Recording method and recording device

Abstract

To record a high quality image in which a time difference irregularity is reduced in bidirectional multi-pass recording with 3 or greater passes.SOLUTION: Images of unit regions R1, R2 of a recording medium P are recorded by 2N+1 times (N is a natural number) of bidirectional recording scan with a recording head H. At this time, a recording permission ratio of the even-numbered recording scan among 2N+1 times of recording scan is set to be lower than the recording permission ratio of the odd-numbered recording scan.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a recording method and a recording apparatus. [Background technology]

[0002] In a serial type inkjet printing device, multi-pass printing may be performed to complete an image in an area that can be printed by a single print scan of the print head by performing multiple print scans with intervening transport operations of a distance shorter than the print width of the print head. By performing such multi-pass printing, even if there is a variation in the ejection characteristics among the multiple nozzles arranged in the print head, it is possible to make the density unevenness caused by this variation in the ejection characteristics less noticeable in the image.

[0003] On the other hand, some serial type inkjet printing apparatuses perform bidirectional printing in which ink is ejected during both forward and backward scans of the print head to print an image, in order to improve throughput.

[0004] However, when the multi-pass printing is performed in a bidirectional manner, a new problem called time difference unevenness may occur. Here, time difference unevenness refers to uneven density and color development caused by the fact that the time elapsed between multiple printing scans required to complete an image of a unit area differs depending on the position of the unit area on the printing medium.

[0005] Patent Document 1 discloses a method for reducing time difference unevenness in two-pass bidirectional multi-pass printing by making the print duty of the first pass for each unit area greater than the print duty of the second pass while changing the transport amount and transport direction in each transport operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-236287 A Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, in inkjet recording devices, it is common to change the number of passes in multi-pass recording depending on the type of recording medium, the purpose of the image, etc. However, while Patent Document 1 discloses a case where two-pass bidirectional multi-pass recording is performed, it does not explain multi-pass recording of three or more passes. In other words, in conventional inkjet recording devices, it has been difficult to reduce time difference unevenness when performing three or more passes of multi-pass recording.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to print high-quality images with reduced time difference unevenness in bidirectional multi-pass printing of three or more passes. [Means for solving the problem]

[0009] To this end, the present invention provides a printing method for printing an image on a printing medium by performing a printing scan in which a printing head, in which a plurality of nozzles that eject ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the printing medium in a direction intersecting the predetermined direction, and a transport operation in which the printing medium is transported in a direction intersecting the printing scan, the method printing an image in a unit area of ​​the printing medium by 2N+1 printing scans (N is a natural number) in accordance with a predetermined printing permission rate, and of the 2N+1 printing scans, the printing permission rate of even-numbered printing scans is lower than the printing permission rate of odd-numbered printing scans. The print head has a nozzle row in which a plurality of nozzles ejecting a first ink are arranged in the predetermined direction, and a nozzle row in which a plurality of nozzles ejecting a second ink different from the first ink are arranged in the predetermined direction, and the print permission ratios corresponding to each of the 2N+1 print scans are different for the first ink and the second ink. It is characterized by: Effect of the Invention

[0010] According to the present invention, in bidirectional multi-pass printing of three or more passes, it is possible to print high-quality images with reduced time difference unevenness. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an outline of a printing unit of an inkjet printing apparatus. [Diagram 2] FIG. 1 is a diagram for explaining the ejection port surface of a recording head H. [Diagram 3] FIG. 1 is a block diagram illustrating a control configuration of an inkjet printing system. [Figure 4] Flowchart for explaining the image processing steps [Diagram 5] Diagram for explaining dot arrangement patterns [Figure 6] A diagram for explaining 3-pass bidirectional multi-pass printing. [Figure 7] FIG. 13 is a diagram showing the timing of ink application in three-pass bidirectional multi-pass printing. [Figure 8] Schematic diagram for comparing ink application timing between regions [Figure 9] Schematic diagram showing ink penetration state according to ink application amount and timing [Figure 10] A diagram showing mask patterns commonly used in three-pass bidirectional multi-pass printing. [Figure 11] FIG. 1 is a diagram showing a mask pattern and an ink application process used in the first embodiment. [Figure 12] FIG. 13 is a diagram showing a mask pattern and an ink application process used in Modification 1. [Figure 13] FIG. 13 is a diagram showing a mask pattern and an ink application process used in Modification 2. [Figure 14] FIG. 13 is a diagram showing another example of a mask pattern and an ink application process used in Modification 2. [Figure 15] FIG. 13 is a diagram showing a mask pattern and an ink application process used in Modification 3. [Figure 16] A diagram for explaining 5-pass bidirectional multi-pass printing. [Figure 17] A diagram showing mask patterns commonly used in 5-pass bidirectional multi-pass printing. [Figure 18] FIG. 13 is a diagram showing a mask pattern and an ink application process used in the second embodiment. [Figure 19]A diagram for explaining 4-pass bidirectional multi-pass printing. [Figure 20] A diagram showing mask patterns commonly used in 4-pass bidirectional multi-pass printing. [Figure 21] FIG. 13 is a diagram showing a mask pattern and an ink application process used in the third embodiment. [Figure 22] FIG. 13 is a diagram showing another example of a mask pattern and an ink application process used in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment) 1 is a diagram showing an outline of a printing section of an inkjet printing apparatus 100 (hereinafter, simply referred to as a printing apparatus) that can be used in the present invention. In the figure, the X direction indicates the scanning direction of the printing head H, the Y direction indicates the transport direction of the printing medium P, and the Z direction indicates the direction opposite to the ejection direction of the printing head H. In this embodiment, the Z direction is the direction opposite to gravity.

[0013] The print head H of this embodiment is detachably mounted on a carriage 108. The carriage 108 carrying the print head H is movable in the ±X directions using a carriage motor 305M (see FIG. 3) as a drive source while being guided and supported by guide rails 109 and 110. A platen 103 is disposed at a position facing the ejection port surface of the print head H, and supports the print medium P from below in an area where printing is performed by the print head H.

[0014] In the transport direction (Y direction), a transport roller 101 and a pinch roller 102 driven by the transport roller 101 are disposed upstream of the platen 103. A discharge roller 105 and a spur 106 driven by the transport roller 101 are disposed downstream of the platen 103. The nip between the transport roller 101 and the pinch roller 102, the nip between the discharge roller 105 and the spur 106, and the support of the platen 103 keep the recording medium P in the area facing the recording head H smooth against the ejection port surface of the recording head H.

[0015] The print head H of this embodiment is capable of ejecting four colors of ink: black (K), cyan (C), magenta (M), and yellow (Y). The printing device 100 is provided with a tank mounting section 104 for replaceably mounting ink tanks 110 that individually accommodate these four colors of ink. The ink accommodated in the ink tanks 110 is supplied to the print head H via ink tubes 111.

[0016] While the carriage 108 moves in the +X or -X direction at a predetermined speed, the print head H ejects ink in accordance with the print data, thereby printing one band of image on the print medium P. When the print scan for one band is completed, the conveyance motor 304M (see FIG. 3) serves as a drive source to rotate the conveyance rollers 101 and discharge rollers 105, and convey the print medium P by a predetermined amount in the Y direction intersecting with the print scan direction. By alternately repeating the print scan and conveyance operation as described above, an image is formed on the print medium P in stages.

[0017] After the recording, the recording medium P is conveyed in the Y direction by the rotation of the discharge roller 105 and is discharged onto the discharge tray 107 .

[0018] 2(a) and (b) are diagrams for explaining the ejection port surface of the print head H. FIG. 2(a) is an overall view of the ejection port surface. On the ejection port surface of the print head H, two nozzle rows ejecting black (K), cyan (C), magenta (M), and yellow (Y) inks are arranged symmetrically in the X direction. Specifically, at both ends in the X direction, K1 row and K2 row ejecting black ink are arranged, and on the inside thereof, C1 row and C2 row ejecting cyan ink are arranged. On the inside thereof, M1 row and M2 row ejecting magenta ink are arranged, and further on the inside thereof, Y1 row and Y2 row ejecting yellow ink are arranged.

[0019] When a print scan is performed using such a print head, the order in which ink is applied to the print medium is black → cyan → magenta → yellow → yellow → magenta → cyan → black, whether it is a forward scan in the +X direction or a return scan in the -X direction. In other words, the order in which ink is applied to the print medium is kept constant even when bidirectional printing is performed, and uneven color order caused by differences in the order in which ink is applied, which is a common issue with serial-type inkjet printing devices, can be reduced. Hereinafter, a head in which multiple ink nozzle rows are arranged symmetrically in the X direction in this way is called a symmetric head.

[0020] 2(b) is an enlarged view of the K1 column. Here, the K1 column will be described as an example, but the other columns have a similar configuration. The K1 column has an Even column and an Odd column, and in each of the Even column and the Odd column, 120 nozzles 201 capable of ejecting 5 pl of ink are arranged in the Y direction at a pitch of 600 dpi (dots per inch). The Even column and the Odd column are arranged with a shift of half a pitch (1200 dpi) in the Y direction.

[0021] A heater (not shown) is installed directly below (in the +Z direction) each nozzle 201. When the heater is heated in accordance with the print data, film boiling occurs in the ink directly above the heater, and the growth energy of the generated bubbles causes ink to be ejected as droplets from each nozzle 201.

[0022] With this configuration, by ejecting ink from each nozzle 201 in accordance with print data while moving the print head H in the ±X directions, dots can be printed on the print medium in the Y direction with a resolution of 1200 dpi.

[0023] 3 is a block diagram for explaining the control configuration of an inkjet printing system applicable to this embodiment. The inkjet printing system in this embodiment includes an inkjet printing apparatus 100 and an image processing apparatus 200.

[0024] In the inkjet printing apparatus 100, a printing apparatus main control unit 301 is composed of a CPU, ROM, RAM, etc., and controls the entire printing apparatus. A print buffer 302 stores print data as raster data before it is transferred to the print head H. A head driver 303 controls the drive of the print head H according to the print data stored in the print buffer 302.

[0025] The conveying motor driver 304 drives a conveying motor 304M to control the feeding, conveying, and discharging of the recording medium P. The carriage motor driver 305 drives a carriage motor 305M to control the movement of the carriage .

[0026] A recording device interface (I / F) 306 transmits and receives data signals to and from the image processing device 200. A data buffer 307 temporarily stores image data received from the image processing device 200. A system bus 308 connects the various functions of the recording device 100.

[0027] In the image processing device 200, an image processing device main control unit 309 is configured with a CPU, ROM, RAM, etc., and controls the entire image processing device. An image processing device interface (I / F) 310 exchanges data signals with the recording device 100. A display unit 311 is configured with an LCD, etc., and displays various information to the user. An operation unit 312 is an operation unit that allows the user to perform operations, and for example, a keyboard and a mouse can be applied. A system bus 313 connects each function of the image processing device 200.

[0028] The I / F signal line 314 connects the printing device 100 and the image processing device 200. The type of the I / F signal line 314 may be, for example, one conforming to Centronics Corporation specifications.

[0029] 4 is a flowchart for explaining the steps of image processing performed by the inkjet recording system of this embodiment when a recording command is generated. This process is started by the user inputting a recording command via the operation unit 312 when recording an image generated by an application or the like of the image processing device 200. This process is performed by the image processing device main control unit 309 and the recording device main control unit 301 in cooperation with each other, and there is no restriction on which steps are performed by the image processing device main control unit 309 and which steps are performed by the recording device main control unit 301. Here, the description will be given assuming that the image processing device main control unit 309 performs up to the quantization process in S404, and the recording device main control unit 301 performs the index expansion process in S405 and onwards.

[0030] When a recording command is generated, first, in step S401, color correction processing is performed on the image data to be processed. In this embodiment, the image data generated by the application of the image processing device 200 is 600 dpi 8-bit RGB data. In the color correction processing, the 8-bit RGB data expressed in the s-RGB space is converted into 8-bit RGB data corresponding to the color space that can be expressed by the recording device 100. Specifically, a lookup table prepared in advance is used to convert pixel values ​​(R, G, B) into pixel values ​​of other values ​​(R', G', B').

[0031] In step S402, color conversion processing is performed on the image data after the color correction processing. In the color conversion processing, 8-bit RGB data, which is a brightness value, is converted into 8-bit CMYK data, which is a density value. Here, CMYK corresponds to the ink colors cyan, magenta, yellow, and black used by the recording device 100, respectively. Specifically, using a lookup table prepared in advance, 8-bit (256 gradations) pixel values ​​(R', G', B') are converted into 8-bit (256 gradations) pixel values ​​(C, M, Y, K).

[0032] In step S403, tone correction processing is performed on the image data after color conversion processing. Generally, there is no linear relationship between the number of dots recorded on a recording medium and the optical density realized on the recording medium by that number of dots. Therefore, in order to make this relationship linear, each of the pixel values ​​C, M, Y, and K, which are density values, is corrected. Specifically, a one-dimensional lookup table prepared for each ink color is used to convert each of the 8-bit (256 gradations) pixel values ​​C, M, Y, and K into the same 8-bit pixel values ​​C', M', Y', and K'.

[0033] In step S404, quantization processing is performed on the image data after the gradation correction. The quantization processing method is not particularly limited, but in this embodiment, a dither pattern in which a threshold value for each pixel is previously determined is referenced. Then, 8-bit (256 gradations) pixel values ​​C', M', Y', K' are converted into 2-bit (3 gradations) pixel values ​​C'', M'', Y'', K'' expressed at levels 0 to 2.

[0034] In step S405, index expansion processing is performed on the image data after quantization processing. In the index expansion processing, based on the pixel value (0 to 2) of each pixel of 600 dpi x 600 dpi, dot printing or non-printing is set for each pixel of 600 dpi in the X direction x 1200 dpi in the Y direction. At this time, for pixels set to print dots, it is set whether to print by column 1 or column 2.

[0035] 5(a) and (b) are diagrams for explaining dot arrangement patterns referenced in the index development process. FIG. 5(a) is a diagram showing the relationship between pixel values ​​(left side) corresponding to one pixel region of 600 dpi x 600 dpi and dot arrangement patterns (right side). One pixel region of 600 dpi in the X direction x 600 dpi in the Y direction corresponds to two pixel regions adjacent in the Y direction at a resolution of 600 dpi in the X direction x 1200 dpi in the Y direction. Of the two pixel regions, the upper one is a pixel region that can be recorded by nozzles in the odd row, and the lower one is a pixel region that can be recorded by nozzles in the even row. In the diagram, of these two pixel regions, black pixels indicate pixel regions where dots are recorded, and white pixels indicate pixel regions where dots are not recorded.

[0036] If a pixel value is 0, then no dot is printed in either of the two image areas corresponding to that pixel.

[0037] When a pixel value is 1, a dot is recorded in one of the two pixel regions corresponding to that pixel. Furthermore, that dot is recorded by either nozzle row 1 or nozzle row 2 (see FIG. 2(a)). That is, when a pixel value is 1, there are four patterns, A to D, for the method of recording a dot. Here, pattern A indicates that a dot is recorded by nozzle row 1 in the upper pixel region. Pattern B indicates that a dot is recorded by nozzle row 1 in the lower pixel region. Pattern C indicates that a dot is recorded by nozzle row 2 in the upper pixel region. Pattern D indicates that a dot is recorded by nozzle row 2 in the lower pixel region.

[0038] In this manner, in this embodiment, four dot arrangement patterns shown in A to D are prepared. Four dot arrangement patterns shown in A to D are also prepared when the pixel value is 2. In this embodiment, these four patterns are used by switching between them in sequence depending on the position on the recording medium.

[0039] FIG. 5(b) shows an index table in which the dot arrangement patterns A to D are set to correspond to pixel positions (XY coordinate positions) of 600 dpi x 600 dpi. Here, an index table of 8 pixels x 8 pixels is shown, but the index table may be larger or smaller. Such an index table is used repeatedly in the X and Y directions. By setting the dot arrangement patterns A to D in the index table without bias, it is possible to equalize the ejection frequency of the multiple nozzle rows arranged in the recording head H and stabilize the refill of each nozzle. The dot arrangement patterns shown in FIG. 5(a) and the index table shown in FIG. 5(b) are stored in advance in a ROM or the like.

[0040] Returning to the flowchart in Figure 4, in step S406, mask processing is performed on the image data after the index expansion processing. In the mask processing, for each nozzle array, it is determined which printing scan will be used to print dots for pixels set as dot printing (1).

[0041] FIG. 6 is a diagram for explaining the multi-pass printing employed in this embodiment. In this embodiment, three-pass bidirectional multi-pass printing is employed. When performing three-pass multi-pass printing, 120 nozzles arranged in one nozzle row (Odd row or Even row) are divided into three regions of 40 nozzles each, and a mask pattern that determines whether dot printing is permitted (1) or not permitted (0) for each pixel is assigned to each divided region. In FIG. 6, the mask pattern used in the first divided region on the most upstream side in the Y direction is shown as P1, the mask pattern used in the second divided region in the center is shown as P2, and the mask pattern used in the third divided region on the most downstream side is shown as P3. The mask patterns P1, P2, and P3 have a mutually complementary relationship. The print data to be actually printed in each print scan is determined by performing a logical AND operation between the print data of each pixel determined by the index development process and the mask patterns P1 to P3.

[0042] In the first print scan, the first divided area is used and print scan is performed in the forward direction (+X direction). As a result, a dot pattern according to the mask pattern P1 is printed in the first image area of ​​the print medium P. When the first scan is completed, the print medium P is transported in the +Y direction by a distance (40 nozzles) corresponding to the divided area. For the sake of explanation, FIG. 6 shows the print head H moving in the -Y direction relative to the print medium P.

[0043] In the second printing scan, the first divided area and the second divided area are used to perform printing scan in the backward direction (-X direction). As a result, a dot pattern according to mask pattern P1 is printed in the second image area of ​​the printing medium P. Also, in the first image area, a dot pattern according to mask pattern P2 is printed superimposed on the dot pattern printed according to mask pattern P1. When the second printing scan is completed, the printing medium P is transported in the +Y direction by the distance of 40 nozzles.

[0044] In the third recording scan, the first to third divided areas are used to perform a recording scan in the forward direction (+X direction). As a result, a dot pattern according to mask pattern P1 is recorded in the third image area of ​​the recording medium P. In addition, a dot pattern according to mask pattern P2 is recorded and superimposed on the dot pattern recorded according to mask pattern P1 in the second image area. In the first image area, a dot pattern according to mask pattern P3 is recorded and superimposed on the dot pattern recorded according to mask patterns P1 and P2. Since mask patterns P1, P2, and P3 have a mutually complementary relationship, the image in the first image area is completed at the end of the third recording scan. When the third recording scan is completed, the recording medium P is transported in the +Y direction by the amount of 40 nozzles.

[0045] After that, backward print scans and forward print scans using the first to third divided areas are performed alternately, with a transport operation for 40 nozzles being performed between each print scan. Each time a print scan is performed, an image in one image area is completed.

[0046] 7 is a diagram for explaining the timing of ink application for each area when the above-mentioned three-pass bidirectional multi-pass printing is performed. The first to fourth print scans shown in FIG. 7 correspond to the first to fourth print scans shown in FIG.

[0047] As also explained in Fig. 6, the first image area is printed by the first printing scan which is a forward scan, the second printing scan which is a backward scan, and the third printing scan which is a forward scan. Therefore, ink is applied to area R1 located at the left edge of the first image area at the start of the first printing scan, the end of the second printing scan, and the start of the third printing scan. On the other hand, the second image area is printed by the second printing scan which is a backward scan, the third printing scan which is a forward scan, and the fourth printing scan which is a backward scan. Therefore, ink is applied to area R2 located at the left edge of the second image area at the end of the second printing scan, the start of the third printing scan, and the start of the fourth printing scan.

[0048] That is, although regions R1 and R2 adjacent in the Y direction are both applied with ink in three printing scans, the intervals at which ink is applied are different. Note that ink is applied at the same intervals as region R1 to the region located at the left edge of the third image region adjacent to region R2, and ink is applied at the same intervals as region R2 to the region located at the left edge of the fourth image region adjacent to that region. That is, at the left edge of the printing medium, two types of regions with different intervals at which ink is applied are alternately arranged in the Y direction.

[0049] 8(a) and (b) are schematic diagrams for comparing the ink application timing between regions.

[0050] In region R1, between the time when ink is applied in the first print scan and the time when ink is applied in the second print scan, the time it takes for the carriage 108 to move to the right end, the time it takes for a transport operation to be performed, and the time TL it takes for the carriage 108 to move to the left end elapse. In contrast, between the time when ink is applied in the second print scan and the time when ink is applied in the third print scan, only the time TS it takes for the transport operation to be performed elapses. That is, in region R1, the time TL that elapses from the first application of ink to the second application of ink is long, and the time TS that elapses from the second application of ink to the third application of ink is short.

[0051] On the other hand, in region R2, only the time TS for the transport operation elapses between when ink is applied in the second print scan and when ink is applied in the third print scan. In contrast, between when ink is applied in the third print scan and when ink is applied in the fourth print scan, the time for the carriage 108 to move to the right end in the forward scan, the time for the transport operation, and the time for the carriage to move to the left end in the return scan elapse. That is, in region R2, the elapsed time TS from when ink is applied for the first time to when ink is applied for the second time is short, and the elapsed time TL from when ink is applied for the second time to when ink is applied for the third time is long.

[0052] In Fig. 8(a), the timing of applying ink to regions R1 and R2 is shown along the time axis. Meanwhile, in Fig. 8(b), the timing of applying ink to regions R1 and R2 is shown based on a longer elapsed time TL. Hereinafter, a print scan performed before the elapsed time TL will be called the first print, and a print scan performed after the elapsed time TL will be called the second print. That is, in region R1, printing according to mask pattern P1 is the first print, and printing according to mask patterns P2 and P3 is the second print. Meanwhile, in region R2, printing according to mask patterns P1 and P2 is the first print, and printing according to mask pattern P3 is the second print.

[0053] Here, if the scanning width of the carriage 108 is 8 inches and the scanning speed is 20 inches / second, the scanning time in the forward direction and the scanning time in the backward direction are both 0.4 seconds. Also, the time required for the transport operation is approximately 0.1 seconds. In this case, of the two elapsed times that occur between the three ink applications, the longer elapsed time TL is approximately 0.9 seconds and the shorter elapsed time TS is approximately 0.1 seconds.

[0054] 9(a) to (d) are schematic diagrams for explaining the ink penetration state according to the amount and timing of ink application. Here, cross-sectional views are shown of the state in which ink is applied to a recording medium P. Inside the recording medium P, there are large capillaries through which ink penetrates relatively easily and small capillaries through which ink penetrates relatively less easily.

[0055] Figures 9(a) and (b) are diagrams for explaining the relationship between the timing of applying ink and the ink penetration state. Figure 9(a) shows the ink penetration state when a predetermined amount of ink is applied to a recording medium P and then the same amount of ink is applied relatively soon after. In this case, when the subsequent ink is applied, the preceding ink has permeated into the large capillaries but has not permeated into the small capillaries. Therefore, the subsequent ink permeates in the depth direction, avoiding the preceding ink, and is fixed at a deeper position than the preceding ink. In Figure 9(a), the permeation distance of the ink in the depth direction is indicated as D1.

[0056] FIG. 9(b) shows the ink penetration state when a predetermined amount of ink is applied to the recording medium P and then the same amount of ink is applied a relatively long time later. In this case, when the subsequent ink is applied, the preceding ink has already penetrated into the small capillaries. Therefore, the subsequent ink does not progress very far in the depth direction, but penetrates into the large capillaries near the surface and settles near the surface at the same level as the preceding ink that penetrated into the small capillaries. In FIG. 9(b), the penetration distance of the ink in the depth direction is indicated as D2. When FIG. 9(a) and (b) are compared, FIG. 9(b), in which more ink settles on the surface, has a higher optical density than FIG. 9(a) (D1>D2).

[0057] Figures 9(c) and (d) are diagrams for explaining the relationship between the amount of ink applied and the ink permeation state. Figure 9(c) shows the ink permeation state when a small amount of ink is applied to a recording medium P, and then a large amount of ink is applied after a predetermined period of time. Since the amount of the preceding ink is small, it permeates into the large capillaries near the surface, and then permeates and settles in the small capillaries near the surface. On the other hand, the following ink permeates and settles in the large capillaries after the preceding ink has passed. In Figure 9(c), the permeation distance of the ink in the depth direction is indicated as D3.

[0058] FIG. 9(d) shows the ink penetration state when a large amount of ink is applied to the recording medium P, and then a small amount of ink is applied after a specified period of time. A large amount of the preceding ink penetrates in the depth direction along the large capillaries. The preceding ink penetrates into the surrounding small capillaries, but most of it remains in the large capillaries. When a small amount of subsequent ink is applied, the subsequent ink penetrates in the depth direction, avoiding the preceding ink in the large capillaries, and settles at a deeper position than the preceding ink. In FIG. 9(d), the penetration distance of the ink in the depth direction is indicated as D4. Comparing FIG. 9(c) and (d), FIG. 9(c), in which more ink settles on the surface, has a higher optical density (D3) than FIG. 9(d). <D4)。

[0059] 8(b), it can be considered that ink is applied to region R1 by a combination of Figures 9(b) and (c), and ink is applied to region R2 by a combination of Figures 9(b) and (d). In other words, at the left end of the recording medium, region R1 with high optical density and region R2 with low optical density are arranged alternately in the Y direction, and this is perceived as time difference unevenness.

[0060] This kind of time difference unevenness also occurs at the right end of the image. However, the relationship between the optical density at the right end of the first image area (the odd-numbered image area) and the optical density at the right end of the second image area (the even-numbered image area) is reversed from that at the left end. Also, this kind of time difference unevenness is more noticeable at both ends than in the center.

[0061] As described above, in three-pass bidirectional multipass printing, the degree of time difference unevenness depends on the time elapsed between the first and second printing, and the amount of ink applied in the first and second printing (printing duty). However, the former, i.e., the time elapsed between the first and second printing, cannot be easily changed due to mechanical constraints. On the other hand, the latter, i.e., the amount of ink applied in the first and second printing (printing duty), can be controlled by adjusting the mask patterns P1 to P3 already described. In view of the above circumstances, the present inventors have created mask patterns in which time difference unevenness is less noticeable in three-pass bidirectional multipass printing.

[0062] First, mask patterns that are generally used in 3-pass bidirectional multi-pass printing will be described with reference to Figs. 10(a) and (b). The left side of Fig. 10(a) shows a general mask pattern P0 used by an odd or even column of any nozzle column. Mask pattern P0 has a pixel area of ​​100 pixels in the X direction by 120 pixels in the Y direction. Each pixel corresponds to one pixel of 600 dpi by 600 dpi, and the allowance (black) or non-allowance (white) of dot printing is determined for each pixel area. The number of pixels in the Y direction corresponds to the number of nozzles in the odd or even column, and the area of ​​1 to 40 pixels on the upstream side is mask pattern P1, the area of ​​41 to 80 pixels in the center is mask pattern P2, and the area of ​​81 to 120 pixels on the downstream side is mask pattern P3 (see Fig. 6). Mask pattern P0 is used repeatedly in the X direction. Such mask patterns are prepared for each of the odd and even columns of each nozzle column.

[0063] In the figure, to the right of the mask pattern, the nozzle row of print head H and the print permission rate corresponding to each nozzle are shown. In the nozzle row, the 40 nozzles from the upstream side in the Y direction correspond to the first divided area that uses mask pattern P1. The 40 nozzles in the center correspond to the second divided area that uses mask pattern P2. The 40 nozzles on the downstream side correspond to the third divided area that uses mask pattern P3.

[0064] In this specification, the print permission rate refers to the ratio of pixel areas that are permitted to be printed among multiple pixel areas printed in one print scan. In a typical mask pattern P0 used in 3-pass multi-pass printing, the print permission rate of each pixel area in the Y direction is an almost uniform value (33% ≒ 100% / 3), as shown in Figure 10(a).

[0065] FIG. 10B is a diagram comparing the ink application process in regions R1 and R2 when the mask pattern P0 in FIG. 10A is used. In region R1, about 33% of the area is printed in the first printing (first scan), and then about 67% of the area is printed in the second printing (second and third scans). On the other hand, in region R2, about 67% of the area is printed in the first printing (second and third scans), and then about 33% of the area is printed in the second printing (fourth scan). That is, in region R1, ink is applied by the method of FIG. 9C, in which the amount of ink applied in the second printing is greater than the amount of ink applied in the first printing. On the other hand, in region R2, ink is applied by the method of FIG. 9D, in which the amount of ink applied in the first printing is greater than the amount of ink applied in the second printing. As a result, there is a risk that time difference unevenness will be detected at both ends of the printing medium.

[0066] 11(a) and (b) are diagrams showing the mask patterns and ink application process used in this embodiment in three-pass bidirectional multi-pass printing. As shown in FIG. 11(a), in this embodiment, the print permission rate of the mask pattern P1 of the first divided region and the mask pattern P3 of the third divided region are both set to 49%. On the other hand, the print permission rate of the mask pattern P2 of the second divided region is set to 2%, which is lower than the mask patterns P1 and P3.

[0067] In this case, as shown in FIG. 11(b), in the region R1, after about 49% of the printing is performed in the first printing (first scan), about 51% of the printing is performed in the second printing (second and third scan). On the other hand, in the region R2, after about 51% of the printing is performed in the first printing (second and third scan), about 49% of the printing is performed in the second printing (fourth scan). That is, by using the mask pattern P0 of this embodiment, the ink application amount of the first printing and the ink application amount of the second printing can be made substantially equal in the regions R1 and R2. That is, it is possible to keep the elapsed time TL between the first printing and the second printing and the ratio of the ink application amount of the first printing and the second printing (5:5) substantially constant between the regions R1 and R2. As a result, it is possible to reduce the time difference unevenness occurring at both ends of the printing medium.

[0068] (Variation 1) When the mask pattern of FIG. 11(a) is used, in region R1, the printability rate of forward scanning is 98%, and the printability rate of backward scanning is 2%. In region R2, the printability rate of forward scanning is 2%, and the printability rate of backward scanning is 98%. In this way, region R1, where most dots are printed by forward scanning, and region R2, where most dots are printed by backward scanning, are adjacent to each other, so that the difference in the printability of forward scanning and the printability of backward scanning may be noticeable in the image. For example, if there is a shift in the dot landing position in the X direction between forward scanning and backward scanning, the ruled line extending in the Y direction will be in a state of alternating wobbles in the ±X direction. In addition, if the occurrence state of satellites differs between forward scanning and backward scanning, image regions with many satellites and image regions with few satellites will be arranged alternately in the Y direction, and this may be perceived as density unevenness. Hereinafter, such image defects that appear due to the difference in printability between forward scanning and backward scanning will be called bidirectional unevenness.

[0069] 11(a), the occurrence of bidirectional unevenness is caused by setting the print permission rate in the second divided region too low compared to the first and third divided regions. Therefore, in this modified example, a mask pattern is prepared that keeps both the time difference unevenness caused by the difference in the ink application amount between the first and second recording, and the bidirectional unevenness caused by the difference in the print permission rate between the forward scan and the backward scan within the allowable range.

[0070] 12(a) and (b) are diagrams showing the mask pattern P0 and ink application process used in this modified example in 3-pass bidirectional multi-pass printing. As shown in Fig. 12(a), in this modified example, the print permission rate of the mask pattern P1 of the first divided area and the mask pattern P3 of the third divided area is set to 38%, and the print permission rate of the mask pattern P2 of the second divided area is set to 24%.

[0071] In this case, as shown in Fig. 12(b), in region R1, about 38% of the area is printed in the first printing (first scan), and then about 62% of the area is printed in the second and third scans. Meanwhile, in region R2, about 62% of the area is printed in the first printing (second and third scan), and then about 38% of the area is printed in the second printing (fourth scan).

[0072] In this manner, in this modified example, the print permission rate of the mask pattern P2 of the second divided region is set lower than that of the conventional mask pattern shown in Fig. 10(a) and higher than that of the mask pattern shown in Fig. 11(a). As a result, it is possible to suppress within the allowable range both the time difference unevenness caused by the difference in the ink application amount between the first printing and the second printing, and the bidirectional unevenness caused by the difference in the print permission rate between the forward scan and the backward scan.

[0073] In the above description, the print permission rates are set to 38% and 24% as an example, but these values ​​may be adjusted as appropriate depending on how noticeable the time difference unevenness and the bidirectional unevenness are. For example, when a photographic image is printed, the mask pattern in FIG. 11(a) may be used to prioritize reducing the time difference unevenness, and when a character or a ruled line is printed, the mask pattern in FIG. 12(a) or FIG. 10(a) may be used to prioritize reducing the bidirectional unevenness. The print permission rate may be different for each color. For example, the mask pattern in FIG. 11(a) may be used for color inks, and the mask pattern in FIG. 12(a) or FIG. 10(a) may be used for black inks.

[0074] (Variation 2) 11(a), white or black streaks may occur between image areas due to errors in the transport operation. Specifically, if the transport amount is larger than the design value, white streaks will occur between adjacent image areas, and if the transport amount is smaller than the design value, black streaks will occur.

[0075] Such white and black streaks become noticeable when the difference in print permission rate between adjacent divided areas is too large. Therefore, in this modified example, a mask pattern is prepared that gradually changes the print permission rate at the boundary between the first and second divided areas, and at the boundary between the second and third divided areas.

[0076] 13(a) and (b) are diagrams showing the mask patterns and ink application process used in this modified example in three-pass bidirectional multi-pass printing. As shown in FIG. 13(a), in this modified example, the print permission rate of the mask pattern P1 of the first divided area is changed stepwise in the Y direction from 41%, 49%, and 41%. Also, the print permission rate of the mask pattern P2 of the second divided area is changed stepwise in the Y direction from 18%, 2%, and 18%. Furthermore, the print permission rate of the mask pattern P3 of the third divided area is changed stepwise in the Y direction from 41%, 49%, and 41%. That is, in this modified example, in the first divided area and the third divided area, the print permission rate of the center is set higher than the print permission rate of the end portion, and in the second divided area, the print permission rate of the center is set lower than the print permission rate of the end portion.

[0077] In this case, as shown in FIG. 13(b), each of the regions R1 and R2 can be considered as being divided into three regions. At the ends of the ±Y direction of the region R1, about 41% of the recording is performed in the first recording (first scan), and then about 59% of the recording is performed in the second recording (second and third scan). At the center of the region R1, about 49% of the recording is performed in the first recording (first scan), and then about 51% of the recording is performed in the second recording (second and third scan). On the other hand, at the ends of the ±Y direction of the region R2, about 59% of the recording is performed in the first recording (second and third scan), and then about 41% of the recording is performed in the second recording (fourth scan). At the center of the region R2, about 51% of the recording is performed in the first recording (second and third scan), and then about 49% of the recording is performed in the second recording (fourth scan).

[0078] According to the mask pattern of this modification, the difference in print permission ratio at the boundary between the first and second divided regions and the boundary between the second and third divided regions is 23% (=41%-18%). Also, even at the boundaries where the print permission ratio changes within each divided region, the difference in print permission ratio is 5% or 16%, which is a sufficiently small value. In other words, by using the mask pattern P0 of this modification, it is possible to reduce time difference unevenness without making white or black streaks more noticeable, even if an error is included in the transport operation.

[0079] Fig. 14 shows a mask pattern in which the print permission rate in each divided area is changed with a gradient, in comparison with the mask pattern P0 in Fig. 13(a). Even when such a mask pattern is used, it is possible to reduce time difference unevenness without making white and black streaks more noticeable, as with the mask pattern in Fig. 13(a).

[0080] (Variation 3) 15(a) and (b) are diagrams showing the mask patterns and ink application processes used in this modified example in 3-pass bidirectional multi-pass printing. As shown in Fig. 15(a), in this modified example, the print permission rate of mask pattern P1 in the first divided area is 39%, the print permission rate of mask pattern P2 in the second divided area is 2%, and the print permission rate of mask pattern P3 in the third divided area is 59%.

[0081] In this case, as shown in FIG. 15B, in the region R1, after about 39% of the printing is performed in the first printing (first scan), about 61% of the printing is performed in the second printing (second and third scan). On the other hand, in the region R2, after about 41% of the printing is performed in the first printing (second and third scan), about 59% of the printing is performed in the second printing (fourth scan). That is, by using the mask pattern P0 of this modification, the ratio of the ink application amount of the first printing to the ink application amount of the second printing can be unified to about 4:6 in the regions R1 and R2. That is, it is possible to keep the elapsed time between the first printing and the second printing and the ratio of the ink application amount of the first printing to the second printing (4:6) approximately constant between the regions R1 and R2. In addition, in this modification, the ink application amount of the first printing scan is suppressed and the ink application amount of the last printing scan is increased, thereby obtaining the effect of improving the optical density and color development as described in FIG. 9B and FIG. 9C. In other words, by using the mask pattern of this modified example, it is possible to further improve optical density and color development while equally suppressing the time difference unevenness that occurs at both ends of the recording medium compared to when the mask pattern described in Figure 11 is used.

[0082] The ratio of the amount of ink applied in the pre-recording and the amount of ink applied in the post-recording can be changed as appropriate. For example, if there is a concern that the surface layer of the recording medium may peel off if a large amount of color material is present near the surface, or if there is a need to improve fixability, the print permission rate of the first divided region may be set higher than the print permission rate of the third divided region.

[0083] As described above, in this embodiment, in three-pass bidirectional multi-pass printing, the first printing and the second printing are determined with the longer elapsed time TL between the elapsed time from the first scan to the second scan and the elapsed time from the second scan to the third scan for the end area as the boundary. Then, a mask pattern is used that suppresses the print permission rate of the second divided area to be smaller than the print permission rates of the first divided area and the third divided area so that the ratio of the ink application amount of the first printing to the ink application amount of the second printing is approximately constant. This makes it possible to keep the elapsed time between the first printing and the second printing and the ratio of the ink application amount of the first printing to the second printing approximately constant, and reduce the time difference unevenness that occurs at both ends of the print medium.

[0084] Second Embodiment In this embodiment as well, the inkjet recording apparatus described in Figures 1 to 3 is used, and the image processing described in Figures 4 and 5 is carried out. However, in this embodiment, five-pass bidirectional multi-pass recording is performed.

[0085] 16 is a diagram for explaining multi-pass printing employed in this embodiment. When performing 5-pass multi-pass printing, the 120 nozzles arranged in the nozzle row are divided into 5 regions of 24 nozzles each, and mask patterns P1 to P5, which have a mutually complementary relationship, are assigned to each divided region. In this embodiment as well, a logical AND operation is performed between the print data of each pixel determined by the index expansion process and a mask pattern that determines whether dot printing is permitted (1) or not permitted (0), thereby determining whether or not to print a dot for each pixel.

[0086] In the first print scan, a print scan is performed in the forward direction (+X direction) using the first divided area of ​​the print head H. As a result, a dot pattern according to the mask pattern P1 is printed in the first image area of ​​the print medium P. When the first print scan is completed, the print medium P is transported in the +Y direction by a distance (24 nozzles) corresponding to the divided area.

[0087] In the second print scan, a print scan is performed in the return direction (-X direction) using the first and second divided areas of print head H. As a result, a dot pattern according to mask pattern P1 is printed in the second image area of ​​print medium P. Also, in the first image area, a dot pattern according to mask pattern P2 is printed superimposed on the dot pattern printed according to mask pattern P1. When the second print scan is completed, print medium P is transported in the +Y direction by 24 pixels.

[0088] In the third printing scan, the first to third divided regions of the printing head H are used to perform printing scans in the forward direction (+X direction). As a result, a dot pattern according to mask pattern P1 is printed in the third image region of the printing medium P. Also, in the second image region, a dot pattern according to mask pattern P2 is printed and superimposed on the dot pattern printed and superimposed on the dot pattern printed and superimposed on the mask pattern P1. In the first image region, a dot pattern according to mask pattern P3 is printed and superimposed on the dot pattern printed and superimposed on the mask patterns P1 and P2.

[0089] In the fourth print scan, the first to fourth divided regions of the print head H are used to perform print scan in the backward direction (-X direction). As a result, a dot pattern according to the mask pattern P1 is printed in the fourth image region of the print medium P. Also, a dot pattern according to the mask pattern P2 is printed and superimposed on the dot pattern printed and superimposed on the mask pattern P1 in the third image region of the print medium P. In the second image region of the print medium, a dot pattern according to the mask pattern P3 is printed and superimposed on the dot pattern printed and superimposed on the mask patterns P1 and P2. In the first image region of the print medium, a dot pattern according to the mask pattern P4 is printed and superimposed on the dot pattern printed and superimposed on the mask patterns P1 to P3.

[0090] In the fifth recording scan, the first to fifth divided regions of the recording head H are used to perform a recording scan in the forward direction (+X direction). As a result, a dot pattern according to the mask pattern P1 is recorded in the fifth image region of the recording medium P. Also, a dot pattern according to the mask pattern P2 is recorded and superimposed on the dot pattern recorded according to the mask pattern P1 in the fourth image region of the recording medium P. A dot pattern according to the mask pattern P3 is recorded and superimposed on the dot pattern recorded according to the mask patterns P1 and P2 in the third image region of the recording medium. A dot pattern according to the mask pattern P4 is recorded and superimposed on the dot pattern recorded according to the mask patterns P1 to P3 in the second image region of the recording medium. A dot pattern according to the mask pattern P5 is recorded and superimposed on the dot pattern recorded according to the mask patterns P1 to P4 in the first image region of the recording medium.

[0091] Since the mask patterns P1 to P5 have a mutually complementary relationship, the image of the first image area is complete when the fifth recording scan is completed. When the fifth recording scan is completed, the recording medium P is transported in the +Y direction by 24 pixels.

[0092] Thereafter, backward and forward print scans are alternately performed using the first to fifth divided areas of the print head H, with a transport operation of 24 pixels between each print scan. Then, each time a print scan is performed, printing of one image area is completed.

[0093] Figures 17(a) and (b) are diagrams for explaining mask patterns that are generally used in 5-pass multi-pass printing. The left side of Figure 17(a) shows a general mask pattern P0 that is used by the odd or even rows of any nozzle row. The right side of the mask pattern shows the print permission rate corresponding to each pixel region in the Y direction. In the general mask pattern P0 used in 5-pass multi-pass printing, the print permission rate of each pixel region in the Y direction is an approximately uniform value (20%=100% / 5), as shown in Figure 17(a).

[0094] FIG. 17B is a diagram comparing the ink application process when the mask pattern P0 in FIG. 17A is used, between an area R1 located at the left end of the first image area and an area R2 located at the left end of the second image area. In a 5-pass bidirectional multi-pass, in the area R1, an elapsed time TL elapses between the application of ink in the first print scan and the application of ink in the second scan. An elapsed time TS elapses between the application of ink in the second print scan and the application of ink in the third print scan. Also, an elapsed time TL elapses between the application of ink in the third print scan and the application of ink in the fourth print scan. Furthermore, an elapsed time TS elapses between the application of ink in the fourth print scan and the application of ink in the fifth print scan. That is, in the area R1, the elapsed time TL from the first application of ink to the second application of ink and the elapsed time TL from the third application of ink to the fourth application of ink are longer. In contrast, the elapsed time TS from the second application of ink to the third application of ink, and the elapsed time TS from the fourth application of ink to the fifth application of ink are short.

[0095] On the other hand, in the region R2, an elapsed time TS elapses between when ink is applied in the second print scan and when ink is applied in the third print scan. An elapsed time TL elapses between when ink is applied in the third print scan and when ink is applied in the fourth print scan. Also, an elapsed time TS elapses between when ink is applied in the fourth print scan and when ink is applied in the fifth print scan. Furthermore, an elapsed time TL elapses between when ink is applied in the fifth print scan and when ink is applied in the sixth print scan. That is, in the region R2, the elapsed time TS from when ink is applied for the first time to when ink is applied for the second time, and the elapsed time TS from when ink is applied for the third time to when ink is applied for the fourth time are short. In contrast, the elapsed time TL from when ink is applied for the second time to when ink is applied for the third time, and the elapsed time TL from when ink is applied for the fourth time to when ink is applied for the fifth time are long.

[0096] In Fig. 17(b), the timing of applying ink to regions R1 and R2 is shown based on the longer elapsed time TL. In the figure, the print scan performed before two elapsed times TL is shown as first print, the print scan performed between two elapsed times TL is shown as middle print, and the print scan performed after two elapsed times TL is shown as last print. That is, in region R1, print according to mask pattern P1 is first print, print according to mask patterns P2 and P3 is middle print, and print according to mask patterns P4 and P5 is last print. On the other hand, in region R2, print according to mask patterns P1 and P2 is first print, print according to mask patterns P3 and P4 is middle print, and print according to mask pattern P5 is last print.

[0097] In this case, in the region R1, after about 20% of the printing is performed in the first printing (first scan), about 40% of the printing is performed in the middle printing (second and third scans), and about 40% of the printing is performed in the latter printing (fourth and fifth scans). On the other hand, in the region R2, after about 40% of the printing is performed in the first printing (second and third scans), about 40% of the printing is performed in the middle printing (fourth and fifth scans), and about 20% of the printing is performed in the latter printing (sixth scan). That is, in the region R1, a lot of ink is applied by the middle printing and the latter printing, and in the region R2, a lot of ink is applied by the first printing and the middle printing. As a result, there is a risk that time difference unevenness will be detected at both ends of the printing medium.

[0098] Figures 18(a) and (b) are diagrams showing the mask patterns and ink application process used in this embodiment in 5-pass bidirectional multi-pass printing. As shown in Figure 18(a), in this embodiment, the print permission rate of mask pattern P1 of the first divided region, mask pattern P3 of the third divided region, and mask pattern P5 of the fifth divided region is set to 32%. On the other hand, the print permission rate of mask pattern P2 of the second divided region and mask pattern P3 of the fourth divided region is set to 2%, which is lower than mask patterns P1, P3, and P5.

[0099] In this case, as shown in FIG. 18B, in the region R1, after about 32% of the recording is performed in the first recording (first scan), about 34% of the recording is performed in the middle recording (second and third scans), and about 34% of the recording is performed in the latter recording (fourth and fifth scans). On the other hand, in the region R2, after about 34% of the recording is performed in the first recording (second and third scans), about 34% of the recording is performed in the middle recording (fourth and fifth scans), and about 32% of the recording is performed in the latter recording (sixth scan). That is, by using the mask pattern of this embodiment, the ink application amount of the first recording, the ink application amount of the middle recording, and the ink application amount of the latter recording can be made approximately equal in the regions R1 and R2. That is, it is possible to maintain the elapsed time TL between the first recording, the middle recording, and the latter recording, and the ratio (3:3:3) of the ink application amount of the first recording, the middle recording, and the latter recording, approximately constant between the regions R1 and R2. As a result, it is possible to reduce the time difference unevenness occurring at both ends of the recording medium.

[0100] In this embodiment, the print permission rate for each divided area can be changed as appropriate. For example, for color ink, the mask pattern in Fig. 18(a) may be used with priority given to reducing time difference unevenness, and for black ink, the mask pattern in Fig. 17(a) may be used with priority given to reducing bidirectional unevenness.

[0101] (Third embodiment) In this embodiment as well, the inkjet recording apparatus described in Figures 1 to 3 is used, and the image processing described in Figures 4 and 5 is carried out. However, in this embodiment, four-pass bidirectional multi-pass recording is performed.

[0102] FIG. 19 is a diagram for explaining multi-pass printing employed in this embodiment. When performing 4-pass multi-pass printing, 120 nozzles arranged in an odd or even row of any nozzle row are divided into four regions of 30 nozzles each, and mask patterns that are complementary to each other are assigned to each divided region. FIG. 19 shows a state in which mask patterns P1 to P4 are assigned to each divided region from the most upstream side in the Y direction. In this embodiment as well, a logical AND operation is performed between the print data of each pixel determined by the index expansion process and a mask pattern that determines whether dot printing is permitted (1) or not permitted (0), thereby determining whether dot printing (1) or not (0) is performed for each pixel.

[0103] Figures 20(a) and (b) are diagrams for explaining mask patterns that are generally used in 4-pass multi-pass printing. The left side of Figure 20(a) shows a general mask pattern P0 that is used by the odd or even rows of any nozzle row. The right side of the mask pattern shows the print permission rate corresponding to each pixel region in the Y direction. In the general mask pattern P0 used in 4-pass multi-pass printing, the print permission rate of each pixel region in the Y direction is an approximately uniform value (25%=100% / 4), as shown in Figure 20(a).

[0104] FIG. 20B is a diagram comparing the ink application process when the mask pattern P0 in FIG. 20A is used, between an area R1 located at the left end of the first image area and an area R2 located at the left end of the second image area. In a four-pass bidirectional multi-pass, in the area R1, an elapsed time TL elapses between the application of ink in the first print scan and the application of ink in the second print scan. An elapsed time TS elapses between the application of ink in the second print scan and the application of ink in the third print scan. Also, an elapsed time TL elapses between the application of ink in the third print scan and the application of ink in the fourth print scan. That is, in the area R1, the elapsed time TL from the first application of ink to the second application of ink and the elapsed time TL from the third application of ink to the fourth application are long. In contrast, the elapsed time TS from the second application of ink to the third application of ink is short.

[0105] On the other hand, in region R2, an elapsed time TS elapses between when ink is applied in the second print scan and when ink is applied in the third scan. An elapsed time TL elapses between when ink is applied in the third print scan and when ink is applied in the fourth print scan. Also, an elapsed time TS elapses between when ink is applied in the fourth print scan and when ink is applied in the fifth print scan. That is, in region R2, the elapsed time TS from when ink is applied the first time to when ink is applied the second time, and the elapsed time TS from when ink is applied the third time to when ink is applied the fourth time are short. In contrast, the elapsed time TL from when ink is applied the second time to when ink is applied the third time is long.

[0106] 20(b) shows the timing of applying ink to regions R1 and R2 based on the elapsed time TL. In this case, in region R1, printing according to mask pattern P1 is the first printing, printing according to mask patterns P2 and P3 is the middle printing, and printing according to mask pattern P4 is the last printing. Meanwhile, in region R2, printing according to mask patterns P1 and P2 is the first printing, printing according to mask patterns P3 and P4 is the middle printing, and there is no last printing. In other words, the middle printing is essentially the last printing.

[0107] In this case, in the region R1, after about 25% of the printing is performed in the first printing (first scan), about 50% of the printing is performed in the middle printing (second and third scans), and about 25% of the printing is performed in the post printing (fourth scan). On the other hand, in the region R2, after about 50% of the printing is performed in the first printing (second and third scans), about 50% of the printing is performed in the middle printing (fourth and fifth scans), and no post printing is performed. That is, in the region R1, ink is applied in three stages by the first printing, middle printing, and post printing, but in the region R2, ink is applied in two stages by the first printing and middle printing. In this way, when the timing of applying ink is allocated with a long elapsed time TL as a boundary, in even-numbered pass bidirectional multi-pass printing, the number of times of applying ink differs between adjacent regions (R1 and R2). As a result, there is a risk that time difference unevenness will be detected at both ends of the print medium.

[0108] 21(a) and (b) are diagrams for explaining the mask patterns and ink application process used in this embodiment in four-pass bidirectional multi-pass printing. As shown in FIG. 21(a), in this embodiment, the print permission rate of the mask pattern P1 of the first divided region and the mask pattern P3 of the third divided region is set to 36%. The print permission rate of the second divided region is set to 23%, which is lower than the first and third divided regions, and the print permission rate of the fourth divided region is set to an even lower 5%.

[0109] In this case, as shown in Fig. 21(b), in region R1, after about 36% of the printing is done in the first printing (first scan), about 59% of the printing is done in the middle printing (second and third scans), and about 5% of the printing is done in the last printing (fourth scan). In other words, most of the ink is applied in two passes, the first printing and the middle printing. On the other hand, in region R2, after about 59% of the printing is done in the first printing (second and third scans), about 41% of the printing is done in the middle printing (fourth and fifth scans), and there is no last printing.

[0110] In this manner, in this embodiment, the amount of ink applied in the post-printing to the region R1 is reduced by suppressing the print permission rate of the fourth divided region to a low value. As a result, the number of timings for applying ink to both the region R1 and the region R2 is approximately two times each, and it is possible to generate approximately the same situation as the first embodiment, which performs three-pass bidirectional multi-pass printing. In addition, by suppressing the print permission rate of the second divided region to a value smaller than that of the first and third divided regions, as in the first embodiment, it is possible to reduce the time difference unevenness that occurs at both ends of the print medium, as in the first embodiment.

[0111] (Modification) 22(a) and (b) are diagrams showing modified mask patterns that can be used in the fourth embodiment. In this modified example, the print permission rate of the mask pattern P2 of the second divided region and the mask pattern P4 of the fourth divided region is set to 36%. The print permission rate of the third divided region is set to 23%, which is lower than the second and fourth divided regions, and the print permission rate of the first divided region is set even lower at 5%.

[0112] In this case, as shown in Fig. 22(b), in region R1, after about 5% printing is performed in the pre-printing (first scan), about 59% printing is performed in the middle printing (second and third scans), and about 36% printing is performed in the post-printing (fourth and fifth scans). In other words, most of the ink is applied in two passes, the middle printing and the post-printing. On the other hand, in region R2, there is no pre-printing, after about 41% printing is performed in the middle printing (second and third scans), about 59% printing is performed in the post-printing (fourth and fifth scans).

[0113] In this manner, in this modified example, the amount of ink applied in the previous printing to the region R1 is reduced by suppressing the print permission rate of the first divided region to a small value. As a result, the number of timings for applying ink to both the region R1 and the region R2 is approximately two times each, and it is possible to generate approximately the same situation as the first embodiment in which three-pass bidirectional multi-pass printing is performed. Furthermore, by suppressing the print permission rate of the third divided region to a smaller value than the second and fourth divided regions, as in the first embodiment, it is possible to reduce the time difference unevenness that occurs at both ends of the print medium, as in the first embodiment.

[0114] In this embodiment, the print permission rate for each divided area can be changed as appropriate. For example, the mask pattern shown in Fig. 21(a) can be used for color inks, and the mask pattern shown in Fig. 22(a) can be used for black ink.

[0115] (Other embodiments) In the above embodiment, 3-pass, 4-pass, and 5-pass multi-pass printing has been described as an example. However, the above printing method can also be applied to multi-pass printing with a larger number of passes. For example, when the number of passes is odd, that is, 2N+1 (N is a natural number), the ink application amount of the even-numbered printing scans for unit areas such as area R1 and area R2 may be controlled to be less than the ink application amount of the odd-numbered printing scans. To achieve this, a mask pattern may be used in which the print permission rate of the divided area corresponding to the even-numbered printing scans for the unit area is set lower than the print permission rate of the divided area corresponding to the odd-numbered printing scans. In this way, the ratio of the ink application amount in each printing process such as the pre-printing and post-printing divided by the elapsed time TL can be kept approximately constant between unit areas, thereby reducing time difference unevenness.

[0116] On the other hand, when the number of multi-passes is an even number, that is, 2N times (N is a natural number), the ink application amount in the first or last print scan for the unit area may be controlled to be less than the ink application amount in the other 2N-1 print scans that follow it. In addition, a mask pattern may be used in which the print permission rate of the divided area corresponding to the even-numbered print scans is set lower than the print permission rate of the divided area corresponding to the odd-numbered print scans among the 2N-1 print scans. In other words, in the unit area, a print scan according to the above control when the number of multi-passes is an odd number (2N-1 times) is performed, and then a print scan with a print permission rate lower than these may be performed before or after the consecutive (2N-1) print scans. In this way, the ratio of the number of print processes in which ink is mainly applied, which are divided by the elapsed time TL, and the ink application amount in each print process may be kept approximately constant between unit areas, thereby reducing time difference unevenness.

[0117] The above-described embodiments and modifications can be combined with each other. For example, when recording on plain paper, the three-pass bidirectional multi-pass recording described in the first embodiment can be performed, and when recording on coated paper, the five-pass bidirectional multi-pass recording described in the second embodiment can be performed. In addition, while adopting the first embodiment, the mask pattern of modification 3 shown in Fig. 15(a) can be used for black ink, and the mask pattern shown in Fig. 14 can be used for color inks.

[0118] In the above embodiment, the color sequence unevenness caused by the difference in the application order of ink, which is likely to be a problem in a color inkjet recording device, is suppressed by using the symmetric head described in FIG. 2. However, in the above embodiment, the use of symmetric heads is not an essential requirement. For example, in a monochromatic inkjet recording device using only black ink or an inkjet recording device in which nozzle rows of each color are arranged in the transport direction (Y direction), color sequence unevenness does not occur even when bidirectional recording is performed. However, even in such an inkjet recording device, time difference unevenness occurs if multi-pass bidirectional recording is performed. That is, if a serial type inkjet recording device performs bidirectional multi-pass recording, time difference unevenness occurs, and by using the mask pattern described in the above embodiment, time difference unevenness can be reduced and image quality can be improved.

[0119] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions. [Explanation of symbols]

[0120] 100 Inkjet recording device 201 Nozzle H Recording head P Recording medium R1, R2 unit area

Claims

1. A recording method for recording an image on a recording medium by performing a recording scan in which a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the recording medium in a direction intersecting the predetermined direction, and a transport operation in which the recording medium is transported in a direction intersecting the recording scan, An image of a unit area of ​​a recording medium is recorded by the recording scan 2N+1 times (N is a natural number) in accordance with a predetermined recording permission ratio; Among the 2N+1 printing scans, the print permission rate of an even-numbered printing scan is lower than the print permission rate of an odd-numbered printing scan, The printing method is characterized in that the printing head has a nozzle row in which a plurality of nozzles that eject a first ink are arranged in the predetermined direction, and a nozzle row in which a plurality of nozzles that eject a second ink different from the first ink are arranged in the predetermined direction, and the printing permission rate corresponding to each of the 2N+1 printing scans is different for the first ink and the second ink.

2. The recording method described in Claim 1, characterized in that, for each of the first ink and the second ink, the recording tolerance rates of the odd-numbered recording scans among the 2N+1 recording scans are equal.

3. The recording method described in Claim 1, characterized in that, for each of the first ink and the second ink, the recording acceptance rate of the last of the 2N+1 recording scans is higher than the recording acceptance rate of the first of the recording scans.

4. A recording method described in any one of claims 1 to 3, characterized in that, for each of the first ink and the second ink, the recording tolerance rates of the even-numbered recording scans among the 2N+1 recording scans are equal.

5. A recording method as described in any one of claims 1 to 4, characterized in that, for each of the first ink and the second ink, among the 2N+1 recording scans for the unit area, in odd-numbered recording scans, the recording acceptance rate of the central part in the specified direction is higher than the recording acceptance rate of the end parts, and in even-numbered recording scans, the recording acceptance rate of the central part in the specified direction is lower than the recording acceptance rate of the end parts.

6. The recording method described in Claim 5, characterized in that, for each of the first ink and the second ink, among the 2N+1 recording scans for the unit area, in odd-numbered recording scans, the recording tolerance ratio decreases from the center toward the ends in the specified direction, and in even-numbered recording scans, the recording tolerance ratio increases from the center toward the ends in the specified direction.

7. 7. The recording method according to claim 1, wherein N is 1 or 2.

8. A recording method described in any one of claims 1 to 7, characterized in that, for each of the first ink and the second ink, a recording scan having a recording tolerance rate lower than that of the 2N+1 recording scans is further performed consecutively to the 2N+1 recording scans in the unit area.

9. 9. A printing method according to claim 1, wherein the first ink is a black ink and the second ink is a color ink, and the print permission rate of the even-numbered printing scans of the first ink for the unit area is higher than the print permission rate of the even-numbered printing scans of the second ink for the unit area.

10. 10. The printing method according to claim 9, wherein the print permission ratios of the first ink for the unit area are equal to each other for the 2N+1 printing scans.

11. A printing method according to any one of claims 1 to 10, characterized in that the printing permission rate is set by a mask pattern that determines whether or not printing of dots in each pixel area of ​​a printing medium is permitted for each of 2N+1 divided areas obtained by dividing the multiple nozzles in the specified direction.

12. a recording head in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction; a scanning means for performing a print scan by moving the print head alternately in a forward direction and a backward direction relative to a print medium in a direction intersecting the predetermined direction; a conveying means for conveying a recording medium in a direction intersecting the recording scanning direction; a control means for controlling the recording head, the scanning means and the conveying means in order to record an image on a recording medium according to image data; A recording device comprising: the recording head has a nozzle row in which a plurality of nozzles for ejecting a first ink are arranged in the predetermined direction, and a nozzle row in which a plurality of nozzles for ejecting a second ink different from the first ink are arranged in the predetermined direction, the control means controls the recording apparatus so that an image of a unit area on a recording medium is recorded by 2N+1 recording scans (N is a natural number), and among the 2N+1 recording scans, the recording permission rate of the even-numbered recording scans is lower than the recording permission rate of the odd-numbered recording scans, and the recording permission rate corresponding to each of the 2N+1 recording scans is different for the first ink and the second ink.

13. 13. The printing apparatus according to claim 12, wherein the control means controls the print permission ratios of the first ink and the second ink in odd-numbered print scans among the 2N+1 print scans so that they are equal to each other.

14. 13. The printing apparatus according to claim 12, wherein the control means controls, for each of the first ink and the second ink, such that the print permission ratio of the last printing scan among the 2N+1 printing scans is higher than the print permission ratio of the first printing scan.

15. 15. The printing apparatus according to claim 12, wherein the control means controls the print permission ratios of the first ink and the second ink in even-numbered print scans among the 2N+1 print scans so that the print permission ratios are equal for each of the first ink and the second ink.

16. 16. The printing apparatus according to claim 12, wherein the control means controls, for each of the first ink and the second ink, so that, among the 2N+1 printing scans for the unit area, in odd-numbered printing scans, the print permission ratio of the central part in the specified direction is higher than the print permission ratio of the end parts, and, in even-numbered printing scans, the print permission ratio of the central part in the specified direction is lower than the print permission ratio of the end parts.

17. 17. The printing apparatus according to claim 16, wherein the control means controls, for each of the first ink and the second ink, among the 2N+1 printing scans for the unit area, so that in odd-numbered printing scans, the print permission ratio decreases from the center toward the ends in the predetermined direction, and in even-numbered printing scans, the print permission ratio increases from the center toward the ends in the predetermined direction.

18. 18. The recording apparatus according to claim 12, wherein the N is 1 or 2.

19. 19. The printing apparatus according to claim 12, wherein the control means controls the printing scans having a print permission rate lower than that of the 2N+1 printing scans for the unit area for each of the first ink and the second ink so as to be consecutive to the 2N+1 printing scans.

20. 20. A printing apparatus according to claim 12, wherein the first ink is a black ink and the second ink is a color ink, and the printing permission rate of the even-numbered printing scans of the first ink for the unit area is higher than the printing permission rate of the even-numbered printing scans of the second ink for the unit area.

21. 21. The printing apparatus according to claim 20, wherein said control means controls so that print permission rates of said first ink for said unit area are equal for said 2N+1 print scans.

22. 22. The printing apparatus according to claim 12, wherein the control means controls the print permission rate for each of 2N+1 divided areas obtained by dividing the plurality of nozzles in the specified direction in accordance with a mask pattern that determines whether or not dot printing is permitted for each pixel area of ​​the printing medium.

23. A method for recording an image on a recording medium by performing a recording scan in which a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the recording medium in a direction intersecting the predetermined direction, and a transport operation in which the recording medium is transported in a direction intersecting the recording scan, An image of a unit area of ​​a recording medium is recorded by the recording scan 2N+1 times (N is a natural number) in accordance with a predetermined recording permission ratio; Among the 2N+1 printing scans, the print permission rate of an even-numbered printing scan is lower than the print permission rate of an odd-numbered printing scan, a print permission ratio of a last print scan among the 2N+1 print scans is higher than a print permission ratio of a first print scan.

24. A method for recording an image on a recording medium by performing a recording scan in which a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the recording medium in a direction intersecting the predetermined direction, and a transport operation in which the recording medium is transported in a direction intersecting the recording scan, An image of a unit area of ​​a recording medium is recorded by the recording scan 2N+1 times (N is a natural number) in accordance with a predetermined recording permission ratio; Among the 2N+1 printing scans, the print permission rate of an even-numbered printing scan is lower than the print permission rate of an odd-numbered printing scan, The printing method, wherein the print permission ratios of even-numbered printing scans among the 2N+1 printing scans are equal to each other.

25. A method for recording an image on a recording medium by performing a recording scan in which a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the recording medium in a direction intersecting the predetermined direction, and a transport operation in which the recording medium is transported in a direction intersecting the recording scan, An image of a unit area of ​​a recording medium is recorded by the recording scan 2N+1 times (N is a natural number) in accordance with a predetermined recording permission ratio; Among the 2N+1 printing scans, the print permission rate of an even-numbered printing scan is lower than the print permission rate of an odd-numbered printing scan, a print permission ratio of a central portion in the specified direction being higher than the print permission ratio of an end portion in odd-numbered print scans among the 2N+1 print scans in the unit area, and a print permission ratio of a central portion in the specified direction being lower than the print permission ratio of an end portion in even-numbered print scans.

26. A method for recording an image on a recording medium by performing a recording scan in which a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, is moved alternately in a forward direction and a backward direction relative to the recording medium in a direction intersecting the predetermined direction, and a transport operation in which the recording medium is transported in a direction intersecting the recording scan, An image of a unit area of ​​a recording medium is recorded by the recording scan 2N+1 times (N is a natural number) in accordance with a predetermined recording permission ratio; Among the 2N+1 printing scans, the print permission rate of an even-numbered printing scan is lower than the print permission rate of an odd-numbered printing scan, a print scan having a print permission rate lower than that of the 2N+1 print scans is further performed consecutively to the 2N+1 print scans in the unit area.

27. ​​A recording head having a plurality of nozzles for ejecting ink arranged in a predetermined direction; a scanning means for performing a print scan by moving the print head alternately in a forward direction and a backward direction relative to a print medium in a direction intersecting the predetermined direction; a conveying means for conveying a recording medium in a direction intersecting the recording scanning direction; a control means for controlling the recording head, the scanning means and the conveying means in order to record an image on a recording medium according to image data; A recording device comprising: the control means controls the recording medium so that an image of a unit area on the recording medium is recorded by 2N+1 recording scans (N is a natural number), and among the 2N+1 recording scans, a print permission ratio of an even-numbered recording scan is lower than a print permission ratio of an odd-numbered recording scan; and a print permission ratio of a last print scan among the 2N+1 print scans is controlled to be higher than the print permission ratio of a first print scan.

28. A recording head having a plurality of nozzles for ejecting ink arranged in a predetermined direction; a scanning means for performing a print scan by moving the print head alternately in a forward direction and a backward direction relative to a print medium in a direction intersecting the predetermined direction; a conveying means for conveying a recording medium in a direction intersecting the recording scanning direction; a control means for controlling the recording head, the scanning means and the conveying means in order to record an image on a recording medium according to image data; A recording device comprising: the control means controls the recording medium so that an image of a unit area on the recording medium is recorded by 2N+1 recording scans (N is a natural number), and among the 2N+1 recording scans, a print permission ratio of an even-numbered recording scan is lower than a print permission ratio of an odd-numbered recording scan; and A printing apparatus comprising: a printing apparatus that performs control such that the print permission ratios of even-numbered print scans among the 2N+1 print scans are equal to each other.

29. A recording head having a plurality of nozzles for ejecting ink arranged in a predetermined direction; a scanning means for performing a print scan by moving the print head alternately in a forward direction and a backward direction relative to a print medium in a direction intersecting the predetermined direction; a conveying means for conveying a recording medium in a direction intersecting the recording scanning direction; a control means for controlling the recording head, the scanning means and the conveying means in order to record an image on a recording medium according to image data; A recording device comprising: the control means controls the recording medium so that an image of a unit area on the recording medium is recorded by 2N+1 recording scans (N is a natural number), and among the 2N+1 recording scans, a print permission ratio of an even-numbered recording scan is lower than a print permission ratio of an odd-numbered recording scan; and a control unit for controlling a print permission ratio of a central portion in the specified direction to be higher than the print permission ratio of an end portion in odd-numbered print scans of the 2N+1 print scans in the unit area, and a control unit for controlling a print permission ratio of a central portion in the specified direction to be lower than the print permission ratio of an end portion in even-numbered print scans.

30. A recording head having a plurality of nozzles for ejecting ink arranged in a predetermined direction; a scanning means for performing a print scan by moving the print head alternately in a forward direction and a backward direction relative to a print medium in a direction intersecting the predetermined direction; a conveying means for conveying a recording medium in a direction intersecting the recording scanning direction; a control means for controlling the recording head, the scanning means and the conveying means in order to record an image on a recording medium according to image data; A recording device comprising: the control means controls the recording medium so that an image of a unit area on the recording medium is recorded by 2N+1 recording scans (N is a natural number), and among the 2N+1 recording scans, a print permission ratio of an even-numbered recording scan is lower than a print permission ratio of an odd-numbered recording scan; and a print area for printing the unit area by a print scan having a print permission rate lower than that of the 2N+1 print scans, the print area being controlled so as to be continuous with the 2N+1 print scans.

Images