JP2020116823A - Ink jet printer - Google Patents

Abstract

To provide an ink jet printer capable of more properly reducing unevenness in wind ripples.SOLUTION: An ink jet printer comprises: a printing processing part 30 that performs printing processing by discharging ink to a printing medium from an ink jet head; a conveyance part that conveys the printing medium toward the printing processing part 30; a solid region detection part 61 that detects a solid region from image information printed on the printing medium; and a density correction processing part 62 that performs density correction processing for a pixel within the solid region, on the basis of the size of the solid region, a solid region position within the printing medium and a pixel position within the solid region.SELECTED DRAWING: Figure 3

Description

The present invention relates to an inkjet printing apparatus that performs a printing process by ejecting ink toward a print medium while conveying the print medium.

Conventionally, there has been proposed an inkjet printing apparatus that performs a printing process by ejecting ink from an inkjet head onto a print medium that is transported on a transport path.

In such an inkjet printing apparatus, an air flow is generated by transporting the print medium directly below the inkjet head.

Further, when ink is continuously ejected from the nozzles of the inkjet head, the ink droplets are ejected along with a self-air flow, and this self-air flow acts as a wall that blocks the air flow due to the transportation of the print medium described above. Then, the airflow generated by the transportation of the print medium may hit the wall of the self-airflow, and the airflow may be complicatedly disturbed. Due to this turbulent air flow, the landing position of the ink ejected from the inkjet head may be displaced from the desired position, which may cause density unevenness called so-called wind pattern unevenness.

As a method of correcting this density unevenness, in Patent Document 1, attention is paid to the fact that the strength of the self-airflow changes depending on the discharge density of the ink discharged from the nozzles of the inkjet head, and based on the discharge density of the ink There has been proposed a method for correcting the ejection amount of.

JP, 2014-61624, A

However, in the method described in Patent Document 1, since the ejection amount is only corrected based on the ejection density of the ink to control the landing position, for example, it occurs in a solid area formed with the same ink ejection density. It is difficult to improve wind pattern unevenness.

Further, when the print medium is sucked onto the transport belt and is transported, the ink mist that causes unevenness of the wind print is sucked toward the transport belt at the leading end and the rear end of the print medium in the transport direction, and the pattern of the uneven print changes. However, as described in Patent Document 1, it is difficult to improve the wind print unevenness that varies depending on the position in the print medium by only controlling the ink discharge amount based on the ink discharge density.

Furthermore, at the beginning of the printing process on the print medium, the self-air flow due to the ink droplets described above is not so strong, and as the print medium is conveyed and the print process progresses, the self-air flow due to the ink droplets becomes stronger. As a result, the manner in which unevenness of the wind print is generated changes in the transport direction. That is, the wind-print unevenness changes with the passage of time, but even if the density correction is performed only with the ink discharge density as in Japanese Patent Laid-Open No. 2004-187, it is not possible to sufficiently perform the density correction of the dynamically changing wind-print unevenness.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an inkjet printing apparatus that can more appropriately reduce wind pattern unevenness.

A first inkjet printing apparatus of the present invention includes a print processing unit that ejects ink from an inkjet head onto a print medium to perform print processing, a transport unit that transports the print medium toward the print processing unit, and a print medium. Based on the size of the solid area, the size of the solid area, the position of the solid area in the print medium, and the position of the pixel in the solid area, the solid area detection unit that detects the solid area from the image information printed on And a density correction processing unit for performing density correction processing on the.

According to the first inkjet printing apparatus of the present invention, the solid area is detected from the image information printed on the print medium, the size of the solid area, the position of the solid area in the print medium, and the pixels in the solid area. Since the density correction processing is performed on the pixels in the solid area based on the position of, the unevenness of the wind pattern can be reduced more appropriately.

The figure which shows schematic structure of 1st Embodiment of the inkjet printing apparatus of this invention. Head unit top view Block diagram showing a schematic configuration of a control system of the inkjet printing apparatus shown in FIG. FIG. 3 is a diagram for explaining a solid area, wind fingerprint unevenness, and density correction coefficient. The figure which shows an example of the division area set to the print medium. A diagram showing an example of a table of density correction coefficients Flowchart for explaining the process of the first embodiment of the inkjet printing apparatus of the present invention The figure which shows schematic structure of 2nd Embodiment of the inkjet printing apparatus of this invention. FIG. 3 is a diagram for explaining a method of performing density correction processing from the average value of read image information.

Hereinafter, a first embodiment of an inkjet printing apparatus of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus according to the present embodiment is characterized by density correction processing for correcting density unevenness of a print image. First, the overall configuration will be described. FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus 1 of this embodiment. The up, down, left, and right directions shown in FIG. 1 are the up, down, left, and right directions of the inkjet printing apparatus 1 of this embodiment. Further, the front side of the paper of FIG. 1 is the front direction, the back side of the paper is the rear direction, and the front-back direction is the main scanning direction described later.

As shown in FIG. 1, the inkjet printing apparatus 1 of the present embodiment includes a side paper feed unit 10, an internal paper feed unit 20, a print processing unit 30, a paper discharge unit 40, a reversing unit 50, and a control unit. 60 and an operation panel 70.

The print processing unit 30, the internal paper feeding unit 20, and the control unit 60 are housed and installed in a housing formed of metal or resin. In addition, the side paper feed unit 10, the paper discharge unit 40, and the reversing unit 50 are installed in a state where a part of the side paper feed unit 10, the paper discharge unit 40, and the reversing unit 50 are housed inside the housing and part of the housing protrudes outside the housing.

The side paper feed section 10 is a paper feed tray 11 on which the print medium P is placed, and a primary paper feed section that feeds out only the uppermost print medium P from the paper feed tray 11 and conveys it onto the paper feed conveyance path FR. 12 and a secondary paper feeding unit 14 that carries the print medium P carried by the primary paper feeding unit 12 onto the circulation carrying path CR.

The internal paper feed unit 20 is a primary paper feed unit 21a on which the print medium P is placed, and a primary paper feed unit that feeds out only the uppermost print medium P from the paper feed base 21a and conveys it onto the paper feed conveyance route FR. 22a, a paper feed table 21b on which the print medium P is placed, a primary paper feed section 22b for feeding only the uppermost print medium P from the paper feed table 21b and carrying it to the paper feed path FR, and printing The paper feed table 21c on which the medium P is placed, the primary paper feed section 22c for feeding out only the uppermost print medium P from the paper feed tray 21c and carrying it to the paper feed carrying path FR, and the print medium P are placed. It is provided with a paper feed table 21d to be placed and a primary paper feed section 22d for feeding out only the uppermost print medium P from the paper feed table 21d and carrying it to the paper feed path FR.

As described above, the print medium P is conveyed from the side paper feed unit 10 or the internal paper feed unit 20 to the secondary paper feed unit 14, and the print medium P is further carried from the reversing unit 50 described later.

Therefore, in front of the secondary paper feed unit 14 in the transport direction, the transport path of the print medium P fed from the internal paper feed unit 20 and the print medium P on which one surface transported from the reversing unit 50 is printed. There is a confluence point where the transportation route of the vehicle merges. A path on the paper feed mechanism side is referred to as a paper feed conveyance path FR, and other paths are referred to as a circulation conveyance path CR with reference to this joining point.

The print processing unit 30 includes a head unit 31 and an annular transport belt 133 (corresponding to a transport unit of the invention) provided so as to face the head unit 31.

The conveyor belt 133 is formed of an annular endless belt and has a large number of suction holes. The print medium P fed from the secondary paper feed unit 14 is conveyed to the circular conveyance belt 133. Then, the print medium P is adsorbed onto the conveyor belt 133 by the suction of the suction fans 131 and 132 installed on the back side of the conveyor road surface of the conveyor belt 133, and is conveyed at a predetermined conveying speed. Then, while the print medium P is being transported by the transport belt 133, ink is ejected from the head unit 31 to the print medium P, whereby the print processing is performed on the print medium P.

The head unit 31 includes four line heads 32a, 32b, 32c, 32d and a head holder 33 in which the four line heads 32a, 32b, 32c, 32d are installed. Each of the line heads 32 a to 32 d extends in a direction orthogonal to the transport direction of the print medium P, and ejects ink onto the print medium P transported by the transport belt 133. As shown in FIG. 1, the four line heads 32a to 32d are arranged at predetermined intervals along the conveyance path of the print medium P. The four line heads 32a to 32d eject ink of different colors (for example, black, cyan, magenta, and yellow).

The head holder 33 is a member on which the inkjet head 34 included in each of the line heads 32a to 32d is installed. FIG. 2 is a top view of a state in which the inkjet head 34 of each of the line heads 32a to 32d is installed in the head holder 33 as seen from above.

The head holder 33 is composed of a box-shaped support member, and the bottom surface of the head holder 33 has a plurality of installation holes in which the inkjet heads 34 are fitted and installed. The installation hole is a through hole, and is formed so that the ink ejection surface of each inkjet head 34 is exposed outside the bottom surface of the head holder 33.

The dotted squares shown in FIG. 2 indicate the range of installation holes in which the six inkjet heads 34 of each of the line heads 32a to 32d are arranged.

As shown in FIG. 2, each of the line heads 32a to 32d has two head rows in which three inkjet heads 34 are arranged at equal intervals in a direction (front-back direction) orthogonal to the transport direction of the print medium P, The two head rows are arranged in a staggered manner so as to overlap by a predetermined number of nozzles.

The print medium P printed by the print processing unit 30 is conveyed on the circulation conveyance route CR by the conveyance rollers arranged on the circulation conveyance route CR. A switching mechanism 43 for switching between guiding the print medium P transported on the circulation transport route CR to the paper discharge unit 40 or recirculating on the circulation transport route CR is provided on the circulation transport route CR. There is. The switching mechanism 43 specifically switches between the transport path on the side of the paper discharge unit 40 and the transport path on the side of the reversing unit 50.

The paper discharge unit 40 includes a tray-shaped paper discharge base 41 protruding from the housing of the inkjet printing apparatus 1, and a pair of paper discharge rollers 42 that discharge the print medium P onto the paper discharge base 41. Then, the print medium P guided by the switching mechanism 43 to the transport path on the side of the paper discharge unit 40 is discharged onto the paper discharge tray 41 by the paper discharge rollers 42.

The reversing unit 50 conveys the print medium P from the circulation conveyance route CR to the reversal stage 51 and the reversal table 51 for reversing the print medium P, and transfers the print medium P conveyed to the reversal stage 51 on the circulation conveyance route CR. And a reversing roller 52 for returning to.

The print medium P guided to the reversing unit 50 by the switching mechanism 43 is conveyed by the reversing rollers 52 from the circulation conveyance path CR to the reversing table 51, and is returned from the reversing table 51 to the circulation conveyance path CR again so that the front and back are reversed. In this state, it is conveyed on the circulation conveyance route CR. Then, the print medium P whose front and back are reversed is again conveyed toward the print processing unit 30 by a plurality of rollers such as the conveyance roller 53 provided on the circulation conveyance path CR.

The operation panel 70 is composed of a touch panel having a liquid crystal display, displays various setting input screens, and receives various setting inputs such as a print start instruction input.

FIG. 3 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus 1 of this embodiment.

The control unit 60 controls the entire inkjet printing apparatus 1, and includes a CPU (Central Processing Unit), a semiconductor memory, a hard disk, and the like. The control unit 60 controls the operation of each unit of the inkjet printing apparatus 1 by executing a program stored in advance in a storage medium such as a semiconductor memory or a hard disk and operating an electric circuit.

Further, the control unit 60 communicates with the control unit 90 of the print job output device 2 and receives the print job output from the control unit 90. Then, the control unit 60 controls the head unit 31 of the print processing unit 30 based on the image data (corresponding to the image information of the present invention) included in the input print job. Then, density correction processing is performed on the image data.

Specifically, as shown in FIG. 3, the control unit 60 includes a solid area detection unit 61 and a density correction processing unit 62.

The solid area detection unit 61 detects a solid area from the image data included in the print job. The solid region is a region formed by ejecting ink continuously from the nozzles of the inkjet head 34 in the transport direction and the direction orthogonal to the transport direction.

The solid area detection unit 61 detects the solid area by extracting an area where ink is continuously ejected from the nozzles of the inkjet head 34 in the transport direction and the direction orthogonal to the transport direction based on the image data. As a solid area detection method, various known methods can be used.

The density correction processing unit 62 performs density correction processing on the solid area detected by the solid area detection unit 61. The density correction processing unit 62 according to the present embodiment performs density correction processing on pixels in the solid area based on the size of the solid area, the position of the solid area in the print medium P, and the position of the pixel in the solid area. Give.

Here, the size of the solid region is the length of the solid region in the transport direction and the direction orthogonal to the transport direction. In this specification, the length of the solid area in the carrying direction is called the height of the solid area, and the length of the solid area in the direction orthogonal to the carrying direction is called the width of the solid area.

The density correction processing is performed based on the height of the solid area because the above-described wind pattern unevenness changes in the transport direction of the print medium P. This is because, at the beginning of the printing process on the print medium P, the self-air flow due to the above-described ink droplets is not so strong, and as the print medium P is transported and the print process progresses, the self-air flow due to the ink droplets. Is stronger, and the manner in which wind fingerprint unevenness occurs changes in the transport direction.

Further, the density correction processing is performed based on the width of the solid area because the above-described wind pattern unevenness changes in the direction orthogonal to the transport direction of the print medium P (hereinafter, also referred to as the main scanning direction). This is because the turbulent airflow generated between the inkjet heads 34 and the print medium P causes the ink landing positions of the inkjet heads 34 to shift in the main scanning direction, and as a result, the manner in which wind print unevenness occurs differs in the main scanning direction. Because.

FIG. 4 is a diagram illustrating an example of a solid area and wind pattern unevenness generated in the solid area. FIG. 4A is a diagram showing an example of a solid region, and FIG. 4B is a diagram showing an example of wind fingerprint unevenness generated in the solid region. As shown in FIG. 4B, the wind pattern unevenness changes in the carrying direction, and also periodically changes in the main scanning direction. It should be noted that the wind pattern unevenness periodically changes in the main scanning direction because the print areas of the inkjet heads 34 adjacent to the main scanning overlap due to the deviation of the ink landing position of each inkjet head 34 in the main scanning direction. The density becomes higher or lower than other areas, and the overlapping area is periodically formed in the main scanning direction.

FIG. 4C shows an example of the density correction coefficient K1 when the width of the solid area is W1 and the height is H1, and the density correction coefficient K2 when the width of the solid area is W1 and the height is H2. It is a figure. The vertical axis of FIG. 4C is the magnitude of the density correction coefficient, and the horizontal axis is the position of the pixel in the main scanning direction within the solid area.

When the width of the solid area is W1 and the height is H1, the density correction processing unit 62 refers to the density correction coefficient K1 shown in FIG. 4C, and for each pixel in the solid area, The density correction processing is performed by multiplying the density correction coefficient K1 according to the position. When the width of the solid area is W1 and the height is H2, the density correction coefficient K2 shown in FIG. 4C is referred to, and for each pixel in the solid area, the density corresponding to the position of the pixel is calculated. The density correction processing is performed by multiplying the correction coefficient K2. In addition, in the example described here, for the pixels having the same position in the main scanning direction in the solid region, all the pixels are multiplied by the same density correction coefficient. However, different density correction coefficients may be set for the respective pixels having the same position but different positions in the transport direction.

Further, the density correction processing unit 62 of the present embodiment also changes the density correction coefficient depending on the position of the solid area in the print medium P. Specifically, in the present embodiment, the print medium P is adsorbed by the conveyor belt 133 and conveyed. At this time, at the end of the print medium P, the ink mist is sucked into the suction holes of the conveyor belt 133. Therefore, it is difficult to form satellites. That is, at the end portion of the print medium P, the ink mist is unlikely to adhere to the print medium P, so that the wind pattern unevenness is unlikely to occur.

Therefore, if there is a solid area at the end of the print medium P, the density correction processing unit 62 of the present embodiment sets the density correction coefficient of all pixels to “1.0” for the solid area. , A density correction coefficient smaller than the density correction coefficient for a solid area arranged at a position other than the end portion of the print medium P.

In consideration of the above contents, the density correction processing unit 62 of the present embodiment divides the print area of the print medium P into 6×4 divided areas R as shown in FIG. 5, and for each divided area R, A table in which the density correction coefficient is set according to the size of the solid area is stored. FIG. 6 is a diagram showing an example of a table of density correction coefficients set in each divided region R. In the table shown in FIG. 6, density correction coefficients K11 to Knm corresponding to solid region widths W1 to Wn and solid region heights H1 to Hm are set. The density correction processing unit 62 has the table shown in FIG. 6 for each divided region R, that is, has a total of n×m×6×4 density correction coefficients. Then, in FIG. 5, the density correction coefficient of the table of the divided area R at the end shown in gray is set to be smaller than the density correction coefficients of the tables of the other divided areas R. It should be noted that the density correction coefficient is acquired by performing test printing or the like in advance and analyzing the wind print unevenness.

Further, when the width W and the height H of the solid area are values other than the widths W1 to Wn and the heights H1 to Hm shown in FIG. 6, the density correction coefficient corresponding to the width W and the height H sandwiching the values. The density correction coefficient may be acquired by interpolating.

Then, when the solid area is detected by the solid area detection unit 61, the density correction processing unit 62 specifies the divided area R in which the center of the solid area is located, and the width W and height H of the solid area. 6, the density correction coefficient K is determined from the table shown in FIG. 6, and each pixel in the solid area is multiplied by the density correction coefficient K to obtain the density correction processing according to the position of each pixel in the solid area. Give. Thus, if the density correction coefficient K is determined using the table shown in FIG. 6, the density correction coefficient K according to the position, height and width of the solid area can be immediately obtained by a simpler method.

Then, the control unit 60 controls the head unit 31 based on the image data subjected to the density correction processing by the density correction processing unit 62.

Returning to FIG. 3, the print job output device 2 is composed of a computer. The print job output device 2 has a document creation application for creating image data to be printed and a printer driver for creating a print job including the image data installed. The print job output device 2 creates a print job based on the image data created by the document creation application and printing conditions such as the number of prints set on the printer driver, and outputs the print job to the inkjet printing device 1.

Next, the process of the inkjet printing apparatus 1 according to the first embodiment will be described with reference to the flowchart shown in FIG. Note that, here, the density correction processing described above will be mainly described.

First, a print job is output from the print job output device 2 and accepted by the control unit 60 of the inkjet printing device 1 (S10).

The print job received by the control unit 60 is input to the solid area detection unit 61, and the solid area detection unit 61 confirms whether the image data included in the input print job includes a solid area, If the solid area is included (S12, YES), the solid area is detected (S14). Then, the solid area detection unit 61 obtains the position of the detected solid area in the print medium P and the width and height of the solid area, and outputs this information to the density correction processing unit 62 (S16).

The density correction processing unit 62 obtains the density correction coefficient K by referring to the table shown in FIG. 6 based on the information on the position, width W, and height H of the input solid area in the print medium P (S18). .. Then, the density correction processing unit 62 performs density correction processing by multiplying each pixel of the solid area included in the input image data by the density correction coefficient K corresponding to the pixel (S20).

Then, the control unit 60 confirms whether or not the solid areas have been detected for the image data of all the pages included in the print job (S22). When the solid area detection and the density correction processing have been performed on the image data of all the pages (S22, YES), the control unit 60, based on the image data subjected to the density correction processing, the print processing unit 30. The head unit 31 is controlled to print the print medium P (S24).

On the other hand, if the detection of the solid area has not been completed for the image data of all pages (S22, NO), the processing from S12 to S20 is repeated.

The above is the description of the processing of the inkjet printing apparatus 1 according to the first embodiment.

In the inkjet printing apparatus 1 according to the first embodiment described above, different density correction coefficients are set for the end region (the region shown in gray in FIG. 5) of the print medium P and the other regions. However, the end area may be changed according to the size of the print medium P. Specifically, it is considered that the smaller the print medium P, the easier the ink mist around the edge of the print medium P is sucked by the transport belt 133. Therefore, the smaller the print medium P is, the larger the area of the edge is. You may

Further, since the edge portion of the print medium P is not easily affected by the ink mist as described above, the density correction coefficient may not be set for the edge region. As a result, the storage area for storing the density correction coefficient can be reduced, so that the cost can be reduced.

Further, in the inkjet printing apparatus 1 according to the first embodiment, the density correction coefficient is set according to the height H of the solid area. However, when the height H of the solid area is small, the wind pattern unevenness is generated. When the height H of the solid area is smaller than a preset threshold value, the density correction coefficient may not be set and the density correction process may not be performed.

In addition, wind pattern unevenness often appears periodically in the main scanning direction, as shown in FIG. 4B. Therefore, for the density correction coefficient corresponding to the position of the solid area in the main scanning direction, for example, only the density correction coefficient corresponding to one cycle of wind pattern unevenness is stored, and the one cycle of the density correction coefficient is stored in the main scanning direction. It may be used repeatedly. As a result, the storage area for the density correction coefficient can be reduced.

Next, a second embodiment of the inkjet printing apparatus of the present invention will be described. FIG. 8 is a diagram showing a schematic configuration of the inkjet printing apparatus 5 of the present embodiment. The vertical and horizontal directions shown in FIG. 8 are the vertical and horizontal directions of the inkjet printing apparatus 5 of this embodiment.

In the inkjet printing apparatus 1 of the first embodiment, the density correction processing unit 62 uses the preset density correction coefficient K to perform the density correction processing on the image data of the solid area. Since the density correction coefficient K is a value obtained in advance by test printing or the like as described above, appropriate density correction is not always performed depending on the image data of the actual print target or the characteristics of the inkjet printing apparatus itself. For example, it may be possible that the unevenness cannot be eliminated due to over-emphasized or insufficient density enhancement.

Therefore, the inkjet printing apparatus 5 according to the second embodiment actually reads the print image of the print medium P that has been subjected to the print processing by the print processing unit 30 to acquire read image information, and the density correction processing unit 62 The density correction processing is adjusted based on the read image information.

Specifically, the inkjet printing apparatus 5 according to the second embodiment further includes an image reading unit 80, as shown in FIG. The other configurations of the inkjet printing apparatus 5 of the second embodiment are the same as those of the inkjet printing apparatus 1 of the first embodiment. Hereinafter, the inkjet printing apparatus 5 of the second embodiment will be described focusing on the points different from the inkjet printing apparatus 1 of the first embodiment.

The image reading unit 80 is composed of, for example, a camera including a complementary metal oxide semiconductor (CMOS) image sensor, a CCD (Charge Coupled Device) image sensor, and the like.

The image reading unit 80 is arranged in the vicinity of the downstream side of the head unit 31, photoelectrically reads the print image of the print medium P transported by the transport belt 133, and outputs the read image information to the control unit 60.

Then, the read image information received by the control unit 60 is input to the solid area detection unit 61, and the solid area is detected as in the first embodiment. The image data of the solid area detected by the solid area detection unit 61 is input to the density correction processing unit 62, and the density correction processing unit 62 adjusts the density correction processing based on the image data of the solid area of the read image information. To do.

Specifically, the control unit 60 performs the density correction process using the density correction coefficient K on the solid area of the image data of the first page using the method of the first embodiment described above, and the density Printing processing is performed based on the corrected image data.

Then, the image reading unit 80 reads the print medium P on which the image data of the first page is printed, and the read image information is input to the solid area detection unit 61. The solid area detection unit 61 detects a solid area from the input read image information and outputs the image data of the detected solid area to the density correction processing unit 62.

When performing the density correction processing on the image data of the second page, the density correction processing unit 62 confirms the image data of the solid area detected from the read image information of the first page. Specifically, the density correction processing unit 62 detects the unevenness of the image data of the solid area detected from the read image information of the first page.

Then, the density correction processing unit 62 analyzes the unevenness of the solid area on the first page, and if the density enhancement by the density correction processing using the density correction coefficient is insufficient, the solid image of the image data on the second page is obtained. When the density correction processing is applied to the area, the density correction coefficient is adjusted to be large. At this time, if the density correction coefficient is "1.0", no particular adjustment is performed.

On the other hand, the density correction processing unit 62 analyzes the unevenness of the solid area on the first page, and as a result, the density correction processing using the density correction coefficient is overemphasized, and the originally expected wind pattern unevenness is uneven. When the density correction processing is performed on the solid area of the image data of the second page, the range in which the density correction coefficient is large and the range in which the density correction coefficient is small are reversed to perform the adjustment. Specifically, in the case where the high density portion and the light density portion of the wind pattern unevenness shown in FIG. 4B are reversed, the position of the mountain portion of the density correction coefficient shown in FIG. 4C is shifted in the main scanning direction, Reverse the mountain and valley. At this time, the magnitude of the density correction coefficient may be adjusted according to the density difference of the unevenness of the solid area on the first page.

As described above, the density correction processing unit 62 adjusts the preset density correction coefficient based on the unevenness of the solid area on the first page, and uses the adjusted density correction coefficient on the second page. A density correction process is performed on the image data in the solid area.

Then, the control unit 60 controls the head unit 31 based on the image data of the second page after the density correction process, and performs the printing process of the second page.

According to the inkjet printing apparatus 5 of the second embodiment, the density correction processing is adjusted based on the read image information read by the image reading unit 80. Therefore, the density correction coefficient is set as the actual image data of the print target. It can be optimized according to the characteristics of the inkjet printing apparatus itself, and the unevenness of the wind pattern can be reduced more appropriately. Moreover, since the density correction processing is performed based on the read image information of the immediately preceding page, even if the wind pattern unevenness dynamically changes, the density unevenness can be made inconspicuous. Moreover, since the density correction processing is performed based on the read image information of the immediately preceding page, density unevenness that occurs in the main scanning direction such as pitch unevenness can be made inconspicuous.

In the above description of the second embodiment, the read image information of the first page is used when the density correction processing of the image data of the second page is performed. If the density correction processing is adjusted using the read image information of one page or more, the read image information of the immediately preceding page is not necessarily required. For example, the read image information of the first page may be used when performing the density correction processing of the image data of the third page and the image data of the fourth page. However, in order to perform the density correction processing more appropriately, it is preferable to use the read image information of the immediately preceding page as described above.

Further, in the description of the second embodiment, the density correction coefficient is adjusted using the read image information of a single page, but in this case, the density difference of the wind pattern unevenness increases or decreases only for that page. In some cases, the density correction process may result in overcorrection and reverse correction in which the position of the unevenness is reversed, or there may be insufficient density emphasis.

Therefore, for example, when the same image data is printed on a plurality of printing media P, the density correction coefficient may be adjusted using the average value of the read image information of a plurality of pages. Specifically, for example, when performing the density correction processing of the image data of the third page, the average value of the solid area of the read image information of the first page and the solid area of the read image information of the second page is calculated, It is also possible to adjust the density correction coefficient when performing the density correction processing of the solid area of the third page by analyzing the unevenness of the average value in the solid area.

As described above, by adjusting the density correction coefficient based on the average value of the solid areas of the read image information of a plurality of pages, the density correction coefficient can be set to a value according to more actual image data, and unevenness in the wind pattern can be prevented. It can be reduced more appropriately. Further, it is possible to prevent the above-described inverse correction and insufficient density enhancement.

Further, in the inkjet printing apparatus 5 of the second embodiment described above, the preset density correction coefficient is adjusted based on the read image information, but the present invention is not limited to this, and the preset density correction coefficient is not limited to this. Instead of using, the density correction table may be generated from the read image information, and the density correction processing may be performed on the image data based on the density correction table.

Specifically, when printing the image data as shown in FIG. 9A on a plurality of printing media P, the density correction processing unit 62 performs the density correction processing of the image data of the third page, for example, the first page. The average value of the solid area of the read image information and the solid area of the read image information of the second page is calculated. 9B shows a solid area of the image data shown in FIG. 9A, and FIG. 9C calculates an average value of the solid area of the read image information of the first page and the solid area of the read image information of the second page. It is a figure which shows an example of the result.

The density correction processing unit 62 generates a density correction table based on the average value of the solid area shown in FIG. 9C. Specifically, the density correction table is a table for reducing unevenness in the solid area shown in FIG. 9C, and, for example, a coefficient larger than “1” is set in the light density portion in the solid area shown in FIG. 9C. However, the table is a table in which a coefficient "1" is set in the dark portion. The size of the coefficient set in the low density portion is changed according to the density. Specifically, a smaller coefficient is set as the density is lower. As a result, the density correction table in which the coefficients corresponding to all solid areas are set is generated.

The density correction processing unit 62 performs density correction processing by multiplying each coefficient of the density correction table generated as described above by the solid area of the image data of the third page.

The read image information used when generating the density correction table is not limited to the two pages as described above, and the read image information of three or more pages may be used. Further, instead of using the read image information of a plurality of pages as described above, the density correction table may be generated using only the read image information of the page immediately before the page to be subjected to the density correction processing.

As described above, if the density correction table is generated from the read image information and the density correction processing is performed on the image data based on the density correction table, it is not necessary to store the density correction coefficient in advance. Therefore, the capacity of the storage medium can be reduced and the cost can be reduced. Further, it is possible to perform density correction processing according to more actual image data, and it is possible to more appropriately reduce wind pattern unevenness. Further, it is possible to make the density unevenness inconspicuous even if the wind fingerprint unevenness dynamically changes. Furthermore, by acquiring the read image information of the immediately preceding page, it is possible to make density unevenness such as pitch unevenness that occurs in the main scanning direction inconspicuous.

Regarding the inkjet printing apparatus of the present invention, the following additional notes are disclosed.
(Appendix)

The first inkjet printing apparatus of the present invention may include an image reading unit that reads the print image of the print medium that has been subjected to the print processing by the print processing unit and outputs the read image information. Can adjust the density correction processing by using the read image information of one page or more before the image information of the density correction processing target.

Moreover, in the first inkjet printing apparatus of the present invention, the density correction processing unit can adjust the density correction processing based on the average value of the read image information of a plurality of pages.

Further, in the first inkjet printing apparatus of the present invention, the density correction processing unit displays a density correction coefficient corresponding to the size of the solid area, the position of the solid area in the print medium, and the position of the pixel in the solid area. Can be stored as

A second inkjet printing apparatus of the present invention includes a print processing unit that ejects ink from an inkjet head onto a print medium to perform print processing, a transport unit that transports the print medium toward the print processing unit, and a print medium. A solid area detection unit that detects a solid area from image information printed on the image, an image reading unit that reads the print image of the print medium that has been subjected to the print processing by the print processing unit, and outputs read image information; and a density correction processing And a density correction processing unit that performs density correction processing on a solid area of the image information by using the read image information of one page or more before the target image information.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Print job output apparatus 5 Inkjet printing apparatus 10 Side paper feeding unit 11 Paper feeding table 12 Primary paper feeding section 14 Secondary paper feeding section 20 Internal paper feeding section 21a Paper feeding table 21b Paper feeding table 21c Paper feeding Table 21d Paper feed table 22a Primary paper feed section 22b Primary paper feed section 22c Primary paper feed section 22d Primary paper feed section 30 Print processing section 31 Head units 32a to 32d Line head 33 Head holder 34 Inkjet head 40 Paper ejection Part 41 Paper ejection table 42 Paper ejection roller 43 Switching mechanism 50 Reversing section 51 Reversing table 52 Reversing roller 53 Conveying roller 60 Control section 61 Solid area detecting section 62 Density correction processing section 70 Operation panel 80 Image reading section 90 Control section 131, 132 Suction fan 133 Conveying belt CR Circulating conveying path FR Paper feeding conveying path P Printing medium R Divided area

Claims (5)

A print processing unit that performs a print process by ejecting ink from an inkjet head onto a print medium,
A transport unit that transports the print medium toward the print processing unit,
A solid area detection unit for detecting a solid area from image information printed on the print medium,
A density correction processing unit that performs a density correction process on pixels in the solid area based on the size of the solid area, the position of the solid area in the print medium, and the position of pixels in the solid area. Inkjet printing device equipped with. An image reading unit that reads a print image of a print medium that has been subjected to print processing by the print processing unit and outputs read image information,
The inkjet printing apparatus according to claim 1, wherein the density correction processing unit adjusts the density correction processing by using the read image information that is one page or more before the image information that is the target of the density correction processing. The inkjet printing apparatus according to claim 2, wherein the density correction processing unit adjusts the density correction processing based on an average value of the read image information of a plurality of pages. 4. The density correction processing unit stores, as a table, a density correction coefficient corresponding to a size of the solid area, a position of the solid area in the print medium, and a position of a pixel in the solid area. The inkjet printing apparatus according to claim 1. A print processing unit that performs a print process by ejecting ink from an inkjet head onto a print medium,
A transport unit that transports the print medium toward the print processing unit,
A solid area detection unit for detecting a solid area from image information printed on the print medium,
An image reading unit that reads a print image of a print medium that has been subjected to print processing by the print processing unit and outputs read image information;
An inkjet printing apparatus, comprising: a density correction processing unit that performs density correction processing on the solid area of the image information by using the read image information that is one or more pages before the image information to be subjected to the density correction processing.