Printing apparatus, control method of printing apparatus, computer program product, and storage medium

Abstract

The invention discloses a printing apparatus, a control method of the printing apparatus, a computer program product, and a storage medium. The printing apparatus is operable to form dots on a print medium by repeating a forward scan and a reverse scan, and includes a generation unit configured to generate first data of a dot pattern to be formed in the forward scan and second data of the dot pattern to be formed in the reverse scan. The generation unit generates the first data and the second data such that a dot pattern to be formed in the forward scan and a dot pattern to be formed in the reverse scan have a blue noise characteristic or a green noise characteristic as spatial frequency characteristics, and the number of points to be formed in the forward scan and the number of points to be formed in the reverse scan are substantially the same.

Description

Technical Field

[0001] The present invention relates to a printing device and a control method of the printing device, and more particularly to a printing technology for forming dots on a printing medium by repeating forward scanning and reverse scanning. Background Art

[0002] There is known a printing apparatus that prints an image by repeating a printing scan in which a print head having a nozzle array in which a plurality of nozzles for ejecting ink is arranged is moved relative to a unit area on a printing medium while ejecting ink, and conveying a printing medium in a direction perpendicular to the printing scan. There is known a so-called multi-pass printing method in which an image is formed by performing a plurality of scans on a unit area in such a printing apparatus. In such a multi-pass printing method, print data to be used for printing is generally generated by quantizing multi-valued data corresponding to an image to be printed to generate quantized data and then allocating the quantized data to a plurality of scans.

[0003] Japanese Patent No. 4519876 mentions that when an image generated using a quantization pattern is distributed among multiple scans and printed, printing substantially the same amount of image data in each pass is important for image quality; and as a method for achieving this, a pass mask (passmask) designed for distributing image data among multiple scans and printing the image data is mentioned.

[0004] In addition, Japanese Patent Laid-Open No. 2007-15359 describes that, as a result of distributing images generated by quantization patterns in multiple scans, by increasing the dispersion of each of images printed in the forward direction and images printed in the reverse direction, image quality degradation that occurs when forward and reverse printing position deviations occur can be reduced.

[0005] However, in the configuration shown in Japanese Patent No. 4519876, as a method of replacing a multi-value input image with printable binary data as image data, binary data corresponding to an m×n (m and n are positive integers, and at least one of m and n is an integer greater than or equal to 2) area (hereinafter referred to as an index pattern) is used. In addition, a mask pattern is designed so that a group of print permission areas in units of integer multiples of the above-mentioned m×n area is arranged non-periodically. In this way, the amount of image data printed in each pass is made substantially the same. However, when the image data is binarized using a combination of fixed patterns such as m×n, the number of images to be printed forward and reverse is not necessarily the same. For example, Japanese Patent Laid-Open No. 9-46522 discloses a method of expressing the tone of an input image having five levels of tone values ​​by printing or not printing four dots in a 2×2 area. In addition, the same reference discloses a method of preparing multiple patterns of dot arrangement in a 2×2 area for the same tone value and arranging multiple dot arrangement patterns sequentially or randomly. Regarding the 2×2 index pattern, assuming that the image to be rasterized using the level 4 pattern (so-called solid image) has a 100% duty cycle, the image rasterized using only the level 1 pattern has a 25% duty cycle. Therefore, in an image with a duty cycle to be rasterized using an index pattern of a single level, it is considered that the pattern arrangement makes it easy to align the corresponding amounts of image data to be printed forward and reverse to be substantially the same. However, in images of other duty ratios, index patterns of different levels are mixed, so it is difficult to align the amounts of image data in the forward and reverse directions. In addition, when forward and reverse printing is performed according to a specific fixed interval knockout pattern, it is necessary to arrange the index pattern in consideration of the fixed interval knockout pattern, so it is considered that it will be more difficult to make the corresponding amounts of image data to be printed forward and reverse the same. In addition, if the amount of data to be printed forward and reverse cannot be made the same, it is expected that the dispersion of each pass will naturally deteriorate.

[0006] Additionally, however, the configuration described in Japanese Patent Laid-Open No. 2007-15359 does not mention generating inter-color quantized data, and does not describe a method for reducing image quality degradation caused by inter-color printing position deviation occurring when inter-color printing pixels are exclusively arranged with particular consideration given to granularity. Summary of the invention

[0007] The present invention provides a technique for suppressing image degradation caused by interaction between inks in a pass and improving the granularity of an image to be printed.

[0008] Furthermore, the present invention provides a technique for suppressing image quality degradation even when a print position deviation occurs between a print scan in a forward direction and a print scan in a reverse direction or between colors.

[0009] According to a first aspect of the present invention, a printing device is provided, which is capable of operating to form dots on a printing medium by repeating forward scanning and reverse scanning, and the printing device includes: a generating unit, which is configured to generate first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein the generating unit generates the first data and the second data so that the dot pattern to be formed in the forward scan and the dot pattern to be formed in the reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and the number of dots to be formed in the forward scan and the number of dots to be formed in the reverse scan are substantially the same.

[0010] According to a second aspect of the present invention, a control method for a printing device is provided, wherein the printing device is operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the control method comprising: generating first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein, in the generation, the first data and the second data are generated so that the dot pattern to be formed in the forward scan and the dot pattern to be formed in the reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and the number of dots to be formed in the forward scan and the number of dots to be formed in the reverse scan are substantially the same.

[0011] According to a third aspect of the present invention, a printing device is provided, which is capable of operating to form dots on a printing medium by repeating forward scanning and reverse scanning, and the printing device includes: a generating unit, which is configured to generate first data of a dot pattern to be formed in the forward scanning and second data of a dot pattern to be formed in the reverse scanning, wherein the generating unit generates the first data and the second data so that the dot pattern to be formed in the forward scanning and the dot pattern to be formed in the reverse scanning have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and the generating unit makes the dot pattern to be formed in the forward scanning and the dot pattern to be formed in the reverse scanning different between colors.

[0012] According to a fourth aspect of the present invention, a control method for a printing device is provided, wherein the printing device is operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the control method comprising: generating first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein, in the generation, the first data and the second data are generated so that the dot pattern to be formed in the forward scan and the dot pattern to be formed in the reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and wherein in the generation, the dot pattern to be formed in the forward scan and the dot pattern to be formed in the reverse scan are different between colors.

[0013] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is an external perspective view showing an example of the appearance of the inkjet printing apparatus.

[0015] Figure 2 It is a cross-sectional view of the interior of the printing device in the direction in which the carriage prints the medium.

[0016] Figure 3 is a diagram showing a configuration example of the print head 3 .

[0017] Figure 4 is a block diagram showing an example of a hardware configuration in a printing apparatus.

[0018] Figure 5 A diagram for explaining a dither method using a dither pattern.

[0019] Figure 6 This is a diagram for explaining multi-pass printing.

[0020] Figure 7 This is a diagram for explaining column thinning printing.

[0021] Figure 8 This is a diagram for explaining block thinning printing.

[0022] Fig. 9 A diagram for explaining a method of creating dither corresponding to column thinning printing.

[0023] Fig. 10A It is a flowchart of the printing operation of the printing device.

[0024] Fig. 10B is a flow chart of a method for creating a jitter sync mask.

[0025] Fig.11 It is a diagram for explaining the effects of the first embodiment.

[0026] Fig.12 is a diagram for explaining a method of creating a dither pattern to be applied to block thinning printing.

[0027] Fig.13 is a diagram showing a configuration example of an index pattern.

[0028] Fig.14 It is a diagram for explaining a state in which a multi-value input image has been binarized using an index pattern and a rasterization table.

[0029] Fig.15is a diagram for explaining a method of creating a synthetic dither pattern in a system using an index pattern and a rasterization table.

[0030] Fig.16 is a diagram showing an example of a pattern for creating a synthetic dither pattern in a system using an index pattern and a rasterization table.

[0031] Fig.17 : is a diagram showing a synthetic dither pattern created using a pattern for creating a synthetic dither pattern in a system using an index pattern and a rasterization table.

[0032] Fig.18 is a block diagram showing an example of a hardware configuration in a printing apparatus.

[0033] Fig.19A 2 is a schematic diagram showing a configuration example of the quantization pattern 60 .

[0034] Fig.19B is an enlarged view of a specific area 60 a in the quantization pattern 60 .

[0035] Fig. 20A is a diagram showing a quantized input image 401 .

[0036] Fig. 20B is a diagram showing division patterns 402a and 402b.

[0037] Fig. 20C is a diagram showing the first print data 403 .

[0038] Fig.20D is a diagram showing the second print data 404 .

[0039] Fig.21 is a diagram for explaining a method of creating a dither pattern.

[0040] Fig.22A is a block diagram showing an example of a functional configuration for performing inter-color processing in a printing apparatus.

[0041] Fig. 22B yes Fig.22A Flowchart of the operation of each functional unit.

[0042] Fig. 22C This is a flowchart of the overall process related to the generation of print data by the printing device.

[0043] Fig.23 : is a diagram showing the threshold value range determined as "ink is to be ejected".

[0044] Fig.24 is a diagram showing an example of print data.

[0045] Fig.25It is a diagram for explaining the change in image quality caused by the deviation of the printing position.

[0046] Fig.26 A diagram for explaining print data and changes in image quality caused by print position deviation.

[0047] Fig. 27 is a diagram showing index patterns according to the fourth embodiment.

[0048] Fig.28 is a diagram showing a synthesized dither pattern according to the fourth embodiment.

[0049] Fig.29 is a diagram showing an example of a pass mask for a forward direction according to the fourth embodiment.

[0050] Fig. 30A is a diagram showing quantization of an input image according to a synthetic dither pattern.

[0051] Fig. 30B is a diagram showing the superposition of a synthetic dither pattern and a pass mask.

[0052] Fig. 30C is a diagram showing a rasterization table created based on a synthetic dither pattern and a pass mask. DETAILED DESCRIPTION

[0053] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention. A plurality of features are described in the embodiments, but are not limited to inventions requiring all such features, and a plurality of such features may be appropriately combined. In addition, in the accompanying drawings, the same reference numerals are given to the same or similar configurations, and redundant descriptions thereof are omitted.

[0054] [First embodiment]

[0055] In this specification, it is assumed that "printing" not only means a case where meaningful information such as characters and graphics are formed, but also broadly means a case where an image, design or pattern, etc. is formed on a printing medium regardless of whether they are meaningful or meaningless, or a case where the medium is processed. In addition, it is not important whether "printing" is expressed so as to be perceptible by human vision.

[0056] It is assumed that the "print medium" not only means paper used in a general printing device but also broadly means a substance that can accept ink such as cloth, plastic film, metal plate, glass, ceramic, wood, and leather.

[0057] In addition, "ink" should be interpreted broadly as in the definition of "print" above, and is assumed to mean a liquid applied to a print medium to form an image, design, pattern, etc., to process the print medium, or to process the ink. Examples of ink processing include solidifying or insolubilizing colorants in the ink applied to the print medium.

[0058] First, refer to Figure 1 The external perspective view of FIG. 1 depicts an example of the appearance of an inkjet printing apparatus as an example of a printing apparatus according to the present embodiment. Figure 1 As shown, an inkjet printing apparatus (hereinafter referred to as a printing apparatus) is provided with a print head 3 that performs printing by ejecting ink according to an inkjet method. A driving force generated by a carriage motor M1 is transmitted from a transmission mechanism 4 to a carriage 2 provided with the print head 3, and the carriage 2 moves forward and backward in the direction of an arrow X as a main scanning direction (forward and reverse scanning). Together with the forward and reverse scanning, a printing medium P such as printing paper is fed and conveyed to a printing position, for example, by a feeding mechanism 5, and printing is performed by ejecting ink from the print head 3 on the printing medium P to the printing position.

[0059] Figure 2 2 is a cross-sectional view of the interior of the printing device in the direction of conveying the print medium of the carriage. Two pairs of conveying rollers are arranged near the print head 3 in the Y direction. One pair of conveying rollers is a pair of feed rollers arranged on the upstream side of the print head 3 in the Y direction (upstream side in the conveying direction), and is composed of a feed roller 25 and a pinch roller 26. The other pair of conveying rollers is a pair of discharge rollers arranged on the downstream side of the print head 3 in the Y direction (downstream side in the conveying direction), and is composed of a discharge roller 28 and a pinch roller 29. The feed roller 25 and the discharge roller 28 are formed by a member that is continuous in the X direction, and the pinch rollers 26 and 29 are formed to be divided in the X direction. While the print medium P is held between the pair of feed rollers and the pair of discharge rollers, the print medium P is conveyed to the downstream side in the Y direction by rotating the feed roller 25 and the discharge roller 28 between the scans of the above-mentioned print head 3.

[0060] In addition to the print head 3, an ink tank 6 for containing ink to be supplied to the print head 3 is mounted on the carriage 2 of the printing apparatus. The print head 3 and the ink tank 6 are attachable to and detachable from the carriage 2.

[0061] Figure 1 The printing apparatus shown is capable of color printing, and therefore the carriage 2 is provided with four ink tanks containing magenta (M), cyan (C), yellow (Y), and black (K) inks, respectively. Figure 32 is a diagram showing an example of the configuration of the print head 3. In the print head 3, four nozzle arrays 31M, 31C, 31Y and 31Bk capable of ejecting magenta, cyan, yellow and black inks respectively are arranged in this order in the X direction. In these nozzle arrays, 768 nozzles for ejecting each ink are arranged at a density of 1200dpi. Therefore, the nozzle array has a length corresponding to 768 pixels in the arrangement direction. The nozzles at positions adjacent to each other in the arrangement direction are arranged at positions deviated from each other in a direction perpendicular to the arrangement direction. The carriage 2 and the print head 3 are configured so that the joint surfaces of the two components are properly in contact, so that the required electrical connection can be achieved and maintained. The print head 3 applies energy according to the print signal to selectively eject ink from a plurality of nozzles and print.

[0062] like Figure 1 As shown, the carriage 2 is connected to a portion of the drive belt 7 of the transmission mechanism 4 for transmitting the driving force of the carriage motor M1, and is slidably guided and supported along the guide shaft 13 in the direction of the arrow X. Therefore, the carriage 2 is scanned in the forward and reverse directions along the guide shaft 13 by the forward rotation and reverse rotation of the carriage motor M1. In addition, a scale 11 for indicating the position of the carriage 2 in the main scanning direction (the direction of the arrow X) of the carriage 2 is provided.

[0063] Furthermore, in the printing apparatus, a platen (not shown) is disposed so as to face the ejection orifice face where the ejection orifices of the print head 3 are formed. By ejecting ink from the print head 3 while the carriage 2 provided with the print head 3 is scanned forward and reversely, printing is performed over the entire width of the printing medium P conveyed on the platen.

[0064] Next, we will refer to Figure 4 The block diagram depicts an example of a hardware configuration in a printing device. Figure 4 The configuration related to the following description is shown, and not all the hardware configurations in the printing apparatus are shown.

[0065] The controller 600 controls the operation of the entire printing apparatus. The controller 600 includes a RAM 604 , an ASIC 603 , a system bus 605 , a ROM 602 , an MPU 601 , and an A / D converter 606 .

[0066] The MPU 601 executes various processes using computer programs and data stored in the RAM 604, performs operation control of the entire printing apparatus, and executes or controls various processes described as to be performed by the printing apparatus.

[0067] The ROM 602 stores setting data of the printing apparatus, computer programs and data related to activation of the printing apparatus, and computer programs and data related to basic operations of the printing apparatus, etc. The ROM 602 also stores computer programs and data for causing the MPU 601 to execute or control various processes described as processes performed by the printing apparatus.

[0068] The A / D converter 606 performs A / D conversion on various analog signals (a signal indicating the position of a printing medium, a signal indicating the temperature inside the printing apparatus, etc.), and notifies the MPU 601 and an application specific integrated circuit (ASIC) 603 and the like of these signals.

[0069] The RAM 604 includes areas such as an area for storing computer programs and data loaded from the ROM 602, an area for storing data received from the host device 610, and a work area used when the MPU 601 performs various processes. That is, the RAM 604 can provide various areas as appropriate.

[0070] The ASIC 603 generates control signals for controlling the carriage motor M1 , for controlling the transport motor M2 , and for controlling the print head 3 .

[0071] Based on the “control signal for controlling the carriage motor M1 ” generated by the ASIC 603 , the carriage motor driver 640 drives and controls the carriage motor M1 .

[0072] The conveyance motor driver 642 drives and controls the conveyance motor M2 based on the “control signal for controlling the conveyance motor M2” generated by the ASIC 603. The conveyance motor M2 controls the conveyance of the printing medium by operating the conveyance roller pair described above by drive control.

[0073] The print head 3 performs ink ejection control based on a “control signal for controlling the print head 3 ” generated by the ASIC 603 . The MPU 601 , the RAM 604 , and the ASIC 603 are connected to a system bus 605 .

[0074] The printing device can perform data communication with a host device 610 as an external device of the printing device via an interface 611. For example, the printing device can receive images and commands transmitted from the host device 610 via the interface 611, or transmit a status signal indicating a status in the printing device to the host device 610 via the interface 611.

[0075] Next, we will refer to Figure 6 Describes multi-pass printing. Figure 6 In FIG. 1 , a print head and a print pattern are schematically shown. Figure 6 In the following, the case where the print head 1001 including 16 nozzles is used will be described. Figure 6 As shown, 16 nozzles included in the print head 1001 are divided into four groups, namely the first group, the second group, the third group and the fourth group, and therefore, each group includes four nozzles. Then, a corresponding mask pattern 1002 is assigned to each group. The area where the nozzle can print (printing permission position) is indicated by a black rectangle in the mask pattern 1002. The dot patterns printed by the respective groups have a complementary relationship to each other, and when these patterns are superimposed, the printing of the area corresponding to the 4×4 area is completed.

[0076] In the first round of printing scan (first printing scan), as shown in time series 1003, a 4×4 dot pattern corresponding to the mask pattern 1002 corresponding to the first group is printed by the first group.

[0077] In the second round of printing scan (second printing scan), as shown in time series 1004, the second group further prints a 4×4 dot pattern corresponding to the mask pattern 1002 corresponding to the second group on the previously printed pattern (the printing result is the top 4×4 pattern in time series 1004).

[0078] In the third round of printing scan (third printing scan), as shown in time series 1005, the third group further prints a 4×4 dot pattern corresponding to the mask pattern 1002 corresponding to the third group on the previously printed pattern (the printing result is the top 4×4 pattern in time series 1005).

[0079] In the fourth round of printing scan (the fourth printing scan), as shown in time series 1006, the fourth group further prints a 4×4 dot pattern corresponding to the mask pattern 1002 corresponding to the fourth group on the previously printed pattern (the printing result is the top 4×4 pattern in time series 1006).

[0080] Therefore, the image is completed by repeating the print scan. Each time the print scan is completed, the print media is Figure 6 The width of one group is conveyed in the direction of the arrow in FIG. Therefore, in the same area (area corresponding to the width of each group) of the print medium, the image is completed using four print scans.

[0081] By adopting this multi-pass printing, image defects such as the above-mentioned streaks and uneven density can be reduced. This is because even if there are variations in the ejection characteristics and delivery amount of each nozzle, these characteristics will be dispersed over a wide range and become less noticeable. Figure 6In the embodiment, four-pass multi-pass printing in which four print scans are performed on the same image area has been described as an example, but the multi-pass printing is not limited thereto. Two-pass multi-pass printing in which an image is completed in two print scans or multi-pass printing in which an image is completed in five or more print scans may be adopted. The greater the number of multi-passes, the wider the dispersion range of the variation of the ejection characteristics and the conveying amount of each nozzle, and thus a smoother image can be obtained.

[0082] Many methods have been proposed and disclosed for so-called binarization processing, which is a process of converting multi-valued tone data indicating the density of an image to be printed into "ejection data indicating whether ink droplets (dots) are printed on a printing medium", and basically any method may be used. For example, a method using a method such as Figure 5 A dithering method using a dithering pattern shown in FIG. 1 is a method for generating a dithering image using a dithering pattern. In the dithering method, the pixel value of the input image is compared with the threshold value of the dithering pattern, and ejection data indicating that "for pixels having pixel values ​​greater than or equal to the threshold value, ink droplets are printed (on) on the print medium, and for pixels having pixel values ​​less than the threshold value, ink droplets are not printed (off) on the print medium" is generated. The dithering pattern can be appropriately set according to the resolution of the print, and if the resolution of the input image is 1200 dpi and the print resolution is also 1200 dpi, the input image can be directly converted into ejection data (binary data). On the other hand, in view of the trend that the print resolution is becoming larger and larger and the number of ink color types of the printing device is increasing, there is a situation where the burden is too great to perform overall image processing of all colors at the same resolution as the print resolution. For example, in recent years, a printing system has been provided in which main image processing is performed in a host device at a resolution lower than the print resolution, and then a quantization process is performed for reducing the tone value to several levels for each pixel, and then a final binarization process is performed in the printing device. In this case, since the tone of one pixel output by the host device is expressed using a plurality of levels of density, it can be said that this is a good method for applications where tonality is considered important, such as photographic image quality.

[0083] Several proposals and practices have been made for methods of converting multi-value density data of several levels into binary data. As an example thereof, Japanese Patent Laid-Open No. 9-46522 discloses a method of expressing the tone of an input image having five levels of tone values ​​by printing or not printing four dots in a 2×2 area. In addition, the same reference discloses a method of preparing multiple patterns of dot arrangement in a 2×2 area for the same tone value and arranging multiple dot arrangement patterns sequentially or randomly. Doing so prevents the dot arrangement patterns of each tone from being fixed, so that the pseudo contour when pseudo halftone processing is performed and the so-called "sweeping phenomenon" that appears at the edge portion of the image are reduced. It is also described that the averaging of the use of multiple printing elements arranged in the print head has an impact. As described above, the method of converting multi-value density data of several levels included in low-resolution pixels into binary data of higher resolution is a useful technology in an inkjet printing device for printing fine dots with high definition. Next, two types of fixed interval elimination printing, namely "column interval elimination printing" and "block interval elimination printing", will be described below.

[0084] (Column thinning printing)

[0085] Figure 7 Column thinning printing is a schematic diagram for explaining column thinning printing. Column thinning printing is a printing method that prints binary data arranged in the main scanning direction while thinning at predetermined intervals, and here, the case of alternately printing data of every other column is shown. In multi-pass printing, binary data as image data is converted into masked binary data masked using a pass mask. Figure 7 As shown, among the masked binary data, the forward printing data is printed in the forward direction as data (dots) of even (E) columns, and the reverse printing data is printed in the reverse direction as data (dots) of odd (O) columns.

[0086] When performing column thinning printing, the drive frequency for ejecting ink from each nozzle can be set according to the frequency of printing columns. As a result, the main scanning speed whose upper limit is limited by the drive frequency can be further increased, and even in the same multi-pass printing, when column thinning printing is used in combination, the image can be output at a higher speed.

[0087] (Block thinning printing)

[0088] Figure 8 Schematic diagram for explaining block thinning printing. Block thinning is a printing method based on the drive control of the inkjet head. In multi-pass printing, among the image data (masked binary data) that has passed through the pass mask, the image data located in the forward direction is printed. Figure 8The image of the black portion in the image is printed in the reverse direction, and the image of the white portion is printed in the reverse direction.

[0089] In this embodiment, a case where the above-mentioned column thinning printing is performed as fixed thinning printing will be described. In order to perform, it is important to create a dither pattern corresponding to the printing method. Fig. 9 Describes the method of creating dithering corresponding to column thinning printing. First, as Fig. 9 As shown, two dither patterns (dither pattern A and dither pattern B) having blue noise or green noise characteristics are prepared. Then, according to a fixed interval elimination pattern (column interval elimination pattern, which is a pattern indicating column interval elimination), the threshold of dither pattern A is assigned to (arranged in) the black line portion (column E), and the threshold of dither pattern B is assigned to (arranged in) the white line portion (column O) to create a synthetic dither pattern. Here, it is assumed that the original dither pattern A and dither pattern B have a size of 256 elements in the X direction and 256 elements in the Y direction. For each of these 256×256=65536 elements, a threshold of any value among 256 values ​​in the range of 0 to 255 is assigned, and the number of thresholds of the same value is equal, where each threshold is assigned 256 instances. Although the size of the dither pattern can be made smaller than 256×256, a certain size is necessary to ensure the dispersion of the threshold, that is, to design a dither pattern having a blue noise characteristic or a green noise characteristic. The size of the resulting composite dither pattern is 512 components in the X direction (which is twice as large as the original dither pattern) and 256 elements in the Y direction (which is the same as the original dither pattern).

[0090] If the synthetic dither pattern thus created is used, for example, in all images in which the pixel values ​​have a single value from 0 to 255 and the graininess is obvious, when the image is converted into print data according to the binarization process of the input image previously described, the amount of ejection data (dots) to be printed in the forward direction and the amount of ejection data (dots) to be printed in the reverse direction can be made substantially the same. That is, due to the method of creating the synthetic dither pattern, naturally, the E column printed in the forward direction and the O column printed in the reverse direction always include the same number of threshold values ​​of the same value. Therefore, the amount of ejection data of the E column and the O column (that is, the number of dots formed in the forward scan and the number of dots formed in the reverse scan) is made equal by the binarization process.

[0091] Will be based on Fig. 10AThe flowchart of describes the printing operation of the printing device. In step S1001, the MPU 601 obtains the multi-value input image to be printed from the host device 610 via the interface 611, for example. In step S1002, the MPU 601 generates a synthetic dither pattern as described above. In step S1003, the MPU 601 performs binarization processing on the multi-value input image using the synthetic dither pattern to generate ejection data (first data) of the dot pattern to be printed in the forward scan and ejection data (second data) of the dot pattern to be printed in the reverse scan. The first data is the data of the pixel group binarized using the threshold value of the E column in the synthetic dither pattern, and the second data is the data of the pixel group binarized using the threshold value of the O column in the synthetic dither pattern.

[0092] The ASIC 603 controls the carriage motor driver 640, the transport motor driver 642, and the print head 3. Thus, in forward scanning, a dot pattern is formed on the printing medium based on the first data, and in reverse scanning, a dot pattern is formed on the printing medium based on the second data.

[0093] Therefore, in a printing device that forms dots on a printing medium by repeating forward scanning and reverse scanning, first data of a dot pattern to be formed in the forward scanning and second data of a dot pattern to be formed in the reverse scanning are generated. In this generation, the first data and the second data are generated so that the dot pattern to be formed in each of the forward scanning and the reverse scanning has a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic. The number of dots to be formed in the forward scanning and the number of dots to be formed in the reverse scanning are substantially the same.

[0094] Furthermore, by designing a pass mask synchronized with the created synthetic dither pattern, it is possible to achieve an effect of making the forward and reverse ejection data amounts substantially the same, and to improve the dispersion of ejection data for each pass. Next, this will be described in detail.

[0095] Will be based on Fig. 10B The flowchart of describes a method for creating a pass mask synchronized with a dither pattern (hereinafter referred to as a dither synchronization mask). In step S101, the MPU 601 obtains the following file (hereinafter referred to as a mask shape file) as an input file, which includes such as Fig. 9 The “information required for creating a dither synchronization mask” is shown, which includes a dither pattern with a threshold value from 0 to 255, the number of passes, and the usage rate of the nozzles of the head to be used for each pass. Here, since the threshold value of the dither pattern to be used is 0 to 255, the multi-value input image is an input image in which the pixel value has any value (8-bit value) from 0 to 255.

[0096] The method of obtaining the mask shape file by the MPU 601 is not limited to a specific obtaining method. For example, the MPU 601 may load the mask shape file from the ROM 602 into the RAM 604 , or may download the mask shape file from the host device 610 into the RAM 604 via the interface 611 .

[0097] In step S102, the MPU 601 assumes one of the unselected levels (256 levels from 0 to 255, or 256 tones if the levels are expressed in tones, since the pixel values ​​of the multi-value input image are 8-bit values) as the selected level and generates a seed file for the selected level.

[0098] Here, the case where the selected level is level 1 is described as an example. The MPU 601 generates an image (binary image) in which the level 1 image (an image composed of pixels whose pixel values ​​in the input multi-valued image are 1) has been binarized using a dither pattern (synthetic dither pattern). The binary image is a binary image indicating that pixels corresponding to elements whose threshold values ​​are 1 or less in the dither pattern are turned on and pixels corresponding to elements whose threshold values ​​are greater than 1 in the dither pattern are turned off. Next, the MPU 601 divides the binary image into corresponding "images to be printed with the number of passes specified in the mask shape file" (seed files). The MPU 601 assumes one of the unselected passes in all passes as the selected pass, and creates an image in which points are arranged using random numbers in the selected pass as a seed file.

[0099] In this way, the MPU 601 creates a seed file of the selected pass for the selected level. In addition, the important point here is that, with respect to the pass mask, as described above, the feed amount and the vertical size (size in the Y direction) of the print medium need to be consistent. Therefore, the vertical size of the dither pattern used when creating the dither synchronization mask is also made consistent with the feed amount of the print medium in each pass in multi-pass printing.

[0100] Naturally, in the state of the seed file, the dispersion of each pass is not guaranteed, therefore, in step S103, the MPU 601 generates the result of optimizing the seed file of the selected pass generated for the selected level as a jitter synchronization pass mask, and the optimizing calculation is used to print each pass with good dispersion using a repulsive potential method such as the method disclosed in Japanese Patent 4280732.

[0101] In step S104, the MPU 601 determines whether all passes have been selected as selected passes (whether the process of step S103 has been performed on all passes). As a result of this determination, if all passes have been selected as selected passes, the process proceeds to step S106, and if there are still passes that have not been selected as selected passes, the process proceeds to step S105.

[0102] In step S105, the MPU 601 selects one unselected pass among all the passes as the selected pass. Then, the process proceeds to step S103, and the process of step S103 is performed on the selected pass.

[0103] In step S106, the MPU 601 determines whether all the levels have been selected as the selected levels (whether the processing of step S102 and the processing of step S103 have been performed on all the levels). As a result of this determination, if all the levels have been selected as the selected levels, the process proceeds to step S108, and if there are still levels that have not been selected as the selected levels, the process proceeds to step S107.

[0104] In step S107, the MPU 601 selects one unselected class among all the classes as the selected class. Then, the process proceeds to step S102, and the process from step S102 is performed for the selected class.

[0105] In step S108, the MPU 601 generates a jitter synchronization pass mask file generated for all levels as a mask file, and outputs the generated mask file. The output destination of the mask file is not limited to a specific output destination. For example, the MPU 601 can transmit the mask file to the host device 610 via the interface 611, or can output the mask file to the RAM 604.

[0106] Here, the processing of step S103 is usually carried out sequentially from a lower level to a higher level. Of course, it is possible to process in the opposite way from a higher level to a lower level; however, since the level at which the optimization calculation has been completed once is fixed, the degree of freedom of calculating the arrangement with good dispersion decreases as the processing proceeds, and in principle, the dispersion deteriorates. Therefore, it is desirable to start the calculation from a low level where the granularity is easily noticed. In addition, in actual processing, instead of starting from level 1, the concept of "increment" is used, for example, 256 tones are divided into 32 parts (32 increments) to form groups, each group has 8 levels, and a seed file to which the levels of each group have been added is created, and by optimizing the file, the problem of deterioration of dispersion in the second half of the level as the processing proceeds described above can be alleviated and good optimization of dispersion can be achieved on average for all levels. Alternatively, a method such as the following can also be envisioned: the "increment" from the low tone to the middle tone, which is considered to affect the granularity, is made finer (the value becomes larger) and the "increment" to the high tone is made coarser (the value becomes smaller). By introducing such a concept, it is also possible to weight the dispersion of each level.

[0107] By using the dither synchronization mask created in this way, it is possible to perform printing that controls an image binarized using a corresponding dither pattern for each pass. For example, when designing a four-pass mask, it is also possible to design the mask so that a low-tone image up to level 20 is printed in two passes. However, it goes without saying that the dispersion of the dither pattern itself used for mask design is necessary in order to perform printing with high dispersion for each pass. For this purpose, the dither pattern is generally designed to have blue noise or green noise characteristics. On the other hand, in order to ensure dispersion in reciprocating printing and dispersion of each pass, it is important to first disperse the print pixels themselves between forward scanning and reverse scanning, and to make the number of print pixels substantially the same.

[0108] However, there is no guarantee that the amount of data printed in the forward and reverse directions will be the same in such general dithering (usually different). In contrast, in the present embodiment, the dispersion of reciprocating printing and the dispersion of each pass are achieved by creating a composite dither pattern combining two dither patterns having blue noise or green noise characteristics and designing a mask synchronized with the composite dither pattern.

[0109] Fig.11 The upper side shows the result of verification by using a six-pass dither synchronization pass mask created for general blue noise dither (a dither pattern corresponding to blue noise) using the above method to simulate the state of printed images from the first pass to the sixth pass when printing a specific monochrome image.

[0110] Fig.11The lower side of shows the result of verification by simulating the state of the printed image of each pass from the first pass to the sixth pass when printing a specific monochrome image using the six-pass dither synchronization pass mask created by the creation method according to the present embodiment. Fig.11 As shown, it can be seen that the dispersion is very different in the second half.

[0111] It has been found that the dispersibility of each pass greatly affects the final image quality. Although the ink droplets ejected onto the print medium are absorbed by the print medium, their speed varies according to the characteristics of the print medium. If the ink droplets of the subsequent pass come into contact with the ink droplets ejected in the previous pass before the ink droplets ejected in the previous pass are completely absorbed, image quality defects such as beading will result. General inkjet-compatible print media quickly promote the absorption of ink by applying a special process called a receiving layer on the surface. However, it is believed that the dispersibility of each pass is particularly important in anti-absorption and non-absorption media such as print media for offset printing and media for marking (e.g., PVC), and the present embodiment is advantageous in improving the image quality in such print media.

[0112] [Second embodiment]

[0113] In this embodiment, the fixed-interval thinning pattern when creating a composite dither pattern from two dither patterns is different from the first embodiment. As described above, various fixed-interval thinning patterns can be considered based on the constraints of the entire system, and Fig.12 The block thinning patterns shown are examples.

[0114] As in the first embodiment, the threshold of dither pattern A is assigned to the black portion of the block thinning pattern (printed in the forward scan), and the threshold of dither pattern B is assigned to the white portion (printed in the reverse scan), thereby creating a single composite dither pattern. A pass mask synchronized with the created composite dither pattern can be created using a method similar to that of the first embodiment.

[0115] The fixed thinning pattern used to create the synthetic dither pattern is not limited to the patterns described in the first and second embodiments. If the printing method of data to be printed forward and reverse is determined to be a fixed pattern due to system constraints, the concepts of various embodiments including this embodiment can be applied.

[0116] [Third embodiment]

[0117] In the first and second embodiments, descriptions have been given assuming that the resolution of the multi-value input image and the resolution of the print image are equal (for example, both are 1200 dpi). That is, it is assumed that the multi-value input image (8 bits) is directly converted into a binary print image using a dither pattern.

[0118] In contrast, in this embodiment, a case where the resolution of a multivalue input image and the resolution of a print image are different will be described (as an example, a case where the resolution of the multivalue input image is 600 dpi and the resolution of the print image is 1200 dpi).

[0119] At this time, as a method of converting a 600-dpi multi-value input image into a 1200-dpi binary image using a dither pattern, a method of expressing the tone of an input image having five levels of tone values ​​by printing or not printing four dots in a 2×2 area as described in the aforementioned Japanese Patent Laid-Open No. 9-46522 is used.

[0120] Fig.13 A 2×2 pattern (hereinafter referred to as an index pattern) is shown. Fig.13 Index patterns of level 1 to level 4 are shown, but an all-blank index pattern is assumed to be an index pattern of level 0, and index patterns of level 0 to level 4 are used (there are five levels of tone values).

[0121] Fig.13 The rasterization table is shown, which is a table for regularly determining the arrangement of index patterns according to the rasterization table, rather than randomly selecting index patterns of the same level. In short, if an image with a duty cycle of 100% is solid fill (an image binarized using an index pattern of level 4), an image with a duty cycle of 25% is binarized by arranging index patterns of level 1 according to the rasterization table. This state is as shown in FIG. Fig.14 That is, the rasterization table is spread out in a tiled form, and the index pattern of the level that matches its number is selected. This is the rasterization table.

[0122] When binarization is performed by combining a dither pattern (synthetic dither pattern) and an index pattern, first, the threshold of the dither pattern is divided into the number of levels of the index pattern. For example, if the threshold of the dither pattern is 256 tones and the number of levels of the index pattern to be used is 4, the threshold is divided into 4 groups, each group having 256 / 4=64 thresholds. That is, the group with a threshold of 0 to 63 is group 1, the group with a threshold of 64 to 127 is group 2, the group with a threshold of 128 to 191 is group 3, and the group with a threshold of 192 to 255 is group 4. When compared with the threshold of the dither pattern, the index pattern to be selected is determined by which group the pixel value of the multi-value input image belongs to. If the pixel value of the multi-value input image belongs to group 1, the level 1 index pattern is selected. If the pixel value of the multi-value input image belongs to group 2, the level 2 index pattern is selected. If the pixel value of the multi-value input image belongs to group 3, the level 3 index pattern is selected. If the pixel values ​​of the multivalued input image belong to group 4, the level 4 index pattern is selected. Then, the multivalued input image is binarized based on the selected index pattern to generate a print image (first data and second data).

[0123] A method of creating a synthetic dither pattern to be used in a system in which a multi-value input image is binarized by combining a dither pattern and an index pattern in this manner will be described.

[0124] In the first and second embodiments, since the print image is uniquely determined using the dither pattern, it is sufficient to create a single synthetic dither pattern by assigning two dither patterns to the fixed-interval culling pattern. However, in the case of an index pattern, when reciprocating printing is ultimately performed at a fixed-interval culling degree, it is necessary to arrange the index patterns so that the number of print images for the forward and reverse directions is substantially the same (as a result, design a rasterization table). Here, the rasterization table is designed so that a 25% duty cycle multi-value input image that is binarized using only the previously described level 1 index pattern satisfies the above condition. When the image is binarized using the level 1 index pattern, the level 1 index pattern is assigned to the image. Fig.14 The rasterization table shown in the figure is used to perform column thinning printing on a 25% duty cycle image that is binarized. Fig.15 As shown, the number of dots (data amount) of forward printing is the same as the number of dots (data amount) of reverse printing.

[0125] Based on this point, as a pattern for creating a synthetic dither pattern in this embodiment, Fig.16 As shown, use Fig.15 The forward printing data (or reverse printing data) is sufficient. Fig.17As shown, the threshold value of the dither pattern A for which dispersion is ensured is assigned to the black portion of the pattern for creating the composite dither pattern, and the threshold value of the dither pattern B for which dispersion is ensured is similarly assigned to the white portion of the pattern for creating the composite dither, to create a single composite dither pattern. The dispersion of the index pattern at the time of forward and reverse division is determined by the design of the original dither pattern A and the dither pattern B and the rasterization table. Therefore, in the design of the rasterization table, it is important that, in addition to the forward and reverse image data amounts being substantially equal, the images at the time of forward and reverse division are in a state where the dispersion is as high as possible. So far, the pattern for creating the composite dither pattern has been described assuming column interval culling printing, but the concept remains the same even when the fixed interval culling used for printing is block interval culling.

[0126] The vertical size (size in the Y direction) of the dither pattern to be used here will be mentioned. In both the first embodiment and the second embodiment, the vertical size of the dither pattern is consistent with the feed amount of the print medium per pass in the multi-pass printing. However, in the present embodiment, a multi-value input image is converted into a binary image using a 2×2 index pattern, and therefore the vertical size of the dither pattern to be used is half (1 / 2) of the print medium per pass. That is, the vertical size of the synthetic dither pattern is the same as the value obtained by dividing the feed amount of the print medium per pass in the multi-pass printing by the vertical size (size in the Y direction) of the index pattern.

[0127] The method for creating the jitter sync pass mask is the same as previously described, and Fig. 10B In step S102, binarization is performed when creating seed files for each level by combining synthetic dithering, index patterns and rasterization tables, and subsequent processing remains unchanged.

[0128] [Fourth embodiment]

[0129] In this embodiment, a method of first designing a synthetic dither pattern and a pass mask if the resolution of the multi-value input image and the resolution of the print image are different will be described. Up to the third embodiment, a method of using a fixed-interval thinning pattern has been described. However, the fixed-interval thinning pattern cannot be used in a print mode with fewer passes such as two passes. This is because, as Figure 7 and Figure 8As shown, regarding image data, when the print data is assigned to each pass using a pass mask, the print data is the data itself to be printed in the forward and reverse directions, respectively, and cannot be further thinned out. In this case, the synthetic dithering combining the index pattern and the thinning out pattern described in the third embodiment cannot be created. In this embodiment, a print pattern with fewer passes, particularly a print pattern with two passes, is considered. Here, a case where the resolution of a multi-value input image is 600 dpi and the resolution of a print image is 600 dpi×1200 dpi will be described as an example.

[0130] In this embodiment, when outputting a print image, similar to the third embodiment, a method of binarization combining a dither pattern and an index pattern is adopted. In this embodiment, a 1×2 pattern is used as an index pattern to output a 600dpi multi-value input image as a 600dpi×1200dpi print image. In this case, Fig. 27 As shown, the levels of the index pattern are 0 to 2, which results in three levels of tone values. In order to divide the multi-value input image into the number of levels of the index pattern (described as quantization below), the group of the threshold value 0 to 127 of the dither pattern is set to group 1, and the group of the threshold value 128 to 255 is set to group 2. Then, the pixel value of the multi-value input image and the threshold value of the dither pattern are compared to determine which group the pixel value belongs to, and determine the index pattern to be selected. Such a system for binarization by combining the dither pattern and the index pattern is considered. Here, a description will be given by taking the case of selecting the level 1 index pattern for the multi-value input image by the dither pattern as an example.

[0131] In this embodiment, synthetic dither creation is first performed. Two dither patterns (dither pattern A and dither pattern B) having blue noise or green noise characteristics are prepared. Here, the resolution of each dither pattern is 600dpi. The elements constituting dither pattern A and dither pattern B are the same as those described in the first embodiment. Then, the two dither patterns are synthesized into a single dither pattern by arranging them in a staggered arrangement. That is, as Fig.28As shown, the threshold of the dither pattern A is arranged to correspond to the black part of the synthetic dither pattern, and the threshold of the dither pattern B is arranged to correspond to the white part of the synthetic dither pattern. Here, it is considered that the dither pattern A is the threshold for printing in the forward direction, and the dither pattern B is the threshold for printing in the reverse direction. In the case of a two-pass printing pattern, the print data determined by the threshold of the dither pattern A is the print data for the forward direction (first pass) as it is, and the print data determined by the threshold of the dither pattern B is the print data for the reverse direction (second pass) as it is. The reason for arranging the dither patterns A and B in a staggered arrangement when generating a synthetic dither pattern is to increase the dispersion of the print data of each pass. Although an example of arranging in a staggered arrangement when creating a synthetic dither pattern has been described, the two dither patterns that have been prepared may be arranged randomly. In order to increase the dispersion of each pass, it is preferred that the arrangement is performed so that the dither pattern A or the dither pattern B is not locally concentrated or dispersed when creating the synthetic dither pattern.

[0132] Next, the pass mask will be described. The pass mask determines the data to be printed in each pass, and has the same resolution as the resolution of the printed image to be output. In the present embodiment, it has a resolution of 600dpi×1200dpi. In the two-pass printing mode, the pass mask itself is the print data of a corresponding one of the forward direction and the reverse direction. Therefore, the duty cycle of the pass mask is designed to be 50%, so that the amount of forward print data and reverse print data is approximately the same. Here, when the duty cycle is set to 50%, the resolution of the multi-value input image is taken into consideration. That is, consider as follows: in units of 600dpi×600dpi, the duty cycle is 50%. In view of the above, the application of such Fig.29 An example of a blue noise pass mask is shown. Fig.29 The content shown in represents the pass mask in the forward direction, and the black part is the print data in the forward direction. In the case of the two-pass printing mode, the print data in the reverse direction is Fig.29 By applying a blue noise mask, the following effects can be expected: preventing band noise in the sub-scanning direction perpendicular to the main scanning direction and unevenness between the forward direction and the reverse direction, where the forward / reverse direction is the main scanning direction. Here, the blue noise mask has been given as an example, but other than that, it only needs to be a mask that satisfies the concepts of resolution and duty cycle.

[0133] When generating the synthetic dither pattern, dither pattern A is defined for the forward direction, and dither pattern B is defined for the reverse direction. That is, the area to which the threshold of dither pattern A is assigned needs to be printed using the pass mask in the forward direction. In order to achieve this synchronization, the rasterization table is finally set.

[0134] If the level 1 index pattern is currently selected by the synthetic dither pattern, then Fig. 27 The two patterns shown in the row of level 1 in are used as index patterns. Since a 1×2 index pattern is considered for an input pixel with a resolution of 600 dpi, Fig. 27 The one box shown in has a resolution of 600 dpi x 1200 dpi and has the same resolution as the pass mask ( Fig.29 That is, a rasterization table can be used to synchronize the synthesis of the dither pattern and the pass mask.

[0135] The following describes the use of Fig.28 and Fig.29 Example of a synthetic dither pattern and pass mask. Fig. 30A , Fig. 30B and Fig. 30C is the graph when 8×8 pixels of the input image have been extracted and considered. Fig. 30A As shown, use Fig.28 The multi-value input image is quantized using a synthetic dither pattern of the input image. At this time, the content described in white text on a black background in the box represents the result output according to the threshold value of the dither pattern A for the forward direction, and the content described in black text on a white background in the box represents the result output according to the threshold value of the dither pattern B for the reverse direction. The numbers in the box indicate the levels of the index patterns. At this time, it is assumed that the level 1 index has been selected as described above. Fig. 30B Shows Fig. 30A Quantified images and Fig.29 The minimum unit of the frame is 600dpi×1200dpi, and when viewed in units of 1×2 frames, Fig. 30A The gray filled portion in the figure indicates the area to which the dither pattern A has been assigned, and the portion other than that indicates the area to which the dither pattern B has been assigned. In addition, when viewed in terms of the smallest unit of the frame, the black dot portion indicates the pass mask pattern in the forward direction. When considering the synchronization of the dither pattern and the pass mask, in the case of the two-pass printing mode, it is sufficient to consider the synchronization in the forward direction or the reverse direction. Here, the synchronization in the forward direction is considered. Fig. 30B In FIG. 1 , the area filled with gray corresponds to the dither pattern A assigned to the forward direction, and therefore needs to be printed in the forward direction. That is, if the pass mask (black dots) for the forward direction is located at the same position as Fig. 30B The 1×2 box is proportional to the upper side of the gray area, then the rasterization table is set so that Fig. 27"Pt.1" is selected in the level 1 index pattern shown. On the other hand, the area not filled with gray corresponds to the dither pattern B assigned to the reverse direction and is therefore set not to be printed in the forward direction. That is, if the pass mask (black dots) for the forward direction is located at the same Fig. 30B The 1×2 box is proportional to the upper side of the non-gray area, then the rasterization table is set so that Fig. 27 Select "Pt.0" in the level 1 index pattern shown. The rasterization table thus created is as follows Fig. 30C shown.

[0136] By executing the above-described process, it is possible to set the data amounts of the forward printing and the reverse printing to approximately the same amount, and output an image in which the dispersion of the respective print data is ensured.

[0137] [Fifth embodiment]

[0138] Hereinafter, differences from the above-described embodiment will be described, and unless otherwise specified, it is assumed that the present embodiment is similar to the above-described embodiment.

[0139] Will refer to Fig.18 The block diagram depicts an example of a hardware configuration in a printing device. Fig.18 The configuration related to the following description is shown, and not all the hardware configurations in the printing apparatus are shown.

[0140] In the present embodiment, the A / D converter 606 performs A / D conversion on an analog signal output from the sensor group 630 to convert into a digital signal, and notifies the MPU 601 and an application specific integrated circuit (ASIC) 603 and the like of the digital signal.

[0141] The printing device further includes a switch group 620 that can input various instructions to the printing device through operation by a user. The switch group 620 includes a power switch 621, a print switch 622, and a recovery switch 623.

[0142] The power switch 621 is a switch that can turn on or off the power of the printing device by user operation. The print switch 622 is a switch that can input a print instruction to the printing device by user operation. The recovery switch 623 is a switch for instructing the printing device to perform a recovery operation when a failure such as a paper jam occurs by user operation.

[0143] The printing apparatus further includes a sensor group 630 for detecting various conditions related to the printing apparatus. The sensor group 630 includes a position sensor 631 and a temperature sensor 632. The position sensor 631 is a sensor capable of detecting the positions of the carriage and the print medium, and the temperature sensor 632 is a sensor capable of detecting the temperature inside the printing apparatus or the temperature around the printing apparatus. Analog signals indicating the detection results of the respective sensors included in the sensor group 630 are input to the A / D converter 606.

[0144] In the present embodiment, an image is printed on a unit area of ​​a printing medium according to a so-called bidirectional multi-pass printing method in which an image is printed on a unit area by causing the print head 3 to scan a plurality of times while operating in forward and reverse directions relative to the unit area. As described above, by increasing the dispersion of the image to be printed in each of forward and reverse printing, it is possible to reduce image quality degradation that occurs when a print position deviation occurs.

[0145] Fig.19A : is a schematic diagram showing a configuration example of the quantization pattern 60 used in the quantization process according to the present embodiment. Fig.19B yes Fig.19A An enlarged view of a specific area 60a in the quantization pattern 60 is shown. In the present embodiment, a dither pattern defining threshold values ​​is used as the quantization pattern, wherein each threshold value is used to determine whether ink is ejected or not ejected for each of a plurality of pixels.

[0146] like Fig.19A As shown in FIG. 1 , the dither pattern 60 to be used in this embodiment has a size of 768 pixels in the X direction and a size of 768 pixels in the Y direction. Fig.19B As shown in the enlarged view of , at each pixel position in the dither pattern 60, any value in the range from 1 to 255 (any one of 255 values) is set as a threshold.

[0147] In the quantization process of the present embodiment, the tone value indicated by the multivalued data of the pixel at the pixel position of interest in the input image and the threshold value set at the position corresponding to the pixel position of interest in the dither pattern 60 are compared.

[0148] Then, if the tone value is greater than or equal to the threshold, for the pixel position of interest, the "value indicating that ink is to be ejected" is output as the "quantized data corresponding to the multi-valued data" so that a dot corresponding to the pixel at the pixel position of interest is printed on the printing medium.

[0149] On the other hand, if the tone value is less than the threshold, for the pixel position of interest, a "value indicating no ink ejection" is output as "quantized data corresponding to multi-valued data" so that a dot corresponding to the pixel at the pixel position of interest is not printed on the print medium.

[0150] Therefore, by performing the quantization process on the input image using the dither pattern, quantized data obtained by quantizing the multi-valued data of the pixel is generated for each pixel in the input image.

[0151] Here, in Fig.19A In the dither pattern 60 shown, the threshold values ​​for 768×768 pixels are determined in such a manner that 256 levels of ink ejection amounts can be reproduced based on 256 tone values ​​from 0 to 255 indicated by the multi-valued data.

[0152] For example, when multi-value data having 64 (=256 / 4) tone values ​​is input for all 768×768 pixels corresponding to the quantization pattern 60, the corresponding threshold is determined to generate quantized data indicating ink ejection or non-ink ejection for approximately 147456 (=768×768 / 4) pixels. That is, Fig.19A The dither pattern 60 shown in is defined so that there are about 147456 pixels defining a threshold value of 64 or less. In other words, in the dither pattern 60, the number of pixels defining the respective threshold values ​​from 1 to 255 is substantially the same.

[0153] Fig. 20A is a diagram showing a quantized input image 401 obtained by performing a quantization process on the input image using the dither pattern 60. The pixel data in the quantized input image 401 as a result of quantizing the input image using the dither pattern 60 is "quantized data obtained by quantizing multi-valued data of pixels in the input image using the dither pattern 60".

[0154] When an image is formed by performing a plurality of print scans based on the quantized input image 401 , it is necessary to generate print data to be used for printing in each print scan from the quantized input image 401 .

[0155] In this embodiment, an image is formed by performing two print scans (one forward and one reverse). Fig. 20B The illustrated dividing patterns 402a and 402b generate print data to be used in a print scan in the forward direction and print data to be used in a print scan in the reverse direction.

[0156] like Fig. 20B As shown, the partition patterns 402a and 402b have a 2×4 staggered pattern, and black-filled rectangles (pixels) indicate ON bits (pixel value=1), and white-filled rectangles (pixels) indicate OFF bits (pixel value=0).

[0157] In order to generate print data (first print data) to be used in the print scan in the forward direction, first, the division pattern 402a is repeatedly arranged in a tiled form to generate a map having the same size as that of the quantized input image 401 as the first map. Then, the logical product of the pixel value at the pixel position of interest in the quantized input image 401 and the pixel value at the pixel position of interest in the first map is obtained, and the value of the logical product is set to the pixel value at the pixel position of interest in the first print data. Fig. 20C is a diagram showing first print data 403 generated using the quantized input image 401 and the division pattern 402 a as described above.

[0158] In order to generate print data (second print data) to be used in the print scan in the reverse direction, first, the division pattern 402b is repeatedly arranged in a tiled form to generate a map having the same size as that of the quantized input image 401 as the second map. Then, the logical product of the pixel value at the pixel position of interest in the quantized input image 401 and the pixel value at the pixel position of interest in the second map is obtained, and the value of the logical product is set to the pixel value at the pixel position of interest in the second print data. Fig.20D is a diagram showing second print data 404 generated using the quantized input image 401 and the division pattern 402 b as described above.

[0159] In the print scan in the forward direction, ink ejection control is performed based on the first print data 403 , and in the print scan in the reverse direction, ink ejection control is performed based on the second print data 404 .

[0160] When the quantized input image 401 is assigned as print data to be used in a plurality of printing operations, a pattern that is discontinuously ejected in the scanning direction in this manner is generally used in consideration of the influence of the vibration of the liquid surface of the nozzle on the formation of ink droplets to be ejected subsequently and ensuring the time width of the pulse signal to be applied to the print head. At this time, as in the first print data 403 or the second print data 404, if the pattern has poor dispersion, that is, there are dense and sparse parts, the image quality will be greatly deteriorated when the forward and reverse print position deviation occurs as described above. Therefore, it is necessary to generate the quantized input image 401 so that the dispersion of each of the forward data and the reverse data increases, and for this purpose, it is important to prepare a dither pattern that takes into account the segmentation patterns 402a and 402b.

[0161] Fig.21 is a diagram for explaining a method of creating such a dither pattern. Fig.21The dither patterns 701a and 701b shown are each independently generated dither patterns. The dither patterns 701a and 701b have a blue noise characteristic or a green noise characteristic, and have a size of 384 pixels in the X direction and a size of 768 pixels in the Y direction.

[0162] Region 702a is the region at the upper left corner of the dither pattern 701a, and Fig.21 In FIG. 701 , each rectangle (pixel) in region 702a is assigned an index. Region 702b is the region at the upper left corner of the dither pattern 701b, and Fig.21 In FIG. 702 , each rectangle (pixel) in region 702 b is assigned an index.

[0163] The two dither patterns (dither patterns 701a and 701b) are combined using the division pattern 402a or the division pattern 402b to generate a composite dither pattern 701c.

[0164] For example, by repeatedly arranging the segmentation pattern 402a in a tiled form, a graph having a size of 768 pixels in the X direction and a size of 768 pixels in the Y direction is generated. Then, the threshold value of the corresponding position in the dither pattern 701a is arranged at the ON position in the graph, and the threshold value of the corresponding position in the dither pattern 701b is arranged at the OFF position. In this way, a graph in which the threshold value of the dither pattern 701a and the threshold value of the dither pattern 701b are arranged according to the segmentation pattern 402a is generated as a synthetic dither pattern 701c. When the synthetic dither pattern is generated using the segmentation pattern 402b, a similar method can be applied. The method of generating a synthetic dither pattern using the segmentation pattern 402a or the segmentation pattern 402b is not limited to the above method.

[0165] Area 702c is the area at the upper left corner of the synthesized dither pattern 701c. Fig.21 As shown, when the area 702a is divided into units of 1 pixel×2 pixel blocks (first blocks) and the area 702b is divided into units of 1 pixel×2 pixel blocks (second blocks), the first blocks and the second blocks are alternately arranged in each direction in the X direction and the Y direction in the area 702c.

[0166] Here, if Fig.21 As shown, the arrangement order of the first blocks in the area 702c is the same as the arrangement order of the first blocks in the area 702a, and the arrangement order of the second blocks in the area 702c is the same as the arrangement order of the second blocks in the area 702b.

[0167] In area 702c, the threshold value of the first block is a threshold value to be used for comparison with pixels assigned to the print scan in the forward direction, and in area 702c, the threshold value of the second block is a threshold value to be used for comparison with pixels assigned to the print scan in the reverse direction. The above description is not limited to the partial areas (areas 702a, 702b, and 702c), and similarly applies to the entire area of ​​the dither pattern.

[0168] By using a synthetic dither pattern created by this method to generate a quantized input image, even if the quantized input image is divided into forward and reverse scans using a division pattern, each print data is generated from an independently generated dither pattern having blue noise characteristics or green noise characteristics, so that a pattern with high dispersion and less dense and sparse parts can be generated, and even when a print position deviation occurs between the forward and reverse print scans, degradation of image quality can be reduced.

[0169] Next, inter-color processing for generating print data of a plurality of colors using the synthetic dither pattern thus generated will be described. Fig.22A 1 is a block diagram showing an example of a functional configuration for performing color processing in a printing device. Fig.22A The various functional units shown are implemented in software (computer program). Fig.22A The illustrated functional units will be described as performers of processing, but actually, the functions of the respective functional units are performed by the MPU 601 executing computer programs corresponding to the functional units. Fig.22A The functional units shown may be implemented in hardware.

[0170] Will be based on Fig. 22B Flowchart description Fig.22A Hereinafter, a case will be described in which black (K) among the colors (cyan (C), magenta (M), yellow (Y), and black (K)) of an input image is a processing object, but the following description is equally applicable even when the processing object is other colors.

[0171] In step S806, the quantization processing unit 803 obtains the black (K) tone data In1 (x, y) from the tone data of each color of the pixel at the pixel position (x, y) in the input image. The calculation unit 804 obtains the tone data In2 (x, y), In3 (x, y), and In4 (x, y) of the colors (cyan (C), magenta (M), and yellow (Y)) other than black (K) from the tone data of each color of the pixel at the pixel position (x, y) in the input image.

[0172] In step S807 , the calculation unit 804 calculates the threshold offset Ofs_1 (x, y) corresponding to the tone data In1 (x, y) according to the following equation (1).

[0173] Ofs_1(x, y) = Σi[Ini(x, y)] ... (1)

[0174] As shown in the following equations (1-1) to (1-4), the expression "Σi[Ini(x,y)]" used to obtain the sum of the tone values ​​indicated by the tone data Ini(x,y) differs depending on the left side (the method of obtaining the corresponding threshold offset differs depending on the processing object color).

[0175] Ofs_1(x, y) = Σi[Ini(x, y)] = 0 ... (1-1)

[0176] Ofs_2(x, y) = Σi[Ini(x, y)] = In1(x, y) ... (1-2)

[0177] Ofs_3(x, y) = Σi[Ini(x, y)] = In1(x, y) + In2(x, y) ... (1-3)

[0178] Ofs_4(x, y) = Σi[Ini(x, y)] = In1(x, y) + In2(x, y) + In3(x, y)... (1-4)

[0179] In step S808, the threshold value obtaining unit 802 obtains the synthesized dither pattern generated as described above. Then, the adding unit 805 obtains the threshold value Dt(x, y) corresponding to the pixel position (x, y) in the synthesized dither pattern.

[0180] In step S809, the adding unit 805 offsets the difference between the threshold value Dth(x,y) and the tone data In1(x,y) as described below. Specifically, the adding unit 805 obtains the result of subtracting the threshold offset value Ofs_1(x,y) from the threshold value Dth(x,y) as shown in the following equation (2) as the quantization threshold value Dth'(x,y).

[0181] Dth'(x,y)=Dth(x,y)-Ofs_1(x,y)...(2)

[0182] When Dth′(x, y) is a negative value, the adding unit 805 adds the maximum threshold value Dth_max (255 in this embodiment) as shown in the following equation (3) to correct the quantization threshold value Dth′(x, y).

[0183] When Dth'(x,y)<0,

[0184] Dth'(x,y)=Dth'(x,y)+Dth_max...(3)

[0185] Next, in step S810 , the quantization processing unit 803 compares the tone data In1 (x, y) and the quantization threshold Dth′(x, y) in a state where the difference between the threshold Dth(x, y) and the tone data In1 (x, y) has been offset by the adding unit 805 .

[0186] Then, if the value (tone value) of the tone data In1(x,y) is greater than or equal to the quantization threshold Dth'(x,y), the quantization processing unit 803 outputs "a value indicating that ink is to be ejected" as "quantized data Out(x,y) corresponding to the tone data In1(x,y)".

[0187] On the other hand, if the value (tone value) of the tone data In1(x,y) is smaller than the quantization threshold Dth'(x,y), the quantization processing unit 803 outputs a "value indicating that ink is not ejected" as the "quantized data Out(x,y) corresponding to the tone data In1(x,y)".

[0188] If the quantization threshold Dth'(x,y) is a threshold in the forward direction, the quantized data Out(x,y) in the forward direction is output. If the quantization threshold Dth'(x,y) is a threshold in the reverse direction, the quantized data Out(x,y) in the reverse direction is output.

[0189] By processing all pixel positions in the input image and all colors of the input image (C, M, Y, and K in the above example) from step S806 to step S810, quantized data of each color corresponding to each pixel in the input image can be generated and output.

[0190] Will be based on Fig. 22C The flowchart in describes the overall processing of the above-mentioned printing apparatus to generate print data. In step S891, the MPU 601 generates a composite dither pattern 701c from the dither patterns 701a and 701b according to the division pattern 402a or the division pattern 402b.

[0191] In step S892, the MPU 601 Fig. 22BThe flowchart of performs color processing on all pixel positions in the input image and all colors of the input image to generate a quantized input image having quantized data corresponding to each pixel in the input image as pixel data (pixel value) of each pixel for each color. That is, in step S892, the MPU 601 generates a quantized input image for each color corresponding to the input image.

[0192] In step S893, the MPU 601 generates, for each color, the print data to be used in the print scan in the forward direction and the print data to be used in the print scan in the reverse direction, using the segmentation pattern corresponding to the color, from the quantized input image corresponding to the color. Then, the MPU 601 outputs the “print data to be used in the print scan in the forward direction and the print data to be used in the print scan in the reverse direction” for each color to the ASIC 603.

[0193] In the forward direction printing scan, the ASIC 603 performs ejection control of ink of each color (dot printing on the printing medium) based on the print data of each color generated for the forward direction. In the reverse direction printing scan, the ASIC 603 performs ejection control of ink of each color (dot printing on the printing medium) based on the print data of each color generated for the reverse direction.

[0194] In this way, the printing device according to the present embodiment is a printing device that forms dots on a printing medium by repeating forward scanning and reverse scanning, and generates first data of a dot pattern to be formed in the forward scanning and second data of a dot pattern to be formed in the reverse scanning. In the generation, the first data and the second data are generated so that the dot pattern to be formed in each of the forward scanning and the reverse scanning has a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic. In addition, in the generation, the dot pattern to be formed in the forward scanning and the dot pattern to be formed in the reverse scanning are different between colors.

[0195] Fig.23 is a diagram showing a threshold range determined as “ink to be ejected” among a plurality of thresholds 0 to Dth_max arranged in a dither pattern when first to fourth multivalued data (In1 to In4) indicating intermediate densities are input for first to fourth inks, respectively.

[0196] In the case of this embodiment, for the first ink, according to equation (1-1), Ofs_1 = 0. Therefore, for the pixel position corresponding to the threshold value from 0 to In1 (reference numerals 900 to 901) from 0 to Dth_max, it is determined that "ink is to be ejected".

[0197] For the second ink, according to equation (1-2), Ofs_2=In1. Therefore, when quantization is performed using threshold Dth', pixel positions corresponding to thresholds from In1 to In1+In2 (reference numerals 902 to 903) among thresholds 0 to Dth_max arranged in the dither pattern are determined as "ink to be ejected".

[0198] For the third ink, according to formula (1-3), Ofs_3=In1+In2. Therefore, when quantization is performed using the threshold value Dth', for the pixel position corresponding to the threshold value from In1+In2 to In1+In2+In3 (reference numerals 904 to 905) arranged in the dither pattern, it is determined that "ink is to be ejected". However, in this example, it is assumed that In1+In2+In3 exceeds Dth_max. In this case, for the area exceeding Dth_max, for the pixel position corresponding to the threshold value from 0 to In1+In2+In3-Dth_max, it is determined that "ink is to be ejected". That is, the range of the threshold value determined as "ink is to be ejected" is from In1+In2 to Dth_max (reference numerals 904 to 906) and from 0 to In1+In2+In3-Dth_max (reference numerals 907 to 908).

[0199] For the fourth ink, according to formula (1-4), Ofs_4 = In1 + In2 + In3. Therefore, when quantization is performed using the threshold value Dth', for the pixel position corresponding to the threshold value from In1 + In2 + In3 to In1 + In2 + In3 + In4 among the threshold values ​​0 to Dth_max arranged in the dither pattern, it is determined that "ink is to be ejected". However, in this example, the entire area from In1 + In2 + In3 to In1 + In2 + In3 + In4 exceeds DTh_max. Therefore, for the pixel position corresponding to the threshold value from In1 + In2 + In3 - Dth_max to In1 + In2 + In3 + In4 - Dth_max (reference numerals 909 to 910), it is determined that "ink is to be ejected".

[0200] Therefore, in this embodiment, while using a common dither pattern, offset values ​​different from each other are added to the threshold value to obtain a quantization threshold value unique to each color. Then, by using the newly obtained quantization threshold value, even when similar tone data indicating an intermediate density is input for each color, the position at which printing is performed on the print medium can be made different for each color, thereby allowing good dispersion.

[0201] Fig.24is a diagram showing an example of print data. 17% of all pixels of the black quantized input image 51001 are pixels having a "value indicating that ink is not ejected", and 10% of all pixels of the cyan quantized input image 51002 are pixels having a "value indicating that ink is not ejected". Generally, pixels filled with black are pixels to be printed, and pixels filled with white are pixels not to be printed, but here, for the cyan quantized input image, pixels to be printed are filled with gray to distinguish them from pixels to be printed in black. As described above, the quantized input images 51001 and 51002 are segmented into print data 51003 to 51006 using segmentation patterns 402a and 402b.

[0202] Print data 51003 is print data to be used in a print scan in the forward direction for the quantized input image 51001, and print data 51004 is print data to be used in a print scan in the reverse direction for the quantized input image 51001.

[0203] Print data 51005 is print data to be used in a print scan in the forward direction for the quantized input image 51002, and print data 51006 is print data to be used in a print scan in the reverse direction for the quantized input image 51002.

[0204] Each of the forward and reverse print scans is performed based on the print data 51003 to 51006, but at this time, not only the forward and reverse print position deviations occur, but also the print position deviations between black and cyan occur in each of the forward direction and the reverse direction. These can be attributed to the following: vibrations during the print head scan; and the height between the print head and the print medium fluctuates due to the instability of the print head scanning direction height of the platen supporting the print medium due to the inaccuracy of the machine body. Such print position deviations may occur periodically in the scanning direction and may cause a decrease in the uniformity of the density and deterioration of the image quality.

[0205] The change in print data when a print position deviation occurs between black and cyan during forward printing scanning will be described with reference to print data 51008 when a print position deviation is occurring and print data 51007 when a print position deviation is not occurring. Fig.24 It is obvious that when the two are compared, their uniformity is greatly different. When this change in uniformity occurs periodically in the print scanning direction, the density becomes uneven and the image quality deteriorates.

[0206] In the present embodiment, such image quality degradation is reduced by changing the division pattern for generating print data from the black quantized input image and the division pattern for generating print data from the cyan quantized input image to be similar between one or more other colors. For this reason, in the present embodiment, the pattern for obtaining "print data to be used in the print scan in the forward direction" and "print data to be used in the print scan in the reverse direction" from the result of the quantization process (quantized input image) is different between colors (inverted as an example).

[0207] exist Fig.24 In FIG. 1 , the division patterns 402a and 402b are used in this order to generate the black and cyan forward and reverse print data, but here, the patterns obtained by inverting these division patterns are used to generate the cyan forward and reverse print data.

[0208] like Fig.25 As shown, the segmentation patterns 1101a and 1101b are segmentation patterns for generating black print data, and the segmentation patterns 1102a and 1102b are segmentation patterns for generating cyan print data. The segmentation pattern 1101a is a segmentation pattern for generating print data to be used in a black print scan in a forward direction. The segmentation pattern 1101b is a segmentation pattern for generating print data to be used in a black print scan in a reverse direction. The segmentation pattern 1102a is a segmentation pattern for generating print data to be used in a cyan print scan in a forward direction. The segmentation pattern 1102a is a pattern obtained by inverting the segmentation pattern 1101a, and is the same segmentation pattern as the segmentation pattern 1101b. The segmentation pattern 1102b is a segmentation pattern for generating print data to be used in a cyan print scan in a reverse direction. The segmentation pattern 1102b is a pattern obtained by inverting the segmentation pattern 1101a, and is the same segmentation pattern as the segmentation pattern 1101b.

[0209] Print data 1102 is print data to be used in a black print scan in the forward direction, and print data 1103 is print data to be used in a black print scan in the reverse direction. Print data 1104 is print data to be used in a cyan print scan in the forward direction, and print data 1105 is print data to be used in a cyan print scan in the reverse direction.

[0210] Print data 1102 and print data 1103 are respectively Fig.24 The print data 51003 and the print data 51004 are the same, but for the cyan print data, Fig.24 and Fig.25That is, the cyan print data 1104 in the forward direction is equal to the print data 51006, and the cyan print data 1105 in the reverse direction is equal to the print data 51005.

[0211] Print data 1106 and print data 1107 are comparisons of changes in print data when a print position deviation occurs between black and cyan during forward printing. It can be seen that no uniformity change occurs between print data 1106 and print data 1107, such as Fig.24 The change in uniformity of the print data 51008 relative to the print data 51007 is shown, etc. The difference between these changes in uniformity will be described.

[0212] As described so far, since the patterns at the time of forward printing and reverse printing are determined using the segmentation patterns 402a and 402b, in order to improve the dispersion of each color, a dither pattern obtained by combining the two dither patterns 701a and 702b is used and the corresponding print data is generated while shifting the threshold so that the print position on the print medium is different between black and cyan. Therefore, the print data 51007 obtained by combining the black print data 51003 in the forward direction and the cyan print data 51005 in the forward direction without positional deviation has the blue noise characteristic or the green noise characteristic of the dither pattern 701a. However, when a positional deviation occurs between black and cyan, the characteristic is reduced, and therefore, in the print data 51008, the uniformity is poor and the difference in image quality from that of the print data 51007 is large. On the other hand, as described above, when the division patterns 1101a and 1102b obtained by inverting the division patterns are used, in the printing at the time of the forward direction, the black print data has the dispersion of the dither pattern 701a, and the cyan print data has the dispersion of the dither pattern 702a. Therefore, the print data 1106 obtained by combining these has a reduced blue noise characteristic or a green noise characteristic, and even if a positional deviation occurs as in the print data 1107, the change in uniformity is small. Therefore, even when the positional deviation between the colors periodically occurs, it is less likely to be visually recognized as density unevenness, and the image quality can be improved.

[0213] Therefore, even in a configuration in which the position for printing on a print medium is made different for each color among colors in consideration of the granularity, image quality degradation caused by forward and reverse printing position deviation and printing position deviation between colors can be suppressed.

[0214] [Sixth embodiment]

[0215] In the fifth embodiment, the division pattern for obtaining print data is reversed between two colors to suppress image quality degradation caused by forward and reverse print position deviations and print position deviations between colors. In contrast, in this embodiment, the case between three colors will be described. In the following embodiments including this embodiment, differences from the fifth embodiment will be described, and unless otherwise specified below, it is assumed that these embodiments are similar to the fifth embodiment.

[0216] Hereinafter, description will be given using yellow as the third color. Fig.26 As shown, the division patterns 1200a and 1200b are division patterns for yellow print data, and are different from the division patterns 1101a and 1101b for obtaining black print data, respectively. The quantized input images 1201 and 1202 are black and yellow quantized input images, respectively. Similar to the fifth embodiment, 17% of all pixels in the black quantized input image 1201 are pixels having a "value indicating that ink is not ejected", and 10% of all pixels in the cyan quantized input image 1202 are pixels having a "value indicating that ink is not ejected". Here, for the yellow quantized input image, the pixels to be printed are filled with gray so as to be distinguished from the pixels to be printed in black.

[0217] As in the fifth embodiment, the printing apparatus generates print data 1203 to be used in a print scan in the forward direction using the yellow quantized input image 1202 and the segmentation pattern 1200a. As in the fifth embodiment, the printing apparatus generates print data 1204 to be used in a print scan in the reverse direction using the yellow quantized input image 1202 and the segmentation pattern 1200b. Segmentation is performed using a segmentation pattern different from the combination method of the synthetic dither pattern obtained by combining two dither patterns, so that the dispersion is high when segmented into forward and reverse parts, and thus the dispersion of each of them is low. Therefore, when a print position deviation occurs, the change in uniformity is large, and the image quality is easily degraded. However, since the brightness of yellow is high, the uniformity change of yellow tends to be less visually perceptible than that of black and cyan. On the other hand, with respect to a pattern combining black and yellow, since the brightness of black is low, the uniformity change caused by the position deviation between these colors is easily visually recognized, and the degree of image quality degradation is large.

[0218] Print data 1206 indicates print data when print position deviation has not occurred at the time of forward printing scan of black and yellow, and print data 1205 indicates print data when print position deviation has occurred. In this example, similar to the effect obtained by inverting the cyan pattern shown in the fifth embodiment, the blue noise characteristic and the green noise characteristic of the pattern obtained by combining black and yellow are reduced. Therefore, the change in uniformity of print data 1205 and print data 1206 is small, and image quality degradation caused by position deviation between colors can be suppressed.

[0219] Although the relationship between black and yellow has been described above, the relationship between cyan and yellow is similar, and the uniformity change caused by the presence or absence of the print position deviation between the two can be suppressed. That is, not only the uniformity change caused by the print position deviation between the two colors described in the fifth embodiment can be suppressed, but also the uniformity change caused by the print position deviation between the three colors of black, cyan and yellow can be suppressed.

[0220] Here, a description of three colors is given, but it goes without saying that similar control can be performed between a larger number of colors by appropriately changing the division pattern. In addition, a configuration has been described in which the print data of each color is generated using the same dither pattern for all colors, but the present invention is not necessarily limited to this configuration. In view of improving image quality by not printing the same pixels, by applying the above-described embodiment between colors using the same dither pattern, image quality degradation can be suppressed.

[0221] [Seventh embodiment]

[0222] In the fifth and sixth embodiments, as a method of increasing the dispersion of each print data when dividing the quantized input image into forward and reverse print data, a method of combining two dither patterns by referring to the division pattern has been described. However, the method is not necessarily limited to the above method as long as print data having high dispersion in each of the forward direction and the reverse direction can be generated. In a method of creating a dither pattern by calculating a threshold value while referring to a pattern divided by a division pattern each time, a similar effect can be obtained, and the above embodiment can be applied even to the dither pattern thus created.

[0223] In addition, the configuration between the three colors has been described in the sixth embodiment. Here, the following configuration is described: the printing position deviation between the colors is given priority over the forward and reverse position deviations, assuming that the deviation within the color is difficult to visually recognize at the time of forward and reverse scanning due to the high brightness of yellow. However, by appropriately setting the segmentation pattern according to the size and frequency of occurrence of the actual position deviation occurring in the printing device main body and the characteristics of each ink, the image quality degradation can be better suppressed.

[0224] Furthermore, it may be configured such that, for at least two colors among the plurality of ink colors, dots are generated using the same dither pattern so that dots are not generated in the same pixel until a maximum value of a threshold value is reached.

[0225] Furthermore, configuration may be made such that a pattern obtained by combining print data to be used in a print scan in a forward direction and print data to be used in a print scan in a reverse direction has a lower frequency component greater than the respective spatial frequency characteristics.

[0226] The frequency of the segmentation pattern can be 1 to 32 times the print resolution in both the print scan direction and the direction perpendicular to the print scan direction. In addition, a configuration can be adopted so that with respect to each dot pattern formed in the forward and reverse scans, the lower the brightness of the ink, the smaller the low-frequency component.

[0227] Furthermore, although the printing apparatus and the method of printing using the printing apparatus have been described in the fifth embodiment and the subsequent embodiments, the present invention can be applied to an image processing apparatus or an image processing method that generates data for performing the printing method described in the fifth embodiment and the subsequent embodiments. Furthermore, the present invention is also applicable to a form in which a program for performing the printing method according to each embodiment is prepared separately from the printing apparatus.

[0228] In order to provide specific explanations, the numerical values, processing timing, processing order, processing entity, color space, data (information) acquisition method / transmission destination / transmission source / storage location, etc. used in the above-mentioned embodiments have been given as examples, and the present invention is not intended to be limited to these examples.

[0229] In addition, some or all of the above embodiments may be used in appropriate combination. In addition, some or all of the above embodiments may be used selectively.

[0230] Other embodiments

[0231] The embodiments of the present invention may also be implemented by providing software (program) for performing the functions of the above-described embodiments to a system or device via a network or various storage media, and a computer or a central processing unit (CPU) or a microprocessing unit (MPU) of the system or device reads and executes the program.

[0232] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest description so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A printing device operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the printing device comprising: a generating unit configured to generate first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein the generating unit generates the first data and the second data so that a dot pattern to be formed in a forward scan and a dot pattern to be formed in a reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and The number of points to be formed in the forward scan is the same as the number of points to be formed in the reverse scan.

2. The printing device according to claim 1, wherein: The generation unit generates the same number of synthetic dither patterns of thresholds of the same value using two dither patterns having blue noise characteristics or green noise characteristics as spatial frequency characteristics, and generates the first data and the second data by binarizing an input image using the synthetic dither patterns.

3. The printing device according to claim 2, wherein: The generation unit generates the composite dither pattern by arranging threshold values ​​in the two dither patterns according to a column thinning pattern.

4. The printing device according to claim 1, wherein: The generating unit generates a composite dither pattern having the same number of thresholds of the same value using two dither patterns having a blue noise characteristic or a green noise characteristic as spatial frequency characteristics, divides the thresholds in the composite dither pattern into a plurality of groups, and generates the first data and the second data by performing a binarization process based on an index pattern corresponding to the group to which the pixel value in the input image belongs.

5. The printing device according to any one of claims 2 to 4, further comprising a unit configured to print dots on the printing medium using a pass mask designed to be synchronized with the synthetic dither pattern in addition to the first data and the second data.

6. The printing device according to claim 1, further comprising the following unit, which is configured to: generating the same number of synthetic dither patterns of threshold values ​​of the same value using two dither patterns having a blue noise characteristic or a green noise characteristic as spatial frequency characteristics, and Generate a pass mask so that the print duty cycle in units of the resolution of the input image is equal for each pass, in, The first data and the second data are generated based on an index pattern designed so that the synthetic dither pattern and the pass mask are synchronized with each other.

7. The printing device according to claim 5, wherein: The pass mask is a mask generated based on a result of binarizing pixel values ​​of each tone of the input image according to the synthetic dither pattern.

8. The printing device according to claim 2, wherein: The vertical size of the synthetic dither pattern is the same as the feed amount of the printing medium in each pass in the multi-pass printing.

9. The printing device according to claim 4, wherein: The vertical size of the synthetic dither pattern is the same as a value obtained by dividing a feed amount of a print medium in each pass in multi-pass printing by the vertical size of the index pattern.

10. A control method of a printing device operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the control method comprising: generating first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein, in the generating, the first data and the second data are generated so that a dot pattern to be formed in a forward scan and a dot pattern to be formed in a reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and The number of points to be formed in the forward scan is the same as the number of points to be formed in the reverse scan.

11. A printing device operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the printing device comprising: a generating unit configured to generate first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein the generating unit generates the first data and the second data so that a dot pattern to be formed in a forward scan and a dot pattern to be formed in a reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and The generating unit makes a dot pattern to be formed in the forward scanning and a dot pattern to be formed in the reverse scanning different between colors.

12. The printing device according to claim 11, wherein The generating unit generates a composite dither pattern using two dither patterns having a blue noise characteristic or a green noise characteristic as spatial frequency characteristics, and performs quantization processing of the first color in the input image based on hue data of a second color related to hue data of the first color in the input image and the composite dither pattern.

13. The printing device according to claim 12, wherein: The generation unit performs quantization processing of the first color in the input image using a difference between a total value of tone values ​​indicated by the tone data of the second color and a threshold value of the synthetic dither pattern.

14. The printing device according to claim 12, wherein: The generation unit generates the composite dither pattern by arranging threshold values ​​of the two dither patterns, and patterns for obtaining the first data and the second data from a result of quantization processing are different between colors.

15. The printing device according to claim 12, wherein: The generation unit generates the composite dither pattern by arranging threshold values ​​of the two dither patterns, and patterns for obtaining the first data and the second data from a result of quantization processing are inverted between colors.

16. The printing device according to claim 14, further comprising: The setting unit is configured to set a pattern.

17. A control method of a printing device operable to form dots on a printing medium by repeating forward scanning and reverse scanning, the control method comprising: generating first data of a dot pattern to be formed in a forward scan and second data of a dot pattern to be formed in a reverse scan, wherein, in the generating, the first data and the second data are generated so that a dot pattern to be formed in a forward scan and a dot pattern to be formed in a reverse scan have a blue noise characteristic or a green noise characteristic as a spatial frequency characteristic, and In the generation, a dot pattern to be formed in the forward scanning and a dot pattern to be formed in the reverse scanning are made different between colors.

18. A computer program product comprising a program for causing a computer to execute the control method according to claim 10 or 17.

19. A computer-readable storage medium storing a program for causing a computer to execute the control method according to claim 10 or 17.

Images