JP2017024347A - Print control unit and print control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a print control unit suppressing image quality deterioration most likely to occur when a joint region is provided and printing is performed.SOLUTION: A print control unit realizes printing of an image onto a printing medium by discharging ink from a plurality of nozzles in association with movement of a print head having a nozzle array in which the plurality of nozzles disposed side-by-side in a predetermined nozzle array direction in a direction intersecting with the nozzle array. The print control unit comprises a density correction section correcting density of a joint region out of the image where the printing is performed by superimposing a second scan discharging the ink from the nozzles in association with movement subsequent to that of a first scan on the first scan discharging the ink from the nozzles in association with the movement. The density correction section executes correction according to PG being a distance between the print head and the printing medium and the density of the joint region in accordance with image data expressing the image.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a print control apparatus and a print control method.

  Printing an image on a print medium by ejecting ink from each nozzle while moving a print head having a nozzle row in which a plurality of nozzles are arranged in the nozzle row direction in a direction intersecting the nozzle row (scanning of the print head) Inkjet printers that perform this are known. In such an ink jet printer, printing of a user-desired image is completed by alternately repeating scanning of the print head a predetermined number of times and transport of the print medium by a predetermined transport amount.

  In printing as described above, a method is adopted in which a part of an area printed by scanning before one conveyance of a print medium and a part of an area printed by scanning after the conveyance are overlapped. Sometimes. By generating such an overlap (generating a connection area), it is possible to prevent a gap from being generated between areas printed in each scan before and after the conveyance.

  Of the recording elements in the recording head, recording interval information regarding the recording interval by the pair of recording elements corresponding to the recording raster lines at both ends in the recording area for each recording medium of the recording medium and recording by the recording medium transport system A recording method is known in which density correction relating to a recording raster line by the pair of recording elements is performed based on conveyance amount information relating to the conveyance amount of one medium (see Patent Document 1).

JP 2000-301708 A

  In the case where the above-described method for providing a connection area is employed, a difference in image quality is likely to occur in a print result between a connection area and an area that is not a connection area (non-connection area). It was sometimes recognized as a kind of image quality degradation. Here, the landing position of the ink droplets ejected from the nozzle on the printing medium may include a deviation (landing error) from the ideal landing position. Landing errors can occur in ink droplets ejected from any nozzle, but in particular, nozzles closer to the end of the nozzle row tend to cause landing errors in ejected ink droplets. Since the joining area is printed using the nozzles close to the end of the nozzle row, the image quality is more affected by the landing error than the non-joining area. The difference, that is, the density unevenness easily occurs.

  There are several factors that may cause landing errors. Also, the degree of landing error varies depending on the degree of such factors. Therefore, in order to appropriately suppress the above-described density unevenness caused by the landing error, it is necessary to perform processing in consideration of such several factors.

  The present invention has been made in view of at least the above-described problems, and provides a print control apparatus and a print control method capable of suppressing image quality deterioration that is likely to occur when printing is performed with a connection region.

  One aspect of the present invention is that a print head having a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction ejects ink from the nozzle as the print head moves in a direction intersecting the nozzle row. A print control apparatus that realizes printing of an image on a print medium, wherein the first scan of the image causes ink to be ejected from the nozzle in association with the movement, and the movement after the first scan. A density correction unit that corrects the density of a connection region that is printed redundantly in the second scan that ejects ink from the nozzle, and the density correction unit is a paper that is a distance between the print head and the print medium. The correction is executed in accordance with a gap (hereinafter referred to as PG) and the density of the joint region when following image data representing the image.

  According to this configuration, the density correction unit corrects the density of the connection area according to the density of the connection area according to the PG and the image data that cause the landing error. As a result, it is possible to appropriately suppress the density unevenness that is likely to occur when printing is performed with a connection region.

One of the aspects of the present invention may be that the density correction unit corrects the degree of increasing the density of the connection region as the PG is wider.
According to this configuration, as the PG becomes wider, the landing error increases, so that appropriate density correction (darkening correction) can be performed for the connection region where the color of the print result tends to be light.

According to one aspect of the present invention, the density correction unit corrects the degree of increasing the density of the connection area as the gradation value indicating the density of the connection area according to the image data is higher. You may do that.
According to this configuration, since the landing error increases as the density according to the image data increases, an appropriate density correction is performed for a connection region in which the color of the print result tends to be lighter than the target color. (Correction for darkening) can be performed.

One aspect of the present invention is that, when the image data has gradation values for each of a plurality of ink colors ejected by the print head, the density correction unit is configured to connect the connection region according to the image data. The correction may be executed according to the feature value calculated based on the gradation values of all ink colors.
According to this configuration, it is possible to correct the density of the connection area based on the feature value that accurately captures the density of the connection area when following the image data representing the image.

According to one aspect of the present invention, the density correction unit divides the connection area of the image data into a plurality of unit areas, and the correction according to the density according to the image data for each unit area. May be executed.
According to this configuration, it is possible to efficiently perform density correction of the connection area.

In one aspect of the present invention, the density correction unit may vary the degree of correction according to the number of times of the first scan and the second scan required for printing the connection area.
In one aspect of the present invention, the density correction unit may vary the degree of correction in accordance with the number of raster lines that form the connection area of the image data.
According to these configurations, a degree suitable for suppressing the density unevenness according to various factors such as the number of first and second scans required for printing the connection region and the number of raster lines forming the connection region. Thus, the density correction of the connecting region can be performed.

  The technical idea of the present invention is also realized by a device other than a printing control device. For example, the present invention relates to various methods such as a method (print control method) including a step executed by a print control apparatus, a computer program for causing a computer to execute the method, and a computer-readable storage medium storing the program. May be realized in categories.

The block diagram which illustrates the device composition concerning this embodiment. 6 is a flowchart showing print control processing. FIG. 3 is a diagram illustrating a configuration of a print head. The figure which shows a structure when the partial range of a printing part is seen from the side. The figure which shows an example of a correlation with a landing error and its factor. The figure which shows the other example of the correlation with a landing error and its factor. 6 is a flowchart illustrating processing for generating print data. The figure which shows an example of the correspondence of a nozzle and a pixel. The figure which illustrates the correction coefficient table according to PG. The figure which shows the other example of the correspondence of a nozzle and a pixel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each drawing is only an example for explaining an embodiment, and may not be in alignment with each other.

1. Schematic description of the device:
FIG. 1 is a block diagram illustrating functions of the print control apparatus 10 and the like according to the present embodiment. The print control apparatus 10 is grasped as a product such as a printer or a multifunction peripheral including a printer function. The print control apparatus 10 is configured to include a printing unit 30 that actually performs printing on a print medium and a partial configuration (for example, a control unit 11 described later) for controlling the behavior of the printing unit 30. In this case, a part of the configuration may be referred to as the print control apparatus 10. The print control apparatus 10 may be called a printing apparatus, an image processing apparatus, or the like. Each configuration of the print control apparatus 10 illustrated in FIG. 1 is not limited to a single location or a case where the configurations are integrated in a single case, but the configurations exist in locations away from each other and are communicable. One system may be constructed. For example, the print control apparatus 10 includes a device (such as a personal computer) that controls a printer mounted with a program (such as a printer driver) for controlling the behavior of a printer that actually performs printing on a print medium. It may be done.

  In FIG. 1, the print control apparatus 10 is illustrated as a configuration including a control unit 11, an operation input unit 16, a display unit 17, a communication interface (I / F) 18, a slot unit 19, a printing unit 30, and the like. The control unit 11 includes, for example, an IC having a CPU, a ROM, a RAM, and other storage media. In the control unit 11, various processing (for example, print control processing described later) is realized by the CPU executing arithmetic processing according to a program stored in a ROM or the like using the RAM or the like as a work area. .

  The operation input unit 16 is a device for accepting an operation by a user, and includes, for example, various buttons and keys. The display unit 17 is a part for displaying various information related to the print control apparatus 10 and is configured by, for example, a liquid crystal display (LCD). A part of the operation input unit 16 may be realized as a touch panel displayed on the display unit 17.

  The printing unit 30 is a mechanism for printing an image on a print medium. When the printing method employed by the printing unit 30 is an inkjet method, the printing unit 30 mainly uses a print head 31 (see FIG. 3), a carriage 35 that moves the print head 31 along a predetermined main scanning direction, and a print medium. It has the structure of the conveyance part 36 etc. which convey along the conveyance direction which cross | intersects a scanning direction.

  The print head 31 receives supply of ink from an ink cartridge (not shown). When the printing unit 30 is an apparatus capable of performing color printing, the print head 31 includes a plurality of types of ink (for example, cyan (C) ink, magenta (M) ink, yellow (Y) ink, and black (K) ink. , Etc.) Each ink is supplied from each ink cartridge. The print head 31 can eject (eject) ink (ink droplets) from a plurality of nozzles 34 (see FIG. 3). When the ejected ink lands on the print medium, dots are formed on the print medium and printing is realized. “Dot” basically refers to an ink droplet that has landed on a print medium, but the expression “dot” is also used as appropriate in the description of the process before the ink droplet has landed on the print medium. The specific types and number of liquids used by the printing unit 30 are not limited to those described above. For example, various inks and liquids such as light cyan, light magenta, orange, green, gray, light gray, white, metallic ... It can be used.

  The transport unit 36 includes a roller for supporting and transporting the print medium, a motor for rotating the roller (all not shown), and the like. The print medium is typically paper. However, in the present embodiment, materials other than paper are included in the concept of the printing medium as long as the material can record the liquid and can be transported by the transport unit 36.

The communication I / F 18 is a generic name for interfaces for connecting the print control apparatus 10 to the external device 100 by wire or wirelessly. Examples of the external device 100 include various devices that are input sources of image data for the print control apparatus 10 such as a smartphone, a tablet terminal, a digital still camera, and a personal computer (PC). The print control apparatus 10 can be connected to the external device 100 via the communication I / F 18 by various means and communication standards such as a USB cable, a wired network, a wireless LAN, and e-mail communication.
The slot part 19 is a part for inserting an external storage medium such as a memory card. That is, the print control apparatus 10 can also input image data stored in the storage medium from an external storage medium such as a memory card inserted in the slot unit 19.

  FIG. 2 is a flowchart showing print control processing executed by the control unit 11. When inputting image data representing an image to be printed (step S100), the control unit 11 executes image processing for generating print data from the image data (step S200). Various formats of the image data input in step S100 are conceivable, for example, bitmap data expressed in gradation (for example, 256 gradations from 0 to 255) in RGB (red, green, blue) for each pixel. . The control unit 11 appropriately performs image processing such as resolution conversion processing, color (color system) conversion processing, density correction processing, and halftone processing on the image data, so that an image to be printed is formed with a plurality of pixels. Print data expressed by a pattern is generated.

  A dot pattern (dot pattern) is an array of dots on (dot formation or ink ejection) and off (dot non-formation or ink non-ejection). It also defines dot on / off for each pixel. I can say that. When the print head 31 ejects, for example, CMYK ink, the print data includes data defining dot on / off for each pixel for each CMYK. Details of step S200 will be described later.

  The control unit 11 determines the nozzle 34 to be assigned to each pixel constituting such print data, rearranges the print head 31 in a predetermined order for transfer to the print head 31 according to the determination. (Step S300). By such allocation of each pixel to the nozzle 34, it is determined by which nozzle 34 of the print head 31 the dot of each pixel constituting the print data is formed.

  The print head 31 drives each nozzle 34 based on the transferred print data. For example, it is assumed that a drive signal (a kind of pulse) for driving each nozzle 34 is given to the print head 31 by the control unit 11. Although detailed explanation is omitted, in the print head 31, the application of the drive signal to the drive element provided for each nozzle 34 is switched according to the dot on / off information for each pixel represented by the print data. To do. Thereby, each nozzle 34 realizes ink ejection / non-ejection according to the information of the pixel assigned to itself. As a result, the image to be printed is printed on the print medium.

  FIG. 3 simply illustrates the configuration of the print head 31 and the like. FIG. 3 illustrates the arrangement of the nozzles 34 on the ink ejection surface 31 a of the print head 31 from the viewpoint from above the print head 31. In FIG. 3 (and FIGS. 8 and 10), the nozzle 34 is indicated by a circle. The ink ejection surface 31a is a surface on which the nozzles 34 are opened, and is a surface facing the print medium S that is transported along the transport direction by the transport unit 36. In FIG. 3, a direction D1 corresponds to the main scanning direction, and a direction D2 corresponds to the transport direction. Basically, the main scanning direction D1 and the transport direction D2 are orthogonal to each other.

  In the example of FIG. 3, the print head 31 corresponds to the nozzle row 33C corresponding to the discharge of C ink, the nozzle row 33M corresponding to the discharge of M ink, the nozzle row 33Y corresponding to the discharge of Y ink, and the discharge of the K ink. The nozzle row 33K is provided. In each of the nozzle arrays 33C, 33M, 33Y, and 33K, a plurality of nozzles 34 for ejecting ink of the corresponding color are arranged at a predetermined interval (a constant nozzle pitch NP) in a predetermined nozzle array direction D3.

  The nozzle row direction D3 to which the nozzle row faces intersects the main scanning direction D1. Although depending on the design of the printing unit 30, the nozzle row direction D3 is orthogonal to the main scanning direction D1 or intersects at an oblique angle that is not orthogonal (90 degrees). In the following, for ease of explanation, it is assumed that the nozzle row direction D3 is orthogonal to the main scanning direction D1. Therefore, the nozzle row direction D3 and the transport direction D2 are parallel. In this specification, even when expressions that are originally strictly interpreted as orthogonal, parallel, constant, etc. are used, these do not mean strictly orthogonal, parallel, constant, but in terms of product performance. It also includes an allowable error and an error that may occur during product manufacturing. In addition to being ejected by one nozzle row, the ink of one color may be ejected by, for example, a plurality of nozzle rows arranged so as to be shifted from each other in the nozzle row direction D3.

  The carriage 35 on which the print head 31 is mounted receives power from a carriage motor (not shown) and moves in parallel with the main scanning direction D1. The print head 31 realizes printing by ejecting ink from the nozzles 34 to the print medium S while moving together with the carriage 35. The process in which the print head 31 ejects ink in association with the movement from one end side to the other end side in the main scanning direction D1 or the movement from the other end side to the one end side in the main scanning direction D1 is performed once as “scanning”. Or “path”. According to such a configuration, the print control apparatus 10 controls the print head 31 having a nozzle row (for example, nozzle rows 33C, 33M, 33Y, 33K) in which a plurality of nozzles 34 are arranged in the nozzle row direction D3. It can be said that printing is realized.

2. Explanation about printing conditions and PG:
Next, the printing conditions set by the user and the PG corresponding to the printing conditions will be described. Before starting the print control process (FIG. 2), the user operates the operation input unit 16 while viewing the user interface (UI) screen displayed on the display unit 17, for example. Conditions can be set arbitrarily. Specifically, the user can select a menu on the UI screen (for example, a menu such as “plain paper” and “envelope” for selecting a print medium, a menu for selecting “single-sided printing” or “double-sided printing”, a rubbing reduction mode The printing conditions can be easily set by selecting desired conditions from a menu for selecting “validation” or “invalidation”. The rubbing reduction mode is an option that is activated when it is desired to reliably avoid contact between the print head 31 and the print medium S.

  The control unit 11 determines PG according to the printing conditions set in response to a user operation. Note that the control unit 11 has information (table) that preliminarily defines the correspondence between the printing conditions (combination of printing conditions) and the PG. For example, the control unit 11 prints “plain paper, single-sided printing, rubbing reduction mode OFF (invalidation)”, “plain paper, single-sided printing, rubbing reduction mode ON (validation)”, “plain paper” , Different PGs are determined in accordance with various printing condition patterns such as printing conditions of “duplex printing, rubbing reduction mode OFF” and printing conditions of “envelope and single-sided printing”.

  FIG. 4 simply shows a configuration when a partial range of the printing unit 30 is viewed from the side. In the printing unit 30, a platen 32 is provided so as to face the ink ejection surface 31 a of the print head 31. The print medium S is transported onto the platen 32 along the transport direction D2 by the transport unit 36. In FIG. 4, the main scanning direction D1 is a direction perpendicular to the drawing sheet. The printing unit 30 adjusts the height from the printing medium S on the platen 32 to the print head 31 (ink ejection surface 31a), that is, PG by adjusting the position of the carriage 35 in the height direction as is known. Is possible.

  Accordingly, when the printing unit is set in response to the user operation as described above, the control unit 11 determines a PG corresponding to the printing condition and sets the determined PG (the printing medium used at that time). PG is adjusted by the printing unit 30 (in consideration of the thickness of S and the like). As a concept similar to PG (paper gap), the term platen gap indicating the height from the platen 32 to the print head 31 (ink ejection surface 31a) is known. Changing PG is also changing the platen gap. Therefore, the adjustment of PG may be regarded as a process of adjusting the PG as a result by changing the platen gap.

3. Correlation between landing error and factors:
FIGS. 5A and 5B and FIGS. 6A and 6B are diagrams illustrating the correlation between the landing error obtained from the test pattern printed by the printing unit 30 based on the test pattern image data expressing the predetermined test pattern and the factor thereof. It is. In each of FIGS. 5A and 5B and FIGS. 6A and 6B, numerical values 1 to 199 shown on the horizontal axis are specific nozzle rows (nozzle rows 33C, 33M, 33Y, and 33K used for printing the test pattern. For example, Nozzle row 33K.) The nozzle numbers assigned to the nozzles 34 arranged from one end side (downstream side in the transport direction D2) to the other end side (upstream side in the transport direction D2) in the nozzle row direction D3 constituting the nozzle row 33K. Yes. In each of FIGS. 5A and 5B and FIGS. 6A and 6B, the vertical axis indicates the landing error for each nozzle number. Specifically, the ideal position of the ink droplet landing position on the print medium is defined for all nozzle numbers, and the ideal position and actual ink for each nozzle number obtained from the analysis result of the printed test pattern. The deviation from the droplet landing position (dot formation position) is defined as a landing error for each nozzle number.

  As the ideal position for each nozzle number, an ideal position corresponding to one nozzle number (for example, nozzle number 100) is determined on the print medium, and the nozzle position NP is spaced along the nozzle row direction D3 with the determined position as a reference. It can be defined by defining each ideal position corresponding to each other nozzle number. The landing error for each nozzle number is ideally zero, but in practice, the landing error is often not zero. In FIGS. 5A and 5B and FIGS. 6A and 6B, a minus landing error indicates a landing error corresponding to a shift from the corresponding ideal position to the downstream side in the transport direction D2, and a plus landing error indicates the corresponding ideal position. The landing error corresponding to the deviation to the upstream side in the transport direction D2 is shown.

  The notations of PG1 and PG2 shown in FIGS. 5A, 5B, 6A, and 6B indicate specific PGs adopted by the printing unit 30 when printing a test pattern, and here, PG1 <PG2. 5A, 5B, and FIGS. 6A and 6B, the notations of duty 20% and 60% are image densities according to the test pattern image data. The test pattern image data is, for example, bitmap data composed of pixels having only the gradation value (density) of the ink (specific color, for example, K) ejected by the specific nozzle row. That is, the test pattern image data corresponding to a duty of 20% is composed of pixels having only a gradation value of a specific color corresponding to 20% when normalized to 0 to 100%. The corresponding test pattern image data is composed of pixels having only a gradation value of a specific color corresponding to 60% when normalized to 0 to 100%.

Accordingly, FIG. 5A is obtained from the test pattern printed by the printing unit 30 using the specific nozzle row based on the print data generated from the test pattern image data corresponding to the duty 20% with PG adjusted to PG1. Shows the landing error.
5B is obtained from the test pattern printed by the printing unit 30 using the specific nozzle row based on the print data generated from the test pattern image data corresponding to the duty of 60% by adjusting PG to PG1. Shows the landing error.
6A is obtained from a test pattern printed by the printing unit 30 using the specific nozzle row based on print data generated from test pattern image data corresponding to a duty of 20% by adjusting PG to PG2. Shows the landing error.
6B is obtained from the test pattern printed by the printing unit 30 using the specific nozzle row based on the print data generated from the test pattern image data corresponding to the duty of 60% by adjusting PG to PG2. Shows the landing error.

  According to the comparison between FIG. 5A and FIG. 6A or the comparison between FIG. 5B and FIG. 6B, it can be seen that the landing error increases as the PG becomes wider even when printing images of the same density. This is because the wider the PG, the more time it takes for the ink droplets ejected from the nozzles 34 to land on the printing medium, so the flight trajectory is more easily affected by the influence of the surrounding air current, and as a result This is because the position is easily disturbed.

  Further, according to the comparison between FIG. 5A and FIG. 5B or the comparison between FIG. 6AB and FIG. 6B, it can be seen that the landing error increases as the density of the image to be printed increases even if the PG is the same. Each time an ink droplet is ejected from the nozzle 34, an airflow is generated around the ejected ink droplet, and the airflow affects the flight of the ink droplet ejected from other nozzles 34 in the vicinity. Such an air flow becomes a larger and more complex air flow (air wall) as ink droplets are ejected from more nozzles 34 all at once, and disturbs the flight trajectory of each ink droplet. In other words, the higher the density of the image to be printed (the greater the number of dots formed per fixed area of the print medium), the more likely the disturbance of the ink droplets to fly due to the influence of such an air flow. Increases landing error.

  According to such consideration based on FIGS. 5A, 5B, 6A, and 6B, the difference in PG and the density of the image to be printed are all factors that change the degree of landing error. Further, as can be seen from FIGS. 5B, 6A, and 6B, it can be said that the landing positions of the ink droplets ejected from each nozzle 34 tend to be shifted from the center of the nozzle row to both end sides in the nozzle row direction D3. . In addition, a larger landing error tends to occur as the ink droplets are ejected from the nozzle 34 closer to the end of the nozzle row. In the present embodiment, in consideration of such circumstances, density correction processing as described later is executed in the process of generating print data.

4). Generation of print data including density correction processing:
FIG. 7 is a flowchart showing details of step S200 (print data generation) in FIG. In step S210, the control unit 11 performs resolution conversion processing on the image data input in step S100 (FIG. 2). That is, conversion (pixel interpolation or thinning) is performed so that the horizontal resolution and vertical resolution of the image data match the horizontal printing resolution and vertical printing resolution adopted by the printing unit 30, respectively. The horizontal print resolution is the print resolution in the main scanning direction D1, and the vertical print resolution is the print resolution in the transport direction D2. The user can change the default settings of the horizontal printing resolution and the vertical printing resolution adopted by the printing unit 30 via the UI screen described above. When such a change is made, the control unit 11 adopts the horizontal print resolution and the vertical print resolution according to the changed setting. On the other hand, if such a change has not been made, the control unit 11 may adopt the default setting.

  In step S220, the control unit 11 performs color conversion processing on the image data after step S210 to express each density of CMYK ink with gradation (for example, 256 gradations from 0 to 255) for each pixel. Convert to image data. The color conversion process can be performed by defining a conversion relationship between RGB and CMYK and referring to a look-up table (color conversion LUT) stored in a predetermined memory in advance.

  In step S230, the control unit 11 performs density correction processing on the image data after step S220. The density correction processing referred to here is density correction for a “connection region” as will be described later, and FIG. 7 shows details of step S230 (steps S231 to S235).

  FIG. 8 shows an example of the correspondence between the nozzles 34 and the pixels assigned to the nozzles 34. FIG. 8 shows a nozzle row (for example, the nozzle row 33K) corresponding to one ink color among the plurality of nozzle rows of the print head 31, and among the image data obtained in step S220, A part of the image data KID (image data expressing the density of K ink for each pixel in gradation) relating to the ink (K ink) ejected by the nozzle row (nozzle row 33K) is shown. The image data is composed of a plurality of pixels PX arranged corresponding to the main scanning direction D1 and the carrying direction D2, respectively. For convenience of explanation, the orientation of the pixels constituting the image data may be expressed by the directions D1 and D2, but this is only the correspondence between the orientation of the image and the directions D1 and D2 when the printing unit 30 executes printing. Based on (match) relationship. In FIG. 8, for the purpose of simplifying the illustration, the number of nozzles 34 constituting the nozzle row corresponding to one ink color is only eight. In FIG. 8, the numbers # 1 to # 8 assigned to the nozzles 34 are nozzle numbers. That is, for convenience of explanation, nozzle numbers # 1 to # 8 are assigned to the nozzles 34 arranged from one end side in the nozzle row direction D3 (downstream side in the transport direction D2) to the other end side (upstream side in the transport direction D2). ing.

  FIG. 8 shows the allocation relationship between the nozzles 34 and the pixels PX when the printing unit 30 employs band printing in which a joining area is provided as a printing method. The number (any one of 1 to 8) written in the rectangle representing the pixel PX is the nozzle number of the nozzle 34 to which the pixel PX is assigned. In the band printing, generally, a bundle (band) of raster lines corresponding to the number of the nozzles 34 constituting the nozzle row is printed in one pass of the print head 31, and such a pass and a print medium are printed. This is a printing method in which conveyance (paper feeding) is repeated alternately. A raster line is an area expressed by a set (also referred to as a pixel row) of a plurality of pixels PX continuous along the main scanning direction D1, and basically forms one raster line in band printing. The pixel PX is assigned to one common nozzle 34 and printed. Of course, the printing method that can be adopted by the printing unit 30 is not limited to band printing, but any printing method can be used after the printing method is determined by a user instruction through the UI screen. The unit 11 can recognize and determine which pixel constituting the image data should be assigned to which nozzle 34 (at any timing of steps S200 and S300).

  In FIG. 8, the position of the nozzle row 33K (relative position with respect to the image data KID in the transport direction D2) changes for each pass (first pass, second pass, third pass,...) By the print head 31. It also shows what to do. Of course, the print head 31 does not actually move along the transport direction D2, but the print medium is fed in the transport direction D2 by the transport unit 36 every time a pass is completed, and the band to be printed in the next pass. Information on the pixel relating to is assigned to the nozzle 34.

  Further, in FIG. 8, for convenience of explanation, a band printed in the first pass is represented as a band BD1, a band printed in the second pass is represented as a band BD2, a band printed in the third pass is represented as a band BD3. doing. In addition, a region where the band BD1 and the band BD2 overlap is expressed as a connection region OL1, a region where the band BD2 and the band BD3 overlap is expressed as a connection region OL2,. When attention is paid to the relationship between the band BD1 and the band BD2, the pass for printing the band BD1 is the first scan, and the pass for printing the band BD2 is the second scan, and these first scan and The connection region OL1 is printed by overlapping the second scan. Further, when attention is paid to the relationship between the band BD2 and the band BD3, the pass for printing the band BD2 is the first scan, and the pass for printing the band BD3 is the second scan, and these first scans. The joining area OL2 is printed by partially overlapping the scanning range and the second scanning range.

  In the example of FIG. 8, one raster line is printed by one nozzle 34 in an area that does not correspond to the connection area (non-connection area) in the band as described above. However, one raster line is printed in a plurality of nozzles 34, that is, a plurality of passes (overlap printing) in the connection region. Specifically, all of the connecting regions OL1, OL2, OL3... Go to the two nozzles 34 (nozzles 34 of nozzle numbers # 7 and # 8) on the other end side of the nozzle row 33K corresponding to the first scan. Some pixels PX are allocated, and the remaining pixels PX are allocated to the two nozzles 34 (nozzles 34 of nozzle numbers # 1 and # 2) on the one end side of the nozzle row 33K corresponding to the second scan. As described above, the pixels PX assigned to the first scan and the pixels PX assigned to the second scan in the connection regions OL1, OL2, OL3,... Basically exist alternately in the directions D1, D2. Further, in order to generate such connection areas OL1, OL2, OL3,..., The conveyance unit 36 changes the distance of one paper feed from the length of the band in the conveyance direction D2 to the length of the connection area in the conveyance direction D2. The distance obtained by subtracting the distance (in the example of FIG. 8, the nozzle pitch NP × 6) is used.

  Returning to the description of FIG. In step S231, the control unit 11 pays attention to one pixel belonging to the connection area (in the example of FIG. 8, the connection areas OL1, OL2, OL3,...) Among the pixels constituting the image data. Select as a pixel. Next, in step S232, the control unit 11 calculates a feature value T based on the gradation values (CMYK) of all ink colors of the target pixel. Several methods for calculating the feature value T can be considered. For example, an average value ((C + M + Y + K) / 4) of gradation values of all ink colors of the target pixel is used as the feature value T. Such a feature value T can be said to be a kind of value that simply indicates the density of the ink of the pixel of interest, and can also be said to be a kind of density of the connection area according to the image data.

  In step S233, the control unit 11 acquires the correction coefficient r for the target pixel according to PG and the feature value T. The control unit 11 refers to the correction coefficient table RT corresponding to the current PG among the plurality of correction coefficient tables RT stored in a predetermined memory and associated with each of the plurality of PGs, thereby correcting the correction coefficient. Get r. The current PG is a PG that has been adjusted according to the printing conditions set according to the user's operation before starting the printing control process (FIG. 2) as described above. There are a plurality of PGs that can be adopted by the printing unit 30, including the above-described PG1 and PG2. If the printing unit 30 can adjust the PG to five levels, there are five types of correction coefficient tables RT corresponding to the five levels of PG. Here, it is assumed that the current PG = PG2.

  FIG. 9 illustrates a correction coefficient table RT associated with PG2. The correction coefficient table RT defines, for example, a one-to-one correspondence between values (0 to 255) that can be taken by the feature value T calculated in step S232 and the correction coefficients r (0) to r (255). Yes. Of course, each correction coefficient table RT corresponding to a different PG defines a different correction coefficient r for the same feature value T. The control unit 11 can acquire the correction coefficient r according to the current PG and the feature value T by referring to such a correction coefficient table RT.

  In step S234, the control unit 11 corrects the gradation values CMYK of all ink colors of the target pixel by using the correction coefficient r acquired in step S233. For example, if the correction coefficient r is a value of “1.1”, the correction coefficient r is multiplied by 1.1 for each CMYK of the pixel of interest. The above is the density correction of the target pixel.

  In step S235, the control unit 11 determines whether or not all the pixels belonging to the connection area among the pixels constituting the image data have been selected as the target pixel. If an unselected pixel remains in the connection area (“No” in step S235), the process returns to step S231, and an unselected pixel belonging to the connection area is newly selected as one target pixel. Then, step S232 and subsequent steps are executed again. On the other hand, if no unselected pixels remain in the connection area (“Yes” in step S235), the density correction has been performed for all the pixels belonging to the connection area, and thus step S230 is completed.

  According to such step S230, the control unit 11 determines the density of the connection region to be printed redundantly in the first scan and the second scan after the first scan among the images to be printed. It can be said that correction is performed according to the density of the connection region when the PG and the image data representing the image are used. Moreover, it can be said that the control part 11 functions as the density | concentration correction | amendment part 11a (refer FIG. 1) by the point which performs step S230.

  In step S240, the control unit 11 performs halftone processing on the image data after step S230 (image data for which the density correction of the connecting area has been completed), thereby generating print data representing each CMYK dot pattern. To do. The halftone process is executed by, for example, a dither method or an error diffusion method. According to the halftone process, the higher the tone value of each ink color of a pixel, the higher the probability of determining dot-on of each ink color for that pixel.

Here, the correction coefficient r defined by the correction coefficient table RT will be supplemented.
The joint area printed by the nozzles 34 at the ends (in the example of FIG. 8, nozzles # 1, # 2, # 7, and # 8) in which a relatively large landing error occurs in the ejected ink droplets is not When compared with the joint area, the color of the printed result tends to be light. This is because a landing error occurs in spite of the fact that dots are expected to exist at substantially equal intervals (for example, nozzle pitch NP) in the transport direction D2 (nozzle row direction D3) on the print medium. This is because the actual dot arrangement varies (dots are too far apart or overlap each other in the transport direction D2). Due to such variation in dot arrangement, the coverage area of the print medium with ink is reduced in the connection region, and as a result, the color tends to be lighter than that in the non-connection region.

  Thus, the tendency for the color of the print result to become lighter becomes more prominent as the landing error increases. In other words, as described above, the landing error tends to increase as the PG is wider and the density of the image to be printed is higher. Therefore, as the PG is wider and the density of the image to be printed is higher, It can be said that the color of the connecting region is likely to be lighter. In view of such circumstances, in the present embodiment, the correction coefficient table RT defines a correction coefficient r that increases the density of the connection area as the PG corresponds to a wider PG. In addition, the correction coefficient table RT defines a correction coefficient r that increases the density of the connection region as the feature value T is higher.

  For example, when the correction coefficient table RT corresponding to PG1 is compared with the correction coefficient table RT corresponding to PG2, even if the correction coefficient r is defined in association with the same feature value T, the correction coefficient table corresponding to PG1. The correction coefficient r defined by the correction coefficient table RT corresponding to PG2 is higher than the correction coefficient r defined by RT. Even within the same correction coefficient table RT (for example, the correction coefficient table RT corresponding to PG2), the higher the characteristic value T, the higher the correction coefficient r defined in association with it. . That is, the control unit 11 performs the correction so as to increase the degree to which the density of the connection area is increased as the PG is widened by the density correction process, and the gradation value indicating the density of the connection area according to the image data is high. The correction is made so as to increase the degree of increasing the density of the connection region.

  As described above, according to the present embodiment, the control unit 11 (density correction unit 11a) prints redundantly between the first scan and the second scan after the first scan among the images to be printed. The density of the connecting area is corrected in accordance with the density of the connecting area according to PG and the image data representing the image (step S230 in FIG. 7). As a result, a high-quality printing result is obtained in which density unevenness between the non-joining area and the joining area is suppressed. Further, the control unit 11 calculates a feature value T indicating the density of the connection region according to the image data based on the gradation values (CMYK) of all ink colors of the target pixel (step S232 in FIG. 7). ). As a result, it is possible to accurately grasp whether the color of the pixel is dark or light, and it is possible to obtain a correction coefficient r optimum for the color density of the pixel. However, the feature value T of the target pixel is not limited to the average value of the gradation values (CMYK) of all ink colors, and is, for example, the sum of the gradation values (CMYK) of all ink colors. Also good. In this case, the correction coefficient table RT defines a one-to-one correspondence between values (0 to 255 × 4) that the feature value T can take and correction coefficients r (0) to r (255 × 4).

5. Variations:
The present invention is not limited to the above-described embodiment, and can be carried out in various modes without departing from the gist thereof. For example, the following modifications can be adopted. A configuration in which the above-described embodiments and modifications are appropriately combined also falls within the disclosure scope of the present invention. In the description of the following modified examples, the description of matters common to the above-described embodiment will be omitted as appropriate.

<< Modification 1 >>
In step S230 (FIG. 7), the control unit 11 divides the connection region of the image data into a plurality of unit regions, and executes correction according to the density according to the image data for each unit region. Good. For example, the control unit 11 divides the connection area of the image data into blocks (unit areas) that are sets of a plurality of pixels, selects one block and one pixel belonging to the block, and selects the selected pixel ( A feature value T is calculated from the pixel of interest (steps S231 and S232). Then, the control unit 11 acquires a correction coefficient r according to the PG and the feature value T calculated from the target pixel (step S233), and the acquired correction coefficient r is used to calculate all the pixels belonging to the selected block. The gradation values CMYK for all ink colors are respectively corrected (step S234).

  In step S235, the control unit 11 determines whether or not the target pixel has been selected one by one from all the blocks in the connection area of the image data. If an unselected block remains in the connection area (“No” in step S235), the process returns to step S231, and one pixel belonging to the unselected block is selected as a target pixel. Select Then, step S232 and subsequent steps are executed again. On the other hand, if there is no block in which the pixel of interest has not been selected remains in the connection area (“Yes” in step S235), the density correction has been performed for all the pixels belonging to the connection area, and thus step S230 is completed.

  According to the first modification, the correction coefficient r corresponding to the feature value T calculated from the target pixel is similarly applied to a plurality of surrounding pixels including the target pixel when correcting the density of the connection region. Therefore, it is possible to greatly reduce the amount of calculation required for correcting the density of the connection area. The size of one block as the unit area is generally considered as a size composed of two or more pixels. However, assuming that the size is one pixel, this is the same as treating all pixels belonging to the connection area as the target pixel. Note that the control unit 11 may change the size of the block according to PG. For example, when the PG is narrow to some extent, the control unit 11 sets the block size large and gives priority to reducing the amount of calculation required for the density correction because the necessity for density correction of the connection region is not so high. On the other hand, as the PG becomes wider, the necessity of density correction in the connection area increases. Therefore, the block size is set small, and density correction more suitable for each pixel belonging to the connection area is executed.

<< Modification 2 >>
In the description with reference to FIG. 8 so far, an example has been introduced in which the first scan and the second scan required for printing the joint area are each performed once, and the joint area is printed in a total of two passes. However, the number of passes required for printing the connection area is not limited to two.
FIG. 10 shows an example of the correspondence relationship between the nozzles 34 and the pixels assigned to the nozzles 34, and shows an example different from FIG. The view of FIG. 10 applies the view of FIG. 8 mutatis mutandis. 10 also shows the nozzle row corresponding to one ink color (for example, the nozzle row 33K) among the plurality of nozzle rows of the print head 31 as in FIG. 8, and the image data obtained in step S220. 4 shows a part of image data KID (image data expressing gradation of K ink density for each pixel) relating to ink (K ink) ejected by the nozzle row (nozzle row 33K). For convenience of illustration, the nozzle row 33K shown in FIG. 8 and the nozzle row 33K shown in FIG.

  FIG. 10 shows an allocation relationship between the nozzles 34 and the pixels PX when the printing unit 30 employs pseudo band printing in which a joining area is provided as a printing method. Pseudo band printing is also referred to as microfeed (MF) printing. The pseudo band printing is generally an area having a higher printing resolution in the transport direction D2 than the above-described band printing (pseudo) by executing a plurality of passes with a paper feed at a distance shorter than the nozzle pitch NP. Band) and printing such a pseudo band and paper feeding of a relatively long distance of the print medium are alternately repeated. More specifically, in the example of FIG. 10, the pseudo band BD1 is printed by sandwiching a paper feed of a distance of half the nozzle pitch NP between the first pass and the second pass. The pseudo band BD2 is printed by sandwiching a paper feed that is half the nozzle pitch NP between the fourth pass and the fourth pass. Further, a paper feed of a distance substantially corresponding to the length of the pseudo band in the transport direction D2 is executed between the second pass and the third pass.

  In FIG. 10, for convenience of explanation, an area where the pseudo band BD1 and the pseudo band BD2 overlap is expressed as a connection area OL1. When attention is paid to the relationship between the pseudo band BD1 and the pseudo band BD2, the first and second passes for printing the pseudo band BD1 are the first scan, and then the third and the third pass for printing the pseudo band BD2. The fourth pass is the second scan. Then, the first scan and the second scan partially overlap to print the connection area OL1. In the example of FIG. 10, one raster line is printed by one nozzle 34 in an area that does not correspond to the connection area (non-connection area) in the band. However, one raster line is printed in a plurality of nozzles 34, that is, a plurality of passes (overlap printing) in the connection region. Specifically, in each of the connection areas OL1, OL2,..., A part of the pixels PX is supplied to one nozzle 34 (nozzle 34 of nozzle number # 8) on the other end side of the nozzle row 33K corresponding to the first scan. And the remaining pixels PX are assigned to one nozzle 34 (nozzle 34 of nozzle number # 1) on the one end side of the nozzle row 33K corresponding to the second scan. As described above, the pixels PX assigned to the first scan and the pixels PX assigned to the second scan in the connection areas OL1, OL2,... Basically exist alternately in the directions D1, D2. Further, in order to generate such connection regions OL1, OL2,..., The transport unit 36 transports the paper feed distance between the first scan and the second scan from the length of the pseudo band in the transport direction D2. A distance obtained by subtracting the length of the connecting region in the direction D2 (nozzle pitch NP × 7 in the example of FIG. 10).

  In the second modification, the control unit 11 varies the degree of correction for the joint area according to the number of first scans and second scans required for printing the joint area. In this case, as the total number of times of the first scan and the second run required for printing the connection area is increased, the degree of increasing the density of the connection area is reduced. Therefore, comparing the case where the printing method described with reference to FIG. 8 is adopted and the case where the printing method described with reference to FIG. 10 is adopted, the control unit 11 is more likely to adopt the printing method described with reference to FIG. For the same combination of PG and feature value T, the density correction of the joint region is executed using a lower correction coefficient r. This is a measure in view of the fact that the higher the number of passes required for printing, the easier the printing result is to achieve high image quality. In other words, in the print result by the print head 31, various errors such as landing errors appear for each executed pass, but the same area is recorded in one pass by printing it in multiple passes. The error is relatively inconspicuous. Therefore, in the case where the printing method described with reference to FIG. 8 is employed and the case where the printing method described with reference to FIG. 10 is employed, the latter is less likely to be visually recognized in the latter case. As described above, according to the second modification, the density correction is performed to the extent necessary to eliminate the difference between the connected area and the non-connected area, in accordance with the number of first and second scans required for printing the connected area. be able to.

<< Modification 3 >>
In both the examples of FIGS. 8 and 10, the number of raster lines constituting one connecting region is two rasters. The number of raster lines constituting one connecting region is not limited to two rasters, and can be set variously such as three rasters, four rasters, and more. For example, in response to a direct or indirect instruction related to the number of raster lines by the user through the UI screen, the control unit 11 determines the number of raster lines in the image data and assigns pixels to the nozzles 34. Can do.

  In the third modification, the control unit 11 varies the degree of correction for the connection area according to the number of raster lines that form the connection area of the image data. In this case, as the number of raster lines constituting one connection area in the image data increases, the degree of increasing the density of the connection area is increased. For example, comparing the case where the number of raster lines constituting one connecting region is 2 rasters with the case of 4 rasters, the control unit 11 indicates that the combination of the same PG and feature value T is the case of 4 rasters. On the other hand, the density correction of the joint region is executed using a higher correction coefficient r. This is due to the fact that the greater the number of raster lines that make up the connected area, the more noticeable the presence of the connected area in the entire image, and the unevenness of the non-connected area is more noticeable. Measures. As described above, according to the third modification, the density correction necessary to eliminate the difference between the connected area and the non-connected area can be performed according to the number of raster lines constituting the connected area of the image data.

<< Modification 4 >>
The control unit 11 refers to the color conversion LUT (corrected color conversion LUT) corrected in advance with the correction coefficient r, instead of correcting the image data after color conversion with reference to the color conversion LUT with the correction coefficient r. Then, color conversion may be executed. Specifically, for the image data after the resolution conversion process (step S210), the control unit 11 performs a color conversion process using a normal color conversion LUT on the pixels belonging to the non-joining area, and sets the joined data in the joining area. For the pixel to which it belongs, color conversion processing using the corrected color conversion LUT is executed (step S220). In this case, since the color conversion process (step S220) substantially doubles as the density correction process (step S230) of the connecting region, the process proceeds to the halftone process (step S240). The corrected color conversion LUT is associated with the input value (RGB) in the normal color conversion LUT by the correction coefficient r defined by the correction coefficient table RT corresponding to the PG at that time in association with the feature value T. This is a color conversion LUT after correcting the output value (CMYK). That is, the output value (CMYK) can be corrected by the correction coefficient r associated with the feature value T that matches the feature value (average value of CMYK) calculated from the output value (CMYK) of the normal color conversion LUT. it can.

<< Modification 5 >>
The control unit 11 may exclude a region whose density is equal to or lower than a predetermined value from the above-described density correction even if it belongs to the connection area. An area having a density equal to or lower than a predetermined value refers to, for example, an area composed of pixels in the connection area whose characteristic value T calculated in step S232 is equal to or lower than a predetermined threshold value. If the pixel has only a relatively low density, the surrounding area is often relatively light in color, so there is a tendency for the deviation of the landing positions of the dots to be formed to be small, and no dots are formed in the first place. There are also many. Therefore, it can be said that the necessity for correction with the correction coefficient r is low. According to the fifth modification, it is possible to avoid the execution of correction that is less necessary, and to further reduce the amount of calculation required for density correction of the connection region.

<< Modification 6 >>
The print head 31 may eject ink droplets of a plurality of sizes from each nozzle 34. Since there are a plurality of sizes, at least two types of ink droplets can be ejected. For example, it is assumed that each nozzle 34 can eject three types of ink droplets called large dots, medium dots, small dots, and the like, each having a different ink weight per droplet. In this case, in the halftone process (step S240), the control unit 11 does not generate binary data (print data) in which dot on / off is determined for each pixel and for each ink color CMYK. For each ink color CMYK, four-value data (print data) that defines one of large dot on, medium dot on, small dot on, and dot off is generated.

DESCRIPTION OF SYMBOLS 10 ... Print control apparatus, 11 ... Control part, 11a ... Density correction part, 30 ... Printing part, 31 ... Print head, 32 ... Platen, 33C, 33M, 33Y, 33K ... Nozzle row, 34 ... Nozzle, 35 ... Carriage, 36: conveying unit, 100: external device, RT: correction coefficient table, S: printing medium

Claims (8)

Printing of an image on a printing medium is realized by ejecting ink from the nozzle as the print head having a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction moves in the direction intersecting the nozzle row. A printing control device for
In the image, the first scan for ejecting ink from the nozzle with the movement and the second scan for ejecting ink from the nozzle with the movement after the first scan overlap. It has a density correction unit that corrects the density of the connecting area,
The density correction unit performs the correction according to a paper gap, which is a distance between the print head and the print medium, and a density of the connection area according to image data representing the image. Control device.   The print control apparatus according to claim 1, wherein the density correction unit performs correction so that the degree of increasing the density of the connection region increases as the paper gap is wider.   The density correction unit performs correction so as to increase the degree to which the density of the connection area is increased as the gradation value indicating the density of the connection area is higher according to the image data. Or the printing control apparatus of Claim 2.   When the image data has gradation values for each of a plurality of ink colors ejected by the print head, the density correction unit converts the gradation values of all ink colors in the joint area according to the image data. The print control apparatus according to claim 1, wherein the correction is performed in accordance with a feature value calculated based on the feature value.   The density correction unit divides the connection area of the image data into a plurality of unit areas, and executes the correction according to the density according to the image data for each unit area. The printing control apparatus in any one of Claims 1-4.   The density correction unit varies the degree of correction according to the number of times of the first scan and the second scan required for printing the joint area. The printing control apparatus described.   The print control according to any one of claims 1 to 6, wherein the density correction unit varies the degree of correction according to the number of raster lines constituting the connection area of the image data. apparatus. Printing of an image on a printing medium is realized by ejecting ink from the nozzle as the print head having a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction moves in the direction intersecting the nozzle row. A printing control method,
In the image, the first scan for ejecting ink from the nozzle with the movement and the second scan for ejecting ink from the nozzle with the movement after the first scan overlap. A density correction process for correcting the density of the connecting area;
In the density correction step, printing that performs the correction according to a paper gap, which is a distance between the print head and the print medium, and a density of the joint area according to image data representing the image. Control method.

Images