A method of inkjet printing that handles the overlap region of the nozzles

Abstract

The application discloses a printing method for processing a nozzle overlapping area, belongs to the technical field of digital printing, and relates to a printing technology of a wide-format inkjet printing device, and comprises a selected image generating process and a printing process using the selected image; the printing of an input image is completed by determining a selected image meeting a condition and using the determined selected image. The application can effectively solve the imaging defects caused by the errors of two adjacent nozzles in the width direction and the vertical direction of the width, and improve the quality of the printed output image.

Description

Technical Field

[0001] This invention belongs to the field of digital printing technology, and relates to inkjet printing technology for wide-format inkjet printing equipment, and particularly to a printing method for processing overlapping areas of printheads. Background Technology

[0002] The core imaging unit in inkjet digital printing is the inkjet head (hereinafter referred to as the printhead). Industrial printheads typically have a narrow printable width, generally much smaller than the printing width. In such cases, multiple printheads need to be joined together along the printing width to meet the requirements, and usually, the imaging areas of adjacent printheads will overlap to some extent. For example... Figure 1 As shown, three printheads, each containing 10 nozzles, form a printing system with a width of 26 nozzles / pixel. Printhead 1 and printhead 2, and printhead 2 and printhead 3 each have an overlapping imaging area of ​​2 nozzles / pixels.

[0003] In the overlapping areas of adjacent nozzle imaging regions, the corresponding nozzles of the two nozzles should theoretically be in exactly the same position perpendicular to the width direction. However, due to splicing errors, they often have an error of -1 to 1 pixel (at the physical resolution of the nozzles). Figure 1 As shown, the two vertical dashed lines represent the precise horizontal positions of nozzle 1 of nozzle 2 and nozzle 3, respectively. However, the position of nozzle 1 of nozzle 2 is slightly to the left, with a negative error; while the position of nozzle 1 of nozzle 3 is slightly to the right, with a positive error.

[0004] In a multi-head printing system, during imaging, the overlapping area of ​​adjacent printhead imaging regions can be printed using either the left or right printhead. The simplest strategy (hereinafter referred to as the simple strategy) is to select a point along the width of the overlapping area; pixels to the left of this point are printed using the left printhead, and pixels to the right are printed using the right printhead. For example... Figure 1 As shown, the effect of the simple strategy is that nozzles 1 and 2 only use their first 8 nozzles, but all 10 nozzles of nozzle 3 are working.

[0005] When outputting a uniform image, due to stitching errors, a simple strategy results in a visually varying line of different shades near the transition point between the left and right printheads. This difference in average ink coverage compared to other areas leads to the line appearing to be either darker or lighter. When the stitching error is less than 0, a darker line appears near the transition point compared to the sides; when the stitching error is greater than 0, a lighter line appears near the transition point. Figure 1 When the printing system shown outputs a uniform image, a line parallel to the direction of the dotted line and slightly darker in color than the sides will appear near the nozzle 1 of printhead 2; and a line parallel to the direction of the dotted line and slightly lighter in color than the sides will appear near the nozzle 1 of printhead 3.

[0006] To address the problems arising from simplistic strategies, the industry has developed technologies such as... Figure 2 The random selection strategy shown. Figure 2 The image shown consists of black and white dots, with its width equal to the width of the overlapping area of ​​adjacent printhead imaging regions. The probability of black dots decreasing and the probability of white dots increasing from left to right. On the same horizontal line, the black and white dots exhibit a somewhat random distribution. Black dots indicate printing using the left printhead, and white dots indicate printing using the right printhead. This method is effective in handling splicing errors in the width direction, significantly reducing the appearance of darker or lighter lines near transition points compared to the simpler strategy described earlier. However, the random selection strategy ignores the imaging defects caused by excessive alternating printing by the left and right printheads in the direction perpendicular to the width direction. Figure 2 For example, in the middle part of the overlapping area, two printheads will alternately print every 1-2 pixels. Figure 3 This indicates the use of, for example Figure 2 The diagram illustrates the actual imaging effect of the overlapping area when adjacent printheads have an error of one pixel in the direction perpendicular to the image width, using a random selection strategy. Black dots represent areas where at least one of the two printheads can print, while white dots represent areas where neither printhead can print. The closer to the center of the image in the vertical direction, the more dots are not printed. This means that when the input image is uniform, the color of the overlapping area of ​​adjacent printheads will be lighter, and the lighter the color will be, especially closer to the center of the overlapping area. Therefore, existing technologies struggle to effectively address the imaging deficiencies caused by simple and random selection strategies. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a printing method for processing overlapping areas of printheads. This invention can effectively solve the imaging defects caused by printing using simple strategies and random selection strategies, and is applicable to various printing processes.

[0008] This invention provides a printing method for processing overlapping areas of printheads. The method includes two processes: determining a selected image and printing using the selected image. By determining and using the selected image to complete the printing of the input image, the quality of the printed output image is improved. Specifically, it includes the following steps:

[0009] S1. Generate the initial selection image;

[0010] S2: Randomize the initial selection image to obtain the randomized selection image;

[0011] S3: Determine whether the current randomized selection image meets the requirements. If it does, output the selection image for use in subsequent steps.

[0012] Step S4: Initialize processing conditions and set the first line for printing;

[0013] Step S5: Print the current row of the input image;

[0014] Step S6: Determine whether the last row of the input image has been printed.

[0015] If successful, the processing ends; otherwise, the current row of the input image is set to the next row.

[0016] Step S7: Determine whether the current row of the selected image is the last row.

[0017] If yes, either reset the current row of the selected image to the first row, or repeat steps S1-S3 to regenerate a new selected image and set the current row of the selected image to its first row; if no, set the current row of the selected image to the next row.

[0018] Repeat steps S5 to S7 to achieve printing in the overlapping area of ​​the printhead.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] Compared to inkjet printing techniques based on simple strategies and random selection strategies, the technology of this invention can effectively solve the imaging defects caused by errors between two adjacent printheads in the width direction and perpendicular to the width direction, thereby improving the quality of printed images. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a printing system consisting of multiple printheads; the printing system in the figure includes 3 printheads, each printhead having 10 nozzles.

[0022] Figure 2 This is a schematic diagram of a random selection strategy.

[0023] Figure 3 This is a schematic diagram of the actual imaging process using a random selection strategy.

[0024] Figure 4 This is a schematic diagram of the initial image selection.

[0025] Figure 5 This is a schematic diagram of image selection after randomization.

[0026] Figure 6 A flowchart for generating the selected image.

[0027] Figure 7It is a flow chart for printing an input image using a selection image. DETAILED DESCRIPTION

[0028] The present invention will be further described below by way of embodiments with reference to the accompanying drawings, but the scope of the present invention is not limited in any way.

[0029] The present invention provides a printing method for processing an overlapping area of nozzles, the printing method comprising two processes of generating a selection image and printing with the selection image.

[0030] Steps S1 to S3 are the process of generating the selection image, as shown in Figure 6 .

[0031] Step S1: determining an initial selection image;

[0032] The width of the selection image is the width of the imaging overlapping area of two adjacent nozzles, and the height is any positive integer greater than 0. The selection image is completely composed of black dots and white dots, wherein the black dots and white dots indicate that printing is performed by the nozzles on both sides respectively. In the specific implementation of the present invention, black indicates that the point is printed by the left nozzle, and white indicates that the point is printed by the right nozzle. The selection image is used to control whether a certain pixel is printed by the left nozzle or the right nozzle during the printing process, and the method of the present invention is suitable for various printing processes.

[0033] Assume that the width of the initial selection image is N and the height is M. Let B(x) represent the number of black dots in the x-th column, and S(x) represent the number of alternations of black dots and white dots from top to bottom in the x-th column (if the entire x-th column is composed of black dots or white dots, then S(x)=0), wherein 0 ≤ x < N. For a given small positive integer C, whose value ranges from 2 to M / 2, that is M / 2 ≥ C ≥ 2, the initial selection image must satisfy the following two conditions:

[0034] 1. If 0 ≤ x1 ≤ x2 < N, then B(x1) ≥ B(x2), where x1 and x2 represent column numbers of the image;

[0035] 2. S(x) ≤ C, 0 ≤ x < N.

[0036] The smaller the value of C is, the better the imaging effect of image printing by using the corresponding selection image is.

[0037] As shown in Figure 4 , the image has a width of 31 pixels and a height of 32 pixels. B(x)=31-x; S(x)=1, which satisfies the above two requirements and can be used as the initial selection image.

[0038] However, the existing selection strategy based on random selection (such as Figure 2perform image jet printing as shown. The value of S([N+1 / 2]) adopted in the selected image thereof is approximately equal to M. It is obvious that the selected image adopted by this method cannot meet the condition requirements for determining the initial selected image in the present invention.

[0039] Step S2: Randomizing the initial selected image to obtain a randomized selected image; the selected image after randomized processing also satisfies the above two conditions.

[0040] Select a random function R(x) with an integer value, wherein 0 ≤ x < N, 0 ≤ R(x) < M. Assuming that the initial selected image is Image_I and the randomized image is Image_R, then

[0041] Image_R(x,y) = Image_I(x,(y+R(x))mod M), wherein x represents the column number of the pixel, and y represents the row number of the pixel.

[0042] For example Figure 4 the image obtained by subjecting the initial selected image to randomized processing is as shown in Figure 5 . The selected image after randomized processing still meets the condition requirements of the initial selected image. Figure 5 is a schematic diagram of the selected image after randomization.

[0043] Step S3: Determining whether the current randomized selected image meets the requirement, if yes, generating a selected image; for example as shown in Figure 5 .

[0044] For example in Figure 5 , the randomized selected image consists of a plurality of black and white connected regions ( Figure 5 the number of connected regions is 21). If the number of connected regions of the randomized selected image is less than a certain threshold T (T is an integer greater than 2), outputting the current randomized selected image as the selected image for the jet printing process; otherwise returning to step S1.

[0045] Steps S4 to S7 are processes of performing jet printing by using the selected image, as shown in Figure 7 .

[0046] Step S4: Initializing processing conditions and setting a first row;

[0047] Setting the current row of the input image as the first row, and simultaneously setting the current row of the selected image as the first row.

[0048] Step S5: Jet printing the current row of the input image;

[0049] Extract the sub-image corresponding to the overlapping area of ​​two adjacent nozzles in the current row of the input image. This sub-image has the same width as the selected image. Process each pixel of the sub-image: if the pixel corresponding to the current row of the selected image is black, then that pixel is printed using the left nozzle; otherwise, it is printed using the right nozzle.

[0050] Step S6: Determine whether the last row of the input image has been printed.

[0051] If successful, the processing ends; otherwise, the current row of the input image is set to the next row.

[0052] Step S7: Determine whether the current row of the selected image is the last row.

[0053] If so, either reset the current row of the selected image to the first row, or repeat steps S1-S3 to regenerate a selected image and set the current row of the selected image to its first row;

[0054] If not, set the current row of the selected image to the next row.

[0055] Repeat steps S5 to S7.

[0056] It should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the scope of the claims.

Claims

1. A printing method for processing overlapping areas of printheads, characterized in that, By determining a selected image that satisfies the conditions and using the determined selected image to complete the printing of an input image, the quality of the printed output image is improved; It comprises a selected image generation process and a printing process using the selected image; Steps S1 to S3 are the selected image generation process: S1. Determine an initial selected image; The width of the selected image is the width of the imaging overlapping area of two adjacent nozzles, and the height is any positive integer greater than 0; the selected image is entirely composed of black dots and white dots, wherein black dots and white dots represent printing by the nozzles on both sides respectively; The initial selected image is an image that satisfies both of the following two conditions; First condition: if 0 ≤ x1 ≤ x2 < N, then B(x1) ≥ B(x2), where x1 and x2 are both column numbers of the image; N is the width of the image; B(x) represents the number of black dots in the x-th column; Second condition: S(x) ≤ C, 0 ≤ x < N; where S(x) represents the number of alternations between black dots and white dots from top to bottom in the x-th column; if the x-th column is entirely composed of black dots or white dots, then S(x) = 0; C is a small positive integer, with a value ranging from 2 to M / 2; S2: Perform randomization processing on the initial selected image to obtain a randomized selected image; the randomized selected image is composed of a plurality of black and white connected regions; S3: Set a threshold, and determine whether the number of connected regions of the current randomized selected image is less than the set threshold. If it is less than the threshold, output the current randomized selected image; otherwise, return to step S1; Using the randomized selected image output in S3 as the selected image for the printing process to perform printing can realize the printing of the overlapping area of nozzles.

2. The method of printing according to claim 1, wherein the processing of the overlap region of the printheads is characterized by, In step S1, black dots are printed by the left nozzle, and white dots are printed by the right nozzle.

3. The printing method for processing overlapping areas of printheads as described in claim 1, characterized in that, In step S2, the method for randomizing the initial selected image is specifically expressed as: Image_R(x,y)=Image_I(x,(y+R(x))mod M) Wherein, Image_I is the initial selected image; Image_R is the randomized selected image; x represents the column number of pixels of the initial selected image, y represents the row number of pixels of the initial selected image; R(x) is a random function with integer values, where 0 ≤ x < N, 0 ≤ R(x) < M; M is the height of the initial selected image.

4. The printing method for processing overlapping areas of printheads as described in claim 1, characterized in that, In step S3, the value of the threshold is an integer greater than 2.

5. The printing method for processing overlapping areas of printheads as described in claim 1, characterized in that, The printing process using the selected image comprises steps S4 to S7: Step S4: Initialize processing conditions: set the current row of the input image as the first row to be printed, and set the current row of the selected image as the first row to be printed at the same time; Step S5: Print the current row of the input image; Step S6: Determine whether the last row of the input image has been printed; if completed, the processing process ends; otherwise, set the current row of the input image as the next row to be printed; Step S7: Determine whether the current row of the selected image is the last row; If yes, reset the current row of the selected image as the first row to be printed, or repeat steps S1 to S3 to regenerate a selected image and set the current row of the selected image as the first row to be printed; If not, select the current row of the image as the next row to be printed; Repeat steps S5-S7 to achieve printing in the overlapping areas of the printheads.

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