JP2016221750A - Image formation apparatus and image correction method in the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve the density difference due to the impact time difference while reducing a load applied to processing.SOLUTION: An image formation apparatus comprises: a first recording head which discharges a first droplet (chromatic ink); a second recording head which discharges a second droplet (achromatic ink) not in parallel in the recording direction with the first recording head; means which stores the impact time difference between the first droplet and the second droplet onto a recording medium; means 131 which divides a recording region into a plurality of regions in the recording direction; and droplet amount correction means 137 which corrects the droplet amounts discharged from the first and second recording heads. The droplet amount correction means corrects the droplet amounts to be discharged in accordance with the impact time difference between the first and second droplets for each of the plurality of divided regions.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus and an image correction method in the image forming apparatus.

In order to improve the recording speed when performing color recording on plain paper or the like in an image forming apparatus of an ink jet recording method, the head moves in both the forward and backward directions in the scanning direction of the recording head and ejects ink. So-called bidirectional recording is generally known.
In this bi-directional printing, depending on the arrangement of the nozzle rows that eject ink, a bi-directional color difference is generated by ejecting (discharging) ink in different colors in the forward path and the backward path. In order to avoid this bidirectional color difference, a method of printing chromatic color ink and achromatic color ink at different scanning timings of the recording head is considered.

However, in this method, for example, when an image is formed by ejecting chromatic color ink in the forward path and achromatic color ink in the backward path, a scan area (also referred to as a band) is present at both ends of the scan start position and end position in the band. There is a new problem that the landing time difference between the colored ink and the achromatic ink is different and the density is different.
Therefore, it is known to control density unevenness at both ends of the band by controlling the color conversion means of the recorded image and the dividing means for dividing the recording data for each scan based on the landing time difference information. Yes.

  For example, in Patent Document 1 (Japanese Patent No. 5300352), in order to suppress density unevenness due to a landing time difference during bidirectional printing (bidirectional recording), recording is performed based on information of a recording time interval (that is, a landing time difference). An image forming apparatus and an image forming method in which density unevenness at both ends in a band is suppressed by controlling an image color converting unit and a recording data dividing unit for each scan are disclosed.

  However, in the conventional control based on the landing time difference, the landing time difference is called for each pixel, and the density unevenness correction control is performed, so that the processing increases. For this reason, the conventional method has problems such as an increase in processing time, a decrease in productivity, and an increase in cost due to the installation of a high-spec processing mechanism, and there is still room for improvement.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a difference in landing time between the first droplet and the second droplet generated on the recording medium during bidirectional recording in the image forming apparatus. It is to be able to eliminate the density difference due to the above while reducing the processing load as compared with the prior art.

  The present invention includes a first recording head that discharges first droplets, a second recording head that discharges second droplets that are not parallel to the first recording head in the recording direction, Storage means for storing the landing time difference between the first and second droplets on the recording medium, means for dividing the recording area into a plurality of areas in the recording direction, and ejection from the first and second recording heads A droplet amount correcting unit that corrects the droplet amount to be performed, and the droplet amount correcting unit includes the first and second droplets according to a landing time difference between the first and second droplets for each of a plurality of divided regions. An image forming apparatus that corrects the amount of liquid droplets ejected from a second recording head.

  According to the present invention, in the image forming apparatus, the density difference caused by the landing time difference between the first droplet and the second droplet on the recording medium, which occurs during bidirectional recording, is eliminated while reducing the processing load compared to the conventional method. Can be able to.

1 is an overall image of an ink jet recording apparatus according to an embodiment of an image forming apparatus of the present invention. FIG. 2 is a diagram schematically illustrating an example of an arrangement of recording heads that eject ink droplets of the inkjet recording apparatus. It is a figure explaining the colorant distribution inside the paper when the dye-based ink is driven into the same location. FIG. 6 is a diagram for explaining a color distribution inside a sheet when pigment-based ink is driven into the same portion of the sheet. FIGS. 5A and 5B are conceptual diagrams showing penetration depth into a sheet due to a difference in landing time. FIG. 5A shows a case where the landing time difference is small, and FIG. The vertical axis represents density, and the horizontal axis represents the difference in landing time. It is an image figure of the density nonuniformity which arises in the high-speed printing which completes the image of 1 band by one scan. It is a block diagram which shows the outline | summary of the control part of the inkjet recording device which concerns on embodiment of this invention. FIG. 9A is a functional block diagram of a printer driver used in the image processing method (image processing method according to the first embodiment) executed by the inkjet recording apparatus, and FIG. 9B is the image processing method according to the first embodiment. It is a flowchart which shows the process sequence for ink discharge amount correction | amendment. FIG. 9B is a diagram illustrating an example for executing density correction by area division shown in FIG. 9B in the image processing method according to the first embodiment. FIG. 11A is a functional block diagram of a printer driver of a host used in the image processing method according to the second embodiment, and FIG. 11B shows a processing procedure for ink ejection amount correction in the image processing method according to the second embodiment. FIG. It is a figure explaining an example of switching of the gamma correction parameter in an image processing method concerning a 2nd embodiment of the present invention. FIG. 13A is a functional block diagram of a printer driver of a host used in the image processing method according to the third embodiment, and FIG. 13B shows a processing procedure for ink ejection amount correction in the image processing method according to the third embodiment. FIG. It is explanatory drawing which shows an example of the drive waveform in the image processing method which concerns on the 3rd Embodiment of this invention. It is explanatory drawing which shows an example of the drive waveform pattern in the image processing method which concerns on the 3rd Embodiment of this invention. FIG. 16A is a functional block diagram of a printer driver used in the image processing method according to the fourth embodiment, and FIG. 16B is a flowchart showing a processing procedure for ink ejection amount correction in the image processing method according to the fourth embodiment. FIG. An example of the assigned multi-value / low-value matrix in the image processing method according to the fourth embodiment of the present invention will be described. FIG. 18A is a functional block diagram of a printer driver used in the image processing method according to the fifth embodiment, and FIG. 18B is a flowchart showing a processing procedure for ink ejection amount correction in the image processing method according to the fifth embodiment. FIG. It is explanatory drawing of the image processing method which concerns on 6th Embodiment which added the process which judges whether the adhesion amount correction | amendment in a landing time difference is further implemented by determination of an object to 1st to 5th embodiment. It is explanatory drawing regarding the correction | amendment in the boundary of an area | region in the image processing method which concerns on the 7th Embodiment of this invention. It is explanatory drawing regarding the correction | amendment in the boundary of an area | region in the image processing method which concerns on the 8th Embodiment of this invention.

Next, an embodiment of the present invention will be described.
FIG. 1 is an overall image of an ink jet recording apparatus according to an embodiment of an image forming apparatus of the present invention.
The inkjet recording apparatus 1 forms an image while scanning an inkjet head in the width direction of a sheet as a recording medium, conveys the sheet after one or more scans are completed, and forms the next recording line. This is a so-called serial type ink jet recording apparatus.

  The ink jet recording apparatus 1 includes an image forming unit 2, a sheet conveying unit 3, and a roll paper storage unit 4. These units are arranged inside the apparatus main body 1a. In the image forming unit 2, a guide rod 13 and a guide rail 14 are spanned on both side plates, and a carriage 15 is held on the guide rod 13 and the guide rail 14 so as to be slidable in the direction of arrow A. The carriage 15 is mounted with a recording head 15a (see FIG. 2) that ejects ink droplets of black (K), yellow (Y), magenta (M), and cyan (C).

The main scanning mechanism 10 includes a carriage drive motor 21 disposed on one side in the sheet width direction, a drive pulley 22 driven to rotate by the carriage drive motor 21, and a driven pulley 23 disposed on the other side in the sheet width direction. The belt member 24 is provided between the drive pulley 22 and the driven pulley 23.
The driven pulley 23 is tensioned outward by a tension spring, that is, in a direction away from the drive pulley 22.

The belt member 24 pulls the carriage 15 in the sheet width direction by being partly fixed and held by a belt fixing portion provided on the back side of the carriage 15.
An encoder sheet 40 (see FIG. 2) is arranged along the sheet width direction of the carriage 15 to detect the main scanning position of the carriage 15.
The main scanning position of the carriage 15 is detected by reading an encoder sheet by an encoder sensor provided on the carriage 15.
In the main scanning area of the carriage 15, in the recording area, the roll paper 30 is intermittently conveyed by the sheet conveying unit 3 in the direction orthogonal to the sheet width direction, that is, in the sheet conveying direction (direction indicated by arrow B in the drawing). Is done.

A main cartridge 18 containing each color ink to be supplied to the sub tank of the recording head 15a is located outside the carriage movement area in the sheet width direction or in one end side area of the main scanning area with respect to the apparatus main body 1a. It is attached detachably.
In addition, on the other end side of the carriage movement region, that is, the idle ejection position side (left side in the figure), an idle ejection operation for ejecting ink droplets that do not contribute to image recording is performed in order to eject thickened ink. An empty discharge receiver for receiving ink droplets when performing is provided.

Each recording head 15a performs idle ejection at the above-described idle ejection position in order to maintain and recover ejection performance when a predetermined condition is satisfied.
Further, a maintenance / recovery mechanism 19 that performs maintenance / recovery of the recording head 15a is disposed on one end side of the carriage movement region, that is, on the carriage home position side (right side in the drawing).

The maintenance / recovery mechanism 19 includes caps for capping each nozzle surface of the recording head 15a, a wiper blade as a blade member for wiping the nozzle surface, and the like.
Depending on the specifications of the apparatus, for example, an empty discharge receiver may be provided on the carriage home position side and included in the maintenance / recovery mechanism 19 like the cap and the wiper blade, or the carriage home position side and the empty discharge position side may be included. A configuration may also be adopted in which idle discharge receptacles are provided on both of them.

The roll paper storage unit 4 is a paper supply unit, and the roll paper 30 is set as an image recording sheet. In the roll paper storage unit 4, roll papers having different sizes in the sheet width direction can be set.
The roll paper 30 is accommodated in the roll paper accommodating portion 4 by mounting flanges 31 on both sides of the paper roll and placing the flanges 31 on the flange receivers 32.
A support roller is provided inside the flange receiver 32, and the support roller contacts the outer periphery of the flange 31, so that the flange 31 rotates and the roll paper 30 is sent out to the sheet conveyance path.
However, the configuration of the apparatus is not limited to the above, and the present invention can also be applied to a serial type inkjet recording apparatus that supports only a small cut sheet.

FIG. 2 is a diagram schematically illustrating an example of the arrangement of the recording heads 15 a that eject ink droplets of the inkjet recording apparatus 1.
As shown in FIG. 2A, a recording head 15 a is mounted on the carriage 15 held by the guide rod 13 and the guide rail 14. As shown in FIG. 2B, the recording head 15a has nozzle rows K1 to K4, C1 to C2, and M1 that eject inks of K (black), C (cyan), M (magenta), and Y (yellow). ~ M2 and Y1 ~ Y2. Here, the odd-numbered nozzle row and the even-numbered nozzle row are arranged at positions shifted by ½ of the nozzle pitch, thereby doubling the printing resolution per scan.

Here, two recording heads 15 a (K 1, K 2; K 3, K 4) having nozzle rows that discharge K ink are arranged in a column in order to improve the printing speed of monochrome images, and one of them (K 1, K 2). ) Is in parallel in the recording direction with a recording head having a nozzle array for discharging CMY inks, and the other (K3, K4) is in a position not parallel in the recording direction. Also, the nozzle rows (Y1, M1; C1, C2; M2, Y2) that discharge CMY inks are symmetrical in the main scanning direction in order to avoid bidirectional color differences (see FIGS. 3 and 4) due to the landing order of the ink colors. Is arranged.
The arrangement of the recording head 15a is not limited to this. For example, the nozzle rows K3 to K4 may be provided on the opposite side of the sub-scanning direction with respect to K1 to K2, or the color of the CMY ink If the order is also symmetrical, the arrangement of CMY may be changed.

3 and 4 are diagrams for explaining the cause of the bidirectional color difference.
As ink-jet colorant fixing characteristics, when ink droplets of different colors are ejected to the same location on the paper, there is a characteristic that the color of the ink ejected first becomes dominant.
FIG. 3 is a diagram for explaining the colorant distribution inside the paper when the dye-based ink is driven into the same location.
That is, as shown in FIG. 3A, when the A color droplet and the B color droplet are sequentially ejected onto the paper, ie, the roll paper 30, as shown in FIG. When it penetrates into the paper 30 and a B-color drop is injected here, as shown in FIG. C, the B-color drop only penetrates within the A-color infiltration region. The droplets spread over a wider range than the B-color droplets that were shot later, resulting in a difference in the fixing range of the colorant. For this reason, in the secondary color (C + M, M + Y, etc.), the color of the previously ejected drop becomes a more dominant color component.

FIG. 4 is a view for explaining the color distribution inside the paper when the pigment-based ink is applied to the same portion of the paper.
That is, as shown in FIG. 4A, when the A color droplet and the B color droplet are sequentially ejected onto the paper, here, the roll paper 30, as shown in FIG. When a B-color droplet is injected into the ink, as shown in FIG. 3C, the B-color droplet penetrates through the A-colored permeation region and is included in the ink that has been previously injected. The colorant stays on the surface of the paper, and the colorant that is driven later sinks into the paper.
As a result, the characteristics of the colorant (A-color ink) on the side closer to the paper surface (the direction of the previously ejected droplets) become stronger and become the dominant color component.

3 and 4 describe the recording object through which the liquid droplet permeates, the same phenomenon also occurs in the recording object through which the liquid droplet does not penetrate.
For this reason, for example, nozzle rows that discharge CMY inks are not symmetrically arranged in the main scanning direction, and an image of one band (scanning area) is completed by one scanning (forward scanning and backward scanning) of the recording head 15a. In this case, since the order of CMY inks is switched between the forward scanning and the backward scanning in the main scanning direction, the color difference is caused by switching the ink color that controls the color tone between the bands. However, even if the order of CMY ink is changed in units of one nozzle within one scan, it is not recognized as a color difference by human eyes.
From the above, it is desirable that the nozzle rows for ejecting CMY inks be symmetrically arranged so that the nozzle firing color order is not switched between bands.

  However, when the nozzles are arranged in the order of the nozzle colors shown in FIG. 2B, the arrangement relationship between the K ink and the CMY ink is not symmetrical. Resulting in. In order to avoid this, it is more desirable to use only K3 to K4 in FIG. 2B in order to always land K ink after CMY ink in a printing mode in which one band image is completed by one scan.

FIG. 5 is an image diagram showing the penetration depth into the paper due to the landing time difference. FIG. 5A shows a case where the landing time difference is small, and FIG. 5B shows a case where the landing time difference is large.
According to the experiments by the present inventors, it is known that a difference in penetration depth occurs in the landing time difference as shown in the image diagram of FIG.
As shown in FIG. 5A, when the landing time difference is small, the chromatic ink dots that land first (corresponding to the first droplets of the present invention) are not completely dry and the achromatic ink dots (Corresponding to the second droplet of the present invention) land. For this reason, the ink tends to penetrate into the recording paper and the density tends to be low. On the other hand, as shown in FIG. 5B, when the landing time difference is large, the achromatic ink dots land while the chromatic ink dots that land first are dry, so that the ink penetrates into the recording paper. Since it is difficult, the concentration tends to increase.

FIG. 6 is a graph showing the relationship between density on the vertical axis and difference in landing time (S) on the horizontal axis.
That is, the relationship between the landing time difference and the density when scanning at a certain recording head moving speed V [m / S] is as follows. As shown in FIG. There is a tendency for the concentration to saturate.
Here, as an example, when considering a printing method for achieving high-speed printing in which an image of one band is completed by one scanning (forward scanning and backward scanning), as shown in FIG. A band that discharges CMY ink while scanning the carriage in the forward direction (forward scanning) and discharges K ink while scanning the carriage in the backward direction during the second scanning (return scanning) (the lowermost part in the paper passing direction in FIG. 7) Focusing on the band, the density becomes lower at the left end in FIG. 7, and the density becomes higher at the right end.
Therefore, as shown in FIG. 7, there are “dark” and “thin” portions at the left and right end portions in the band, and the arrangement of “dark” and “thin” portions is repeated for each band while being reversed. Is recognized as density unevenness.

FIG. 8 is a block diagram showing an outline of the control unit 100 of the ink jet recording apparatus according to the embodiment of the present invention.
The control unit 100 temporarily stores a central processing unit (CPU) 101 that controls the entire apparatus, a ROM (read only memory) 102 that stores programs executed by the CPU 101 and other fixed data, and image data. A RAM (Random Access Memory) 103, a non-volatile memory (NVRAM) 104 for holding data even while the power of the apparatus is shut off, image processing for performing various signal processing, rearrangement, and other entire apparatus And an ASIC (Application Specific Integrated Circuit) 105 that processes input / output signals for control. The ROM 102 further includes a landing time difference storage unit 102a that stores a landing time difference for each paper size.

The control unit 100 drives a host I / F (interface) 106 for transmitting and receiving data and signals to and from the host 90 side such as a personal computer including the ink jet recording apparatus of the present embodiment, and the recording head 15a. A head drive control unit 107 and a head driver 108 that generate drive waveforms for control, a main scanning motor drive unit 111 for driving the main scanning motor 110, and a sub scanning motor drive for driving the sub scanning motor 112 Unit 113, high-voltage circuit (AC bias supply unit) 114 for supplying AC bias to charging roller 34, environmental sensor 118 for detecting environmental temperature and / or environmental humidity, and detection signals from various sensors (not shown). An I / O (input / output unit) 116 and the like are provided.
The control unit 100 is connected to an operation panel 117 for inputting and displaying information necessary for the apparatus.

Here, the control unit 100 cable print data including image data from the host 90 side such as an image processing apparatus or data processing apparatus such as a personal computer, an image reading apparatus such as an image scanner, or an imaging apparatus such as a digital camera. Alternatively, it is received by the host I / F 106 via the network.
Note that the printer driver 91 on the host 90 side generates and outputs print data for the control unit 100 (corresponding to the droplet amount correcting means of the present invention).
The CPU 101 reads and analyzes the print data in the reception buffer included in the host I / F 106, performs data rearrangement processing by the ASIC 105, and transfers the image data to the head drive control unit 107.

As described above, print data for image output is converted into bitmap data by converting the image data into bitmap data by the printer driver 91 on the host 90 side, and this apparatus (control unit 100). For example, the font data may be stored in the ROM 102.
The head drive control unit 107 includes a D / A converter that performs D / A conversion on the drive pulse pattern data, and the head driver displays a drive waveform composed of one drive pulse (drive signal) or a plurality of drive pulses. To 108.

The head driver 108 selectively selects drive pulses constituting a drive waveform supplied from the head drive control unit 107 based on image data (dot pattern data) corresponding to one line of the recording head 15a input serially. The recording head 15a is driven by applying it to the pressure generating means of the recording head 15a.
For example, the head driver 108 includes a shift register that inputs a clock signal and serial data, a latch circuit that latches a register value of the shift register with a latch signal, and a level conversion circuit (level shifter) that changes the output value of the latch circuit. In addition, an analog switch array (switch means) whose on / off is controlled by this level shifter is included. The head driver 108 controls on / off of the analog switch array to selectively apply a required drive waveform included in the drive waveform from the head drive control unit 107 to the pressure generating means of the recording head 15a for recording. The head 15a is driven.
Here, the drive waveform is composed of a plurality of drive pulses, and by giving one or a plurality of drive pulses, four types of gradations of large droplets, medium droplets, small droplets, and no droplets can be reproduced. .

FIG. 9A is a functional block diagram of the printer driver 91 of the host 90 used in the image processing method (image processing method according to the first embodiment) executed by the inkjet recording apparatus, and FIG. 9B is related to the first embodiment. It is a flowchart which shows the process sequence for the ink discharge amount correction | amendment in an image processing method.
The printer driver 91 is a host-side program that transfers image data (print data) to the inkjet recording apparatus in order to form an image.
As shown in FIG. 9A, the printer driver 91 includes a division processing unit 131, a calling unit 133, a CMM (Color Management Module) processing unit 134, a first determination unit 135, a second determination unit 136, and a halftone processing unit 138. A correction processing unit 137 is provided.
The image processing apparatus may further include a γ correction unit that performs total amount restriction processing for limiting the total amount of ink adhesion, and input / output correction that reflects the characteristics of the printing apparatus and user preferences.

  In FIG. 9B, when image data is input to the printer driver 91 (S101), the division processing unit 131 matches the image data given from the application software or the like with a plurality of areas obtained by dividing the recording area in the recording direction. Divide into a plurality of regions (S102). Next, the calling unit 133 refers to the landing time difference storage unit 102a of the ROM 102 shown in FIG. 8, which is a storage unit that stores the landing time difference between the black ink and the color ink for each divided area (S103). A landing time difference that matches the image size and division position of the image data is called (S104).

Next, the CMM processing unit 134 performs conversion from the monitor display color space to the color space for the recording apparatus (RGB color system → CMYK color system) (S105).
Here, since the density difference between the left and right edges occurs when the black ink and the color ink overlap, the first determination unit 135 determines whether or not there is black ink data after data conversion to CMYK. Judgment is made (S106). If it is determined that the black ink data exists (S106, YES), the process proceeds to step S107, and the second determination unit 136 determines whether any of the CMY ink data exists. (S107). If the second determination unit 136 determines in step S107 that CMY ink data exists (S107, NO), a density correction process is executed (S108).

Next, the correction processing unit 137 (the halftone processing unit 138) performs halftone processing including a multi-value / low-value matrix that replaces image data with a pattern arrangement of dots ejected (discharged) from the ink jet recording apparatus (S109). ).
If it is determined in step S106 that black ink data does not exist (S106, NO) and if it is determined in step S107 that CMY ink data does not exist (S107, YES), density correction is necessary. Since there is no, the process proceeds to halftone processing in step S109. That is, the density correction process corresponding to the landing time difference in step S108 is executed only when black ink and color ink data exist.

Next, when all the pixels are processed (S110, YES) and the processing for all the regions is completed (S111, YES), this processing is ended.
If it is determined in step S110 that all the pixels have not been processed, that is, if there is an unprocessed pixel (S110, NO), the process returns to step S105 to perform the subsequent processes.
If it is determined in step S111 that all areas have not been processed, i.e., there is an unprocessed area (S111, NO), the process returns to step S103, and the subsequent processes are performed.
Note that the printer driver 91 may further include a total amount regulation process for limiting the total amount of ink adhesion, and a γ correction unit that performs input / output correction reflecting characteristics of the printing apparatus and user preferences.

The landing time difference is calculated from the carriage moving speed and the center pixel position of the region of interest as follows.
For example, the region of interest is the leading end of the recording paper and the recording start position on the forward path (region 1 in FIG. 10). The center pixel position of the attention area is the center position in the main area in both the main scanning and sub-scanning directions.
When the distance from the center pixel position to the forward path end position is L1 [mm], the distance from the return path start position to the target pixel position is L2 [mm], and the carriage moving speed is V [mm / S (seconds)], The time difference between the forward recording timing and the backward recording timing at the center pixel position, that is, the landing time difference between the color ink and the black ink at the target pixel position is obtained by the following equation.
Landing time difference of center pixel position of attention area = (L1 + L2) / V [Sec]
Here, when a certain time is required even when the scanning direction is switched, the calculation may be performed by adding the amount of time.

If the landing time difference of the center pixel position of the attention area can be calculated, the landing time difference of the center pixel position of the area separated by n in the main scanning direction can be mechanically obtained by the following equation.
Landing time difference of center pixels in regions separated by n in the main scanning direction = {(L1-n * L / N) + (L2-n * L / N)} / V [Sec]
Here, L is the length to be divided in the main scanning direction, and N is the number of divisions in the main scanning direction (the number of divided areas, four in FIG. 10).

The landing time difference of the center pixel obtained here is applied to all the pixels in the area and corrected.
Since the distances L1, L2, and L are values that vary depending on the recording paper size, the landing time difference storage unit 102a holds the landing time differences corresponding to the respective divided areas for each recording paper size as table data.
Further, the landing time difference of the target pixel position may be measured while scanning the carriage using a traveling time measuring unit as described in Japanese Patent Application Laid-Open No. 2004-082449, which is a known technique.

FIG. 10 is a diagram illustrating an example for executing density correction by area division shown in FIG. 9B in the image processing method according to the first embodiment.
9A divides the image data into a plurality of areas in the main scanning direction for each scan as shown in FIG. 10 (step S101; in FIG. 10, the image data is divided into four).
The landing time difference for each area is obtained by the above-described method, and the density correction in the area is performed.
Note that the number of divisions may be larger or smaller. Further, it may be changed according to the recording paper size.
Table 1 is a diagram for explaining an example of a correction table for executing density (recording density) correction according to the landing time difference T [S] in the first embodiment, and correction gradation values corresponding to the landing time difference. Are collectively shown.

The correction processing unit 137 shown in FIG. 9A refers to the density correction value for each gradation value from the landing time difference T shown in Table 1, and sets the corrected gradation value. The correction values in Table 1 are based on the density when the landing time difference T, which tends to decrease in density, is less than 0.5 (no correction), and the gradation value decreases as the landing time difference increases (the density decreases). Correct) direction. This is because the aim is to make the density as the output result uniform.
Further, as shown in FIG. 6, when the difference in landing time exceeds a certain value, the concentration saturates and does not fluctuate. Therefore, in the example of Table 1, the correction value is constant when T is a value of 1.5 (S) or more.
The landing time difference T [S] values and correction values in Table 1 are examples, and are not limited to those in Table 1. The correction accuracy improves as the number of landing time difference divisions increases.

FIG. 11A is a functional block diagram of the printer driver 91 of the host 90 used in the image processing method according to the second embodiment, and FIG. 11B is a process for correcting the ink ejection amount in the image processing method according to the second embodiment. It is a flowchart which shows a procedure.
In this embodiment, as shown in FIG. 11A, the printer driver 91 includes a γ correction parameter assigning unit 150 that assigns γ correction parameters according to the landing time difference. In step S108 in FIG. 9B, the density is determined according to the landing time difference. It differs from the flow of FIG. 9B in that γ correction (S208) is performed instead of executing the correction process (S108), and the other points are the same.
Therefore, the description other than step S208 uses the description of FIG. 9B and is omitted here.

FIG. 12 is a diagram illustrating an example of switching of γ correction parameters in the image processing method according to the second embodiment.
FIG. 12 shows the correlation between the input value and output value of the gradation of each color. A plurality of patterns are provided as the correlation curve, and the γ correction parameter assignment unit 150 in FIG. 11 performs γ correction using a pattern corresponding to the landing time difference.
Table 2 is a table showing an example of switching of the γ correction parameter depending on the landing time difference in the image processing method according to the second embodiment of the present invention, and shows the relationship between the landing time difference and the γ correction pattern.

The γ correction parameter switching (step S208) by the γ correction parameter allocating unit 150 shown in FIG. 11 is used at the time of droplet discharge by referring to the γ correction pattern from the landing time difference T described in Table 2.
The landing time difference T [S] is not limited to that in Table 2.

FIG. 13A is a functional block diagram of the printer driver 91 of the host 90 used in the image processing method according to the third embodiment, and FIG. 13B is a process for correcting the ink discharge amount in the image processing method according to the third embodiment. It is a flowchart which shows a procedure.
As shown in FIG. 13A, the printer driver 91 according to the present embodiment includes a drive waveform pattern assignment unit 160 that assigns a drive waveform pattern according to the landing time difference. In step S108 of FIG. 9B, the density correction process according to the landing time difference. Instead of executing the above, drive waveform pattern assignment (S308) for assigning a drive waveform pattern according to the landing time difference is performed. The processing procedure of this embodiment is different from the flow of FIG. 9B in this point, and is the same in other points.
Therefore, the description other than step S308 uses the description of FIG. 9B and is omitted here.
Table 3 is an example of a table for executing drive waveform pattern switching according to the landing time difference T [S] in the third embodiment, and shows the relationship between the landing time difference and the driving waveform pattern.

The drive waveform pattern assigning unit 160 shown in FIG. 13 according to the present invention refers to the drive waveform pattern from the landing time difference T [S] shown in Table 3 and uses it at the time of droplet discharge.
The landing time difference T [S] is not limited to that in Table 3.

FIG. 14 is an explanatory diagram showing an example of drive waveforms in the image processing method according to the third embodiment of the present invention.
When ejecting droplets from the recording head, as shown in FIG. 14, within one printing cycle (one drive cycle), a waveform element that falls from the reference potential Ve, a waveform element that rises from the state after the fall, and the like A drive signal (drive waveform) composed of eight drive pulses P1 to P8 constituted by the following is generated and output. One printing cycle is determined by the maximum driving frequency.

FIG. 15 is an explanatory diagram illustrating an example of a drive waveform pattern in the image processing method according to the third embodiment.
When the rise and fall amounts of the voltage are large as in the waveform pattern 1, the discharge droplet amount is large. On the other hand, when the rise and fall amounts of the voltage are small as in the waveform pattern n, the discharge droplet amount is Get smaller.
The shorter the landing time difference, the higher the concentration by discharging droplets using a drive waveform with a larger discharge amount, and the longer the landing time difference, the lower the concentration by discharging droplets using a driving waveform with a smaller discharge amount. By doing so, the density difference due to the landing time can be made uniform.

FIG. 16A is a functional block diagram of a printer driver used in the image processing method according to the fourth embodiment, and FIG. 16B is a flowchart showing a processing procedure for ink ejection amount correction in the image processing method according to the fourth embodiment. FIG.
As shown in FIG. 16A, the printer driver 91 includes a multi-value / low-value matrix assigning unit 170 that assigns a multi-value / low-value matrix used for halftone processing according to the landing time difference. Thus, instead of executing the density correction processing according to the landing time difference (S108), a point where a multi-value / low-value matrix used for halftone processing is allocated according to the landing time difference (S407, NO, S408; S406, NO, S409; S407, YES, S409), which is different from the flow of FIG. 9B and is otherwise the same.

That is, Steps S401 to S407 are the same as Steps S101 to S107, but if it is determined in Step S407 that CMY ink data exists (S407, NO), a later-described diagram of the multi-value / low-value matrix will be described. Halftone processing based on pattern 1 of 17 is performed (S408).
On the other hand, when it is determined that the black ink data does not exist (S406, NO) and when it is determined that the CMY ink data does not exist (S407, YES), the multi-value / low-value matrix shown in FIG. Halftone processing based on pattern 2 is performed (S409).

FIG. 17 illustrates an example of a multi-value / low-value matrix to be assigned in the image processing method according to the fourth embodiment of the present invention.
FIG. 17 shows a matrix used for halftone processing for each 16 × 16 pixel. Further, for the sake of simplification of explanation, consider a case where control is performed by switching between two values of whether or not a droplet is hit. The numerical value in each pattern is a threshold value when the density is expressed by 255 gradations. The number of gradations of the input image is compared with the numerical value in the pattern, and processing is performed so that a drop is hit if it is greater than or equal to the numerical value in the pattern, and no drop is hit if it is less. By changing the value in the pattern, you can change the way the droplets are struck.
Table 4 is a diagram for explaining an example of a table for executing matrix pattern switching of halftone processing according to the landing time difference T [S] in the fourth embodiment of the present invention.

The multi-value / low-value matrix allocation unit 170 described in relation to FIG. 16 according to the present embodiment refers to the matrix pattern from the landing time difference T described in Table 4 and uses it at the time of droplet discharge.
The landing time difference T [S] is not limited to that in Table 4.

FIG. 18A is a functional block diagram of the printer driver 91 used in the image processing method according to the fifth embodiment, and FIG. 18B shows a processing procedure for correcting the ink discharge amount in the image processing method according to the fifth embodiment. FIG.
As a correction execution determination criterion, there is provided a means for determining a pixel that causes K ink and CMY ink to land on the same pixel by determining that K ink data exists and CMY ink data exists. Although common to the first to fourth embodiments, as illustrated in FIG. 18A, a determination unit (third determination unit) 139 is further provided to determine whether or not C + M + Y + K exceeds a predetermined threshold Tc.

That is, in the flow of FIG. 18, for example, in the flow shown in FIG. 9B, the third determination unit 139 determines in step S <b> 107 that the second determination unit 136 determines whether any data of CMY ink exists. step S108 in that the step of performing judgment of "whether C + M + Y + K exceeds a predetermined threshold value T _0" between "performing the density correction process in accordance with the landing time difference" (S508) is added, different, The other points are the same. Note that the threshold T ₀ and the third determination unit 139 correspond to a printing rate determination unit that determines the printing rate and the printing rate of the input image of the present invention, respectively.
Here, when the C + M + Y + K exceeds a predetermined threshold value _{T 0} (S508, YES), performs a density correction (S509), C + M + Y + If K does not exceed the predetermined threshold value _{T 0} (S508, NO), performing the density correction First, the process proceeds to halftone processing including the multi-value / small-value matrix in step S509.
The description other than step S508 uses the description of FIG. 9B and is omitted here.
In the present embodiment, it is possible to determine whether the image data has the gradation of the highlight area or the gradation of the shadow area by making the above determination.

  As described above, the difference in the density of the landed ink is generated by the difference in penetration depth caused by superimposing the chromatic color ink and the achromatic color ink on the same pixel at different landing timings. Since the area has a low ink dot generation rate, the ratio of chromatic ink and achromatic ink overlapping on the same pixel is also low. Therefore, the density difference due to the landing time difference is less likely to occur.

On the other hand, when density correction is performed in the highlight area, an image having a low density is corrected in the direction of lowering the density, resulting in a problem of poor visibility.
Therefore, in the present embodiment, the threshold value T ₀ for determining whether or not to perform density correction is set to the sum of CMYK gradation values, which are ink amounts that allow the density difference caused by the landing time difference, thereby highlight region The density difference due to the landing time difference can be suppressed without reducing the visibility.
In the example shown in FIG. 18, the threshold value T ₀ is used as the gradation value, but the gradation value is not limited to this. The gradation value after conversion from RGB data to CMYK data by the CMM processing unit 134 is changed to the ink adhesion amount. It is good also as the sum of the adhesion amount at the time of conversion. Further, the threshold value T ₀ may be a ratio of the K ink adhesion amount and the CMY ink adhesion amount in a value converted into the ink adhesion amount. Moreover, although this embodiment is based on the flowchart in 1st Embodiment, it is applicable also to 2nd-4th embodiment.

FIG. 19 illustrates an image processing method according to the sixth embodiment, in which processing for determining whether or not to perform adhesion amount correction in the landing time difference is further performed based on object determination in addition to the first to fifth embodiments. FIG.
The above-described density difference due to the landing time difference is recognized when a certain area or more is formed with the same ink composition, but in the case of a character image, it is rare to form a certain area or more with the same ink composition. In addition, when the adhesion amount correction is performed, there is a problem that the readability of characters deteriorates.

Therefore, by dividing the image into a character image portion and an image other than that (graphic portion or the like) by the object determination, the character image portion is not subjected to the adhesion amount correction described in the first to fifth embodiments, so It is possible to avoid impairing readability. In addition to the character image portion, the density difference caused by the landing time can be suppressed by performing the adhesion amount correction.
That is, according to the present embodiment, as shown in FIG. 19, the image data is divided into a graphic portion and a character image portion, the adhesion amount correction is performed for the graphic portion, and the adhesion amount correction is not performed for the character image portion. Then, image data obtained by synthesizing them is obtained. Whether the character image portion or the graphic portion is determined is determined based on information embedded in the original image.
In each embodiment of the present invention, since the adhesion amount correction is performed for each region, if there is a character image portion other than the character image portion in the region, the correction is performed based on the landing time, and if only the character image portion is corrected, the correction is performed. By avoiding this, the density difference can be suppressed.

FIG. 20 is an explanatory diagram regarding correction at the boundary of an area in the image processing method according to the seventh embodiment of the present invention.
In the first to sixth embodiments, correction is performed for each region. However, since the correction method is different between adjacent regions, there is a possibility that it is visually recognized as density unevenness or streaks. Therefore, this can be suppressed by changing the correction method only for the adjacent portions of the regions.
FIG. 20 is an enlarged view of the divided regions 1 and 2 shown in FIG. The upper diagram of FIG. 20 is an explanatory diagram of correction related to the adjacent portions in the main scanning direction of the regions 1 and 2. Of the adjacent portions, the correction of the area 2 is performed on the area 1 side, and conversely, the correction of the area 1 is performed on the area 2 side.
The lower diagram in FIG. 20 is an explanatory diagram of correction related to the adjacent portions of the region 1 and the region 5 in the sub-scanning direction. Of the adjacent portions, the correction of the region 5 is performed on the region 1 side, and conversely, the correction of the region 1 is performed on the region 5 side. In the present embodiment, the width of the adjacent portion is preferably about several pixels.

FIG. 21 is an explanatory diagram regarding correction at the boundary of an area in the image processing method according to the eighth embodiment of the present invention.
In other words, FIG. 21 is an enlarged view of the adjacent portions of the regions 1 and 2 shown in FIG. 20, and each square represents one pixel. Area 1 correction is applied to pixels that are blacked out, and area 2 correction is applied to white pixels. In this manner, density unevenness and streaks can be suppressed by changing the correction method for adjacent portions in stages. The width of the adjacent portion and the correction of which region is applied to how many pixels is an example, and the present invention is not limited to this.

As described above, according to the present embodiment, it is possible to eliminate the density difference due to the landing time difference while reducing the load on processing.
That is, the smaller the landing time difference between the first droplet and the second droplet, the lower the density on the recording paper, and the larger the landing time difference, the higher the density on the recording paper. It is possible to make the density of recorded matter uniform by correcting so that the smaller the landing time difference, the larger the amount of ejected droplets, and the larger the landing time difference, the smaller the amount of ejected droplets. It becomes.
In addition, since the correction value is determined for each area divided in the moving direction of the recording head, it is possible to reduce the processing load rather than determining the correction value for each pixel.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet recording apparatus, 2 ... Image formation part, 3 ... Sheet conveyance part, 4 ... Roll paper storage part, 10 ... Main scanning mechanism, 13 ... Guide rod, 14 * ..Guide rail, 15 ... carriage, 18 ... main cartridge, 19 ... maintenance and recovery mechanism, 21 ... carriage drive motor, 22 ... drive pulley, 23 ... driven pulley, 24. ..Belt member, 30 ... roll paper, 31 ... flange, 32 ... flange receiver, 34 ... charging roller, 40 ... encoder sheet, 90 ... host, 91 ... printer Driver, 100 ... Control unit, 101 ... CPU, 102 ... ROM, 103 ... RAM, 104 ... Non-volatile memory (NVRAM), 105 ... ASIC, 106 ... Host I F, 107 ... head drive control unit, 108 ... head driver, 110 ... main scanning motor, 111 ... main scanning motor driving unit, 112 ... sub-scanning motor, 113 ... sub-scanning Motor drive unit, 114 ... AC bias supply unit, 116 ... I / O, 117 ... operation panel, 118 ... environment sensor, 131 ... division processing unit, 133 ... calling unit, 134: CMM processing unit, 135: first determination unit, 136: second determination unit, 137: correction processing unit, 138: halftone processing unit, 139: third determination , 150... Γ correction parameter allocation unit, 160... Drive waveform pattern allocation unit, 170.

Japanese Patent No. 5300352

Claims (10)

A first recording head for discharging a first droplet;
A second recording head that discharges second droplets that are not parallel to the first recording head in the recording direction;
Storage means for storing a landing time difference between the first droplet and the second droplet on the recording medium;
Means for dividing the recording area into a plurality of areas in the recording direction;
Droplet amount correcting means for correcting the amount of droplets discharged from the first and second recording heads,
The droplet amount correcting means corrects the droplet amount ejected from the first and second recording heads according to the landing time difference between the first and second droplets for each of the plurality of divided areas. An image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the droplet amount correcting unit corrects a recording density in accordance with a landing time difference between the first droplet and the second droplet. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the droplet amount correcting unit switches a γ correction parameter according to a landing time difference between the first droplet and the second droplet. The image forming apparatus according to claim 1,
The droplet amount correcting means switches a drive waveform pattern to be applied to the first and second recording heads when a droplet is ejected according to a difference in landing time between the first droplet and the second droplet. A featured image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the droplet amount correcting unit switches a matrix of a halftone processing unit in accordance with a landing time difference between the first droplet and the second droplet. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the droplet amount correcting unit further includes a printing rate determining unit that determines a printing rate of the input image. A first recording head for discharging a first droplet;
A second recording head that discharges second droplets that are not parallel to the first recording head in the recording direction;
Storage means for storing a landing time difference between the first droplet and the second droplet on the recording medium;
Object image dividing means for dividing an image for each object;
A droplet amount correcting means for correcting a droplet amount discharged from the first and second recording heads;
The droplet amount correcting unit applies the first and second droplets to the region other than the region determined as the character image portion by the object image dividing unit according to the landing time difference between the first and second droplets. An image forming apparatus that corrects the amount of liquid droplets ejected from a recording head. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the droplet amount correcting means further replaces the correction method of each other at an adjacent portion between the regions. An image in an image forming apparatus provided with a first recording head that discharges first droplets and a second recording head that discharges second droplets that are not parallel to the first recording head in the recording direction A storage method for storing a landing time difference between the first droplet and the second droplet on the recording medium in a storage means,
Dividing the recording area into a plurality of areas in the recording direction;
A droplet amount correcting step of correcting the droplet amount discharged from the first and second recording heads by a droplet amount correcting unit,
In the droplet amount correcting step, the droplet amount discharged from the first and second recording heads is corrected in accordance with the landing time difference between the first and second droplets for each of the plurality of divided recording regions. An image correction method characterized by the above. An image in an image forming apparatus provided with a first recording head that discharges first droplets and a second recording head that discharges second droplets that are not parallel to the first recording head in the recording direction A storage method for storing a landing time difference between the first droplet and the second droplet on the recording medium in a storage means,
An object image dividing step of dividing the image into objects by the object image dividing means;
A droplet amount correcting step of correcting the droplet amount discharged from the first and second recording heads by a droplet amount correcting unit,
In the droplet amount correcting step, the first and second droplets are applied to a region other than the region determined as the character image portion in the object image dividing step according to the landing time difference between the first and second droplets. An image correction method comprising correcting the amount of liquid droplets ejected from the recording head.

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