Image processing apparatus, computer program, and method

Abstract

To prevent a difference of a color from becoming conspicuous.SOLUTION: An image processing device for a printing execution unit which performing printing by executing partial printing that forms a dot on a printing medium by a printing head and medium movement that moves the printing medium in the medium movement direction with respect to the printing head executes direction decision processing of deciding the head movement direction of the plural times of partial printing to any of the first direction and second direction by using object image data. An object image includes: a first partial image printed in the first partial printing, a second partial image printed in the second partial printing, and an intermediate image printed in both of the first partial printing and second partial printing. The direction decision processing, in a case where a specific condition at least including a first condition indicating that a color difference pixel exists over a boundary between the first partial image and the intermediate image and a color difference pixel exists over a boundary between the second partial image and the intermediate image is satisfied, decides the head movement direction of the first partial printing and the head movement direction of the second partial printing in the same direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This specification relates to an image processing apparatus, a computer program, and a method for a printing execution unit.

Background Art

[0002] Patent Document 1 discloses a multifunction printer that prints one image by printing a plurality of band images. In this technology, when it is assumed that the target band image is printed in the forward direction, the color to be printed, and when it is assumed that the target band image is printed in the reverse direction, it is determined whether a first color condition indicating a large difference between the colors to be printed is satisfied. When this condition is satisfied, it is determined whether a second color condition indicating that a pixel of a color with a large difference described above included in the target band image is included in other band images by a predetermined number or more. When the first color condition and the second color condition are satisfied, the target band image and the other band images are printed in the same printing direction. As a result, it is said that it is possible to suppress the conspicuousness of the color difference caused by the different printing directions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above technology, for printing in which there is an image printed in both the first partial printing and the second partial printing between the image printed in the first partial printing and the image printed in the second partial printing, it is not considered.

[0005] This specification discloses a technique for suppressing noticeable color differences in printing where an image printed in a first partial print and an image printed in a second partial print are interspersed with an image printed in both the first and second partial prints. [Means for solving the problem]

[0006] The technologies disclosed herein can be implemented in the following applications:

[0007] [Application Example 1] A printing execution unit comprising a print head having a first type nozzle for ejecting a first type of ink and a second type nozzle for ejecting a second type of ink, the print execution unit performing printing by repeatedly executing head movement, which moves the print head in either the first direction or the second direction opposite to the first direction with respect to the printing medium, and media movement, which moves the printing medium in a media movement direction intersecting the first direction with respect to the print head, the image processing device for the printing execution unit, is used to print a target image The process includes: an image acquisition process to acquire target image data representing an image; a direction determination process to determine the direction of the head movement for each of a plurality of partial prints, including a first partial print and a second partial print performed after the first partial print, using the target image data representing the target image, to be one of the first direction and the second direction; and a print control process to cause the print execution unit to print the target image by causing the print execution unit to perform the plurality of partial prints using the target image data, wherein the head movement for the plurality of partial prints is performed in the direction determined by the direction determination process. The target image includes a first partial image printed by the first partial print, a second partial image printed by the second partial print, and an intermediate image located between the first partial image and the second partial image, which is printed by both the first partial print and the second partial print. The direction determination process includes: determining whether a specific condition is met, which includes at least a first condition indicating that color difference pixels exist across the boundary between the first partial image and the intermediate image, and that color difference pixels exist across the boundary between the second partial image and the intermediate image; determining the direction of head movement for the first partial print and the direction of head movement for the second partial print to be the same direction if the specific condition is met, and determining the direction of head movement for the first partial print and the direction of head movement for the second partial print to be different directions if the specific condition is not met.The color difference pixel is a pixel in which the difference between the color printed when printed by the partial printing in the first direction and the color printed when printed by the partial printing in the second direction is greater than that of a different pixel.

[0008] According to the above configuration, when specific conditions are met indicating that color-different pixels exist across the boundary between the first partial image and the intermediate image, and that color-different pixels also exist across the boundary between the second partial image and the intermediate image, the direction of head movement for the first partial print and the direction of head movement for the second partial print are determined to be the same direction. As a result, in printing where there is an image printed in both the first and second partial prints between the image printed in the first partial print and the image printed in the second partial print, the visibility of color differences can be suppressed. Furthermore, when the specific conditions are not met, the direction of head movement for the first partial print and the direction of head movement for the second partial print are determined to be different directions from each other. As a result, in printing where there is an image printed in both the first and second partial prints between the image printed in the first partial print and the image printed in the second partial print, the decrease in printing speed can be suppressed.

[0009] Furthermore, the technologies disclosed herein can be realized in various forms, for example, in the form of a printing apparatus, a method for controlling a printing apparatus, an image processing method, a computer program for realizing the functions of these apparatuses and methods, a recording medium on which the computer program is stored, and so on. [Brief explanation of the drawing]

[0010] [Figure 1] A block diagram showing the configuration of the embodiment. [Figure 2] A diagram showing the schematic configuration of the printing mechanism 100. [Figure 3] A diagram showing an example of a printed image PI printed on paper M. [Figure 4] A diagram illustrating the recording rate for partial printing. [Figure 5] Diagram illustrating the evaluation table VT. [Figure 6] A flowchart of the printing process. [Figure 7] Flowchart of the direction determination process in the first embodiment. [Figure 8] Flowchart of the direction determination process in the first embodiment. [Figure 9] Diagram illustrating the determination of the printing direction. [Figure 10] Flowchart of the print orientation determination process in the second embodiment. [Figure 11] Flowchart of the print orientation determination process in the third embodiment. [Modes for carrying out the invention]

[0011] A. First example: A-1: Configuration of Printer 200 Next, embodiments will be described based on examples. Figure 1 is a block diagram showing the configuration of an embodiment.

[0012] The printer 200 includes, for example, a printing mechanism 100 as a printing execution unit, a CPU 210 as a control device for the printing mechanism 100, a non-volatile storage device 220 such as a hard disk drive, a volatile storage device 230 such as a hard disk or flash memory, an operation unit 260 such as buttons or a touch panel for acquiring user input, a display unit 270 such as a liquid crystal display, and a communication unit 280. The printer 200 is connected to an external device, such as a user's terminal device (not shown), via the communication unit 280.

[0013] The volatile memory device 230 provides a buffer area 231 for temporarily storing various intermediate data generated when the CPU 210 performs processing. The non-volatile memory device 220 stores the computer program CP and the evaluation table VT. In this embodiment, the computer program CP is a control program for controlling the printer 200. The evaluation table VT will be described later.

[0014] The computer program CP and the evaluation table VT can be stored in and provided by the non-volatile storage device 220 when the printer 200 is shipped. Also, the computer program CP and the evaluation table VT are provided in a form downloaded from a server. Instead of this, the computer program CP and the evaluation table VT may be provided in a form stored in a DVD-ROM or the like. The CPU 210 controls the printing mechanism 100 to execute the printing process described later by executing the computer program CP.

[0015] The printing mechanism 100 ejects each ink (droplet) of cyan (C), magenta (M), yellow (Y), and black (K) to perform printing. The printing mechanism 100 includes a print head 110, a head drive unit 120, a head movement unit 130, and a conveyance unit 140.

[0016] FIG. 2 is a diagram showing a schematic configuration of the printing mechanism 100. As shown in FIG. 2(A), the head movement unit 130 includes a carriage 133 on which the print head 110 is mounted, and a sliding shaft 134 that holds the carriage 133 so as to be reciprocally movable along the head movement direction (the X-axis direction in FIG. 2). The head movement unit 130 reciprocates the carriage 133 along the sliding shaft 134 using the power of a motor (not shown). Thereby, head movement for reciprocating the print head 110 along the head movement direction with respect to the paper M is realized.

[0017] The conveyance unit 140 conveys the paper M in the conveyance direction AR (the +Y direction in FIG. 2) that intersects the head movement direction while holding the paper M. As shown in FIG. 2(A), it includes a paper tray 145, an upstream roller pair 142, and a downstream roller pair 141. Hereinafter, the upstream side (-Y side) in the conveyance direction AR is also simply referred to as the upstream side, and the downstream side (+Y side) in the conveyance direction AR is also simply referred to as the downstream side.

[0018] The upstream roller pair 142 holds the paper M upstream (-Y side) of the print head 110, and the downstream roller pair 141 holds the paper M downstream (+Y side) of the print head 110. The paper tray 145 is positioned between the upstream roller pair 142 and the downstream roller pair 141, and facing the nozzle forming surface 111 of the print head 110. The paper M is transported by driving the downstream roller pair 141 and the upstream roller pair 142 with a transport motor (not shown).

[0019] The head drive unit 120 (Figure 1) drives the print head 110 by supplying a drive signal to the print head 110 while the head moving unit 130 is moving the print head 110. The print head 110 ejects ink onto the paper being transported by the transport unit 140 according to the drive signal, forming dots.

[0020] Figure 2(B) illustrates the configuration of the print head 110 as viewed from the -Z side (the bottom side in Figure 2). As shown in Figure 2(B), the nozzle forming surface 111 of the print head 110 has multiple nozzle rows consisting of multiple nozzles, namely nozzle rows NC, NM, NY, and NK that eject the C, M, Y, and K inks mentioned above. Each nozzle row contains multiple nozzles NZ arranged along the transport direction AR. The multiple nozzles NZ are positioned at different locations in the transport direction AR (+Y direction) and are arranged along the transport direction AR with a predetermined nozzle spacing NT. The nozzle spacing NT is the length in the transport direction AR between two adjacent nozzles NZ in the transport direction AR. The nozzle NZ located furthest upstream (-Y side) among the nozzles constituting these nozzle rows is also called the upstream nozzle NZu. The nozzle NZ located furthest downstream (+Y side) among these nozzles is also called the downstream nozzle NZd. The length obtained by adding the nozzle spacing NT to the length AR in the transport direction from the upstream nozzle NZu to the downstream nozzle NZd is also called the nozzle length D.

[0021] The nozzle rows NC, NM, NY, and NK are positioned differently in the direction of head movement (X direction in Figure 2(B)), but their positions in the transport direction AR (Y direction in Figure 2(B)) overlap. For example, in the example in Figure 2(B), nozzle row NM is positioned in the +X direction of nozzle row NY, which ejects Y ink.

[0022] A-2. Overview of Printing The printing mechanism 100 prints a print image PI onto the paper M by alternately performing partial printing, in which the print head 110 forms dots on the paper M while the head movement unit 130 moves the head, and transporting the paper M by the transport unit 140 (hereinafter also referred to as sheet transport) multiple times. In one partial printing, with the paper M stopped on the paper tray 145, the print head 110 makes one head movement and ejects ink onto the paper M, thereby printing a portion of the image to be printed onto the paper M. One sheet transport is transport that moves the paper M in the transport direction AR by a predetermined transport amount. In this embodiment, the CPU 210 causes the printing mechanism 100 to perform partial printing m times (where m is an integer of 2 or more).

[0023] Figure 3 shows an example of a print image PI printed on paper M. The print image PI extends in the X direction (the direction of head movement during printing) and contains multiple raster lines RL (e.g., RL1 in Figure 3) whose positions in the Y direction differ from each other. Each raster line RL is a line on which multiple dots can be formed. Each raster line of the print image PI corresponds one-to-one with each raster line of the RGB image RI, which will be described later.

[0024] In the example in Figure 3, the print image PI is printed in five partial prints (m=5). Furthermore, Figure 3 illustrates the head position, that is, the relative position of the print head 110 in the transport direction with respect to the paper M, for each partial print (i.e., each head movement). For multiple partial prints, a pass number k (where k is an integer between 1 and m) is assigned in the order of execution, and the head position P at the time of the kth partial print is called the head position Pk. The sheet transport that takes place between the kth partial print and the (k+1)th partial print is also called the kth sheet transport Tk. Figure 3 illustrates the head positions P1 to P5 and the sheet transports T1 to T4.

[0025] In Figure 3, the printed image PI formed on the paper M includes multiple normal regions NA1 to NA5 and multiple overlapping regions SA1 to SA4.

[0026] Normal regions NA1 to NA5 are regions where each raster line RL within the region is printed in only one partial print. For example, in the normal region NAk in Figure 3, dots are formed on each raster line RL only during the k-th partial print, i.e., the partial print performed at head position Pk. No dots are formed on each raster line RL in the normal region NAk during the (k+1)th or (k-1)th partial print. Therefore, a dot of a specific color on each raster line RL in the normal region NAk, for example, a dot of color C, is formed using one nozzle in the nozzle row NC that corresponds to that raster line RL.

[0027] The overlapping region SA is the region where the raster line RL is printed in two partial prints. For example, in the overlapping region SAk in Figure 3, dots are formed on each raster line RL by the k-th partial print and the (k+1)-th partial print. That is, dots are formed on each raster line RL in the overlapping region SAk by the partial print performed at head position Pk and the partial print performed at head position P(k+1). Therefore, a dot of a specific color on each raster line RL in the overlapping region SAk, for example, a dot of color C, is formed using two nozzles in the nozzle row NC that correspond to that raster line RL. The two nozzles corresponding to the raster line RL in the overlapping region SAk are the nozzle corresponding to the raster line RL in the partial print and the nozzle corresponding to the raster line RL in the partial print.

[0028] The overlapping region SAk is located between the normal region NAk and the normal region NA(k+1). The length Ha in the transport direction of the overlapping region SA (also called the overlapping region length Ha) is, for example, the length of several to several tens of raster lines RL.

[0029] As shown in Figure 3, the printable partial area RA1 in the first partial printing includes an overlapping area SA1 that includes the upstream end of partial area RA1, and a normal area NA1 that is downstream of overlapping area SA1. The printable partial areas RA2 to RA4 in the second to fourth partial printings each include an overlapping area SAk that includes the upstream end of partial area RAk, an overlapping area SA(k-1) that includes the downstream end of partial area RAk, and a normal area NAk that is downstream of overlapping area SAk and upstream of overlapping area SA(k-1) (where k is one of 2 to 4). The printable partial area RA5 in the last partial printing includes an overlapping area SA4 that includes the downstream end of partial area RA5, and a normal area NA5 that is upstream of overlapping area SA4.

[0030] Let me explain the reason for creating the overlapping area SA. Suppose the printed image is composed only of images printed in the normal area, without the overlapping area SA. In this case, due to variations in the amount of paper M being transported, a defect called banding may occur, where white or black streaks appear at the boundary between two adjacent normal areas in the transport direction AR. Banding degrades the image quality of the printed image PI. By creating an overlapping area SA between two normal areas NA and printing the image within this area, the aforementioned defect called banding can be suppressed. This is because, in the overlapping area SA, dots on one raster line RL are formed by two partial prints, thus preventing all dots on one raster line RL from being misaligned in the same way as all dots on other raster lines.

[0031] Figure 4 is an explanatory diagram of the recording rate for partial printing. The recording rates R2, R3, and R4 in Figure 4 are the recording rates for partial printing at head positions P2, P3, and P4, respectively. In Figure 4, the recording rates R2, R3, and R4 are shown for each position in the transport direction AR. In the range of the transport direction AR corresponding to the normal area NA2, the recording rate R2 is 100%. Similarly, in the ranges of the transport direction AR corresponding to the normal areas NA3 and NA4, the recording rates R3 and R4 are 100%.

[0032] In the range of the transport direction AR corresponding to the overlapping region SA2, the recording rate R2 decreases linearly as you move upstream in the transport direction AR (lower side of Figure 4). In the range of the transport direction AR corresponding to the overlapping region SA2, the recording rate R3 decreases linearly as you move downstream in the transport direction AR (upper side of Figure 4). In the range of the transport direction AR corresponding to the overlapping region SA2, the sum of the recording rates R2 and R3 is 100%. The same applies to the recording rates R3 and R4 in the range of the transport direction AR corresponding to the overlapping region SA3.

[0033] Note that while Figure 4 only shows the recording rate for partial printing at head positions P2 to P4, the same recording rate is observed at other head positions P1 and P5. This allows for 100% recording rate printing in both the normal areas NA1 to NA5 and the overlapping areas SA1 to SA4. By varying the recording rate in the overlapping area SA according to the position of the transport direction AR, banding can be effectively suppressed.

[0034] The printing direction for each partial print in Figure 3 is either the forward direction D1 or the return direction D2. That is, partial printing is either forward printing, where the head moves in the forward direction D1 (the +X direction in Figure 3) to form dots, or return printing, where the head moves in the return direction D2 (the -X direction in Figure 3) to form dots. Hereafter, the direction of head movement during partial printing will also be referred to as the printing direction (forward direction D1 or return direction D2). In Figure 3, the printing direction for partial printing in each partial region RA1 to RA5 is shown.

[0035] In this embodiment, printing is performed using all nozzles with a nozzle length of D. Therefore, the amount of material transported by sheet transporters T1 to T4 is the nozzle length D minus the overlapping region length Ha (D-Ha).

[0036] When partial printing is performed consecutively in the same printing direction, for example, when forward printing is performed consecutively, the print head moves between the two consecutive partial prints without forming a dot. This type of print head movement, which does not form a dot (i.e., does not print a partial image), is also called a printless print head movement. For example, in the example in Figure 3, both the third and fourth partial prints are forward prints, so a printless print head movement occurs between the third and fourth partial prints.

[0037] In contrast, when two consecutive partial prints are performed in different printing directions, for example, when a forward print is followed by a return print, no printhead movement occurs between the two partial prints. For example, in the example in Figure 3, the first partial print is a forward print and the second partial print is a return print, so no printhead movement occurs between the first and second partial prints. From the viewpoint of printing speed, it is preferable that two consecutive partial prints are performed in different printing directions.

[0038] Here, as shown in Figure 2(B), the CMYK nozzle rows NY, NM, NC, and NK on the print head 110 are positioned differently in the printing direction (direction of head movement). Therefore, when forming CMYK dots at the same position on the paper M, the dot formation order differs between the forward and return printing passes. For example, in the example in Figure 2(B), the dots are formed in the order K, C, M, Y during the forward printing pass, and conversely, in the return printing pass, the dots are formed in the order Y, M, C, K. As a result, in areas where multiple colored dots overlap, the order in which the dots overlap differs between the image printed during the forward printing pass (also called the forward print image) and the image printed during the return printing pass (also called the return print image). For this reason, even when using the same dot data, the printed colors may differ between the forward and return print images. This difference in printed color between the forward and return print images will be referred to as inter-return color difference below. If all partial printing is performed in the same direction, for example, if all partial printing is done in the forward direction, no color difference will occur between the forward and reverse directions. Therefore, from the viewpoint of image quality, it is preferable that all partial printing be done in the same direction.

[0039] In this embodiment, as will be explained in detail later, in principle, two consecutive partial prints are performed in different printing directions, but under certain conditions, two consecutive partial prints are performed in the same printing direction. This achieves a balance between printing speed and image quality.

[0040] A-3. Evaluation Table VT Figure 5 is an explanatory diagram of the evaluation table VT (Figure 1). At the top of Figure 5 is the RGB color space CC, which is the color space of the RGB color system containing the three component values ​​of red (R), green (G), and blue (B). Each of the eight vertices of the RGB color space CC is assigned a code indicating the color (specifically, black vertex Vk(0,0,0), red vertex Vr(255,0,0), green vertex Vg(0,255,0), blue vertex Vb(0,0,255), cyan vertex Vc(0,255,255), magenta vertex Vm(255,0,255), yellow vertex Vy(255,255,0), white vertex Vw(255,255,255)). The numbers in parentheses indicate the values ​​of each color component (R, G, B). The R value of each grid GD is one of the Q+1 values ​​obtained by dividing the range of R (here, from 0 to 255) into Q equal parts. The same applies to the green G and blue B values ​​of each grid GD. In this embodiment, since Q=9, 9 to the power of 3 (729) grid GDs are set within the RGB color space CC.

[0041] An example of the evaluation table VT is shown at the bottom of Figure 5. The evaluation table VT shows the correspondence between the color values ​​(also called RGB values) 301 of the RGB color system and the weights 302. Each component value of the RGB value is a 256-level grayscale value. The RGB value 301 represents the RGB values ​​of the multiple grid GDs mentioned above. The weight 302 represents the degree of color difference between the outbound and return printing. The larger the weight 302 corresponding to the RGB value 301, the greater the color difference between the outbound and return printing of the image represented by the RGB value 301. In other words, the larger the weight 302 corresponding to the RGB value 301, the greater the color difference between the color printed when the image represented by the RGB value 301 is printed in the outbound printing and the color printed when the image represented by the RGB value 301 is printed in the return printing.

[0042] For example, the evaluation table VT is created by the printer 200 manufacturer experimentally determining weights 302 corresponding to the RGB values ​​301 of each grid. For example, the first patch is printed by printing a uniform image represented by the RGB values ​​of each grid GD in the forward pass, and the second patch is printed by printing the same image in the return pass. Each patch is a region of uniform color represented by one pixel value. Then, weights 302 are determined according to the color difference between the first and second patches. For example, the weight 302 is determined to be larger the greater the color difference (distance in the CIELab color space) identified from the respective colorimetric values ​​(e.g., color values ​​in the L*a*b* color space) of the two patches.

[0043] For example, white (255,255,255) is not a color represented by dots (it is represented by the background color of paper M), so the weight 302 associated with the white grid GD is 0. Also, for colors represented by a single type of dot, such as the primary colors C, M, Y, and K, there is no overlap of multiple colored dots as described above, so the weight 302 associated with the grid GD of these colors is 0. However, for colors represented by multiple colored dots, there is overlap of multiple colored dots as described above, so the weight 302 associated with the grid GD of these colors can take a value greater than 0.

[0044] A4. Printing Process The CPU 210 of printer 200 (Figure 1) executes the printing process based on a print command from the user. The print command includes specifying image data that indicates the image to be printed. Figure 6 is a flowchart of the printing process.

[0045] In S200, the CPU 210 acquires the image data specified by the print command from the non-volatile storage device 220 as the target image data. In this embodiment, the target image data is RGB image data. RGB image data is bitmap data that includes RGB values ​​for each pixel. If the acquired image data is in a format different from RGB image data, the CPU 210 converts the acquired image data to RGB image data. For example, if the image data is image data described in a page description language or image data in EMF (Enhanced Meta File) format, the CPU 210 performs a rasterization process to convert the image data to RGB image data.

[0046] In S210, CPU210 performs direction determination processing. Direction determination processing determines the printing direction of each of the multiple partial prints for printing the target image represented by the target image data to be either the forward direction D1 or the return direction D2. Details of this process will be described later.

[0047] In S220, the CPU210 performs a color conversion process on the target image data. The color conversion process converts the value of each pixel in the target image from RGB values ​​to CMYK values. CMYK values ​​are color values ​​of the CMYK color system that include component values ​​corresponding to the inks used for printing (in this embodiment, the component values ​​of C, M, Y, and K). The color conversion process is performed, for example, by referring to a known lookup table that defines the correspondence between RGB values ​​and CMYK values.

[0048] In S230, the CPU210 performs halftone processing on the color-converted target image data to generate dot data. The dot data represents the dot formation state for each pixel for each CMYK color component. The value of each pixel in the dot data indicates, for example, a two-tone dot formation state of "no dot" and "with dot," or a four-tone dot formation state of "no dot," "small," "medium," and "large." Halftone processing is performed using known methods such as dithering and error diffusion.

[0049] In S240, the CPU210 generates print data using the generated dot data. The print data includes multiple partial print data for multiple partial prints. Each partial print data includes information representing the printing direction of the partial print (forward direction D1 or return direction D2), dot data for the partial print, and information representing the amount of sheet transported after the partial print.

[0050] In S250, the CPU 210 supplies the generated print data to the printing mechanism 100. The printing mechanism 100 performs multiple partial prints and multiple sheet transports according to the print data. As a result, the print image PI (Figure 3) is printed on the paper M.

[0051] A-5. Direction determination process Figures 7 and 8 are flowcharts of the direction determination process. In S300 of Figure 7, the CPU 210 determines the printing direction of the first partial print to be the forward direction D1. In S305, the CPU 210 selects the next partial print as the partial print of interest.

[0052] In S310, the CPU210 identifies the overlapping area of ​​interest as the area of ​​interest in the RGB image RI indicated by the target image data (RGB image data), specifically the area printed by the area of ​​interest printout and the area printed immediately preceding the area of ​​interest printout (hereinafter referred to as the preceding area printout).

[0053] The RGB image RI, represented by RGB image data, corresponds to the printed image PI in Figure 3. For this reason, Figure 3 can also be said to be a diagram showing the RGB image RI. The RGB image RI contains multiple raster lines RL (e.g., RL1 in Figure 3) that extend in the X direction (corresponding to the printing directions D1 and D2) in Figure 3 and whose positions in the Y direction differ from each other. Each raster line RL is a line that extends in the printing direction in Figure 3 and is composed of multiple pixels. As described above, there is a one-to-one correspondence between each raster line RL of the printed image PI, where dots are formed, and each raster line RL of the RGB image RI, which is composed of pixels. For this reason, in this specification and drawings, the raster lines of the printed image PI and the raster lines of the RGB image RI are denoted by the same reference numerals. Furthermore, in the RGB image RI, the regions corresponding to the overlapping region SA, normal region NA, and partial region RA of the printed image PI are referred to as the overlapping region SA, normal region NA, and partial region RA of the RGB image RI. In an RGB image RI, the direction corresponding to the transport direction AR of the printed image PI is called the transport direction AR in the RGB image RI.

[0054] For example, if the area of ​​interest printing is the second partial print, then the preceding partial print is the first partial print. In this case, the overlapping area SA1 in Figure 3 is identified as the area of ​​interest. If the area of ​​interest printing is the third partial print, then the preceding partial print is the second partial print. In this case, the overlapping area SA2 in Figure 3 is identified as the area of ​​interest.

[0055] In S315, the CPU210 divides the area of ​​interest into multiple block BLs. Specifically, the area of ​​interest is divided into multiple rectangular block BLs arranged in the printing direction (X direction in Figure 3). The length of each block BL in the transport direction AR (Y direction in Figure 3) is the overlapping area length Ha. The overlapping area length Ha is a predetermined length, for example, several tens to several hundred pixels.

[0056] In S320, the CPU210 selects one block of interest from among multiple block BLs in the area of ​​interest. For example, multiple block BLs in the area of ​​interest are selected one by one as blocks of interest, starting from the upstream side in the X direction.

[0057] In S325, the CPU 210 calculates the evaluation value EV of the block of interest. For example, the CPU 210 identifies the weight 302 (Figure 5) corresponding to each pixel in the block of interest by referring to the evaluation table VT (Figure 5). For example, the weight 302 associated with the grid GD closest to the RGB value of a particular pixel is identified as the weight 302 corresponding to that particular pixel. Alternatively, the weight 302 corresponding to the particular pixel may be identified by an interpolation operation using weights 302 associated with multiple grid GDs close to the RGB value of that particular pixel. The CPU 210 calculates the average value of the weights 302 of multiple pixels in the block of interest as the evaluation value EV of the block of interest.

[0058] In S330, CPU210 determines whether the evaluation value EV of the block of interest is greater than or equal to the threshold THv. For example, the threshold THv is experimentally determined so that the evaluation value EV is greater than or equal to the threshold THv when the majority (e.g., 70% or more) of the multiple pixels within the block of interest are color-difference pixels. Color-difference pixels are pixels with a relatively large color difference between the forward and reverse printing paths, as described above. In other words, color-difference pixels are pixels where the difference between the color printed when printed in the forward printing path and the color printed when printed in the reverse printing path is larger compared to pixels that are not color-difference pixels.

[0059] For example, in the example in Figure 3, assume that the hatched areas of objects OBa and OBa are composed of color-different pixels. When the block of interest is block BLa or block BLb, the evaluation value EV is determined to be greater than or equal to the threshold THv because the entirety of blocks BLa and BLb is composed of color-different pixels.

[0060] In the example in Figure 3, the hatched areas of objects OBC and OBC are assumed to be composed of color-different pixels. A gap sp exists between objects OBC and OBC, and since the gap sp is located in block BLc, not the majority of block BLc is composed of color-different pixels. For this reason, when the block of interest is block BLc, the evaluation value EV is judged to be less than the threshold THv. Also in the example in Figure 3, there are no objects in block BLd, and the color of several pixels within block BLd is white. For this reason, when the block of interest is block BLd, the evaluation value EV is judged to be less than the threshold THv. Furthermore, even if an object exists throughout the block of interest, if the color of that object is different from that of the color-different pixels, the evaluation value EV is judged to be less than the threshold THv (not shown). Hereafter, blocks with an evaluation value EV of THv or greater will also be referred to as color-different blocks.

[0061] If the evaluation value EV of the block of interest is greater than or equal to the threshold THv (S330:YES), in S335, the CPU210 sets adjacent blocks UB and DB on the upstream and downstream sides of the block of interest. For example, in the example in Figure 3, if the block of interest is block BLa, the upstream adjacent block UBA and the downstream adjacent block DBa are set. If the block of interest is block BLb, the upstream adjacent block UBb and the downstream adjacent block DBb are set.

[0062] The upstream adjacent block UB is a block adjacent to the upstream side of the block of interest, and the downstream adjacent block DBa is a block adjacent to the downstream side of the block of interest. In other words, the upstream adjacent block UB is a block that is part of the normal area NA3 and is set along the boundary between the normal area NA3 and the overlapping area SA3. Similarly, the downstream adjacent block DBa is a block that is part of the normal area NA4 and is set along the boundary between the normal area NA4 and the overlapping area SA3. In this embodiment, the size (number of pixels in the printing direction and transport direction AR) of the upstream adjacent block UB and the downstream adjacent block DBa is the same as that of the block of interest. The size of the upstream adjacent block UB and the downstream adjacent block DBa may be different from that of the block of interest.

[0063] In S340, CPU210 calculates the evaluation value EV for two adjacent blocks, namely the upstream adjacent block UB and the downstream adjacent block DB. The method for calculating the evaluation value EV is the same as the method described above for the block of interest.

[0064] In S345, the CPU210 determines whether the evaluation value EV of two adjacent blocks is greater than or equal to the threshold THv. In the example in Figure 3, if the block of interest is block BLa, then both the upstream adjacent block UBa and the downstream adjacent block DBa adjacent to block BLa have color difference pixels throughout their entirety, so the evaluation value EV of both adjacent blocks is determined to be greater than or equal to the threshold THv. If the block of interest is block BLb, then both the upstream adjacent block UBb and the downstream adjacent block DBb adjacent to block BLb have color difference pixels throughout their entirety, so the evaluation value EV of both adjacent blocks is determined to be greater than or equal to the threshold THv.

[0065] If the evaluation value EV of both adjacent blocks is greater than or equal to the threshold THv (S345: YES), then in S350, the hue of the color-different pixels in the two adjacent blocks is calculated. For example, in this embodiment, since the evaluation value EV of each adjacent block is greater than or equal to the threshold THv, it is known that most of the pixels in each adjacent block are color-different. For this reason, in this embodiment, the average value of the hues of multiple pixels in the downstream adjacent block DB is calculated as the hue Hd of the color-different pixels in the downstream adjacent block DB. The average value of the hues of multiple pixels in the upstream adjacent block UB is calculated as the hue Hu of the color-different pixels in the upstream adjacent block UB. For example, the CPU 210 converts the RGB values ​​of each pixel in the adjacent block to color values ​​of the HSV color system (also called HSV values). An HSV value includes three component values: an H value indicating hue, an S value indicating saturation, and a V value indicating lightness. The CPU 210 calculates the above-mentioned hues Hu and Hd by calculating the average value of the H values ​​indicating hue.

[0066] In S355, the CPU 210 determines whether the hue difference ΔH between two adjacent blocks is less than or equal to the threshold THh. For example, the absolute value of the difference (Hu-Hd) between the hue Hu of the color-difference pixels in the upstream adjacent block UB and the hue Hd of the color-difference pixels in the downstream adjacent block DB is calculated as the hue difference ΔH, and it is determined whether this hue difference ΔH is less than or equal to a predetermined threshold THh.

[0067] In the example in Figure 3, the color of the color-different pixels in the upstream adjacent block UBa and the color of the color-different pixels in the downstream adjacent block DBa are similar, and the hue difference ΔH between these colors is judged to be less than or equal to the threshold THh. Furthermore, the color of the color-different pixels in the upstream adjacent block UBb and the color of the color-different pixels in the downstream adjacent block DBb are not similar, and the hue difference ΔH between these colors is judged to be greater than the threshold THh.

[0068] If the hue difference ΔH between two adjacent blocks is less than or equal to the threshold THh (S355: YES), in S360, the CPU 210 determines the printing direction of the section of interest to be the same as the printing direction of the previous section of interest. In the example in Figure 3, if the section of interest is block BLa, the hue difference ΔH between the two adjacent blocks UBa and DBa is less than or equal to the threshold THh. For this reason, the printing direction of the section of interest, i.e., the fourth section of interest performed at head position P4, is determined to be the same as the printing direction of the third section of interest performed at head position P3. As a result, as shown in Figure 3, the printing direction of the fourth section of interest is the forward direction D1, just like the printing direction of the third section of interest.

[0069] If the evaluation value EV of the block of interest is less than the threshold THv (S330:NO), if the evaluation value EV of at least one of the two adjacent blocks is less than THv (S345:NO), or if the hue difference ΔH between the two adjacent blocks is greater than the threshold THh (S355:NO), the CPU 210 proceeds to S365.

[0070] In S365, CPU210 determines whether all block BLs within the area of ​​interest have been processed as blocks of interest. If there are any unprocessed block BLs (S365:NO), CPU210 returns to S320 and selects the unprocessed block BLs as blocks of interest.

[0071] If all block BLs within the area of ​​interest have been processed (S365:YES), in S370, the CPU 210 determines the printing direction of the area of ​​interest to be the opposite of the printing direction of the previously printed area.

[0072] In S360 or S370, once the printing direction for the area of ​​interest is determined, the process proceeds to S375. In S375, it is determined whether the printing direction for all areas of interest has been determined. If there are areas of interest for which the printing direction has not yet been determined (S375: NO), the CPU 210 returns to S305 and selects the next area of ​​interest for printing. If the printing direction for all areas of interest has been determined (S375: YES), the CPU 210 terminates the direction determination process.

[0073] As can be seen from the above explanation, the printing direction of the printout

[0074] Condition 1: The evaluation value EV of block BL is greater than or equal to the threshold THv. Condition 2: The evaluation value EV of the upstream adjacent block UB to the upstream side of block BL is greater than or equal to the threshold THv. Condition 3: The evaluation value EV of the downstream adjacent block DB, which is adjacent to block BL, is greater than or equal to the threshold THv. Condition 4: The hue difference ΔH between the upstream adjacent block UB and the downstream adjacent block DB is less than or equal to the threshold THh.

[0075] If the same-direction determination condition is not met, that is, if none of the multiple block BLs within the area of ​​interest satisfy at least one of the above conditions 1 to 4, the printing direction of the area of ​​interest print will be determined to be different from the printing direction of the immediately preceding area print.

[0076] The conditions for determining the same direction will be explained further. Figure 9 is an explanatory diagram for determining the printing direction. Figures 9(A) to 9(F) conceptually illustrate a pattern in which there are multiple color difference objects OB1 to OB8, each consisting of multiple color difference pixels that are identical or similar to each other, in relation to the overlapping region of interest SAt, the normal region NAt upstream of the overlapping region of interest SAt, and the normal region NAp downstream of the overlapping region of interest SAt.

[0077] In the pattern shown in Figure 9(A), the color-difference object OB1 spans the area of ​​interest overlapping region SAt, the upstream normal region NAt, and the downstream normal region NAp. In this case, if the printing direction of the area of ​​interest printing that prints the area of ​​interest overlapping region SAt and the upstream normal region NAt, and the printing direction of the preceding area printing that prints the area of ​​interest overlapping region SAt and the downstream normal region NAp are different directions (opposite directions), the color difference will be more noticeable. This is because when consecutive identical or similar colors are printed as different colors due to the color difference between the two directions, the difference between the color printed in the upstream normal region NAt and the color printed in the downstream normal region NAp will be particularly noticeable. Therefore, in this case, it is preferable that the printing direction of the area of ​​interest printing and the printing direction of the preceding area printing be determined to be the same direction.

[0078] In the pattern shown in Figure 9(B), the color-difference object OB2 spans both the area of ​​interest overlapping SAt and the downstream normal area NAp, but is not present in the upstream normal area NAt. In this case, even if the printing direction of the area of ​​interest print and the printing direction of the preceding area print are different, the color difference is less noticeable compared to the pattern shown in Figure 9(A). Therefore, in this embodiment, it is preferable that the printing direction of the area of ​​interest print and the printing direction of the preceding area print are determined to be different from each other.

[0079] In the pattern shown in Figure 9(C), the color-different object OB3 spans both the area of ​​interest overlapping region SAt and the upstream normal region NAt, but is not present in the downstream normal region NAp. In this case, similar to the pattern shown in Figure 9(B), it is preferable that the printing direction of the area of ​​interest print and the printing direction of the immediately preceding area print are determined to be different from each other.

[0080] In the pattern shown in Figure 9(D), the color-difference object OB4 is present in the overlapping region SAt, but not in the upstream normal region NAt or the downstream normal region NAp. In this case, even if the overlapping region SAt is printed in both the forward and return printing passes, the color of the color-difference object OB4 is considered to be an intermediate color between the color printed in the forward and return printing passes. Therefore, in this case, the color difference between the forward and return passes is not noticeable, and it is preferable that the printing direction of the area of ​​interest print and the printing direction of the preceding area print be determined to be different directions from each other.

[0081] In the pattern shown in Figure 9(E), the color-difference object OB6 spans both the area of ​​interest overlapping region SAt and the upstream normal region NAt. Furthermore, a color-difference object OB5, having the same or similar hue as color-difference object OB6, spans both the area of ​​interest overlapping region SAt and the downstream normal region NAp. A gap sp exists between color-difference objects OB5 and OB6, meaning they are not connected. When color-difference objects OB5 and OB6 are not connected, even if there is a color difference between them due to a back-and-forth color difference, the color difference is less noticeable compared to the case where color-difference objects OB5 and OB6 are connected. In this case, it is preferable that the printing direction of the area of ​​interest print and the printing direction of the immediately preceding area print are determined to be different directions from each other.

[0082] In the pattern shown in Figure 9(F), the color-difference object OB8 spans both the area of ​​interest overlapping region SAt and the upstream normal region NAt. Furthermore, a color-difference object OB7, having a different hue than color-difference object OB8, also spans both the area of ​​interest overlapping region SAt and the downstream normal region NAp. Color-difference objects OB7 and OB8 are connected. Even though color-difference objects OB7 and OB8 are connected, if their hues are different, the color difference between them due to the cross-sectional color difference will not be noticeable. In this case, it is preferable that the printing direction of the area of ​​interest print and the printing direction of the immediately preceding area print are determined to be different directions from each other.

[0083] For each of the patterns described above, conditions for determining the same printing direction, including conditions 1 to 4 mentioned above, have been determined so that the printing direction can be appropriately determined. In the case of the pattern in Figure 9(A), for example, the evaluation value EV of block BL, where the color difference object OB1 exists, is greater than or equal to the threshold THv, so condition 1 is satisfied. In addition, the color difference object OB1 also exists in the downstream adjacent block DB and adjacent block UB adjacent to block BL, which satisfies condition 1. Therefore, the evaluation values ​​EV of these adjacent blocks DB and UB are also greater than or equal to the threshold THv, so conditions 2 and 3 are satisfied. Furthermore, the color of the color difference pixel in the downstream adjacent block DB and the color difference pixel in the upstream adjacent block UB are the same or similar. Therefore, the hue difference ΔH between these adjacent blocks DB and UB is less than or equal to the threshold THh, so condition 4 is satisfied. Thus, in the pattern in Figure 9(A), the printing direction of the area of ​​interest and the printing direction of the immediately preceding area are appropriately determined to be the same direction.

[0084] Thus, when conditions 1 to 3 above are met, there is a high probability that color-difference pixels exist across the boundary between the overlapping region of interest SAt and the downstream normal region NAp, and that color-difference pixels also exist across the boundary between the overlapping region of interest SAt and the upstream normal region NAt.

[0085] In the pattern shown in Figure 9(B), the upstream adjacent block UB, which is adjacent to block BL where the color-different object OB2 exists, does not contain the color-different object OB2. For this reason, in the pattern shown in Figure 9(B), at least condition 2 is not satisfied.

[0086] In the pattern shown in Figure 9(C), the downstream adjacent block DB, which is adjacent to block BL where the color-different object OB3 exists, does not contain the color-different object OB3. For this reason, in the pattern shown in Figure 9(C), at least condition 3 is not met.

[0087] In the pattern shown in Figure 9(D), the color-different object OB4 does not exist in the two adjacent blocks DB and UB that are adjacent to block BL, where the color-different object OB4 exists. For this reason, in the pattern shown in Figure 9(D), at least conditions 2 and 3 are not met.

[0088] In the pattern shown in Figure 9(E), a gap sp exists between the color-different object OB5 and the color-different object OB6. Therefore, in the overlapping region SA, there is no block BL that is mostly composed of color-different pixels. Consequently, in the pattern shown in Figure 9(E), at least condition 1 is not satisfied.

[0089] In the pattern shown in Figure 9(F), in the downstream adjacent block DB of block BL, where color-difference objects OB7 and OB8 exist, only color-difference object OB7 exists, and in the upstream adjacent block UB of block BL, only color-difference object OB8 exists. Since the hues of color-difference object OB7 and color-difference object OB8 are different, the hue difference ΔH between the downstream adjacent block DB and the upstream adjacent block UB is greater than or equal to the threshold THh. Therefore, in the pattern shown in Figure 9(F), at least condition 4 is not satisfied.

[0090] As described above, in the cases of patterns 9(B) to (F), at least one of conditions 1 to 4 is not met. Therefore, in the cases of patterns 9(B) to (F), the printing direction of the area of ​​interest and the printing direction of the preceding area are appropriately determined to be different directions from each other.

[0091] According to the embodiment described above, the CPU 210 performs an image acquisition process to acquire target image data (S200 in Figure 6), a direction determination process to determine the printing direction of each of the multiple partial prints using the target image data, to be either the forward direction D1 or the return direction D2, which are aligned with the direction of head movement (S210 in Figure 6), and a print control process to cause the printing mechanism 100 to print the target image (print image PI) by causing the printing mechanism 100 to execute multiple partial prints using the target image data. The head movement for the multiple partial prints is performed in the direction determined by the direction determination process (Figure 3, etc.). The printed image PI includes a first partial image (e.g., an image within the downstream normal region NAp) printed by a first partial print (e.g., a partial print that prints the overlapping region SAt of interest and the downstream normal region NAp in Figure 9), a second partial image (e.g., an image within the upstream normal region NAt) printed by a second partial print (e.g., a partial print that prints the overlapping region SAt of interest and the upstream normal region NAt in Figure 9), and an intermediate image located between the first and second partial images (e.g., an image within the overlapping region SAt of interest in Figure 9) which is printed by both the first and second partial prints. The direction determination process includes a process to determine whether the same direction determination condition is met (S320-S355 in Figure 7), and if the same direction determination condition is met, the printing direction of the first partial print and the printing direction of the second partial print are determined to be the same direction (S360 in Figure 7), and if the same direction determination condition is not met, the printing direction of the first partial print and the printing direction of the second partial print are determined to be different directions (S370 in Figure 8). The same direction determination condition includes at least the condition that color difference pixels exist across the boundary between the first partial image and the intermediate image, and that color difference pixels exist across the boundary between the second partial image and the intermediate image (conditions 1-3 above, see Figure 9). As a result, in printing where there is an image printed in both the first and second partial prints between the image printed in the first partial print and the image printed in the second partial print, the noticeable difference in color can be suppressed.Furthermore, in printing where there is an image printed in both the first and second parts of the print job, between the image printed in the first part and the image printed in the second part, the decrease in printing speed can be suppressed.

[0092] As shown in the pattern in Figure 9(A), when color-difference pixels exist across the boundary between the image of the overlapping region SAt and the image of the downstream normal region NAp, and also across the boundary between the image of the overlapping region SAt and the image of the upstream normal region NAt, the color difference due to the reciprocal color difference may be noticeable. On the other hand, when the color difference due to the reciprocal color difference is not noticeable, it is preferable to print in both directions from the viewpoint of printing speed. According to the above embodiment, when the color difference due to the reciprocal color difference may be noticeable, the printing direction of the first partial print and the printing direction of the second partial print can be determined to be the same direction. Also, when the color difference due to the reciprocal color difference is not noticeable, the printing direction of the first partial print and the printing direction of the second partial print can be determined to be opposite directions. Therefore, it is possible to appropriately suppress the noticeable color difference due to the reciprocal color difference and the reduction in printing speed.

[0093] As explained with reference to Figure 9(E), if the color-difference object OB5 and the color-difference object OB6 are not connected in the overlapping region SAt of interest, then the majority of the overlapping region SAt of interest will not be occupied by color-difference pixels, and therefore condition 2 is not satisfied. Thus, the same-direction determination condition can be said to be a condition that indicates that a region composed of color-difference pixels existing across the boundary between the downstream normal region NAp and the overlapping region SAt of interest (e.g., a color-difference object) is connected to a region composed of color-difference pixels existing across the boundary between the upstream normal region NAt and the overlapping region SAt of interest (e.g., a color-difference object). In this embodiment, the same-direction determination condition includes such condition 2 as a necessary condition. Including such a condition allows for a more precise determination of whether or not the color difference is noticeable. As a result, it is possible to more appropriately suppress the noticeableness of color differences caused by the color difference between the front and back lines, and to suppress the reduction in printing speed. For example, it is possible to suppress the reduction in printing speed caused by repeated partial printing in the same direction, even if the color difference is not noticeable.

[0094] Furthermore, as explained with reference to Figure 9(F), when the hue difference ΔH between the hue of a color-difference pixel existing across the boundary between the downstream normal area NAp and the area of ​​interest SAt (e.g., the hue of color-difference object OB7) and the hue of a color-difference pixel existing across the boundary between the upstream normal area NAt and the area of ​​interest SAt (e.g., the hue of color-difference object OB8) is large, the color difference caused by the color difference between the two directions is less noticeable. In this embodiment, the same-direction determination condition includes as a necessary condition condition 4 that the hue difference ΔH is less than or equal to the threshold THh. Including such a condition allows for a more precise determination of whether or not the color difference is noticeable. As a result, it is possible to more appropriately suppress the visibility of color differences caused by the color difference between the two directions and to suppress the reduction in printing speed. For example, it is possible to suppress the reduction in printing speed caused by repeated partial printing in the same direction, even if the color difference is not noticeable.

[0095] Furthermore, in this embodiment, the same-direction determination condition is determined using three determination regions (target block BL, upstream adjacent block UB, and downstream adjacent block DB). Specifically, the same-direction determination condition includes condition 3, which indicates that multiple color-different pixels exist in the downstream adjacent block DB set within the downstream normal region NAp; condition 2, which indicates that multiple color-different pixels exist in the upstream adjacent block UB set within the upstream normal region NAt; and condition 1, which indicates that multiple color-different pixels exist in the target overlap region SAt. In this way, since the same-direction determination condition is determined using three determination regions, it is possible to appropriately determine whether color-different pixels exist across the boundary between the downstream normal region NAp and the target overlap region SAt, and whether color-different pixels exist across the boundary between the upstream normal region NAt and the target overlap region SAt.

[0096] Furthermore, in this embodiment, the downstream adjacent block DB of the three determination regions is a part of the downstream normal region NAp and is set along the boundary between the downstream normal region NAp and the area of ​​interest overlapping region SAt (Figure 3). The upstream adjacent block UB of the three determination regions is a part of the upstream normal region NAt and is set along the boundary between the upstream normal region NAt and the area of ​​interest overlapping region SAt (Figure 3). By setting the downstream adjacent block DB and the upstream adjacent block UB as determination regions in this way, it is possible to more appropriately determine whether color difference pixels exist across the boundary between the downstream normal region NAp and the area of ​​interest overlapping region SAt, and whether color difference pixels exist across the boundary between the upstream normal region NAt and the area of ​​interest overlapping region SAt.

[0097] Furthermore, according to this embodiment, as shown in Figure 4, the recording rate of the overlapping region SA changes depending on the position AR in the transport direction. Specifically, the recording rate for printing the overlapping region SAt of interest by partial printing that prints the downstream normal region NAp increases as it approaches the downstream normal region NAp, and the recording rate for printing the overlapping region SAt of interest by partial printing that prints the upstream normal region NAt also increases as it approaches the upstream normal region NAt. As a result, even when the color difference between the two directions is relatively large, the color in the overlapping region SAt of interest changes in steps depending on the position AR in the transport direction. Therefore, it is possible to suppress abrupt changes in color depending on the position AR in the transport direction and suppress the visibility of banding caused by the color difference between the two directions.

[0098] B. Second Example In the second embodiment, the printer 200 can perform printing in two types of printing modes: a first printing mode and a second printing mode. In the first printing mode, the overlapping area length Ha, which is the length of the transport direction AR of the overlapping area SA, is set to a first length Ha1. In the second printing mode, the overlapping area length Ha is set to a second length Ha2, which is shorter than the first length Ha1.

[0099] The longer the overlapping region length Ha, the greater the distance between the downstream normal region NAp and the upstream normal region NAt. The greater the distance between the downstream normal region NAp and the upstream normal region NAt, the more difficult it becomes to perceive the difference in color between the downstream normal region NAp and the upstream normal region NAt. For this reason, the longer the overlapping region length Ha, the less noticeable the color difference caused by the color difference between the two directions is, and the shorter the overlapping region length Ha, the more noticeable the color difference caused by the color difference between the two directions is. In view of this, in the second embodiment, the method for determining the printing direction is changed between the first printing mode and the second printing mode.

[0100] Figure 10 is a flowchart of the print direction determination process in the second embodiment. In S400, the CPU 210 determines whether the print mode is the first print mode or the second print mode. The print mode is set, for example, based on instructions entered by the user. Alternatively, the print mode may be set based on the type of printing medium (material and size).

[0101] If the print mode is the first print mode (S400:YES), in S410, the CPU 210 determines the printing direction for multiple partial prints so that forward printing and return printing are performed alternately, regardless of the type of image the target image (RGB image RI, print image PI) is.

[0102] If the print mode is the second print mode (S400:NO), in S420, the CPU 210 executes the direction determination process of the first embodiment (S300 to S375 in Figures 7 and 8).

[0103] In the second embodiment, the configuration of the part that differs from the direction determination process is the same as in the first embodiment, so its explanation will be omitted.

[0104] According to the second embodiment described above, in the second printing mode, compared to the first printing mode, the printing direction of one partial print and the printing direction of the next partial print are more likely to be determined in the same direction. As mentioned above, the shorter the length of the transport direction AR of the overlapping region SA, the more noticeable the color difference caused by the color difference between the two directions becomes, so there is a high need to make the printing direction of one partial print and the printing direction of the next partial print the same direction. According to the second embodiment, the printing direction of the partial print can be appropriately determined according to the overlapping region length Ha. Therefore, it is possible to more appropriately achieve both the suppression of noticeable color differences caused by the color difference between the two directions and the suppression of a decrease in printing speed.

[0105] More specifically, in the second embodiment, the same direction determination process as in the first embodiment is performed in the second printing mode (S420 in Figure 10), and in the first printing mode, unlike in the first embodiment, the printing direction of one partial print and the printing direction of the next partial print are always determined to be different directions (opposite directions), regardless of whether the target image satisfies the same direction determination conditions (S410 in Figure 10). As a result, the printing direction can be appropriately determined according to the printing mode, thus achieving a better balance between suppressing noticeable color differences caused by color differences between the front and back prints and suppressing a decrease in printing speed.

[0106] C. Third Example A third embodiment describes another example in which the method for determining the printing direction is changed between the first and second printing modes.

[0107] Figure 11 is a flowchart of the print direction determination process in the third embodiment. In S500, the CPU 210 determines whether the print mode is the first print mode or the second print mode.

[0108] If the print mode is the first print mode (S500:YES), in S510, the CPU 210 determines the judgment threshold THv to be the first threshold THv1. If the print mode is the second print mode (S500:NO), in S520, the CPU 210 determines the judgment threshold THv to be the second threshold THv2, which is smaller than the first threshold THv1.

[0109] In S530, the CPU 210 executes the direction determination process of the first embodiment (S300 to S375 in Figures 7 and 8). At this time, different values ​​are used for the threshold THv used in S330 and S355 in Figure 7, depending on the printing mode. Specifically, in the first printing mode, the first threshold THv1 determined in S510 is used, and in the second printing mode, the second threshold THv2 determined in S520 is used.

[0110] In the second embodiment, the configuration of the part that differs from the direction determination process is the same as in the first embodiment, so its explanation will be omitted.

[0111] According to the third embodiment described above, in the second printing mode, compared to the first printing mode, the printing direction of one partial print and the printing direction of the next partial print are more likely to be determined in the same direction. Therefore, it is possible to more appropriately achieve both the suppression of noticeable color differences due to color differences between the two print jobs and the suppression of a decrease in printing speed.

[0112] In the third embodiment, in the first printing mode, the printing direction is determined using a first specific condition (specifically, a condition determined using a first threshold THv1) as the same-direction determination condition. In the second printing mode, the printing direction is determined using a second specific condition (specifically, a condition determined using a second threshold THv2) that is more easily satisfied than the first specific condition. As a result, in the second printing mode, compared to the first printing mode, the printing direction of one partial print and the printing direction of the next partial print are more likely to be determined in the same direction. Therefore, since the printing direction can be appropriately determined using different specific conditions depending on the printing mode, it is possible to more appropriately achieve both the suppression of noticeable color differences and the suppression of a decrease in printing speed.

[0113] More specifically, the first threshold THv1 used in the first specific condition is a larger threshold than the second threshold THv2 used in the second specific condition. The larger the threshold THv, the larger the evaluation value EV of the block being judged is allowed to be. In other words, even if the evaluation value EV of a block is relatively large, it is difficult to determine that the evaluation value EV is less than or equal to the threshold THv. The evaluation value EV is an index value that increases as the number of color-different pixels present in the block increases. For this reason, when the first threshold THv1 is used, the number of color-different pixels in the judgment block that are allowed to be determined in order for the printing direction of the area of ​​interest to be determined to be in the opposite direction to the printing direction of the preceding area of ​​interest is greater than when the second threshold THv2 is used. In this way, by adjusting the threshold THv used in the same-direction determination condition according to the printing mode, the same-direction determination condition can be appropriately set according to the printing mode. Thus, the first threshold THv1 is adjusted to a greater extent than the second threshold THv2 to allow the presence of color-different pixels in at least one of the overlapping area of ​​interest and the normal areas upstream and downstream of the overlapping area of ​​interest.

[0114] D. Variations (1) The conditions for determining the same direction in the above embodiment are the conditions consisting of conditions 1 to 4 described above. However, the conditions for determining the same direction are not limited to these, and various conditions may be used. For example, the conditions for determining the same direction may be that the following two conditions are satisfied. Condition A: There are a predetermined number or more color-different pixels in the raster line at the upstream end of the overlapping region SAt and in the raster line at the downstream end of the normal region NAt on the upstream side. Condition B: There are a predetermined number or more color-different pixels in the raster line at the downstream end of the overlapping region SAt and in the raster line at the upstream end of the normal region NAp on the downstream side.

[0115] Whether or not a pixel has a different color is determined, for example, by whether the weight 302 corresponding to the RGB value of the pixel is above a predetermined threshold.

[0116] In addition to conditions A and B, the condition may also include the existence of multiple color-different pixels connected from the raster line at the upstream end of the overlapping region SAt to the raster line at the downstream end of the overlapping region SAt.

[0117] (2) In the same direction determination conditions of the first embodiment, condition 4 may be omitted. Also, condition 1 may be that the number of color-different pixels included in block BL is greater than or equal to a threshold. Similarly, conditions 2 and 3 may be that the number of color-different pixels included in the upstream adjacent block UB or the downstream adjacent block DB is greater than or equal to a threshold. Also, condition 4 may be, for example, that the hue difference between the hue of a color-different pixel located on the raster line at the upstream end of the overlapping region of interest SAt and the hue of a color-different pixel located on the raster line at the downstream end of the overlapping region of interest SAt is less than or equal to a threshold.

[0118] (3) The weight 302 described in Figure 5 may be a value that indicates the magnitude of the difference in various color values ​​representing the printed color, not limited to the magnitude of the difference in color measurement values. For example, a patch printed by partial printing in the forward direction D1 and a patch printed by partial printing in the return direction D2 may be photographed using a digital camera. The value that indicates the magnitude of the difference in RGB values ​​(for example, the Euclidean distance between RGB values) of the two patch images obtained by the photography may be adopted as the weight 302. Such a weight 302 may be the same as the difference in color values, or it may be a value that is pre-associated with the difference in color values. Thus, the weight 302 may be various values ​​that correlate with the difference in color values. In any case, it is preferable that the weight 302 is larger the greater the difference in color values.

[0119] (4) The configuration of the printing mechanism 100 may be any other configuration in addition to the above configuration. For example, in the printing mechanism 100 of the above embodiment, the transport unit 140 transports the paper M, thereby moving the paper M relative to the print head 110 in the transport direction. Alternatively, the print head 110 may be moved in the opposite direction to the transport direction AR relative to the print head 110, thereby moving the paper M relative to the transport direction AR with respect to the fixed paper M.

[0120] Furthermore, the total number of inks (more generally, colorants) available to the printing mechanism 100 can be any number of two or more. For example, three types of inks may be available: cyan (C), magenta (M), and yellow (Y).

[0121] (5) The format of the target image data may be any format other than the bitmap format in the RGB color space. For example, the target image data in bitmap format in the YCbCr color space may be used for printing. In this way, the pixel values ​​used for printing may be pixel values ​​expressed in any color space other than the RGB pixel values, such as YCbCr pixel values.

[0122] (6) In place of paper M, other media such as film for OHP, CD-ROM, or DVD-ROM may be used as the printing medium.

[0123] (7) In each of the above embodiments, the device that performs the printing process shown in Figure 6 is the printer 200. Alternatively, a terminal device such as a personal computer connected to the printer 200 may perform the printing process shown in Figure 6. In this case, the CPU of the terminal device performs the printing process shown in Figure 6, for example, by executing a printer driver program.

[0124] Furthermore, the device that performs the printing process in Figure 6 may be, for example, a server that acquires image data from a printer or terminal device and generates print data using said image data. Such a server may be a group of computers that can communicate with each other via a network.

[0125] (8) In each of the above embodiments, some of the configurations implemented by hardware may be replaced with software, and conversely, some or all of the configurations implemented by software may be replaced with hardware. For example, when the printing process in Figure 6 is performed on the printer 200, the halftone processing and color conversion processing may be implemented, for example, by a dedicated hardware circuit (e.g., ASIC) that operates according to instructions from the CPU 210 of the printer 200.

[0126] The present invention has been described above based on examples and modifications. However, the embodiments of the invention described above are for the purpose of facilitating understanding of the present invention and do not limit it. The present invention can be modified and improved without departing from its spirit and claims, and the present invention includes equivalents thereof. [Explanation of Symbols]

[0127] 100…Printing mechanism, 110…Print head, 120…Head drive unit, 130…Head movement unit, 133…Carriage, 134…Sliding shaft, 140…Conveyor unit, 141…Downstream roller pair, 142…Upstream roller pair, 145…Paper tray, 200…Printer, 210…CPU, 220…Non-volatile memory device, 230…Volatile memory device, 231…Buffer area, 260…Operation unit, 270…Display unit, 280…Communication unit, CP…Computer program, M…Paper, NA…Normal area, NZ…Nozzle

Claims

1. A printing execution unit comprising a print head having a first type nozzle for ejecting a first type of ink and a second type nozzle for ejecting a second type of ink, the print execution unit performing printing by repeatedly executing: partial printing, in which the print head forms dots on the printing medium while performing head movement, in which the print head is moved in either the first direction or the second direction opposite to the first direction relative to the printing medium; and medium movement, in which the printing medium is moved in a medium movement direction intersecting the first direction relative to the print head; and an image processing apparatus for the printing execution unit, Image acquisition process to obtain target image data that represents the target image, A direction determination process that determines the direction of the head movement for each of the multiple partial prints, including a first partial print and a second partial print performed after the first partial print, using target image data representing the target image, to be either the first direction or the second direction. A print control process that causes the print execution unit to print the target image by performing multiple partial prints using the target image data, wherein the head movement for the multiple partial prints is performed in a direction determined by the direction determination process, and the print control process is such that Execute, The target image includes a first partial image printed by the first partial printing, a second partial image printed by the second partial printing, and an intermediate image located between the first partial image and the second partial image, which is printed by both the first partial printing and the second partial printing. The aforementioned direction determination process is, A process for determining whether a specific condition is met, which includes at least a first condition indicating that color-difference pixels exist across the boundary between the first partial image and the intermediate image, and that color-difference pixels exist across the boundary between the second partial image and the intermediate image, The process involves determining the direction of head movement for the first partial printing and the direction of head movement for the second partial printing to be the same direction when the aforementioned specific conditions are met, and determining the direction of head movement for the first partial printing and the direction of head movement for the second partial printing to be different directions when the aforementioned specific conditions are not met. Includes, An image processing apparatus wherein the color difference pixel is a pixel in which the difference between the color printed when printed by the partial printing in the first direction and the color printed when printed by the partial printing in the second direction is greater than that of a different pixel.

2. An image processing apparatus according to claim 1, The aforementioned specific condition includes a second condition indicating that a region composed of color-difference pixels existing across the boundary between the first partial image and the intermediate image is connected to a region composed of color-difference pixels existing across the boundary between the second partial image and the intermediate image. An image processing apparatus in which it is determined that the specific condition is met when the first condition and the second condition are met.

3. An image processing apparatus according to claim 1 or 2, The aforementioned specific condition includes a third condition indicating that the hue difference between the hue of the color-difference pixel existing across the boundary between the first partial image and the intermediate image and the hue of the color-difference pixel existing across the boundary between the second partial image and the intermediate image is below a certain standard. An image processing apparatus in which the specific condition is determined to be met when the first condition and the third condition are met.

4. An image processing apparatus according to claim 1 or 2, A first printing mode is possible in which the length of the intermediate image in the media movement direction is set to a first length, and a second printing mode is possible in which the length of the intermediate image in the media movement direction is set to a second length that is shorter than the first length. An image processing apparatus wherein, in the second printing mode, compared to the first printing mode, the direction of head movement for the first partial printing and the direction of head movement for the second partial printing are more likely to be determined in the same direction.

5. An image processing apparatus according to claim 4, In the second printing mode, the direction determination process is executed, Image processing apparatus, in the first printing mode, performs a process different from the direction determination process, which determines the direction of head movement for the first partial printing and the direction of head movement for the second partial printing to be in different directions from each other, regardless of whether the specific conditions are met.

6. An image processing apparatus according to claim 4, The aforementioned specific condition includes a first specific condition determined using a first threshold and a second specific condition determined using a second threshold. In the first printing mode, the direction of the head movement is determined using the first specific condition, In the second printing mode, the direction of the head movement is determined using the second specific condition. An image processing apparatus in which the first threshold is adjusted to a greater extent than the second threshold to allow the presence of the color difference pixels in at least one of the first partial image, the intermediate image, and the second partial image.

7. An image processing apparatus according to any one of claims 1 to 6, The recording rate for printing the intermediate image by the first partial printing increases as it approaches the first partial image. An image processing apparatus wherein the recording rate for printing the intermediate image by the second partial printing increases as it approaches the second partial image.

8. An image processing apparatus according to any one of claims 1 to 7, The first condition includes a condition indicating that a plurality of color-different pixels exist within a first determination region set in the first partial image, a condition indicating that a plurality of color-different pixels exist within a second determination region set in the second partial image, and a condition indicating that a plurality of color-different pixels exist within an intermediate determination region set in the intermediate image, in an image processing apparatus.

9. An image processing apparatus according to claim 8, The first determination region is a part of the first partial image and is a region set along the boundary between the first partial image and the intermediate image. The image processing apparatus wherein the second determination region is a part of the second partial image and is set along the boundary between the second partial image and the intermediate image.

10. A printing execution unit comprising a print head having a first type nozzle for ejecting a first type of ink and a second type nozzle for ejecting a second type of ink, the print execution unit performing printing by repeatedly executing head movement, which moves the print head in either the first direction or the second direction opposite to the first direction with respect to the printing medium, and partial printing, which moves the printing medium in a medium movement direction intersecting the first direction with respect to the print head, and a computer program for the printing execution unit, wherein printing is performed by repeatedly executing: head movement, which moves the print head in either the first direction or the second direction opposite to the first direction with respect to the printing medium; and medium movement, which moves the printing medium in a medium movement direction intersecting the first direction with respect to the print head. An image acquisition function that obtains target image data that represents the target image, A direction determination function that determines the direction of the head movement for each of the multiple partial prints, including a first partial print and a second partial print performed after the first partial print, using target image data representing the target image, to be either the first direction or the second direction. A print control function that causes the print execution unit to print the target image by performing multiple partial prints using the target image data, wherein the head movement for the multiple partial prints is performed in a direction determined by the direction determination function, and the print control function To make this a reality on a computer, The target image includes a first partial image printed by the first partial printing, a second partial image printed by the second partial printing, and an intermediate image located between the first partial image and the second partial image, which is printed by both the first partial printing and the second partial printing. The aforementioned direction determination function is, A function for determining whether a specific condition is met, which includes at least a first condition indicating that color-difference pixels exist across the boundary between the first partial image and the intermediate image, and that color-difference pixels exist across the boundary between the second partial image and the intermediate image, A function that, when the aforementioned specific conditions are met, determines the direction of the head movement for the first partial printing and the direction of the head movement for the second partial printing to be the same direction, and when the aforementioned specific conditions are not met, determines the direction of the head movement for the first partial printing and the direction of the head movement for the second partial printing to be different directions from each other. Includes, A computer program in which the color difference pixel is a pixel in which the difference between the color printed when printed by the partial printing in the first direction and the color printed when printed by the partial printing in the second direction is greater than that of a different pixel.

11. A printing execution unit comprising a print head having a first type nozzle for ejecting a first type of ink and a second type nozzle for ejecting a second type of ink, the second nozzle being positioned differently from the first type nozzle in the first direction, the printing execution unit comprising repeatedly performing partial printing, in which the print head forms dots on the printing medium while performing head movement, in which the print head is moved in either the first direction or the second direction opposite to the first direction relative to the printing medium, and media movement, in which the printing medium is moved in a media movement direction intersecting the first direction relative to the print head, the method for the printing execution unit, The image acquisition process involves obtaining target image data that represents the target image, A direction determination step in which, using target image data representing the target image, the direction of the head movement for each of the multiple partial prints, including a first partial print and a second partial print performed after the first partial print, is determined to be either the first direction or the second direction. A print control step in which the print execution unit prints the target image by having the print execution unit perform multiple partial prints using the target image data, wherein the head movement for the multiple partial prints is performed in a direction determined by the direction determination step, Equipped with, The target image includes a first partial image printed by the first partial printing, a second partial image printed by the second partial printing, and an intermediate image located between the first partial image and the second partial image, which is printed by both the first partial printing and the second partial printing. The aforementioned direction determination step is, A step of determining whether a specific condition is met, which includes at least a first condition indicating that a color-different pixel exists across the boundary between the first partial image and the intermediate image, and that the color-different pixel exists across the boundary between the second partial image and the intermediate image, The process includes determining the direction of head movement for the first partial printing and the direction of head movement for the second partial printing to be the same direction when the aforementioned specific conditions are met, and determining the direction of head movement for the first partial printing and the direction of head movement for the second partial printing to be different directions when the aforementioned specific conditions are not met. Includes, A method in which the color difference pixel is a pixel in which the difference between the color printed when printed by the partial printing in the first direction and the color printed when printed by the partial printing in the second direction is greater than that of a different pixel.

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