Printing device, printing system, printing method, and printing control program

Abstract

The present invention realizes multi-screening in a printing device with a simple circuit.　The present invention is provided with: a threshold matrix set (710) including at least one threshold matrix (71) comprising a plurality of thresholds for comparison with gradation values of a plurality of pixels included in raster data (64) for printing; a threshold set including at least one threshold (72) for comparison with the gradation value of each pixel included in the raster data (64); and a halftone processing unit (52) for generating halftone image data (65) on the basis of the result of comparing the gradation value of each pixel included in the raster data (64) with the threshold. The halftone processing unit (52) switches, for each pixel, the referent of the threshold to be compared with the gradation value in the raster data (64) between the threshold matrix set (710) and the threshold set (720) according to the magnitude of the gradation value in the raster data (64).

Description

Printing device, printing system, printing method, and print control program

[0001] The present invention relates to a printing device that prints by ejecting ink onto a printing medium, and more particularly to halftone processing (screening processing) that converts multi-tone data into halftone dot data when printing is performed by the printing device.

[0002] Inkjet printing devices are known that print by ejecting ink onto a print medium such as printing paper or film using heat or pressure. Inkjet printing devices are equipped with a head unit consisting of multiple ink ejection heads, each for a different ink color, extending in a direction perpendicular to the transport direction of the print medium. Each ink ejection head includes multiple nozzles that eject ink. The gradation of a printed image is expressed by controlling the on / off state of ink ejection from each of the multiple nozzles, or by controlling the drop size of ink ejected from each of the multiple nozzles in multiple stages.

[0003] When printing is performed with an inkjet printing device, input data written in, for example, a page description language is first rasterized. The multi-tone data resulting from the rasterization process is then converted into data indicating whether or not ink will be ejected from each nozzle, or into data indicating the size of the ink droplets ejected from each nozzle. That is, a halftone process (also called a "screening process") is performed, converting data representing a grayscale image in continuous tones into halftone data representing the grayscale image using halftone dots. The ejection of ink from each nozzle is then controlled based on the data obtained from the halftone process, forming a grayscale image on the printing medium.

[0004] One known specific halftone processing technique involves preparing a threshold matrix in which a large number of thresholds are arranged in a matrix (two-dimensionally), and generating halftone dot data by comparing, for each pixel, the tone values ​​of the multi-tone data after rasterization with the thresholds in the threshold matrix. In this regard, if only one size is provided as the ink drop size ejected from each nozzle, one type of threshold matrix is ​​prepared. Alternatively, if, for example, three types (three levels) of drop sizes are provided, three types of threshold matrices are prepared. The threshold matrix is ​​also called a "screen pattern."

[0005] FIG. 16 shows a configuration for halftone processing when three drop sizes (S, M, and L) are provided. In this configuration, a threshold matrix set 910 is provided, consisting of a threshold matrix 91(S) for S size, a threshold matrix 91(M) for M size, and a threshold matrix 91(L) for L size. For reference, an example of the threshold matrix 91(S) for S size is shown in FIG. 17, an example of the threshold matrix 91(M) for M size is shown in FIG. 18, and an example of the threshold matrix 91(L) for L size is shown in FIG. 19. The halftone processing unit 900 compares the gradation value of each pixel in the input data (multi-tone data after rasterization) 98 with the corresponding threshold value in each of the three threshold matrices 91. Then, depending on the comparison result, the data value of the pixel in halftone image data (halftone dot data) 99, which is the output data, is determined, for example, as follows: For pixels whose gradation values ​​in the input data 98 ​​are equal to or greater than the threshold value in the threshold matrix 91(L) for L size, the data value in the halftone image data 99 is set to a value indicating that L size ink is to be applied (e.g., "3"). For pixels whose gradation values ​​in the input data 98 ​​are equal to or greater than the threshold value in the threshold matrix 91(M) for M size but less than the threshold value in the threshold matrix 91(L) for L size, the data value in the halftone image data 99 is set to a value indicating that M size ink is to be applied (e.g., "2"). For pixels whose gradation values ​​in the input data 98 ​​are equal to or greater than the threshold value in the threshold matrix 91(S) for S size but less than the threshold value in the threshold matrix 91(M) for M size, the data value in the halftone image data 99 is set to a value indicating that S size ink is to be applied (e.g., "1"). For pixels whose gradation values ​​in the input data 98 ​​are less than the threshold value in the threshold matrix 91(S) for S size, the data value in the halftone image data 99 is set to a value indicating that no ink is to be applied (e.g., "0"). In this way, halftone image data 99 for controlling the ejection of ink from each nozzle is generated.

[0006] Another proposed technique involves preparing two types of threshold matrix sets and selectively using the two types of threshold matrix sets depending on the attributes of the data to be processed. FIG. 20 shows an example of a configuration using this technique. The configuration shown in FIG. 20 includes a first threshold matrix set 930 consisting of a threshold matrix 93(S) for S size, a threshold matrix 93(M) for M size, and a threshold matrix 93(L) for L size, and a second threshold matrix set 940 consisting of a threshold matrix 94(S) for S size, a threshold matrix 94(M) for M size, and a threshold matrix 94(L) for L size. The halftone processing unit 920 receives tone value data 981 and attribute data 982 as input data 98. The attribute data 982 has different data values ​​for, for example, line drawings (including characters) and images. The halftone processing unit 920 includes a reference destination switching unit 921 and a drop size determination unit 922. Based on attribute data 982, the reference switching unit 921 switches the reference for the data (threshold values) to be compared with the gradation values ​​of each pixel between a first threshold matrix set 930 and a second threshold matrix set 940. The drop size determination unit 922 compares the gradation values ​​of each pixel in the gradation value data 981 with the corresponding threshold values ​​in each of the three threshold matrices included in the reference threshold matrix set. Based on the comparison results, the data values ​​of the pixels in halftone image data 99, which is output data, are determined. This technique of performing halftone processing (screening) using different data depending on the attributes of the data to be processed is called "multi-screening." An inkjet printing device that performs such multi-screening is disclosed in Japanese Patent Application Laid-Open No. 2010-221584.

[0007] Japanese Patent Publication No. 2010-221584

[0008] 20 , conventional multi-screening employing the configuration shown in FIG. 20 requires data (attribute data 982) for switching the reference threshold matrix set for each pixel. This, for example, can cause problems such as insufficient data bandwidth in inkjet printing devices that perform high-speed printing, as well as high costs to ensure sufficient data bandwidth. Furthermore, a large-capacity memory is required to simultaneously read out data from two types of threshold matrix sets, and the circuitry for comparing the gradation values ​​in the input data 98 ​​with thresholds is also large. From these perspectives, the system is also expensive.

[0009] In view of the above circumstances, an object of the present invention is to realize multi-screening in an inkjet printing apparatus using a simple circuit.

[0010] A first aspect of the present invention is a printing device having a plurality of nozzles that prints by ejecting ink from the plurality of nozzles onto a printing medium, the printing device comprising: a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds that are to be compared with the gradation values ​​of a plurality of pixels included in raster data for printing, the plurality of thresholds being arranged two-dimensionally; a threshold set including at least one threshold that is to be compared with the gradation values ​​of each pixel included in the raster data; and a halftone processing unit that generates halftone image data based on a result of comparing the gradation values ​​of each pixel included in the raster data with the thresholds, wherein when generating the halftone image data, the halftone processing unit switches, for each pixel, the reference destination of the threshold to be compared with the gradation values ​​in the raster data between the threshold matrix set and the threshold set depending on the magnitude of the gradation value in the raster data.

[0011] In a second aspect of the present invention, in the first aspect of the present invention, K is a predetermined gradation value, and the halftone processing unit uses the threshold matrix set as a reference for thresholds to be compared with the gradation value in the raster data for pixels whose gradation value in the raster data is (K-1) or less, and uses the threshold set as a reference for thresholds to be compared with the gradation value in the raster data for pixels whose gradation value in the raster data is K or more.

[0012] A third aspect of the present invention is the ink jet recording apparatus according to the first or second aspect of the present invention, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is N threshold matrices, and the at least one threshold included in the threshold set is N thresholds.

[0013] In a fourth aspect of the present invention, in the third aspect of the present invention, the maximum value of the gradation value is M, and for pixels in the raster data whose gradation value is (M-N) or less, the halftone processing unit uses the threshold matrix set as a reference for a threshold to be compared with the gradation value in the raster data, and for pixels in the raster data whose gradation value is (M-N+1) or more, uses the threshold set as a reference for a threshold to be compared with the gradation value in the raster data.

[0014] A fifth aspect of the present invention is a printing system including the printing device according to the first aspect of the present invention and a printing raster data generation device that generates the raster data based on input data including a plurality of objects, wherein the plurality of objects are classified into first type objects and second type objects in accordance with predetermined conditions, wherein a maximum value of gradation value is M and K is a predetermined gradation value, the threshold value matrix set is associated with a first gradation range that is a range of gradation values ​​from 0 to (K-1), and the threshold value set is associated with a second gradation range that is a range of gradation values ​​from K to M, the printing raster data generation device comprising: a gradation value conversion unit that generates intermediate data by converting the gradation values ​​of the first type objects of the plurality of objects to gradation values ​​within the first gradation range and converting the gradation values ​​of the second type objects of the plurality of objects to gradation values ​​within the second gradation range, and a rasterization processing unit that generates the raster data by performing a rasterization process on the intermediate data.

[0015] A sixth aspect of the present invention is directed to the fifth aspect of the present invention, wherein the plurality of objects include at least image objects and line drawing objects, the image objects are classified into the first type of object, and the line drawing objects are classified into the second type of object.

[0016] A seventh aspect of the present invention is the ink jet recording apparatus according to the fifth or sixth aspect of the present invention, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is N threshold matrices, and the at least one threshold included in the threshold set is N thresholds.

[0017] An eighth aspect of the present invention is based on the seventh aspect of the present invention, wherein the halftone processing unit uses the threshold matrix set as a reference for thresholds to be compared with the gradation values ​​in the raster data for pixels having gradation values ​​in the raster data that are (M-N) or less, and uses the threshold set as a reference for thresholds to be compared with the gradation values ​​in the raster data for pixels having gradation values ​​in the raster data that are (M-N+1) or more.

[0018] A ninth aspect of the present invention is a printing method using a printing device having a plurality of nozzles that eject ink onto a printing medium, the method comprising: a halftone processing step of generating halftone image data based on a result of comparing the gradation value of each pixel included in raster data to be printed with a threshold; and an ink ejection control step of controlling the ejection of ink from the plurality of nozzles based on the halftone image data, wherein the printing device comprises: a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds to be compared with the gradation values ​​of the plurality of pixels included in the raster data, the plurality of thresholds being arranged two-dimensionally; and a threshold set including at least one threshold to be compared with the gradation value of each pixel included in the raster data, wherein in the halftone processing step, when generating the halftone image data, the reference destination of the threshold to be compared with the gradation value in the raster data is switched between the threshold matrix set and the threshold set depending on the magnitude of the gradation value in the raster data.

[0019] A tenth aspect of the present invention is the halftone processing step according to the ninth aspect of the present invention, wherein K is a predetermined gradation value, and for pixels in the raster data whose gradation value is (K-1) or less, the threshold matrix set is used as a reference for a threshold to be compared with the gradation value in the raster data, and for pixels in the raster data whose gradation value is K or more, the threshold set is used as a reference for a threshold to be compared with the gradation value in the raster data.

[0020] an eleventh aspect of the present invention is related to the ninth aspect of the present invention, wherein the printing method further includes: an input step of receiving input data including a plurality of objects; a gradation value conversion step of generating intermediate data by converting gradation values ​​of the plurality of objects; and a rasterization processing step of generating the raster data by performing a rasterization process on the intermediate data, wherein the plurality of objects are classified into first type objects and second type objects in accordance with predetermined conditions, wherein a maximum value of the gradation value is M and K is a predetermined gradation value, the threshold matrix set is associated with a first gradation range that is a range of gradation values ​​from 0 to (K-1), and the threshold set is associated with a second gradation range that is a range of gradation values ​​from K to M, and in the gradation value conversion step, the gradation values ​​of the first type objects of the plurality of objects are converted to gradation values ​​within the first gradation range, and the gradation values ​​of the second type objects of the plurality of objects are converted to gradation values ​​within the second gradation range.

[0021] A twelfth aspect of the present invention is the method according to the eleventh aspect of the present invention, wherein the plurality of objects include at least image objects and line drawing objects, the image objects are classified into the first type of object, and the line drawing objects are classified into the second type of object.

[0022] A thirteenth aspect of the present invention is related to any one of the ninth to twelfth aspects of the present invention, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is N threshold matrices, and the at least one threshold included in the threshold set is N thresholds.

[0023] A fourteenth aspect of the present invention is the thirteenth aspect of the present invention, wherein in the halftone processing step, for pixels in the raster data whose gradation value is (M-N) or less, the threshold matrix set is used as a reference for a threshold to be compared with the gradation value in the raster data, and for pixels in the raster data whose gradation value is (M-N+1) or more, the threshold set is used as a reference for a threshold to be compared with the gradation value in the raster data.

[0024] A fifteenth aspect of the present invention is a print control program for controlling the operation of a printing device having a plurality of nozzles that eject ink onto a printing medium, the program causing a computer included in the printing device to execute: a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds that are to be compared with gradation values ​​of a plurality of pixels included in raster data for printing, the plurality of thresholds being arranged two-dimensionally; and a threshold set including at least one threshold that is to be compared with gradation values ​​of each pixel included in the raster data; a halftone processing step for generating halftone image data based on a result of comparing the gradation values ​​of each pixel included in the raster data with the thresholds; and an ink ejection control step for controlling the ejection of ink from the plurality of nozzles based on the halftone image data; and in the halftone processing step, when generating the halftone image data, the reference destination of the threshold to be compared with the gradation value in the raster data is switched between the threshold matrix set and the threshold set for each pixel depending on the magnitude of the gradation value in the raster data.

[0025] According to a first aspect of the present invention, a printing device that prints by ejecting ink from nozzles is provided with a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds arranged two-dimensionally, and a threshold set including at least one threshold, as data to be compared with the gradation value of each pixel during halftoning. During halftoning, the reference source for the data (threshold) to be compared with the gradation value of each pixel is switched between the threshold matrix set and the threshold set depending on the magnitude of the gradation value of each pixel. In this manner, the reference source is switched based on the gradation value of each pixel. That is, the reference source is switched without adding special data for switching the reference source to the raster data for printing. Therefore, there is no need to expand the data bandwidth to achieve multiscreening. Furthermore, the data provided for comparison with the gradation value of each pixel is not a plurality of threshold matrix sets, but a threshold matrix set and a threshold set. Therefore, multiscreening can be achieved by simply making slight modifications to a general configuration that does not employ multiscreening. As described above, multiscreening in a printing device can be achieved with a simpler circuit than conventional devices.

[0026] According to a second aspect of the present invention, for high-gradation pixels, the data (thresholds) compared with the gradation values ​​of the pixels during halftoning are referenced to a threshold set rather than a threshold matrix set. This allows the gradation values ​​of pixels in high-gradation regions to be compared with a fixed threshold. As a result, the uniformity of the contours of line drawing objects is improved, thereby improving the print quality of high-gradation regions.

[0027] According to a third aspect of the present invention, when multiple drop sizes are available, it is possible to eject ink from each nozzle at an appropriate drop size both in an area where halftone processing has been performed with reference to a threshold matrix set and in an area where halftone processing has been performed with reference to a threshold set.

[0028] According to a fourth aspect of the present invention, it is possible to associate the N maximum gradation values ​​with N drop sizes. For example, if three drop sizes (S, M, and L) are provided and the maximum gradation value is 255, it is possible to associate the gradation value "255" with the L size, the gradation value "254" with the M size, and the gradation value "253" with the S size. This allows ink to be ejected in high gradation regions at a specific drop size corresponding to the gradation value, improving print quality in high gradation regions.

[0029] According to the fifth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0030] According to a sixth aspect of the present invention, it is possible to use different reference data (threshold values) for comparing the gradation values ​​of each pixel for image data and line drawing data, thereby enabling ink to be ejected from each nozzle in an appropriate drop size in both image and line drawing areas.

[0031] According to the seventh aspect of the present invention, the same effects as those of the third aspect of the present invention can be obtained.

[0032] According to the eighth aspect of the present invention, the same effects as those of the fourth aspect of the present invention can be obtained.

[0033] According to the ninth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0034] According to the tenth aspect of the present invention, the same effects as those of the second aspect of the present invention can be obtained.

[0035] According to the eleventh aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0036] According to the twelfth aspect of the present invention, the same effects as those of the sixth aspect of the present invention can be obtained.

[0037] According to the thirteenth aspect of the present invention, the same effects as those of the third aspect of the present invention can be obtained.

[0038] According to the fourteenth aspect of the present invention, the same effects as those of the fourth aspect of the present invention can be obtained.

[0039] According to the fifteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0040] 1 is a diagram illustrating the overall configuration of a printing system according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an example of the configuration of an inkjet printing device in the embodiment. FIG. 3 is a plan view illustrating an example of the configuration of a recording unit in the embodiment. FIG. 4 is a diagram for explaining an example of an arrangement of nozzles in the embodiment. FIG. 5 is a block diagram illustrating the hardware configuration of a print control device in the embodiment. FIG. 6 is a block diagram illustrating a schematic functional configuration of a control unit implemented by execution of a print control program in the print control device in the embodiment. FIG. 7 is a block diagram illustrating a configuration related to halftone processing in the embodiment. FIG. 8 is a diagram for explaining a reference destination of data (threshold values) to be compared with the gradation values ​​of each pixel in the embodiment. FIG. 9 is a diagram for explaining halftone processing for pixels included in a line image region in the embodiment. FIG. 10 is a diagram for explaining halftone processing for pixels included in an image region in the embodiment. FIG. 11 is a block diagram illustrating the functional configuration of a print data generating device in the embodiment. FIG. 12 is a diagram for explaining gradation value conversion of a first type object in the embodiment. FIG. 13 is a diagram for explaining gradation value conversion of a second type object in the embodiment. FIG. 14 is a flowchart illustrating the overall procedure for print output in the embodiment. FIG. 15 is a block diagram illustrating a configuration related to halftone processing in a modified example of the embodiment. FIG. 16 is a block diagram illustrating a conventional general configuration related to halftone processing. FIG. 17 is a diagram illustrating an example of a threshold matrix for S size. FIG. 18 is a diagram illustrating an example of a threshold matrix for M size. FIG. 19 is a diagram illustrating an example of a threshold matrix for L size. FIG. 1 is a block diagram showing a conventional configuration for realizing multi-screening.

[0041] An embodiment of the present invention will be described below with reference to the accompanying drawings. In the following embodiment (including modified examples), it is assumed that the minimum gradation value is 0 and the maximum gradation value is 255.

[0042] 1. Overall Configuration of the Printing System FIG. 1 is a diagram illustrating the overall configuration of a printing system according to one embodiment of the present invention. This printing system comprises an inkjet printing device 10 and a print data generating device 30. The inkjet printing device 10 and the print data generating device 30 are connected to each other via a LAN 4. The print data generating device 30 generates raster data for printing by performing rasterization processing on input data. In this embodiment, it is assumed that the input data is a PDF file. The raster data generated by the print data generating device 30 is transferred to the inkjet printing device 10 via the LAN 4. The inkjet printing device 10 comprises a printing machine main body 200 and a print control device 100 that controls the operation of the printing machine main body 200. The inkjet printing device 10 outputs a print image on printing paper as a printing medium based on the raster data transferred from the print data generating device 30, without using a printing plate. The present invention can also be applied when a printing medium other than printing paper (e.g., film) is used.

[0043] 2. Configuration of the Main Body of the Inkjet Printing Apparatus> Fig. 2 is a schematic diagram showing an example configuration of the inkjet printing apparatus 10. As described above, the inkjet printing apparatus 10 is made up of the print control device 100 and the printing machine main body 200.

[0044] The printing machine main body 200 includes a paper feed section 21 that supplies printing paper 5 to the printing mechanism 22, the printing mechanism 22 that prints on the printing paper 5, and a paper winding section 28 that winds up the printing paper 5 into a roll after printing.

[0045] The printing mechanism 22 includes a first drive roller 221 for transporting the printing paper 5 inside, a plurality of support rollers 222 for transporting the printing paper 5 inside the printing mechanism 22, a recording unit 223 for recording a print image on the printing paper 5, a drying mechanism 224 for drying the printing paper 5 on which the print image has been recorded, an inline scanner 225 as an imaging device for capturing an image of the print image recorded on the printing paper 5 by the recording unit 223, and a second drive roller 226 for outputting the printing paper 5 from inside the printing mechanism 22. The image data obtained by the inline scanner 225 capturing the print image is sent to the print control device 100. The recording unit 223 is made up of a K head unit 23K that ejects K (black) ink, a C head unit 23C that ejects C (cyan) ink, an M head unit 23M that ejects M (magenta) ink, and a Y head unit 23Y that ejects Y (yellow) ink. In the following description, when the color of ink ejected from a head unit is not to be distinguished, the head unit will be denoted by the reference numeral 23.

[0046] FIG. 3 is a plan view showing an example of the configuration of the recording unit 223. As shown in FIG. 3, the recording unit 223 is composed of a K-color head unit 23K, a C-color head unit 23C, an M-color head unit 23M, and a Y-color head unit 23Y, which are arranged in a row in the transport direction (sub-scanning direction) of the printing paper 5. Each head unit 23 is composed of a plurality of ink ejection heads (print heads) 231 arranged in a staggered pattern. Each ink ejection head 231 includes a number of nozzles (not shown in FIG. 3) that eject ink. Each nozzle of the ink ejection head 231 included in the K-color head unit 23K ejects K-color ink, each nozzle of the ink ejection head 231 included in the C-color head unit 23C ejects C-color ink, each nozzle of the ink ejection head 231 included in the M-color head unit 23M ejects M-color ink, and each nozzle of the ink ejection head 231 included in the Y-color head unit 23Y ejects Y-color ink.

[0047] FIG. 4 is a diagram illustrating an example of the arrangement of nozzles in the ink ejection head 231. The ink ejection head 231 shown in FIG. 4 includes four rows of nozzle groups, each consisting of a plurality of nozzles arranged in the main scanning direction (a direction perpendicular to the transport direction of the printing paper 5). The portion labeled 41 in FIG. 4 schematically shows the landing position on the printing paper 5 of ink ejected from each nozzle. The nozzles in the ink ejection head 231 are arranged so that the landing positions of ink ejected from the nozzles in the first row of nozzle groups, the second row of nozzle groups, the third row of nozzle groups, and the fourth row of nozzle groups are all different from one another. For example, the landing positions of ink ejected from the nozzles in the first row of nozzle groups are between the landing positions of ink ejected from the nozzles in the third row of nozzle groups and the landing positions of ink ejected from the nozzles in the fourth row of nozzle groups. In the example shown in Figure 4, the landing position 42 of ink ejected from the nozzle marked with the symbol 26(p) is a position between the landing position 43 of ink ejected from the nozzle marked with the symbol 26(q) and the landing position 44 of ink ejected from the nozzle marked with the symbol 26(r).

[0048] The configurations shown in FIGS. 2 to 4 are merely examples, and the specific configurations of the printing mechanism 22, the recording unit 223, and the ink ejection head 231 are not particularly limited.

[0049] <3. Print Control Device> <3.1 Hardware Configuration> Figure 5 is a block diagram showing the hardware configuration of the print control device 100. As shown in Figure 5, the print control device 100 includes a main body 110, an auxiliary storage device 121, an optical disk drive 122, a display unit 123, a keyboard 124, and a mouse 125. The main body 110 includes a CPU 111, a memory 112, a first disk interface unit 113, a second disk interface unit 114, a display control unit 115, an input interface unit 116, and a communication interface unit 117. The CPU 111, the memory 112, the first disk interface unit 113, the second disk interface unit 114, the display control unit 115, the input interface unit 116, and the communication interface unit 117 are connected to one another via a system bus. The auxiliary storage device 121 is connected to the first disk interface unit 113. The optical disk drive 122 is connected to the second disk interface unit 114. The display unit (display device) 123 is connected to the display control unit 115. A keyboard 124 and a mouse 125 are connected to the input interface unit 116. The printing machine main body 200 is connected to the communication interface unit 117 via a communication cable. The communication interface unit 117 is also connected to the LAN 4. The auxiliary storage device 121 is a magnetic disk device or the like. An optical disk 19, which is a computer-readable recording medium such as a CD-ROM or DVD-ROM, is inserted into the optical disk drive 122. The display unit 123 is a liquid crystal display or the like. The display unit 123 is used to display information desired by the operator. The keyboard 124 and mouse 125 are used by the operator to input instructions to this print control device 100.

[0050] The auxiliary storage device 121 stores a print control program 13 (a program for controlling the execution of printing processing by the printer main body 200). The CPU 111 reads the print control program 13 stored in the auxiliary storage device 121 into the memory 112 and executes it to realize various functions of the print control device 100. The memory 112 includes RAM (random access memory) and ROM (read only memory). The memory 112 functions as a work area for the CPU 111 to execute the print control program 13 stored in the auxiliary storage device 121. The print control program 13 is provided by being stored on the computer-readable recording medium (non-transitory recording medium). That is, a user, for example, purchases an optical disk 19 as a recording medium for the print control program 13, inserts it into the optical disk drive 122, reads the print control program 13 from the optical disk 19, and installs it in the auxiliary storage device 121.

[0051] In the example shown in FIG. 5 , the print control device 100 is provided with only one CPU 111 as a processor, but this is not limited to this. A configuration using multiple processors, such as a configuration using multiple CPUs, can also be adopted. In addition to the CPU 111, other processors such as an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor) can also be adopted. A combination of multiple types of processors can also be used. For example, with regard to the internal components of the control unit 50 (described later) (see FIG. 6 ), some components and the remaining components can be implemented by different processors. Furthermore, a configuration including an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) can also be adopted.

[0052] 3.2 Configuration of the Control Unit FIG. 6 is a block diagram illustrating the general functional configuration of the control unit 50, which is implemented by the print control program 13 executed by the print control device 100. As shown in FIG. 6, the control unit 50 generally includes a transport control unit 51, a halftone processing unit 52, an ink ejection control unit 53, a drying control unit 54, and an imaging control unit 55. The transport control unit 51 controls the speed at which the transport mechanism 29 transports the print paper 5 (transport speed). In this embodiment, the transport mechanism 29 is implemented by the paper feed unit 21, the first drive roller 221, the multiple support rollers 222, the second drive roller 226, and the paper winding unit 28 (see FIG. 2). The halftone processing unit 52 performs halftone processing on the printing raster data 64 sent from the print data generation device 30 to generate halftone image data (halftone dot data) 65, which includes information indicating the ink drop size corresponding to each pixel. In this embodiment, three ink drop sizes (S size, M size, and L size) are provided. In other words, each of the multiple nozzles included in the recording unit 223 is capable of ejecting ink in three different drop sizes. The halftone processing unit 52 will be described in detail later. The ink ejection control unit 53 controls the ejection of ink from each nozzle of each ink ejection head 231 included in each head unit 23 that makes up the recording unit 223 based on halftone image data 65. For example, the ink ejection timing and drop size are controlled. The drying control unit 54 controls the temperature (drying temperature) used by the drying mechanism 224 to dry the printing paper 5 after printing. The imaging control unit 55 controls the timing of capturing an image of the print image by the inline scanner 225.

[0053] Generally, RGB format data is sent from the print data generating device 30 to the print control device 100 as raster data 64 for printing, and color conversion processing is performed in the print control device 100 to convert the RGB format data into CMYK format data before halftone processing is performed. However, since the color conversion processing is not directly related to the present invention, a description of the color conversion processing will be omitted.

[0054] <4. Halftone Processing> Next, the halftone processing of this embodiment will be described in detail. FIG. 7 is a block diagram showing the configuration related to the halftone processing. The halftone processing unit 52 is composed of a reference destination switching unit 521 and a drop size determination unit 522. As can be seen from FIG. 7, a threshold matrix set 710 is provided, which includes a threshold matrix 71(S) for S size, a threshold matrix 71(M) for M size, and a threshold matrix 71(L) for L size, and a threshold set 720 is provided, which includes a threshold matrix 72(S) for S size, a threshold matrix 72(M) for M size, and a threshold matrix 72(L) for L size. As in the conventional case, each threshold matrix 71 constituting the threshold matrix set 710 includes a plurality of thresholds arranged two-dimensionally for comparison with the gradation values ​​of a plurality of pixels included in the raster data 64 for printing. The threshold matrix set 710 and the threshold set 720 are stored, for example, in the auxiliary storage device 121 and are read into the memory 112 and referenced when print output is performed. As described above, in the conventional configuration shown in FIG. 20, two types of threshold matrix sets are provided to realize multi-screening, whereas in this embodiment, one type of threshold matrix set 710 and one type of threshold set 720 are provided to realize multi-screening.

[0055] Based on the gradation value of each pixel in the raster data 64, the reference destination switching unit 521 switches the reference destination for the data (threshold values) to be compared with the gradation value of each pixel between the threshold matrix set 710 and the threshold set 720. In this embodiment, the reference destination is switched depending on whether each pixel is included in an image area or a line drawing area (including a character area). In this regard, pixels in the raster data 64 with a gradation value of 252 or less are considered to be included in an image area, and pixels in the raster data 64 with a gradation value of 253 or more are considered to be included in a line drawing area. The threshold matrix set 710 is referenced when processing pixels included in an image area, and the threshold set 720 is referenced when processing pixels included in a line drawing area. That is, as shown in FIG. 8 , the reference destination switching unit 521 sets the reference destination to the threshold matrix set 710 when processing pixels in the raster data 64 with a gradation value of 252 or less, and sets the reference destination to the threshold set 720 when processing pixels in the raster data 64 with a gradation value of 253 or more.

[0056] The drop size determination unit 522 determines a drop size corresponding to each pixel based on the gradation values ​​in the raster data 64 (in other words, determines the data value of each pixel in the halftone image data 65, which is output data). With regard to the processing of each pixel, if the reference destination switching unit 521 has set the threshold matrix set 710 as the reference destination, the drop size determination unit 522 compares the gradation values ​​in the raster data 64 with the corresponding threshold values ​​in each of the three threshold matrices 71 included in the threshold matrix set 710. If the reference destination switching unit 521 has set the threshold set 720 as the reference destination, the drop size determination unit 522 compares the gradation values ​​in the raster data 64 with the three threshold values ​​72 included in the threshold set 720. The data value of each pixel in the halftone image data 65 is determined based on the comparison result.

[0057] As described above, pixels in the raster data 64 with a gradation value of 253 or greater are considered to be included in a line drawing area, and the threshold set 720 is referenced when processing pixels included in the line drawing area. With regard to the threshold set 720, the threshold 72 (S) for the S size is set to "253," the threshold 72 (M) for the M size is set to "254," and the threshold 72 (L) for the L size is set to "255." With the thresholds set in this manner, as shown in Fig. 9, the drop size is set to S for pixels in the raster data 64 with a gradation value of 253, the drop size is set to M for pixels in the raster data 64 with a gradation value of 254, and the drop size is set to L for pixels in the raster data 64 with a gradation value of 255.

[0058] As described above, pixels in the raster data 64 with a gradation value of 252 or less are considered to be included in the image area, and the threshold matrix set 710 is referenced when processing the pixels included in the image area. The three threshold matrices 71 that make up the threshold matrix set 710 (threshold matrix 71(S) for S size, threshold matrix 71(M) for M size, and threshold matrix 71(L) for L size) can be substantially the same as those used conventionally (see FIGS. 17 to 19) (however, the maximum gradation value is 252). By determining the drop size using the three threshold matrices 71, the relationship between the print rate for S size, the print rate for M size, and the print rate for L size for each gradation value becomes, for example, as shown in FIG. 10. Note that in FIG. 10, the solid line labeled 81 represents the print rate for S size, the thick dotted line labeled 82 represents the print rate for M size, and the thick solid line labeled 83 represents the print rate for L size.

[0059] As described above, in this embodiment, during halftone processing, the reference destination for the data (threshold values) to be compared with the gradation value of each pixel is switched between the threshold matrix set 710 and the threshold set 720 depending on the magnitude of the gradation value.

[0060] According to this embodiment, for pixels in the raster data 64 whose gradation value is 252 or less, the halftone processing unit 52 references the threshold matrix set 710 as the threshold to be compared with the gradation value, and for pixels in the raster data 64 whose gradation value is 253 or more, the halftone processing unit 52 references the threshold set 720 as the threshold to be compared with the gradation value. However, the present invention is not limited to this. With K as a predetermined gradation value, the halftone processing unit 52 may reference the threshold matrix set 710 as the threshold to be compared with the gradation value for pixels in the raster data 64 whose gradation value is (K-1) or less, and may reference the threshold set 720 as the threshold to be compared with the gradation value for pixels in the raster data 64 whose gradation value is K or more.

[0061] Furthermore, in this embodiment, three ink drop sizes are provided, and the maximum gradation value is 255, but the present invention is not limited to this. In a case where N ink drop sizes (N is a natural number) are provided, and the maximum gradation value is M, the halftone processing unit 52 may refer to the threshold matrix set 710 as the threshold to be compared with the gradation value of pixels in the raster data 64 whose gradation value is (M-N) or less, and may refer to the threshold set 720 as the threshold to be compared with the gradation value of pixels in the raster data 64 whose gradation value is (M-N+1) or more.

[0062] 5. Configuration of the Print Data Generating Device In the halftone processing unit 52, pixels in the raster data 64 with a gradation value of 252 or less are considered to be included in the image area, and pixels in the raster data 64 with a gradation value of 253 or more are considered to be included in the line drawing area. However, with regard to the input data (PDF file) provided to the print data generating device 30, both line drawing data and image data can have gradation values ​​of 0 to 255. Therefore, for image data, values ​​of 0 to 255 must be converted to values ​​of 0 to 252, and for line drawing data, values ​​of 0 to 255 must be converted to values ​​of 253 to 255. Therefore, in this embodiment, the print data generating device 30 performs a process of converting the gradation values ​​of the input data. The configuration of the print data generating device 30 will be described below. Note that in this embodiment, the print data generating device 30 realizes a printing raster data generating device.

[0063] The hardware configuration of the print data generating device 30 is almost the same as the hardware configuration (see FIG. 5) of the print control device 100. However, unlike the print control device 100, the communication interface unit 117 is not connected to the printing machine main body 200 via a communication cable, and the auxiliary storage device 121 stores a program for generating raster data 64 for printing from input data.

[0064] Fig. 11 is a block diagram showing the functional configuration of the print data generating device 30. As shown in Fig. 11, the print data generating device 30 functionally includes a PDF analysis unit 310, a tone value conversion unit 320, and a rasterization processing unit 330. Note that Fig. 11 shows only the components related to the present invention.

[0065] The PDF analysis unit 310 analyzes the internal data that constitutes the PDF file as the submitted data 61. This identifies the type of each of the multiple objects included in the submitted data 61. The PDF analysis unit 310 outputs a PDF analysis result 62 that includes object type information that indicates the type of each object.

[0066] The gradation value conversion unit 320 generates intermediate data 63 by converting the gradation values ​​of the multiple objects included in the submitted data 61 based on the object type information included in the PDF analysis result 62. In this embodiment, the multiple objects included in the submitted data 61 are classified into first-type objects and second-type objects according to predetermined conditions. For example, image objects and background objects are classified as first-type objects, and line drawing objects and text objects are classified as second-type objects. The gradation value conversion unit 320 converts the gradation values ​​in the submitted data 61 of the first-type objects to values ​​between 0 and 252. This conversion is performed so that the relationship between the gradation values ​​before and after conversion is, for example, as shown in FIG. 12 . The gradation value conversion unit 320 converts the gradation values ​​in the submitted data 61 of the second-type objects included in the submitted data 61 to values ​​between 253 and 255. The conversion is performed so that the relationship between the tone values ​​before conversion and the tone values ​​after conversion is as shown in FIG. 13, for example.

[0067] Generally speaking, where the maximum value of the gradation value is M and K is a predetermined gradation value, the threshold matrix set 710 can be associated with a first gradation range, which is a range of gradation values ​​from 0 to (K-1), and the threshold set 720 can be associated with a second gradation range, which is a range of gradation values ​​from K to M. Under this premise, the gradation value conversion unit 320 generates intermediate data 63 by converting the gradation values ​​of first-type objects of the multiple objects included in the submitted data 61 into gradation values ​​within the first gradation range, and by converting the gradation values ​​of second-type objects of the multiple objects included in the submitted data 61 into gradation values ​​within the second gradation range.

[0068] The rasterization processing unit 330 performs rasterization processing on the intermediate data 63 by referring to the PDF analysis result 62. This generates raster data 64 for printing. The raster data 64 is transferred from the print data generating device 30 to the print control device 100.

[0069] 6. Print Output Procedure The overall print output procedure (printing method) in this printing system will be described with reference to the flowchart shown in Fig. 14. First, a PDF file including a plurality of objects is provided to the print data generating device 30 as input data 61 (step S10).

[0070] Next, in the print data generating device 30, the gradation value conversion unit 320 generates intermediate data 63 by converting the gradation values ​​of the multiple objects included in the PDF file, which is the submitted data 61 (step S20). In this step S20, as described above, the gradation values ​​of the first type objects are converted to values ​​within the range of 0 to 252, and the gradation values ​​of the second type objects are converted to values ​​within the range of 253 to 255.

[0071] Next, in the print data generating device 30, the rasterization processing unit 330 performs a rasterization process on the intermediate data 63 generated in step S20 to generate raster data 64 for printing (step S30). The raster data 64 is then transferred from the print data generating device 30 to the print control device 100 in the inkjet printing device 10 (step S40).

[0072] Thereafter, in the print control device 100, the halftone processing unit 52 generates halftone image data 65 based on the results of comparing the gradation values ​​of each pixel included in the raster data 64 with the threshold value (step S50). That is, halftone processing is performed. At this time, for each pixel, the reference destination for the threshold value to be compared with the gradation value in the raster data 64 is switched between the threshold matrix set 710 and the threshold set 720 depending on the magnitude of the gradation value in the raster data 64. Specifically, as described above, the threshold matrix set 710 is referenced when processing pixels in the raster data 64 whose gradation value is 252 or less, and the threshold set 720 is referenced when processing pixels in the raster data 64 whose gradation value is 253 or more.

[0073] After the halftone process is completed, the ink ejection control unit 53 controls the ejection of ink from each nozzle included in the recording unit 223 based on the halftone image data 65 generated in step S50 (step S60), thereby recording a print image on the printing paper 5 (step S70).

[0074] In this embodiment, step S10 realizes the manuscript submission step, step S20 realizes the tone value conversion step, step S30 realizes the rasterization processing step, step S50 realizes the halftone processing step, and step S60 realizes the ink ejection control step.

[0075] 7. Effects According to this embodiment, the inkjet printing device 10, which has three drop sizes for ejecting ink from nozzles, is provided with a threshold matrix set 710 including three threshold matrices 71 each consisting of a plurality of thresholds arranged two-dimensionally, and a threshold set 720 including three thresholds 72 as data for comparison with the gradation values ​​of each pixel during halftoning. During halftoning, the reference data (thresholds) for comparison with the gradation values ​​of each pixel is switched between the threshold matrix set 710 and the threshold set 720 depending on the gradation value of each pixel. In this manner, the reference data is switched based on the gradation values ​​of each pixel. That is, the reference data is switched without adding special data for switching the reference data, such as the attribute data 982 shown in FIG. 20 , to the printing raster data 64. This eliminates the need to expand the data bandwidth to achieve multi-screening. Furthermore, the data provided for comparison with the gradation values ​​of pixels in line image regions is not a threshold matrix set, but a threshold value for each drop size. Therefore, multi-screening can be performed by simply making slight modifications to a general configuration that does not employ multi-screening. As described above, according to this embodiment, multi-screening in the inkjet printing device 10 can be achieved with simpler circuitry than in the past.

[0076] Furthermore, according to this embodiment, in each line image area, the nozzles eject ink in a fixed drop size, either S size, M size, or L size. Therefore, when recording a single line image on the printing paper 5, for example, the ink ejected from the nozzles does not contain a mixture of multiple drop sizes. In other words, when recording a line image on the printing paper 5, the nozzles eject ink in a fixed drop size. This improves the print quality of the line image area.

[0077] 8. Modifications In the above embodiment, three types (three levels) of sizes were provided as the drop sizes of ink ejected from each nozzle. Correspondingly, the threshold matrix set 710 was made up of three threshold matrices 71, and the threshold set 720 was made up of three thresholds 72. However, the present invention is not limited to this. The present invention can also be applied to cases where only one type of size is provided as the drop size of ink ejected from each nozzle. Therefore, as a modification of the above embodiment, a case where only one type of size is provided as the drop size of ink ejected from each nozzle will be described.

[0078] 15 is a block diagram showing the configuration related to halftone processing in this modified example. As in the above embodiment, halftone processing unit 52 is made up of reference destination switching unit 521 and drop size determination unit 522. In this modified example, the data value of each pixel in halftone image data 65 generated by drop size determination unit 522 indicates whether or not ink is to be ejected.

[0079] In this modification, because there is only one type of drop size, threshold matrix set 710 is made up of one threshold matrix 71, and threshold set 720 is made up of one threshold 72. In this modification, too, when processing pixels included in an image area, reference destination switching unit 521 sets the reference destination to threshold matrix set 710, and when processing pixels included in a line drawing area, reference destination switching unit 521 sets the reference destination to threshold set 720. Then, with regard to processing of each pixel, if the reference destination is set to threshold matrix set 710, drop size determination unit 522 compares the gradation value in raster data 64 with the corresponding threshold in threshold matrix 71, and if the reference destination is set to threshold set 720, drop size determination unit 522 compares the gradation value in raster data 64 with threshold 72. The data value of each pixel in halftone image data 65 is determined based on the comparison result.

[0080] According to this modification, the reference data to be compared with the gradation value of each pixel during halftoning is switched between the threshold matrix 71 and the threshold 72 depending on the magnitude of the gradation value of each pixel. With this configuration, as with the above embodiment, there is no need to expand the data bandwidth to achieve multi-screening, and multi-screening can be performed with just a slight modification to a general configuration that does not employ multi-screening. As described above, this modification also makes it possible to achieve multi-screening in the inkjet printing device 10 with simpler circuitry than conventional configurations.

[0081] 9. Others The present invention is not limited to the above-described embodiment (including modifications) and can be implemented in various modifications without departing from the spirit of the present invention. For example, the above-described embodiment (including modifications) employs an inkjet printing apparatus 10 that performs color printing. However, the present invention is not limited to this, and an inkjet printing apparatus that performs monochrome printing may also be employed. Furthermore, the above-described embodiment (including modifications) employs an inkjet printing apparatus 10 that uses aqueous ink. However, the present invention is not limited to this, and an inkjet printing apparatus that uses UV ink (ultraviolet-curable ink), such as an inkjet printing apparatus for label printing, may also be employed. In this case, an ultraviolet irradiation mechanism that cures the UV ink on the printing paper 5 by ultraviolet irradiation, instead of the drying mechanism 224, is provided inside the printing mechanism 22 (see FIG. 2 ).

[0082] 10... Inkjet printing device 30... Print data generating device 50... Control unit 52... Halftone processing unit 61... Submitted data 64... Raster data 65... Halftone image data 71... Threshold matrix 72... Threshold 100... Print control device 200... Printer main body 310... PDF analysis unit 320... Tone value conversion unit 330... Rasterization processing unit 521... Reference destination switching unit 522... Drop size determination unit 710... Threshold matrix set 720... Threshold set

Claims

1. A printing device having a plurality of nozzles that prints by ejecting ink from the plurality of nozzles onto a printing medium, comprising: a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds arranged in a two-dimensional manner for comparing with the gradation values ​​of a plurality of pixels included in raster data for printing; a threshold set including at least one threshold for comparing with the gradation values ​​of each pixel included in the raster data; and a halftone processing unit that generates halftone image data based on the result of comparing the gradation values ​​of each pixel included in the raster data with the thresholds, wherein when generating the halftone image data, the halftone processing unit switches, for each pixel, the reference destination of the threshold to be compared with the gradation value in the raster data between the threshold matrix set and the threshold set depending on the magnitude of the gradation value in the raster data.

2. The printing device described in claim 1, wherein K is a predetermined gradation value, and the halftone processing unit references the threshold matrix set as a reference for thresholds to be compared with the gradation value in the raster data for pixels in the raster data whose gradation value is (K-1) or less, and references the threshold set as a reference for thresholds to be compared with the gradation value in the raster data for pixels in the raster data whose gradation value is K or more.

3. A printing device as described in claim 1 or 2, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is a matrix of N thresholds, and the at least one threshold included in the threshold set is a matrix of N thresholds.

4. A printing device as described in claim 3, wherein the maximum gradation value is M, and the halftone processing unit references the threshold matrix set as a reference for thresholds to be compared with the gradation value in the raster data for pixels in the raster data whose gradation value is (M-N) or less, and references the threshold set as a reference for thresholds to be compared with the gradation value in the raster data for pixels in the raster data whose gradation value is (M-N+1) or more.

5. A printing system including the printing device of claim 1 and a printing raster data generating device that generates the raster data based on input data including a plurality of objects, wherein the plurality of objects are classified into a first type object and a second type object in accordance with a predetermined condition, a maximum value of gradation value is M and K is a predetermined gradation value, the threshold matrix set corresponds to a first gradation range that is a range of gradation values ​​from 0 to (K-1), and the threshold set corresponds to a second gradation range that is a range of gradation values ​​from K to M, the printing raster data generating device comprising: a gradation value conversion section that generates intermediate data by converting the gradation values ​​of the first type objects of the plurality of objects to gradation values ​​within the first gradation range and converting the gradation values ​​of the second type objects of the plurality of objects to gradation values ​​within the second gradation range, and a rasterization processing section that generates the raster data by performing a rasterization process on the intermediate data.

6. The printing system of claim 5, wherein the plurality of objects includes at least image objects and line drawing objects, the image objects being classified into the first type of object, and the line drawing objects being classified into the second type of object.

7. A printing system as described in claim 5 or 6, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is a matrix of N thresholds, and the at least one threshold included in the threshold set is a matrix of N thresholds.

8. The printing system described in claim 7, wherein the halftone processing unit uses the threshold matrix set as a reference for thresholds to be compared with the gradation values ​​in the raster data for pixels whose gradation values ​​in the raster data are (M-N) or less, and uses the threshold set as a reference for thresholds to be compared with the gradation values ​​in the raster data for pixels whose gradation values ​​in the raster data are (M-N+1) or more.

9. A printing method using a printing device having a plurality of nozzles that eject ink onto a printing medium, comprising: a halftone processing step of generating halftone image data based on a result of comparing the gradation value of each pixel included in raster data for printing with a threshold; and an ink ejection control step of controlling the ejection of ink from the plurality of nozzles based on the halftone image data, wherein the printing device comprises: a threshold matrix set including at least one threshold matrix consisting of a plurality of thresholds arranged in a two-dimensional shape for comparing with the gradation values ​​of a plurality of pixels included in the raster data; and a threshold set including at least one threshold for comparing with the gradation value of each pixel included in the raster data, wherein in the halftone processing step, when generating the halftone image data, the reference destination of the threshold to be compared with the gradation value in the raster data is switched between the threshold matrix set and the threshold set depending on the magnitude of the gradation value in the raster data.

10. A printing method as described in claim 9, wherein in the halftone processing step, for pixels in the raster data whose gradation value is (K-1) or less, the threshold matrix set is used as a reference for the threshold to be compared with the gradation value in the raster data, where K is a predetermined gradation value, and for pixels in the raster data whose gradation value is K or more, the threshold set is used as a reference for the threshold to be compared with the gradation value in the raster data.

11. A printing method according to claim 9, further comprising: an input step of receiving input data including a plurality of objects; a gradation value conversion step of generating intermediate data by converting gradation values ​​of the plurality of objects; and a rasterization processing step of generating the raster data by performing a rasterization process on the intermediate data, wherein the plurality of objects are classified into a first type object and a second type object in accordance with a predetermined condition, a maximum gradation value is M and K is a predetermined gradation value, the threshold matrix set is associated with a first gradation range which is a range of gradation values ​​from 0 to (K-1), and the threshold set is associated with a second gradation range which is a range of gradation values ​​from K to M, and in the gradation value conversion step, the gradation values ​​of the first type objects of the plurality of objects are converted to gradation values ​​within the first gradation range, and the gradation values ​​of the second type objects of the plurality of objects are converted to gradation values ​​within the second gradation range.

12. The printing method of claim 11, wherein the plurality of objects includes at least image objects and line drawing objects, the image objects being classified into the first type of object, and the line drawing objects being classified into the second type of object.

13. A printing method described in any one of claims 9 to 12, wherein each of the plurality of nozzles is capable of ejecting ink in N different drop sizes, the at least one threshold matrix included in the threshold matrix set is a matrix of N thresholds, and the at least one threshold included in the threshold set is a matrix of N thresholds.

14. A printing method as described in claim 13, wherein in the halftone processing step, for pixels in the raster data whose gradation value is (M-N) or less, the threshold matrix set is used as a reference for the threshold to be compared with the gradation value in the raster data, and for pixels in the raster data whose gradation value is (M-N+1) or more, the threshold set is used as a reference for the threshold to be compared with the gradation value in the raster data.

15. A print control program for controlling the operation of a printing device having a plurality of nozzles that eject ink onto a printing medium, the print control program causing a computer included in the printing device to execute a halftone processing step for generating halftone image data based on a result of comparing the gradation values ​​of each pixel included in the raster data with the thresholds, the halftone processing step generating halftone image data based on a result of comparing the gradation values ​​of each pixel included in the raster data with the thresholds, and an ink ejection control step for controlling the ejection of ink from the plurality of nozzles based on the halftone image data, wherein in the halftone processing step, when generating the halftone image data, the reference destination of the threshold to be compared with the gradation value in the raster data is switched between the threshold matrix set and the threshold set for each pixel depending on the magnitude of the gradation value in the raster data.

Images