JP2023016332A - Image processing device - Google Patents

Abstract

To enable an image that is free from a strange feeling to be formed, even when there is a joint portion between head blocks in an inkjet head that is used in forming an image.SOLUTION: An image processing device comprises: a plurality of recording heads 241a having a plurality of nozzles 241c for discharging ink; and an image processing unit 25 that generates data for discharging from input image data. The recording heads 241a are arranged zigzag so that the nozzles 241c at end parts partially overlap with the nozzles 241c of the other recording heads 241a. In the case where a pitch Lb of the nozzle 241c at a joint portion at which the nozzle 241c of the recording head 241a partially overlaps therewith is shorter than a pitch La of the nozzle 241c in the recording head 241a, the image processing unit 25 generates data for discharging in which an image of the input image data by ink discharged from the nozzle 241c at the joint portion is extended in a main scanning direction Y, in order to form one pixel by fitting the nozzles 241c at the joint portion to each other.SELECTED DRAWING: Figure 13

Description

The present invention relates to an image processing device.

2. Description of the Related Art In an inkjet recording apparatus that forms an image on a recording medium that is transported along a transport path, an image is formed on the recording medium using ink ejected from nozzles of an inkjet head. 2. Description of the Related Art In an inkjet printing apparatus, an inkjet head may be composed of a plurality of head blocks arranged along a main scanning direction perpendicular to the transport direction of a printing medium. Two adjacent head blocks of the inkjet head are arranged in a staggered manner so that their ends are partially overlapped with each other in the conveying direction (sub-scanning direction) of the recording medium.

JP 2015-3455 A

At the joint where the ends of the two head blocks overlap in the main scanning direction, the spacing between the nozzles at each end in the main scanning direction depends on the positioning accuracy of both head blocks, and the same head block is adjacent in the main scanning direction. It may differ from the nozzle spacing that fits. If the nozzle spacing in the joint portion is different from the nozzle spacing in the other portions, the dot spacing of the landed ink will deviate. Such deviations in dot spacing are caused by, for example, white streaks and black dots in the transport direction at locations corresponding to the above-described joints in an image formed on a recording medium when ink is uniformly ejected from each nozzle. This may cause unnatural images such as streaks.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to enable formation of an image without discomfort even if an inkjet head used for image formation has a joint portion between head blocks. .

In order to achieve the above object, an image processing device according to one aspect of the present invention comprises:
a plurality of recording heads having a plurality of nozzles for ejecting ink;
an image processing unit that generates ejection data from input image data;
the recording head has a staggered arrangement in which the nozzles at the ends partly overlap with the nozzles of other recording heads;
When the pitch of the nozzles in the joint portion where the nozzles of the recording head partially overlap is shorter than the pitch of the nozzles in the recording head, the image processing unit combines the nozzles in the joint portion to form one pixel. In order to form the image, the image of the input image data formed by ink ejected from the nozzles of the joint portion is extended in the main scanning direction to generate ejection data.

According to the present invention, even if there is a joint portion between head blocks in an inkjet head used for image formation, it is possible to form a natural image.

FIG. 1 is a block diagram showing a configuration example of a printing system according to an embodiment of the invention. FIG. 2 is a diagram for explaining quantization number reduction processing by a quantization control unit in the printing system shown in FIG. 3A and 3B are diagrams for explaining halftone processing by the multi-value halftone processing unit shown in FIG. FIG. 4 is a diagram for explaining halftone processing in which the quantized values (6, 4, 2, 1) shown in FIG. 3 are thinned out. FIG. 5 is a diagram for explaining halftone processing in which the quantized values (6, 5, 3, 1) shown in FIG. 3 are thinned out. FIG. 6 is a diagram illustrating quantization patterns of pixels at odd-numbered positions and even-numbered positions of pixel data. FIG. 7 is a diagram showing an arrangement when pixels are sorted by quantization pattern applied to quantization of each pixel of pixel data. FIG. 8 is an explanatory diagram showing a schematic configuration of the inkjet printing section of FIG. FIG. 9 is an explanatory diagram showing the printer section of FIG. 8 from below. FIG. 10 is an explanatory diagram showing the arrangement of pixels sorted according to the quantization patterns shown in FIG. 7 when the nozzle spacing at the joint of the inkjet head shown in FIG. 9 matches the nozzle spacing of the nozzle array. FIG. 11 is an explanatory diagram showing an arrangement of pixels sorted according to the quantization patterns shown in FIG. 7 when the interval between nozzles at the joint of the inkjet head shown in FIG. 9 is shorter than the interval between nozzles in the nozzle row. FIG. 12 is a diagram showing an arrangement when pixels are sorted according to a partially modified quantization pattern applied to quantization of each pixel of pixel data. FIG. 13 is an explanatory diagram showing an arrangement of pixels sorted according to the quantization patterns shown in FIG. 12 when the interval between nozzles at the joint of the inkjet head in FIG. 9 is shorter than the interval between nozzles in the nozzle row. FIG. 14 is a block diagram showing a schematic configuration of the control unit of FIG. 8; FIG. 15 is a flow chart showing an example of a procedure for setting a pattern for multilevel error diffusion processing, which is referred to when the main controller in FIG. 14 restores the number of drops.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent reference numerals are given to the same or equivalent parts and components throughout each drawing. However, it should be noted that the drawings are schematic and differ from reality. In addition, it is a matter of course that there are portions with different dimensional relationships and ratios between the drawings.

Further, the embodiments shown below are examples of apparatuses and the like for embodying the technical idea of the present invention. etc. are not specified below. The technical idea of this invention can be modified in various ways within the scope of claims.

FIG. 1 is a block diagram showing a configuration example of a printing system including an image processing apparatus according to an embodiment of the invention. A printing system 1 shown in FIG. 1 includes a terminal device 100 , an inkjet printing device 200 (image forming device), and a network 300 .

The terminal device 100 generates a print job and outputs it to the network 300 . The inkjet printing device 200 executes a print job received from the terminal device 100 via the network 300 and prints an image on printing paper.

In the printing system 1 of the present embodiment, the inkjet printing device 200 can constitute the image processing device of the present invention. In the present embodiment, the terminal device 100 reduces the data amount of the image data of the print job, and reduces the image quality of the image formed on the printing paper by printing the image data of the print job received by the inkjet printing device 200. The image data is processed so as to suppress the In this embodiment, when the inkjet printing apparatus 200 performs image processing on the image data of the print job received from the terminal device 100 via the network 300 according to the processing performed by the terminal device 100, the present invention is applied. can be implemented.

(Terminal device)
First, the terminal device 100 will be described. The terminal device 100 includes an application section 11 , a printer driver section 12 , a print data generation section 13 , an input/output section 14 and a terminal side communication section 15 . The application unit 11 and the printer driver unit 12 can be virtually constructed on the terminal device 100 by executing a program installed in the terminal device 100 by the CPU or the like.

The application unit 11 has a program for generating document data such as documents and images. Document data generated by the application unit 11 is output to the printer driver unit 12 .

The printer driver unit 12 causes the output function of the input/output unit 14 to display a print operation screen, a print setting screen, etc., receives print settings from the user via the input function of the input/output unit 14, and sets the print settings. Information and print status are notified to the user via the output function of the input/output unit 14 . The printer driver unit 12 generates print job data (for example, PDL data) based on information (print setting information) set by the user and document data. The print job data includes document image data indicating the content of the document and job data relating to print setting information.

The input/output unit 14 has an input function and an output function. The input function is configured with a keyboard or the like, and the output function is configured with a liquid crystal display monitor or the like. The input/output unit 14 allows the user to input various data, and outputs the input data to the printer driver unit 12 or the application unit 11 . Also, the input/output unit 14 notifies the user of the output result from the printer driver unit 12 or the application unit 11 .

The print data generation unit 13 generates print job data for causing the inkjet printer 200 to print the image of the document data. The print data generation unit 13 includes a RIP processing unit 131 , an RGB-CMYK conversion unit 132 , a multilevel halftone processing unit 133 , a print density data storage unit 134 and a quantization control unit 135 .

The RIP processing unit 131 extracts predetermined red (hereinafter, R) component, green (hereinafter, G) component, and blue (hereinafter, B) component based on the document image data of the print job data output from the printer driver unit 12 . developed print job data (hereinafter referred to as developed print job data), which is raster data as a result of being developed into a bitmap with a resolution of . Here, in the developed print job data, for each pixel rendered at a predetermined resolution (corresponding to each coordinate position in the developed print job data), the value of the R component (for example, 0 to 255), the value of the G component values (eg, 0 to 255) and B component values (eg, 0 to 255) are associated with each other.

The RGB-CMYK conversion unit 132 converts the R, G, and B component development print job data generated by the RIP processing unit 131 into a cyan (hereinafter, C) component, a magenta (hereinafter, M) component, and a yellow (hereinafter, C) component. , Y) component, and black (hereinafter referred to as K) component. In the developed print job data, the C component value (eg, 0 to 255), the M component value (eg, 0 to 255), the Y component value (eg, 0 to 255), and the value of the K component (for example, 0 to 255).

The multi-value halftone processing unit 133 applies multi-value halftone to reduce the number of gradations according to the quantization number set by the quantization control unit 135 for the rasterized print job data converted by the RGB-CMYK conversion unit 132. Processing is performed to generate print target data having the quantization number as the number of gradations.

A specific description will be given with reference to FIG. In the development print job data, the multi-value halftone processing unit 133 quantizes the values (0 to 255) of the color components (C to K components) for each coordinate position (FIG. 2A). 10, 28, 56, 85, . Then, the quantization value 0, which is the quantized value for the color component value 0, the quantization value 1 for the color component values 1 to 28, and the quantization value for the color component values 29 to 56. 2 . . . By associating a quantization value of 9 with the color component values 227 to 256, quantization processing is performed for a quantization number of 10, and quantization is performed from the expanded print job data of 256 gradations. produces a quantized value that is the quantized value. As a result, the quantization values that can be taken after quantization are 0 to 9 and the number of gradations is 10 for the color component values (0 to 255) that the development print job data can take. The quantization process described above is performed for each of the C, M, Y, and K color components.

Here, the quantization control unit 135 is connected to a print density data storage unit 134 that stores a print density table indicating possible print densities when quantization is performed with a predetermined quantization number. As an example of the print density table, for example, a quantization value that can be taken after quantization with a predetermined quantization number and a print density when printing with the number of ink drops corresponding to the quantization value by the inkjet printing apparatus 200. I have a table showing the relationship between

An example of the print density table is shown below. Here, the quantization values (0 to 9) that can be taken when quantization is performed with the quantization number of 10 correspond to the numbers of 0 drops to 9 drops of ink.

Then, the print density when the number of drops is changed from 1 drop to 9 drops is obtained experimentally for each ink color and each type of printing paper. Then, the user inputs the print density and the like to the input/output unit 14, so that the numbers of 1 drop to 9 drops correspond to the print density and the type of printing paper (plain paper, matte paper, . . . ). The attached print density table is stored in the print density data storage unit 134 for each ink color (C, M, Y, K).

The quantization control unit 135 refers to the print density table, and deletes at least one of the print densities that are close to each other based on the distribution of print densities that can be obtained when quantization is performed with a predetermined quantization number. First, a quantization number less than a predetermined quantization number is determined.

Specifically, the quantization control unit 135 refers to the print density table, and sequentially reduces one of the corresponding two quantization values from the case where the difference in print density is the smallest. Determine the small quantization number. At this time, the quantization number determination process is performed independently for each color component.

A detailed description of the processing of this quantization control unit 135 will be given below. The quantization control unit 135 refers to the print density table and obtains the print density corresponding to each of the quantization values 0 to 9 corresponding to the quantization number 10. FIG. The quantization control unit 135 sequentially reduces one of the corresponding two quantization values from the distribution of print densities corresponding to each of the quantization values 0 to 9, starting with the smallest print density difference. is repeated to determine the quantization number so as to be equal to or less than the quantization number determined above. Thus, the quantization control section 135 includes quantization number determination means.

For example, as shown in FIG. 2, the case where the predetermined quantization number is 10 and the print densities corresponding to the quantization values 0-9 are 0-80 will be described as an example. The quantization control unit 135 determines the print density between quantization values (between 1 and 2 and between 8 and 9) based on the distribution of print density for each quantization in the print density table (FIG. 2B). A search is made for a combination of quantized values in which the difference between is within a predetermined value. Here, the predetermined value is, for example, the printing conditions (printing paper, ink, ejection driving conditions (driving waveform voltage, etc.), etc.) of the inkjet printing apparatus 200, when printing is performed with the number of ejection drops corresponding to each quantization value. , is determined by experimentally obtaining a visually equivalent range of quantization values, although there are differences in print density values.

As a result of the above search, the quantization control unit 135 extracts a combination of quantization values in which the print density difference between the quantization values (between 1 and 2 and between 8 and 9) is within a predetermined value. At this time, the quantization control unit 135 sequentially determines whether the combination of quantization values is within a predetermined value, starting with the smallest print density difference, and reduces one of the two corresponding quantization values. repeat to do For example, in the case of FIG. 2B, when the predetermined value is 5, the quantization control unit 135 selects a combination of quantization values (quantization values 1 and 2 and quantization values 8 and 9 ), and since the difference 2 is within a predetermined value of 5, it decides to delete the quantized values 2 and 8. At this time, the quantization control unit 135 determines to delete the quantized value that makes the difference between the adjacent print density values more even, of the two adjacent quantized values to be deleted. Then, the quantization control unit 135 searches for a combination of quantization values (quantization values 1, 3, etc.) with the next smallest print density difference, and since the difference 10 is greater than the predetermined value 5, the quantization value is deleted. decides not to do any more.

Then, the quantization control unit 135 quantizes the developed print job data with the determined quantization number (for example, 8) to generate print target data. As a result, in the data to be printed, the C component value (eg, 0 to 7), the M component value (eg, 0 to 7), the Y component value (eg, 0 to 7), and the Y component value ( 0 to 7) and K component values (for example, 0 to 7) are associated, and the color component value for each coordinate position is converted from a 4-bit value to a 3-bit value to The number of bits (data amount) is reduced. At this time, information from which the quantization values 2 and 8 are deleted is also included in the data to be printed. Thus, the quantization control unit 135 includes quantization control means for quantizing the expanded print job data.

The print data generation unit 13 generates print job data including the print target data processed by the multi-value halftone processing unit 133 and the job data in the print job data generated by the printer driver unit 12 .

The terminal-side communication unit 15 transfers print job data to the inkjet printer 200 via the network 300 .

(inkjet printer)
Next, the inkjet printer 200 will be described. The inkjet printing device 200 includes a printing side communication section 21 , a control section 22 (image processing device), and an inkjet printing section 23 . The print-side communication unit 21 receives print job data transferred via the network 300 .

The control unit 22 converts the value of each color component in the print target data included in the print job data into the number of ink drops. A specific description of this process is given below.

The predetermined quantization number (for example, 10) is transmitted from the terminal device 100 to the control unit 22 in advance. Then, when the print-side communication unit 21 receives the print job data, the control unit 22 generates color component values (quantized values) 0, 1, 2, 3, . . . Based on the deletion of quantization values 2 and 8 for 7, 8, and 9, the value of each color component for each coordinate position developed at a predetermined resolution in the print target data included in the print job data. It has a drop number conversion (high bpp conversion) function for converting 0 to 7 into ink drop numbers 0, 1, 3, 4, 5, 6, 7, and 9 (see FIG. 2(c)).

The control unit 22 also includes ejection heads corresponding to the C component value, the M component value, the Y component value, and the K component value. The inkjet printing unit 23 includes a feed/discharge unit that feeds printing paper and discharges the printed paper after the discharge operation is performed by the discharge head. The inkjet printing unit 23 forms an image at a predetermined position on the printing paper fed from the paper feeding unit based on the number of drops of each color component for each coordinate position output by the drop number conversion function of the control unit 22. Ink ejection control of each ejection head is performed so as to perform

As described above, with reference to the print density table, predetermined quantization is performed so as to delete at least one of print densities that are close to each other based on the distribution of print densities that can be obtained when quantization is performed with a predetermined quantization number. A method for determining a quantization number less than a number has been described.

Next, a method for reducing the amount of image transfer by thinning out the quantization number of print target data in print job data to be output to the network 300 in the terminal device 100 will be described.

The above-described multi-value halftone processing is equivalent to diffusing an error in gradation expression, so it may also be called multi-value error diffusion processing. The image processing apparatus described below reduces the amount of image transfer for each pixel by thinning out the number of drops in each pixel by a certain number when converting to a desired number of multi-level drops with low gradation by multi-level error diffusion. .

First, multilevel error diffusion before thinning out the quantization number will be described with reference to FIG. The first column from the left in FIG. 3 is the input density (0-255). The higher the numerical value of the input density, the darker the density of each component.

The second column from the left in FIG. 3 shows multilevel thresholds for quantizing the input density when the quantization number is set to 0-7. In this case, since 256 input densities are quantized into 8, the input densities are divided by 256/8=32. Therefore, the multilevel thresholds are set to 32, 64, 96, 128, 160, 192, and 224, for example.

A quantization value of 0, which is a quantized value, is assigned to an input density value of 0. Therefore, since the input density (0 to 255) is divided into 7, the quantization thresholds are set to 36 (256/7=36), 72, 108, 144, 180, 216, and 255.

As a result, the quantization values that can be taken after quantization are 0 to 7 and the number of gradations is 8 for the color component values (0 to 255) that the development print job data can take. The multi-value halftone processing unit 133 converts the input density into a smaller number of gradations for each of the C, M, Y, and K color components.

For example, if the input density of the pixel of interest is 186, the quantization threshold for this input density is 180 and the quantization value is 5 because it is between multilevel threshold values 160 and 192. The error here is obtained by input density-quantization threshold value, and 186-180=6 is diffused to peripheral pixels with desired weighting.

The quantization control unit 135 refers to the print density table, thins out a specific quantization value based on the distribution of print densities that can be obtained when quantization is performed with a predetermined quantization number, and thins out a specific quantization value between adjacent pixels. The operation of the multilevel halftone processing unit 133 is controlled so that at least one or more quantization values to be thinned out are different.

FIG. 4 is a diagram showing multilevel error diffusion in which quantized values 6, 4, 2, and 1 are thinned out from the quantized values 1 to 7 described above. As shown in FIG. 4, there are three quantization values, 3, 5, and 7. This quantized value (0, 3, 5, 7) is made to correspond to one pixel.

FIG. 5 is a diagram showing multilevel error diffusion in which quantized values 6, 5, 3, and 1 are thinned out from the quantized values 1 to 7 described above. There are three quantization values, 2, 4, and 7, as shown in FIG. This quantized value (0, 2, 4, 7) is made to correspond to the pixel adjacent to the pixel to which the above quantized value (0, 3, 5, 7) is made to correspond.

By making the quantization values different between adjacent pixels, the number of gradations can be locally increased. That is, in the above example, the quantization values of two adjacent pixels (local) are 0, 2, 3, 4, 5, 7, and the quantization values can be increased from 3 to 5. . In addition, the quantization number is changed from a high bpp (bits per pixel) value with a quantization number of 8 (Fig. 2: 3bit/pixel) before thinning to a low bpp value with a quantization number of 4 (Fig. 3: 2bit/pixel). can be reduced.

FIG. 6A is a diagram showing a print density table. The print density table indicates the quantization pattern for each pixel position. The print density table indicates the number of ink drops to be ejected at each pixel position.

As shown in FIG. 6(a), the odd line (row)/odd position (column) drop numbers are obtained by thinning out the quantized values (6, 5, 3, 1) and performing multilevel error diffusion. is. The number of drops for odd lines/even positions is a value obtained by thinning out the quantized values (6, 4, 2, 1) and performing multilevel error diffusion. In this example, the quantization value and the number of drops match. Note that the quantized value and the number of drops do not have to match. The relationship between the quantization value and the number of drops is obtained in advance by experiment.

The even lines are the inverse of the odd lines. In this way, for example, the number of drops assigned to halftone pixels may be different for odd-numbered lines (rows) and even-numbered lines (rows) so as to represent a checkerboard pattern (checkered pattern). Differentiate between positions (rows) and even positions (rows).

FIG. 6B shows numerical values that can be represented by 2 bits corresponding to four types of drop numbers at each pixel position. 7 drops are converted to value 3, 4 drops and 5 drops are converted to value 2, 2 drops and 3 drops are converted to value 1. The terminal device 100 transmits to the inkjet printing device 200 print job data including print target data obtained by converting a quantized value (number of drops) corresponding to the color component value of each pixel into a numerical value that can be represented by 2 bits. Also, the conversion relationship from the quantized value of each pixel to a numerical value that can be represented by 2 bits is transmitted from the quantization control unit 135 to the inkjet printer 200 .

As described above, the quantization control means of the quantization control unit 135 thins out a specific quantization value based on the distribution of print densities that can be obtained when quantization is performed with a predetermined quantization number. The quantization of the expanded print job data is controlled so that at least one quantization value to be thinned out by is different. As a result, the number of dropped drops can be generated in the peripheral pixels while reducing the amount of data transfer per pixel. As a result, 6 gradations can be expressed in this example, which is more than the number of quantized values (8-4=4) that are decimated. Therefore, it is possible to improve the print image quality as compared with the case where the number of print density gradations is reduced in accordance with the data transfer amount after the reduction per pixel.

Further, by patterning the number of drops for each pixel position as shown in FIG. 6A, the bias in the number of drops is eliminated. Also, since the maximum number of drops (7 drops) is not thinned out, the density of the solid print portion is not reduced. In addition, since the number of drops is switched according to the color component, an interference pattern in color printing is less likely to occur.

In the shaded pixels in FIG. 6(a), the terminal device 100 uses the multi-level error diffusion processing of pattern A in which the quantized values (6, 5, 3, 1) are thinned out to drop the data to be printed. The number has been converted to a 2-bit number. In the non-shaded pixels in FIG. 6(a), the terminal device 100 uses multilevel error diffusion processing of pattern B in which the quantized values (6, 4, 2, 1) are thinned out, and the print object is The data drop value has been converted to a 2-bit number.

Therefore, in the inkjet printing apparatus 200, from the 2-bit numerical value (low bpp value) of each pixel in the print target data of the print job data received from the network 300, the coordinates of the line (row) and position (column) of each pixel are obtained. The number of drops (high bpp value) for each pixel is recovered based on the corresponding multilevel error diffusion pattern.

FIG. 6(c) is a diagram showing quantized values (number of drops) corresponding to color component values of each pixel restored from numerical values that can be represented by 2 bits in FIG. 6(b). A number represented by 2 bits (low bpp value) is a drop number of 0, 2, 3, 4, 5, 7 based on the transformation relation high bpp value).

For odd line (row)/odd position (column) pixels, the quantization value ( 6, 5, 3, 1) are decimated, the original number of drops (high bpp value) is restored from the numerical value (low bpp value) represented by 2 bits.

For odd line (row)/even position (column) pixels, the quantization value ( 6, 4, 2, 1) are decimated, the original number of drops (high bpp value) is restored from the numerical value (low bpp value) represented by 2 bits.

For even line (row)/odd position (column) pixels, the quantization value ( 6, 4, 2, 1) are decimated, the original number of drops (high bpp value) is restored from the numerical value (low bpp value) represented by 2 bits.

For even line (row)/even position (column) pixels, the quantization value ( 6, 5, 3, 1) are decimated, the original number of drops (high bpp value) is restored from the numerical value (low bpp value) represented by 2 bits.

Therefore, in the print target data of the print job data received from the terminal device 100 by the inkjet printing apparatus 200, as shown in FIG. The arrangement of PXa and the pixels PXb whose drop number is converted to a 2-bit numerical value by the multilevel error diffusion processing of pattern B forms a checkered pattern.

FIG. 8 is an explanatory diagram showing a schematic configuration of the inkjet printing section 23 of FIG. The inkjet printing section 23 has an image forming path CR<b>1 and a printer section 24 . In the inkjet printing section 23, the printer section 24 arranged above the image forming path CR1 prints an image on the printing paper P transported in the transport direction X on the image forming path CR1.

FIG. 8 shows the image transport path CR1 from the side. The image forming path CR1 has an endless conveying belt 221, a driving roller 222 and a driven roller 223 which are a driving mechanism of the conveying belt 221, and the like. In the image forming path CR1, the printing paper P is transported in the transport direction X at a speed determined by the printing conditions by the transport belt 221. FIG. A printer unit 24 , which will be described later, is arranged above the conveying belt 221 so as to face it.

FIG. 9 is an explanatory view showing the printer section 24 from below. The printer section 24 has a plurality of line heads 241 . As shown in FIG. 9, the line heads 241 are provided for each color of C (cyan), K (black), M (magenta), and Y (yellow). The line head 241 for each color is configured by arranging a plurality of inkjet heads 241a (recording heads) in the main scanning direction Y orthogonal to the sub-scanning direction which is the conveying direction X of the printing paper P. The main scanning direction Y coincides with the width direction of the printing paper P transported in the transport direction X. As shown in FIG.

Each inkjet head 241a has a nozzle row 241b, as schematically shown in FIG. 9 as a representative example of one of the K (black) inkjet heads 241a. Each nozzle row 241b is composed of a plurality of nozzles 241c arranged in the main scanning direction Y at regular intervals. Each nozzle 241c ejects ink of each color line by line onto the printing paper P on the transport belt 221 to form a plurality of images so as to overlap each other.

The inkjet head 241a of the line head 241 for each color is held by a head holder 242 arranged above the transport belt 221, as shown in FIG. As shown in FIG. 9, the head holder 242 is a box having a head holder surface 242a on its bottom surface. A plurality of rows are formed in units.

A plurality of mounting openings 242b corresponding to each line head 241 are arranged in a zigzag pattern, and each mounting opening 242b is formed in the same shape as the horizontal cross section of the inkjet head 241a. The inkjet head 241a of each line head 241 is inserted into each mounting opening 242b of the corresponding row, and the nozzle row 241b side protrudes from the head holder surface 242a as shown in FIG.

As shown in FIG. 9, the inkjet heads 241a of the line heads 241 of each color held by the head holder 242 are arranged side by side in the main scanning direction Y, and alternately arranged in the sub-scanning direction (conveyance direction X). are staggered. As a result, the ends of two adjacent inkjet heads 241a of the same color are arranged in a staggered manner so that they partially overlap in the main scanning direction Y. As shown in FIG.

A plurality of ink chambers (not shown) communicating with the nozzles 241c are formed inside each inkjet head 241a. Ink is supplied to each ink chamber, and the ink in each ink chamber is ejected from each nozzle 241c by changing the volume of each ink chamber using, for example, a piezo element.

Each nozzle 241c of the inkjet head 241a can change the number of ink drops ejected to the same pixel.

At the joint where the ends of two adjacent inkjet heads 241a overlap in the main scanning direction Y, the nozzles 241c positioned at the extreme ends of the respective inkjet heads 241a become the adjacent nozzles 241c in the main scanning direction Y.

7 is applied to each nozzle 241c across the two inkjet heads 241a shown in the explanatory diagram of FIG. For the nozzle 241c, in the odd-numbered lines (rows) from the upstream side in the transport direction X (sub-scanning direction), a quantized value restored from a 2-bit numerical value based on the multi-level error diffusion of pattern A drawn with diagonal lines. The number of drops obtained by thinning (6, 5, 3, 1) is ejected. In the even-numbered lines (rows) from the upstream side in the transport direction X (sub-scanning direction), quantized values ( 6, 4, 2, 1) are thinned out, and the ink is ejected.

Each nozzle 241c located at an even-numbered position (column) in the main scanning direction Y has a multi-value pattern B that is not shaded on an odd-numbered line (row) from the upstream side in the transport direction X (sub-scanning direction). Ink is ejected in the number of drops obtained by thinning out the quantized value (6, 4, 2, 1) restored from the 2-bit numerical value based on the error diffusion. In even-numbered lines (rows) from the upstream side in the transport direction X (sub-scanning direction), quantized values (6 , 5, 3, 1) are thinned out, and the ink is ejected.

Therefore, the nozzles 241c at odd-numbered positions (rows) and the nozzles 241c at even-numbered positions (rows) in the main scanning direction Y have the same intermediate gradation (numerical value 1 or numerical value 2), ink with mutually different numbers of drops (number of drops = 3 or 5 for one nozzle 241c, number of drops = 2 or 4 for the other nozzle 241c) converted from a 2-bit number. Dispense each.

The interval between the nozzles 241c at the joint is determined according to the length of the joint distance. The joint distance is the distance of the portion where two adjacent inkjet heads 241a overlap in the main scanning direction Y at the joint.

If there is no error between the design value of the joint distance and the actual joint distance, as shown in FIG. pitch) is the same as the interval La (nozzle pitch in the printhead) between adjacent nozzles 241c in a portion other than the joint.

For example, when an image with a uniform density exists in each pixel corresponding to each nozzle 241c of the two inkjet heads 241a, the interval Lb between the nozzles 241c at the joint is the same as the interval La between the nozzles 241c at the portion other than the joint. If so, the halftone image printed with 5 and 3 drops of ink and the halftone image printed with 4 and 2 drops of ink are printed at the joints of the two inkjet heads 241a but not at the joints. However, it prints with a uniform distribution.

In this case, there is no locally shortened portion in the main scanning direction Y, that is, in the position (column) direction, in which the period of change in the number of ink drops for printing a halftone image is formed. The resulting image is a natural image in which streaks or the like along the transport direction X of the printing paper P are not conspicuous at the seams.

On the other hand, if there is an error between the design value of the joint distance and the actual joint distance, the interval Lb between the nozzles 241c at the joint becomes different from the interval La between the nozzles 241c in the nozzle row 241b. For example, as shown in the explanatory diagram of FIG. 11, if the actual joint distance is longer than the design value, the interval Lb between the nozzles 241c at the joint becomes shorter than the interval La between the nozzles 241c in the nozzle row 241b.

For example, when an image with a uniform density exists in each pixel corresponding to each nozzle 241c of the two inkjet heads 241a, the interval Lb between the nozzles 241c at the joint is shorter than the interval La between the nozzles 241c at the portion other than the joint. , the intermediate gradation image printed with 5 and 3 drops of ink and the intermediate gradation image printed with 4 and 2 drops of ink are printed at the joint of the two inkjet heads 241a. printed with a narrower distribution than

In this case, the period in which the number of ink drops for printing a halftone image changes is locally shortened in the position (column) direction. Even if the gradation is the same, this portion is inked with a different number of ink drops than the pixels on both sides, so there is a difference in density between the images of the pixels on both sides. Due to this difference in density, the image formed on the printing paper P becomes an unnatural image in which streaks along the transport direction X of the printing paper P are conspicuous in the area corresponding to the seam.

The printing of such an unnatural image can be alleviated by changing the pattern of multilevel error diffusion processing that is referred to when restoring the 2-bit numerical value of the print target data to the drop value. can.

For example, as shown in the explanatory diagram of FIG. 12, for pixels corresponding to each nozzle 241c of one of the two inkjet heads 241a partially overlapping at the joint, a drop value The pattern of the multilevel error diffusion process referred to when restoring to is changed to a pattern opposite to the normal pattern.

Then, the arrangement of the pixels using the multi-level error conversion process of pattern A and the pixels using the multi-level error conversion process of pattern B becomes a left-right reversed arrangement with the center in the position (column) direction as a boundary. Then, in the two nozzles 241c at the joint between the two inkjet heads 241a, as shown in the explanatory diagram of FIG. 5,3 drops or 4,2 drops) of ink.

In this case, in the image formed on the printing paper P, the portion formed by the ink from the two nozzles 241c at the joint constitutes one pixel in the main scanning direction Y, that is, in the position (column) direction. It becomes an image that looks like For this reason, the period of change in the number of ink drops for printing a halftone image does not locally shorten in the position (row) direction. Therefore, the image formed on the printing paper P is less likely to have a difference in density between images of adjacent pixels at the seam, and streaks or the like along the transport direction X of the printing paper P are less noticeable at the seam. A closer image.

The control unit 22 in FIG. 1 controls the operations of the print-side communication unit 21 and the inkjet printing unit 23 of the inkjet printing device 200 . The control unit 22 can change the pattern of the multilevel error diffusion process referred to when restoring the drop value from the 2-bit numerical value of the print target data described above.

FIG. 14 is a block diagram showing a schematic configuration of the control section 22. As shown in FIG. As shown in FIG. 14, the control section 22 has a main controller 25 (image processing unit), a mechanical controller 26 and a head control circuit 27 . The main controller 25, the mechanical controller 26 and the head control circuit 27 each comprise a processor including a CPU (Central Processing Unit) and memory, a storage device, and various interface circuits, although not shown. The memory includes ROM (Read Only Memory) and RAM (Random Access Memory). A processor can function as one or more information processing circuits.

In the present embodiment, an example in which the information processing circuit included in the processor is implemented by software will be described. Of course, the information processing circuit may be configured by preparing dedicated hardware for executing the information processing described below. It is possible. Moreover, when there are a plurality of information processing circuits, a part of the information processing circuits may be configured by individual hardware.

In this embodiment, the information processing circuit of the processor can be virtually constructed on the hardware of the processor by the processor executing a program stored in the memory. A storage device functions as an accessible storage device. The storage device can be configured to include, for example, a main storage device and an auxiliary storage device. The main memory can be configured by RAM, for example. The auxiliary storage device can be composed of, for example, an SSD (Solid State Drive) or HDD (Hard Disk Drive).

The main controller 25 divides a print job input from the terminal device 100 via the network 300 into data to be printed (image data) and job data. The main controller 25 performs image processing on the data to be printed and outputs the processed data to the head control circuit 27 . The main controller 25 outputs job data to the mechanical controller 26 .

The mechanical controller 26 drives the motors and the like of the inkjet printer 200 based on job data input from the main controller 25 . The motor includes the motor that rotates the drive roller 222 of FIG. The mechanical controller 26 controls the operation of the mechanism portion including the transport portion of the printing paper P in the inkjet printing apparatus 200 .

The mechanical controller 26 has a data holding section 261 in the main memory. The mechanical controller 26 executes a program stored in the main storage device to drive the motor of the inkjet printing device 200 to convey the printing paper P, and various sensors ( (not shown) is utilized.

The mechanical controller 26 sets parameters and the like for causing the main controller 25 and the head control circuit 27 to execute processing in synchronization with the transportation of the printing paper P in accordance with the transportation timing of the printing paper P. FIG. The set parameters can be stored, for example, in the main memory.

In the data holding unit 261 of the mechanical controller 26, it is determined whether or not to change the pattern of the multilevel error diffusion processing that the main controller 25 refers to when restoring the 2-bit numerical value of the data to be printed to the drop value. information for reference is stored. Information stored in the data holding unit 261 includes joint distance information, pattern switching determination threshold information, and joint correction information.

The joint distance information is information indicating the distance in the main scanning direction Y between the joints of the two inkjet heads 241 a in each line head 241 . The joint distance information can be, for example, information indicating a design interval in the main scanning direction Y of each inkjet head 241a. The joint distance information is used to specify the design value of the joint distance at which two adjacent inkjet heads 241a overlap in the main scanning direction Y at the joint. The joint distance can be used to calculate the interval Lb of the nozzles 241c at the joint.

The pattern switching determination threshold information is information indicating the threshold Th for the interval Lb of the nozzles 241c at the joint. The pattern switching determination threshold information is compared with the interval Lb to determine whether the pattern of the multilevel error diffusion process that the main controller 25 refers to when restoring the drop value from the 2-bit numerical value of the data to be printed is changed. It is used to judge whether or not

The joint correction information is information indicating the measured value of the joint distance. The seam correction information may be the measured value of the seam distance or the difference between the measured value of the seam distance and the design value of the seam distance. The seam correction information can be used to specify the measured value of the seam distance from the design value of the seam distance specified from the seam distance information, and to calculate the interval Lb between the nozzles 241c at the seam from the measured value of the seam distance.

Information stored in the data holding unit 261 can be updated by input from an input unit (not shown). The input unit may be, for example, an operation unit including numeric keys or an input device such as a keyboard.

Each information processing circuit of the main controller 25 can mainly control operations related to printing of an image on the printing paper P by the printer section 24 . The information processing circuit of the main controller 25 includes a high bpp conversion section 251 , an image processing section 252 , a conversion pattern setting section 253 and a main scanning direction pixel counting section 254 .

The high bpp conversion unit 251 converts the line (row) of each pixel and the The original number of drops (high bpp value) is restored based on the multilevel error diffusion pattern (pattern A or pattern B) corresponding to the position (column). The pattern of multilevel error diffusion processing used to restore the number of drops for each pixel is set by the conversion pattern setting unit 253 for each pixel.

The image processing unit 252 generates print data for causing each nozzle 241c of each inkjet head 241a to eject the ink of the number of drops of each pixel restored by the high bpp conversion unit 251 for each pixel.

The conversion pattern setting unit 253 uses the high bpp conversion unit 251 to restore the original number of drops (high bpp value) based on the joint distance information, the pattern switching determination threshold information, and the joint correction information in the data holding unit 261. A pattern for multilevel error diffusion processing is set for each pixel of data to be printed. The conversion pattern setting unit 253 sets a common multilevel error diffusion pattern for pixels corresponding to the nozzles 241c having the same position in the main scanning direction Y of each line (row).

The main controller 210 executes the processing of the procedure shown in the flowchart of FIG. 15 for each line (row) of the image data (print target data) of the image to be printed by executing the print job.

The main controller 210 first converts the image data of the pixels on one line into the image data of the pixels for restoring the original number of drops (high bpp value) from the numerical value represented by 2 bits (low bpp value). The bpp conversion unit 251 reads pixels one by one from the upstream side in the main scanning direction Y (step S11).

The main controller 210 causes the conversion pattern setting section 253 to check whether or not the pixel into which the image data is read corresponds to the pixel positioned at the joint of the inkjet head 241a (step S13). The conversion pattern setting unit 253 can confirm whether or not a pixel corresponds to a pixel positioned at a joint using joint distance information in the data holding unit 261, for example.

If the pixel does not correspond to the pixel positioned at the joint (NO in step S13), the process proceeds to step S19, which will be described later. If the pixel corresponds to the pixel located at the joint (YES in step S13), the main controller 210 determines the distance Lb between the nozzle 241c corresponding to the pixel and the adjacent nozzle 241c across the joint of the inkjet head 241a. The conversion pattern setting unit 253 confirms whether or not it is shorter than the threshold Th of the pattern switching determination threshold information in the holding unit 261 (step S15).

If the interval Lb of the nozzles 241c at the joint is equal to or greater than the threshold value Th (NO in step S15), the process proceeds to step S19. If the interval Lb is less than the threshold value Th (YES in step S15), the main controller 210 causes the conversion pattern setting unit 253 to apply the same pattern as that used in the previous pixel whose drop number was restored. After setting the pattern of the multilevel error diffusion process used for restoring the number of drops (step S17), the process proceeds to step S25.

In step S19, the main controller 210 determines whether or not the pattern of the multilevel error diffusion process used for the pixel whose drop number was restored by the high bpp conversion unit 251 immediately before is pattern A. be confirmed by

If it is pattern A (YES in step S19), the main controller 210 causes the conversion pattern setting unit 253 to set the pattern of multilevel error diffusion processing used for restoring the number of drops to pattern B (step S21 ), and the process proceeds to step S25. If the pattern is not pattern A (step S23), the main controller 210 causes the conversion pattern setting unit 253 to set the pattern of the multilevel error diffusion process used for restoring the number of drops to pattern A (step S21), and then step S25. to process.

In step S25, the main controller 210 determines whether or not the pixel from which the image data was read out in step S11 reaches the endmost (last) pixel in the main scanning direction Y on one line. 251 to confirm.

Each time the high bpp conversion unit 251 reads out the pixel image data in step S11, the main scanning direction pixel count unit 254 increments the internal count value. The high-bpp conversion unit 251 determines whether or not the pixel from which the image data was read in step S11 reaches the endmost (last) pixel in the main scanning direction Y on one line. 254 count value.

If the pixel for which image data has been read in step S11 has not reached the end pixel in the main scanning direction Y (NO in step S25), the process returns to step S11. (YES in step S25), and the series of processing ends.

The head control circuit 27 can control the ink ejection operation of each inkjet head 241 a of the printer section 24 based on the control output of the main controller 25 .

In the printing system 1 of the present embodiment described above, the high bpp conversion unit 251 of the inkjet printing device 200 is represented by 2 bits of the pixel located at the joint of the print target data received by the printing side communication unit 21. The pattern of the multilevel error diffusion process used to restore the original number of drops (high bpp value) from the numerical value (low bpp value) is determined by the conversion pattern setting unit based on the interval Lb of the nozzles 241c corresponding to the pixels at the joint. 253 decides.

When the number of drops is restored by the multilevel error diffusion processing of the pattern determined by the conversion pattern setting unit 253, for example, when the interval Lb of the nozzles 241c at the joint portion is less than the image size of one pixel, in the main scanning direction Y An image for one pixel is formed with ink ejected from each of the two adjacent nozzles 241c. As a result, an image is obtained in which the pixels corresponding to the nozzles 241c located at the joint of the interval Lb, which is less than the image size of one pixel, are slightly extended in the main scanning direction Y, and white streaks, black streaks, etc. in the transport direction X are obtained. can be suppressed from occurring in the image.

Therefore, even if an image is printed on the printing paper P using the ink ejected from the nozzles 241c located at the joint of the two adjacent inkjet heads 241a, it is possible to form a natural image.

In a solid image or a blank image in which pixels of maximum or minimum density are uniformly distributed, no density distribution occurs and unnatural streaks do not occur in the image. For an image in which a solid portion or a blank portion is distributed in pixels corresponding to the nozzles 241c positioned at the joints of the inkjet heads 241a, the print target data of the pixels corresponding to the nozzles 241c positioned at the joints is printed in this embodiment. It is not necessary to perform the described restoration processing of the number of drops.

The printing paper P on which the inkjet printing apparatus 200 prints an image may be cut paper or roll paper.

Furthermore, the present invention is not limited to the above-described embodiments, and can be embodied by modifying constituent elements without departing from the scope of the present invention at the implementation stage. Also, various inventions can be formed by appropriate combinations of the plurality of constituent elements disclosed in the above embodiments. For example, some components may be omitted from all components shown in the embodiments.

[Note]
The embodiments described above disclose the following aspects of the invention.

That is, as one aspect of the invention,
a plurality of recording heads having a plurality of nozzles for ejecting ink;
an image processing unit that generates ejection data from input image data;
the recording head has a staggered arrangement in which the nozzles at the ends partly overlap with the nozzles of other recording heads;
When the pitch of the nozzles in the joint portion where the nozzles of the recording head partially overlap is shorter than the pitch of the nozzles in the recording head, the image processing unit combines the nozzles in the joint portion to form one pixel. Disclosed is an image processing apparatus that generates ejection data by extending an image of the input image data in the main scanning direction in order to form an image of the ink ejected from the nozzles of the joint portion.

According to the above aspect of the invention, even if there is a joint portion between the head blocks in the ink jet head used for image formation, it is possible to form a natural image.

22 control unit (image processing device)
25 main controller (image processing unit)
241a inkjet head (recording head)
241c Nozzle La spacing (the pitch of nozzles in the recording head)
Lb interval (nozzle pitch at joint)

Claims (1)

a plurality of recording heads having a plurality of nozzles for ejecting ink;
an image processing unit that generates ejection data from input image data;
the recording head has a staggered arrangement in which the nozzles at the ends partly overlap with the nozzles of other recording heads;
When the pitch of the nozzles in the joint portion where the nozzles of the recording head partially overlap is shorter than the pitch of the nozzles in the recording head, the image processing unit combines the nozzles in the joint portion to form one pixel. An image processing apparatus that generates ejection data by extending an image of the input image data in a main scanning direction in order to form an image of the ink ejected from the nozzles of the joint portion.

Images