JP2019080278A - Image processing apparatus, image processing method, and printing apparatus - Google Patents

Abstract

To prevent image quality deterioration.SOLUTION: An image processing apparatus that generates print data used for printing includes a halftone processing unit that generates halftone data that defines the presence/absence and size of a dot for each pixel on the basis of image data, a dot replacement unit that replaces the dot defined by the halftone data, and a print data generation unit that generates the print data on the basis of the halftone data after the dot replacement, and the dot replacement unit perform replacement with larger sized dots by using dots other than the dots at the end on the late side of the recording order from among the dots constituting a specific dot continuous portion in which dots having a size smaller than a predetermined size in the halftone data are continuous in the predetermined direction as a target.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image processing apparatus, an image processing method, and a printing apparatus.

  There is known a method of printing by discharging droplets (dots) and causing them to land on a medium. In such printing, in order to prevent the bleeding of droplets generated at the outline portion (edge portion) of the image to be printed, the edge processing which reduces the size of the dots constituting the edge portion or thins out the dots is performed. There is known a method of preventing bleeding and making a printing result clear by performing (see Patent Document 1).

JP 2011-167896 A

  The trajectory of a dot (following dot) discharged following a previously discharged dot (preceding dot) is affected by changes in air flow and air pressure caused by the preceding dot. The degree of such influence differs depending on whether dots of relatively small size are continuously ejected or not. Therefore, in the case where dots of relatively small size are continuously ejected and in the case where that is not the case, the trajectory of the subsequent dots is different, and as a result, the distance between the dots that land on the medium may be different. Such differences in the distance between the dots can cause image quality deterioration. In addition, such image quality deterioration may occur when the above-described edge processing is performed, or may result even if the edge processing is not performed.

  The present invention has been made in view of the above problems, and provides an image processing apparatus, an image processing method, and a printing apparatus that are effective for preventing image quality deterioration.

  One aspect of the present invention is an image processing apparatus that generates print data used for printing, and is halftone (HT) data that defines the presence / absence and size of dots for each pixel based on image data. An HT processing unit that generates the print data, a dot replacement unit that replaces the dot defined by the HT data, and a print data generation unit that generates the print data based on the HT data after the replacement of the dot, The dot replacement unit targets dots other than the dots at the end on the late side of the recording order among the dots constituting the specific dot continuous portion in which dots of a size smaller than the predetermined size in the HT data continue in the predetermined direction. Perform substitution for dots of larger size.

  According to the configuration, the image processing apparatus extracts a specific dot continuous portion in which dots of a relatively small size continue in a predetermined direction in the HT data, and the recording order is slow among the dots constituting the specific dot continuous portion. Increase the size of the dots excluding the dots at the side edge. As a result, it is possible to prevent the image quality deterioration that is likely to occur when dots of relatively small size are continuously recorded.

In one aspect of the present invention, the HT processing unit generates the HT data subjected to edge processing for reducing the size of dots forming an edge portion of an image, and the dot replacement unit performs the edge processing by the edge processing. The replacement may be performed on the generated specific dot continuous portion.
According to this configuration, it is possible to properly avoid the image quality deterioration that is likely to be caused by the execution of the edge processing.

One of the aspects of the present invention is an image processing apparatus that generates the print data used by a printing apparatus that scans a print head that discharges dots in the main scanning direction and executes printing on a print medium, the dots The replacement unit is a dot in which the small size dot in the HT data constitutes the specific dot continuous portion continuous in the main scanning direction, the dot on the end on the side where the discharge order by the print head is late The replacement may be performed on the excluded dots.
According to this configuration, when printing is performed by a serial printing apparatus in which the trajectory of the subsequent dot is easily affected by the change in air flow or air pressure due to the leading dot, dots of relatively small size are continuously in the main scanning direction. It is possible to prevent the image quality deterioration that is likely to occur when recorded.

  The technical idea of the present invention is realized by something other than an image processing apparatus. For example, a printing apparatus that executes the same process as the image processing apparatus can be regarded as an invention. In addition, a method (image processing method, printing method) including processing steps performed by the image processing apparatus and the printing apparatus, a program that causes a computer to execute these methods, and a computer readable storage medium storing the program are also included. As an invention.

The figure which shows an apparatus configuration simply. The figure which shows a printing head and a printing medium simply. 6 is a flowchart showing image processing. FIG. 4A is a diagram schematically showing an example of the relationship between the nozzle drive waveform and the dots, and FIG. 4B is a diagram schematically showing another example of the relationship between the nozzle drive waveform and the dots. The flowchart which shows dot substitution processing. The figure which illustrates each state corresponding to each process of the dot substitution process about HTD. The figure which illustrates the correspondence of HTD and the move direction of a printing head. FIG. 8A is a diagram illustrating a conventional print result, and FIG. 8B is a diagram illustrating a print result according to the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each drawing is merely an example for describing the present embodiment.

1. General Description of Device Configuration:
FIG. 1 simply shows the device configuration according to the present embodiment. The image processing apparatus 10 includes, for example, a control unit 11, a display unit 17, an operation reception unit 18, a communication interface (IF) 19, and the like. The image processing apparatus 10 is realized by, for example, a personal computer (PC) or an information processing apparatus having the same processing capability as that of the PC. Also, hardware capable of realizing the control unit 11 according to the present embodiment may be referred to as an image processing apparatus.

  The control unit 11 appropriately includes one or more ICs having the CPU 11a, the ROM 11b, the RAM 11c and the like, and other storage media such as a memory and a hard disk drive. In the control unit 11, the CPU 11a controls the behavior of the image processing apparatus 10 by executing arithmetic processing according to a program stored in the ROM 11b or the like using the RAM 11c or the like as a work area. The control unit 11 incorporates the program A, and implements the functions such as the image data acquisition unit 12, the color conversion unit 13, the HT processing unit 14, the dot replacement unit 15, the print data generation unit 16 according to the program A. The program A can be called an image processing program, a print control program, a printer driver or the like.

  The communication IF 19 is a generic name of IFs in which the control unit 11 communicates with the outside of the image processing apparatus 10 in accordance with a predetermined communication standard. The display unit 17 is a means for displaying visual information, and includes, for example, a liquid crystal display (LCD), an organic EL display, or the like. The display unit 17 may be configured to include a display and a drive circuit for driving the display. The operation accepting unit 18 is a means for accepting an operation by the user, and is realized by, for example, a physical button, a touch panel, a mouse, a keyboard, or the like. Of course, the touch panel may be realized as one function of the display unit 17. The display unit 17 and the operation reception unit 18 can be collectively referred to as an operation panel or the like.

  The image processing apparatus 10 is communicably connected to the printing unit 20 via the communication IF 19. The printing unit 20 is a mechanism capable of executing printing based on print data generated by the image processing apparatus 10 (control unit 11). The image processing apparatus 10 and the printing unit 20 may be independent apparatuses. When the image processing apparatus 10 and the printing unit 20 are independent apparatuses, the printing unit 20 is called a printing apparatus, the image processing apparatus 10 is called a printing control apparatus, and the configuration including the image processing apparatus 10 and the printing unit 20 is printed. It can be called system 1.

  Alternatively, the image processing apparatus 10 and the printing unit 20 may be included in one apparatus as a whole. When the image processing apparatus 10 and the printing unit 20 are included in one apparatus, a configuration (one apparatus) including the image processing apparatus 10 and the printing unit 20 can be referred to as the printing apparatus 1. The printing apparatus 1 has at least a printing function. Therefore, the printing apparatus 1 may be a multifunction peripheral having a plurality of functions such as a scanner and a facsimile in addition to the printing function.

  FIG. 2 simply shows the print head 21 and the print medium P provided in the print unit 20. The printing unit 20 is, as is known, a print head 21 for discharging a liquid such as ink, a carriage (not shown) for moving the print head 21, and a transport (not shown) for transporting the print medium P. It has a mechanism. The print head 21 may be called a print head, a print head, a liquid discharge (jet) head, or the like. The print medium P is typically paper, but the print medium P may be a material other than paper, as long as the material is capable of recording by discharging liquid.

  The carriage moves the print head 21 along a predetermined main scanning direction D1 with the print head 21 mounted. The transport mechanism transports the print medium P along the transport direction D2 intersecting the main scanning direction D1. The term "crossing" as used herein is basically orthogonal, but the directions D1 and D2 may not be exactly orthogonal due to various errors in the printing unit 20 as a product, for example.

  The print head 21 includes a plurality of nozzles 23 for discharging a liquid. The code | symbol 22 has shown the nozzle surface 22 which the nozzle 23 opens, and has shown an example of the arrangement | sequence of the nozzle 23 in the nozzle surface 22 in FIG. The print head 21 discharges ink of a plurality of colors (for example, ink of a plurality of colors such as cyan (C), magenta (M), yellow (Y), black (K), etc.). 24 is provided. The nozzle row 24 is composed of a plurality of nozzles 23 whose intervals along the transport direction D2 are constant. In the example of FIG. 2, the print head 21 has four nozzle rows 24 and is configured to be able to eject four colors of ink. Needless to say, the aspect of the arrangement of the nozzles 23 constituting the nozzle row 24 corresponding to one color of ink does not have to be one linear as shown in FIG. 2 and may be, for example, composed of a plurality of rows .

  The printing unit 20 alternates, based on print data, liquid discharge (scanning) by the print head 21 along with movement of the print head 21 by the carriage, and conveyance of a print medium P by a conveyance mechanism by a predetermined distance (so-called paper feed). Printing on the print medium P is realized. The scan of the print head 21 is also referred to as a pass. The printing unit 20 (or the configuration including the printing unit 20 (code 1)) can be called an inkjet printer. The liquid (droplet) discharged from the nozzle 23 by the print head 21 is called a dot. However, in the present embodiment, the term “dot” is used for convenience also when describing the image processing before the dot is ejected.

2. Image processing:
FIG. 3 is a flowchart showing image processing that the control unit 11 executes according to the program A. At least a part of the flowchart corresponds to the image processing method according to the present invention. The image processing is also processing for causing the printing unit 20 to execute printing, and may be called print control processing.
The control unit 11 (image data acquisition unit 12) acquires image data representing a print target (step S100). The print target is, for example, characters, photographs, CG, or a combination thereof. For example, when the user operates the operation reception unit 18, image data is selected. The image data acquisition unit 12 acquires the selected image data from the storage source. The storage source of the image data is various, for example, a storage medium incorporated in the image processing apparatus 10 or a storage medium externally connected to the image processing apparatus 10. The image data acquisition unit 12 passes the acquired image data to the next step S110.

  The image data that the image data acquisition unit 12 passes to step S110 is, for example, a gradation value represented by 256 gradations (for example, 0 to 255, for example) per RGB (red, green, blue) for each pixel. It is assumed that the RGB data is in bitmap format having The image data acquisition unit 12 executes format conversion and resolution conversion of the acquired image data as necessary before delivering the image data to step S110.

  In step S110, the control unit 11 (color conversion unit 13) executes color conversion processing on the image data. The color conversion process is a process of converting image data (RGB data) into data (CMYK data) of a color space of ink used by the printing unit 20 for printing. As is known, the color conversion unit 13 can execute color conversion processing with reference to a table (color conversion lookup table) in which RGB gradation values and CMYK gradation values are associated with each other. The image data (CMYK data) after the color conversion process is bitmap data having gradation values for each CMYK (for example, gradation values expressed by 256 gradations of 0 to 255) for each pixel.

  In step S120, the control unit 11 (HT processing unit 14) executes HT processing for each ink color (CMYK) on the image data after color conversion processing. The HT processing converts, for example, data representing 256 gradations into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations. HT processing can be performed using a dither method, γ correction, an error diffusion method, or the like. The image data after HT processing is called HT data. The HT data is data for each ink color, and defines the presence / absence and size of dots for each pixel.

  In the present embodiment, the print head 21 provided in the printing unit 20 can eject dots of a plurality of sizes different in liquid amount per droplet. For example, the print head 21 can eject three types of dots (large dots, medium dots, small dots) of different sizes from each nozzle 23. The amount of liquid per dot of each different size is predetermined in design of the printing unit 20. Therefore, the HT data for each ink color is data that defines for each pixel whether there is a dot or not, and if it is, it is a large dot, a medium dot, or a small dot.

  Here, edge processing will be briefly described. Patent document 1 may be referred to for edge processing. In printing by an inkjet printer, dots are absorbed by the print medium to fix the image on the print medium, but when a large amount of ink is discharged onto the print medium, the print medium can not absorb the ink and the ink overflows There are times when In particular, when the ink overflows at the edge portion of the image, the image quality of the print result may be degraded. Therefore, the control unit 11 suppresses the overflow of the ink at the edge portion by performing edge processing to reduce the amount of ink ejected corresponding to the edge portion of the image.

  In the flow of image processing (FIG. 3), for example, the HT processing unit 14 executes edge processing in step S120. The HT processing unit 14 copies the image data after the color conversion processing in step S110, and specifies an edge pixel corresponding to an edge in the image based on the copied image data. The method of identifying (extracting) edge pixels is not particularly limited, and various known methods can be employed. For example, the HT processing unit 14 specifies edge pixels by applying a filter such as a Laplacian filter or a Sobel filter to the image data.

  As described above, the HT processing unit 14 performs HT processing on the image data after the color conversion processing to generate HT data. Then, the dot size of the edge pixel identified as described above among the pixels constituting the HT data is changed to a smaller size. For example, when a large dot is defined in an edge pixel included in the HT data, the HT processing unit 14 changes the large dot to a medium dot or a small dot. In addition, when a middle dot is defined in an edge pixel included in the HT data, the HT processing unit 14 may change the middle dot to a small dot. Such edge processing (identification of edge pixels and dot size change for edge pixels) is also performed on HT data for each ink color.

The HT processing unit 14 passes the image data after the process of step S120, that is, the HT data for each ink color obtained by performing the HT process and the edge process to step S130.
In step S130, the control unit 11 (dot replacement unit 15) executes a dot replacement process for replacing the dots defined by the HT data, targeting the HT data after the process of step S120. Details of the dot replacement process will be described later.

  Then, in step S140, the control unit 11 (print data generation unit 16) generates print data to be used for printing by the printing unit 20 based on the HT data after the dot replacement process, and prints the generated print data. Output to unit 20. That is, the print data generation unit 16 has already set the pixels lined up in a matrix that constitutes the HT data after the dot replacement process when the image processing is started (for example, specified by the user) The data is rearranged in the order of data to be transferred to the printing unit 20 according to the recording method. Such rearrangement is also called rasterization processing, and data subjected to rasterization processing is called print data. The recording method is, for example, a method combining various conditions such as whether to perform unidirectional printing or bidirectional printing, whether to perform overlap printing, the amount of paper feed between passes, etc. Depending on the recording method, the order in which the data of which pixel is given to which nozzle 23 is determined.

  The print data generation unit 16 may add a command corresponding to the recording method to the print data subjected to the rasterization process. As the command, for example, there is data etc. which indicate the transport speed of the print medium P. The print data generation unit 16 outputs (transfers) the print data generated through these processes to the printing unit 20 via the communication IF 19. The printing unit 20 executes printing based on the print data output in this manner. As a result, the print target represented by the image data acquired in step S100 is reproduced on the print medium P.

3. Dot replacement process:
Next, the dot replacement process will be described. Before that, the image quality deterioration to be solved by the dot replacement process in the present embodiment will be described with reference to FIGS. 4A and 4B.
4A and 4B respectively show the relationship between the drive waveform given to (the drive element of) one nozzle 23 of the print head 21 and the dots ejected and formed by the one nozzle 23 according to the drive waveform. An example is shown briefly. In FIGS. 4A and 4B, dots are represented by white circles. Further, “discharge dot” refers to a dot in the air immediately after the nozzle 23 discharges, and “formation dot” refers to a dot formed by landing on the print medium P. In the description of FIGS. 4A and 4B, it is assumed that the print head 21 is executing a pass moving toward one side S1 in the main scanning direction D1. For example, a path moving to one side S1 in the main scanning direction D1 of the print head 21 is referred to as an outward path, and a path moving to the other side (S2 (see FIG. 7)) in the main scanning direction D1 is a return path. You may call it.

  As is known, the print head 21 has a drive element (for example, a piezoelectric element) for each nozzle 23, and applies a drive waveform (pulse) to the drive element based on print data to the drive element. The dots are ejected from the corresponding nozzles 23. In the example of FIG. 4A, during the movement of the print head 21 to one side S1, one nozzle 23 forms three dots in the order of large dot, medium dot, and medium dot. On the other hand, in the example of FIG. 4B, during the movement of the print head 21 to the one side S1, one nozzle 23 forms three dots in the order of large dot, large dot, and medium dot. The numbers in parentheses next to the dot size indicate the dot formation order.

  In the example of FIGS. 4A and 4B, in the case of forming a large dot in the nozzle 23 corresponding to one pixel, two pulses are sequentially given to the drive element. Then, in accordance with the two pulses, two dots (dots at the time of ejection) are continuously ejected from the nozzle 23, these two ejected dots merge during flight or landing, and are ejected onto the printing medium P. One large dot (large dot) equivalent to two dots is formed. On the other hand, in the case of forming a medium dot in the nozzle 23 corresponding to one pixel, only one of the two pulses is applied to the drive element. As a result, one dot (dot at the time of ejection) is ejected from the nozzle 23 according to one pulse, and this ejected one dot lands on the print medium P, and the dot for one ejection dot (medium Dots are formed.

  Here, when one nozzle 23 ejects a dot continuously, the trajectory of the subsequent dot ejected following the preceding dot ejected earlier is influenced by the change of the air flow or air pressure caused by the preceding dot. Receive Specifically, a drop in air pressure due to the leading dot displacing air or the generation of an air vortex causes a phenomenon (slip stream) of sucking nearby air or an object. Due to the effect of the slip stream, the subsequent dot is attracted to the leading dot side while flying, and the landing position approaches the landing position of the leading dot.

  As described with reference to FIGS. 4A and 4B, the middle dot of the nozzle 23 is made to correspond to one pixel rather than the number of pulses given to the drive element to cause the nozzle 23 to form a large dot corresponding to one pixel. The number of pulses given to the drive element to form the Therefore, when the leading dot is a large dot and the trailing dot is a smaller middle dot, the application of the last pulse of the number of pulses necessary for forming the leading dot (large dot) to the drive element is After completion, the time required for applying the pulse necessary for forming the subsequent dot (medium dot) to the drive element is relatively short. On the other hand, when the leading dot and the trailing dot are both medium dots smaller than the large dot, the trailing dot (middle dot) is applied after the application of the pulse necessary for forming the leading dot (middle dot) to the driving element is completed. It takes a relatively long time for the application of the pulses necessary for the formation of the driving element to the driving element to start. As the pulse-to-pulse generation interval is longer, the influence of the slip stream due to the leading dot is reduced, and the landing position of the trailing dot is likely to be farther away from the landing position of the leading dot.

  In FIGS. 4A and 4B, the presence or absence of the influence of the slip stream is indicated by the presence or absence of the inclination of the arrow from the discharge dot to the formation dot. That is, since the leading dot is the large dot in the middle dot of the second ejection order shown in FIG. 4A, the landing position approaches the landing position of the leading dot (large dot) under the influence of the slip stream. However, since the preceding dot is a medium dot, the medium dot having the third ejection order shown in FIG. 4A is hardly affected by the slip stream, and the landing position is from the landing position of the preceding dot (middle dot) (slip stream Far) than when affected by FIG. 4A shows a distance W1 as an example of the distance (the distance along the main scanning direction D1) between the leading dot and the trailing dot when the trailing dot lands without being affected by the slipstream due to the leading dot. .

  On the other hand, since the leading dot is the large dot in the second large dot shown in FIG. 4B, the landing position approaches the landing position of the leading dot (large dot) under the influence of the slip stream. Further, since the leading dot is a large dot in the middle dot having the third ejection order shown in FIG. 4B, the landing position approaches the landing position of the leading dot (large dot) under the influence of the slip stream. FIG. 4B shows a distance W2 as an example of the distance between the leading dot and the trailing dot (the distance along the main scanning direction D1) when the trailing dot lands under the influence of the slip stream due to the leading dot. As apparent from the comparison of FIGS. 4A and 4B, the distance W1> the distance W2 holds. Such a difference between the distances W1 and W2 leads to an image quality difference in the printing result. More specifically, when the third middle dot in the ejection order shown in FIGS. 4A and 4B corresponds to the edge portion of the image, in the example of FIG. 4A, the middle dot in the edge portion is a position away from the preceding dot. The image is visually recognized as blurring of the edge (deterioration of image quality). On the other hand, in the example of FIG. 4B, the medium dot in the edge portion is formed at a position (ideal position) close to the preceding dot, so that the edge is visually recognized as a clean edge with no looseness. Therefore, in the present embodiment, the dot replacement process is performed to avoid the occurrence of the situation as illustrated in FIG. 4A and to create the situation as illustrated in FIG. 4B.

  Although small dots are not described in FIGS. 4A and 4B, the nozzles 23 can form small dots as described above. For example, when the print head 21 provides an amplitude difference to the two consecutive pulses for forming a large dot and causes the nozzle 23 to form a medium dot, the amplitude of the two consecutive pulses to the drive element In the case where small dots are to be formed in the nozzle 23 by applying only the larger one of the two pulses, it is also possible to apply only the smaller one of the two consecutive pulses to the drive element. Alternatively, when the print head 21 causes the nozzle 23 to form a large dot, the print head 21 gives three consecutive pulses to the drive element, and when the nozzle 23 forms a medium dot, the two consecutive pulses to the drive element When forming small dots in the nozzle 23, one pulse may be given to the drive element. In any case, the number of pulses as drive signals given to the drive element when forming small dots is smaller than the number of pulses as drive signals given to the drive element when forming large dots. Therefore, even if "medium dot" is rephrased as "small dot" in the description of FIG. 4A, it can be said that the image quality deterioration due to the influence reduction of the slip stream as described above is likely to occur as well.

FIG. 5 is a flowchart showing the dot replacement process of step S130. Further, FIG. 6 illustrates each state corresponding to each process of the dot replacement process for a part of HT data (HTD) to be subjected to the dot replacement process.
In step S132, the dot replacement unit 15 extracts a specific dot continuous portion DP in which dots having a size smaller than a predetermined size in the HTD are continuous in a predetermined direction. The size smaller than the predetermined size means a size in which image quality deterioration (occurrence of the distance W1) easily occurs due to the influence of the slip stream as shown in FIG. 4A when dots of the size are continuously formed. In the present embodiment, it is assumed that dots of a size smaller than a predetermined size indicate medium dots and small dots smaller than a large dot (predetermined size). Further, when the print head 21 is configured to move along the main scanning direction D1 as shown in FIG. 2, the predetermined direction is a direction corresponding to the main scanning direction D1 in the vertical and horizontal directions of the image data (HTD). Point to.

The dot replacement unit 15 extracts, as a specific dot continuous portion DP, pixel continuous portions meeting the following conditions, for example, in raster data units. The raster data is a pixel row that constitutes the HTD, and is a pixel row in which pixels are arranged along the predetermined direction.
Condition: A dot having a size smaller than the predetermined size is a pixel continuous portion continuing in the predetermined direction, and a pixel having an edge pixel at the end on the side where the recording (dot ejection) order is late among both end sides of the predetermined direction. Be a continuous part.

  In the upper part of FIG. 6, the specific dot continuous portion DP extracted from the HTD in step S132 is shown surrounded by a thick frame. In the example of the upper stage of FIG. 6, three specific dot continuous parts DP are shown. In FIG. 6, the individual rectangles that make up the HTD are the HTD pixels. The HTD shown in FIG. 6 is an HTD corresponding to one ink color (for example, K). The numbers 1 to 3 described for each pixel for convenience indicate the presence / absence and the size of the dot for each pixel defined by the HTD. That is, “0” means no dot (dot off), “1” means small dot on, “2” means medium dot on, and “3” means large dot on. Further, in FIG. 6, pixels with dots (dots on) are represented in gray for easy understanding. The pixels constituting the specific dot continuous portion DP are all “2” or “1”. As can be understood from the description of the edge processing described above, all or part of such a specific dot continuous portion DP is produced through the edge processing.

  FIG. 6 also shows the correspondence between the HTD and the main scanning direction D1. HTD (a part of HTD) shown in FIG. 6 is data recorded in a pass (forward pass) in which the print head 21 moves toward the one side S1 in the main scanning direction D1 according to the recording method. Therefore, in FIG. 6, the one side S1 corresponds to the later side of the recording order among the two end sides in the predetermined direction. Therefore, in FIG. 6, the pixel at the first side S1 of each specific dot continuous portion DP corresponds to an edge pixel. In other words, in step S132, the dot replacement unit 15 has a medium dot or a small dot and a pixel having a medium dot or a small dot on the side where the recording order is earlier with the pixel corresponding to the edge pixel as the end of one side S1. A continuous pixel continuous portion is extracted as a specific dot continuous portion DP. Whether or not the pixel corresponds to an edge pixel has already been identified in the edge processing.

  FIG. 7 illustrates the correspondence between the HTD and the moving direction of the print head 21. According to the recording method, for example, the control unit 11 causes the printing unit 20 to print an image of one page by band printing. Band printing is a recording method of printing a band-like image area called band BD in one pass. The band BD is an image area (a bundle of raster data) in which a plurality of raster data are arranged in the transport direction D2. In band printing, each raster data forming the band BD is printed by one nozzle 23 in one pass. Therefore, the control unit 11 is configured to print raster data of a printable number per pass of the print head 21, that is, a bundle of raster data corresponding to the number of nozzles aligned in the transport direction D2 in the nozzle row 24 corresponding to one ink color. Is defined as one band BD.

  The control unit 11 associates the moving direction of the print head 21 with each band BD constituting the HTD (it is determined for each band BD whether to print in the forward pass or the return pass). In the example of FIG. 7, for each band BD constituting an HTD for one page, the one side S1, the other side S2, the one side S1 ... alternately in the main scanning direction D1 in order from the page top side. Corresponds to the movement direction. Raster data belongs to any one band BD. Therefore, by associating the moving direction of the print head 21 with each band BD, it is possible to determine the moving direction of the print head 21 for each raster data constituting the HTD.

  In step S132, the dot replacement unit 15 tries to extract the specific dot continuous portion DP from the raster data in accordance with the movement direction of the print head 21 for each raster data thus determined. That is, in raster data in which the moving direction of the print head 21 is the one side S1, the middle dot or the small dot is present, and the pixel corresponding to the edge pixel is the middle dot on the opposite side (the other side S2) Alternatively, a pixel continuous portion in which pixels having small dots are continuous is extracted as a specific dot continuous portion DP. Conversely, in raster data where the moving direction of the print head 21 is the other side S2, a pixel having medium dots or small dots and corresponding to an edge pixel is set as the end of the other side S2 to the opposite side (one side S1) A pixel continuous portion in which pixels having dots or small dots are continuous is extracted as a specific dot continuous portion DP.

  In step S134, the dot replacement unit 15 selects a replacement target dot from the specific dot continuous portion DP extracted in step S132. The dot to be replaced is a dot excluding the dot at the end on the side where the printing order is late among the dots constituting the specific dot continuous portion DP. As in the example of FIG. 6, in the specific dot continuous portion DP extracted from HTD (a part of HTD) recorded in a pass (forward pass) in which the print head 21 moves toward one side S1 in the main scanning direction D1. The pixels other than the pixels on the first side S1 of each specific dot continuous portion DP correspond to replacement target dots. In the middle stage (and the lower stage) of FIG. 6, in order to facilitate understanding, the pixels on the first side S1 of each specific dot continuous portion DP are marked with a cross. That is, in the middle stage (and the lower stage) of FIG. 6, the pixels not marked with x in the specific dot continuous portion DP correspond to replacement target dots.

  In step S134, the dot replacement unit 15 may select all dots except for the dot at the end on the late side of the recording order among the dots constituting the specific dot continuous portion DP as the replacement target dot, or such an end A part of the dots excluding the dots of may be selected as the replacement target dots. However, when the dot replacement unit 15 selects a part of the dots excluding the dot at the end as the dot to be replaced, the dot adjacent to the recording order earlier than the dot at the end is at least the dot to be substituted. select.

  In step S136, the dot replacement unit 15 replaces the replacement target dot selected in step S134 with a dot of a larger size. Since the substitution target dot is a medium dot or a small dot, in the present embodiment, the dot substitution unit 15 substitutes “3”, that is, a large dot, for the substitution target dot selected in step S134. The lower part of FIG. 6 shows a state in which the selected replacement target dot is replaced with a large dot. Thus, the dot replacement process of step S130 is completed. Accordingly, the HTD as illustrated in the lower part of FIG. 6 is delivered to step S140, and becomes a processing target by the print data generation unit 16. Of course, dot replacement processing is also performed for each HT data for each ink color.

  FIG. 8A exemplifies the conventional printing result when the dot replacement process is not performed. On the other hand, FIG. 8B illustrates the printing result according to the present embodiment when the dot replacement process is performed. The print result shown in FIG. 8A is the result of printing on a part of the print medium P based on the HTD shown in the upper part of FIG. 6, and the print result shown in FIG. 8B is the HTD shown in the lower part of FIG. It can be understood that the printing result is a result of printing on a part of the print medium P based on the above. In FIGS. 8A and 8B, dots formed on the print medium P are indicated by circles, and these dots are all dots of the same ink color (for example, K).

  In FIGS. 8A and 8B, the dots at the end on the side where the recording order is late in the specific dot continuous portion DP of each raster data are hatched for convenience. The hatched dots are also dots corresponding to edge pixels. Further, in FIG. 8B, dots except for the dot at the end on the side where the recording order is late in the specific dot continuous portion DP for each raster data are excluded, that is, selected as the replacement target dot in step S134 and replaced with large dots in step S136. The dots are shown in gray for convenience.

  According to FIG. 8A, since the leading dot is smaller than the predetermined size (large dot), the dot of the edge pixel is hardly affected by the slip stream and deviates from the preceding dot compared to the case of being affected by the slip stream. It is formed in the following position. As a result, a gap Z is generated in the main scanning direction D1 between the dot of the edge pixel and the preceding dot, and this gap Z makes it easy for the user to visually recognize the edge rattling (image quality deterioration). On the other hand, according to FIG. 8B, since the replacement target dot is replaced with the large dot, the dot (following dot) of the edge pixel ejected after the replacement target dot (preceding dot) is affected by the slip stream. It is formed at a position close to the leading dot (ideal position). As a result, the gap Z as shown in FIG. 8A does not occur, and a clean (small) clean edge is recognized.

4. Summary:
As described above, according to the present embodiment, the image processing apparatus or printing apparatus defines the HT processing unit 14 that generates HT data that defines the presence / absence and size of dots for each pixel based on image data, and HT data. And a print data generation unit 16 that generates print data based on HT data after dot substitution, and the dot substitution unit 15 has a size smaller than a predetermined size in HT data Of the dots that make up the specific dot continuous portion DP in which the dots are continuous in a predetermined direction, replacement with dots of a larger size is performed on the dots excluding the dots at the end on the late side of the recording order (step S130) ). According to this configuration, it is possible to effectively prevent the image quality deterioration that is likely to occur due to the reduction of the influence of the slip stream on the subsequent dots when dots of relatively small size are continuously recorded. In particular, as can be seen from a comparison of FIGS. 8A and 8B, the present invention is effective in improving the image edge rattling.

  Further, according to the present embodiment, the HT processing unit 14 generates HT data subjected to edge processing to reduce the size of the dots forming the edge portion of the image (step S120), and the dot replacement unit 15 generates an edge The replacement is performed for the specific dot continuous portion DP generated by the processing. That is, when edge pixels are converted to dots of relatively small size such as medium dots and small dots by edge processing, the problem of image quality deterioration due to the influence of the slip stream is more likely to occur. The present invention addresses such a problem by providing dots adjacent to the dot on the earlier printing order side with the dot on the edge side (the dot on the end side of the dots constituting the specific dot continuous portion DP on the late printing order side). , Replace with larger sized dots. As a result, it is possible to properly avoid image quality deterioration (edge rattling) that is likely to be caused by execution of edge processing.

  In addition, since the specific dot continuous portion DP is often generated as a result of edge processing, the dot replacement unit 15 eventually executes the replacement for the specific dot continuous portion DP generated by the edge processing. However, the specific dot continuous portion DP may exist in the HT data independently of the edge processing. That is, even in the part of the HT data which has not been subjected to the edge processing, it may be extracted as the specified dot continuous part DP in step S132 (FIG. 5).

  Further, according to the present embodiment, an image for generating print data used by the printing apparatus (code 1 or 20) that executes printing on the print medium P by causing the print head 21 that discharges dots to scan in the main scanning direction D1. In the processing device 10, the dot replacement unit 15 selects the print head 21 among dots constituting a specific dot continuous portion DP in which dots of a size smaller than a predetermined size in HT data are continuous corresponding to the main scanning direction D1. The above replacement is performed on the dots except for the dots at the end on the side where the ejection order is late. According to the configuration, dots of relatively small size are continuously recorded when printing is performed by the serial type printing apparatus in which the trajectory (and the landing position) of the subsequent dots is easily changed depending on the presence or absence of the slip stream. It is possible to prevent the image quality deterioration that is likely to occur in some cases.

5. Modification:
The present invention is not limited to the embodiments described above, and may include various modifications as described below, for example. Of course, the combination of the above-described embodiment and each modification is also included in the disclosure scope of the present specification.

Modification 1:
The control unit 11 may perform edge processing and dot replacement processing substantially simultaneously at the time of HT processing (step S120). Specifically, when the control unit 11 (HT processing unit 14) specifies an edge pixel in image data, it is assumed that a plurality of edge pixels are continuous along a direction corresponding to the main scanning direction D1. . In such a case, the control unit 11 (HT processing unit 14, dot replacement unit 15) reduces the dot size to a small size (medium dot or small dot) by edge processing for all of the plurality of consecutive edge pixels. Instead, the dot size is left as the large dot (or replaced with the large dot) for the edge pixels except for the edge pixel at the end on the side where the recording order is late. According to such a modification, HT processing, edge processing and dot replacement processing are substantially completed when step S120 is finished, and it is not necessary to execute step S130 thereafter. In other words, there is no need to perform two size changes such as changing the dot size to a small size after changing one dot size to a small size, and changing the dot size to 0 times or 1 time for the one pixel. And the processing amount of the control unit 11 can be reduced.

Modification 2:
In the dot replacement process (step S130), the dot replacement unit 15 may replace the dot at the end of the specific dot continuous portion DP on the side of the late printing order with no dot, that is, “0”. As described above, by not changing the dot at the end on the side where the recording order is slow in the specific dot continuous portion DP without forming a dot, the gap from the leading dot as illustrated in FIG. 8A to the one side S1 It is possible to extinguish the existence of the subsequent dot formed by vacating Z. This can improve edge rattling.

Modification 3:
Edge processing is not an essential process in the present embodiment. That is, the present invention also includes an aspect in which the HT processing unit 14 does not perform the above-described edge processing in the HT processing (step S120). In this case, in step S130, the dot replacement unit 15 performs the dot replacement process on the HT data (HT data not subjected to edge processing) after the process of step S120. Even in the HT data to which the edge processing is not applied, the specific dot continuous portion DP may exist. That is, regardless of whether or not the HT data is edge-processed, the dot replacement unit 15 can execute the dot replacement process described above when the specific dot continuous portion DP can be extracted from the HT data. Even if the edge processing is not executed, the control unit 11 executes the processing for identifying the edge pixel before the HT processing, and the result of identifying the edge pixel from the HT data is a specific dot continuous portion Used when extracting DP.

Modification 4:
The print head 21 may not be a so-called serial type head moving along the main scanning direction D1, but may be a so-called line type head which has a length across the width of the print medium P and is fixed. When the print head 21 is a line type head, referring to FIG. 2, the main scanning direction D1 is the longitudinal direction of the print head 21. In this case, the print head 21 has a nozzle row consisting of a plurality of nozzles formed at regular intervals along the longitudinal direction for each ink color. Then, the plurality of nozzle rows for each ink color are arranged in the transport direction D2. The print medium P is transported along a transport direction D2 that intersects (orthogonalizes) the longitudinal direction of the print head 21. Even when such a line type head is used for printing, the slip stream by the leading dot can affect the landing position of the subsequent dot, although not as much as a serial type head in which the head itself moves. Therefore, the image processing apparatus 10 generates print data used by a printing apparatus (code 1 or 20) that ejects dots to the line type print head 21 and executes printing on the print medium P, and the dot replacement unit 15 Among the dots constituting a specific dot continuous portion in which dots of a size smaller than the predetermined size in the HT data are continuous corresponding to the predetermined direction (conveyance direction D2), the side having the slower discharge order by the print head 21 (conveyance direction D2 It is possible to grasp a configuration in which replacement with a dot of a larger size is performed on the dots except for the dots at the end of the upstream side of.

DESCRIPTION OF SYMBOLS 1 printing system (or printing apparatus) 10 image processing apparatus 11 control part 12 image data acquisition part 13 color conversion part 14 HT processing part 15 dot substitution part 16 print data Generation, 17: display unit, 18: operation reception unit, 19: communication IF, 20: printing unit, 21: printing head, 23: nozzle, 24: nozzle array, A: program, P: printing medium

Claims (5)

An image processing apparatus for generating print data used for printing, comprising:
A halftone processing unit that generates halftone data that defines the presence / absence and size of dots for each pixel based on image data;
A dot replacement unit that replaces dots defined by the halftone data;
A print data generation unit that generates the print data based on the halftone data after replacement of the dots;
The dot replacement unit targets dots other than the dots at the end on the late side of the recording order among the dots constituting the specific dot continuous portion in which dots of a size smaller than the predetermined size in the halftone data are continuous in the predetermined direction. An image processing apparatus characterized in that replacement with dots of larger size is performed. The halftone processing unit generates the halftone data subjected to edge processing to reduce the size of dots forming an edge portion of an image.
The image processing apparatus according to claim 1, wherein the dot replacement unit performs the replacement for the specific dot continuous portion generated by the edge processing. An image processing apparatus that generates the print data used by a printing apparatus that performs printing on a printing medium by causing a print head that discharges dots to scan in the main scanning direction,
The dot replacement unit is an end on the side where the discharge order by the print head is late among dots constituting the specific dot continuous portion in which the small size dots in the halftone data are continuous corresponding to the main scanning direction. The image processing apparatus according to claim 1 or 2, wherein the replacement is performed on dots excluding dots of (1). A printing apparatus that executes printing based on print data, comprising:
A halftone processing unit that generates halftone data that defines the presence / absence and size of dots for each pixel based on image data;
A dot replacement unit that replaces dots defined by the halftone data;
A print data generation unit that generates the print data based on the halftone data after replacement of the dots;
The dot replacement unit targets dots other than the dots at the end on the late side of the recording order among the dots constituting the specific dot continuous portion in which dots of a size smaller than the predetermined size in the halftone data are continuous in the predetermined direction. A printing apparatus characterized in that replacement with dots of larger size is performed. An image processing method for generating print data used for printing, comprising:
A halftone processing step of generating halftone data in which presence / absence and size of dots for each pixel are defined based on image data;
A dot replacement step of replacing dots defined by the halftone data;
A print data generation step of generating the print data based on the halftone data after replacement of the dots;
In the dot replacement step, among dots constituting a specific dot continuous portion in which dots of a size smaller than a predetermined size in the halftone data are continuous in a predetermined direction, dots excluding the dots at the end on the late side of the recording order are targeted. An image processing method characterized in that replacement with a dot of a larger size is performed.