JP7483539B2 - Image recording device and image recording method - Google Patents

Description

The present invention relates to an image recording device and an image recording method.

In image recording devices such as inkjet recording devices, the recording head may be driven in a time-division manner to reduce the device's power supply capacity. Time-division driving is a drive control in which multiple nozzles arranged in the same nozzle row are divided into several sections, and the timing of applying a voltage pulse to the recording element is shifted within one pixel range between multiple nozzles in the same section. By performing such time-division driving, the number of nozzles driven simultaneously can be reduced, the power supply capacity can be reduced, and the cost of the device can be reduced. On the other hand, on the recording medium, slight recording position deviations that occur due to the above-mentioned timing shifts can cause streaks and texture, reducing the image quality.

To address the above issue, Patent Document 1 discloses a recording control that makes the recording position shift that occurs with time-division driving less noticeable by shifting image data in accordance with the section configuration of time-division driving.

JP 2006-159698 A

However, when the printing control of Patent Document 1 is adopted, although printing position deviation and texture are not noticeable, there is an issue that the entire image is tilted due to the effect of image data shift. This issue will be explained below.

Figure 36 shows a typical time-division drive. In time-division drive, multiple nozzles arranged on a print head 3600 are divided into multiple sections. The figure shows an example in which 128 nozzles are divided into 8 sections of 16 nozzles each. The first nozzle in each section is then classified as the first block, the second nozzle as the second block, and so on. Then, as shown in timing chart 3601, the timing for driving each nozzle is shifted sequentially by block.

When the recording head 3600 is moved in the main scanning direction under such drive control, an inclined straight line like the dot pattern 3602 is formed on the recording medium even at the same pixel position in the scanning direction. In other words, on the recording medium, oblique lines with a constant inclination with respect to the direction of movement of the recording head 3600 are repeatedly arranged in the nozzle arrangement direction.

Figures 37(a) to (d) are diagrams for explaining the print control of Patent Document 1, which is performed under the above drive control. Here, the X direction is the main scanning direction of the print head, and the Y direction is the nozzle arrangement direction. In binary image data 3701, black pixels indicate dot printing (1), and white pixels indicate dot non-printing (0). When such binary image data 3701 is printed under the drive control described in Figure 36, an image such as pre-correction dot pattern 3702 is printed on the print medium. The shift in the X direction that occurs at the boundary between adjacent sections is noticeable, and is a cause of image degradation.

According to Patent Document 1, in order to correct such misalignment between adjacent sections, correction data 3703 is generated by shifting binary image data 3701 on a section-by-section basis in the direction opposite to the misalignment. Then, when correction data 3703 is recorded under the above drive control, a uniform image such as corrected dot pattern 3704 can be recorded on the recording medium. From corrected dot pattern 3704, it can be seen that the misalignment between adjacent sections has been corrected.

However, in the corrected dot pattern 3704, the image data is shifted in sections, so the entire image is tilted with respect to the Y axis. In this case, the edges of the tilted image may extend into the margin area of the recording medium, causing a risk of image information being lost in that area.

The present invention was made to solve the above problems. Its purpose is to record high-quality images in an image recording device that uses time-division driving.

To this end, the present invention provides an image recording device that records an image on a recording medium by moving a recording head, in which a plurality of nozzles that eject ink are arranged in a predetermined direction, relative to the recording medium in a direction intersecting the predetermined direction, the image recording device comprising: a quantization means that quantizes a gradation value possessed by multi-value data of a pixel to be processed by comparing it with a threshold value corresponding to the pixel position of the pixel to be processed in a threshold matrix in which a plurality of threshold values are arranged, and generates quantized data for the pixel to be processed; and a quantization means that, when a time corresponding to the ejection operation of one pixel is divided into N periods, sequentially drives nozzles included in a first adjacent nozzle group among the plurality of nozzles in the predetermined direction every K periods (K<N), sequentially drives nozzles included in a second adjacent nozzle group adjacent to the first adjacent nozzle group in the predetermined direction every K periods, and sequentially drives the nozzles included in the first adjacent nozzle group in the predetermined direction every K periods. The device includes a drive control means for performing time-division drive control, which drives the nozzles closest to the second adjacent nozzle group of the nozzle group with a delay of L period (N/2<L<N) from the nozzles closest to the first adjacent nozzle group of the second adjacent nozzle group, and a recording means for ejecting ink from the recording head according to the quantized data generated by the quantization means while the drive control means is performing the time-division drive control, and the quantization means performs quantization processing using a threshold matrix obtained by offsetting the threshold corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold corresponding to the first adjacent nozzle group, with respect to a basic threshold matrix from which quantized data in which a predetermined pattern is periodically arranged is obtained when image data of a predetermined gradation value is uniformly input.

According to the present invention, it is possible to record high-quality images in an image recording device that performs time-division driving.

FIG. 1 is a perspective view showing an outline of a printing unit in an inkjet printing apparatus. FIG. 2 is a schematic diagram of a recording head observed from the nozzle surface. FIG. 2 is a block diagram illustrating a control configuration of the inkjet printing system. FIG. 2 is a block diagram for illustrating the overall configuration of an electrical circuit of the printing apparatus. FIG. 4 is a block diagram showing the internal configuration of the main board. FIG. 2 is a diagram showing the configuration of a drive circuit for a recording head. 11 is a flowchart for explaining image processing. FIG. 4 is a diagram showing a nozzle array development table. FIG. 13 is a diagram showing an example of a multi-value mask pattern. FIG. 13 is a diagram showing a table to which a controller refers. 4 is a diagram for explaining time-division driving in the first embodiment. FIG. FIG. 4 is a schematic diagram for explaining two-pass multi-pass printing. FIG. 1 is a diagram showing the relationship between a general threshold matrix and a dot pattern. 5A and 5B are diagrams showing the relationship between a threshold matrix and a dot pattern according to the first embodiment. FIG. 1 is a diagram for explaining the mechanism by which high dispersibility is obtained. FIG. 2 is a schematic diagram of a recording head observed from the nozzle surface. FIG. 11 is a diagram for explaining time-division driving in a second embodiment. 3A and 3B are diagrams showing dot arrangement patterns and basic index patterns. 13A and 13B are diagrams for explaining a threshold matrix and an index pattern according to the second embodiment. 13A to 13C are diagrams showing dot patterns when print control according to a second embodiment is performed. 6A and 6B are diagrams showing a state in which the drive timing is shifted in forward and backward print scans. 5A and 5B are diagrams for explaining printing position deviation between scans. 13 is a flowchart for explaining steps of image processing in a third embodiment. 13A and 13B are schematic diagrams for explaining two-pass multi-pass printing in a third embodiment. 11 is a diagram comparing dot patterns in forward and backward scans. 13A and 13B are diagrams showing a threshold matrix and index patterns according to the third embodiment; 11A and 11B are diagrams for explaining adjustment of drive timings of the LEv column and the LOd column. 13A and 13B are diagrams showing results of quantization processing according to the third embodiment. FIG. 13 is a diagram showing a dot pattern when time-division driving is performed. FIG. 13 is a diagram showing a comparative example of a dot pattern. 13A to 13C are diagrams showing results of quantization processing in the third embodiment. 13A to 13C are diagrams showing dot patterns formed on a recording medium in a third embodiment. FIG. 13 is a diagram showing a comparative example of a dot pattern. 10A and 10B are schematic diagrams illustrating multi-pass printing in a modified example. FIG. 10 is a diagram for explaining an index pattern used in the modified example. FIG. 1 is a diagram showing a general time-division driving. FIG. 1 is a diagram for explaining a conventional recording control method.

First Embodiment
<Hardware configuration overview>
1A and 1B are schematic diagrams of a printing unit in an inkjet printing apparatus 2 (hereinafter, simply referred to as a printing apparatus) that can be used in this embodiment. In the drawings, the X direction indicates the scanning direction of a carriage 106, and the Y direction indicates the transport direction of a printing medium P. Fig. 1A is a perspective view of the printing apparatus 2, and Fig. 1B is a cross-sectional view of the carriage 106 portion.

The carriage 106 is fixed to a carriage belt 108 that moves using a carriage motor E0001 (see FIG. 4) as a drive source, and is guided and supported by a carriage shaft 109, allowing it to move back and forth in the ±X directions in the figure. While the carriage 106 moves, the print head 102 mounted on the carriage 106 ejects ink according to ejection data, thereby recording one band of an image on the print medium P. The print medium P in the area where such printing scanning is performed is supported from behind by a platen 107, and the distance between the nozzle surface of the print head 102 and the print medium P is kept constant.

When the printing scan for one band is completed, the roller pair of conveying roller 103 and auxiliary roller 104 that nip the printing medium P, and the paper feed roller pair 105 rotate in the direction of the arrow in the figure, and convey the printing medium P a distance corresponding to the distance of the one band in the Y direction that intersects with the X direction. By alternating between the printing scan and the conveying operation as described above, an image is formed in stages on the printing medium P.

The carriage 106 is equipped with four ink cartridges 101 for supplying ink to the print head 102. In this embodiment, the four ink cartridges 101 contain cyan (C), magenta (M), yellow (Y), and black (K) ink, respectively. When no printing operation is being performed, the carriage 106 waits at the home position H.

Figures 2(a) to (c) are views of the print head 102 as viewed from the nozzle surface. Figure 2(a) is an overall view of the nozzle surface, and Figures 2(b) and (c) are enlarged views of each nozzle row arranged on the nozzle surface. As shown in Figure 2(a), the print head 102 has a K row that ejects black ink, a C row that ejects cyan ink, an M row that ejects magenta ink, and a Y row that ejects yellow ink, arranged in parallel in the X direction. In each nozzle row, multiple nozzles for ejecting the corresponding ink are arranged in the Y direction at a predetermined pitch. These nozzle rows are formed using semiconductor technology, but in this embodiment, only the K row that ejects black ink is formed on a chip separate from the other nozzle rows.

Figure 2(b) is an enlarged view of the K row. In the K row, two black nozzle rows 201 are arranged in the X direction, each row having 64 nozzles that eject black ink at a pitch of 300 dpi in the Y direction. These two nozzle rows 201 are arranged with a half pitch (one pixel of 600 dpi) offset in the Y direction. Such a K row is processed as having 128 nozzles arranged at a resolution of 600 dpi in the Y direction, and an image with a resolution of 600 dpi in the Y direction can be recorded on the recording medium by performing an ejection operation while moving the K row in the X direction. In this embodiment, each nozzle arranged in the nozzle row 201 ejects approximately 25 pl of black ink and records a dot with a diameter of approximately 60 μm on the recording medium.

Figure 2(c) is an enlarged view of rows C, M, and Y. In each of rows C, M, and Y, a nozzle row 202 that ejects 5 pl of ink and a nozzle row 203 that ejects 2 pl of ink are arranged in parallel in the X direction. In the nozzle rows 202 and 203, 128 nozzles are arranged in the Y direction at a pitch of 600 dpi. 5 pl of ink forms dots with a diameter of approximately 38 μm on the recording medium, and 2 pl of ink forms dots with a diameter of approximately 28 μm on the recording medium.

Directly below each nozzle (in the -Z direction) is a heater (not shown) that serves as a recording element. When a voltage pulse is applied to this heater, film boiling occurs in the rapidly heated ink, and the growth energy of the resulting bubbles causes the ink to be ejected.

Figure 3 is a block diagram for explaining the control configuration of an inkjet recording system applicable to this embodiment. The inkjet recording system in this embodiment includes the inkjet recording device 2 described in Figure 1 and an image processing device 1. The image processing device 1 can be, for example, a PC.

The image processing device 1 generates image data that can be recorded by the recording device 2. In the image processing device 1, the main control unit 308 is composed of a CPU, ROM, RAM, ASIC, etc., and performs image creation in the image processing device 1 and image processing when the created image is recorded by the recording device 2. The image processing device I/F 309 exchanges data signals with the recording device 2. The display unit 310 displays various information to the user, and can be, for example, an LCD. The operation unit 314 is an operation unit for the user to perform operations, and can be, for example, a keyboard or a mouse. The system bus 312 connects the main control unit 308 to each function. The I/F signal line 313 connects the image processing device 1 and the recording device 2. As the type of I/F signal line 313, for example, one that meets the specifications of Centronics Corporation can be used.

In the recording device 2, a controller 301 is configured with a CPU, ROM, RAM, etc., and controls the entire recording device 2. A print buffer 302 stores image data as raster data before it is transferred to the print head 102. The inkjet print head 102 ejects ink from each nozzle according to the image data stored in the print buffer 302.

The paper feed/eject motor control unit 304 drives the LF motor E0002 (see FIG. 4) and controls the transport and paper feed/ejection of the recording medium P. The carriage motor control unit 300 drives the carriage motor E0001 (see FIG. 4) and controls the reciprocating scanning of the carriage 106. The data buffer 306 temporarily stores image data received from the image processing device 1. The system bus 307 connects the various functions of the recording device 2.

Figure 4 is a block diagram for explaining the overall configuration of the electrical circuit of the recording device 2. The electrical configuration of the recording device 2 is mainly composed of the carriage board E0013, the main board E0014, the power supply unit E0015, and the front panel E0106.

The power supply unit E0015 is connected to the main board E0014 and supplies various driving power sources.

The carriage board E0013 is a printed circuit board unit mounted on the carriage 106. The carriage board E0013 exchanges signals with the print head 102 through the head connector E0101, and supplies drive power to the print head 102 via the flexible flat cable (CRFFC) E0012. The carriage board E0013 also detects changes in the positional relationship between the encoder scale E0005 and the encoder sensor E0004 based on a pulse signal output from the encoder sensor E0004 as the carriage 106 moves. The carriage board E0013 then outputs the output signal to the main board E0014 via the flexible flat cable (CRFFC) E0012.

The main board E0014 is a printed circuit board unit that controls the drive of each part of the recording device 2. The main board E0014 has a host interface E0017 and receives image data from a host computer that is the image processing device 1. The main board E0014 is also connected to various motors, such as a carriage motor E0001 that serves as a drive source for scanning the carriage 106 and an LF motor E0002 that serves as a drive source for transporting the recording medium, to control the drive of each function. The main board E0014 is also connected to a sensor signal line E0104 for transmitting control signals to various sensors that detect the operating status of each part of the device, such as an LF encoder sensor, and for receiving detection signals from the sensors. Furthermore, the main board E0014 has an interface for sending and receiving information to the front panel E0106 via a panel signal E0107.

Figure 5 is a block diagram showing the internal configuration of the main board E0014. The ASIC (Application Specific Integrated Circuit) E1102 is a one-chip semiconductor integrated circuit with a built-in arithmetic processing unit. The ASIC E1102 is connected to the ROM E1004 via a control bus, and performs various controls according to the programs stored in the ROM E1004. The functions of the controller 301 described in Figure 3 are realized by the ASIC E1102.

The ASIC E1102 performs various logical operations and conditional judgments according to the connection and data input status of the host interface E0017, controls each component, and is responsible for controlling the recording device.

The power for the ASIC E1102 is supplied from the power supply unit E0015, and the supplied power is voltage converted as necessary before being supplied to each part inside and outside the main board E0014. The ASIC E1102 also transmits a power supply unit control signal E4000 to the power supply unit E0015 to control the low power consumption mode of the recording device, etc.

The ASIC E1102 outputs the motor control signal E1106, the power supply control signal E1024, the power supply unit control signal E4000, and the like. The ASIC E1102 also transmits and receives sensor signals E0104 related to various sensors.

The ASIC E1102 detects the state of the encoder signal (ENC) E1020 to generate a timing signal, and controls the printing operation of the printhead 102 with the head control signal E1021. The encoder signal (ENC) E1020 shown here is the output signal of the encoder sensor E0004 input through the CRFFC E0012. The head control signal E1021 is connected to the carriage board E0013 through the flexible flat cable E0012, and is supplied to the printhead 102 via the head connector E0101. Various information from the printhead 102 is transmitted to the ASIC E1102 in the reverse direction to that described above.

The DRAM E3007 is used as a data buffer for recording, a buffer for data received from the host computer, and as a work area required for various control operations. The EEPROM E1005 is used to store various information such as recording history and to call it up as necessary. The power supply control circuit E1010 controls the power supply to each sensor having a light-emitting element according to the power supply control signal E1024 from the ASIC E1102. The host interface E0017 transmits the host interface signal E1128 from the ASIC E1102 to the host interface cable E1029 connected to the outside, and also transmits the signal from this cable E1029 to the ASIC E1102.

<Printhead driving circuit>
FIG. 6 is a configuration diagram of the drive circuit of the printhead 102. Here, for simplicity, the drive circuit for M print elements included in the nozzle array 202 (see FIG. 2) that ejects cyan ink is shown. In the figure, one end of the M print elements R01 to RM is commonly connected to a drive voltage VH, and the other end is connected to an M-bit driver 601. A logical product (AND) signal of an output signal from an M-bit latch 602 and an N-bit block enable selection signal (BE1 to BEN) is input to the M-bit driver 601. The M-bit latch 602 connected to an M-bit shift register 603 latches (records and holds) M-bit data stored in the M-bit shift register 603 upon receiving a latch signal (LAT). The M-bit shift register 603 aligns the binary print signal S_IN sent in synchronization with the print data transfer clock (SCLK) in correspondence with the print elements R01 to RM, and temporarily stores it.

The block enable selection signals (BE1 to BEN) are signals for dividing M recording elements (heaters) R01 to RM into N blocks and driving them. The M recording elements R01 to RM correspond to one of the N block enable selection signals (BE1 to BEN). A drive voltage VH is applied to each of the M recording elements R01 to RM based on the recording signal stored in the M-bit latch when the corresponding block enable selection signal is turned ON. The transmission of the block enable selection signals (BE1 to BEN) is controlled by the ASIC E1102 and is sent to the recording head 102 as the head control signal E1021 in FIG. 5.

The ASIC E1102 transmits N block enable selection signals (BE1 to BEN) at timings that are shifted by a time t. Here, time t corresponds to the time required for the ejection operation of one pixel divided into N. This control, which drives N blocks at different timings even in the same one pixel area, is called time-division drive control.

When using a print head consisting of many nozzles as described in Figure 2, a large power supply capacity is required to drive all the nozzles simultaneously. In addition, driving all the nozzles simultaneously causes a large current to flow instantaneously, which raises concerns about noise generation. By performing time-division driving as in this embodiment, the number of printing elements driven simultaneously can be reduced, the power supply capacity required for the printing device can be reduced, and noise generation can be suppressed.

<Image processing flow>
7 is a flowchart for explaining a series of image processing operations executed by the main control unit 308 of the image processing device 1 and the controller 301 of the recording device 2 when an arbitrary image is recorded by the recording device 2. This processing operation is started when the user inputs a command to record an arbitrary image.

When this process starts, the main control unit 308 first performs color correction processing in step S701. In this embodiment, image data generated by an application or the like is arranged at 600 dpi, with each pixel having an 8-bit, 256-level luminance value for each of R (red), G (green), and B (blue). In the color correction processing, the main control unit 308 converts this RGB data of each pixel into R'B'G' data expressed in a color space specific to the recording device 2. A specific conversion method can be, for example, by referring to a lookup table stored in advance in memory.

In step S702, the main control unit 308 performs color separation processing on the R'G'B' data. Specifically, the main control unit 308 refers to a lookup table stored in advance in memory and converts the luminance value R'G'B' of each pixel into 8-bit, 256-level density values C1, M1, Y1, and K1 that correspond to the ink colors used by the recording device 2.

In step S703, the main control unit 308 performs tone correction processing on the density values C1, M1, Y1, and K1. Tone correction processing is a correction for making the input density values and the optical density expressed on the recording medium P have a linear relationship. This is usually performed by referencing a one-dimensional lookup table prepared in advance. By the tone correction processing in step S703, the 8-bit 256-level density values C1, M1, Y1, and K1 are converted into 8-bit 256-level tone values C2, M2, Y2, and K2.

In step S704, the main control unit 308 performs a predetermined quantization process on the gradation data C2, M2, Y2, and K2 to generate quantized data C3, M3, Y3, and K3. In this embodiment, the quantized data K3 for black ink is binary data indicating whether a dot is printed (1) or not printed (0). On the other hand, the quantized data C3, M3, and Y3 for cyan, magenta, and yellow inks are ternary data indicating one of three gradation values (0, 1, and 2). In this embodiment, this quantization process is performed by a dither method using a threshold matrix.

In this embodiment, the processes from S701 to S704 are performed by the main control unit 308 of the image processing device 1. The main control unit 308 transmits the quantized data C3, M3, Y3, and K3 generated in step S704 to the recording device 2.

After receiving the quantized data C3, M3, Y3, and K3, the controller 301 of the recording device 2 first performs nozzle array expansion processing in step S705.

Figure 8 shows the nozzle array development table that the controller 301 refers to in step S705. As described in Figure 2, in the print head 102 of this embodiment, the C, M, and Y arrays include a nozzle array 202 that ejects 5 pl of ink and a nozzle array 203 that ejects 2 pl of ink. The controller 301 determines nozzle tone values C4, M4, and Y4 for the 5 pl nozzle array 202 and the 2 pl nozzle array 203, respectively, according to the quantization values C3, M3, and Y3 indicated by the quantization data. In this example, the nozzle tone value C4 of the 2 pl nozzle array 203 is not generated, and the nozzle tone values C4, M4, and Y4 of the 5 pl nozzle array 202 are set to 0, 1, or 2. For the K row, which has two nozzle rows 201 that eject 25 pl of ink, the binary quantized value K3, which indicates printing (1) or non-printing (0), is used as the nozzle tone value K4 as is.

Returning to the explanation of FIG. 7, in step S706, the controller 301 performs mask processing.

Figure 9 is a diagram showing an example of a multi-value mask pattern for CMY used by the controller 301 in step S706. When performing two-pass multi-pass printing, a mask pattern Mp1 for odd passes and a mask pattern Mp2 for even passes are prepared as multi-value mask patterns. Mask patterns Mp1 and Mp2 have a pixel area of 32 x 32 pixels, and a mask value of "1" or "2" is set for each pixel. In the figure, pixels shown in gray are pixels to which a mask value of "1" is set, and pixels shown in black are pixels to which a mask value of "2" is set. Mask patterns Mp1 and Mp2 have a complementary relationship with each other for mask values "1" and "2". The controller 301 uses these mask patterns Mp1 and Mp2 repeatedly in the XY directions.

On the other hand, although not shown, a mask pattern for odd passes and a mask pattern for even passes, each having a pixel area of 32 x 32 pixels, are also prepared for black ink. The mask pattern for black ink is a binary mask pattern, with a mask value of "1" or "0" set for each pixel. The mask patterns for odd passes and the mask patterns for even passes have a complementary relationship with respect to the mask values "1" and "0". Note that the mask patterns for black ink may be ones in which the mask values (1, 2) of the mask patterns Mp1 and Mp2 shown in FIG. 9 are rewritten to mask values (0, 1).

By referring to the above mask pattern, the controller 301 obtains the mask value for the odd pass and the mask value for the even pass of the pixel to be processed based on the coordinates (x, y) of the pixel to be processed.

Figure 10 shows the table that the controller 301 refers to in step S706. The controller 301 determines the binary print values C5, M5, Y5, K5 for the pixel to be processed by combining the nozzle tone values C4, M4, Y4, K4 obtained in step S705 and the mask values obtained from the mask patterns Mp1 and Mp2 described above. The print values C5, M5, Y5, K5 are values that indicate whether a dot is printed (1) or not printed (0) for the pixel to be processed.

For example, if the nozzle tone value C4 is 0, the recording value C5 of the pixel being processed will be 0 (non-recorded) regardless of the mask value. If the nozzle tone value C4 is 1, the recording value C5 will be 1 (recorded) only if the mask value is 1. If the nozzle tone value C4 is 2, the recording value C5 will be 1 (recorded) if the mask value is 1 or 2.

By the masking process described above, the recording values C5, M5, Y5, and K5 that determine whether or not a dot is recorded for the pixel being processed are determined for each of the odd-numbered and even-numbered passes. As a result, a pixel with a gradation value of C4=2 will have one dot recorded in each of the odd-numbered and even-numbered passes. A pixel with a gradation value of C4=1 will have one dot recorded in either the odd-numbered or even-numbered pass. Furthermore, a pixel with a gradation value of C4=0 will have no dot recorded in either the odd-numbered or even-numbered pass.

Returning to the explanation of FIG. 7, in S707, the controller 301 transmits the print values C5, M5, Y5, and K5 generated in step S706 to the driver of the print head 102. The head driver generates ejection data according to the received print values and drives the print elements of the print head 102 to perform an ejection operation. This completes the process.

<Block drive control>
11A and 11B are diagrams for explaining the time-division driving adopted in this embodiment. In the time-division driving of this embodiment, the nozzles arranged in each nozzle row are divided into 16 blocks, and the timing of applying a voltage pulse to the heater is shifted for each block. Such time-division driving is realized by the driving circuit described in FIG.

Figure 11 (a) shows the block numbers and the drive order of each block. It shows that the nozzles in block 1 are driven at the first timing, the nozzles in block 2 are driven at the fourth timing, and the nozzles in block 16 are driven at the 14th timing. Each of the 16 blocks is driven at one of the 1st to 16th timings obtained by dividing the period corresponding to one pixel of 600 dpi into 16 parts.

The information shown in FIG. 11(a) is stored as a block drive order setting table in the RAM E3007, ROM E1004, or a storage area inside the ASIC E1102 described in FIG. 5. When performing time-division driving, the ASIC E1102 generates block enable selection signals (BE1 to BEN) based on this block drive order setting table.

Figure 11(b) shows the nozzles arranged in nozzle row 202 of row C, a drive timing chart for each nozzle, and the dot recording state on the recording medium. The nozzles arranged in the Y direction are sorted into 16 different blocks, starting from the first nozzle on the -Y direction side, namely block 1, block 4, etc. Additionally, the 17th to 32nd nozzles are sorted into 16 different blocks in the same order as the 1st to 16th nozzles. Such a group of 16 consecutive nozzles is referred to as a section in this specification.

Timing chart 1100 shows the drive timing of each nozzle according to the table in FIG. 11(a). Here, the drive timing of the nozzles included in the first section is shown, but timing chart 1100 is repeated from the second section onwards. In the figure, the horizontal axis indicates time, and the vertical axis indicates the drive voltage VH applied to the heater of each nozzle. According to the figure, the period corresponding to one pixel of 600 dpi is divided into 16 parts, and the nozzles are driven sequentially with a one period shift in the order of block 1, block 12, block 7, block 2, etc., until the nozzle in block 6 is driven last.

When the carriage 106 (see FIG. 1) is moved in the +X direction under such drive control, a dot pattern 1101 is formed on the recording medium. Since the ejection is performed while the carriage 106 is moving in the +X direction, the dots are arranged with a shift in the +X direction according to the drive order. To explain in more detail, when one pixel area of 600 dpi is divided into 16 sections, the dots printed by six adjacent nozzles, such as 1st to 6th, 7th to 12th, and 13th to 16th, are arranged with a shift of three sections. As a result, on the recording medium, oblique lines with a certain inclination with respect to the X direction are repeatedly arranged in the Y direction.

In this embodiment, the first to sixth nozzle groups, which are arranged with a shift of three sections, are called adjacent nozzle group 1, the seventh to eleventh nozzle groups are called adjacent nozzle group 2, and the twelfth to sixteenth nozzle groups are called adjacent nozzle group 3. Such adjacent nozzle groups 1 to 3 are included in each section in the same way.

When the time-division driving is performed as described above, the number of nozzles driven simultaneously can be reduced, and the power supply capacity can be reduced. On the other hand, as in dot pattern 1101, there will be variation in the dot recording position within one pixel area of 600 dpi. In the case of Figure 11, there is a shift of 13 intervals (≒ 34 μm) at the boundary between adjacent nozzle groups.

Figure 12 is a schematic diagram for explaining two-pass multi-pass printing, which is executed under the control of the controller 301 in the printing device 2. For ease of explanation, the printing operation of nozzle row C 202 (see Figure 2) out of the multiple nozzle rows arranged in the print head 102 will be explained here. When performing two-pass multi-pass printing, the 128 nozzles included in the nozzle row 202 are divided into a first division area and a second division area.

In the first print scan, the controller 301 moves the print head 102 in the +X direction while using the first divided area to perform an ejection operation according to the print data C5 generated using the mask pattern Mp1. The controller 301 then transports the print medium by 64 pixels in the +Y direction. For convenience, in FIG. 12, the print head 102 is moved in the -Y direction to show the relative positional relationship between each divided area and the unit area of the print medium.

In the second print scan, the controller 301 moves the print head 102 in the +X direction, and uses the first and second divided regions to perform an ejection operation according to the print data C5 generated using the mask pattern Mp2. The controller 301 then transports the print medium in the +Y direction by 64 pixels.

In the third print scan, the controller 301 moves the print head 102 in the +X direction, and uses the first and second divided regions to perform an ejection operation according to the print data C5 generated using the mask pattern Mp1. The controller 1301 then transports the print medium by 64 pixels in the +Y direction.

After this, the printing scans according to mask pattern Mp1 and mask pattern Mp2 are alternately repeated with a transport operation of 64 pixels between them, as described above. As a result, a dot pattern printed according to mask pattern Mp1 and a dot pattern printed according to mask pattern Mp2 are printed in an overlapping manner in each unit area of the printing medium.

<Relationship between Threshold Matrix and Time-Division Driving>
Figures 13(a) to (c) are diagrams showing the relationship between a general threshold matrix that can be used in quantization processing and a dot pattern formed on a recording medium. Figure 13(a) shows a general threshold matrix for binarization. The threshold matrix has a pixel area of 16 x 16 pixels, and each pixel is set to a threshold value Th of 0 to 255. In the following, in order to explain binary quantization, a case will be described in which gradation data C2 is quantized into binary quantized data C3.

When the gradation value C2 of the pixel to be processed and the threshold value Th corresponding to that pixel satisfy the relationship Th≦C2, the main control unit 308 sets the quantization value C3 of that pixel to "1", and when the relationship Th>C2 holds, the main control unit 308 sets the quantization value C3 of that pixel to "0".

Figure 13(b) shows the result of quantization when multi-value data with a gradation value C2 = 128 is uniformly input. In the figure, pixels shown in black are pixels with a quantization value C3 of 1, and pixels shown in white are pixels with a quantization value C3 of 0. In Figure 13(b), it can be seen that black and white patterns with a period shorter than the threshold matrix, i.e., a period of 2 pixels x 2 pixels, are repeatedly arranged in the XY direction, and black pixels indicating dot recording are uniformly distributed. In the threshold matrix shown in Figure 13(a), the threshold value of each pixel is determined so that a repeating pattern with a period shorter than the threshold matrix appears in the quantized data, regardless of the gradation value C2 of any value between 0 and 255.

Figure 13(c) shows a dot pattern recorded on a recording medium when the time-division driving described in Figure 11 is performed according to the quantized data of Figure 13(b). When time-division driving is performed, even if the X coordinate is the same pixel position, the positions where each dot lands will be shifted from each other depending on the corresponding block. Therefore, even if high dispersion is obtained in the quantized data as in Figure 13(b), in the dot pattern formed on the recording medium, the phase of the repeating pattern will be shifted at the boundary between adjacent nozzle groups, resulting in dot sparseness and density as shown in Figure 13(c). In particular, it can be seen that the shift of 13 sections (≒ 34 μm) at the boundary between adjacent nozzle groups is noticeable.

Figures 14(a) to (c) are diagrams showing the relationship between the threshold matrix used in the quantization process of this embodiment and the dot pattern formed on a recording medium. Figure 14(a) shows the threshold matrix used in step S704 of Figure 7 in this embodiment. The threshold matrix of this embodiment is a threshold matrix in which a repeating pattern with a shorter period than the threshold matrix appears, as shown in Figure 13(a), has been subjected to a specified offset process. Hereinafter, the basic threshold matrix shown in Figure 13(a), in which a repeating pattern with a shorter period than the threshold matrix appears in the quantized data and which provides high dispersibility, will be referred to as the basic threshold matrix.

Below, the offset process for the basic threshold matrix will be specifically explained with reference to Figures 13(a) and 14(b). First, the threshold of the area corresponding to adjacent nozzle group 1 (nozzle numbers 1 to 6) is maintained as the basic threshold matrix. The threshold of the area corresponding to adjacent nozzle group 2 (nozzle numbers 7 to 11) is offset by one pixel in the +X direction. At this time, the threshold of the rightmost area (+X side) is moved to the leftmost area (-X side). The threshold of the area corresponding to adjacent nozzle group 3 (nozzle numbers 12 to 16) is offset by two pixels in the +X direction.

Figure 14(b) shows the result of quantization when the threshold matrix of Figure 14(a) is used and multi-value data with a gradation value of C2 = 128 is uniformly input. Compared to Figure 13(b), it can be seen that the phase of the repeating pattern is shifted at the boundary between adjacent nozzle groups, impairing the dispersibility of black pixels. However, when printing is performed using the time-division driving described in Figure 11, a uniform dot pattern such as that shown in Figure 14(c) is obtained. Compared to the dot pattern of Figure 13(c), the dot pattern of Figure 14(c) eliminates the misalignment of the repeating pattern at the boundary and achieves high dispersibility.

Figure 15 is a diagram for explaining how high dispersibility is obtained with the dot pattern of Figure 14(c). As with Figure 11(b), it shows the nozzles arranged in the nozzle row 202, a drive timing chart for each nozzle, and the dot recording state on the recording medium. Here, it shows a timing chart 1500 and a dot pattern 1501 when dots are recorded consecutively on two pixel rows that are consecutive in the X direction.

In dot pattern 1501, when we look at the dot group of the preceding pixel and the dot group of the following pixel, we can see that the following dot group printed by adjacent nozzle group 2 is located on the extension line of the preceding dot group printed by adjacent nozzle group 1. We can also see that these preceding dot groups and following dot groups are arranged continuously at a constant inclination. This is because the drive shift between the sixth nozzle, which is the slowest driven nozzle in adjacent nozzle group 1, and the seventh nozzle, which is the fastest driven nozzle in adjacent nozzle group 2, is 13 intervals, and the drive shift between the preceding pixel of the sixth nozzle and the following pixel of the seventh nozzle is equivalent to three intervals. In other words, the sixth nozzle, which is driven 13 intervals behind the seventh nozzle, is driven at a timing three intervals (=16-13) earlier than the drive timing of the next pixel of the seventh nozzle, and as a result, the dots are arranged at the same interval as other adjacent nozzles. This situation also occurs at the boundary between adjacent nozzle groups 2 and 3.

In view of the above, in this embodiment, a basic threshold matrix that provides high dispersion in the quantized data is prepared in advance, and the quantization process is performed using a threshold matrix in which the contents of the thresholds in this basic threshold matrix are offset according to the rules described in FIG. 14. As a result, it is possible to reproduce, after performing time-division driving, a dot pattern equivalent to that printed using the basic threshold matrix and without performing time-division driving.

In this case, the threshold matrix may be stored in advance in the memory of the image processing device 1, or only the basic threshold matrix may be stored in the memory. In the latter case, a predetermined offset process may be applied to the basic threshold matrix as necessary to generate the threshold matrix to be actually used.

According to the present embodiment described above, the recording position deviation is corrected by quantization processing, so image tilt does not occur as in Patent Document 1, which shifts the quantized data (see FIG. 37). Therefore, image loss due to image tilt is not caused. Furthermore, since there is no need to add a new process to correct the quantized data as in Patent Document 1, the processing load does not increase or the throughput decreases due to correction.

In the above, we have described a case where the print scan is performed only in the forward direction (+X direction) in two-pass multi-pass printing, but this embodiment can also be applied to bidirectional multi-pass printing. That is, in the multi-pass printing described in FIG. 12, odd-numbered scans such as the first and third print scans can be performed by the forward scan of the print head, and even-numbered scans such as the second and fourth print scans can be performed by the return scan of the print head.

However, in this case, if the print head is driven and controlled in the same way as described above, the inclination of the dot arrangement will be reversed between forward and backward scanning. Therefore, for the threshold matrix for the backward scanning, it is necessary to perform offset processing that reverses the left and right of the threshold matrix for the forward scanning described in FIG. 14(a) with respect to the basic threshold matrix. In other words, when applying this embodiment to bidirectional multi-pass printing, it is necessary to prepare a threshold matrix for the forward scanning and a threshold matrix for the backward scanning.

In this case, the memory may store a threshold matrix for forward scanning and a threshold matrix for backward scanning, or may store only the basic threshold matrix. In the latter case, the main control unit 308 of the image processing device performs an offset process that inverts the left and right of the basic threshold matrix stored in the memory to generate a threshold matrix for forward scanning and a threshold matrix for backward scanning.

In the above, the time required for one pixel to be discharged is divided into 16 periods, and the adjacent nozzle groups are driven sequentially every 3 periods, and at the boundary between adjacent nozzle groups, the nozzles are driven every 13 periods. However, in time-division control, the number of divisions of the time required for one pixel to be discharged, the period for sequential driving within the same adjacent nozzle group, and the driving period at the boundary between adjacent nozzle groups are not limited to the above. When the time required for one pixel to be discharged is divided into N periods, the adjacent nozzle groups are driven sequentially every K periods (K<N), and there are K adjacent nozzle groups in one section. In this form, the effect of using a threshold matrix that is offset by one pixel from the basic threshold matrix can be achieved.

Second Embodiment
<Nozzle arrangement configuration>
This embodiment also uses the inkjet recording system and inkjet recording device described in Figures 1, 3 to 6. However, the inkjet recording device 2 of this embodiment ejects ink in gray (G) in addition to cyan (C), magenta (M), yellow (Y), and black (K). For this reason, ink cartridges for five colors are mounted on the carriage 106 described in Figure 1.

Figures 16(a) to (c) are views of the print head 102 of this embodiment as viewed from the nozzle surface. Figure 16(a) is an overall view of the nozzle surface, and Figures 16(b) and (c) are enlarged views of each nozzle row arranged on the nozzle surface. As shown in Figure 16(a), the print head 102 has a K row for black ink, C1 and C2 rows for cyan ink, M1 and M2 rows for magenta ink, Y row for yellow ink, and G1 and G2 rows for gray ink, arranged in parallel as shown. In this embodiment, all of the nozzle rows are formed on the same chip.

Figure 16(b) is an enlarged view of the K row. In the K row, two nozzle rows 1601 are arranged in the X direction, each row having 128 nozzles for ejecting black ink arranged in the Y direction at a pitch of 600 dpi. These two nozzle rows 201 are arranged with a half pitch (one pixel of 1200 dpi) offset in the Y direction. By performing an ejection operation while moving such a K row in the X direction, an image with a resolution of 1200 dpi in the Y direction can be printed on the recording medium. In this embodiment, each nozzle arranged in the nozzle row 1601 ejects approximately 5 pl of black ink and prints a dot with a diameter of approximately 38 μm on the recording medium. Hereinafter, the row arranged in the +Y direction relative to the row is called the LEv row, and the row arranged in the -Y direction relative to the row is called the LOd row. The Y row ejecting yellow ink has the same configuration as the K row ejecting black ink.

Figure 16(c) is an enlarged view of the C1 and C2 rows. In the C1 row, an LEv row that ejects 5 pl of cyan ink, an MEv row that ejects 2 pl of cyan ink, and an SOd row that ejects 1 pl of cyan ink are arranged. On the other hand, in the C2 row, an LOd row that ejects 5 pl of cyan ink, an MOd row that ejects 2 pl of cyan ink, and an SEv row that ejects 1 pl of cyan ink are arranged. In each nozzle row, 128 nozzles are arranged in the Y direction at a pitch of 600 dpi. 5 pl of ink forms dots with a diameter of about 38 μm on the recording medium, 2 pl of ink forms dots with a diameter of about 28 μm, and 1 pl of ink forms dots with a diameter of about 22 μm.

In the C1 and C2 rows, the LEv row is offset by half a pitch (1200 dpi) in the -Y direction from the LOd row, the MEv row is offset by half a pitch (1200 dpi) from the MOd row, and the SEv row is offset by half a pitch (1200 dpi) from the SOd row. In addition, the MEv and MOd rows, which eject 2 pl, and the SEv and SOd rows, which eject 1 pl, are offset by 1/4 pitch (2400 dpi) in the -Y direction from the LEv and LOd rows, which eject 5 pl. Note that the Y-direction positions of Lod and LEv in the C1 and C2 rows are the same as the Y-direction positions of Lod and LEv in the K1 and K2 rows. The M1 and M2 rows, and the G1 and G2 rows have the same configuration as the C1 and C2 rows.

Directly below (in the -Z direction) each of the nozzles that make up the nozzle rows are heaters (not shown) that act as recording elements. When a voltage pulse is applied to these heaters, film boiling occurs in the rapidly heated ink, and the ink is ejected along with the growth energy of the resulting bubbles.

<Block drive control>
17A and 17B are diagrams for explaining the time-division driving adopted in this embodiment.

Figure 17(a) is a diagram showing the block numbers and the drive order of each block in the time-division drive of this embodiment. As with the first embodiment, each of the 16 blocks is driven at one of the 1st to 16th timings obtained by dividing the period corresponding to one pixel at 600 dpi into 16 parts. This shows that the nozzles included in block 1 are driven at the first timing, the nozzles included in block 2 are driven at the fifth timing, and the nozzles included in block 16 are driven at the 16th timing.

Figure 17(b) is a diagram showing the nozzles arranged in the nozzle row 1601, a drive timing chart for each nozzle, and the dot recording state on the recording medium. Here, a timing chart 1700 and dot pattern 1705 are shown when dots are recorded consecutively on two pixel rows that are consecutive in the X direction according to the table in Figure 17(a).

In this embodiment, when one pixel area of 600 dpi is divided into 16 sections, dots printed by adjacent nozzles such as the first to fourth nozzles are arranged with a shift of four sections. In this embodiment, the first to fourth nozzle groups arranged with a shift of four sections are called adjacent nozzle group 1, the fifth to eighth nozzle groups are called adjacent nozzle group 2, the ninth to twelfth nozzle groups are called adjacent nozzle group 3, and the thirteenth to sixteenth nozzle groups are called adjacent nozzle group 4. Such adjacent nozzle groups 1 to 4 are included in each section in the same way.

When the above-described time-division driving is performed, a shift of 11 sections (≈29 μm) occurs at the boundary between adjacent nozzle groups. Looking at dot pattern 1705, it can be seen that the group of dots printed by adjacent nozzle group 2 for the next pixel is located on the extension line of the group of dots printed by adjacent nozzle group 1.

This is because the drive shift between the fourth nozzle, which is the latest driven nozzle in adjacent nozzle group 1, and the fifth nozzle, which is the earliest driven nozzle in adjacent nozzle group 2, is 11 intervals, and the drive shift between the preceding pixel of the fourth nozzle and the succeeding pixel of the fifth nozzle is equivalent to five intervals. In other words, the fourth nozzle, which is driven 11 intervals behind the fifth nozzle, is driven five intervals (=16-11) earlier than the drive timing of the next pixel of the fifth nozzle. As a result, dots are arranged at approximately the same intervals as other adjacent nozzles, which are offset by four intervals each. This situation also occurs at the boundaries between other adjacent nozzle groups.

In this embodiment, based on these printing position shift rules, offset processing is performed on the basic threshold matrix similar to that in the first embodiment, and the obtained threshold matrix is used in the quantization process in Figure 7.

<Image processing flow>
The image processing executed in this embodiment will be described below. In this embodiment, too, image processing can be performed according to the flowchart explained in Fig. 7. Steps that differ from the first embodiment will be described below. Note that the processing resolution in steps S701 to S704 is 600 dpi x 600 dpi, the same as in the first embodiment.

In the nozzle array expansion process of step S705, the controller 301 converts the quantized value C3 of 600 dpi x 600 dpi into a nozzle tone value C4 of 600 dpi x 1200 dpi.

Figures 18(a) and (b) are diagrams showing dot arrangement patterns and basic index patterns used in the nozzle array expansion process of this embodiment. Figure 18(a) is a diagram showing dot arrangement patterns. One pixel area of 600 dpi x 600 dpi is associated with two recording pixels of 600 dpi x 1200 dpi. When the quantization value C3 of one pixel of 600 dpi x 600 dpi is "0", that is, indicating no dot is recorded, no dot is arranged in either recording pixel of 600 dpi x 1200 dpi. On the other hand, when the quantization value C3 of one pixel of 600 dpi x 600 dpi is "1", that is, indicating the recording of a dot, there are two possible positions for actually recording the dot. In this embodiment, a pattern A in which dots are arranged in the upper recording pixel, i.e., the recording pixel on the -Y direction side, and a pattern B in which dots are arranged in the lower recording pixel, i.e., the recording pixel on the +Y direction side, are prepared. In the dot arrangement pattern of this embodiment, dots are printed on the upper recording pixels by nozzles in the LEv row, and dots are printed on the lower recording pixels by nozzles in the LOd row (see FIG. 16(c)).

Figure 18 (b) is a diagram showing a basic index pattern 1800. In the basic index pattern 1800, each square corresponds to one pixel area of 600 dpi x 600 dpi. For each pixel, it is determined whether dots are arranged in pattern A or pattern B when the quantization value of the corresponding pixel is "1". Note that the dot arrangement pattern in Figure 18 (a) is for 5 pl ink droplets, i.e., for the LEv and LOd columns, but it may also be set to output a mixture of 2 pl ink droplets and 1 pl ink droplets.

<Threshold matrix and index pattern>
19A to 19D are diagrams for explaining the threshold matrix and index pattern used in this embodiment. FIG. 19A shows the threshold matrix used in the quantization process in step S704. This threshold matrix is obtained by performing offset processing on the basic threshold matrix described in FIG. 13A based on the rules of time-division driving in this embodiment. Specifically, the basic threshold matrix is offset by one pixel in the +X direction in the area corresponding to adjacent nozzle group 2, by two pixels in the +X direction in the area corresponding to adjacent nozzle group 3, and by three pixels in the +X direction in the area corresponding to adjacent nozzle group 4.

Figure 19(b) shows the quantized data when the threshold matrix in Figure 19(a) is used and multi-value data with a gradation value of C2 = 128 is uniformly input.

On the other hand, FIG. 19C shows the index pattern used in the nozzle expansion process in step S707. The basic index pattern 1800 is generally used repeatedly in the X and Y directions, but in this embodiment, an offset process similar to that of the threshold matrix is performed. That is, the basic index pattern 1800 is used repeatedly in the X direction, but in the Y direction, it is offset by one pixel in the +X direction in units of adjacent nozzle groups.

Specifically, in the area corresponding to adjacent nozzle group 1, basic index pattern 1800 is used repeatedly in the X direction as is. In the area corresponding to adjacent nozzle group 2, basic index pattern 1800 is used with a one pixel offset in the +X direction relative to adjacent nozzle group 1. In the area corresponding to adjacent nozzle group 3, basic index pattern 1800 is used with a two pixel offset in the +X direction, and in the area corresponding to adjacent nozzle group 4, basic index pattern 1800 is used with a three pixel offset in the +X direction.

Figure 19(d) shows binary print data C4 generated using the dot arrangement pattern of Figure 18(a) and the index pattern of Figure 19(c) in accordance with the quantized data C3 of Figure 19(b). In the binary print data C4, dot printing (1) or non-printing (0) is set for each pixel of 600 dpi in the X direction and 1200 dpi in the Y direction.

The threshold matrix and index pattern actually used in the quantization process may be stored in advance in the memory of the image processing device 1, but only the basic threshold matrix and basic index pattern may be stored in the memory. In this case, a predetermined offset process is applied to the basic threshold matrix and basic index pattern as necessary to generate the threshold matrix and basic index pattern that are actually used.

The print control of this embodiment can be applied to bidirectional multi-pass printing, as in the first embodiment. That is, in the multi-pass printing described in FIG. 12, odd-numbered scans such as the first and third print scans can be performed by the forward scan of the print head, and even-numbered scans such as the second and fourth print scans can be performed by the return scan of the print head.

When applying this embodiment to bidirectional multi-pass printing, it is necessary to prepare a threshold matrix for forward scanning, a threshold matrix for backward scanning, and an index pattern for forward scanning, and an index pattern for backward scanning. In this case, the main control unit 308 of the image processing device may generate a threshold matrix for forward scanning and a threshold matrix for backward scanning by performing left-right inverted offset processing on the basic threshold matrix stored in memory. Also, the controller (ASIC) of the recording device 2 may generate an index pattern for forward scanning and an index pattern for backward scanning by performing left-right inverted offset processing on the basic index pattern stored in memory.

Figures 20(a) to (d) are diagrams for explaining dot patterns when the printing control of this embodiment is performed. Figure 20(a) shows a dot pattern formed on a print medium when the ejection operation is performed according to the binary data of Figure 19(d) under the time-division driving of this embodiment described in Figure 17. On the other hand, Figure 20(b) shows a dot pattern formed on a print medium when the ejection operation is performed without performing offset processing on the basic threshold matrix and basic index pattern under the time-division driving of this embodiment. Comparing the two, in Figure 20(b), dot sparseness and density occur due to the influence of deviation that occurs at the boundary between adjacent nozzle groups. In contrast, in the dot pattern of this embodiment shown in Figure 20(a), it can be seen that the dot sparseness and density are reduced and high dot dispersion is obtained.

<Adjustment of Drive Timing of LEv Column and LOd Column>
Incidentally, the dot pattern shown in Fig. 20(a) has a higher dispersion than that shown in Fig. 20(b), but it can be seen that there is a periodic variation in density in units of two dots. This is because the recording resolution in the Y direction and the recording resolution in the X direction are different on the recording medium. Therefore, in this embodiment, in order to reduce the variation in density of dots caused by such a difference in recording resolution, the drive timing of the LEv row and the LOd row is further adjusted by using time-division driving.

Specifically, in the LEv and LOd columns, the dots formed by adjacent nozzles are shifted by four intervals due to the time-division driving described in FIG. 17, so the LOd and LEv columns are positioned at half this offset. To achieve this, in this embodiment, the LOd column is controlled to be shifted in the +X direction relative to the LEv column by (-1200 dpi + 600 dpi ÷ 16 × 2 ≒ 15.9 μm). This makes it possible to print a dot pattern with even better dispersion, as shown in FIG. 20 (c).

Figures 21(a) and (b) are schematic diagrams for explaining how the drive timing is shifted as described above during forward and backward print scans. Figure 21(a) shows the drive timing for the forward scan, and Figure 21(b) shows the drive timing for the return scan. The print head 102 has rows C1 and C2 arranged as shown in Figure 16(c).

In the forward scan, first, when the LEv row reaches the reference position, the LEv row is driven by the time-division drive described above. After that, when the LOd row reaches a position (1200 dpi + 600 dpi ÷ 16 × 2 ≒ 26.5 um) before the reference position, the LOd row is driven by time-division drive, but is not driven when the LOd row reaches the reference position.

In the return scan, the LOd column is not driven when it reaches the reference position, but is driven by time-division driving when it reaches a position (1200 dpi + 600 dpi ÷ 16 x 2 ≒ 26.5 um) further from the reference position. After that, when the LEv column reaches the reference position, the LEv column is driven by time-division driving. In both the forward scan and the return scan, the above adjustments can be made in units of one period obtained by dividing one pixel of 600 dpi in time-division driving by 16.

By performing the drive control as described above, the dot pattern shown in Figure 20(c) is obtained in the forward scan. Also, in the return scan, which is the opposite direction to the forward scan, a dot pattern that is the left-right inversion of Figure 20(c) is obtained.

In the above, the drive timing of the LOd row is shifted relative to the LEv row, but the dot pattern shown in FIG. 20(c) can be obtained by shifting the drive timing of the LEv row relative to the LOd row. Also, the nozzle row whose drive timing is shifted may be switched between the LEv row and the LOd row in the forward scan and the return scan. Also, if there is a limit to the resolution of the shift due to the circumstances of the recording device, it is possible to approach the dot pattern shown in FIG. 20(c) if a shift of at least 1200 dpi is achieved.

As described above, according to this embodiment, a suitable threshold matrix and index pattern are prepared based on the dot landing position when performing time-division driving using a recording head equipped with LOd and LEv columns, and the drive timing of the LOd and LEv columns is adjusted. This makes it possible to output a high-quality image with high dot dispersion without causing image tilt or loss.

In the above, the time required for one pixel to be discharged is divided into 16 periods, and the adjacent nozzle groups are driven sequentially every 4 periods, and the adjacent nozzle groups are driven every 11 periods. However, in time-division control, the number of divisions of the time required for one pixel to be discharged, the period for sequential driving within the same adjacent nozzle group, and the driving period at the boundary between adjacent nozzle groups are not limited to the above. When the time required for one pixel to be discharged is divided into N periods, the adjacent nozzle groups are driven sequentially every K periods (K<N), and the adjacent nozzle groups are driven every L periods (N/2<L<N). In this form, the effect of using a threshold matrix that is offset by one pixel from the basic threshold matrix can be achieved.

Third Embodiment
<Regarding misalignment of print positions between scans>
In multi-pass printing, if a printing position shift occurs between printing scans that print a unit area, the graininess and density unevenness of the image may become noticeable. In particular, in a serial type inkjet printing apparatus as described in Fig. 1, printing position shift occurs suddenly due to variations in the scanning speed of the carriage 106, variations in the conveyance of the conveyance roller 103 and the auxiliary roller 104, cockling of the print medium, etc.

Figures 22(a) and (b) show the dot pattern when misalignment occurs between print scans when the dot pattern in Figure 20(c) is printed by two-pass multi-pass printing according to the printing control described in the second embodiment. Here, approximately half of the dots are printed in the first pass for the unit area, and the remaining half are printed in the second pass, due to the masking process in step S706 using mask patterns Mp1 and Mp2.

Figure 22(a) shows a case where the printing position of the second pass is shifted in the X direction by +42 μm relative to the first pass. Also, Figure 22(b) shows a case where the printing position of the second pass is shifted in the X direction by -42 μm relative to the first pass. Compared to the dot pattern in Figure 20(c) where no shift occurs, it can be seen that the dispersion of the dots has decreased.

In this embodiment, in addition to the print position shift caused by the time-division drive described in the above embodiment, control is also performed to make the print position shift between print scans as described in Figure 22 less noticeable on the image.

<Image processing flow>
23 is a flowchart for explaining the steps of image processing executed in this embodiment. The color correction process in step S2301 and the color separation process in step S2302 are similar to the color correction process in step S701 and the color separation process in step S702 in the first embodiment explained in FIG. 7, and therefore the explanation thereof will be omitted here.

In step S2303, the main control unit 308 performs a division process on the 8-bit 256-level C1, M1, Y1, and K1 data. Then, it generates density data C1_1, M1_1, Y1_1, and K1_1 for the forward scan, and density data C1_2, M1_2, Y1_2, and K1_2 for the return scan. At this time, the main control unit 308 divides the density values of each color indicated by the C1, M1, Y1, and K1 data approximately equally into two.

The same process is then carried out in parallel for each ink color. Therefore, for simplicity, only the cyan data (C1_1, C1_2) will be explained here.

In steps S2304-1 and S2304-2, the main control unit 1308 performs tone correction processing on each of the density values C1_1 and C1_2. The content of the tone correction processing is the same as that of S703 in the first embodiment, so a description thereof will be omitted here. Through the tone correction processing of steps S2304-1 and S2304-2, the 8-bit, 256-level density values C1_1 and C1_2 are converted into 8-bit, 256-level density values C2_1 and C2_2, respectively.

In steps S2305-1 and S2305-2, the main control unit 308 performs a predetermined quantization process on each of the density values C2_1 and C2_2 to generate a quantized value C3_1 for the forward scan and a quantized value C3_2 for the backward scan. The quantized value C3_1 is 1-bit binary data indicating whether each pixel is printed (1) or not printed (0) for the forward scan. The quantized value C3_2 is 1-bit binary data indicating whether each pixel is printed (1) or not printed (0) for the backward scan. Note that, for simplicity of explanation, the quantized values C3_1 and C3_2 are binary data indicating whether each pixel is printed (1) or not printed (0), but the quantized value may be three or more values. The main control unit 308 transmits the quantized data C3-1 and C3-2 generated in steps S2305-1 and S2305-2 to the recording device 2.

In steps S2306-1 and S2306-2, the controller 301 of the recording device 2 performs a nozzle array expansion process. That is, using a prepared index pattern, the 600 dpi x 600 dpi quantized values C3_1 and C3_2 are converted to 600 dpi x 1200 dpi nozzle tone values C4_1 and C4_2. This nozzle array expansion process divides the area of 1 pixel in the X direction x 1 pixel in the Y direction into an area of 1 pixel in the X direction x 2 pixels in the Y direction, and sets dot printing (1) or non-printing (0) for each pixel.

In the above flowchart, a split process is performed between the color separation process and the tone correction process to split the data for forward scanning and return scanning, but the split process may be performed after the tone correction process. In this case, a one-dimensional lookup table for forward scanning and a one-dimensional lookup table for return scanning may be prepared in advance in the tone correction process, and the tone correction process and the split process may be performed simultaneously.

<About bidirectional multi-pass printing>
Fig. 24 is a schematic diagram for explaining the two-pass multi-pass printing of this embodiment, which is executed under the control of the controller 301 in the printing apparatus 2. In the first and second embodiments, the print data for each print scan is generated using the mask patterns Mp1 and Mp2. In contrast, in this embodiment, the mask patterns Mp1 and Mp2 are not used, and a forward scan is performed according to the nozzle tone value C4_1 generated in step S2306-1 of Fig. 23, and a forward scan is performed according to the nozzle tone value C4_2 generated in step S2306-2. Only the points that differ from the multi-pass printing described in Fig. 12 will be explained below.

In the first print scan, the controller 301 moves the print head 102 in the forward direction, i.e., in the +X direction, and uses the first divided area to perform an ejection operation according to the print data C4_1. The controller 301 then transports the print medium in the +Y direction by 64 pixels.

In the second print scan, the controller 301 moves the print head 102 in the return direction, i.e., in the -X direction, and uses the first and second divided regions to perform ejection operations according to the print data C4_2. The controller 301 then transports the print medium by 64 pixels in the +Y direction.

In the third print scan, the controller 301 moves the print head 102 again in the forward direction, i.e., in the +X direction, and uses the first and second divided areas to perform an ejection operation according to the print data C4_1. The controller 1301 then transports the print medium in the +Y direction by 64 pixels.

After that, as described above, forward scanning according to the recording data C4_1 and return scanning according to the recording data C4_2 are repeated alternately, with a transport operation of 64 pixels in between. As a result, the dot pattern recorded by the forward scan and the dot pattern recorded by the return scan are recorded in an overlapping manner in each unit area of the recording medium.

Figures 25(a) and (b) are diagrams comparing the dot patterns formed on the recording medium when the carriage 106 is moved in the +X direction and when it is moved in the -X direction under the time-division drive control described in Figure 17. Figure 25(a) is the dot pattern formed when the carriage 106 is moved in the +X direction, and Figure 25(b) is the dot pattern formed when the carriage 106 is moved in the -X direction. These two dot patterns are symmetrical in the X direction.

<Threshold matrix and index pattern>
Fig. 26 is a diagram showing the threshold matrix and index pattern used in this embodiment. A first threshold matrix 2601 is a threshold matrix for forward scanning used in step S2305-1 in Fig. 23, and a second threshold matrix 2602 is a threshold matrix for backward scanning used in step S2305-2. The first threshold matrix 2601 is obtained by performing offset processing for forward scanning on the basic threshold matrix described in Fig. 13(a) based on the rules of time-division driving in Fig. 17. Specifically, the basic threshold matrix is offset by one pixel in the +X direction in the area corresponding to adjacent nozzle group 2, by two pixels in the +X direction in the area corresponding to adjacent nozzle group 3, and by three pixels in the +X direction in the area corresponding to adjacent nozzle group 4.

The second threshold matrix 2602 is an inverted basic threshold matrix obtained by inverting the basic threshold matrix described in FIG. 13(a) in the X direction, and performing offset processing for the return scan based on the time division drive rules in FIG. 17. Specifically, the inverted basic threshold matrix is offset by one pixel in the -X direction in the area corresponding to adjacent nozzle group 2, two pixels in the -X direction in the area corresponding to adjacent nozzle group 3, and three pixels in the -X direction in the area corresponding to adjacent nozzle group 4. The inverted basic threshold matrix obtained by inverting the basic threshold matrix generated so that a repeating pattern with a shorter period than the threshold matrix appears also has a repeating pattern similar to the basic threshold matrix, and high dot dispersion can be achieved.

On the other hand, the first index pattern 2603 is an index pattern for forward scanning used in step S2306-1 in FIG. 23, and the second index pattern 2604 is an index pattern for backward scanning used in step S2306-2. The first index pattern 2603 is obtained by performing offset processing for forward scanning on the basic index pattern 1800 described in FIG. 18(b) based on the rules of time-division driving in FIG. 17. Specifically, in the area corresponding to adjacent nozzle group 1, the basic index pattern 1800 is repeatedly used as is in the X direction. In the area corresponding to adjacent nozzle group 2, the basic index pattern 1800 is used with an offset of one pixel in the +X direction with respect to adjacent nozzle group 1. In the area corresponding to adjacent nozzle group 3, the basic index pattern 1800 is used with an offset of two pixels in the +X direction, and in the area corresponding to adjacent nozzle group 4, the basic index pattern 1800 is used with an offset of three pixels in the +X direction.

The second index pattern 2604 is an inverted basic index pattern 2500, which is the basic index pattern described in FIG. 18(b) inverted in the X direction, subjected to offset processing for forward scanning based on the rules of time-division driving in FIG. 17. Specifically, in the area corresponding to adjacent nozzle group 1, the inverted basic index pattern 2500 is used repeatedly in the X direction as is. In the area corresponding to adjacent nozzle group 2, the inverted basic index pattern 2500 is used with an offset of one pixel in the -X direction relative to adjacent nozzle group 1. In the area corresponding to adjacent nozzle group 3, the inverted basic index pattern 2500 is used with an offset of two pixels in the -X direction, and in the area corresponding to adjacent nozzle group 4, the inverted basic index pattern 2500 is used with an offset of three pixels in the -X direction.

By using the first threshold matrix 2601 and first index pattern 2603 in FIG. 26 in image processing for forward scanning, the dot pattern shown in FIG. 20(a) can be recorded on a recording medium under the time division drive described in FIG. 17. Also, by using the second threshold matrix 2602 and second index pattern 2604 in image processing for backward scanning, a pattern that is a left-right inversion of the dot pattern shown in FIG. 20(a) can be recorded on a recording medium under the time division drive of this embodiment.

In this embodiment, the threshold matrix and index pattern actually used in the quantization process may be generated as needed. That is, a basic threshold matrix and a basic index pattern are stored in memory, and an inversion process and a predetermined offset process are performed on these as needed to generate the threshold matrix and basic index pattern actually used.

<Adjustment of Drive Timing of LEv Column and LOd Column>
27A and 27B are schematic diagrams for explaining the state of adjusting the drive timing of the LEv row and the LOd row in this embodiment. Fig. 27A shows the drive timing of the forward scan, and Fig. 27B shows the drive timing of the backward scan. The printhead 102 has C1 row and C2 row arranged as shown in Fig. 16C.

In the forward scan, first, when the LEv row reaches the reference position, the LEv row is driven by the time-division drive described above. After that, when the LOd row reaches the reference position, it is not driven, but when the LOd row reaches a position that is (1200 dpi + 600 dpi ÷ 16 × 2 ≒ 26.5 um) ahead of the reference position, the LOd row is driven by the time-division drive.

In the return scan, the LOd row is not driven when it reaches the reference position, but is driven by time-division driving when it reaches a position (1200 dpi + 600 dpi ÷ 16 × 2 ≒ 26.5 um) further from the reference position. After that, when the LEv row reaches the reference position, the LEv row is driven by time-division driving.

In the above, the drive timing of the LOd row is shifted relative to the LEv row, but the drive timing of the LEv row may be shifted relative to the LOd row. Also, the nozzle row whose drive timing is shifted may be switched between the LEv row and the LOd row in the forward scan and the return scan.

<Relationship between printing position deviation and dot pattern>
28(a) and (b) show quantized data obtained by the quantization process of this embodiment. Fig. 28(a) shows the result of performing quantization process using the first threshold matrix shown in Fig. 26 when the density value C2_1 after the tone correction process is uniformly 64. In the first threshold matrix, the quantized value of a pixel having a threshold value Th of 64 or less is recorded (1), and is shown as a black pixel in the figure. Compared to the case of quantization using the basic threshold matrix, the pixel is shifted by one pixel in the +X direction for every four rasters corresponding to the adjacent nozzle groups.

On the other hand, FIG. 28(b) shows the result of quantization processing using the second threshold matrix 2602 shown in FIG. 26 when the density value C2_2 after tone correction processing is uniformly 64. In the second threshold matrix, the quantization value of a pixel for which a threshold value Th of 64 or less is set is recorded (1), and is shown as a black pixel in the figure. Compared to the case of quantization using the inverted basic threshold matrix, there is a shift of one pixel in the -X direction for every four rasters corresponding to adjacent nozzle groups.

As already explained, the first threshold matrix 2601 and the second threshold matrix 2602 shown in FIG. 26 are symmetrical in the X direction, so the quantization results shown in FIGS. 28(a) and (b) also are symmetrical in the X direction.

Figure 29 is a diagram showing dot patterns formed on a recording medium when ejection is performed while performing time-division driving based on the quantized data shown in Figure 28. The first dot pattern 2901 is a dot pattern formed on a recording medium when ejection is performed in a forward scan while performing time-division driving according to the first index pattern 2603 based on the quantized data shown in Figure 28 (a). The second dot pattern 2902 is a dot pattern formed on a recording medium when ejection is performed in a backward scan while performing time-division driving according to the second index pattern 2604 based on the quantized data shown in Figure 28 (b). In addition, the composite dot pattern 2903 is a dot pattern in which the first dot pattern 2901 and the second dot pattern 2902 are composited without any misalignment. Furthermore, the reciprocating shift dot pattern 2904 shows a state in which the second dot pattern 2902 is shifted in the +X direction by one pixel of 1200 dpi (≒ 21 μm) with respect to the first dot pattern 2901.

According to this embodiment, both the first dot pattern 2901 and the second dot pattern 2902 have high dot dispersion. Moreover, no matter which dot is the center, the distance from the surrounding dots is almost constant. Furthermore, when comparing the composite dot pattern 2903 and the reciprocating shift dot pattern 2904, they are almost the same pattern, and the dot coverage area on the recording medium is also almost the same. In other words, in this embodiment, in which the first dot pattern 2901 is recorded in the forward scan and the second dot pattern 2902 is recorded in the backward scan, even if the recording position of the forward scan and the backward scan is shifted by about one pixel, a uniform image without density unevenness can be recorded.

Figure 30 is a diagram showing a comparative example of the dot pattern of this embodiment shown in Figure 29. Here, the quantization process and nozzle expansion process are performed using a basic threshold matrix and a basic index pattern without offset processing, and the ejection operation is performed under the time-division drive of this embodiment. The first dot pattern 3001 shows a dot pattern printed in the forward scan, and the second dot pattern 3002 shows a dot pattern printed in the backward scan. The composite dot pattern 3003 shows a dot pattern in which the first dot pattern 3001 and the second dot pattern 3002 are combined without any misalignment. Furthermore, the reciprocating misalignment dot pattern 3004 shows a state in which the second dot pattern 3002 is shifted in the +X direction by one pixel of 1200 dpi (≒ 21 μm) with respect to the first dot pattern 3001.

In this comparative example, the first dot pattern 3001 and the second dot pattern 3002 are misaligned by 11 sections at the boundary between adjacent nozzle groups, impairing the dispersion of the dots. In other words, when focusing on an arbitrary dot, the distance from the surrounding dots is not constant. Also, when comparing the composite dot pattern 3003 and the back-and-forth misaligned dot pattern 3004, the two patterns are significantly different. In other words, in this comparative example, in which the first dot pattern 3001 is printed in the forward scan and the second dot pattern 3002 is printed in the backward scan, if the printing positions of the forward scan and the backward scan are misaligned by about one pixel, the dot coverage rate and pattern will change, and there is a concern that uneven density will occur.

In Figures 28 and 29, we have described a case where the gradation data is C2_1 = C2_2 = 64, but of course, in this embodiment, the above effect can also be obtained when other density values are input.

Figures 31(a) and (b) show the results of the quantization process in steps S2305-1 and S2305-2 when gradation data of C2_1 = C2_2 = 255 is uniformly input to all 32 pixels x 32 pixels. When C2_1 = C2_2 = 255, the quantized values of all pixels are recorded (C3_1 = 1, C3_2 = 1) in the first threshold matrix 2601 for the forward scan and the second threshold matrix 2602 for the backward scan.

Figure 32 is a diagram showing dot patterns formed on a recording medium when a discharge operation is performed while performing time-division driving based on the quantized data shown in Figure 31. The first dot pattern 3201 is a dot pattern formed on a recording medium when a discharge operation is performed in a forward scan while performing time-division driving according to the first index pattern 2603 based on the quantized data shown in Figure 31 (a). The second dot pattern 3202 is a dot pattern formed on a recording medium when a discharge operation is performed in a backward scan while performing time-division driving according to the second index pattern 2604 based on the quantized data shown in Figure 31 (b). In addition, the composite dot pattern 3203 is a dot pattern obtained by combining the first dot pattern 3201 and the second dot pattern 3202 without any misalignment. Furthermore, the reciprocating shift dot pattern 3204 shows a state in which the second dot pattern 3202 is shifted in the +X direction by one pixel of 1200 dpi (≒ 21 μm) with respect to the first dot pattern 3201.

In both the first dot pattern 3201 and the second dot pattern 3202, patterns having a period shorter than the threshold matrix are repeatedly arranged in the XY direction, resulting in high dot dispersion. Furthermore, when comparing the composite dot pattern 3203 and the back-and-forth shift dot pattern 3204, the two are almost the same type of pattern, and the dot coverage area on the recording medium is also equivalent. In other words, according to this embodiment, even in such a high gradation area, it is possible to record a uniform image without uneven density, regardless of the recording position shift between the forward scan and the return scan.

Figure 33 is a diagram showing a comparative example of the dot pattern shown in Figure 32. Here, it shows a case where quantization processing and nozzle expansion processing are performed using a basic threshold matrix and a basic index pattern without offset processing when gradation data of C2_1 = C2_2 = 255 is uniformly input. The first dot pattern 3301 is a dot pattern printed in the forward scan, and the second dot pattern 3302 is a dot pattern printed in the backward scan. In addition, the composite dot pattern 3303 shows a dot pattern in which the first dot pattern 3301 and the second dot pattern 3302 are composited without misalignment. Furthermore, the reciprocating shift dot pattern 3304 shows a state in which the second dot pattern 3002 is shifted in the +X direction by one pixel of 1200 dpi (≒ 21 μm) with respect to the first dot pattern 3301.

In this comparative example, the first dot pattern 3301 and the second dot pattern 3302 are misaligned by 11 sections at the boundary between adjacent nozzle groups, causing the dot dispersion to be disrupted. In addition, when comparing the composite dot pattern 3303 with the back-and-forth misaligned dot pattern 3304, the two patterns are different. In other words, in this comparative example, in which the first dot pattern 3301 is printed in the forward scan and the second dot pattern 3302 is printed in the return scan, if the printing positions of the forward scan and the return scan are misaligned by about one pixel, the dot coverage rate and pattern will change, and there is a risk that uneven density will be detected.

As described above, according to this embodiment, a threshold matrix and index pattern are prepared that will obtain the first dot pattern 2901 and second dot pattern 2902 in FIG. 29 based on the dot landing positions when performing time-division driving in bidirectional multi-pass printing. In more detail, a threshold matrix and index pattern are prepared that will obtain grid patterns such as the first dot pattern 2901 and second dot pattern 2902 described in FIG. 29 at a predetermined gradation value (e.g., C2_1 = C2_2 = 64). These are then set as the basic threshold matrix and basic index pattern.

Then, offset processing for forward scanning and offset processing for return scanning are performed on these basic threshold matrices and basic index patterns based on time-division driving, and the resulting threshold matrices and index patterns are used to perform image processing according to Figure 23. This makes it possible to print composite dot patterns at each tone that are highly dispersive and resistant to misalignment of the printing position between forward and backward scans.

(Modification of the third embodiment)
In the above embodiment, a case where two-pass bidirectional multipass printing is performed has been described as an example. However, in multipass printing, which alternately repeats the print head print scan and the print medium conveying operation, black and white streaks may occur at the boundaries of unit areas due to variations in conveyance error. For example, if the conveyance amount is larger than the design value, white streaks may occur at the boundaries, and if the conveyance amount is smaller than the design value, black streaks may occur. In this modified example, a print control is described in which three-pass multipass printing is performed only on the boundaries between unit areas in order to make the black and white streaks caused by such variations in conveyance amount less noticeable.

Figure 34 is a schematic diagram for explaining multi-pass printing in this modified example. In this modified example, the 128 nozzles included in the nozzle row 202 are divided into three regions, R1 to R3. Specifically, the 1st to 16th nozzles in the transport direction are region R1, the 17th to 112th nozzles are region R2, and the 113th to 128th nozzles are region R3.

In the first print scan, the controller 301 moves the print head 102 in the forward direction, i.e., in the +X direction, and performs a discharge operation using half of the regions R1 and R2. Thereafter, the controller 301 transports the print medium by 48 pixels in the +Y direction, and in the second print scan, moves the print head 102 in the backward direction, i.e., in the -X direction, and performs a discharge operation using regions R1 and R2. Furthermore, the controller 301 transports the print medium by 48 pixels in the +Y direction, and in the third print scan, moves the print head 102 in the forward direction, i.e., in the +X direction, and performs a discharge operation using regions R1 to R3. Thereafter, forward and backward scans using regions R1 to R3 are alternately repeated, with a transport operation of 64 pixels in between.

Figure 35 is a diagram for explaining the index patterns used in this modified example. In this modified example, the index patterns used in S2306-1 and S2306-2 in Figure 23 are different for each of the regions R1 to R3.

Specifically, for region R2, as in the third embodiment, the first index pattern 2603 is used in the forward scan and the second index pattern 2604 is used in the backward scan. For region R1, index pattern A1 is used in the forward scan and index pattern B1 is used in the backward scan. For region R3, index pattern A2 is used in the forward scan and index pattern B2 is used in the backward scan.

Each of the index patterns A1, A2, B1, and B2 has a 16x16 pixel area, with blank pixels meaning that no dots are printed. In R1 and R3, which have an area for 16 nozzles, these index patterns are used in a repeated arrangement in the X direction.

Here, index pattern A1 used in region R1 and index pattern A2 used in region R3 are obtained by distributing the parameters of the first index pattern 2603 so that the ejection frequency is lower for nozzles closer to the ends. In other words, the dot pattern obtained using index pattern A1 and the dot pattern obtained using index pattern A2 have a complementary relationship.

Similarly, index pattern B1 used in region R1 and index pattern B2 used in region R3 are obtained by distributing the parameters of second index pattern 2604 so that the ejection frequency is lower for nozzles closer to the ends. In other words, the dot pattern obtained using index pattern B1 and the dot pattern obtained using index pattern B2 have a complementary relationship.

Now, let us refer again to FIG. 34. On the recording medium, the first boundary area between the first unit area and the second unit area is recorded by an outward scan through area R1, a return scan through area R2, and an outward scan through area R3. The dot pattern for the outward scan is completed by complementing the outward scan of area R1 and the outward scan of area R3, so that an image similar to the other unit areas can be recorded in the first boundary area.

The second boundary area between the second and third unit areas is recorded by a return scan using area R1, an outward scan using area R2, and a return scan using area R3. The dot pattern for the return scan is completed by complementing the return scan of area R1 with the return scan of area R3, so an image similar to that of the other unit areas is recorded in the second boundary area as well.

In this modified example, the nozzles closer to the ends are controlled to have a lower ejection frequency, so even if there is variation in the transport operation, the occurrence of black and white streaks at the boundaries can be suppressed.

In the above, the time required for one pixel to be discharged is divided into 16 periods, and the adjacent nozzle groups are driven sequentially every 4 periods, and at the boundary between adjacent nozzle groups, the nozzles are driven every 11 periods. However, in time-division control, the number of divisions of the time required for one pixel to be discharged, the period for sequential driving within the same adjacent nozzle group, and the driving period at the boundary between adjacent nozzle groups are not limited to the above. When the time required for one pixel to be discharged is divided into N periods, the adjacent nozzle groups are driven sequentially every K periods (K<N), and at the boundary between adjacent nozzle groups, the nozzles are driven every L periods (N/2<L<N). In this form, the effect of using a threshold matrix that is offset by one pixel from the basic threshold matrix can be achieved.

Other Embodiments
In the above embodiment, when the time required for one pixel to be discharged is divided into N periods, the adjacent nozzle groups are sequentially driven every K periods (K<N), and the adjacent nozzle groups are driven at the boundary between them at L periods (N/2<L<N). However, the number of divisions of the time required for one pixel to be discharged, the period for sequentially driving the adjacent nozzle groups, and the drive period at the boundary between the adjacent nozzle groups, which are described in the above embodiment, are merely examples. When the time required for one pixel to be discharged is divided into N periods, the adjacent nozzle groups are sequentially driven every K periods (K<N), and there are K adjacent nozzle groups in one section. In this form, it is possible to achieve the effect of using a threshold matrix that is offset by one pixel from the basic threshold matrix.

In the above embodiment, a case where two-pass multi-pass printing is performed using the serial inkjet printing device shown in FIG. 1 has been described as an example, but the present invention is not limited to this form. One-pass printing without multi-pass printing may be used, or multi-pass printing with three or more passes may be used. Time-division driving is also useful in full-line inkjet printing devices, and the same problems as above arise. For this reason, the printing control of the above embodiment, which uses a threshold matrix with offset processing based on time-division driving, can be made to function effectively even in full-line inkjet printing devices.

In the above, in the series of image processing described in FIG. 7 and FIG. 23, the image processing device 1 performs the steps up to the quantization process, and the recording device 2 performs the nozzle array expansion process and subsequent steps, but the present invention is not limited to this configuration. The image processing device may perform the steps up to the nozzle array expansion process, or all of the steps shown in the figure may be executed by the controller 301 of the inkjet recording device. In any case, a system having a function for performing a predetermined time-division drive control and a function for performing a print data generation process using a threshold matrix that has been subjected to the offset process as described above in order to record an image under that time-division control constitutes the image recording device of the present invention. That is, in the case of the first to third embodiments described above, the entire system including the image processing device 1 and the recording device 2 constitutes the image recording device of the present invention.

The number of bits and resolution of the input/output data shown in each step of the image processing in the above embodiment are just examples, and the number of bits and resolution can be changed in various ways depending on the situation. The number of colors in the recording device is also not limited to the above embodiment. It may be a recording device that uses similar colors with different densities, such as light cyan and light magenta, or spot colors such as red, green, and blue. In this case, in the color separation process, it is sufficient to generate a type of gradation data corresponding to the number of colors, and in subsequent processes, the above-mentioned image processing can be performed for each color.

In addition, in the above embodiments, a thermal jet type recording head is used that ejects ink by applying a voltage pulse to a heater, but the ejection type is not particularly limited in any of the above embodiments. For example, the present invention can be effectively applied to various recording devices, such as so-called piezo type inkjet recording devices that eject ink using a piezoelectric element.

The present invention can also be realized by supplying a program that realizes one or more of the functions of the above-mentioned embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that realizes one or more functions.

Reference Signs List 1 Image processing device 2 Inkjet recording device 102 Recording head

Claims (26)

An image recording device that records an image on a recording medium by moving a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, relative to the recording medium in a direction intersecting the predetermined direction,
a quantization means for quantizing a gradation value contained in the multi-value data of a pixel to be processed by comparing the gradation value with a threshold value corresponding to the pixel position of the pixel to be processed in a threshold value matrix in which a plurality of threshold values are arranged, thereby generating quantized data for the pixel to be processed;
a drive control means for performing time division drive control, when a time corresponding to a discharge operation of one pixel is divided into N periods, sequentially driving nozzles included in a first adjacent nozzle group among the plurality of nozzles in the predetermined direction every K periods (K<N), sequentially driving nozzles included in a second adjacent nozzle group adjacent to the first adjacent nozzle group in the predetermined direction every K periods, and driving nozzles of the first adjacent nozzle group closest to the second adjacent nozzle group with a delay of L periods (N/2<L<N) relative to nozzles of the second adjacent nozzle group closest to the first adjacent nozzle group;
a recording means for ejecting ink from the recording head in accordance with the quantized data generated by the quantization means while the drive control means is performing the time division drive control;
Equipped with
an image recording device characterized in that the quantization means performs a quantization process using a threshold matrix obtained by offsetting the threshold value corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold value corresponding to the first adjacent nozzle group, with respect to a basic threshold matrix from which quantized data in which a predetermined pattern is periodically arranged is obtained when image data of a predetermined gradation value is uniformly input. the recording means repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the quantized data, thereby recording an image on the recording medium;
The quantization means
for the forward scan, the quantization process is performed using a threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the forward scan direction with respect to the basic threshold matrix, with respect to the threshold values corresponding to the first adjacent nozzle group;
the image recording device according to claim 1, characterized in that, for the backward scan, the quantization process is performed using a threshold matrix obtained by inverting the basic threshold matrix in the intersecting direction, and offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the backward scan relative to the threshold values corresponding to the first adjacent nozzle group. The image recording device according to claim 1 or 2, characterized in that the quantization means performs the quantization process using the threshold matrix stored in advance in a memory. The image recording device according to claim 1 or 2, characterized in that the quantization means generates the threshold matrix by applying the offset to the basic threshold matrix stored in advance in a memory, and performs the quantization process using the threshold matrix. a print data generating means for generating print data to be printed by said printing means from said quantized data, using an index pattern generated by repeatedly arranging a basic index pattern, which determines whether or not to print a dot for each of a plurality of print pixels arranged at a print resolution of said print head, in said predetermined direction and said intersecting direction;
An image recording device as described in any one of claims 1 to 4, characterized in that the recording data generation means arranges the basic index pattern in the pixel area corresponding to the second adjacent nozzle group by offsetting it by one pixel in the intersecting direction with respect to the basic index pattern in the pixel area corresponding to the first adjacent nozzle group. the recording means repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the quantized data, thereby recording an image on the recording medium;
The recording data generating means
In the forward scan, the basic index pattern in the pixel region corresponding to the second adjacent nozzle group is offset by one pixel in the forward scan direction with respect to the basic index pattern in the pixel region corresponding to the first adjacent nozzle group;
an inverted basic index pattern obtained by inverting the basic index pattern in the intersecting direction during the return scan is offset by one pixel in the return direction with respect to the inverted basic index pattern in the pixel area corresponding to the first adjacent nozzle group; An image recording device that records an image on a recording medium by moving a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, relative to the recording medium in a direction intersecting the predetermined direction,
a division means for dividing a gradation value included in the multi-value data of a pixel to be processed into a first gradation value and a second gradation value to generate first gradation data and second gradation data;
a quantization means for quantizing the first gradation value by comparing it with a threshold value corresponding to the pixel position of the target pixel in a first threshold matrix in which a plurality of threshold values are arranged, thereby generating first quantized data for the target pixel, and for quantizing the second gradation value by comparing it with a threshold value corresponding to the pixel position of the target pixel in a second threshold matrix different from the first threshold matrix, thereby generating second quantized data for the target pixel;
a drive control means for performing time division drive control, when a time corresponding to a discharge operation of one pixel is divided into N periods, sequentially driving nozzles included in a first adjacent nozzle group among the plurality of nozzles in the predetermined direction every K periods (K<N), sequentially driving nozzles included in a second adjacent nozzle group adjacent to the first adjacent nozzle group in the predetermined direction every K periods, and driving nozzles of the first adjacent nozzle group closest to the second adjacent nozzle group with a delay of L periods (N/2<L<N) relative to nozzles of the second adjacent nozzle group closest to the first adjacent nozzle group;
a recording means for discharging ink from the recording head in accordance with the first quantized data and the second quantized data generated by the quantization means while the drive control means is performing the time division drive control;
Equipped with
an image recording device characterized in that the quantization means performs a quantization process using a first threshold matrix obtained by offsetting the threshold corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold corresponding to the first adjacent nozzle group, for a first basic threshold matrix from which quantized data in which a first pattern is periodically arranged is obtained when image data of a predetermined gradation value is uniformly input, and performs a quantization process using the second threshold matrix obtained by offsetting the threshold corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold corresponding to the first adjacent nozzle group, for a second basic threshold matrix from which quantized data in which a second pattern different from the first pattern is periodically arranged is obtained when image data of the predetermined gradation value is uniformly input. the recording means repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the first quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the second quantized data, thereby recording an image on the recording medium;
the first basic threshold matrix and the second basic threshold matrix are in an inverted relationship in the intersecting direction,
The quantization means
for the forward scan, the quantization process is performed using the first threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the forward scan direction with respect to the first basic threshold matrix;
The image recording device according to claim 7, characterized in that, for the return scan, the quantization processing is performed using the second threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the return direction with respect to the second basic threshold matrix with respect to the threshold values corresponding to the first adjacent nozzle group. The image recording device according to claim 7 or 8, characterized in that the quantization means performs the quantization process using the first threshold matrix and the second threshold matrix that are stored in advance in a memory. The image recording device according to claim 7 or 8, characterized in that the quantization means generates the first threshold matrix and the second threshold matrix based on the first basic threshold matrix stored in advance in a memory, and performs the quantization process using the first threshold matrix and the second threshold matrix. a print data generating means for generating first print data and second print data to be printed by said printing means from said first quantized data and said second quantized data, respectively, by using an index pattern generated by repeatedly arranging a basic index pattern, the basic index pattern defining whether or not to print a dot for each of a plurality of print pixels arranged at a print resolution of said print head, in said predetermined direction and in said intersecting direction;
An image recording device as described in any one of claims 7 to 10, characterized in that the recording data generation means arranges the basic index pattern in the pixel area corresponding to the second adjacent nozzle group by offsetting it by one pixel in the intersecting direction with respect to the basic index pattern in the pixel area corresponding to the first adjacent nozzle group. the recording means repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the first quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the second quantized data, thereby recording an image on the recording medium;
The recording data generating means
In the forward scan, the basic index pattern in the pixel region corresponding to the second adjacent nozzle group is offset by one pixel in the forward scan direction with respect to the basic index pattern in the pixel region corresponding to the first adjacent nozzle group;
The image recording device according to claim 11, characterized in that, for the return scan, an inverted basic index pattern obtained by inverting the basic index pattern in the intersecting direction is positioned offset by one pixel in the return direction with respect to the inverted basic index pattern in the pixel area corresponding to the first adjacent nozzle group. The image recording device according to any one of claims 1 to 12, characterized in that the recording head ejects ink by the growth energy of bubbles generated in the ink when a voltage pulse is applied by the drive control means to a heater disposed in each of the plurality of nozzles. 1. An image recording method for recording an image on a recording medium by moving a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, relative to the recording medium in a direction intersecting the predetermined direction, comprising:
a quantization step of quantizing a gradation value of the multi-value data of a pixel to be processed by comparing it with a threshold value corresponding to the pixel position of the pixel to be processed in a threshold value matrix in which a plurality of threshold values are arranged, thereby generating quantized data of the pixel to be processed;
a drive control process for performing time division drive control, when a time corresponding to an ejection operation of one pixel is divided into N periods, in which nozzles included in a first adjacent nozzle group among the plurality of nozzles are sequentially driven in the predetermined direction every K periods (K<N), nozzles included in a second adjacent nozzle group adjacent to the first adjacent nozzle group are sequentially driven in the predetermined direction every K periods, and the nozzles of the first adjacent nozzle group closest to the second adjacent nozzle group are driven with a delay of L periods (N/2<L<N) relative to the nozzles of the second adjacent nozzle group closest to the first adjacent nozzle group;
a recording step of ejecting ink from the recording head in accordance with the quantized data generated in the quantization step while the time-division drive control is being performed by the drive control step;
having
an image recording method characterized in that the quantization process performs a quantization process using a threshold matrix obtained by offsetting the threshold value corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold value corresponding to the first adjacent nozzle group, with respect to a basic threshold matrix from which quantized data in which a predetermined pattern is periodically arranged is obtained when image data of a predetermined gradation value is uniformly input. the recording step repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the quantized data, thereby recording an image on the recording medium;
The quantization step includes:
for the forward scan, the quantization process is performed using a threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the forward scan direction with respect to the basic threshold matrix, with respect to the threshold values corresponding to the first adjacent nozzle group;
The image recording method according to claim 14, characterized in that, for the backward scan, the quantization process is performed using a threshold matrix obtained by inverting the basic threshold matrix in the intersecting direction and offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the backward scan relative to the threshold values corresponding to the first adjacent nozzle group. The image recording method according to claim 14 or 15, characterized in that the quantization step performs the quantization process using the threshold matrix stored in advance in a memory. The image recording method according to claim 14 or 15, characterized in that the quantization step generates the threshold matrix by applying the offset to the basic threshold matrix stored in advance in a memory, and performs the quantization process using the threshold matrix. a print data generating step of generating print data to be printed by the printing step from the quantized data using an index pattern generated by repeatedly arranging a basic index pattern in the predetermined direction and the intersecting direction, the basic index pattern defining whether or not to print a dot for each of a plurality of print pixels arranged at the print resolution of the print head,
The image recording method according to any one of claims 14 to 17, characterized in that the recording data generation process positions the basic index pattern in the pixel area corresponding to the second adjacent nozzle group by offsetting it by one pixel in the intersecting direction with respect to the basic index pattern in the pixel area corresponding to the first adjacent nozzle group. the recording step repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the quantized data, thereby recording an image on the recording medium;
The recording data generating step includes:
In the forward scan, the basic index pattern in the pixel region corresponding to the second adjacent nozzle group is offset by one pixel in the forward scan direction with respect to the basic index pattern in the pixel region corresponding to the first adjacent nozzle group;
19. The image recording method according to claim 18, characterized in that, for the return scan, an inverted basic index pattern obtained by inverting the basic index pattern in the intersecting direction is positioned offset by one pixel in the return direction with respect to the inverted basic index pattern in a pixel area corresponding to the first adjacent nozzle group. 1. An image recording method for recording an image on a recording medium by moving a recording head, in which a plurality of nozzles for ejecting ink are arranged in a predetermined direction, relative to the recording medium in a direction intersecting the predetermined direction, comprising:
a division step of dividing a gradation value included in the multi-value data of a pixel to be processed into a first gradation value and a second gradation value to generate first gradation data and second gradation data;
a quantization step of quantizing the first gradation value by comparing it with a threshold value corresponding to the pixel position of the target pixel in a first threshold matrix in which a plurality of threshold values are arranged, thereby generating first quantized data for the target pixel, and quantizing the second gradation value by comparing it with a threshold value corresponding to the pixel position of the target pixel in a second threshold matrix different from the first threshold matrix, thereby generating second quantized data for the target pixel;
a drive control process for performing time division drive control, when a time corresponding to an ejection operation of one pixel is divided into N periods, in which nozzles included in a first adjacent nozzle group among the plurality of nozzles are sequentially driven in the predetermined direction every K periods (K<N), nozzles included in a second adjacent nozzle group adjacent to the first adjacent nozzle group are sequentially driven in the predetermined direction every K periods, and the nozzles of the first adjacent nozzle group closest to the second adjacent nozzle group are driven with a delay of L periods (N/2<L<N) relative to the nozzles of the second adjacent nozzle group closest to the first adjacent nozzle group;
a recording step of ejecting ink from the recording head in accordance with the first quantized data and the second quantized data generated in the quantization step in a state in which the time-division drive control is performed by the drive control step;
having
an image recording method characterized in that the quantization step performs a quantization process using a first threshold matrix obtained by offsetting the threshold corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold corresponding to the first adjacent nozzle group, with respect to a first basic threshold matrix from which quantized data in which a first pattern is periodically arranged is obtained when image data of a predetermined gradation value is uniformly input, and performs a quantization process using the second threshold matrix obtained by offsetting the threshold corresponding to the second adjacent nozzle group by one pixel in the intersecting direction from the threshold corresponding to the first adjacent nozzle group, with respect to a second basic threshold matrix from which quantized data in which a second pattern different from the first pattern is periodically arranged is obtained when image data of the predetermined gradation value is uniformly input. the recording step repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the first quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the second quantized data, thereby recording an image on the recording medium;
the first basic threshold matrix and the second basic threshold matrix are in an inverted relationship in the intersecting direction,
The quantization step includes:
for the forward scan, the quantization process is performed using the first threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the forward scan direction with respect to the first basic threshold matrix;
The image recording method according to claim 20, characterized in that, for the return scan, the quantization processing is performed using the second threshold matrix obtained by offsetting the threshold values corresponding to the second adjacent nozzle group by one pixel in the return direction with respect to the second basic threshold matrix with respect to the threshold values corresponding to the first adjacent nozzle group. The image recording method according to claim 20 or 21, characterized in that the quantization step performs the quantization process using the first threshold matrix and the second threshold matrix that are stored in advance in a memory. The image recording method according to claim 20 or 21, characterized in that the quantization step generates the first threshold matrix and the second threshold matrix based on the first basic threshold matrix stored in advance in a memory, and performs the quantization process using the first threshold matrix and the second threshold matrix. a print data generating step of generating first print data and second print data to be printed in the printing step from the first quantized data and the second quantized data, using an index pattern generated by repeatedly arranging a basic index pattern in the predetermined direction and the intersecting direction, the basic index pattern defining whether or not to print a dot for each of a plurality of print pixels arranged at a printing resolution of the print head,
The image recording method according to any one of claims 20 to 23, characterized in that the recording data generation process positions the basic index pattern in the pixel area corresponding to the second adjacent nozzle group by offsetting it by one pixel in the intersecting direction relative to the basic index pattern in the pixel area corresponding to the first adjacent nozzle group. the recording step repeats a forward scan in which the recording head is moved in a forward direction relative to the recording medium and ink is ejected from the recording head in accordance with the first quantized data, and a backward scan in which the recording head is moved in a backward direction opposite to the forward direction and ink is ejected from the recording head in accordance with the second quantized data, thereby recording an image on the recording medium;
The recording data generating step includes:
In the forward scan, the basic index pattern in the pixel region corresponding to the second adjacent nozzle group is offset by one pixel in the forward scan direction with respect to the basic index pattern in the pixel region corresponding to the first adjacent nozzle group;
The image recording method according to claim 24, characterized in that, for the return scan, an inverted basic index pattern obtained by inverting the basic index pattern in the intersecting direction is positioned offset by one pixel in the return direction with respect to the inverted basic index pattern in a pixel area corresponding to the first adjacent nozzle group. The image recording method according to any one of claims 14 to 25, characterized in that the recording head ejects ink by the growth energy of bubbles generated in the ink when a voltage pulse is applied to a heater arranged in each of the plurality of nozzles by the drive control process.

Images