image input value so as to match the target.

For actual printing, an output table for color conversion is separately created using the created HS table. Subsequently, the setting data 15 including the ink color conversion information according to the output table of the print image is transferred to the printer 13, the image processing unit performs color separation and the like according to the setting data, and the HS correction unit 18 uses the HS table 16. By performing unevenness correction and performing printing on the print medium by the head through the binarization processing, printing with improved image quality can be performed.

From the HS target 4 for each medium and the nozzle cutout data 7 of the HS linear gradation image whose print mode has been previously read and saved and matches the print mode,
The S-table 5 is created, transferred to the printer main body 13, and the chart FIG. 4 for creating the output table is printed, and the output table for each print medium is created by the same means as described above.

When normal image recording is performed, setting data such as color information and image data by an output table corresponding to each medium are stored in the printer main body, and when the medium is switched, the HS table corresponding to the medium is stored in the printer main body. Transfer and print.

Further, when another new medium is added, the gradation image printed on the medium is measured and automatically created.

Further, by printing the chart for creating the output table by performing the HS table and measuring the color, the printing operation on the new medium can be performed.

In the case where the unevenness correction is not effective due to a change over time when the head 20 is replaced or the head is continuously used, a gradation image is again formed on the HS medium in the HS linear state. Printing is performed, nozzle cutout data is obtained from an image read by an optical reading device, and an HS table group for each medium is created when necessary from this and an HS target created for each medium. Thus, printing can be started without having to repeat the same operation of printing an HS linear image for each medium.

The date when the data cut out corresponding to the above-described nozzle is created is stored and compared with the current date and time, whereby a predetermined number of days elapsed since the previous data creation is separately specified. If the expiration date is exceeded, a warning may be given to that effect. With this configuration, it is possible to prevent the uneven density correction from becoming ineffective due to a change with time.

(Second Embodiment) Next, a second embodiment of the present invention will be described in detail. Note that the configuration of the basic system is the same as the configuration of FIG. 1 referred to in the first embodiment, and a detailed description thereof will be omitted.

In the first embodiment described above, the maximum value of the HS target 4 was obtained statistically by measuring the limit value of the maximum density portion of the pattern printed on the HS paper for an arbitrary head.

However, depending on the type of medium used for recording, some inks are difficult to absorb ink, that is, the limit of the ink absorption amount is low, and some ink ejection amounts are high on the printer side. As described above, when the limit of the ink absorption amount of the print medium is low, or when the ink discharge amount on the printer side is large, the image is blurred on the medium at 100% duty and the image quality of the read image is deteriorated. As a result, nozzle unevenness cannot be identified.

In this embodiment, each gradation value of the HS image is set to a value that does not cause bleeding on the medium so that such a problem does not occur. That is, an equal-interval line drawing pattern of various amounts of printing is printed on a gradation image to be printed on a medium, the tolerance of bleeding is determined, and the maximum value of the amount of printing is determined.

H corresponding to the medium density of the maximum ejection amount
The read image value of the image on the medium for S is adjusted to the maximum value of the HS target.

Using two types of HS images, the print target medium 2
No. 2 is printed using a conventional HS image having a maximum density value of 100%, and a newly set H
The image for S (FIG. 5) is printed.

Thereafter, the HS is executed according to the same procedure as in the first embodiment.
A target is created, and an HS table is created using the target.

In the case of a new HS image, a simple example in which image data values are created in a proportional relationship with a conventional image has been described.
A method is also conceivable in which the image values of each gradation are determined so that the values read by the reader after printing on the HS medium are proportional to each other.

The first embodiment and the second embodiment
In the embodiment described above, an example is described in which a gradation image recorded by the printer 13 is read by the reading device 11, the density measuring device 12, and the like, and a table for HS is created in the host PC 1. Is not limited to this,
The image recording apparatus main body has components necessary for creating the HS table, such as the HS table creating section 6, the HS target creating section 8, and the image extracting section 9 in FIG. Input to the inside, create an HS table, and create the created HS
The table may be configured to be stored.

In the embodiment of the present invention described above, a discharge type head using an electrothermal converter for applying thermal energy to ink has been described as an example of a structure for discharging ink. However, the present invention is not limited to this, and can be applied even if another known ejection method is adopted. As another ejection method, a method is known in which a piezo element is used as an electromechanical conversion element that applies mechanical pressure as ejection energy, and a droplet-shaped liquid is ejected by the generated pressure.

The present invention is particularly excellent in a recording apparatus using a so-called bubble jet (registered trademark) type recording head which performs recording by forming flying droplets using thermal energy among ink jet recording methods. It has an effect.

Further, it is preferable to add recovery means for the print head, preliminary auxiliary means, and the like provided as components of the printing apparatus of the present invention since the effects of the present invention can be further stabilized. . If these are specifically mentioned, capping means for the recording head, cleaning means, pressurizing or suction means, preheating means using an electrothermal transducer or another heating element or a combination thereof, and recording Performing a preliminary ejection mode for performing another ejection is also effective for performing stable printing.

Regarding the type and number of print heads to be mounted, the structure having one print head corresponding to a single color and the print colors and densities described in the above embodiments are different. The present invention can be applied to any configuration in which two or more inks are provided corresponding to a plurality of inks.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid. However, an ink which solidifies at room temperature or lower and which softens or liquefies at room temperature may be used. In general, the ink jet method generally controls the temperature of the ink itself within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. Sometimes, the ink may be in a liquid state. In addition, in order to positively prevent temperature rise due to thermal energy by using it as energy for changing the state of the ink from a solid state to a liquid state, or to prevent evaporation of the ink, the ink is solidified in a standing state and heated. May be used. In any case, the application of heat energy causes the ink to be liquefied by the application of the heat energy according to the recording signal and the liquid ink to be ejected, or to start solidifying when it reaches the recording medium. The present invention is also applicable to a case where an ink having a property of liquefying for the first time is used. In such a case, the ink
JP-A-54-56847 or JP-A-60-7
As described in Japanese Patent No. 1260, a mode may be adopted in which the liquid sheet or the solid sheet is held as a liquid or solid substance in the concave portion or through hole of the porous sheet so as to face the electrothermal converter. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, the form of the ink jet recording apparatus of the present invention is not limited to the one used as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader or the like, and a facsimile apparatus having a transmission / reception function. It may take a form.

Further, the present invention may be applied to a system constituted by a plurality of devices or to an apparatus constituted by a single device.

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU provided in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0067]

As described above, according to the present invention, when it is difficult to perform HS on a medium to which an image is to be printed, and when it is necessary to use another HS printing medium, the correlation between them is determined. Create data that takes into account, and use this
By creating the S table, it is possible to create an HS table that performs HS correction suitable for each image printing medium. In addition, since printing on the HS print medium can be commonly used irrespective of the print target medium, it can be performed without having to increase the printing and reading work load.

Further, it is possible to cope with a case where the HS printing medium has a limitation on the amount of ink to be applied.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a conventional example.

FIG. 3 is a diagram showing a gradation image to be recorded in the first embodiment of the present invention.

FIG. 4 is a chart image used for creating an output table in the present invention.

FIG. 5 is a diagram illustrating a gradation image recorded in a second embodiment of the present invention.

FIG. 6 is a diagram showing a correlation graph.

[Explanation of symbols]

 Reference Signs List 1 Host device 2 HS image 5 HS table 6 HS table creation unit 8 HS target creation unit 11 Optical reader 12 Density measuring device 13 Printer 17 Image processing unit 18 HS correction unit 19 Binarization processing unit 20 Head 21 HS printing Medium 22 Medium to be printed

Claims (10)

[Claims] 1. A printing system comprising: an image recording apparatus that performs recording according to image data using an inkjet head having a plurality of nozzles; and a host device that supplies the image data to the image recording apparatus. The image printing target medium, based on image data corresponding to a predetermined gradation image received from the host device, and a control unit that records an image on a correction medium different from the image printing target medium, The host device optically reads an image recorded on each of the image printing target medium and the correction medium, and target data serving as a target value of image data corresponding to the gradation image, A correction data creation unit for creating correction data for correcting density unevenness caused by a plurality of nozzles of the inkjet head is provided. , The correction data generation means, said in the creation of correction data, the print system, characterized in that to create the correction data according to the characteristics correlation with the printing object medium and the correction medium. 2. The method according to claim 1, wherein the correction data creating means reflects the correlation characteristic of a medium on which the gradation image is recorded on at least target data which is a target value of image data corresponding to the gradation image. The print system according to claim 1. 3. The method according to claim 1, wherein the correlation characteristic of a recording medium is reflected on at least the gradation image.
The printing system according to 1. 4. The target data is created and created by obtaining the characteristic correlation based on measurement data obtained by reading the gradation image recorded on each of the image printing target medium and the correction medium. The printing system according to claim 1, wherein the printing is performed. 5. A printing system comprising: an image recording apparatus that performs recording on a recording medium in accordance with image data using an inkjet head having a plurality of nozzles; and a host apparatus that supplies the image data to the image recording apparatus. Correction data corresponding to each of the plurality of nozzles, for correcting density unevenness caused by the plurality of nozzles; correction means for correcting the image data based on the correction data; and a predetermined gradation on a correction medium. Storage means for cutting out and holding data corresponding to each of the plurality of nozzles from data obtained by optically reading a result of recording an image, and means for detecting medium change information from means for instructing switching of the recording medium Determining means for determining the presence or absence of correction data corresponding to the switched recording medium; If it is determined that there is correction data corresponding to the changed recording medium, the correction data is changed to correction data corresponding to the recording medium, and then an image is recorded, and the correction data corresponding to the switched recording medium is changed. If it is determined that there is no print data, the printing system prints the image after creating the correction data corresponding to the switched recording medium. 6. A system further comprising means for storing date and time data relating to creation of data cut out corresponding to each of the nozzles, and warning when the number of days elapsed until the present exceeds a separately specified predetermined time limit. The printing system according to claim 5, wherein: 7. An image recording apparatus which performs recording in accordance with image data using an ink jet head having a plurality of nozzles, wherein a recording target medium used for image recording and a correction recording medium have a predetermined gradation. Tone image recording means for recording a tone image, the tone image recorded on the recording medium, and the tone image recorded on the correction recording medium, based on a result of optically reading the tone image, An image recording apparatus, comprising: correction data creation means for creating correction data corresponding to each of a plurality of nozzles of an inkjet head. 8. The correction table creation means according to a correlation between characteristics of the recording target medium and the correction recording medium, the optical reading result and a target serving as a target value of the gradation image. The image recording apparatus according to claim 7, wherein the correction data is created from the data. 9. The image recording apparatus according to claim 7, wherein the inkjet head applies thermal energy to the ink to discharge the ink from the nozzle. 10. A medium for recording used for image recording and a recording medium for correction in the method for correcting uneven density of the inkjet head in an image recording apparatus for performing recording in accordance with image data using an inkjet head having a plurality of nozzles. A gradation image recording step of recording a gradation image of a predetermined gradation with respect to, the gradation image recorded on the recording medium, and the gradation image recorded on the correction recording medium, A correction data creation step of creating correction data corresponding to each of the plurality of nozzles of the inkjet head based on the result of optical reading corresponding to each of the plurality of nozzles. Head density unevenness correction method