JP2010274485A - Correction value setting method, fluid ejecting apparatus, and fluid ejecting apparatus manufacturing method - Google Patents

Abstract

The present invention provides a method for suppressing the occurrence of density unevenness caused by fluctuations in dot positions.
A first ejection operation for ejecting fluid by relatively moving in a first direction intersecting a direction along a nozzle row, a transport operation for relatively moving a medium in a second direction along the nozzle row, and a first direction And a second injection operation for ejecting fluid relative to each other, and in the first injection operation and the second injection operation, the nozzles in the nozzle row that partially overlap in the direction along the second direction share the same The amount of fluid ejected per unit area in a partly overlapping range compared to the amount of fluid ejected per unit area in a partly nonoverlapping range The correction pattern is formed, the density of the correction pattern is measured for each pixel column composed of a plurality of pixels arranged in the first direction, and the gradation is determined based on the measured density for each pixel column. To correct the value Correction value setting method comprising, obtaining a correction value for each pixel row.
[Selection] Figure 24

Description

  The present invention relates to a correction value setting method, a fluid ejecting apparatus, and a method for manufacturing a fluid ejecting apparatus.

  Used by an ink jet printer that forms an image on a medium by repeatedly ejecting ink while the head moves in the head movement direction and moving the medium such as paper in the transport direction intersecting the head movement direction Has been. In such a printer, a dot line is formed by dots arranged in the head moving direction. In forming a dot line, there is a case where one dot line is formed by a plurality of passes (passing of the head) including a sheet transport operation. At this time, the medium is accurately conveyed so that the dots are linearly aligned to form a dot line.

JP 2005-178042 A

However, even if the medium is transported accurately, if meandering occurs during movement in the head movement direction, density unevenness may occur in a range where raster lines are formed by sharing a plurality of passes. This is due to the fact that the position of the dots formed by the landing of the fluid fluctuates in the transport direction because the head slightly moves in the transport direction of the medium while the head is moving. Density unevenness reduces print quality. Therefore, it is necessary to suppress the occurrence of density unevenness caused by such fluctuations in dot positions.
The present invention has been made in view of such circumstances, and an object thereof is to suppress the occurrence of uneven density.

The main invention for achieving the above object is:
(A) forming a correction pattern based on gradation values,
A first ejecting operation for ejecting a fluid by relatively moving in a first direction intersecting a direction along the nozzle row with respect to the medium;
A transport operation for relatively moving the medium in a second direction along the nozzle row;
A second ejection operation for ejecting the fluid by relatively moving in the first direction;
Have
In the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share the formation of a common dot line to form the correction pattern. The correction pattern is formed by increasing the amount of the fluid ejected per unit area in the partially overlapping range than the amount of the fluid ejected per unit area in the non-overlapping range. And
(B) measuring the density of the correction pattern for each pixel column composed of a plurality of pixels arranged in the first direction;
(C) obtaining a correction value for correcting the gradation value for each pixel column based on the measured density for each pixel column;
(D) storing the correction value in a storage unit of a fluid ejection device provided with the nozzle row;
This is a correction value setting method including

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

It is explanatory drawing of a term. 1 is a block diagram illustrating a configuration of a printing system 100. FIG. FIG. 3A is a schematic diagram of the overall configuration of the printer 1, and FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. FIG. 4A is an explanatory diagram of the head 41 in the head unit 40, and FIG. 4B is a diagram illustrating the structure of the head. It is explanatory drawing of a head position and the mode of dot formation. It is a figure for demonstrating the overlap process of a reference example. FIG. 10 is an explanatory diagram of processing by a printer driver. FIG. 8A is an explanatory diagram of a state when dots are ideally formed, FIG. 8B is an explanatory diagram of when uneven density occurs, and FIG. 8C is a diagram illustrating a state where the occurrence of uneven density is suppressed. It is. It is a figure which shows the flow of a correction value acquisition process. It is explanatory drawing of correction pattern CP. It is a graph which shows the calculation density | concentration for every raster line about the sub pattern CSP whose command gradation value is Sa, Sb, and Sc. FIG. 12A is an explanatory diagram of a procedure for calculating a density correction value Hb for correcting the command gradation value Sb for the i-th raster line, and FIG. 12B corrects the command gradation value Sb for the j-th raster line. It is explanatory drawing about the procedure which calculates the density | concentration correction value Hb for performing. FIG. 6 is a diagram showing a correction value table stored in a memory 53. It is a figure for demonstrating the brightness change when the corresponding nozzles correspond in the conveyance direction. It is a figure for demonstrating the brightness change when the width | variety of the nozzle row comprised by the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 has shifted | deviated to the direction which becomes narrow. It is a figure for demonstrating the brightness change when the width | variety of the nozzle row comprised by the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 has shifted | deviated to the direction which becomes wide. It is a figure for demonstrating the relationship of the brightness change with respect to the relative position of the nozzle between passes. It is a figure for demonstrating the implementation method of an overlap process. It is a figure for demonstrating the production method of the overlap mask of a reference example. It is a figure explaining an example of formation of a dot when the total nozzle usage ratio is 100% about the overlapping area | region of a nozzle row. It is a figure explaining an example when the position of the dot by the nozzle row 411 of pass 2 has shifted in the nozzle row direction. It is a figure explaining an example of formation of a dot when the total nozzle use ratio exceeds 100% about the overlapping area | region of a nozzle row. It is a figure explaining an example of dot formation when the total nozzle use ratio exceeds 100% about the overlapping part of a nozzle row, and the position of the dot by the nozzle row 411 of pass 2 has shifted in the nozzle row direction. . It is a figure explaining the nozzle usage ratio of pass 1 and pass 2 when the total nozzle usage ratio exceeds 100% in the overlapping region. It is a figure for demonstrating the matrix for producing the overlap mask in this embodiment. FIG. 26A is a diagram illustrating a nozzle usage ratio in the present embodiment, and FIG. 26B is a diagram illustrating a gradation value with respect to the nozzle usage ratio in the present embodiment. It is a figure for demonstrating the overlap mask of the nozzle row 411 of the pass 1 in this embodiment. It is a figure for demonstrating progress in the middle of the overlap mask preparation of the nozzle row 411 of pass 2 in this embodiment. It is a figure for demonstrating the overlap mask of the nozzle row 411 of the pass 2 in this embodiment. It is a figure which shows a matrix when performing a logical product operation about the overlap mask of the 1st nozzle row 411A and the overlap mask of the 2nd nozzle row 411B in this embodiment. It is a figure which shows a matrix when performing an OR operation about the overlap mask of pass 1 and the overlap mask of pass 2 in the present embodiment. FIG. 6 is a flowchart of print processing performed by a printer driver under a user. It is a figure for demonstrating a dot output ratio and a density | concentration correction coefficient.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) forming a correction pattern based on gradation values,
A first ejecting operation for ejecting a fluid by relatively moving in a first direction intersecting a direction along the nozzle row with respect to the medium;
A transport operation for relatively moving the medium in a second direction along the nozzle row;
A second ejection operation for ejecting the fluid by relatively moving in the first direction;
Have
In the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share the formation of a common dot line to form the correction pattern. The correction pattern is formed by increasing the amount of the fluid ejected per unit area in the partially overlapping range than the amount of the fluid ejected per unit area in the non-overlapping range. And
(B) measuring the density of the correction pattern for each pixel column composed of a plurality of pixels arranged in the first direction;
(C) obtaining a correction value for correcting the gradation value for each pixel column based on the measured density for each pixel column;
(D) storing the correction value in a storage unit of a fluid ejection device provided with the nozzle row;
Correction value setting method including
By doing in this way, generation | occurrence | production of density | concentration unevenness can be suppressed.

In this correction value setting method, it is preferable that the correction pattern is formed by increasing the amount of the fluid ejected per unit area in the center rather than the end portion in the partially overlapping range. Further, in the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share a part to form a common dot line, thereby partially overlapping. It is desirable that the correction pattern is formed such that the density of the pixel columns in the range is higher than the density of the pixel columns in the non-overlapping range. Further, increasing the amount of the fluid ejected per unit area means that dots formed in the dot lines corresponding to the partially overlapping range are overlapped with the dot lines in the non-overlapping range. It is desirable to be performed by increasing the number.
By doing in this way, generation | occurrence | production of density | concentration unevenness can be suppressed.

(A) a first ejection operation for ejecting a fluid by relatively moving in a first direction intersecting a direction in which the nozzles are arranged with respect to the medium, and a relative movement of the medium in the second direction in which the nozzles are arranged, A nozzle row that performs a second operation of ejecting the fluid by relatively moving in a first direction,
A nozzle row partially overlapping in the second direction in the first injection operation and the second injection operation;
(B) Control in which fluid is ejected from the nozzle row of the first ejection operation and the nozzle row of the second ejection operation to form a plurality of dot lines in which the plurality of dots are arranged in the first movement direction in the second direction. Part,
In the dot line corresponding to the partially overlapping range, the correction value for correcting the gradation value to be lower than the dot line in the partially overlapping range, and the dot line corresponding to the partially overlapping range A control unit that ejects the fluid in the first ejection operation and the second ejection operation based on a mask that forms more dots than dot lines in a partially non-overlapping range;
A fluid ejection device comprising:

In this fluid ejecting apparatus, the mask includes a first mask for the nozzle row in the first ejection operation and a second mask for the nozzle row in the second ejection operation in the partially overlapping range. By applying the first mask and the second mask to the image to be formed, the dot lines corresponding to the partially overlapping range are formed to be overlapped with the dot lines in the non-overlapping range. It is desirable to increase the number of dots. The correction value is preferably obtained based on the amount of dots formed by applying the mask.
By doing in this way, generation | occurrence | production of density | concentration unevenness can be suppressed.

(A) forming a correction pattern based on gradation values,
A first ejecting operation for ejecting a fluid by relatively moving in a first direction intersecting a direction along the nozzle row with respect to the medium;
A transport operation for relatively moving the medium in a second direction along the nozzle row;
A second ejection operation for ejecting the fluid by relatively moving in the first direction;
Have
In the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share the formation of a common dot line to form the correction pattern. The correction pattern is formed by increasing the amount of the fluid ejected per unit area in the partially overlapping range than the amount of the fluid ejected per unit area in the non-overlapping range. And
(B) measuring the density of the correction pattern for each pixel column composed of a plurality of pixels arranged in the first direction;
(C) obtaining a correction value for correcting the gradation value for each pixel column based on the measured density for each pixel column;
(D) storing the correction value in a storage unit of a fluid ejection device provided with the nozzle row;
A method of manufacturing a fluid ejecting apparatus including:
By doing in this way, generation | occurrence | production of density | concentration unevenness can be suppressed.

=== Embodiment ===
<Explanation of terms>
First, the meanings of terms used in describing this embodiment will be described.
FIG. 1 is an explanatory diagram of terms.

A “print image” is an image printed on paper. The print image of the ink jet printer is composed of countless dots formed on the paper.
A “dot line” is a row of dots arranged in the direction in which the head and the paper move relative to each other (movement direction). In the case of a serial printer as in an embodiment described later, “dot line” means a row of dots arranged in the moving direction of the head. On the other hand, in the case of a line printer that prints with a fixed head while transporting paper, “dot line” means a row of dots arranged in the paper transport direction. A print image is formed by arranging a large number of dot lines in a direction perpendicular to the moving direction. As shown in the figure, the dot line at the nth position is referred to as the “nth dot line”.

“Image data” is data indicating a two-dimensional image. In an embodiment described later, there are 256 gradation image data, 4 gradation image data, and the like. Further, the image data may indicate image data before conversion to a print resolution described later, or may indicate image data after conversion.
“Print image data” is image data used when printing an image on paper. When the printer controls dot formation with two gradations (with / without dots), the two-gradation print image data indicates the formation state of the dots constituting the print image.
“Read image data” is image data read by a scanner.

A “pixel” is a minimum unit that constitutes an image. An image is formed by arranging these pixels two-dimensionally.
A “pixel column” is a column of pixels arranged in a predetermined direction on image data. As shown in the figure, the nth pixel column is referred to as an “nth pixel column”.
“Pixel data” is data indicating the gradation value of a pixel. In the embodiment described later, multi-gradation data such as 256 gradations is shown before halftone processing, and in the case of print image data of two gradations after halftone processing, each pixel data is converted to 1-bit data. Thus, the dot formation state (with or without dots) of a certain pixel is indicated.
The “pixel area” is an area on the paper corresponding to the pixel on the image data. For example, when the resolution of the print image data is 360 × 360 dpi, the “pixel area” is a square area having a side of 1/360 inch and is a pixel on the paper.

  The “row region” is a region on the paper corresponding to the pixel row, and is a pixel row on the paper. For example, when the resolution of the print image data is 360 × 360 dpi, the row area is an elongated area having a width of 1/360 inch. The “row region” may mean a region on the paper corresponding to the pixel row on the print image data, or may mean a region on the paper corresponding to the pixel row on the read image data. In the lower right part of the figure, a row region in the former case is shown. The “row region” in the former case is also a dot line formation target position. When a dot line is accurately formed in the row region, the dot line corresponds to a raster line. The “row area” in the latter case is also the measurement position (measurement range) on the paper from which the pixel row on the read image data is read, in other words, on the paper on which the image (image piece) indicated by the pixel row exists. It is also the position. As shown in the figure, the row region at the nth position is referred to as an “nth row region”. The nth row region is the formation target position of the nth dot line.

  “Image piece” means a part of an image. On the image data, an image indicated by a certain pixel row is an “image piece” of the image indicated by the image data. In the print image, an image represented by a certain raster line is an “image piece” of the print image. In the print image, an image represented by color development in a certain row region also corresponds to an “image piece” of the print image.

  Incidentally, in the lower right of FIG. 1, the positional relationship between the pixel region and the dots is shown. As a result of the deviation of the second dot line from the second row region due to the influence of the head manufacturing error, the density of the second row region becomes light. Further, in the fourth row region, the density of the fourth row region becomes light as a result of the dot becoming smaller due to the influence of the head manufacturing error. Since it is necessary to explain such density unevenness and density unevenness correction methods, in this embodiment, the meaning and relationship of “dot line”, “pixel column”, “column region”, and the like are described along the above contents. is doing.

  However, the meanings of general terms such as “image data” and “pixel” may be appropriately interpreted in accordance with not only the above description but also common technical common sense.

  In the following description, it is assumed that the density is high when the gradation value is high and the density is low when the gradation value is low. In the description, a high density corresponds to a low brightness.

<About the printing system>
FIG. 2 is a block diagram illustrating a configuration of the printing system 100. As shown in FIG. 2, the printing system 100 according to the present embodiment is a system that includes a printer 1, a computer 110, and a scanner 120.

  The printer 1 is a fluid ejecting apparatus that ejects ink as a fluid onto a medium to form (print) an image on the medium. In this embodiment, the printer 1 is a color ink jet printer. The printer 1 can print images on a plurality of types of media such as paper, cloth, and film sheets. The configuration of the printer 1 will be described later.

  The computer 110 includes an interface 111, a CPU 112, and a memory 113. The interface 111 exchanges data between the printer 1 and the scanner 120. The CPU 112 performs overall control of the computer 110 and executes various programs installed in the computer 110. The memory 113 stores various programs and various data. Among programs installed in the computer 110, there are a printer driver for converting image data output from an application program into print data, and a scanner driver for controlling the scanner 120. Then, the computer 110 outputs the print data generated by the printer driver to the printer 1.

  The scanner 120 includes a scanner controller 125 and a reading carriage 121. The scanner controller 125 includes an interface 122, a CPU 123, and a memory 124. The interface 122 communicates with the computer 110. The CPU 123 performs overall control of the scanner 120. For example, the reading carriage 121 is controlled. The memory 124 stores a computer program and the like. The reading carriage 121 includes three sensors (CCD and the like) (not shown) corresponding to, for example, R (red), G (green), and B (blue).

  With the above configuration, the scanner 120 irradiates light on a document placed on a document table (not shown), detects the reflected light by each sensor of the reading carriage 121, reads the image of the document, and reads the image. Get color information. Then, data indicating the color information of the image (read data) is transmitted to the scanner driver of the computer 110 via the interface 122.

<Printer configuration>
FIG. 3A is a schematic diagram of the overall configuration of the printer 1. FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. Here, the configuration of the printer 1 will be described with reference to FIG.
The printer 1 includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, a controller 60, and a drive signal generation circuit 70.

  In the printer 1, each unit (the conveyance unit 20, the carriage unit 30, the head unit 40, and the drive signal generation circuit 70) is controlled by the controller 60. The controller 60 controls each unit based on the print data received from the computer 110 and prints an image on a medium such as the paper S.

  The transport unit 20 is for transporting the paper S in a predetermined direction (hereinafter referred to as a transport direction). The transport unit 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for feeding the paper S inserted into the paper insertion slot into the printer. The transport roller 23 is a roller that transports the paper S fed by the paper feed roller 21 to a printable area, and is driven by the transport motor 22. The platen 24 supports the paper S being printed. The paper discharge roller 25 is a roller for discharging the paper S to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

  The carriage unit 30 is for moving the head in a predetermined direction (moving direction in the figure). The carriage unit 30 includes a carriage 31 and a carriage motor 32. The carriage 31 can reciprocate in the moving direction and is driven by a carriage motor 32. Further, the carriage 31 detachably holds an ink cartridge that stores ink.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 includes a head 41 having a plurality of nozzles. Since the head 41 is provided on the carriage 31 as the head unit 40, when the carriage 31 moves in the movement direction, the head 41 also moves in the movement direction. Then, when the head 41 is intermittently ejected while moving in the moving direction, dot lines (raster lines) along the moving direction are formed on the paper.

  The detector group 50 represents various detectors that detect information of each part of the printer 1 and send the information to the controller 60.

  The controller 60 is a control unit for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, and a memory 63. The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 62 controls each unit according to a program stored in the memory 63.

  The drive signal generation circuit 70 generates a drive signal COM for ejecting ink droplets by being applied to a drive element such as a piezo element included in a head to be described later. The drive signal generation circuit 70 includes a DAC (not shown). Then, an analog voltage signal is generated based on digital data relating to the waveform of the drive signal sent from the controller 60. The drive signal generation circuit 70 also includes an amplifier circuit (not shown), and performs power amplification on the generated voltage signal to generate a drive signal.

  With such a configuration, printing can be performed on the entire surface of the paper while ejecting ink while the head is moving in the moving direction of the head and repeatedly transporting the paper in the transport direction.

FIG. 4A is an explanatory diagram of the head 41 in the head unit 40. Here, for ease of explanation, the nozzle row that can be seen only from the lower surface is shown to be observable from the upper part.
In the head 41, a black ink nozzle row NK, a cyan ink nozzle row NC, a magenta ink nozzle row NM, and a yellow ink nozzle row NY are formed. Each nozzle row is provided with a plurality of (here, 360) nozzles that eject ink. The plurality of nozzles in each nozzle row are arranged at a constant nozzle pitch (here 360 dpi) along the paper transport direction.

FIG. 4B is a diagram illustrating the structure of the head. In the figure, a nozzle Nz, a piezo element PZT, an ink supply path 402, a nozzle communication path 404, and an elastic plate 406 are shown.
Ink is supplied to the ink supply path 402 from an ink tank (not shown). These inks and the like are supplied to the nozzle communication path 404. A drive pulse of a drive signal described later is applied to the piezo element PZT. When the drive pulse is applied, the piezo element PZT expands and contracts according to the signal of the drive pulse and vibrates the elastic plate 406. An amount of ink droplets corresponding to the amplitude of the drive pulse is ejected from the nozzle Nz.

  FIG. 5 is an explanatory diagram of the head arrangement and dot formation. For simplification of explanation, it is assumed that the head 41 is provided with only the black ink nozzle row 411. Further, it is assumed that the black ink nozzle row of the head 41 is composed of 18 nozzles arranged in the transport direction (y direction) in the sense of 1/360 inch. For each nozzle, the nozzle numbers are shown in order from the top in the figure. In the following description, the paper width direction may be referred to as “x direction”, and the transport direction may be referred to as “y direction”. When the sheet is transported in the transport direction, the head 41 moves in a direction opposite to the transport direction (the negative direction of the y direction).

  Each nozzle forms 28 dot lines on the paper by intermittently ejecting ink droplets from the nozzles to the paper S being conveyed. For example, nozzle # 1 in pass 1 forms the first dot line on the paper, and nozzle # 1 in pass 2 forms the eleventh dot line on the paper. Each dot line is formed along the movement direction (x direction).

  By the way, the nozzles # 11 to # 18 in pass 1 and the nozzles # 1 to # 8 in pass 2 are arranged so as to coincide with each other in the transport direction. Therefore, the eleventh dot line to the eighteenth dot line are formed by sharing these overlapping nozzles.

  FIG. 6 is a diagram for explaining the overlap processing of the reference example. In the figure, the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 and the dot formation ratio when the overlapping nozzles in each pass form a dot line are shown. For example, in forming each dot line, nozzle # 11 in pass 1 is 88.8%, nozzle # 12 is 77.7%, nozzle # 13 is 66.6%, nozzle # 14 is 55.5%, nozzle It is shown that # 15 is 44.4%, nozzle # 16 is 33.3%, nozzle # 17 is 22.2%, and nozzle # 18 is 11.1%. In forming each dot line, nozzle # 1 in pass 2 is 11.1%, nozzle # 2 is 22.2%, nozzle # 3 is 33.3%, nozzle # 4 is 44.4%, nozzle It is shown that dots are formed at a rate of 55.5% for # 5, 66.6% for nozzle # 6, 77.7% for nozzle # 7, and 88.8% for nozzle # 8. Hereinafter, this ratio will be described as a nozzle usage ratio. That is, nozzle # 11 in pass 1 forms a dot line at a nozzle usage ratio of 88.8%.

  For example, when the nozzle usage ratio of nozzle # 11 in pass 1 and nozzle # 1 in pass 2 is summed, the nozzle usage ratio is 100%. When 100 consecutive dots are formed in a common dot line formed by the nozzle # 11 of pass 1 and the nozzle # 1 of pass 2, the nozzle # 11 of pass 1 forms approximately 89 dots. Then, the formation of dots is shared so that nozzle # 1 in pass 2 forms about 11 dots. In this way, in the reference example, the nozzle usage ratio of the nozzle # 1 of pass 1 to the nozzle # 18 of pass 2 is set to be 100% in total.

  In this way, by gradually changing the nozzle usage ratio in the range where the nozzle rows overlap, printing is performed such that the density difference between the range where the two nozzle rows overlap and the range where the nozzle rows do not overlap does not stand out. Be able to.

<About print processing>
In the printer 1, when print data is received from the computer 110, the controller 60 first rotates the paper feed roller 21 by the transport unit 20 and sends the paper S to be printed to the lower part of the head 41. The transport of the paper S is temporarily stopped, and the head 41 ejects ink while moving in the moving direction to form an image.
When the movement from one moving end of the head 41 to the other moving end (movement for one pass) is completed, the sheet S is conveyed in the conveying direction. When the conveyance of the paper S is completed, the head 41 ejects ink while moving in the moving direction again to form an image. Such an operation is repeated. Finally, the controller 60 discharges the paper S on which image printing has been completed.

<Outline of processing by printer driver>
As described above, the printing process starts when print data is transmitted from the computer 110 connected to the printer 1. The print data is generated by processing by the printer driver.

FIG. 7 is an explanatory diagram of processing by the printer driver. Hereinafter, processing by the printer driver will be described with reference to the drawings.
The print image data is generated by executing resolution conversion processing (S102), color conversion processing (S104), halftone processing (S106), and rasterization processing (S108) by the printer driver as shown in the figure. The

  First, in the resolution conversion process, the resolution of the RGB image data obtained by executing the application program is converted into a print resolution corresponding to the designated image quality. Next, in the color conversion process, RGB image data whose resolution has been converted is converted into CMYK image data. Here, the CMYK image data means image data for each color of cyan (C), magenta (M), yellow (Y), and black (K). A plurality of pieces of pixel data constituting the CMYK image data are each represented by 256 gradation values. This gradation value is determined based on RGB image data, and is hereinafter also referred to as a command gradation value.

  Next, in the halftone process, the multi-stage gradation value indicated by the pixel data constituting the image data is converted into a small-stage dot gradation value that can be expressed by the printer 1. That is, the 256-level gradation value indicated by the pixel data is converted into a 4-level dot gradation value. Specifically, no dot corresponding to the dot gradation value [00], formation of a small dot corresponding to the dot gradation value [01], formation of a medium dot corresponding to the dot gradation value [10], and The four levels of formation of large dots corresponding to the dot gradation value [11] are converted. Thereafter, after the dot generation rate is determined for each dot size, pixel data is created using the dither method or the like so that the printer 1 forms the dots in a dispersed manner.

  Next, in the rasterizing process, regarding the image data obtained by the halftone process, the data of each dot is changed in the order of data to be transferred to the printer 1. The rasterized data is transmitted as part of the print data.

<About density unevenness>
FIG. 8A is an explanatory diagram of a state when dots are ideally formed. The ideal formation of a dot means that an ink droplet has landed at the center position of the pixel region, the ink droplet spread on the paper S, and a dot is formed in the pixel region. When each dot is accurately formed in each pixel region, a dot line (dot row in which dots are arranged in the moving direction) is accurately formed in the row region.
FIG. 8B is an explanatory diagram when density unevenness occurs. The dot lines formed in the second row region are formed closer to the third row region due to variations in the flight direction of the ink droplets ejected from the nozzles. As a result, the second row region is light and the third row region is dark. In addition, the ink amount of the ink droplets ejected to the fifth row region is smaller than the prescribed ink amount, and the dots formed in the fifth row region are small. As a result, the fifth row region becomes lighter.
When a printed image composed of raster lines having different shades is viewed macroscopically, striped density unevenness along the transport direction is visually recognized. This uneven density causes a reduction in image quality of the printed image.

  As a measure for suppressing the density unevenness as described above, it is conceivable to correct the gradation value (command gradation value) of the image data. That is, it is only necessary to correct the gradation values of the pixels corresponding to the unit areas constituting the row area so that the row area is formed to be light (dark) for a dark (light) visible row area. For this reason, the density correction value H for correcting the gradation value of the image data is calculated for each raster line. This density correction value H is a value reflecting the density unevenness characteristic of the printer 1.

FIG. 8C is a diagram illustrating a state in which the occurrence of density unevenness is suppressed. If the density correction value H for each raster line has been calculated, the printer driver performs a process for correcting the gradation value of the pixel data for each raster line based on the density correction value H when the halftone process is executed. . When each dot line is formed with the gradation value corrected by this correction processing, the density of the corresponding raster line is corrected, and as a result, the occurrence of density unevenness in the printed image is suppressed as shown in FIG. 8C. It will be.
For example, in FIG. 8C, the dot generation rate of the second and fifth row regions that are visually recognized as light is high, and the dot generation rate of the third row region that is visually recognized as low is low. The gradation value of the pixel data of the corresponding pixel is corrected. In this manner, the dot generation rate of the raster line in each row area is changed, the density of the image pieces in the row area is corrected, and the density unevenness of the entire print image is suppressed.

<Calculation of density correction value H>
Next, a process for calculating the density correction value H for each raster line (hereinafter also referred to as a correction value acquisition process) will be outlined. The correction value acquisition process is performed, for example, under the correction value calculation system in the inspection line of the printer 1 manufacturing factory. The correction value calculation system is a system for calculating the density correction value H according to the density unevenness characteristic of the printer 1 and has the same configuration as the printing system 100 described above. That is, the correction value calculation system includes the printer 1, the computer 110, and the scanner 120 (for convenience, the same reference numerals as those in the printing system 100 are used).
The printer 1 is a target device of the correction value acquisition process. In order to print an image having no density unevenness using the printer 1, the density correction value H for the printer 1 is calculated in the correction value acquisition process. It will be. The computer 110 placed on the inspection line is installed with a correction value calculation program for the computer 110 to execute correction value acquisition processing.

<About correction value acquisition processing>
FIG. 9 is a diagram showing the flow of correction value acquisition processing. When the printer 1 capable of multicolor printing is targeted, the correction value acquisition processing for each ink color is performed in the same procedure. In the following description, correction value acquisition processing for one ink color (for example, black) will be described.

First, the computer 110 transmits print data to the printer 1, and the printer 1 forms a correction pattern CP on the paper S by the same procedure as the above-described printing operation (S202).
FIG. 10 is an explanatory diagram of the correction pattern CP. As shown in FIG. 10, the correction pattern CP is formed by sub-patterns CSP having five different densities.

  Each sub-pattern CSP is a belt-like pattern, and is configured by arranging a plurality of raster lines along the moving direction in the paper width direction. Each sub-pattern CSP is generated from image data having a constant gradation value (command gradation value). As shown in FIG. 10, the density increases in order from the left sub-pattern CSP. Yes. Specifically, 15%, 30%, 45% and 60% from the left. The sub-pattern has a density of 85%. Hereinafter, Sa is a command gradation value of a sub-pattern CSP having a density of 15%, Sb is a command gradation value of a sub-pattern CSP having a density of 30%, Sc is a command gradation value of a sub-pattern CSP having a density of 45%, and The command gradation value of the sub-pattern CSP is represented as Sd, and the command gradation value of the sub-pattern CSP having a density of 85% is represented as Se. For example, the sub-pattern CSP formed with the command gradation value Sa is expressed as CSP (1) as shown in FIG. Similarly, the sub patterns CSP formed by the command gradation values Sb, Sc, Sd, and Se are denoted as CSP (2), CSP (3), CSP (4), and CSP (5), respectively.

  Next, the inspector sets the paper S on which the correction pattern CP is formed on the scanner 120. Then, the computer 110 causes the scanner 120 to read the correction pattern CP and obtains the result (S204). As described above, the scanner 120 has three sensors corresponding to R (red), G (green), and B (blue). The scanner 120 irradiates the correction pattern CP with light, and reflects the reflected light to each sensor. Detect by. Note that the computer 110 has the same number of pixel columns in which pixels are arranged in the direction corresponding to the moving direction and the number of raster lines (number of column regions) constituting the correction pattern on the image data obtained by reading the correction pattern. Adjust so that In other words, the pixel rows read by the scanner 120 and the row regions are made to correspond one-to-one. Then, the average value of the read gradation values indicated by each pixel in the pixel column corresponding to a certain row region is set as the read tone value of the row region.

  Next, the computer 110 calculates the density for each raster line (in other words, for each row region) of each sub-pattern CSP based on the read gradation value acquired by the scanner 120 (S206). Hereinafter, the density calculated based on the read gradation value is also referred to as calculated density.

  FIG. 11 is a graph showing the calculated density for each raster line for the sub-pattern CSP having the command gradation values of Sa, Sb, and Sc. The horizontal axis in FIG. 11 indicates the position of the raster line, and the vertical axis indicates the magnitude of the calculated density. As shown in FIG. 11, each sub-pattern CSP is formed with the same command gradation value, but has a shade for each raster line. This difference in density of raster lines is a cause of uneven density in the printed image.

  Next, the computer 110 calculates a density correction value H for each raster line (S208). The density correction value H is calculated for each command gradation. Hereinafter, the density correction values H calculated for the command gradations Sa, Sb, Sc, Sd, and Se are referred to as Ha, Hb, Hc, Hd, and He, respectively. In order to explain the calculation procedure of the density correction value H, the density correction for correcting the command gradation value Sb so that the calculated density for each raster line of the sub-pattern CSP (2) of the command gradation value Sb is constant. A procedure for calculating the value Hb will be described as an example. In this procedure, for example, the average value Dbt of the calculated densities of all raster lines in the sub-pattern CSP (2) of the command gradation value Sb is determined as the target density of the command gradation value Sb. In FIG. 11, in the i-th raster line whose calculated density is lighter than the target density Dbt, the command gradation value Sb may be corrected to be darker. On the other hand, for the j-th raster line whose calculated density is higher than the target density Dbt, the command gradation value Sb may be corrected to be lighter.

  FIG. 12A is an explanatory diagram of a procedure for calculating a density correction value Hb for correcting the command gradation value Sb for the i-th raster line. FIG. 12B is an explanatory diagram of the procedure for calculating the density correction value Hb for correcting the command gradation value Sb for the j-th raster line. 12A and 12B, the horizontal axis indicates the magnitude of the command gradation value, and the vertical axis indicates the calculated density.

The density correction value Hb for the command gradation value Sb of the i-th raster line is the calculated density Db of the i-th raster line and the command gradation value Sc in the sub-pattern CSP (2) of the command gradation value Sb shown in FIG. 12A. Is calculated based on the calculated density Dc of the i-th raster line in the sub-pattern CSP (3). More specifically, in the sub-pattern CSP (2) of the command gradation value Sb, the calculated density Db of the i-th raster line is smaller than the target density Dbt. In other words, the density of the i-th raster line is lighter than the average density. If it is desired to form the i-th raster line so that the calculated density Db of the i-th raster line is equal to the target density Dbt, the gradation value of the pixel data corresponding to the i-th raster line, that is, the command level As shown in FIG. 12A, the tone value Sb is expressed by the following equation (1) using linear approximation from the correspondence (Sb, Db), (Sc, Dc) between the command gradation value and the calculated density in the i-th raster line. It is sufficient to correct up to the target command gradation value Sbt calculated by the above.
Sbt = Sb + (Sc−Sb) × {(Dbt−Db) / (Dc−Db)} (1)
Then, a density correction value H for correcting the command tone value Sb for the i-th raster line is obtained from the command tone value Sb and the target command tone value Sbt by the following equation (2).
Hb = ΔS / Sb = (Sbt−Sb) / Sb (2)
On the other hand, the density correction value Hb for the command gradation value Sb of the j-th raster line is the calculated density Db of the j-th raster line in the sub-pattern CSP (2) of the command gradation value Sb shown in FIG. It is calculated based on the calculated density Da of the j-th raster line in the sub-pattern CSP (1) of the value Sa. Specifically, in the sub-pattern CSP (2) of the command gradation value Sb, the calculated density Db of the jth raster line is larger than the target density Dbt. If it is desired to form the jth raster line so that the calculated density Db of the jth raster line is equal to the target density Dbt, the command gradation value Sb of the jth raster line is set as shown in FIG. 12B. From the correspondence relationship (Sa, Da), (Sb, Db) between the command gradation value and the calculated density in the jth raster line to the target command gradation value Sbt calculated by the following equation (3) using linear approximation. It may be corrected.
Sbt = Sb + (Sb−Sa) × {(Dbt−Db) / (Db−Da)} (3)
Then, the density correction value Hb for correcting the command gradation value Sb for the j-th raster line is obtained by the above equation (2).

As described above, the computer 110 calculates the density correction value Hb for the command gradation value Sb for each raster line. Similarly, density correction values Ha, Hc, Hd, and He for the command gradation values Sa, Sc, Sd, and Se are calculated for each raster line. For other ink colors, density correction values Ha to He are calculated for each of the command gradation values Sa to Se for each raster line.
Thereafter, the computer 110 transmits the density correction value H data to the printer 1 and stores it in the memory 53 of the printer 1 (S210).

FIG. 13 is a diagram illustrating a correction value table stored in the memory 53. As a result, a correction value table in which the density correction values Ha to He for each of the five command gradation values Sa to Se are collected for each raster line is created in the memory 53 of the printer 1. .
Also, as shown in FIG. 13, the correction value table is created for each ink color. As a result, a correction value table for CMYK four colors is formed. The correction value table is referred to by the printer driver when the image is printed using the printer 1 in order to correct the gradation value of each raster line constituting the image data of the image.
In this embodiment, the density is measured for each raster line corresponding to the pixel row on the paper, and a correction value for correcting the gradation value is obtained based on the measured density. In this way, it is possible to perform density correction for each raster line. Then, the occurrence of color unevenness on the paper can be suppressed.

  By the way, in the printing as described above, when the head moves in the movement direction, the head 41 ideally moves only in the movement direction, and no movement error in the conveyance direction occurs. However, in practice, the head 41 may meander to move in the paper transport direction. Thus, when the head 41 moves in the transport direction, for example, the # 11 nozzle of the nozzle row 411 of pass 1 and the # 1 nozzle of the nozzle row 411 of pass 2 are originally shared and aligned in the movement direction. Although the dot line is supposed to be formed, the positions of the dots may be shifted in the nozzle row direction. As a result, the brightness changes in the overlapping range of the nozzle rows, and density unevenness may occur.

  In the embodiment described below, even when the dot position to be formed is fluctuated due to meandering when the head 41 is moved, the density unevenness is reduced by reducing the change in brightness that appears as a result. Is to suppress the occurrence of

  FIG. 14 is a diagram for explaining a change in brightness when corresponding nozzles coincide with each other in the transport direction. In the figure, the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 when the overlapping range of nozzles match in the transport direction are shown. In addition, the ink amount per unit area and the coverage are shown in “original position”, “when narrowed”, and “when widened”, which will be described later. Here, the moving direction of the head 41 is directed in the vertical direction on the paper surface.

  The ink amount per unit area is that of one raster line formed by two nozzles in the overlapping range, when the ink amount of one raster line formed by one nozzle in the non-overlapping range is 100%. The amount of ink.

  The coverage is a rate at which dots cover the paper. For example, when two dots are formed in the same area, the coverage is high when the two dots do not overlap and are formed in that region, while the two dots overlap and are formed in that region. The coverage of is low. This is due to the fact that two dots overlap and overlap, so that the area covering the paper is reduced by the overlap.

  In the figure, the dot arrangement corresponding to the coverage is shown, but in order to know which dot is formed by the nozzle of the nozzle row of which pass, the hatching direction and dot attached to the nozzle are shown. The hatched direction is the same.

  In the figure showing the coverage, the diagram on the left side shows a state where the dots formed by the nozzle row 411 of the pass 2 are arranged on the right side of the dots formed by the nozzle row 411 of the pass 1. In the figure showing the coverage rate, the diagram on the right side shows a state where the dots formed by the nozzle row 411 of the pass 2 are arranged on the left side of the dots formed by the nozzle row 411 of the pass 1. Yes.

  The ink amount per unit area and the coverage are shown when the original position is maintained, when it is narrowed, and when it is widened. The “original position” is 0, when the overlapping nozzles are aligned so as to coincide with each other in the moving direction of the head 41, as in the case where the state shown in the figure is maintained. This corresponds to the case where no movement in the nozzle row direction occurs during the movement.

  “Narrow” means that movement in the nozzle row direction occurs when the head 41 moves, and the nozzle row direction increases in the direction in which the overlapping range of the nozzle rows in pass 1 and pass 2 increases. This corresponds to the case where printing occurs because of movement (when the width Y1 of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is narrowed). This corresponds to, for example, a case where dots are formed when the head 41 is moved in the pass 2 by a slight movement in the direction opposite to the conveying direction by 0.5 nozzle pitch.

  Further, “becomes wide” means that movement in the nozzle row direction occurs when the head 41 moves, and the direction in which the nozzle rows in the pass 1 and pass 2 overlap decreases in the nozzle row direction. Corresponds to the case where printing is performed (when the width Y1 of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is widened). This corresponds to, for example, the case where dots are formed when the head 41 is moved slightly in the transport direction by 0.5 nozzle pitch during the movement of the head 41 in pass 2.

By the way, the brightness change is obtained by the following equation under the above-described conditions.
Lightness change = change in ink amount per unit area + change in coverage Referring to FIG. 14, the change in lightness results in the following.
At the original position: the ink amount per unit area is always 100%. Moreover, in the figure explaining a coverage, although each dot does not overlap, it is formed side by side so that it may adjoin.

When narrowed: The ink amount per unit area increases. In the left diagram for explaining the coverage, the dots formed by the nozzle row 411 in pass 2 are formed so as to overlap the dots formed by the nozzle row 411 in pass 1. In other words, the result is that the coverage is lowered. Further, in the diagram on the right side for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed away from the dots formed by the nozzle row 411 of pass 1. In this case, since there is no change in that the dots do not overlap with respect to the “original position”, the coverage does not change.
Therefore, since the ink amount per unit area increases (darkens) and the coverage decreases (lightens), the two are almost offset, and the change in brightness does not appear or is small. It is done.

When widened: The amount of ink per unit area decreases. This is because even if the same ink amount is ejected, the overlapping range of nozzles is reduced, so that the ink amount per unit area is reduced. Further, in the figure on the left side for explaining the coverage, dots formed by the nozzle row 411 of pass 2 are formed so as to be away from the dots formed by the nozzle row 411 of pass 1. In this case, since there is no change in that the dots do not overlap with each other at the “original position”, the coverage does not change. Further, in the figure on the right side for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to overlap the dots formed by the nozzle row 411 of pass 1. In this case, the coverage ratio is lowered.
Therefore, the amount of ink per unit area decreases (lightens) and the coverage also decreases (lightens). Therefore, it is considered that the brightness changes to become brighter and can be visually recognized lightly.

  FIG. 15 is a diagram for explaining a change in brightness when the width of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is shifted in the narrowing direction. In FIG. 15, two nozzle rows are shown so that the width of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is reduced by a 1/2 nozzle pitch with respect to the nozzle row in FIG. (Y1> Y2). This is the case, for example, when the paper is transported by a transport amount that is smaller by 0.5 nozzle pitch than the transport amount in FIG. With such a carry amount, the brightness change is as follows.

  At the original position: The ink amount per unit area is larger than that in FIG. This is because the amount of ink per unit area is increased because the overlapping range of the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 is increased by a smaller transport amount than in FIG. At this time, in the figure on the left side for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to overlap the dots formed by the nozzle row 411 of pass 1. Further, in the figure on the right side for explaining the coverage, dots formed by the nozzle row 411 of pass 2 are formed so as to be separated from the dots formed by the nozzle row 411 of pass 1.

When narrowed: In this case, the amount of ink per unit area increases as compared to the “original position”. Further, in the left diagram for explaining the coverage, the dots formed by the nozzle row 411 of the pass 2 are formed so as to overlap the dots formed by the nozzle row 411 of the pass 1. Further, in the figure on the right side for explaining the coverage, the dots formed by the nozzles 411 in the pass 2 are formed so as to be further away from the dots formed by the nozzle rows 411 in the pass 1.
Therefore, since the ink amount per unit area increases (darkens) and the coverage decreases (lightens), the two are almost offset, and the change in brightness does not appear or is small. It is done.

When widened: The amount of ink per unit area decreases compared to the “original position”. Further, in the left diagram for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to be aligned with the dots formed by the nozzle row 411 of pass 1. That is, in this case, the coverage is increased as compared to the “original position”. Also, in the figure on the right side explaining the coverage, although the dots formed by the nozzle row 411 of pass 2 are formed so as to approach the dots formed by the nozzle row 411 of pass 1, both dots do not overlap. Compared to the “original position”, there is no change in the coverage.
Therefore, although the ink amount per unit area decreases (lightens), the coverage increases (darkens), so both cancel each other, and it is considered that the change in brightness does not appear or is small.

  FIG. 16 is a diagram for explaining the change in brightness when the width of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411B in pass 2 is shifted in the increasing direction. In FIG. 16, two nozzle rows are shown so that the width of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is increased by a 1/2 nozzle pitch with respect to the nozzle row in FIG. (Y1 <Y3). This is the case, for example, when the paper is transported by a transport amount that is 0.5 nozzle pitch larger than the transport amount in FIG. At such a relative position of the nozzle row, the change in brightness is as follows.

  At the original position: the ink amount per unit area is smaller than that in FIG. This is because the amount of ink per unit area is reduced because the overlapping range of the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 is reduced by a larger carry amount than in FIG. At this time, in the figure on the left side for explaining the coverage, the dots formed by the nozzle row 411 of the pass 2 are formed apart from the dots formed by the nozzle row 411 of the pass 2. Further, in the diagram on the right side for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to overlap the dots formed by the nozzle row 411 of pass 1.

When narrowed: The amount of ink per unit area increases as compared to the “original position”. Further, in the figure on the left side for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to approach the dots formed by the nozzle row 411 of pass 1. However, since the fact that the dots do not overlap is the same as in the “original position”, the coverage is not changed. Further, in the figure on the right side for explaining the coverage, dots formed by the nozzle row 411 of pass 2 are formed so as to be separated from the dots formed by the nozzle row 411 of pass 1. At this time, the dot that has been duplicated at the “original position” becomes a non-overlapping dot, thereby increasing the coverage.
Therefore, the amount of ink per unit area increases (darkens), and the coverage also increases (darkens). Therefore, it is considered that the lightness changes to become darker.

When widened: The amount of ink per unit area decreases compared to the “original position”. Further, in the left diagram for explaining the coverage, the dots formed by the nozzle row 411 of pass 2 are formed so as to be away from the dots formed by the nozzle row 411 of pass 1. There is no change in the coverage at this time. However, since the fact that the dots do not overlap is the same as in the “original position”, the coverage is not changed. Further, in the figure on the right side for explaining the coverage, the dots formed by the nozzles 411 of the pass 2 are formed so as to more overlap the dots formed by the nozzle rows 411 of the pass 1. The coverage at this time will decrease.
Therefore, the amount of ink per unit area decreases (lightens), and the coverage decreases (lightens), so the lightness is considered to change to become brighter.

  FIG. 17 is a diagram for explaining the relationship of the change in brightness with respect to the relative position of the nozzles between passes. In the drawing, the relative positional relationship between the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is shown on the horizontal axis. Here, “narrow” means that the width of the nozzle row formed by the positions of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is arranged to be narrow (corresponding to FIG. 15). is there. “Wide” means that the width of the nozzle row composed of the positions of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is widened. In addition, brightness is shown on the vertical axis of the figure.

  As described above, the brightness change when the dot position fluctuates by d2 in the “narrow” region is L2. On the other hand, the brightness change when the dot position fluctuates by d1 in the “wide” region is L1. In this way, it can be seen that when the nozzle row composed of the nozzle rows of pass 1 and pass 2 is arranged so as to have a narrow width, the change in brightness due to dot position variation is small.

  In the arrangement of the nozzle rows as described above, when the width of the nozzle row composed of the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 is arranged to be narrow, the dot position fluctuations The reason why the brightness change due to is small is also considered as follows.

  Near the end of the range where the nozzles overlap in the nozzle row 411 of pass 1 and the nozzle row 411 of pass 2 (in FIG. 14, FIG. 15, FIG. 16, nozzle # 11 and nozzle # 11 of pass 1 nozzle row 411 Focusing on the vicinity of nozzle # 1 in the nozzle row 411 and the vicinity of nozzle # 14 in the nozzle row 411 in pass 1 and the nozzle # 4 in the nozzle row 411 in pass 2), as described above, the dots are aligned in the moving direction. For example, the nozzle line that forms a shared dot line, such as the nozzle # 11 in the nozzle row 411 in pass 1 and the nozzle # 1 in the nozzle row 411 in pass 2, The dots of the dot line are formed in such a manner that the lightness is predetermined. Further, in the nozzles in a non-overlapping range, for example, the nozzle # 10 in the nozzle row 411 in pass 1, a dot line is formed by the nozzle alone.

  Here, in the case of FIG. 15, the distance between the dots formed by the nozzle # 1 of the nozzle row 411 of pass 2 and the dots formed by the nozzle # 10 of the nozzle row 411 of pass 1 is narrow. Now, due to head movement error, etc., the formation position in the nozzle row direction of dots formed by the nozzles of the nozzle rows of the two passes is the direction in which the overlapping range of the two nozzle rows is reduced, that is, the nozzle row 411 of pass 2. Let us consider a case where the dots formed by the nozzle # 1 are shifted to the right in the figure. At this time, the distance between the dots formed by the nozzle # 1 of the nozzle row 411 of the pass 2 and the dots formed by the nozzle # 10 of the nozzle row 411 of the pass 1 is widened, and the ink amount per unit area of this region is Although it decreases, the distance between the two dots originally overlapped narrowly, so the overlap of dots decreases and the coverage increases. Therefore, the brightness change in this region is relatively small.

  On the other hand, in the case of FIG. 16, the distance between the dots formed by the nozzle # 1 of the nozzle row 411 of pass 2 and the dots formed by the nozzle # 10 of the nozzle row 411 of pass 1 is large. Now, similarly, consider a case where the formation positions in the nozzle row direction of dots formed by the nozzles of two nozzle rows are shifted in a direction in which the overlapping range of the two nozzle rows is reduced. At this time, the distance between the dot formed by the nozzle # 1 of the nozzle row 411 of the pass 2 and the dot formed by the nozzle # 10 of the nozzle row 411 of the pass 1 becomes wider, and both the dots do not originally overlap. The coverage does not change, and the amount of ink per unit area in this region decreases. Therefore, the brightness change in which the brightness of this region becomes brighter is relatively large.

  Although the above-described influence occurs near the end of the overlapping range of the two nozzle arrays, in practice, the nozzle pitch is very small and the overlapping range is small. In the case of 16, the effect of increasing the brightness is observed relatively large.

  Therefore, as shown in FIG. 15, it is desirable to carry the head so that a partially overlapping range is increased by less than one nozzle pitch (here, 1/2 nozzle pitch). By doing so, even if the dot position to be formed changes in the transport direction due to meandering when the head is moved, the brightness change is small with respect to the change in the position of the dots to be formed. It is because it can be set as a structure.

  However, such a configuration can also be realized by increasing the number of dots on the raster line corresponding to the overlapping nozzles in advance. That is, by pre-creating a pixel region formed so that the dots formed by the nozzle row 411 in pass 1 and the dots formed by the nozzle row 411 in pass 2 overlap, the overlapping range of the two nozzle rows is temporarily reduced. When printing is performed as if the nozzle row 411 in pass 2 has moved (when the width Y1 of the nozzle row composed of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 becomes wider) ), The amount of ink per unit area is reduced, but the coverage is increased by moving the dots formed so as to be separated from each other. Then, both cancel each other and the brightness change is less likely to occur.

  However, if printing is simply performed with such a configuration, printing with high density is performed in a region corresponding to the overlapping range of nozzle rows between passes, and thus the correction value acquisition process as described above (FIG. 9). The gradation value is corrected by performing the process as described above. In other words, as shown below, the relative positions of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 are configured so that the corresponding nozzles in the overlapping range coincide with each other in the nozzle row direction. Higher density printing is performed by forming more dots in the area corresponding to the overlapping range so that the nozzle usage ratio in the overlapping range is higher than the nozzle usage ratio in other than the overlapping range. Thereafter, the correction value acquisition process shown in FIG. 9 is performed. Then, while performing gradation value correction using the obtained correction value, by performing printing with the nozzle configuration when the correction pattern is formed, there is less change in brightness with respect to variation in dot position, and Printing with less density unevenness can be performed.

<About overlap processing in this embodiment>
FIG. 18 is a diagram for explaining a method for realizing the overlap processing. In the upper part of the figure, an input image is shown. Here, a method is shown in which such an input image is formed by being shared by nozzle rows in two passes (nozzle row 411 in pass 1 and nozzle row 411 in pass 2). The lower part of the input image shows the input image distributed to the nozzle array 411 in pass 1 and the nozzle array 411 in pass 2. Further, in the lower stage, a mask (hereinafter referred to as an overlap mask) applied in an overlapping region of the nozzle row 411 in pass 1 (a range partially overlapping with the nozzle row 411 in pass 2), and a nozzle row 411 in pass 2 The overlap mask applied in the overlapping region is shown. As will be described later, by applying such an overlap mask, it is possible to obtain an image formed by sharing for each pass in the overlapping region. In the lowermost part of the figure, an image in which each nozzle row is responsible for the formation is shown.

  For ease of explanation, the image shown here is an image composed of a set of pixels in two states, whether dots are formed or dots are not formed.

  By taking the logical product of the overlap masks corresponding to each nozzle row with respect to the distributed input image, it is possible to specify the image (dot) responsible for the formation of the nozzle row of each pass. In this way, it is possible to specify the dots to be formed for each pass for the nozzles corresponding to the overlapping region.

  FIG. 19 is a diagram for explaining a method of creating an overlap mask of a reference example. In the uppermost part of the figure, the nozzle usage ratio of each nozzle of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is shown. In the lower part of the nozzle usage ratio, when the nozzle usage ratio of the nozzle row 411 in pass 1 is 8 nozzles (for 8 rasters) and the nozzles on both sides thereof (each for 1 raster) form a 255 gradation image. The grayscale is shown.

  For example, the nozzles # 1 to # 10 of the nozzle row 411 in pass 1 have a nozzle usage ratio of 100% in forming the corresponding dot lines. The gradation value at this time is 255. Further, the nozzle # 11 of the nozzle row 411 in pass 1 has a nozzle use ratio of 88.8% (the gradation value is 226) in forming the corresponding dot line. In addition, nozzle # 12 has a nozzle use ratio of 77.7% in forming the corresponding dot line (tone value is 198). In addition, nozzle # 13 has a nozzle usage ratio of 66.6% (tone value is 170) in forming the corresponding dot line. In addition, nozzle # 14 has a nozzle usage ratio of 55.5% (tone value is 142) in forming the corresponding dot line. In addition, nozzle # 15 has a nozzle usage ratio of 44.4% (the gradation value is 113) in forming the corresponding dot line. In addition, nozzle # 16 has a nozzle usage ratio of 33.3% when forming the corresponding dot line (tone value is 85). In addition, nozzle # 17 has a nozzle usage ratio of 22.2% (the gradation value is 57) in forming the corresponding dot line. In addition, nozzle # 18 has a nozzle usage ratio of 11.1% (tone value is 28) in forming the corresponding dot line.

Halftone processing is performed on the gray scale formed in such a correspondence. As the halftone process, a known halftone process using the dither method as described above is used. When halftone processing is performed in this way, an overlap mask for the nozzle array 411 in pass 1 as shown in the lowermost stage of the drawing is created. In the figure, the nozzles of the nozzle row 411 in pass 1 form the dots of the image that overlap the portion shown in black. On the other hand, in the figure, the nozzles of the nozzle row 411 in pass 2 form the dots of the image that overlap with the portions shown in white. A portion shown in white in the drawing is the same as the overlap mask of the nozzle row 411 in pass 2 in FIG.
By doing in this way, the overlap mask according to the nozzle usage ratio of each pass can be created.

FIG. 20 is a diagram illustrating an example of dot formation when the total nozzle usage ratio is 100% for the overlapping regions of the nozzle rows. In the figure, the dots formed by the diagonal lines are dots. For each dot, it is shown that the direction of the diagonal line attached to the nozzle of each pass and the direction of the diagonal line attached to the square coincide with each other so that it can be understood which nozzle is formed by which pass. Has been. Then, as shown in the figure, by forming dots in each pass, each pixel region is always formed by a nozzle in any pass.
Here, dots formed by applying an overlap mask different from the overlap mask shown in FIG. 19 are assigned.

FIG. 21 is a diagram illustrating an example when the position of the dot by the nozzle row 411 in pass 2 is shifted in the nozzle row direction. This is because, for example, in the conveyance after the dot formation by pass 1, the dot is formed by pass 2 after the paper has been conveyed by 0.5 nozzle pitch more than the original conveyance. It corresponds to.
Therefore, the figure shows a state in which the nozzle row 411 in pass 2 is shifted by a 1/2 nozzle pitch in the negative direction of the y-axis with respect to FIG. 20 described above. Further, the dots formed in such pass 1 and pass 2 are indicated by squares. At this time, dots are formed under the same conditions as the dot formation shown in FIG. 20 except that the position of the nozzle row 411 in pass 2 is shifted in the nozzle row direction (conveyance direction).

  As a result of forming the dots in this manner, it can be seen that there are places where the dots are overlapped as shown in the figure, while there are places where the distance between the dots is wide. In this way, there are places where dots are formed overlappingly, while there are places where the distance between the dots is wide, compared to the case of FIG. The rate drops. Then, the color becomes light in this region, and as a result, white stripes appear.

FIG. 22 is a diagram illustrating an example of dot formation when the total nozzle usage ratio exceeds 100% in the overlapping region of the nozzle rows. Again, in the figure, the dots indicated by the diagonal lines are dots. For each dot, the direction of the diagonal line attached to the nozzle of each pass and the direction of the diagonal line attached to the square match so that it can be seen which nozzle is formed by which pass nozzle. It is shown.
Then, by forming dots as shown in the figure, dots are always formed in each pixel area by nozzles in either pass, and in some pixel areas, dots are formed by nozzles in both passes It has come to be.

FIG. 23 illustrates an example of dot formation when the total nozzle usage ratio exceeds 100% for overlapping portions of the nozzle rows and the position of the dots by the nozzle row 411 in pass 2 is shifted in the nozzle row direction. It is a figure to do. This is also the case, for example, when the dot is formed by pass 2 after the paper has been transported by 0.5 nozzle pitch more than originally transported in the transport after the dot formation by pass 1. Equivalent to.
Therefore, the figure shows a state in which the nozzle row 411 of pass 2 is shifted by a 1/2 nozzle pitch in the negative direction of the y-axis with respect to FIG. 22 described above. Further, the dots formed in such pass 1 and pass 2 are indicated by squares. At this time, dots are formed under the same conditions as the dot formation shown in FIG. 22 except that the position of the nozzle row 411 in pass 2 is shifted in the nozzle row direction (conveyance direction).

  As a result of arranging the dots in this way, it can be seen that there are places where the dots are formed overlappingly as shown in the figure, while there are places where the distance between the dots is wide. And a coverage rate falls compared with the time of FIG. However, when the dots are overlapped by the nozzles of the two passes and formed so that the dots are separated from each other, the coverage of the portion increases. Therefore, the decrease and increase in coverage are offset, and as a result, the change in brightness is reduced.

  FIG. 24 is a diagram for explaining the nozzle usage ratios of pass 1 and pass 2 when the total nozzle usage ratio exceeds 100% for overlapping regions. By setting the nozzle usage ratio as shown in the figure, the total nozzle usage ratio for the overlapping region can exceed 100%. Then, in order to make the total nozzle usage ratio in the overlapping region exceed 100%, it is possible to prevent the dot position variation by overlapping the dots at almost the same place by two passes. Lightness change can be reduced. In this way, in order to make the total nozzle use ratio in the overlap region exceed 100%, it is necessary to use an overlap mask in which dots are formed overlappingly at almost the same place by two passes. is there.

  Next, a method for creating an overlap mask corresponding to a case where the total nozzle use ratio in the overlapping region exceeds 100% will be described.

  FIG. 25 is a diagram for explaining a matrix for creating an overlap mask in the present embodiment. Here, an example will be described in which eight nozzles in the pass 1 nozzle row 411 and pass 2 nozzle row 411 overlap in the transport direction. Since 8 nozzles overlap, this matrix consists of 8 × 8 cells. In the following description, each cell of the matrix is cited by specifying m rows and n columns and columns as shown in the figure.

  FIG. 26A is a diagram showing a nozzle use ratio in the present embodiment. In the figure, the nozzle number of the nozzle row 411 in pass 1 and the corresponding nozzle usage ratio are shown. Further, the nozzle number of the nozzle row 411 in pass 2 and the corresponding nozzle usage ratio are shown. The nozzle usage ratio shown here is set higher than the nozzle usage ratio shown in FIG.

  FIG. 26B is a diagram illustrating gradation values with respect to the nozzle usage ratio in the present embodiment. Here, the gradation value with respect to the nozzle usage ratio when the maximum gradation value is 255 is shown. In the figure, the gradation value corresponding to the nozzle number of the nozzle row 411 of pass 1 is shown. Further, gradation values corresponding to the nozzle numbers of the nozzle row 411 in pass 2 are shown.

FIG. 27 is a diagram for explaining the overlap mask of the nozzle row 411 in pass 1 in the present embodiment. In the drawing, the gradation value corresponding to the nozzle usage ratio of the nozzle row 411 of pass 1 in the present embodiment and the overlap mask of the nozzle row 411 of pass 1 created thereby are shown. The overlap mask is indicated by “1” indicating that dots can be formed and “0” indicating that dots are not formed.
In such an overlap mask, the threshold value shown in the matrix in FIG. 25 is compared with the gradation value corresponding to the nozzle usage ratio, and “1” is set when the gradation value is higher. If the gradation value is not higher, it is created by setting “0”.

For example, as shown in the drawing, the gradation value (245) corresponding to nozzle # 11 in pass 1 is compared with the value in the first column (n = 1) of the matrix shown in FIG. Since the value of the first row and first column (m = 1, n = 1) is 191, the gradation value is higher than the gradation value 245. Therefore, “1” is set in the first row and the first column (m = 1, n = 1), which are the corresponding cells. For example, the gradation value (232) corresponding to nozzle # 12 in pass 1 is compared with the value in the second column (n = 2) of the matrix shown in FIG. Since the value of the second row and second column (m = 2, n = 2) is 239, the gradation value is lower than the gradation value 232. Therefore, “0” is set in the second row and the second column (m = 2, n = 2), which are the corresponding cells.
By performing such an operation on a matrix of 8 rows and 8 columns, an overlap mask of the nozzle row 411 of pass 1 as shown in FIG. 27 can be created.

FIG. 28 is a diagram for explaining the progress in the process of creating an overlap mask for the nozzle row 411 in pass 2 in the present embodiment. In the drawing, a gradation value corresponding to the nozzle usage ratio of pass 2 in the present embodiment and an inverted gradation value obtained by subtracting this gradation value from 255 are shown. In addition, an overlap mask before bit inversion of pass 2 created by the inverted gradation value is shown.
Here, as described above, the threshold values shown in the matrix in FIG. 25 are compared with the inverted gradation value, and when the inverted gradation value is higher, “1” is set, and the gradation value is not higher. In this case, it is created by setting “0”.

For example, as shown in the figure, the inversion gradation value (197) corresponding to nozzle # 1 in pass 2 is compared with the first column (n = 1) of the matrix shown in FIG. Since the value of the first row and first column (m = 1, n = 1) is 191, the inverted gradation value is higher than that of 197, which is the inverted gradation value. Therefore, “1” is set in the first row and the first column (m = 1, n = 1) which are the corresponding cells.
By performing such an operation on an 8 × 8 matrix, an overlap mask before bit inversion of pass 2 as shown in FIG. 28 can be created. Then, by inverting each value of the overlap mask before bit inversion (“0” for “1” and “1” for “0”), an overlap mask for pass 2 can be created. it can.

  FIG. 29 is a diagram for explaining the overlap mask of pass 2 in the present embodiment. In the drawing, an overlap mask corresponding to the nozzle number of pass 2 in the present embodiment is shown.

FIG. 30 is a diagram illustrating a matrix when a logical product operation is performed on the overlap mask of pass 1 and the overlap mask of pass 2 in the present embodiment. Here, the result of performing an AND operation on bits corresponding to the same cell in the overlap mask of pass 1 shown in FIG. 27 and the overlap mask of pass 2 shown in FIG. 29 is shown. ing.
For example, the value “1” of the first row and first column (m = 1, n = 1) of the overlap mask of pass 1 and the first row and first column (m = 1, n = 1) of the overlap mask of pass 2 As a result of performing an AND operation with the value “0” of), “0” is shown in the first row and the first column. Also, the value “1” of the fifth row and first column (m = 5, n = 1) of the overlap mask of pass 1 and the fifth row and first column (m = 5, n = 1) of the overlap mask of pass 2 As a result of performing a logical product operation with the value “1” of), “1” is shown in the fifth row and the first column.
In this way, by performing the logical product operation, “1” is shown in the cell where both values are “1” in the two overlap masks. A dot is also formed at that position by pass 1, and a dot is also formed by pass 2. That is, a place where dots are formed overlappingly is indicated by “1”.

The lower part of FIG. 30 shows the total number of overlaps corresponding to the matrix columns. The total number of overlaps indicates how many “1” s exist in the corresponding column. Referring to the figure, it can be seen that, in the nozzles in the overlapping area, the total number of overlaps near the center (corresponding to nozzles # 14 to # 15 in pass 1 and nozzles # 4 to # 5 in pass 2) is large. This is because, as shown in FIG. 24, in the overlap region, the nozzle usage ratio near the center is made higher than the end portion.
In addition, the total number of overlaps is a numerical value of 1 or more. By doing so, the nozzles in the overlapping region can form more dots than the dots formed by the nozzles other than the overlapping region.

  FIG. 31 is a diagram illustrating a matrix when a logical sum operation is performed on the overlap mask of pass 1 and the overlap mask of pass 2 in the present embodiment. In the figure, it is shown that “1” is set in all the matrices. That is, by performing printing using the overlap mask in the present embodiment created by such a method, dots can be formed so as not to be missing in any place, and some places ( As for the pixel region), as shown in FIG. 30, the dots can be overlapped by both the nozzle in pass 1 and the nozzle in pass 2.

  However, if printing is simply performed using such an overlap mask, the density in the range corresponding to the overlapping area is increased as described above, and thus the correction value acquisition process as described above (FIG. 9). The gradation value is corrected by performing the process as described above. That is, the correction pattern is printed with the configuration as shown in FIG. 24, and then the correction value acquisition process shown in FIG. 9 is performed. Then, while performing gradation value correction using the obtained correction value, printing is performed with a configuration similar to that when the correction pattern is formed, thereby performing printing with less influence on fluctuations in dot positions. Will be able to.

  As a result, the printer is set with a density correction value for correcting the gradation value to be lower than the dot line in the non-overlapping range in the dot line corresponding to the partially overlapping range, A printer having an overlap mask that realizes forming more dots in a dot line corresponding to a partially overlapping range than in a non-overlapping range of dot lines is realized.

  Here, the description has been given by taking the path 1 and the path 2 as an example, but the above-described embodiment can be similarly applied to the relationship between the n-th path and the n + 1-th path.

=== Print processing ===
FIG. 32 is a flowchart of print processing performed by the printer driver under the user. A user who has purchased the printer 1 installs a printer driver (or a printer driver downloaded from the homepage of a printer manufacturer) stored in a CD-ROM included with the printer 1 in a computer. This printer driver is provided with code for causing a computer to execute each process in the drawing. The user connects the printer 1 to the computer.

First, the printer driver acquires a correction value table (see FIG. 13) stored in the memory of the printer 1 from the printer 1 (S302).
When the user instructs printing from the application program, the printer driver is called, receives image data (print image data) to be printed from the application program, and performs resolution conversion processing on the print image data (S304). . The resolution conversion process is a process of converting image data (text data, image data, etc.) to a resolution (print resolution) when printing on paper. Here, the print resolution is 360 × 360 dpi, and each pixel data after the resolution conversion processing is data of 256 gradations represented by the RGB color space.

  Next, the printer driver performs color conversion processing (S306). The color conversion process is a process of converting image data in accordance with the color space of the ink color of the printer 1. Here, image data (256 gradations) in the RGB color space is converted into image data (256 gradations) in the CMYK color space.

  As a result, image data of 256-tone CMYK color space is obtained. In the following description, for simplification of description, the image data of the black plane among the image data of the CMYK color space will be described.

Next, the printer driver performs density unevenness correction processing (S308). The density unevenness correction process is a process for correcting the gradation values of the pixel data belonging to each pixel column based on the correction value for each pixel column (corresponding to the raster line) on the paper.
For example, the printer driver of the user's computer 110 determines the gradation value of each pixel data (hereinafter, the gradation value before correction is referred to as “Sin”) based on the density correction value H of the raster line corresponding to the pixel data. Correction is performed (hereinafter, the corrected gradation value is referred to as Sout).

Specifically, if the gradation value Sin of a certain raster line is the same as any one of the command gradation values Sa, Sb, Sc, Sd, and Se, the density correction value H stored in the memory of the computer 110 is used as it is. Can be used. For example, if the gradation value Sin of the pixel data is Sin = Sb, the corrected gradation value Sout is obtained by the following equation.
Sout = Sb × (1 + Hb)
On the other hand, when the gradation value of the pixel data is different from the command gradation values Sa, Sb, Sc, Sd, Se, the correction value is calculated based on the interpolation using the density correction values of the surrounding command gradation values. For example, when the command tone value Sin is between the command tone value Sb and the command tone value Sc, linearity using the density correction value Hb of the command tone value Sb and the density correction value Hc of the command tone value Sc. If the correction value obtained by interpolation is H ′, the gradation value Sout after the correction of the command gradation value Sin is obtained by the following equation.
Sout = Sin × (1 + H ′)
In this way, the density correction process is performed.

  After density unevenness correction processing, the printer driver performs halftone processing. Halftone processing is processing for converting high gradation number data into low gradation number data. Here, the 256 gradation print image data is converted into the four gradation print image data that can be expressed by the printer 1. A dither method or the like is known as a halftone processing method, and this embodiment also performs such a halftone processing.

  In the present embodiment, the printer driver performs halftone processing on pixel data that has been subjected to density unevenness correction processing. As a result, the tone value of the pixel data in the dark and easily visible portion is corrected to be low, so the dot generation rate in that portion is low. On the contrary, the dot generation rate is high in a portion that is faint and easily visible.

  Next, the printer driver performs rasterization processing (S312). The rasterization process is a process of changing the order of arrangement of pixel data on the print image data to the order of data to be transferred to the printer 1. Thereafter, the printer driver generates print data by adding control data for controlling the printer 1 to the pixel data (S314), and transmits the print data to the printer 1 (S316).

  The printer 1 performs a printing operation according to the received print data. Specifically, the controller 60 of the printer 1 controls the transport unit 20 and the like according to the received print data control data, and controls the head unit 40 according to the pixel data of the print data to eject ink from each nozzle. If the printer 1 performs a printing process based on the print data generated in this way, the dot generation rate of each raster line is changed, the density of the image pieces in the row area on the paper is corrected, and the print image Concentration unevenness is suppressed.

=== Second Embodiment ===
As described above, the printer is set with a density correction value for correcting the tone value so that the dot line corresponding to the partially overlapping range between the passes has a lower gradation value than the dot line not partially overlapping. Thus, a printer having an overlap mask that forms more dots than dot lines in a range that does not partially overlap in a dot line that corresponds to a range in which the nozzle rows partially overlap may be realized as follows. it can.

In the second embodiment, the density correction coefficient r is set according to the dot output ratio. Here, density correction for black K will be described as an example. The density K ′ after density correction and the density K before density correction with respect to the density correction coefficient r are expressed by the following equations.
K ′ (iraster) = K ′ (iraster) × r (iraster)
Here, iraster is a raster number.

FIG. 33 is a diagram for explaining the dot output ratio and the density correction coefficient. In the figure, dot output ratios and density correction coefficients corresponding to the relative positions of pass 1 and pass 2 are shown.
Here, the dot output ratio is the percentage of dots that can be formed by each nozzle in pass 1 and each nozzle in pass 2 in each raster line. Here, the dot output ratio of the area where the nozzle array 411 of pass 1 and the nozzle array 411 of pass 2 overlap (the above-described overlapping area) is set to be higher than the dot output ratio of the portion where the nozzle arrays do not overlap. ing.

The density correction coefficient r is a coefficient shown in the above equation, but the density correction coefficient r is determined so that the density after correction is substantially the same in the overlapping area and the area that is not.
For this reason, in the overlapping region in the figure, the dot output ratio is higher than 100%, and the density correction coefficient is set to a low value that lowers the density as much dots are output.

When the dot output ratio is a function f (iraster), the density correction coefficient is expressed by multiplying the inverse thereof by a predetermined coefficient α. That is,
r (iraster) = α × 1 / f (iraster)
It is represented by Here, the coefficient α is set to a value smaller than 1.

  In the printer according to the first embodiment described above, the dot output ratio in the overlapping region is set higher due to its configuration. Accordingly, the correction pattern CP can be formed by setting the density correction coefficient in advance so that the density after correction becomes low. At this time, since the value of α is smaller than 1, the correction pattern CP formed in the overlapping region is printed with a slightly higher density than the portion other than the overlapping region.

  As described above, the density correction coefficient corresponding to the dot output ratio may be set before performing the correction value acquisition process.

  By doing in this way, generation | occurrence | production of density | concentration unevenness can be suppressed.

=== Other Embodiments ===
In the above-described embodiment, the number of nozzles in the overlapping range of the nozzle row 411 in pass 1 and the nozzle row 411 in pass 2 is 8 per nozzle row in the overlapping range. I just need it.

  The above-described embodiment may be performed in a manufacturing process of a printing apparatus such as a printer, or may be performed as a correction value setting method or the like in maintenance after manufacturing. In that case, it may be performed by a user who uses the printing apparatus. The correction value may be stored in a storage unit integrated with the printing apparatus, or may be stored in a storage unit separate from the printing apparatus. In addition to the semiconductor storage unit, the storage unit may be an optically readable storage unit, or another storage unit such as a magnetic storage unit or a visible storage unit.

  In the above-described embodiment, the density unevenness correction process is performed between the S306 color conversion process and the S310 halftone process in FIG. 32. However, the present invention is not limited to this, and finally the dot line formed by dots. The density unevenness correction may be performed at any stage as long as the density correction can be performed.

  In the above-described embodiment, the printer 1 has been described as the fluid ejecting apparatus. However, the printer 1 is not limited to this, and is not limited to this. Other fluids other than ink (liquids, liquids in which particles of functional materials are dispersed, gels) Such a fluid can be embodied in a fluid ejecting apparatus that ejects or ejects the fluid. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, gas vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to the above-mentioned embodiment to the various apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

  The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

<About the head>
In the above-described embodiment, ink is ejected using a piezoelectric element. However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

1 printer,
20 transport unit, 21 paper feed roller, 22 transport motor, 23 transport roller,
24 platen, 25 paper discharge roller,
30 Carriage unit, 31 Carriage,
40 head units, 41 heads,
50 detector groups,
60 controllers, 61 interfaces,
62 CPU, 63 memory,
70 drive signal generation circuit,
110 computers, 111 interfaces,
112 CPU, 113 memory,
120 scanner, 121 reading carriage, 122 interface,
123 CPU, 124 memory, 125 scanner controller,
CP correction pattern

Claims (8)

(A) forming a correction pattern based on gradation values,
A first ejecting operation for ejecting a fluid by relatively moving in a first direction intersecting a direction along the nozzle row with respect to the medium;
A transport operation for relatively moving the medium in a second direction along the nozzle row;
A second ejection operation for ejecting the fluid by relatively moving in the first direction;
Have
In the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share the formation of a common dot line to form the correction pattern. The correction pattern is formed by increasing the amount of the fluid ejected per unit area in the partially overlapping range than the amount of the fluid ejected per unit area in the non-overlapping range. And
(B) measuring the density of the correction pattern for each pixel column composed of a plurality of pixels arranged in the first direction;
(C) obtaining a correction value for correcting the gradation value for each pixel column based on the measured density for each pixel column;
(D) storing the correction value in a storage unit of a fluid ejection device provided with the nozzle row;
Correction value setting method including   2. The correction value setting method according to claim 1, wherein the correction pattern is formed by increasing the amount of the fluid ejected per unit area in the center rather than the end portion in the partially overlapping range.   In the first jetting operation and the second jetting operation, nozzles in a nozzle row that partially overlap in the direction along the second direction share a common dot line, so that in the partially overlapping range 3. The correction value setting method according to claim 1, wherein the correction pattern is formed such that the density of the pixel columns is higher than the density of the pixel columns in a range that does not partially overlap.   Increasing the amount of the fluid ejected per unit area increases the number of dots formed overlapping in the dot lines corresponding to the partially overlapping range than in the non-overlapping range of dot lines. The correction value setting method according to claim 1, wherein the correction value setting method is performed. (A) a first ejection operation for ejecting a fluid by relatively moving in a first direction intersecting a direction in which the nozzles are arranged with respect to the medium, and a relative movement of the medium in the second direction in which the nozzles are arranged, A nozzle row that performs a second operation of ejecting the fluid by relatively moving in a first direction,
A nozzle row partially overlapping in the second direction in the first injection operation and the second injection operation;
(B) Control in which fluid is ejected from the nozzle row of the first ejection operation and the nozzle row of the second ejection operation to form a plurality of dot lines in which the plurality of dots are arranged in the first movement direction in the second direction. Part,
In the dot line corresponding to the partially overlapping range, the correction value for correcting the gradation value to be lower than the dot line in the partially overlapping range, and the dot line corresponding to the partially overlapping range A control unit that ejects the fluid in the first ejection operation and the second ejection operation based on a mask that forms more dots than dot lines in a partially non-overlapping range;
A fluid ejection device comprising: The mask is composed of a first mask for the nozzle row in the first ejection operation and a second mask for the nozzle row in the second ejection operation in the partially overlapping range,
By applying the first mask and the second mask to the image to be formed, the dots formed in the dot lines corresponding to the partially overlapping range are overlapped with the dot lines in the non-overlapping range. The fluid ejecting apparatus according to claim 5, wherein the number is increased.   The fluid ejection device according to claim 5, wherein the correction value is obtained based on an amount of dots formed by applying the mask. (A) forming a correction pattern based on gradation values,
A first ejecting operation for ejecting a fluid by relatively moving in a first direction intersecting a direction along the nozzle row with respect to the medium;
A transport operation for relatively moving the medium in a second direction along the nozzle row;
A second ejection operation for ejecting the fluid by relatively moving in the first direction;
Have
In the first ejection operation and the second ejection operation, the nozzles in the nozzle rows that partially overlap in the direction along the second direction share the formation of a common dot line to form the correction pattern. The correction pattern is formed by increasing the amount of the fluid ejected per unit area in the partially overlapping range than the amount of the fluid ejected per unit area in the non-overlapping range. And
(B) measuring the density of the correction pattern for each pixel column composed of a plurality of pixels arranged in the first direction;
(C) obtaining a correction value for correcting the gradation value for each pixel column based on the measured density for each pixel column;
(D) storing the correction value in a storage unit of a fluid ejection device provided with the nozzle row;
A method of manufacturing a fluid ejecting apparatus including: