Dither matrix generation method, apparatus, and program

Abstract

To provide a dither matrix generation method, apparatus, and program capable of reducing quality deterioration of a printed image by suppressing an influence of past driving of a peripheral nozzle of a predetermined nozzle or the predetermined nozzle itself.SOLUTION: In a dither matrix generation method used when generating print data for driving a head portion having a plurality of nozzle groups driven at different timing, when printing a predetermined pixel of interest by nozzle driving of a predetermined nozzle group, a dither matrix is generated by determining arrangement of thresholds so as to reduce an influence of past driving of other nozzle groups or nozzles for printing the pixel of interest.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method, apparatus, and program for generating a dither matrix used in halftone processing.

Background Art

[0002] Conventionally, an inkjet printing apparatus has been proposed that performs printing processing by ejecting ink from an inkjet head onto a printing medium conveyed on a conveyance path.

[0003] With the recent increase in density and speed of inkjet heads, there is an inkjet head in which the driving pressure of one nozzle of the inkjet head propagates to the driving after that nozzle and the driving of other nozzles.

[0004] When such an inkjet head is used, the ejection pressure of a predetermined nozzle is affected by the driving of surrounding nozzles and the driving that the predetermined nozzle has performed in the past, the ejection state of ink droplets from the predetermined nozzle changes, and there is a problem that the quality of the printed image deteriorates.

[0005] In Patent Document 1, a halftone processing method for suppressing crosstalk of an inkjet head has been proposed. Specifically, by checking the presence or absence of dots in the image area after halftone processing using an error diffusion matrix and changing the threshold value of the error diffusion matrix when there is an influence when forming a dot on a pixel of interest, a method has been proposed to make it difficult to form a dot on that pixel of interest.

[0006] Also, in Patent Document 2, a method has been proposed to additionally apply a specific drive signal according to the physical properties of ink in order to suppress a decrease in ejection performance due to residual vibration of the ink chamber communicating with the nozzle.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] However, Patent Document 1 can be applied only to the case of an inkjet head having nozzles in the same liquid chamber that affect each other by crosstalk, and does not consider the influence from any arbitrary nozzle in the periphery, and thus cannot suppress this. Further, the influence of residual vibration when a predetermined nozzle itself was driven previously cannot be suppressed either.

[0009] Also, although the method described in Patent Document 2 has an effect of suppressing crosstalk, since it is necessary to change the drive signal, the time for driving increases, and there is a possibility that productivity may decrease.

[0010] In view of the above circumstances, an object of the present invention is to provide a dither matrix generation method, apparatus, and program that can suppress the influence of peripheral nozzles of a predetermined nozzle and the influence of past driving of the predetermined nozzle itself, and reduce the deterioration of the quality of a printed image. [Means for Solving the Problems]

[0011] The dither matrix generation method of the present invention is a dither matrix generation method used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings. When printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, a dither matrix is generated by determining the arrangement of threshold values so that the influence of past driving of other nozzle groups or the nozzles printing the target pixel is reduced. [Effects of the Invention]

[0012] According to the dither matrix generation method of the present invention, when printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, the arrangement of the threshold values is determined so that the influence of the past driving of the other nozzle groups or the nozzles printing the target pixel is reduced, and a dither matrix is generated. Therefore, if halftone processing is performed using this to generate print data, the influence of the past driving of the peripheral nozzles of a predetermined nozzle or the predetermined nozzle itself can be suppressed, and a deterioration in the quality of the printed image can be reduced.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Best Mode for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, an embodiment of the dither matrix generation method of the present invention will be described in detail. The dither matrix generation method of this embodiment is a method for generating a dither matrix used when generating print data for driving an inkjet head. Before explaining the specific method of generating the dither matrix, first, the configuration of the inkjet head will be described.

[0015] The inkjet head of this embodiment includes a plurality of nozzles that eject ink onto a print medium. FIG. 1 is a diagram showing the arrangement of ink ejection ports of the nozzles of the inkjet head of this embodiment.

[0016] As shown in FIG. 1, in the inkjet head of this embodiment, there are nozzle groups 1 to 4 in which a plurality of nozzles N are arranged at predetermined intervals in the X direction. And the plurality of nozzle groups 1 to 4 are arranged in the Y direction while being shifted by one nozzle at a time in the X direction. In addition, although four nozzle groups 1 to 4 are shown in FIG. 1, the number of nozzle groups is not limited to this.

[0017] FIG. 2 is a diagram for explaining a method of printing a print image P using the inkjet head shown in FIG. 1. In FIG. 2, a part of the nozzle groups 1 to 4 is shown, and the columns printed by each of the nozzle groups 1 to 4 are indicated by numbers I to IV. Column I is the column printed by nozzle group 1, column II is the column printed by nozzle group 2, column III is the column printed by nozzle group 3, and column IV is the column printed by nozzle group 4.

[0018] Also, in FIG. 2, the order of the pixels printed by each nozzle group 1 to 4 is indicated by numbers on the print image P. In the present embodiment, for each nozzle group 1 to 4 (inkjet head) shown in FIG. 2, the print medium is conveyed in the conveyance direction shown in FIG. 2, and each nozzle group is driven in the order in which the print medium arrives, and ink is ejected from each nozzle group onto the print medium.

[0019] For example, when the position of the first row (the topmost row shown in FIG. 2) of the print image P printed on the print medium reaches the nozzle group 1, ink is ejected from the nozzle group 1. Next, when the position of the first row reaches the nozzle group 2, ink is ejected from the nozzle group 2. Subsequently, when the position of the first row reaches the nozzle group 3, ink is ejected from the nozzle group 3, and when the position of the first row reaches the nozzle group 4, ink is ejected from the nozzle group 4. By ejecting ink from each nozzle group 1 to 4 at different timings as described above and performing printing, the first row of the print image P is printed. For each pixel in the first row of the print image P shown in FIG. 2, the order in which the pixel is printed is indicated, that is, numbers from 1 to 4 are indicated.

[0020] Next, for the second row of the print image P as well, each pixel is printed in the order of the nozzle group 1, the nozzle group 2, the nozzle group 3, and the nozzle group 4, similar to the first row. For each pixel in the second row of the print image P shown in FIG. 2, the order in which the pixel is printed is also indicated, that is, numbers from 5 to 8 are indicated.

[0021] For the third row of the print image P as well, each pixel is printed in the order of the nozzle group 1, the nozzle group 2, the nozzle group 3, and the nozzle group 4, similar to the first row and the second row. For each pixel in the third row of the print image P shown in FIG. 2, the order in which the pixel is printed is also indicated, that is, numbers from 9 to 12 are indicated.

[0022] For the rows after the fourth row of the print image P as well, each pixel is printed in the order of the nozzle group 1, the nozzle group 2, the nozzle group 3, and the nozzle group 4, in the same manner as the first (initial) to third rows.

[0023] Next, a method for generating a dither matrix used when generating print data for driving each nozzle group 1 to 4 of the inkjet head as described above will be described.

[0024] The dither matrix of the present embodiment is generated in consideration of changes in the ejection state due to the past driving of other nozzle groups or nozzles that print the target pixel when printing a predetermined target pixel by driving the nozzles of each nozzle group 1 to 4.

[0025] Specifically, in the dither matrix generation method of the present embodiment, when printing a predetermined target pixel by a predetermined nozzle, a change amount of ejection state that quantifies the degree of influence on the ejection state of the predetermined nozzle by the past driving of the surrounding nozzles and the predetermined nozzle itself is preset.

[0026] In the present embodiment, since the driving timings are different for each of the nozzle groups 1 to 4 as described above, the above-described change amounts of ejection state are preset for each of the nozzle groups 1 to 4. FIG. 3A shows the change amount of ejection state of nozzle group 1, FIG. 3B shows the change amount of ejection state of nozzle group 2, FIG. 3C shows the change amount of ejection state of nozzle group 3, and FIG. 3D shows the change amount of ejection state of nozzle group 4.

[0027] Specifically, the change amount of ejection state indicates the amount by which the momentum or physical quantity (for example, flight speed, ejection volume (droplet amount), landing position, etc.) of the ink droplet when printing the target pixel (hatched pixel shown in FIGS. 3A to 3D) changes from the normal value due to the influence (pressure fluctuation) of the past driving of the nozzles adjacent to both sides or its own nozzle when printing the surrounding pixels (upper, left, upper left, upper right, right pixels) of the target pixel. The value of the change amount of ejection state is preset in consideration of simulations and experiments based on the time difference between the driving timing of the nozzle that prints the target pixel and the driving timing of the nozzle that prints the surrounding pixels.

[0028] An example of the change amount of the ejection state of the nozzle group 1 shown in FIG. 3A will be described. First, when a predetermined nozzle of the nozzle group 1 prints a target pixel surrounded by the thick broken line in FIG. 2, consider the time difference between the driving timing of the nozzle of the nozzle group 1 and the driving timing at which the peripheral pixels with respect to the target pixel were printed in the past.

[0029] The upper left pixel of the target pixel is printed with a time difference of 4 - 5 = -1 with respect to the target pixel. Since this is the driving timing immediately before the driving timing when printing the target pixel, when printing the upper left pixel, the printing of the target pixel (such as the flying speed of the ink) is strongly affected by the pressure fluctuation. Therefore, a large value of 4.0 is set for the value of the change amount of the ejection state.

[0030] On the other hand, since the upper right pixel of the target pixel is printed with a time difference of 2 - 5 = -3 with respect to the target pixel, it is relatively less affected by the pressure fluctuation. Therefore, the value of the change amount of the ejection state is 1.0. Also, the left pixel and the right pixel of the target pixel are printed with time differences of +3 and +1, respectively, with respect to the target pixel. Since this is after the printing of the target pixel, the printing of these pixels does not affect the printing of the target pixel, so the value is 0.0. For the upper pixel, it is set to 0.6 based on the fact that it is printed by driving the same nozzle as the nozzle that prints the target pixel and the relative time.

[0031] Note that for the change amount of the ejection state of the nozzle groups 2 to 4, the value of the change amount of the ejection state is set in the same way as that of the nozzle group 1. However, since the left pixel and the right pixel may be printed at a time before the target pixel, the change amount of the ejection state may not be 0.0.

[0032] Next, the dither matrix used in the halftone process will be described.

[0033] The dither matrix is used when converting multi-tone image data into dot-on / dot-off image data. A threshold value is assigned to each pixel of the dither matrix. The dither matrix is applied to the image data, and for the pixels at the corresponding coordinates, the tone value of the image data is compared with the threshold value of the matrix. If the tone value of the image data is greater, a dot is formed at that pixel.

[0034] Both the tone value of the image data and the threshold value are on a 256-tone scale from 0 to 255 (the larger the value, the darker), and each threshold value is included in the dither matrix the same number of times. For example, in a square dither matrix of 256×256 pixels, the threshold values from 0 to 255 are each included 256 pixels.

[0035] Next, the dither matrix generation method of this embodiment will be described. In this embodiment, for the sake of easy understanding, a method for generating a dither matrix of 16×16 pixels, in which the threshold values from 0 to 255 are each included 1 pixel, will be described.

[0036] Figure 4 shows a matrix (initial matrix) in a state where the threshold values have not yet been determined. The threshold values from 0 to 255 are assigned to each pixel of this initial matrix. The numbers I to IV of the nozzle groups 1 to 4 during dot formation are assigned to each column of the initial matrix. When halftone processing is performed, the dither matrix is applied to the image data so that the numbers I to IV of the nozzle groups 1 to 4 on the image data match the numbers I to IV of the nozzle groups 1 to 4 on the dither matrix.

[0037] Figure 5 is a diagram for explaining the method of assigning threshold values to the initial matrix. Let the coordinates of the top-leftmost pixel of the initial matrix be [x, y] = [0, 0].

[0038] First, select an arbitrary pixel in the initial matrix and assign a threshold value of zero to the selected pixel. In FIG. 5, the pixel [8, 13] is selected. Here, identify which column of the nozzle group the selected pixel [8, 13] is assigned to, and refer to the discharge state change amount shown in any of FIGS. 3A to 3D according to the identified nozzle group. Here, for nozzle group 1, refer to the discharge state change amount shown in FIG. 3A. Superimpose the pixel of interest (hatched pixel) shown in FIG. 3A on the pixel [8, 13] of the initial matrix, assign a threshold value of zero to the pixel [8, 13], and add the value of the discharge state change amount shown in FIG. 3A to the surrounding pixels of [8, 13]. Note that the value of the blank pixel in the initial matrix is zero. The pixel [8, 13] is set as having a determined threshold, is painted black to distinguish it from other pixels, and the threshold value of zero is shown in white.

[0039] Next, assign a threshold value of 1. The position to which the threshold value of 1 is assigned is randomly selected from among the blank pixels to which the discharge state change amount has not been added. For example, as shown in FIG. 5, when the pixel [13, 3] is selected, in the same manner as when the threshold value of zero is assigned, identify the nozzle group 2 that prints the pixel [13, 3], refer to the discharge state change amount of nozzle group 2 shown in FIG. 3B, assign a threshold value of 1 to the pixel [13, 3], and add the value of the discharge state change amount to its surrounding pixels. Thereby, the pixel [13, 3] becomes a pixel with a determined threshold.

[0040] Repeat the process of assigning the threshold value and adding the discharge state change amount to the surrounding pixels as described above while incrementing the threshold value. And when repeating this process, there are cases where a new discharge state change amount is added to a pixel to which the discharge state change amount has already been added. In that case, calculate the total value by adding the new value to the existing value.

[0041] FIG. 6 shows the state of the dither matrix when the process described with reference to FIG. 5 is continued and the threshold value is incremented up to 75. When a solid image with an input gradation value of 76 is halftoned using this dither matrix, dots are formed in the pixels with a threshold value of 75 or less, so a printed image with dots formed at the positions of the black-painted pixels shown in FIG. 6 is obtained.

[0042] That is, it has been determined that the black pixels will already be nozzle-driven. Next, when performing halftone processing on the solid image with the input gradation value of 77, in addition to the black pixels shown in FIG. 6, the threshold value of any pixel with an undetermined threshold value is determined to be 76, and that pixel becomes a dot-forming pixel, and nozzle driving for that purpose will be performed. Here, the numerical value of the pixel with an undetermined threshold value in the dither matrix can be interpreted as a value for evaluating "how much the nozzle driving (such as the flight speed of ink droplets) when forming dots with a determined threshold value changes from the normal state when nozzle driving is performed to form dots in that pixel."

[0043] Therefore, pixels with a small added value of the discharge state change amount are preferentially set as pixels with a determined threshold value. Thereby, the influence of past nozzle driving can be reduced, and the deterioration of the print image quality can be alleviated. For example, when assigning the threshold value of 76, it may be selected from the pixels [4,0], [0,7], "8,9", [12,11] with the minimum added value of the discharge state change amount of 0.1. Thereafter, the same process is performed until all threshold values up to 255 are assigned.

[0044] In this way, by always setting the pixel with the minimum added value of the discharge state change amount as the pixel with a determined threshold value, it is possible to generate a dither matrix that can be converted into a dot presence / absence image such that the discharge state of ink droplets from the nozzle becomes closer to normal.

[0045] Note that the predetermined pixel to which the threshold value is assigned is a pixel at the edge of the initial matrix, and the peripheral pixels of the predetermined pixel may be located outside the initial matrix. In this case, considering that the dither matrix is repeatedly applied to the image data in the left-right and up-down (X direction and Y direction), for example, as shown in FIG. 7, when the pixel P1 to which the change amount of the ejection state is to be added protrudes outside the initial matrix in the X direction, the change amount of the ejection state may be added to the pixel P2 at the opposite end in the X direction. Further, as shown in FIG. 7, when the pixel P3 to which the change amount of the ejection state is to be added protrudes outside the initial matrix in the Y direction, the change amount of the ejection state may be added to the pixel P4 at the opposite end in the Y direction.

[0046] In the dither matrix generation method of the above embodiment, the threshold values from 0 to 255 are set for each pixel, but a plurality of threshold values may be set for each. Even in such a case, they may be set in ascending order from the smallest threshold value in the same manner.

[0047] In the above embodiment, the change amount of the ejection state is set for the pixels above, to the right, to the left, top-right, and top-left of the target pixel. However, the present invention is not limited to this, and the pixels to which the change amount of the ejection state is set may be appropriately changed according to the inkjet head so that the influence of the nozzle drive when printing any other pixel is exerted. For example, the change amount of the ejection state may be set for the peripheral pixels as shown in FIG. 8 with respect to the target pixel (hatched pixel). Also in this case, the change amount of the ejection state may be set based on the time difference between the timing of the nozzle drive when printing the target pixel and the timing of the nozzle drive when printing the peripheral pixels.

[0048] In addition, in the above-described embodiment, a method for generating a dither matrix capable of converting multi-tone image data into dot presence / absence image (binary print data) has been described. However, the dither matrix of the present embodiment is also applicable when converting into print data used in a multi-value printer with variable dot size. For example, as shown in FIG. 9, it is applicable to a multi-value printer using a multi-valuing method in which after arranging small dots in all pixels, large dots are replaced and arranged in the pixels of the existing small dots.

[0049] In the case of such a multi-value printer using a multi-valuing method, for pixels with an input gradation value of the image data from 0 to 127, since it is a process of adding small dots from a state without dots around, the dither matrix generated by the generation method of the above-described embodiment is used. Regarding the amount of change in the ejection state in FIGS. 3A to 3D used when generating the dither matrix, it is set in consideration of the influence of the printing (nozzle driving) of small dots in the past on the surrounding pixels on the printing of small dots of the target pixel.

[0050] In addition, for pixels with an input gradation value of the image data from 128 to 255, since it is a process of adding large dots from a state where the surrounding is filled with small dots as described above, a dither matrix for large dots different from the dither matrix considering the influence of the printing of small dots described above is used to determine the arrangement of large dots.

[0051] The dither matrix for large dots is generated using the amount of change in the ejection state that takes into account the influence of past printing (nozzle driving) of large dots on the surrounding pixels of the target pixel on the printing of the large dot of the target pixel. At this time, among the surrounding pixels, when all pixels other than the target pixel for which the amount of change in the ejection state is obtained are printed with small dots, it is set in consideration of the influence on the printing of the large dot of the target pixel. Specifically, as shown in FIG. 10A, when small dots are printed on all surrounding pixels of the target pixel (hatched pixel) and a large dot is printed on the target pixel, the ejection state amount, and as shown in FIG. 10B, when a large dot is printed on the upper left pixel of the target pixel (hatched pixel) and small dots are printed on the surrounding pixels other than the upper left pixel and a large dot is printed on the target pixel, the difference in the ejection state amount is obtained as the amount of change in the ejection state that takes into account the influence of printing a large dot on the upper left pixel of the target pixel on the printing of the large dot on the target pixel. The same applies when obtaining the amount of change in the ejection state of the left, upper, right, and upper right pixels other than the upper left pixel. Note that the ejection state amount refers to the momentum or physical quantity of the ink droplets when printing the target pixel.

[0052] Also, not only for two types of dot sizes, small dots and large dots, but also when the number of types of dot sizes increases, the dither matrix is created for each type of dot size in the same way, and the dither matrix corresponding to the dot size is appropriately used according to the input gradation value.

[0053] Also, in FIG. 9, the input gradation value of the solid image of small dots is set to 127, but this value of the input gradation value may be changed according to the gradation characteristics to be reproduced. Also, as a method for converting to multi-valued print data, it is not limited to the method using the above-described plurality of types of dither matrices, and it is also possible to generate multi-valued print data using the dither matrix for binary conversion described in the above embodiment. Specifically, multi-valued print data may be generated by obtaining the output image data O(x, y) using the following formula. O(x,y)=int[(n-1) / (m-1)*I(x,y)+d(xd,yd) / (gmax+1)] n: number of output gradations m: Number of input gradation levels O(x, y): Output image data, an integer where 0 ≦ O(x, y) ≦ (n - 1) I(x, y): Input image data, an integer where 0 ≦ I(x, y) ≦ (m - 1) gmax: Maximum value of the dither matrix d(xd, yd): Value of the dither matrix, where 0 ≦ d(xd, yd) ≦ gmax xd = x mod dsize_x yd = y mod dsize_y dsize_x: Size of the dither matrix in the x - direction dsize_y: Size of the dither matrix in the y - direction int[]: Integerization function

[0054] The above is the description of the dither matrix generation method of this embodiment.

[0055] Next, an inkjet printing apparatus using the dither matrix generated by the dither matrix generation method of the above embodiment will be described. FIG. 11 is a schematic configuration diagram of the inkjet printing apparatus 5 of this embodiment.

[0056] The inkjet printing apparatus 5 performs printing processing by ejecting ink onto a sheet - like printing medium such as paper or film based on image data output from a computer or image data output from a document reading apparatus. As shown in FIG. 11, the inkjet printing apparatus 5 includes an image processing unit 10, a head drive control unit 20, an inkjet head unit 30, a conveyance unit 40, and a control unit 50.

[0057] The image processing unit 10 receives the image data output from a computer or a document reading device, and performs various processes on the image data. In the present embodiment, the image processing unit 10 corresponds to an embodiment of the image processing apparatus of the present invention. The image processing unit 10 includes a CPU (Central Processing Unit) and a semiconductor memory. Note that the CPU and the semiconductor memory of the image processing unit 10 may be common to a control unit 50 described later, or may be provided separately.

[0058] The image processing unit 10 executes an image processing program stored in advance in a storage medium such as a semiconductor memory or a hard disk, and operates an electric circuit to perform the processes of the respective units described later.

[0059] As shown in FIG. 11, the image processing unit 10 includes an image data reception unit 11, a color conversion unit 12, and a halftone processing unit 13.

[0060] The image data reception unit 11 receives RGB format image data output from a computer or a document reading device, and outputs it to the color conversion unit 12.

[0061] The color conversion unit 12 converts the RGB format image data into CMYK format image data, and outputs it to the halftone processing unit 13.

[0062] The halftone processing unit 13 performs halftone processing on the C, M, Y, and K image data output from the color conversion unit 12 to generate binary data or multi-valued data.

[0063] The halftone processing unit 13 of the present embodiment performs halftone processing using a dither matrix, and the dither matrix generated by the above-described dither matrix generation method is stored in advance. As a method of halftone processing, a known method is used. For example, the dither matrix is scanned in the X direction and the Y direction with respect to the image data to assign threshold values.

[0064] Note that the image processing unit 10 performs various known image processes such as gamma correction processing and edge enhancement processing, in addition to the above-described processes.

[0065] Based on the print data of each color generated by the halftone processing unit 13, the head drive control unit 20 drives the inkjet head unit 30 to eject ink from each nozzle of the inkjet heads of each color.

[0066] The inkjet head unit 30 includes a plurality of inkjet heads that eject inks of colors C, M, Y, and K. Each inkjet head includes the nozzle groups 1 to 4 shown in FIG. 1. Then, each inkjet head is controlled by the head drive control unit 20 based on the print data of each color as described above to eject ink onto the print medium, and a printed image is formed on the print medium.

[0067] The conveyance unit 40 includes a conveyance mechanism that conveys the print medium to the inkjet head unit 30.

[0068] The control unit 50 includes a CPU, a semiconductor memory, etc., and controls the entire inkjet printing apparatus 5. The control unit 50 executes a control program stored in advance in a storage medium such as a semiconductor memory or a hard disk, and operates an electric circuit to control the operations of each part of the inkjet printing apparatus 5.

[0069] Also, in the inkjet printing apparatus 5, the dither matrix is stored in advance in the halftone processing unit 13 of the image processing unit 10, but in the image processing unit 10, the dither matrix may be generated. Specifically, as shown in FIG. 12, the image processing unit 10 may include a discharge state change amount storage unit 14 that stores in advance the discharge state change amounts as shown in FIGS. 3A to 3D, and a dither matrix generation unit 15 that determines the arrangement of threshold values based on the discharge state change amount as described above to generate a dither matrix.

[0070] Further, the ejection state change amount storage unit 14 and the dither matrix generation unit 15 may be provided in a computer different from the inkjet printing apparatus 5 to constitute a dither matrix generation apparatus. In this case, for example, a dither matrix generation program is installed in a storage medium such as a semiconductor memory or a hard disk, and the dither matrix generation program is executed by a CPU or the like of the computer, so that the above-described dither matrix generation method may be executed by the computer.

[0071] Note that some or all of the functions executed by the dither matrix generation program may be configured by hardware such as an ASCI (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or other electric circuits.

[0072] According to the dither matrix generation method of the above embodiment, when printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, the arrangement of the thresholds is determined so that the influence of the past driving of the other nozzle group or the nozzles for printing the target pixel is reduced, and the dither matrix is generated. Therefore, if halftone processing is performed using this to generate print data, the influence of the past driving of the peripheral nozzles of a predetermined nozzle or the predetermined nozzle itself can be suppressed, and the quality degradation of the printed image can be reduced.

[0073] Further, in the dither matrix generation method of the above embodiment, the ejection state change amount is set in advance for each peripheral pixel, the target pixel is assigned to a predetermined pixel of the initial matrix, a threshold is set for the predetermined pixel, and the ejection state change amount is added to the peripheral pixels of the predetermined pixel. The target pixels are assigned in the order of the pixels with smaller added values to determine the arrangement of the thresholds, and the ejection state change amount is added to the peripheral pixels of the target pixel to generate the dither matrix. Therefore, a dither matrix that further suppresses the influence of past nozzle driving can be generated by simple arithmetic operations.

[0074] Also, in the dither matrix generation method of the above embodiment, as shown in FIGS. 3A to 3D, since the change in ejection state is set for each nozzle group, a more appropriate change in ejection state amount can be used.

[0075] Also, in the dither matrix generation method of the above embodiment, since the change in ejection state amount is set according to the interval between the drive timing of the nozzle for printing the target pixel and the drive timing of the nozzle for printing the peripheral pixels, a change in ejection state amount that more appropriately reflects the influence of past nozzle driving can be set.

[0076] Also, in the dither matrix generation method of the above embodiment, when a predetermined pixel is a pixel at the end of the initial matrix and the peripheral pixels of the predetermined pixel are located outside the initial matrix, the change in ejection state amount added to the peripheral pixels located outside is added to the pixel at the end on the opposite side facing the end of the initial matrix, so that a more appropriate change in ejection state amount can be set.

[0077] Also, the present invention is not limited to the above embodiment, and the components can be modified and embodied without departing from the gist thereof at the implementation stage. Also, various inventions can be formed by appropriately combining the plurality of components disclosed in the above embodiment. For example, all the components shown in the embodiment may be appropriately combined. Needless to say, various modifications and applications are possible within the scope not departing from the gist of the invention.

[0078] Regarding the present invention, the following additional remarks are further disclosed.

[0079] (Additional Remark 1) The dither matrix generation method of the present invention is a method for generating a dither matrix used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings. When printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, the arrangement of threshold values is determined so that the influence of the past driving of other nozzle groups or the nozzles printing the target pixel is reduced, and a dither matrix is generated.

[0080] (Appendix 2) Further, in the dither matrix generation method described in Appendix 1, when the nozzles of a predetermined nozzle group print a target pixel, the amount of change in ejection state representing the degree of influence of the past printing of the peripheral pixels of the target pixel by other nozzle groups or the nozzles printing the target pixel on the printing of the target pixel is preset for each peripheral pixel. A target pixel is assigned to a predetermined pixel of the initial matrix, a threshold value is set for the predetermined pixel, the amount of change in ejection state is added to the peripheral pixels of the predetermined pixel, the target pixel is assigned in the order of pixels with smaller added values to determine the arrangement of the threshold value, and the amount of change in ejection state is added to the peripheral pixels of the target pixel to generate a dither matrix.

[0081] (Appendix 3) Further, in the dither matrix generation method described in Appendix 2, the amount of change in ejection state can be set for each nozzle group.

[0082] (Appendix 4) Further, in the dither matrix generation method described in Appendix 2 or Appendix 3, the amount of change in ejection state can be set according to the interval between the driving timing of the nozzle printing the target pixel and the driving timing of the nozzle printing the peripheral pixel.

[0083] (Appendix 5) Further, in the dither matrix generation method described in any one of Appendix 2 to Appendix 4, when a predetermined pixel is a pixel at the end of the initial matrix and the peripheral pixels of the predetermined pixel are located outside the initial matrix, the amount of change in ejection state added to the peripheral pixels located outside can be added to the pixels at the end on the opposite side facing the end of the initial matrix.

[0084] (Appendix 6) The dither matrix generation device of the present invention is a dither matrix generation device used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings. When printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, a discharge state change amount storage unit that stores in advance a discharge state change amount representing the degree of influence of the past driving of other nozzle groups or the nozzles that print the target pixel, and a dither matrix generation unit that determines the arrangement of threshold values based on the discharge state change amount and generates a dither matrix.

[0085] (Appendix 7) The dither matrix generation program of the present invention is a dither matrix generation program for generating a dither matrix used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings. When printing a predetermined target pixel by driving the nozzles of a predetermined nozzle group, the computer is made to execute a process of determining the arrangement of threshold values so that the influence of the past driving of other nozzle groups or the nozzles that print the target pixel is reduced, and generating a dither matrix.

[0086] (Appendix 8) The image processing method of the present invention performs halftone processing on image data using a dither matrix generated using the dither matrix generation method described in any one of Appendices 1 to 5.

[0087] (Appendix 9) The image processing device of the present invention performs halftone processing on image data using a dither matrix generated using the dither matrix generation method described in any one of Appendices 1 to 5.

[0088] (Appendix 10) The image processing program of the present invention causes a computer to execute a program for performing halftone processing on image data using a dither matrix generated by using the dither matrix generation method described in any one of Appendices 1 to 5.

Explanation of Signs

[0089] 1 to 4 nozzle groups 5 Inkjet printing device 10 Image processing unit 11 Image data reception unit 12 Color conversion unit 13 Halftone processing unit 14 Discharge state change amount storage unit 15 Dither matrix generation unit 20 Head drive control unit 30 Inkjet head unit 40 Conveying unit 50 Control unit N Nozzles

Claims

1. A method for generating a dither matrix used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings, When printing a predetermined target pixel by driving the nozzles of a predetermined one of the nozzle groups, the arrangement of thresholds is determined so that the influence of the past driving of the other nozzle groups or the nozzles printing the target pixel is reduced, and the dither matrix is generated. A method for generating a dither matrix.

2. When the nozzles of the predetermined nozzle group print the target pixel, a discharge state change amount representing the degree of influence of the past printing of the peripheral pixels of the target pixel by the other nozzle groups or the nozzles printing the target pixel on the printing of the target pixel is preset for each of the peripheral pixels, The target pixel is assigned to a predetermined pixel of the initial matrix, the threshold is set for the predetermined pixel, and the discharge state change amount is added to the peripheral pixels of the predetermined pixel. The target pixels are assigned in the order of the pixels with smaller addition values to determine the arrangement of the thresholds, and the discharge state change amount is added to the peripheral pixels of the target pixel to generate a dither matrix. The method for generating a dither matrix according to claim 1.

3. The method for generating a dither matrix according to claim 2, wherein the discharge state change amount is set for each nozzle group.

4. The method for generating a dither matrix according to claim 2, wherein the discharge state change amount is set according to the interval between the driving timing of the nozzles printing the target pixel and the driving timing of the nozzles printing the peripheral pixels.

5. When the predetermined pixel is a pixel at the end of the initial matrix and the peripheral pixels of the predetermined pixel are located outside the initial matrix, the discharge state change amount added to the outer peripheral pixels is added to the pixels at the opposite end facing the end of the initial matrix. The method for generating a dither matrix according to claim 2.

6. A dither matrix generation device used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings, a discharge state change amount storage unit that stores in advance a discharge state change amount representing the degree of influence of the past driving of other said nozzle groups or the nozzles that print the pixel of interest when printing a predetermined pixel of interest by driving the nozzles of a predetermined said nozzle group, and a dither matrix generation unit that determines the arrangement of threshold values based on the discharge state change amount and generates the dither matrix. A dither matrix generation device.

7. A dither matrix generation program for generating a dither matrix used when generating print data for driving a head unit having a plurality of nozzle groups driven at different timings, a dither matrix generation program that causes a computer to execute a process of determining the arrangement of threshold values so that the influence of the past driving of other said nozzle groups or the nozzles that print the pixel of interest is reduced when printing a predetermined pixel of interest by driving the nozzles of a predetermined said nozzle group and generating the dither matrix.

Images