JP2011079171A - Image processing method, image processing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To redistribute pixel values corresponding to a recording element (defective recording element) in which a droplet ejection defect has occurred in a full line head type image forming apparatus to pixels around the defective recording element, Image processing method and image processing apparatus capable of suppressing deterioration in image quality caused by a difference in recording density between pixels around a defective recording element when performing error diffusion processing with the scanning direction of the target pixel as one direction And an image forming apparatus.
A pixel value I (X, Y) (FIG. 7A) corresponding to a defective recording element has pixel values I (X-1, Y), I (corresponding to recording elements adjacent in the X direction. X + 1, Y) is redistributed (added). For this reason, the pixel values I ′ (X−1, Y) and I ′ (X + 1, Y) after the redistribution processing have odd-numbered odd rows (FIG. 7B) and even-numbered even rows (FIG. 7). 7 (c)) and periodically change in the opposite phase.
[Selection] Figure 7

Description

  The present invention relates to an image processing method, an image processing apparatus, and an image forming apparatus, and in particular, in an image forming apparatus that forms an image by discharging liquid onto the surface of a recording medium using a plurality of recording elements. The present invention relates to an image processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus for correcting an image defect caused by a recording element in which a recording failure occurs.

  As a method of recording an image on a recording medium (for example, recording paper), ink droplets are ejected from a liquid ejection head (inkjet head) according to an image signal, and the ink droplets land on the recording medium. Thus, an ink jet drawing method for recording (forming) an image on a recording medium is known.

  In the ink jet drawing type image forming apparatus, as shown in FIG. 12A, a recording element (ejection unit, nozzle) 214 for ejecting ink droplets corresponds to the entire width of one side of the recording medium. There has been proposed one provided with a full-line type liquid discharge head 212 arranged in a shape. In such an image forming apparatus, an image can be formed on the entire surface of the recording medium by conveying the recording medium in a direction (Y direction) orthogonal to the direction (X direction) in which the recording elements are arranged. . That is, according to the full-line head type image forming apparatus, an image can be drawn on the entire surface of the recording medium without moving the liquid ejection head 212 with respect to the recording medium. The speed can be increased.

  However, as shown in FIG. 12B, the full-line head type image forming apparatus is subject to recording due to the failure of the recording element 214, the non-ejection of droplets due to variations or the like, the flight curve or the variation in droplet volume. There is a problem that streaks and unevenness occur in an image recorded on a medium.

  As a method of correcting such image streaks and unevenness, a defective recording element is used without using a recording element (hereinafter referred to as a defective recording element) in which a droplet recording defect has occurred (non-ejection). There has been proposed a technique for correcting streaks and unevenness by using a recording element in the periphery of the image.

  For example, Patent Document 1 discloses an image processing for correcting a print defect by decreasing an image value related to a defective nozzle and increasing an image value related to a nozzle of the same color without a defect adjacent to the defective nozzle. A method is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228867 discloses a recording in which normal recording cannot be performed when a quantization process is performed to convert input multi-gradation pixel data into data having a smaller number of gradations than the number of input gradations. For pixel data determined to be recorded by the element, processing different from other pixel data, for example, pixel data of a recording element that cannot perform normal recording is converted to data representing non-recording. An image processing method is disclosed in which all of the data of the pixel is diffused as an error to surrounding pixels.

JP 2002-029074 A JP 2003-103768 A

  When there is a recording element (defective recording element) in which a recording failure of a droplet (for example, non-ejection, deviation of the landing position of the droplet, inclination of the droplet ejection direction) occurs in the full-line liquid ejection head As shown in FIG. 13A, no droplet is ejected to the pixel row L (X) in the Y direction corresponding to the defective recording element. Therefore, the pixel value (I (X, Y) in FIG. 15A) of the pixel P (X, Y) corresponding to the defective recording element is changed to the pixel P (X-1, Y), P adjacent in the X direction. A redistribution process for redistributing (adding) the pixel values I (X-1, Y) and I (X + 1, Y) of (X + 1, Y) is performed. Thereby, pixel values I ′ (X−1, Y) and I ′ (X + 1, Y) after the redistribution processing shown in FIG. 15B are obtained.

  Next, error variance processing is performed on the image data after the redistribution processing (FIG. 13B). Here, the error dispersion process is a binary image of multi-valued image data, or a low-gradation image (hereinafter referred to as a low-gradation image) having two or more values and a gradation number smaller than the input gradation number of the multi-value image data. The difference between the pixel values of the multi-value image data and the low gradation image is diffused to pixels around the processing target pixel for each pixel to be processed. As shown in FIGS. 16 and 17, when a pixel to be subjected to error dispersion processing is scanned only in one direction (one direction, the direction of arrow A10 in the figure, that is, the + X direction), an unprocessed pixel (for example, P The above error is diffused to the pixel value (for example, I (X + 1, Y)) of (X + 1, Y)), but the pixel value of the processed pixel (for example, P (X-1, Y)) (for example, , I (X-1, Y)) does not diffuse the above error. For this reason, as shown in FIG. 14, in the image formed based on the image data after the error diffusion processing, the pixel column L (X−) adjacent to the pixel column L (X) corresponding to the defective recording element (X). 1) The pixel value (recording density) at L (X + 1) is not flat (a step is generated). For this reason, as shown in FIG. 14, the recording density of one of the pixel columns adjacent to the pixel column L (X) in the X direction (for example, L (X + 1)) is the other pixel column (L (X There is a problem that the so-called one-effect phenomenon that is higher than the recording density of -1)) occurs and the image quality deteriorates.

  In the above Patent Documents 1 and 2, the recording density step that occurs when the error diffusion process is performed with the scanning direction of the pixel value set to one direction is not considered.

  In addition, when the scanning direction of the error diffusion processing is bidirectional (for example, when the scanning direction of the processing target pixel is inverted between the even-numbered row and the odd-numbered row), the pixels adjacent to the pixel column L (X) The recording densities of the rows L (X-1) and L (X + 1) can be made flat. However, the bidirectional error diffusion processing takes time compared to the one-way error diffusion processing. For this reason, in order to correct a defective recording element that suddenly occurs during the image recording operation, it is necessary to re-execute the error diffusion process, and in order to minimize the time loss during the image recording process, it is extremely fast. Processing is required. Therefore, when the scanning direction of the target pixel of the error diffusion processing is bidirectional, there is a problem that the cost of image processing becomes high.

  The present invention has been made in view of such circumstances. In a full-line head type image forming apparatus, pixel values corresponding to a recording element (defective recording element) in which a droplet recording defect has occurred are defectively recorded. When error diffusion processing is performed in which the scanning direction of the processing target pixel is unidirectional after redistribution to the peripheral pixels of the element, image quality degradation caused by a difference in recording density between the peripheral pixels of the defective recording element is reduced. An object is to provide an image processing method, an image processing apparatus, and an image forming apparatus that can be suppressed.

  In order to solve the above problem, an image processing method according to a first aspect of the present invention includes a recording head including a plurality of recording elements arranged along a first direction and a recording medium in the first direction. An image processing method for creating output image data for forming an image on the surface of the recording medium while relatively moving in a second direction perpendicular to the recording medium, wherein each pixel corresponding to the recording head An input step for inputting multi-gradation image data, a detection step for detecting a defective recording element in which a recording defect has occurred from among the plurality of recording elements, and a pixel value corresponding to the detected defective recording element. A process of performing a redistribution process to distribute the first and second pixel values respectively corresponding to the first and second recording elements located on both sides along the first direction with respect to the defective recording element. The first and second images A redistribution processing step of changing the distribution amount of the pixel value with respect to a value so as to have an antiphase in a predetermined cycle along the second direction, and for the pixel value subjected to the redistribution processing, An error diffusion processing step of sequentially performing error diffusion processing in one direction along the first direction to generate output image data.

  According to the first aspect, when the distribution amount of the pixel value corresponding to the defective recording element is allocated to the first and second pixel values corresponding to the recording elements adjacent to the defective recording element, By periodically changing the distribution amount for the second pixel value in the opposite phase along the second direction, deterioration in image quality due to the difference in density between the pixels around the defective recording element is suppressed. be able to.

  In the image processing method according to the second aspect of the present invention, in the redistribution processing step according to the first aspect, the first and second pixel values after the redistribution processing do not exceed a predetermined value. The distribution amount of the pixel value with respect to the first and second pixel values is controlled.

  According to the second aspect, it is possible to prevent the first and second pixel values from exceeding the upper limit value by the redistribution processing.

  In addition to the configuration of the first aspect, the image processing method according to the third aspect of the present invention includes the reprocessing when the first and second pixel values after the redistribution process exceed a predetermined value. The difference between the first and second pixel values after the distribution processing and the predetermined value is set to pixel values corresponding to recording elements other than the defective recording element adjacent to the first and second recording elements, respectively. The step of allocating is further provided.

  In addition to the configuration of the first aspect, the image processing method according to the fourth aspect of the present invention provides the reprocessing when the first and second pixel values after the redistribution process exceed a predetermined value. The difference between the first and second pixel values after the distribution process and the predetermined value is applied to recording elements other than the defective recording element adjacent to the first and second recording elements in the first direction. The method further includes the step of allocating to the corresponding pixel values.

  According to the third and fourth aspects, when the first and second pixel values exceed the upper limit value by the redistribution process, the excess pixel values are distributed to the adjacent pixel values, whereby the pixels Since the change of the value can be smoothed, deterioration of the image quality can be further suppressed.

  In the image processing method according to the fifth aspect of the present invention, in the redistribution processing steps according to the first to fourth aspects, the distribution amount of the pixel value with respect to the first and second pixel values is set as the first distribution value. It is made to change so that it may become an antiphase with a 2 pixel period along the direction of 2. FIG.

  In an image processing apparatus according to a sixth aspect of the present invention, a recording head including a plurality of recording elements arranged along a first direction and a recording medium are arranged in a second direction perpendicular to the first direction. An image processing apparatus for generating output image data for forming an image on the surface of the recording medium while relatively moving, and inputting multi-gradation image data for each pixel corresponding to the recording head Input means for detecting, a detecting means for detecting a defective recording element in which a recording defect has occurred among the plurality of recording elements, and a pixel value corresponding to the detected defective recording element for the defective recording element Means for performing a redistribution process for allocating the first and second pixel values respectively corresponding to the first and second recording elements located on both sides along the first direction, wherein the first and second An arrangement of the pixel values with respect to a pixel value of 2 Redistribution processing means for changing the amount so as to have an antiphase in a predetermined cycle along the second direction, and the pixel value subjected to the redistribution processing along the first direction. And error diffusion processing means for generating image data for output by sequentially performing error diffusion processing in one direction.

  The image processing apparatus according to a seventh aspect of the present invention is the image processing apparatus according to the sixth aspect, wherein the redistribution processing means prevents the first and second pixel values after the redistribution processing from exceeding a predetermined value. The distribution amount of the pixel value with respect to the first and second pixel values is controlled.

  An image processing apparatus according to an eighth aspect of the present invention is the image processing apparatus according to the sixth aspect, wherein the redistribution processing means has the first and second pixel values after the redistribution processing exceeding a predetermined value. A pixel corresponding to a recording element other than the defective recording element that is adjacent to the first and second recording elements and that is the difference between the first and second pixel values after the redistribution processing and a predetermined value. Each is assigned to a value.

  The image processing apparatus according to a ninth aspect of the present invention is the image processing apparatus according to the sixth aspect, wherein the redistribution processing means has the first and second pixel values after the redistribution processing exceeding a predetermined value. The difference between the first pixel value and the second pixel value after the redistribution processing and a predetermined value is set to a value other than the defective recording element adjacent to the first and second recording elements in the first direction. Each pixel value corresponding to the recording element is distributed.

  The image processing apparatus according to a tenth aspect of the present invention is the image processing apparatus according to any one of the sixth to ninth aspects, wherein the redistribution processing means calculates the distribution amount of the pixel values with respect to the first and second pixel values. In this case, the phase is changed so as to have an opposite phase with a period of two pixels along the second direction.

  An image forming apparatus according to an eleventh aspect of the present invention is arranged along the first direction with the image processing apparatus according to any of the sixth to ninth aspects, and A recording head including a plurality of recording elements for forming an image by ejecting liquid droplets on the surface, and the recording head and the recording medium are relatively moved in a second direction perpendicular to the first direction. In addition, image forming means for forming an image on the surface of the recording medium by discharging droplets from the recording element based on output image data created by the image processing apparatus.

  According to the present invention, in a full line head type image forming apparatus, pixel values corresponding to a recording element (defective recording element) in which a droplet recording defect has occurred are redistributed to pixels around the defective recording element. Later, when error diffusion processing is performed in which the scanning direction of the processing target pixel is one direction, it is possible to suppress deterioration in image quality due to a difference in density that occurs between pixels around the defective recording element.

1 schematically shows an image forming apparatus (inkjet recording apparatus) according to an embodiment of the present invention. Top view showing the periphery of the printing unit of an ink jet recording apparatus Block diagram showing control system of inkjet recording apparatus 1 is a block diagram showing an image processing apparatus according to a first embodiment of the present invention. The flowchart which shows the flow of the image processing which concerns on the 1st Embodiment of this invention. (A): graph showing the correction function f0, (b): graph showing the correction function f1 (A): graph showing pixel values before redistribution, (b): graph showing pixel values in odd rows after redistribution, (c): graph showing pixel values in even rows after redistribution The top view which shows the example of the image formed based on the image data in which the image process (pixel value redistribution process) which concerns on the 1st Embodiment of this invention was performed The top view which expands and shows the periphery of the pixel corresponding to the defective recording element of FIG. Graph for comparing the image processing method according to the first embodiment of the present invention and the prior art The block diagram which shows the image processing apparatus which concerns on the 2nd Embodiment of this invention. Diagram showing the liquid discharge head (A) a plan view showing an example of an image formed based on image data that has not been redistributed with pixel values; (b) an example of an image formed based on image data after the redistribution of pixel values; Plan view FIG. 13B is an enlarged plan view showing the vicinity of the defective recording element in FIG. (A) Graph showing pixel values before redistribution, (b) Graph showing pixel values after redistribution Plan view showing scanning direction in error diffusion processing A plan view showing pixels whose pixel values are redistributed by error diffusion processing

  Hereinafter, preferred embodiments of an image processing method, an image processing apparatus, and an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

[Image forming apparatus]
First, the configuration of an image forming apparatus including an image processing apparatus according to an embodiment of the present invention will be described.

  FIG. 1 is a diagram schematically illustrating an image forming apparatus (ink jet recording apparatus) according to an embodiment of the present invention, and FIG. 2 is a plan view illustrating the periphery of a printing unit of the ink jet recording apparatus.

  As shown in FIG. 1, the image forming apparatus (inkjet recording apparatus) 1 according to the present embodiment ejects four colors of black (K), cyan (C), magenta (M), and yellow (Y). Printing unit 10 having liquid discharge heads 12K, 12C, 12M, and 12Y, and printing surface of recording paper 16 from printing unit 10 based on image data input from a host computer (reference numeral 60 in FIG. 3). In this apparatus, four color inks are ejected to form a color image.

  As shown in FIG. 2, in the printing unit 10, line-type liquid ejection heads 12 </ b> K, 12 </ b> C, 12 </ b> M, and 12 </ b> Y having a length corresponding to the maximum paper width of the recording paper 16 are in the paper conveyance direction (sub-scanning direction (Y direction)). ) Arranged in a direction orthogonal to (a main scanning direction (X direction)).

  The ink storage / loading unit 14 stores four colors of inks of KCMY. The ink stored in the ink storage / loading unit 14 is supplied to the liquid ejection head 12 via the ink supply path.

  The ink color and the number of colors are not limited to the above KCMY standard colors (four colors). For example, a liquid discharge head that discharges light ink and dark ink may be added. For example, a liquid discharge head that discharges light ink such as light cyan and light magenta may be added.

  The paper feeding unit 18 supplies the recording paper 16 to the printing unit 10. It has a magazine for rolled paper (continuous paper). A plurality of magazines having different paper widths, paper quality, etc. may be provided. Further, a cassette loaded with cut sheets may be provided.

  The decurling unit 20 heats the recording paper 16 delivered from the paper supply unit 18 by the heating drum 22 to remove curl from the recording paper 16. In the decurling process, it is preferable to control the heating temperature so that the print surface is slightly curled outward.

  The cutter 24 includes a fixed blade 24A disposed on the back side of the printing surface of the recording paper 16, and a round blade 24B disposed on the printing surface side. The recording paper 16 delivered from the paper supply unit 18 is cut into a desired size by the cutter 24. The decurling unit 20 performs the decurling process, and the cut recording paper 16 is sent to the suction belt conveyance unit 26.

  The suction belt conveyance unit 26 includes two rollers 28 and 30 and an endless belt 32 wound between the rollers 28 and 30. The power of the motor is transmitted to at least one of the rollers 28 and 30, and the belt 32 is driven in the clockwise direction in FIG. As a result, the recording paper 16 held on the surface of the belt 32 is conveyed from left to right in FIG.

  The rollers 28 and 30 and the belt 32 are arranged such that portions facing the nozzle surfaces of the liquid ejection heads 12K, 12C, 12M, and 12Y of the printing unit 10 and the sensor surface of the printing detection unit 34 are flat.

  The width of the belt 32 is wider than the width of the recording paper 16 (see FIG. 2). A number of suction holes (not shown) are formed on the surface of the belt 32. An adsorption chamber 36 is provided at a position facing the nozzle surface of the print unit 10 and the sensor surface of the print detection unit 34 inside the belt 32. The suction chamber 36 is set to a negative pressure by a fan 38. As a result, the recording paper 16 is attracted and held on the surface of the belt 32.

  The heating unit 40 heats the recording paper 16 before printing in order to shorten the time from the ink landing on the recording paper 16 to the drying. As the heating unit 40, for example, a heating fan that heats the recording paper 16 by blowing heated air is used.

  The print detection unit 34 includes an image sensor for imaging the ink droplet ejection result by the print unit 10. As shown in FIG. 2, the print detection unit 34 is configured by a line sensor having a light receiving element array wider than the ink ejection width (image recording width) by the liquid ejection heads 12K, 12C, 12M, and 12Y. As the print detection unit 34, for example, an area sensor may be used.

  The post-drying unit 42 is a device that dries the printing surface of the recording paper 16. For example, a heating fan is used as the post-drying unit 42.

  The belt cleaning unit 44 removes ink attached to the belt 32. As a method of cleaning the belt 32, for example, a method of niping a brush roll, a water absorbing roll, or the like, or an air blow method of blowing clean air can be applied.

  The heating / pressurizing unit 46 is a device for controlling the glossiness of the surface of the image printed on the recording paper 16. The heating / pressurizing unit 46 is disposed after the post-drying unit 42, and pressurizes the printing surface with a pressure roller 48 having a predetermined surface irregularity shape while heating the printing surface, thereby forming an irregular shape on the image surface. Transcript.

  The recording paper 16 (printed material) on which an image is printed as described above is discharged from the paper discharge unit 52. The ink jet recording apparatus 1 according to the present embodiment sorts a printed matter on which an image to be printed is printed and a printed matter on which a test pattern for detecting a printing result is printed, and outputs the selected printed matter to each of the paper discharge units 52A and 52B. Sorting means (not shown) for switching the paper discharge path for feeding is provided.

  When the main image and the test print are simultaneously formed on the recording paper 16 in parallel, the test print portion is separated by the cutter 50. As with the cutter 24, the cutter 50 includes a fixed blade 50A and a round blade 50B.

  FIG. 3 is a block diagram showing a control system of the inkjet recording apparatus 1.

  The system controller 64 is a control unit that controls each unit of the inkjet recording apparatus 1. The system controller 64 includes a central processing unit (CPU) and its peripheral circuits, and performs control of communication with the host computer 60, control of reading and writing of the memory 68, and control for controlling the motor 72 and the heater 76. Generate a signal.

  The program storage unit 66 is a storage area for storing various control programs. As the program storage unit 66, for example, a semiconductor memory such as a ROM or an EEPROM, or a magnetic medium such as a hard disk can be used.

  The memory 68 is a storage device including a storage area for various data and a work area when the system controller 64 performs calculations. As the memory 68, for example, a semiconductor memory such as a RAM or a magnetic medium such as a hard disk can be used.

  The communication interface 62 is an interface for performing communication connection with the host computer 60. As the communication interface 62, for example, a serial interface such as USB or IEEE1394, a parallel interface such as Centronics, a wireless network, or Ethernet (registered trademark) can be applied. Image data input via the communication interface 62 is temporarily stored in the memory 68.

  The print control unit 78 performs predetermined signal processing on the image data temporarily stored in the memory 68 in accordance with a control signal input from the system controller 64 to generate a print control signal (dot data). The print controller 78 controls the head driver 82 based on the print control signal, and controls the discharge amount and discharge timing of the ink discharged from each liquid discharge head 12K, 12C, 12M, 12Y of the print unit 10. Do. The print control unit 78 corrects the print control signal based on the ink droplet ejection result obtained from the print detection unit 34. Thereby, a desired dot size and dot arrangement are realized.

  The buffer memory 80 is a storage device including a work area when the print control unit 78 processes image data.

  The head driver 82 generates drive signals for driving the liquid discharge heads 12K, 12C, 12M, and 12Y based on the dot data input from the print control unit 78, and the liquid discharge heads 12K, 12C, 12M, 12Y.

  The motor driver 70 drives the motor 72 in accordance with a control signal input from the system controller 64, transmits power to the rollers 28 and 30 of the suction belt transport unit 26, and controls transport of the recording paper 16.

  The heater driver 74 controls the heating of various heating means (heater 76) included in the decurling unit 20, the heating unit 40, the post-drying unit 42, the heating / pressurizing unit 46, and the like according to a control signal input from the system controller 64. I do.

[First Embodiment]
Hereinafter, the image processing apparatus and the image processing method according to the present embodiment will be described.

  FIG. 4 is a block diagram showing the image processing apparatus according to the first embodiment of the present invention.

  As illustrated in FIG. 4, the image processing apparatus 100 according to the present embodiment includes a rearrangement unit 102 and a rearrangement restriction unit 104.

  The rearrangement unit 102 holds correction functions f0 (I, Y) and f1 (I, Y), and uses the correction functions f0 (I, Y) and f1 (I, Y) to detect defective recording elements. The pixel values I (X, Y) corresponding to the defective recording elements are redistributed (added) to the pixel values I (X−1, Y) and I (X + 1, Y) corresponding to the recording elements adjacent to (details). Later).

  The rearrangement restricting unit 104 redistributes and corrects the pixel values I (X, Y) corresponding to the defective recording elements of the rearrangement unit 102 to obtain pixel values corresponding to the pixel positions X−1 and X + 1, respectively. Output as I ′ (X−1, Y), I ′ (X + 1, Y).

  The function of the image processing apparatus 100 can be realized by hardware provided in the system controller 64 of the image forming apparatus 1 as shown in FIG. The present invention can also be realized as a computer program for executing the process and a recording medium on which the computer program is recorded.

  FIG. 5 is a flowchart showing the flow of image processing according to the first embodiment of the present invention.

  First, the system controller 64 detects a recording element (defective recording element) in which a droplet recording defect has occurred (step S10). In step S10, for example, a defective recording element is detected on the basis of defective recording element data recorded in advance in the memory 68 for specifying the defective recording element. Further, the defective recording element is detected based on the image of the droplet ejection result imaged by the print detection unit 34. Note that the method for detecting a defective recording element is not limited to the above, and other methods may be used.

  Next, image data input from the host computer 60 via the communication interface 62 is sequentially input to the image processing apparatus 100 for each pixel (step S12). In the following description, the pixel value (density value) at the coordinates (X, Y) of the image data is I (X, Y).

  The system controller 64 determines whether the pixel value I (X, Y) corresponds to a defective recording element based on the X coordinate of the input pixel value I (X, Y) (step S14). .

  If the pixel value I (X, Y) does not correspond to a defective recording element (No in step S14), the process proceeds to step S18.

  On the other hand, when the pixel value I (X, Y) corresponds to the defective recording element (Yes in step S14), the system controller 64 responds to the defective recording element by the rearrangement unit 102 and the rearrangement restriction unit 104. The pixel value I (X, Y) to be corrected and the two pixel values I (X-1, Y) and I (X + 1, Y) corresponding to the recording element of the same color adjacent to the defective recording element in the X direction. (Step S16).

  In step S16, the pixel values I (X-1, Y) and I (X + 1, Y) are corrected based on the following equations (1) and (2).

I (X-1, Y) = I (X-1, Y) + f0 (I (X, Y), Y) (1)
I (X + 1, Y) = I (X + 1, Y) + f1 (I (X, Y), Y) (2)
Here, f0 and f1 are correction functions for pixel values on the −X side and + X side with respect to the defective recording element, respectively.

  FIGS. 6A and 6B are graphs showing the correction functions f0 and f1, respectively. In FIG. 6A and FIG. 6B, the horizontal axis is the Y coordinate of the pixel value, and the vertical axis is the value (output value) of the correction function.

  As shown in FIGS. 6A and 6B, the correction functions f0 (I, Y) and f1 (I, Y) are functions of Y that change in the opposite phase and in the period λ, respectively. Expressions (4) and (5) are satisfied.

f0 (I, Y + λ / 2) = f1 (I, Y) (3)
f0 (I, Y + λ) = f0 (I, Y) (4)
For this reason, the pixel values I (X−1, Y) and I (X + 1, Y) corresponding to the recording elements adjacent to the defective recording element change with a period λ with respect to Y by the above correction.

  The correction functions f0 (I, Y) and f1 (I, Y) are also functions of I (X, Y), and the value of I (X, Y) (for example, I (X, Y in the case of 8 bits) ) = 0,..., 255).

  In step S16, based on the above formulas (1) and (2), the pixel value I (X, Y) corresponding to the defective print element shown in FIG. Are redistributed (added) to pixel values I (X-1, Y) and I (X + 1, Y) corresponding to. For this reason, the pixel values I ′ (X−1, Y) and I ′ (X + 1, Y) after the redistribution processing have odd-numbered odd rows (FIG. 7B) and even-numbered even rows (FIG. 7). 7 (c)) and periodically change in the opposite phase.

  In this embodiment, in step S16, the pixel values I ′ (X−1, Y) and I ′ (X + 1, Y) after the redistribution process are set so as not to exceed the upper limit value (for example, 255). It is preferable to adjust the value distribution amount.

  In step S16, the pixel value I (X, Y) is corrected by the following equation (5).

I (X, Y) = I0 = h (I) (5)
Here, I0 is a fixed value (constant) for the defective recording element, and may be, for example, “zero” or according to the ejection amount of the droplet from the defective recording element detected by the print detection unit 34. You may make it select from several values.

  Next, when the above steps S12 to S18 are repeated and the correction process is completed for all the pixel values (Yes in step S18), the system controller 64 converts the process-symmetric pixel value I (X, Y) to the + X direction and + Y. While sequentially scanning in the direction (see FIGS. 16 and 17), error diffusion processing is performed (step S20). In step S20, for example, the multivalued image data after the pixel value redistribution processing in steps S10 to S18 is a binary image, or a binary value or more, and the number of gradations smaller than the input gradation number of the multivalued image data. It is converted to a low-tone image with a logarithm. The system controller 64 forms an image on the recording paper 32 by driving the print control unit 78 based on the binary image or the low gradation image generated by the above processing.

  FIG. 8 is a plan view showing an example of an image formed based on image data subjected to image processing (pixel value redistribution processing) according to the first embodiment of the present invention. FIG. 9 is an enlarged plan view showing the periphery of a pixel corresponding to 8 defective recording elements.

  As shown in FIGS. 8 and 9, according to the present embodiment, the pixels in the pixel columns L (X−1) and L (X + 1) adjacent to the pixel column L (X) in the Y direction corresponding to the defective recording element. The value changes periodically in antiphase. Thereby, the difference in density between the pixel columns L (X−1) and L (X + 1) can be reduced.

  FIG. 10 is a graph for comparing the image processing method according to the first embodiment of the present invention and the prior art. In FIG. 10, the horizontal axis represents the gradation value of the input image data, and the vertical axis represents the ratio of the average value of the pixel values after redistribution in the pixel columns L (X−1) and L (X + 1) (the gradation value ratio). (%))). FIG. 10 shows the gradation value ratio in the image formed based on the image data that has been redistributed according to the present embodiment, and the image redistribution while scanning the processing target pixel in one direction. The gradation value ratio of the image formed in this way (prior art (see FIGS. 13 and 14)) and the gradation value ratio of the image when scanned bidirectionally are shown.

  As shown in FIG. 10, according to the present embodiment, the gradation value ratio is close to 100% as compared with the case of the conventional one-way scanning, and the pixel column adjacent to the defective recording element. The difference between the average values of the pixel values is small. Therefore, according to the present embodiment, it is possible to suppress deterioration in image quality due to a difference in recording density that occurs between pixels around the defective recording element.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the following description, the description of the same configuration as in the first embodiment is omitted.

  FIG. 11 is a block diagram showing an image processing apparatus according to the second embodiment of the present invention.

  As shown in FIG. 11, the image processing apparatus 100 according to the present embodiment further includes a peripheral rearrangement unit 106.

When the pixel values I ″ (X−1, Y) and I ″ (X + 1, Y) after the redistribution processing are below the upper limit value I _MAX (for example, 255), the rearrangement limiting unit 104 As in the first embodiment, the pixel values I ″ (X−1, Y) and I ″ (X + 1, Y) after the redistribution processing are respectively changed to I ′ (X−1, Y) and I ′ (X + 1, Y). ) Is output. On the other hand, when the pixel value I ″ (X ± 1, Y) after the redistribution processing exceeds the upper limit value I _MAX (for example, 255), the rearrangement restriction unit 104 increases the upper limit value to a pixel value equal to or higher than the upper limit value. Substituting I _MAX and outputting it as I ′ (X ± 1, Y) (in the same order as the compound codes).

When the pixel value I ″ (X ± 1, Y) after the redistribution processing exceeds the upper limit value I _MAX (for example, 255), the peripheral rearrangement unit 106 selects the pixel value I ( | I ″ (X ± 1, Y) −I _MAX | is redistributed to X ± 2, Y) (in the same order as the compound codes).

  In addition, the distribution amount (addition amount) of the pixel values with respect to the pixel values I (X ± 1, Y) and I (X ± 2, Y) is not limited to the above, and may be, for example, equal.

  In addition, when the pixel values I ′ (X−1, Y) and I ′ (X + 1, Y) after redistribution exceed the upper limit value, a further distribution destination of the pixel values is a pixel corresponding to the pixel position X ± 2. It is not limited only to the values I (X−2, Y) and I (X + 2, Y), but may be distributed to pixel values corresponding to the pixel positions X ± 3 and X ± 4, for example.

  According to the present embodiment, for example, the redistributed pixel value I (X, Y) is larger than a predetermined value and can be distributed to adjacent pixel values I (X−1, Y) and I (X + 1, Y). Even in the absence, the difference in pixel values between the pixel columns adjacent to the defective recording element can be reduced, and deterioration in image quality can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus (inkjet recording apparatus), 10 ... Printing part, 12 ... Liquid discharge head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feeding part, 20 ... Decal processing part, 22 ... Heating Drum, 24 ... Cutter, 26 ... Suction belt transport unit, 28, 30 ... Roller, 32 ... Belt, 34 ... Print detection unit, 36 ... Suction chamber, 38 ... Fan, 40 ... Heating unit, 42 ... Post-drying unit, 44 ... belt cleaning unit, 46 ... heating / pressurizing unit, 48 ... pressure roller, 50 ... cutter, 52 ... paper discharge unit, 60 ... host computer, 62 ... communication interface, 64 ... system controller, 66 ... program storage unit, 68 ... Memory, 70 ... Motor driver, 72 ... Motor, 74 ... Heater driver, 76 ... Heater, 78 ... Print control unit, 80 ... Buffer memory, 82 ... Ddodoraiba, 100 ... image processing apparatus, 102 ... rearrangement unit, 104 ... relocation limiting part 106 ... peripheral rearrangement unit

Claims (11)

An image is formed on the surface of the recording medium while relatively moving a recording head including a plurality of recording elements arranged along the first direction and a recording medium in a second direction perpendicular to the first direction. An image processing method for creating output image data for forming
An input step of inputting multi-gradation image data for each pixel corresponding to the recording head;
A detection step of detecting a defective recording element in which a recording defect occurs from the plurality of recording elements;
The pixel values corresponding to the detected defective recording elements are first and second corresponding respectively to the first and second recording elements located on both sides of the defective recording element along the first direction. A step of performing redistribution processing to distribute the pixel values so that the distribution amount of the pixel values with respect to the first and second pixel values is in reverse phase in a predetermined cycle along the second direction; Redistribution process to change to
An error diffusion processing step of sequentially performing error diffusion processing in one direction along the first direction to create output image data for the pixel values subjected to the redistribution processing;
An image processing method comprising:   In the redistribution processing step, the distribution amount of the pixel values with respect to the first and second pixel values is controlled so that the first and second pixel values after the redistribution processing do not exceed a predetermined value. The image processing method according to claim 1.   When the first and second pixel values after the redistribution process exceed a predetermined value, the difference between the first and second pixel values after the redistribution process and the predetermined value is determined as the first and second values. The image processing method according to claim 1, further comprising the step of allocating pixel values corresponding to recording elements other than the defective recording element adjacent to the two recording elements.   When the first and second pixel values after the redistribution process exceed a predetermined value, the difference between the first and second pixel values after the redistribution process and the predetermined value is determined as the first and second values. 2. The image processing method according to claim 1, further comprising a step of allocating pixel values corresponding to recording elements other than the defective recording element adjacent to the two recording elements in the first direction.   2. The redistribution processing step, wherein the distribution amount of the pixel value with respect to the first and second pixel values is changed so as to have an antiphase in a two-pixel cycle along the second direction. 5. The image processing method according to any one of 4 above. An image is formed on the surface of the recording medium while relatively moving a recording head including a plurality of recording elements arranged along the first direction and a recording medium in a second direction perpendicular to the first direction. An image processing apparatus for creating output image data for forming
Input means for inputting multi-gradation image data for each pixel corresponding to the recording head;
Detecting means for detecting a defective recording element in which a recording defect has occurred among the plurality of recording elements;
A pixel value corresponding to the detected defective recording element is set to first and second corresponding to the first and second recording elements located on both sides of the defective recording element along the first direction, respectively. A means for performing a redistribution process for distributing the pixel values so that the distribution amount of the pixel values with respect to the first and second pixel values has an opposite phase in a predetermined cycle along the second direction. Redistribution processing means to change to
Error diffusion processing means for sequentially performing error diffusion processing in one direction along the first direction with respect to the pixel values subjected to the redistribution processing to create output image data;
An image processing apparatus comprising:   The redistribution processing means controls the distribution amount of the pixel values with respect to the first and second pixel values so that the first and second pixel values after the redistribution processing do not exceed a predetermined value. The image processing apparatus according to claim 6.   The redistribution processing means, when the first and second pixel values after the redistribution processing exceed a predetermined value, the difference between the first and second pixel values after the redistribution processing and the predetermined value The image processing apparatus according to claim 6, wherein each of the pixel values is allocated to pixel values corresponding to recording elements other than the defective recording element adjacent to the first and second recording elements.   The redistribution processing means, when the first and second pixel values after the redistribution processing exceed a predetermined value, the difference between the first and second pixel values after the redistribution processing and the predetermined value The image processing apparatus according to claim 6, wherein the pixel values are respectively distributed to pixel values corresponding to recording elements other than the defective recording element that are adjacent to the first and second recording elements in the first direction.   The redistribution processing unit changes the distribution amount of the pixel values with respect to the first and second pixel values so as to be in opposite phases in a two-pixel cycle along the second direction. 10. The image processing device according to any one of items 9. An image processing apparatus according to any one of claims 6 to 10,
A recording head that is arranged along the first direction and includes a plurality of recording elements for forming an image by discharging droplets onto the surface of the recording medium;
While moving the recording head and the recording medium relatively in a second direction perpendicular to the first direction, a liquid is discharged from the recording element based on output image data created by the image processing apparatus. Image forming means for discharging droplets to form an image on the surface of the recording medium;
An image forming apparatus comprising:

Images