Image processing apparatus, printing apparatus, and image processing method

Abstract

To provide a technique contributing to an improvement in graininess in accordance with the resolution ratio of an image.SOLUTION: The total sum obtained by multiplying allocation ratios set to allocation destination pixels by a relative position in a first direction with reference to a conversion target pixel in the allocation destination pixels is defined as the first direction total sum, and the first direction total sum is not 0. The total sum obtained by multiplying the allocation ratios set to the allocation destination pixels by a relative position in a second direction with reference to the conversion target pixel in the allocation destination pixels is defined as the second direction total sum, and the second direction total sum is not 0. The ratio of the second direction total sum to the first direction total sum is defined as a total sum ratio. The ratio of second direction resolution to first direction resolution is defined as a resolution ratio. The total sum ratio when the resolution ratio is a first resolution ratio is defined as a first total sum ratio. The total sum ratio when the resolution ratio is a second resolution ratio larger than the first resolution ratio is defined as a second total sum ratio. The allocation ratios are set to the allocation destination pixels so that the second total sum ratio becomes larger than the first total sum ratio.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image processing apparatus, a printing apparatus, and an image processing method capable of performing halftone processing by error diffusion. [Background technology]

[0002] Image processing devices are known that perform halftone processing, which generates dot data representing the dot formation state by reducing the number of gradations in multi-gradation image data in order to form a print image. Halftone processing by error diffusion is known as a method that can obtain high-quality output. Patent Document 1 discloses an image processing device that performs halftone processing by error diffusion. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-137019 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Printed images may have different horizontal and vertical resolutions. In this case, when halftone processing is performed using the error diffusion method, the dot placement may be uneven, which can manifest as a decrease in granularity, especially in the low-tone areas of the image. Thus, there is room for improvement in granularity when performing halftone processing using the error diffusion method. [Means for solving the problem]

[0005] The present invention is an image processing apparatus capable of converting image data in which a first-direction resolution in a first direction and a second-direction resolution in a second direction intersecting the first direction are set into dot data representing the dot formation state by error diffusion method, A conversion unit that determines the dot formation state based on the pixel value and the allocated error in a pixel to be converted that is included in a plurality of pixels constituting the image data, The system includes a diffusion unit that diffuses the error generated in the target pixel to be converted to a plurality of destination pixels that have not been converted, according to the allocation ratio set for each of the destination pixels. The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the first direction with respect to the conversion target pixel is defined as the sum in the first direction, and the sum in the first direction is not 0. The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the second direction with respect to the conversion target pixel is defined as the second-direction sum, and the second-direction sum is not 0, The ratio of the sum in the second direction to the sum in the first direction is defined as the sum ratio. The ratio of the second-direction resolution to the first-direction resolution is defined as the resolution ratio. When the resolution ratio is the first resolution ratio, the sum ratio is defined as the first sum ratio. When the resolution ratio is a second resolution ratio which is greater than the first resolution ratio, the summation ratio is taken as the second summation ratio. Each of the aforementioned allocation ratios has an embodiment in which the allocation destination pixels are set such that the second summation ratio is greater than the first summation ratio.

[0006] Furthermore, the printing apparatus of the present invention is The image processing apparatus and, The present invention includes a printing unit that forms a printed image on a medium according to the dot data, the printed image having the resolution in the first direction and the resolution in the second direction.

[0007] Furthermore, the present invention is an image processing method that converts image data in which a first-direction resolution in a first direction and a second-direction resolution in a second direction intersecting the first direction are set into dot data representing the dot formation state by error diffusion method, In the conversion target pixels included in the plurality of pixels constituting the image data, a conversion step of determining the formation state of the dot based on the pixel value and the allocated error; A diffusion step of diffusing the error generated in the conversion target pixel to the plurality of distribution destination pixels according to the distribution ratio set for each of the plurality of distribution destination pixels that are not yet converted; For the distribution ratio set for each of the distribution destination pixels, the sum of multiplying the relative position in the first direction with respect to the conversion target pixel of the distribution destination pixel is defined as the first direction sum, and the first direction sum is not zero. For the distribution ratio set for each of the distribution destination pixels, the sum of multiplying the relative position in the second direction with respect to the conversion target pixel of the distribution destination pixel is defined as the second direction sum, and the second direction sum is not zero. The ratio of the second direction sum to the first direction sum is defined as the sum ratio. The ratio of the second direction resolution to the first direction resolution is defined as the resolution ratio. The sum ratio when the resolution ratio is the first resolution ratio is defined as the first sum ratio. The sum ratio when the resolution ratio is a second resolution ratio greater than the first resolution ratio is defined as the second sum ratio. Each of the distribution ratios is set for the distribution destination pixel such that the second sum ratio is greater than the first sum ratio.

Brief Description of the Drawings

[0008] [Figure 1] A diagram schematically showing an example of an image processing apparatus. [Figure 2] A diagram schematically showing an example of a nozzle surface of a print head and a dot pattern on a medium. [Figure 3] A diagram schematically showing an example of halftone processing by the error diffusion method. [Figure 4] A diagram schematically showing an example of the resolution of a printed image. [Figure 5] A diagram schematically showing an example of a distribution ratio table according to the resolution ratio. [Figure 6]A diagram schematically showing an example of adjusting the angle θs calculated from the distribution ratio table to the angle θr based on the resolution ratio Ry / Rx. [Figure 7] A diagram schematically showing an example of adjusting the angle θs calculated from the distribution ratio table to the angle θr based on the resolution ratio Ry / Rx. [Figure 8] A flowchart schematically showing an example of a print control process. [Figure 9] A flowchart schematically showing an example of a halftone process. [Figure 10] A diagram schematically showing an example in which dots are arranged so as to be evenly dispersed by bringing the total ratio calculated from the distribution ratio closer to the resolution ratio. [Figure 11] A flowchart schematically showing another example of a print control process. [Mode for Carrying Out the Invention]

[0009] Hereinafter, embodiments of the present invention will be described. Of course, the following embodiments are merely illustrative of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution means of the invention.

[0010] (1) Outline of the technology included in the present invention: First, the outline of the technology included in the present invention will be described with reference to the examples shown in FIGS. 1 to 11. Note that the drawings of the present application are diagrams schematically showing examples, and the magnification ratios in each direction shown in these drawings may be different, and the drawings may not be consistent. Of course, each element of the present technology is not limited to the specific examples indicated by the reference numerals. In the "outline of the technology included in the present invention", the content in parentheses means a supplementary explanation of the immediately preceding word.

[0011] [Aspect 1] As illustrated in Figures 1, 3, and 9, an image processing apparatus U0 according to one aspect of the present technology is an image processing apparatus U0 capable of converting image data (e.g., ink amount data DA2) in which a first-direction resolution (e.g., resolution Rx) in a first direction (e.g., X direction) and a second-direction resolution (e.g., resolution Ry) in a second direction (e.g., Y direction) intersecting the first direction is set into dot data DA3 representing the formation state of dots 38 by an error diffusion method, and comprises a conversion unit U1 and a diffusion unit U2. The conversion unit U1 determines the formation state of the dots 38 in a target pixel P0 included in a plurality of pixels PX0 constituting the image data (DA2) based on the pixel value MP0 and the allocated error EP0. The diffusion unit U2 diffuses the error E0 generated in the target pixel P0 to a plurality of destination pixels Qi according to the allocation ratio Ri set for each of the unconverted destination pixels Qi. Here, as illustrated in Figures 4 and 5, the first-direction sum (e.g., sum Sx) is a non-zero sum obtained by multiplying the allocation ratio Ri set for each allocation destination pixel Qi by the relative position (e.g., Δxi) of the allocation destination pixel Qi in the first direction with respect to the conversion target pixel P0, and the second-direction sum (e.g., sum Sy) is a non-zero sum obtained by multiplying the allocation ratio Ri set for each allocation destination pixel Qi by the relative position (e.g., Δyi) of the allocation destination pixel Qi in the second direction with respect to the conversion target pixel P0. The ratio of the second directional sum (Sy) to the first directional sum (Sx) is defined as the sum ratio (e.g., Sy / Sx), the ratio of the second directional resolution (Ry) to the first directional resolution (Rx) is defined as the resolution ratio (e.g., Ry / Rx), the sum ratio (Sy / Sx) when the resolution ratio (Ry / Rx) is the first resolution ratio RR1 is defined as the first sum ratio SR1, and the sum ratio (Sy / Sx) when the resolution ratio (Ry / Rx) is a second resolution ratio RR2 which is greater than the first resolution ratio RR1 is defined as the second sum ratio SR2. Each allocation ratio Ri is set to the destination pixel Qi such that the second sum ratio SR2 is greater than the first sum ratio SR1.

[0012] Based on the above, dot data DA3 is generated in which the dots 38 are arranged to be more evenly distributed according to the image resolution ratio (Ry / Rx). Therefore, the above embodiment can provide an image processing device that contributes to improving granularity in accordance with the image resolution ratio.

[0013] Here, "first," "second," ... in this application are terms used to identify each component included in a group of similar components, and do not imply any order. Which component among the group of components corresponds to "first," "second," ... is determined relatively. For example, if multiple pixels of image data are arranged in the X and Y directions, when the X direction is fitted to the first direction, the Y direction is fitted to the second direction, and when the Y direction is fitted to the first direction, the X direction is fitted to the second direction. The dot data can be binary data indicating whether or not a dot is formed, or it can be triple or multi-value data including the size of the dot. Furthermore, the above-mentioned supplementary statement also applies in the following embodiments.

[0014] [Aspect 2] As illustrated in Figures 5-7, each allocation ratio Ri may be set to the destination pixel Qi such that the sum ratio (Sy / Sx) matches the resolution ratio (Ry / Rx). In the above case, the dots 38 are arranged to be further evenly distributed according to the image resolution ratio (Ry / Rx). Therefore, the above embodiment can provide a suitable example for improving image quality in terms of granularity.

[0015] [Aspect 3] As illustrated in Figure 3, the image data (DA2) may have at least the pixel values ​​of cyan, magenta, and yellow for each of the pixels PX0. As illustrated in Figure 11, the image processing device may convert the image data (DA2) to the dot data DA3 by the error diffusion method when at least one of the cyan and magenta dots 38 is formed with the yellow background. When cyan and magenta dots 38 are sparsely formed against a yellow background, an uneven distribution of these dots 38 can create an unnatural appearance. In the above embodiment, when cyan and magenta dots 38 are formed against a yellow background, they are arranged to be more evenly distributed according to the image resolution ratio (Ry / Rx), thereby improving the image quality of the output image.

[0016] [Aspect 4] As illustrated in Figure 5, if the first-direction resolution (Rx) is greater than the second-direction resolution (Ry), the range in which the multiple destination pixels Qi are arranged in the first direction may be wider than the range in which the multiple destination pixels Qi are arranged in the second direction. If the second-direction resolution (Ry) is greater than the first-direction resolution (Rx), the range in which the multiple destination pixels Qi are arranged in the second direction may be wider than the range in which the multiple destination pixels Qi are arranged in the first direction. When the resolution in the first direction (Rx) is greater than the resolution in the second direction (Ry), the area in which multiple destination pixels Qi are located in the first direction is wider than the area in which multiple destination pixels Qi are located in the second direction, resulting in a wider area of ​​error diffusion in the first direction than in the second direction. This allows the dots 38 to be distributed more evenly according to the image resolution ratio (Ry / Rx). On the other hand, when the resolution in the second direction (Ry) is greater than the resolution in the first direction (Rx), the area in which multiple destination pixels Qi are located in the second direction is wider than the area in which multiple destination pixels Qi are located in the first direction, resulting in a wider area of ​​error diffusion in the second direction than in the first direction. This allows the dots 38 to be distributed more evenly according to the image resolution ratio (Ry / Rx). Therefore, the above embodiment can provide a suitable example for improving image quality in terms of granularity.

[0017] [Aspect 5] Incidentally, a printing apparatus 1 according to one aspect of this technology, as illustrated in Figure 1, comprises the above-described image processing apparatus U0 and a printing unit U3 that forms a printed image IM0 on a medium ME0 according to the dot data DA3, the printed image IM0 having the first-direction resolution (Rx) in the first direction and the second-direction resolution (Ry) in the second direction. Based on the above, the dots 38 are arranged to be more evenly distributed according to the resolution ratio (Ry / Rx) of the printed image IM0. Therefore, the above embodiment can provide a printing apparatus that contributes to improving granularity in accordance with the resolution ratio of the printed image.

[0018] [Aspect 6] Furthermore, an image processing method according to one aspect of this technology is an image processing method that converts image data (DA2) in which a first-direction resolution (Rx) in a first direction and a second-direction resolution (Ry) in a second direction intersecting the first direction are set into dot data DA3 representing the formation state of dots 38 by error diffusion, and includes the following steps. (A1) A conversion step ST1 in which the formation state of the dot 38 is determined based on the pixel value MP0 and the allocated error EP0 in the conversion target pixel P0 included in a plurality of pixels PX0 constituting the image data (DA2). (A2) A diffusion step ST2 in which the error E0 generated in the target pixel P0 is diffused to the multiple destination pixels Qi that have not been converted, according to the allocation ratio Ri set for each of the multiple destination pixels Qi. Here, as illustrated in Figures 4 and 5, the first-direction sum (Sx) is defined as the sum of the products of the allocation ratio Ri set for each allocation destination pixel Qi and the relative position (Δxi) of the allocation destination pixel Qi in the first direction with respect to the conversion target pixel P0, and the second-direction sum (Sy) is defined as the sum of the products of the allocation ratio Ri set for each allocation destination pixel Qi and the relative position (Δyi) of the allocation destination pixel Qi in the second direction with respect to the conversion target pixel P0, and so on. The ratio of the sum in the second direction (Sy) to the sum in the first direction (Sx) is defined as the sum ratio (Sy / Sx), the ratio of the resolution in the second direction (Ry) to the resolution in the first direction (Rx) is defined as the resolution ratio (Ry / Rx), the sum ratio (Sy / Sx) when the resolution ratio (Ry / Rx) is the first resolution ratio RR1 is defined as the first sum ratio SR1, and the sum ratio (Sy / Sx) when the resolution ratio (Ry / Rx) is greater than the first resolution ratio RR1 (second resolution ratio RR2) is defined as the second sum ratio SR2. Each allocation ratio Ri is set to the destination pixel Qi such that the second sum ratio SR2 is greater than the first sum ratio SR1.

[0019] Based on the above, dot data DA3 is generated in which the dots 38 are arranged to be more evenly distributed according to the image resolution ratio (Ry / Rx). Therefore, the above embodiment can provide an image processing method that contributes to improving granularity in accordance with the image resolution ratio.

[0020] Furthermore, this technology is applicable to a printing system including the image processing apparatus described above, a method for controlling the image processing apparatus described above, a method for controlling the printing system described above, a control program for the image processing apparatus described above, a control program for the printing system described above, a computer-readable recording medium on which any of the control programs described above is recorded, and so on. In addition, the image processing apparatus described above may be composed of multiple distributed parts.

[0021] (2) Specific examples of printing devices including image processing devices: Figure 1 schematically illustrates a printing apparatus 1 including an image processing device U0. In this specific example, the printing apparatus 1 is assumed to be the printer 2 itself, but the printing apparatus 1 may also be a combination of the printer 2 and a host device HO1. Note that the printer 2 may include additional elements not shown in Figure 1. Figure 2 schematically illustrates the nozzle surface 30a of the print head 30 and the dot pattern on the medium ME0.

[0022] The printer 2 shown in Figure 1 is a serial printer, which is a type of inkjet printer. Of course, other printers to which this technology can be applied include line printers with nozzle rows that cover almost the entire width of the medium, and electrophotographic printers such as laser printers that use toner as a colorant. The inkjet printer 2 includes a controller 10, a semiconductor memory (RAM) 21, a communication interface 22, a storage unit 23, an operation panel 24, a print head 30, a drive unit 50, and the like. Here, RAM is an abbreviation for Random Access Memory, and I / F is an abbreviation for Interface. The controller 10, RAM 21, communication interface 22, storage unit 23, and operation panel 24 are connected to a bus, enabling them to input and output information to each other.

[0023] The controller 10 includes a processor CPU 11, a color conversion unit 12, a halftone processing unit 13, a rasterization processing unit 14, a drive signal transmission unit 15, etc. Here, CPU is an abbreviation for Central Processing Unit. The halftone processing unit 13 is an example of an image processing device U0 that includes a conversion unit U1 and a diffusion unit U2. Based on the original image data DA1 acquired from a host device HO1, a memory card (not shown), etc., the controller 10 controls the main scan and sub-scan by the drive unit 50, and the ejection of ink droplets 37 by the print head 30. The original image data DA1 includes, for example, two colors for each pixel: R, G, and B. 8 Tone and 2 16 RGB data, which has integer values ​​for grayscale, can be applied. Here, R represents red, G represents green, and B represents blue. The controller 10 can be configured using an SoC, where SoC is an abbreviation for System on a Chip.

[0024] The CPU 11 is the device that primarily handles information processing and control in the printer 2. The color conversion unit 12, for example, refers to a color conversion LUT that defines the correspondence between the gradation values ​​of R, G, and B and the gradation values ​​of C, M, Y, and K, and converts the RGB data to C, M, Y, and K for each pixel. 8 Tone and 2 16 The data is converted to ink quantity data DA2, which has integer values ​​for the gradation. Here, C means cyan, M means magenta, Y means yellow, K means black, and LUT is an abbreviation for lookup table. The ink quantity data DA2 represents the amount of C, M, Y, and K ink 36 used in units of pixel PX0 (see Figure 2). If the resolution of the RGB data is different from the output resolution Rx,Ry (see Figure 4), the color conversion unit 12 first converts the resolution of the RGB data to the output resolution Rx,Ry, or converts the resolution of the ink quantity data DA2 to the output resolution Rx,Ry. The ink quantity data DA2 with output resolution Rx,Ry is an example of image data with output resolution Rx,Ry set.

[0025] The halftone processing unit 13 reduces the number of gradations in the gradation values ​​of each pixel PX0 constituting the ink amount data DA2 by performing halftone processing using the error diffusion method, thereby generating dot data DA3. The dot data DA3 represents the formation state of dots 38 in units of pixel PX0. The dot data DA3 may be binary data indicating the presence or absence of dot formation, or it may be multi-level data with three or more gradations that can handle dots of different sizes, such as small, medium, and large. The rasterization processing unit 14 generates raster data RA0 by performing a rasterization process that rearranges the dot data DA3 in the order in which the dots 38 are formed by the drive unit 50.

[0026] The drive signal transmission unit 15 generates and outputs a drive signal SG1 corresponding to the voltage signal applied to the drive element 32 of the print head 30 to the drive circuit 31 of the print head 30 from the raster data RA0. For example, if the raster data RA0 is "dot formation", the drive signal transmission unit 15 outputs a drive signal SG1 that ejects ink droplets for dot formation. Also, if the raster data RA0 is quaternary data, the drive signal transmission unit 15 outputs a drive signal SG1 that ejects ink droplets for large dots if the raster data RA0 is "large dot formation", a drive signal SG1 that ejects ink droplets for medium dots if the raster data RA0 is "medium dot formation", and a drive signal SG1 that ejects ink droplets for small dots if the raster data RA0 is "small dot formation". Furthermore, if printer 2 is a line printer, the controller 10 does not need to have a rasterization processing unit 14, and the drive signal transmission unit 15 may generate the drive signal SG1 from the dot data DA3.

[0027] Each of the above parts 11 to 15 may be composed of an ASIC, and may directly read the data to be processed from RAM 21 or directly write the processed data to RAM 21. Here, ASIC is an abbreviation for Application Specific Integrated Circuit.

[0028] The drive unit 50, controlled by the controller 10, comprises a carriage drive unit 51 and a roller drive unit 55. The drive unit 50 moves the carriage 52 back and forth along the main scanning direction D1 by the carriage drive unit 51, and moves the medium ME0 along the transport path 59 in the feed direction D3 by the roller drive unit 55. As shown in Figure 2, the main scanning direction D1 is the direction that intersects with the alignment direction D4 of the nozzles 34, for example, the direction perpendicular to the alignment direction D4. The feed direction D3 is the direction that intersects with the main scanning direction D1, for example, the direction perpendicular to the main scanning direction D1. In Figure 1, the feed direction D3 is to the right, the left side is called the upstream side, and the right side is called the downstream side. The sub-scanning direction D2 shown in Figure 2 is the opposite direction to the feed direction D3. The carriage drive unit 51 moves the carriage 52 back and forth along the main scanning direction D1 according to the control of the controller 10. The carriage drive unit 51 performs a main scan, which changes the relative positional relationship between the print head 30 and the medium ME0 along the main scanning direction D1. The roller drive unit 55 includes a transport roller pair 56 and an ejection roller pair 57. The roller drive unit 55 performs a sub-scan, which moves the medium ME0 in the feed direction D3 by rotating the drive transport roller of the transport roller pair 56 and the drive ejection roller of the ejection roller pair 57 according to the control of the controller 10. The roller drive unit 55 also performs a sub-scan, which changes the relative positional relationship between the print head 30 and the medium ME0 along the sub-scan direction D2, which intersects the main scanning direction D1. The medium ME0 is the material that holds the printed image and is made of paper, resin, metal, etc. The material of the medium ME0 is not particularly limited, and various materials such as resin, metal, and paper are possible. The shape of the medium ME0 is also not particularly limited, and various shapes such as rectangles and rolls are possible, and it may also be a three-dimensional shape.

[0029] A print head 30 is mounted on the carriage 52. The carriage 52 may also be equipped with an ink cartridge 35 that supplies ink 36, which is ejected as ink droplets 37, to the print head 30. Of course, ink 36 may also be supplied to the print head 30 via a tube from an ink cartridge 35 installed outside the carriage 52. The carriage 52 is fixed to an endless belt (not shown) and is movable in the main scanning direction D1 along a guide 53. The guide 53 is a long member whose longitudinal direction is oriented in the main scanning direction D1. The carriage drive unit 51 consists of a servo motor and moves the carriage 52 back and forth along the main scanning direction D1 according to a command from the controller 10.

[0030] The transport roller pair 56 located upstream of the print head 30 sends the nipped medium ME0 towards the print head 30 during sub-scanning by the rotation of the drive transport roller. The discharge roller pair 57 located downstream of the print head 30 transports the nipped medium ME0 towards a medium discharge section (not shown) during sub-scanning by the rotation of the drive discharge roller. The roller drive unit 55 is composed of a servo motor and operates the transport roller pair 56 and the discharge roller pair 57 according to commands from the controller 10, sending the medium ME0 in the feed direction D3.

[0031] The platen 58 is located below the transport path 59 and supports the medium ME0 by contacting it in the transport path 59. The print head 30, controlled by the controller 10, ejects ink droplets 37 toward the medium ME0 supported by the platen 58, thereby adhering ink 36 to the medium ME0.

[0032] The print head 30, which includes a drive circuit 31 and a drive element 32, has a plurality of nozzles 34 on its nozzle surface 30a that eject ink droplets 37, and performs printing by ejecting ink droplets 37 onto the medium ME0 on the platen 58. Here, a nozzle means a small hole from which ink droplets are ejected, and a nozzle row means an arrangement of multiple nozzles. The nozzle surface 30a is the ejection surface for the ink droplets 37. The drive circuit 31 applies a voltage signal to the drive element 32 according to the drive signal SG1 input from the drive signal transmission unit 15. The drive element 32 can be a piezoelectric element that applies pressure to the ink 36 in a pressure chamber communicating with the nozzle 34, a drive element that generates bubbles in the pressure chamber by heat to eject ink droplets 37 from the nozzle 34, etc. Ink 36 is supplied to the pressure chamber of the print head 30 from an ink cartridge 35. The ink 36 in the pressure chamber is ejected as ink droplets 37 from the nozzle 34 toward the medium ME0 by the drive element 32. As a result, ink droplets 37 form dots 38 on the medium ME0. While the print head 30 moves in the main scanning direction D1, dots 38 are formed according to the raster data RA0, and the medium ME0 is fed in the feed direction D3 for one sub-scan, and this process is repeated, thereby forming a printed image IM0 on the medium ME0. A controller 10 including a rasterization processing unit 14 and a drive signal transmission unit 15, a print head 30, and a drive unit 50 are examples of a printing unit U3 that forms a print image IM0 with output resolution Rx,Ry on the medium ME0 according to dot data DA3.

[0033] RAM21 stores raw image data DA1 and other data received from the host device HO1 or memory (not shown). The communication interface 22 is connected to the host device HO1 by wire or wireless connection and inputs and outputs information to the host device HO1. The host device HO1 includes computers such as personal computers and tablet terminals, mobile phones such as smartphones, digital cameras, digital video cameras, etc. The storage unit 23 can use non-volatile semiconductor memory such as flash memory, magnetic storage devices such as hard disks, etc. The operation panel 24 includes an output unit 25 such as a liquid crystal panel for displaying information, an input unit 26 such as a touch panel for receiving operations on the display screen, etc.

[0034] The print head 30 shown in Figure 2 has multiple nozzle rows 33 on its nozzle surface 30a, each containing multiple nozzles 34 arranged in the alignment direction D4 at a predetermined nozzle pitch interval. The multiple nozzle rows 33 include a cyan nozzle row 33C that ejects C ink droplets 37, a magenta nozzle row 33M that ejects M ink droplets 37, a yellow nozzle row 33Y that ejects Y ink droplets 37, and a black nozzle row 33K that ejects K ink droplets 37. Each ink droplet 37 is ejected from the nozzle 34 targeting the pixel PX0 of the medium ME0. Of course, a C dot 38 is formed on the medium ME0 from the C ink droplet 37, an M dot 38 is formed on the medium ME0 from the M ink droplet 37, a Y dot 38 is formed on the medium ME0 from the Y ink droplet 37, and a K dot 38 is formed on the medium ME0 from the K ink droplet 37. Each nozzle row 33 ejects ink droplets 37 toward the medium ME0. The multiple nozzles 34 included in each nozzle row 33 may be arranged in a single row, or in a staggered pattern, i.e., in two rows.

[0035] FIG. 3 schematically illustrates the halftone process performed by the halftone processing unit 13 that converts the ink amount data DA2 into dot data DA3. In FIG. 3, each pixel PX0 of the ink amount data DA2 and the dot data DA3 is shown as a square, and the pixel P0 to be converted is shown as a thick line. When the ink amount data DA2 is 256 gradations, the ink amount data DA2 has, for each pixel PX0, a gradation value C of C 256 , a gradation value M of M 256 , a gradation value Y of Y 256 , and a gradation value K of K 256 . The dot data DA3 has, for each pixel PX0, a dot value C of C d , a dot value M of M d , a dot value Y of Y d , and a dot value K of K d . In the pixel P0 to be converted, the pixel value MP0 of the pixel P0 to be converted is shown in the upper row, and the generated error E0 is shown in the lower row. In a plurality of destination pixels Q1 to Q6 to which the error E0 is distributed according to the distribution ratios R1 to R6, the pixel values M1 to M6 of the destination pixels Q1 to Q6 are shown in the upper row, and the errors E1 to E6 distributed from the pixel P0 to be converted are shown in the lower row. Here, the destination pixels Q1 to Q6 are collectively referred to as the destination pixel Qi, the distribution ratios R1 to R6 are collectively referred to as the distribution ratio Ri, the pixel values M1 to M6 are collectively referred to as the pixel value Mi (not shown), and the errors E1 to E6 are collectively referred to as the error Ei. For the converted pixel PX2, for the sake of convenience, a gradation value based on the 256-gradation ink amount data DA2 is shown as a gradation value corresponding to the dot value.

[0036] The ink volume data DA2 and dot data DA3 have multiple pixels PX0 arranged in an orderly manner in the X direction (horizontal) and the Y direction (vertical) in Figure 3. Here, the X direction is an example of the first direction, and the Y direction is an example of the second direction. The X and Y directions intersect each other and are orthogonal in Figure 3. In Figure 3, the origin of the XY coordinate system is in the upper left, with the X coordinate increasing towards the right and the Y coordinate increasing towards the bottom. The setting order of the pixels to be converted P0 is as shown by the arrow at the top of Figure 3, starting from the origin pixel in the upper left corner and proceeding in order of increasing X coordinate up to the pixel in the upper right corner, and repeating this order one pixel below each pixel, from the leftmost pixel down to the rightmost pixel, and finally ending with the pixel in the lower right corner. According to this setting order, the converted pixels PX2 are the upper pixels with a smaller Y coordinate than the pixels to be converted P0, and the leftmost pixels with the same Y coordinate as the pixels to be converted P0 but with a smaller X coordinate than the pixels to be converted P0. Furthermore, the unconverted pixels PX1 are pixels to the right of the target pixel P0 that have the same Y coordinate but a larger X coordinate than the target pixel P0, and pixels below the target pixel P0 that have a larger Y coordinate. The destination pixel Qi is selected from the unconverted pixels PX1 located to the right or below the target pixel P0. Since ink volume data DA2 is prepared separately for each color, dot data DA3 is generated separately for each color. For example, if ink volume data DA2 for C, M, Y, and K is prepared, dot data DA3 for C, M, Y, and K will be generated.

[0037] The conversion unit U1 included in the halftone processing unit 13 determines the dot formation state of the target pixel P0 based on the pixel value MP0 and the allocated error EP0. For example, if the dot data DA3 is binary data representing the presence or absence of dot 38 formation, the conversion unit U1 determines the dot value of the target pixel P0 to be 0, which corresponds to "no dot", or 1, which corresponds to "dot formation". In Figure 3, each converted pixel PX2 shows a 256-level gradation value of 0 corresponding to a dot value of 0, or a 256-level gradation value of 255, which corresponds to a dot value of 1.

[0038] The diffusion unit U2 included in the halftone processing unit 13 calculates an error E0 associated with the determination of the dot value in the pixel P0 to be converted, and diffuses the resulting error E0 to multiple destination pixels Qi according to the allocation ratio Ri set for each of the multiple destination pixels Qi that have not yet been converted. The diffusion unit U2 determines the error Ei to be allocated to each destination pixel Qi by multiplying the error E0 by the allocation ratio Ri determined from the allocation ratio table TA0 shown at the bottom of Figure 3. For example, in the allocation ratio table TA0 shown in Figure 3, with respect to the pixel P0 to be converted, weights of 4 are assigned to destination pixels Q1 and Q4, weight 3 is assigned to destination pixel Q2, weight 2 is assigned to destination pixels Q3 and Q5, and weight 1 is assigned to destination pixel Q6. The sum of the weights assigned to the destination pixels Q1 to Q6 is 16, so the allocation ratios R1 and R4 are 4 / 16, R2 is 3 / 16, R3 and R5 are 2 / 16, and R6 is 1 / 16. Furthermore, since the errors allocated to each destination pixel Qi may originate from multiple converted pixels PX2, errors other than those shown in Figure 3 (E1-E6) may also be included.

[0039] The printed image IM0 can be set to various resolutions Rx and Ry, as illustrated in Figure 4. Figure 4 schematically illustrates various resolutions for the printed image IM0. Here, the resolution Rx in the X direction is an example of the first-direction resolution in the first direction, the resolution Ry in the Y direction is an example of the second-direction resolution in the second direction, and the resolution ratio Ry / Rx is an example of the ratio of the second-direction resolution to the first-direction resolution. For example, if the resolution Rx is 2400 dpi, it means that in the X direction, the multiple pixels PX0 contained in the printed image IM0 are arranged at a density of 2400 per inch. If the resolution Ry is 600 dpi, it means that in the Y direction, the multiple pixels PX0 contained in the printed image IM0 are arranged at a density of 600 per inch. Therefore, if Rx × Ry = 2400 × 600 dpi, on the printed image IM0, the spacing of pixels PX0 in the X direction is 1 / 4 of the spacing of pixels PX0 in the Y direction, and the spacing of pixels PX0 in the X direction and Y direction are different. Conversely, if Rx × Ry = 600 × 2400 dpi, on the printed image IM0, the spacing of pixels PX0 in the X direction is 4 times the spacing of pixels PX0 in the Y direction, and the spacing of pixels PX0 in the X direction and Y direction are different. Of course, if both resolutions Rx and Ry are 600 dpi, the spacing of pixels PX0 in the X direction and Y direction are the same.

[0040] When halftone processing using the error diffusion method was performed according to a common distribution ratio table for various resolution ratios Ry / Rx, it was found that the dot placement was biased depending on the resolution ratio Ry / Rx. For example, when a printed image was formed using a distribution ratio table designed on the assumption of Ry=Rx, where the resolution Ry in the Y direction was different from the resolution Rx in the X direction, an undesirable continuation of dots called a worm sometimes occurred in the low-tone areas. Thus, the dot placement can be biased depending on the resolution ratio Ry / Rx, and this can manifest as a decrease in granularity, especially in the low-tone areas of printed images. In this specific example, by switching the distribution ratio table TA0 according to the resolution ratio Ry / Rx, the dots 38 are distributed more evenly, improving the image quality of the printed image IM0 in terms of granularity.

[0041] For the sake of explanation, we will refer to one of the multiple resolution ratios Ry / Rx as the first resolution ratio RR1, and any resolution ratio greater than the first resolution ratio RR1 as the second resolution ratio RR2. Figure 4 shows that Ry / Rx = 1 / 4 is assigned to the first resolution ratio RR1, and Ry / Rx = 1 / 2 is assigned to the second resolution ratio RR2. Of course, there are various possible assignments for the first resolution ratio RR1 and the second resolution ratio RR2; for example, Ry / Rx = 1 / 2 could be assigned to the first resolution ratio RR1 and Ry / Rx = 1 could be assigned to the second resolution ratio RR2.

[0042] Figure 5 schematically illustrates the allocation ratio table TA0 according to the resolution ratio Ry / Rx. As shown in Figure 5, different allocation ratio tables TA0 are provided depending on the resolution ratio Ry / Rx. The controller 10 shown in Figure 1 holds multiple allocation ratio tables TA0 corresponding to the resolution ratio Ry / Rx. Figure 5 shows allocation ratio tables TA1, TA2, TA3, TA4, and TA5, which are associated with resolution ratios of 1 / 4, 1 / 2, 1, 2, and 4, respectively. Each allocation ratio table TA0 has a value that represents the allocation ratio Ri assigned to the destination pixel Qi based on the target pixel P0. For example, allocation ratio table TA1 has values ​​of 3, 2, 2, 2, 1, 1, 1, 3, and 1 in the order of i=1 to 9, where i is a variable that identifies n=9 destination pixels Qi. Since the sum of these values ​​is 16, the allocation ratio Ri is 3 / 16, 2 / 16, 2 / 16, 2 / 16, 1 / 16, 1 / 16, 1 / 16, 3 / 16, and 1 / 16 for i=1 to 9, respectively.

[0043] Here, the sum of the first directional sum Sx is obtained by multiplying the allocation ratio Ri set for each allocated pixel Qi by the relative position Δxi in the X direction with respect to the target pixel P0. The sum of the second directional sum Sy is obtained by multiplying the allocation ratio Ri set for each allocated pixel Qi by the relative position Δyi in the Y direction with respect to the target pixel P0. The sums Sx and Sy are expressed by the following equations.

number

[0044] For example, in the allocation ratio table TA1, the sum Sx in the first direction and the sum Sy in the second direction are as follows: Sx=(3×1+2×2+2×3+2×4+1×5-1×2-1×1+3×0+1×1) / 16 =24 / 16 Sy=(3×0+2×0+2×0+2×0+1×0+1×1+1×1+3×1+1×1) / 16 = 6 / 16

[0045] Furthermore, the ratio of the sum in the second direction Sy to the sum in the first direction Sx is defined as the sum ratio Sy / Sx. In each allocation ratio table TA0, each allocation ratio Ri is set to the destination pixel Qi such that the sum ratio Sy / Sx matches the resolution ratio Ry / Rx. For example, in allocation ratio table TA1, the sum ratio Sy / Sx is 1 / 4, which matches the resolution ratio Ry / Rx = 1 / 4. In allocation ratio table TA2, the sum ratio Sy / Sx is 1 / 2, which matches the resolution ratio Ry / Rx = 1 / 2. In allocation ratio table TA3, the sum ratio Sy / Sx is 1, which matches the resolution ratio Ry / Rx = 1. In allocation ratio table TA4, the sum ratio Sy / Sx is 2, which matches the resolution ratio Ry / Rx = 2. In allocation ratio table TA5, the sum ratio Sy / Sx is 4, which matches the resolution ratio Ry / Rx = 4.

[0046] Furthermore, the summation ratio Sy / Sx when the resolution ratio Ry / Rx is the first resolution ratio RR1 is defined as the first summation ratio SR1, and the summation ratio Sy / Sx when the resolution ratio Ry / Rx is greater than the first resolution ratio RR1 (second resolution ratio RR2) is defined as the second summation ratio SR2. For example, as shown in Figure 4, suppose that the resolution ratio Ry / Rx = 1 / 4 is assigned to the first resolution ratio RR1, and the resolution ratio Ry / Rx = 1 / 2 is assigned to the second resolution ratio RR2. In this case, as shown in Figure 5, the summation ratio Sy / Sx = 1 / 4 is assigned to the first summation ratio SR1, and the summation ratio Sy / Sx = 1 / 2 is assigned to the second summation ratio SR2. Each allocation ratio Ri is set to the destination pixel Qi such that the second summation ratio SR2 is greater than the first summation ratio SR1. Of course, there are various ways to apply the first sum ratio SR1 and the second sum ratio SR2. For example, Sy / Sx=Ry / Rx=1 / 2 could be applied to the first sum ratio SR1, and Sy / Sx=Ry / Rx=1 could be applied to the second sum ratio SR2.

[0047] As illustrated in Figures 6 and 7, matching the sum ratio Sy / Sx to the resolution ratio Ry / Rx means that the angle θs = tan based on the sum ratio Sy / Sx. -1 (Sy / Sx) is the angle θr = tan based on the resolution ratio Ry / Rx. -1 This is equivalent to matching (Ry / Rx). Figure 6 schematically shows an example of matching the angle θs calculated from the distribution ratio table TA2, which is linked to the resolution ratio Ry / Rx = 1 / 2, to the angle θr based on the resolution ratio Ry / Rx. Figure 7 schematically shows an example of matching the angle θs calculated from the distribution ratio table TA4, which is linked to the resolution ratio Ry / Rx = 2, to the angle θr based on the resolution ratio Ry / Rx.

[0048] The angle θr, based on the resolution ratio Ry / Rx, represents the interior angle of a right triangle where the length of the adjacent side is the resolution Rx and the length of the opposite side is the resolution Ry, and is expressed as the arctangent value of the resolution ratio Ry / Rx. θr = tan -1 (Ry / Rx) …(3) In the example shown in Figure 4, the angle θr is 14.04° when the resolution ratio Ry / Rx is 1 / 4, 26.57° when the resolution ratio Ry / Rx is 1 / 2, 45.00° when the resolution ratio Ry / Rx is 1, 63.43° when the resolution ratio Ry / Rx is 2, and 75.96° when the resolution ratio Ry / Rx is 2. The angle θs, based on the sum ratio Sy / Sx, represents the interior angle of a right triangle where the lengths of adjacent sides are the sum in the first direction, Sx, and the lengths of opposite sides are the sum in the second direction, Sy. It is expressed as the arctangent value of the sum ratio Sy / Sx. θs = tan -1 (Sy / Sx) …(4) In the example shown in Figure 5, the angle θs is 14.04° when the sum ratio Sy / Sx is 1 / 4, 26.57° when the sum ratio Sy / Sx is 1 / 2, 45.00° when the sum ratio Sy / Sx is 1, 63.43° when the sum ratio Sy / Sx is 2, and 75.96° when the sum ratio Sy / Sx is 2.

[0049] When angle θs is equal to angle θr, the following relationship holds: tan -1 (Sy / Sx) = tan -1 (Ry / Rx) …(4) Sy / Sx = Ry / Rx …(5) Therefore, matching angle θs to angle θr is equivalent to matching the sum ratio Sy / Sx to the resolution ratio Ry / Rx.

[0050] As shown in Figure 6, when the resolution ratio Ry / Rx is 1 / 2, in the printed image IM0, the length of Rx pixels PX0 in the X direction is equal to the length of Ry pixels PX0 in the Y direction. Therefore, in the printed image IM0, the interior angle θp of a right triangle where the length of adjacent sides is the length of Rx pixels PX0 and the length of opposite sides is the length of Ry pixels PX0 is 45°. Accordingly, in the printed image IM0, halftone processing is performed using the error diffusion method so that the dots 38 are evenly distributed in both the X and Y directions according to the resolution ratio Ry / Rx. As shown in Figure 7, even when the resolution ratio Ry / Rx is 2, in the printed image IM0, the length of Rx pixels PX0 in the X direction is equal to the length of Ry pixels PX0 in the Y direction. Therefore, in the printed image IM0, the interior angle θp of a right triangle where the length of adjacent sides is the length of Rx pixels PX0 and the length of opposite sides is the length of Ry pixels PX0 is 45°. Accordingly, in the printed image IM0, halftone processing is performed using the error diffusion method so that the dots 38 are evenly distributed in both the X and Y directions according to the resolution ratio Ry / Rx.

[0051] Furthermore, as shown in the allocation ratio tables TA1 and TA2 in Figure 5, when the resolution Rx in the X direction is greater than the resolution Ry in the Y direction, the range in which multiple allocation pixels Qi are located in the X direction is wider than the range in which multiple allocation pixels Qi are located in the Y direction. As a result, the range in which errors are diffused is wider in the X direction than in the Y direction, and halftone processing using the error diffusion method is performed so that the dots 38 are further evenly distributed in both the X and Y directions in the printed image IM0 according to the resolution ratio Ry / Rx. On the other hand, as shown in the allocation ratio tables TA4 and TA5 in Figure 5, when the resolution Ry in the Y direction is greater than the resolution Rx in the X direction, the range in which multiple allocation pixels Qi are located in the Y direction is wider than the range in which multiple allocation pixels Qi are located in the X direction. As a result, the range in which errors are diffused is wider in the Y direction than in the X direction, and halftone processing using the error diffusion method is performed so that the dots 38 are further evenly distributed in both the X and Y directions in the printed image IM0 according to the resolution ratio Ry / Rx.

[0052] Furthermore, as shown in the allocation ratio table TA3 in Figure 5, if the resolution Rx in the X direction is the same as the resolution Ry in the Y direction, the range in which multiple allocation target pixels Qi are located in the X direction may be the same as the range in which multiple allocation target pixels Qi are located in the Y direction. In this case, halftone processing using the error diffusion method is performed in the printed image IM0 so that the dots 38 are evenly distributed in both the X and Y directions in accordance with the resolution ratio Ry / Rx=1.

[0053] (3) Specific examples of print control processes including halftone processing using error diffusion: Figure 8 schematically illustrates a print control process including halftone processing using the error diffusion method. The print control process shown in Figure 8 is performed by the controller 10 shown in Figure 1. When the controller 10 receives, for example, a print job J1 which will be the source image data DA1 from the host device HO1, it starts the print control process. The print job J1 is stored, for example, in RAM 21. Figure 9 schematically illustrates the halftone processing performed by the controller 10. Here, steps S204 to S206 correspond to the conversion unit U1 and the conversion process ST1, and steps S208 to S210 correspond to the diffusion unit U2 and the diffusion process ST2. Hereafter, the term "step" may be omitted, and the step number may be indicated in parentheses. Figures 1 to 7 will also be used for explanation.

[0054] Print job J1 includes header HE1, body data BO1, etc. Header HE1 includes print resolution Rx, Ry. Body data BO1 corresponds to the original image data DA1, and may be the original image data DA1 itself, for example, RGB data in bitmap format, or drawing data that is converted to the original image data DA1 through interpretation.

[0055] When the print control process starts, the controller 10 obtains the print resolutions Rx and Ry from the print job J1 (S102). Alternatively, the controller 10 may obtain the print resolutions Rx and Ry by accepting the setting of the print resolutions Rx and Ry on the operation panel 24. In this case, the controller 10 may obtain the original image data DA1 from a memory card or the like (not shown). After obtaining the print resolutions Rx and Ry, the controller 10 obtains the original image data DA1 from the print job J1 or a memory card, etc. If the resolution of the original image data DA1 is different from the print resolutions Rx and Ry, the controller 10 converts the resolution of the original image data DA1 to the print resolutions Rx and Ry. Then, the controller 10 performs a color conversion process in the color conversion unit 12 to convert the original image data DA1 to ink amount data DA2 (S104). If the original image data DA1 is RGB data and the ink amount data DA2 is CMK data having, for example, 256 gradations of pixel values ​​for C, M, Y, and K, the controller 10 performs a known color conversion process to convert the RGB data to CMYK data.

[0056] After the color conversion process, the controller 10 selects a distribution ratio table associated with the resolution ratio Ry / Rx from among multiple distribution ratio tables TA0 in the halftone processing unit 13 (S106). For example, if the controller 10 holds distribution ratio tables TA1 to TA5 as shown in Figure 5, the distribution ratio table with a distribution ratio Ri that results in a sum ratio Sy / Sx matching the resolution ratio Ry / Rx is selected from among the multiple distribution ratio tables TA0. Here, it is assumed that the second resolution ratio RR2 is greater than the first resolution ratio RR1, the first sum ratio SR1 corresponds to the first resolution ratio RR1, and the second sum ratio SR2 corresponds to the second resolution ratio RR2. If the resolution ratio Ry / Rx is the first resolution ratio RR1, the distribution ratio table TA0 that results in the first sum ratio SR1 is selected, and if the resolution ratio Ry / Rx is the second resolution ratio RR2, the distribution ratio table TA0 that results in a second sum ratio SR2 which is greater than the first sum ratio SR1 is selected. In the examples shown in Figures 4 and 5, when the resolution ratio Ry / Rx is 1 / 4, allocation ratio table TA1 is selected so that the sum ratio Sy / Sx is 1 / 4, and when the resolution ratio Ry / Rx is 1 / 2, allocation ratio table TA2 is selected so that the sum ratio Sy / Sx is 1 / 2. After selecting the allocation ratio table TA0, the controller 10 performs halftone processing using the error diffusion method in the halftone processing unit 13 (S108).

[0057] Figure 9 illustrates the halftone processing performed in S108. The halftone processing shown in Figure 9 is performed separately for C, M, Y, and K. When halftone processing begins, the halftone processing unit 13 sets the position of the pixel P0 to be converted, as shown in Figure 3 (S202). The process in S202 can also be described as selecting the pixel to be converted to reduce the number of gradations from among the multiple pixels PX0 that make up the ink amount data DA2.

[0058] After setting the position of the pixel P0 to be converted, the halftone processing unit 13 calculates a correction value CP0 by adding the reception error EP0 to the pixel value MP0 at the pixel P0 to be converted (S204). The reception error EP0 is the error assigned to the pixel P0 to be converted, and if errors are assigned from multiple pixels, it becomes the sum of the assigned errors. After calculating the correction value CP0, the halftone processing unit 13 compares the correction value CP0 with the threshold value TH0 and determines the dot value DT0, which represents the formation state of the dot 38 in the pixel P0 to be converted, based on the comparison result (S206).

[0059] For example, suppose the pixel value MP0 is a grayscale value between 0 and 255, the dot value DT0 is a binary value of 0 or 1, and the threshold TH0 is greater than 1 and less than 255. If the correction value CP0 is greater than or equal to the threshold TH0, the halftone processing unit 13 can determine the dot value DT0 to 1, which means dot formation. If the correction value CP0 is less than the threshold TH0, the halftone processing unit 13 can determine the dot value DT0 to 0, which means no dot. As described above, the conversion unit U1 determines the dot formation state of the dot 38 in the conversion target pixel P0 included in the multiple pixels PX0 that constitute the ink amount data DA2, based on the pixel value MP0 and the allocated error EP0.

[0060] Furthermore, the halftone processing unit 13 calculates the error E0 that arises from the determination of the dot value DT0 (S208). In the example described above, if the dot value DT0 is determined to be 1, the halftone processing unit 13 can determine the error E0 to be the correction value CP0 minus 255. If the dot value DT0 is determined to be 0, the halftone processing unit 13 can determine the correction value CP0 to be the error E0. After calculating the error E0, the halftone processing unit 13 distributes the error Ei to each destination pixel Qi according to the distribution ratio table TA0 selected to match the resolution ratio Ry / Rx (S210). As shown in the lower part of Figure 3, the halftone processing unit 13 determines the error Ei to be distributed to each destination pixel Qi by multiplying the error E0 by the distribution ratio Ri determined from the distribution ratio table TA0.

[0061] As described above, the diffusion unit U2 diffuses the error E0 generated in the target pixel P0 to multiple destination pixels Qi according to the allocation ratio Ri set for each of the multiple destination pixels Qi that have not been converted. After the error Ei has been diffused, the halftone processing unit 13 determines whether or not the processing in S202 to S210 has been performed on all pixels PX0 included in the ink amount data DA2 as the target pixels P0 (S212). If there are unconverted pixels PX1 remaining as shown in Figure 3, the halftone processing unit 13 repeats the processing in S202 to S212. If there are no unconverted pixels PX1 remaining, the halftone processing unit 13 terminates the halftone processing as shown in Figure 9. As a result, dot data DA3 is obtained in which each pixel PX0 has a dot value DT0 representing the formation state of the dots 38.

[0062] Furthermore, the dot value DT0 may have three or more values. For example, if the dot value DT0 has four values, a first threshold (let's call it TH1) greater than 0 and less than 253, a second threshold (let's call it TH2) greater than the first threshold TH1 and less than 254, and a third threshold (let's call it TH3) greater than the second threshold TH2 and less than 255 may be provided. The halftone processing unit 13 may determine the dot value DT0 to 3, which means large dot formation, if the correction value CP0 is greater than or equal to the threshold TH3, and determine the error E0 to be the correction value CP0 minus, for example, 255. The halftone processing unit 13 may determine the dot value DT0 to 2, which means medium dot formation, if the correction value CP0 is greater than or equal to the threshold TH2 and less than the threshold TH3, and determine the error E0 to be the correction value CP0 minus, for example, 128. The halftone processing unit 13 may determine the dot value DT0 to 1, which means small dot formation, if the correction value CP0 is greater than or equal to threshold TH1 and less than threshold TH2, and determine the error E0 to be the correction value CP0 minus, for example, 64. The halftone processing unit 13 may determine the dot value DT0 to 0, which means no dot, if the correction value CP0 is less than threshold TH1, and determine the correction value CP0 to be the error E0.

[0063] After the halftone processing shown in Figure 9, the controller 10 generates raster data RA0 by performing a rasterization process in the rasterization processing unit 14, which rearranges the dot data DA3 in the order in which the dots 38 are formed by the drive unit 50 (S110). Note that the rasterization process is optional and is not performed, for example, if the printer 2 is a line printer. After rasterization, the controller 10 generates a drive signal SG1 corresponding to the voltage signal applied to the drive element 32 from the raster data RA0 in the drive signal transmission unit 15 and outputs the drive signal SG1 to the drive circuit 31 of the print head 30 (S112). As a result, the printer 2 drives the print head 30 and the drive unit 50 to form a print image IM0 with output resolution Rx,Ry on the medium ME0 according to the dot data DA3. If the rasterization process in S110 is not performed, the controller 10 may generate a drive signal SG1 corresponding to the voltage signal applied to the drive element 32 from the dot data DA3 in the drive signal transmission unit 15 and output the drive signal SG1 to the drive circuit 31 of the print head 30. After processing in S112, the controller 10 terminates the print control process.

[0064] (4) Effects and benefits related to specific examples: Figure 10 schematically shows an example in which the dots 38 are evenly distributed by bringing the summation ratio Sy / Sx, calculated from the distribution ratio Ri, closer to the resolution ratio Ry / Rx. Figure 10 schematically shows partial dot arrangements 111, 112, 121, 122 that may appear in the low-gradation areas of a printed image depending on the resolution ratio Ry / Rx and the summation ratio Sy / Sx. Of course, the actual dot arrangement will not necessarily be the dot arrangements 111, 112, 121, 122 shown in Figure 10.

[0065] When the resolution ratio Ry / Rx is 1 / 4 and the resolution Rx in the X direction is greater than the resolution Ry in the Y direction, and the summation ratio Sy / Sx is 1 and the weight of the allocation ratio Ri is the same in the X and Y directions, the dot arrangement may be biased, for example, as in dot arrangement 111. This bias in dot arrangement in the low-gradation areas may manifest as an undesirable sequence of dots called a worm. When halftone processing using dithering is performed on the low-tone areas of an image using a Bayer mask that achieves a regular dot arrangement, a periodic pattern inevitably appears in some tone. Such periodic patterns are noticeable and degrade the quality of the printed image. When halftone processing using dithering is performed on the low-tone areas of an image using a dither mask with a threshold set to exclude the tone that will produce the periodic pattern, tonal clarity is not ensured.

[0066] In this specific example, by performing halftone processing using the error diffusion method, gradation is ensured, and by bringing the sum ratio Sy / Sx in the distribution ratio table TA0 close to the resolution ratio Ry / Rx, a uniform dot distribution is achieved in both the X and Y directions. For example, if the resolution ratio Ry / Rx is 1 / 4 and the sum ratio Sy / Sx is adjusted to 1 / 4, the dots will be evenly distributed in both the X and Y directions, as shown in dot arrangement 112. Therefore, a high-quality printed image IM0 is formed that achieves both gradation and even dot distribution.

[0067] When the resolution ratio Ry / Rx is 4 and the resolution Ry in the Y direction is greater than the resolution Rx in the X direction, and the summation ratio Sy / Sx is 1 and the weight of the allocation ratio Ri is the same in the X and Y directions, the dot arrangement may be biased, for example, as in dot arrangement 121. This bias in dot arrangement in the low-gradation areas may manifest as an undesirable sequence of dots called a worm. For example, if the resolution ratio Ry / Rx is 4 and the sum ratio Sy / Sx is adjusted to 4, the dots will be evenly distributed in both the X and Y directions, as shown in dot arrangement 122. Therefore, a high-quality printed image IM0 is formed that achieves both gradation and even dot distribution.

[0068] As explained above, even if the resolution Rx in the X direction and the resolution Ry in the Y direction are different, the dots 38 are arranged to be evenly distributed in both the X and Y directions. Therefore, this specific example can improve the image quality of the printed image IM0 in terms of granularity, especially in the low-gradation areas, and can contribute to improving granularity in accordance with the resolution ratio Ry / Rx of the printed image IM0.

[0069] (5) Variations: Various modifications of this invention are conceivable. For example, the types of colorants used to form a printed image on a medium are not limited to C, M, Y, and K. In addition to C, M, Y, and K, orange, green, light cyan at a lower concentration than C, light magenta at a lower concentration than M, dark yellow at a higher concentration than Y, light black at a lower concentration than K, and uncolored colorants for improving image quality may also be included. Furthermore, this technology can be applied even when some of the colorants C, M, Y, and K are not used.

[0070] The entity performing the above-described processing is not limited to the CPU; it may also be an electronic component other than the CPU, such as an ASIC. Of course, multiple CPUs may cooperate to perform the above-described processing, or a CPU and another electronic component (such as an ASIC) may cooperate to perform the above-described processing. The processes described above can be modified as needed, such as by changing the order of operations. For example, in the print control process shown in Figure 8, the distribution ratio table selection process in S106 can be performed immediately before the color conversion process in S104. Some of the processes described above may be performed by the host device HO1. In this case, the combination of controller 10 and host device HO1 becomes an example of printing device 1. When host device HO1 performs halftone processing using the error diffusion method, host device HO1 becomes an example of image processing device U0.

[0071] In the specific example described above, it was shown that the sum ratio Sy / Sx should match the resolution ratio Ry / Rx. However, as long as the relationship between the resolution ratios (RR1, RR2) and the sum ratios (SR1, SR2) is satisfied, the sum ratio Sy / Sx may deviate from the resolution ratio Ry / Rx. For example, suppose the first resolution ratio RR1 is 1 / 4 and the second resolution ratio RR2 is 1 / 2. In this case, the first sum ratio SR1 may be 11 / 40 (10% increase) and the second sum ratio may be 11 / 20 (10% increase), or the first sum ratio SR1 may be 9 / 40 (10% decrease) and the second sum ratio may be 9 / 20 (10% decrease). Of course, the degree of increase or decrease can be changed in various ways, such as a 15% increase, a 5% increase, a 5% decrease, a 15% decrease, etc. The same applies to cases where the first resolution ratio RR1 is 1 / 2 and the second resolution ratio RR2 is 1, where the first resolution ratio RR1 is 1 and the second resolution ratio RR2 is 2, where the first resolution ratio RR1 is 2 and the second resolution ratio RR2 is 4, and so on.

[0072] Incidentally, in the low-gradation areas of the printed image IM0, the graininess of the dots 38 is more noticeable when the dots 38 are formed with multiple colors, causing blurring, than when the dots 38 are formed with a single color. In particular, when at least one of the C and M dots 38 are sparsely formed against a Y background, an uneven distribution of these dots 38 can create an unnatural appearance. Therefore, the halftone processing using the error diffusion method described above may be limited to cases where at least one of the C and M dots 38 are sparsely formed against a Y background.

[0073] Figure 11 schematically shows another example of the print control process performed by the controller 10 shown in Figure 1. Note that in the print control process shown in Figure 11, parts where the same process as in the print control process shown in Figure 8 is performed are denoted by the same reference numerals as in Figure 8, and detailed explanations are omitted. When the print control process shown in FIG. 11 starts, the controller 10 acquires the print resolutions Rx and Ry (S102), and performs color conversion processing to convert the original image data DA1 into ink amount data DA2 (S104). The ink amount data DA2 has pixel values of C, M, Y, and K for each pixel PX0. Here, the ink amount data DA2 only needs to have pixel values of at least C, M, and Y for each pixel PX0, and may not have a pixel value of K.

[0074] After the color conversion processing, in the halftone processing unit 13, the controller 10 determines whether at least one dot 38 of C and M is formed with Y as the background based on the ink amount data DA2 (S302). For example, assume that the pixel values of the ink amount data DA2 are gradation values from 0 to 255, the threshold value (denoted as THY) for discriminating the background of Y is greater than 128 and less than 255. Also assume that the threshold value (denoted as THZ) for discriminating that dots 38 other than Y are sparsely formed is greater than 0 and less than 127. That is, 0 < THZ < THY < 255 holds. If there are pixels in the plurality of pixels PX0 constituting the ink amount data DA2 where the pixel value of Y is greater than or equal to the threshold value THY and the pixel value of at least one of C and M is less than or equal to the threshold value THZ, the controller 10 can determine that the condition is satisfied in S302. On the other hand, if there are no pixels in the plurality of pixels PX0 constituting the ink amount data DA2 where the pixel value of Y is greater than or equal to the threshold value THY and the pixel value of at least one of C and M is less than or equal to the threshold value THZ, the controller 10 can determine that the condition is not satisfied in S302.

[0075] When the controller 10 determines that the condition is satisfied in S302, in the halftone processing unit 13, it selects the distribution ratio table TA0 associated with the resolution ratio Ry / Rx (S106), and performs halftone processing by the error diffusion method shown in FIG. 9 (S108). On the other hand, when the controller 10 determines that the condition is not satisfied in S302, in the halftone processing unit 13, it performs halftone processing different from S108, for example, halftone processing by the dither method (S304). After the halftone processing in S108 or S304, the controller 10 performs an optional rasterization process (S110) and outputs a drive signal SG1 to the drive circuit 31 of the print head 30 (S112). As a result, the printer 2 drives the print head 30 and the drive unit 50 to form a print image IM0 with output resolution Rx,Ry on the medium ME0 according to the dot data DA3.

[0076] In the example shown in Figure 11, when at least one of the dots 38 of C and M is formed with Y as the background, they are arranged to be more evenly distributed according to the resolution ratio Ry / Rx of the printed image IM0, thereby improving the image quality of the printed image IM0.

[0077] Furthermore, even when Ry > Rx and the range in the Y direction where multiple destination pixels Qi are located is not wider than the range in the X direction where multiple destination pixels Qi are located, a basic effect that contributes to improving granularity in accordance with the image resolution ratio Ry / Rx can still be obtained. Even when Rx > Ry and the range in the X direction where multiple destination pixels Qi are located is not wider than the range in the Y direction where multiple destination pixels Qi are located, a basic effect that contributes to improving granularity in accordance with the image resolution ratio Ry / Rx can be obtained.

[0078] (6) Conclusion: As explained above, according to the present invention, it is possible to provide technologies that contribute to improving granularity in accordance with the resolution ratio of an image, in various embodiments. Of course, even a technology consisting only of the constituent elements of an independent claim can obtain the basic functions and effects described above. Furthermore, configurations obtained by substituting or changing the combinations of each configuration disclosed in the above-mentioned examples, configurations obtained by substituting or changing the combinations of each configuration disclosed in the prior art and the above-mentioned examples, etc., are also possible. The present invention also includes these configurations, etc. [Explanation of Symbols]

[0079] 1…Printing device, 2…Printer, 10…Controller, 13…Halftone processing unit, 24…Operation panel, 30…Print head, 38…Dot, 50…Drive unit, 111,112,121,122…Dot arrangement, DA1…Original image data, DA2…Ink amount data, DA3…Dot data, E0,Ei,EP0…Error, HO1…Host device, IM0…Printed image, MP0…Pixel value, ME0…Medium, P0…Change Pixel to be converted, PX0...pixel, PX1...unconverted pixel, PX2...converted pixel, Qi...destination pixel, Ri...allocation ratio, RR1...first resolution ratio, RR2...second resolution ratio, Rx, Ry...resolution, SR1...first sum ratio, SR2...second sum ratio, ST1...conversion process, ST2...diffusion process, Sx, Sy...sum, TA0, TA1~TA5...allocation ratio table, U0...image processing device, U1...conversion unit, U2...diffusion unit, U3...printing unit.

Claims

1. An image processing apparatus capable of converting image data in which a first-direction resolution in a first direction and a second-direction resolution in a second direction intersecting the first direction are set into dot data representing the dot formation state by error diffusion method, A conversion unit that determines the dot formation state based on the pixel value and the allocated error in a pixel to be converted that is included in a plurality of pixels constituting the image data, The system includes a diffusion unit that diffuses the error generated in the target pixel to be converted to a plurality of destination pixels that have not been converted, according to the allocation ratio set for each of the destination pixels. The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the first direction with respect to the conversion target pixel is defined as the sum in the first direction, and the sum in the first direction is not zero. The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the second direction with respect to the conversion target pixel is defined as the second-direction sum, and the second-direction sum is not zero. The ratio of the sum in the second direction to the sum in the first direction is defined as the sum ratio. The ratio of the second-direction resolution to the first-direction resolution is defined as the resolution ratio. When the resolution ratio is the first resolution ratio, the sum ratio is defined as the first sum ratio. When the resolution ratio is a second resolution ratio which is greater than the first resolution ratio, the summation ratio is taken as the second summation ratio. An image processing device wherein each of the aforementioned allocation ratios is set for the destination pixels such that the second summation ratio is greater than the first summation ratio.

2. The image processing apparatus according to claim 1, wherein each of the aforementioned allocation ratios is set for the destination pixels such that the sum ratio matches the resolution ratio.

3. The image data has at least the pixel values ​​of cyan, magenta, and yellow for each of the pixels. The image processing apparatus according to claim 1, wherein when at least one of the dots of cyan and magenta is formed on a yellow background, the image data is converted into dot data by the error diffusion method.

4. If the resolution in the first direction is greater than the resolution in the second direction, the range in which the plurality of destination pixels are arranged in the first direction is wider than the range in which the plurality of destination pixels are arranged in the second direction. The image processing apparatus according to claim 1, wherein, if the second-direction resolution is greater than the first-direction resolution, the range in which the plurality of destination pixels are arranged in the second direction is wider than the range in which the plurality of destination pixels are arranged in the first direction.

5. An image processing apparatus according to any one of claims 1 to 4, A printing apparatus comprising: a printing unit that forms a printable image on a medium according to the dot data, having the first-direction resolution in the first direction and the second-direction resolution in the second direction.

6. An image processing method that converts image data in which a first-direction resolution in a first direction and a second-direction resolution in a second direction intersecting the first direction are set into dot data representing the dot formation state by error diffusion method, A conversion step in which, in a pixel to be converted that is included in a plurality of pixels constituting the image data, the formation state of the dot is determined based on the pixel value and the distributed error, The process includes a diffusion step in which the error generated in the pixel to be converted is diffused to the plurality of unconverted destination pixels according to the allocation ratio set for each of the plurality of destination pixels, The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the first direction with respect to the conversion target pixel is defined as the sum in the first direction, and the sum in the first direction is not zero. The sum obtained by multiplying the allocation ratio set for each of the allocation destination pixels by the relative position of the allocation destination pixel in the second direction with respect to the conversion target pixel is defined as the second-direction sum, and the second-direction sum is not zero. The ratio of the sum in the second direction to the sum in the first direction is defined as the sum ratio. The ratio of the second-direction resolution to the first-direction resolution is defined as the resolution ratio. When the resolution ratio is the first resolution ratio, the sum ratio is defined as the first sum ratio. When the resolution ratio is a second resolution ratio which is greater than the first resolution ratio, the summation ratio is taken as the second summation ratio. An image processing method in which each of the aforementioned allocation ratios is set in the destination pixels such that the second summation ratio is greater than the first summation ratio.

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