CN101489020A - Image processing for enhanced print quality around edges - Google Patents

Abstract

The present invention provides an image processing device capable of determining the formation state of dots in each printing pixel so as to improve the printing quality. The image processing device specifies a dot formation state when an image is printed with dots of a plurality of sizes based on image data representing an image. The image processing device is provided with: an edge detection unit, from the pixels constituting the image data, detects pixels of the color of the dots used for image printing, that is, dot color edge pixels located at the edge of the image; Pixels are assigned the same size as points.

Description

Image processing to improve print quality near the edges

technical field

The present invention relates to image processing capable of improving print quality near edges in an image.

Background technique

Inkjet printers are known as printing devices for printing images by forming dots on various printing media such as paper, cloth, and film. Inkjet printers, for example, form ink dots on the printing medium by ejecting inks of cyan (C), magenta (M), yellow (Y), and black (K) onto the printing medium, thereby converting the image to the printing medium. Printed on print media. In an inkjet printer, it is possible to form dots of various sizes such as large dots (L dots), medium dots (M dots), and small dots (S dots).

When an inkjet printer prints an image, processing (referred to as halftone processing) of specifying the formation state of dots in each printing pixel is generally performed based on image data representing the image (see, for example, Patent Document 1). Here, specifying the formation state of dots in each printing pixel means specifying which color and which size of dots are to be formed (or not formed) in each printing pixel.

Patent Document 1: JP-A-2007-118238

In halftone processing, in order to suppress occurrence of color bleeding or the like, a limit may be placed on the total amount of ink per unit area of the printing medium. In this case, there is a concern that, for example, dots of different sizes may be mixedly formed in printed pixels constituting text in an image or an edge portion of a line drawing, or no dots may be formed in a part of the printed pixels, due to the Jagged or missing, resulting in reduced printing quality.

In addition, this problem is not limited to printing an image by an inkjet printer, but is a common problem when specifying the formation state of dots in each printing pixel when printing an image using dots.

Contents of the invention

The present invention was made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a technology capable of specifying the formation state of dots in each printing pixel to improve the printing quality.

In order to solve at least part of the above problems, the present invention can be implemented as the following forms or application examples.

[Application example 1] An image processing device that specifies, based on image data representing an image composed of a plurality of pixels, a dot formation state when the image is printed with dots of a plurality of sizes, comprising:

an edge detection section detecting, from among pixels constituting the image data, a pixel of a color of a dot used for printing of the image, that is, a color edge pixel of a dot positioned at an edge in the image; and

The dot allocation unit allocates dots of the same size to the edge pixels of the dot color when the image is printed.

In this image processing device, dot-color edge pixels are detected from pixels constituting image data, and dots of the same size are assigned to dot-color edge pixels during image printing, so that jaggedness or chipping of edges can be suppressed, and printing quality can be improved.

[Application example 2] is the image processing device described in Application example 1,

The dots of the same size are dots other than the dot of the largest size among the dots of the plurality of sizes.

In this image processing device, bleeding or thickening of the edge portion can be suppressed, and the print quality can be further improved.

[Application example 3] is the image processing device described in Application example 1 or Application example 2,

The edge detection unit detects, from pixels constituting the image data, pixels of a dot color used for printing the image, that is, the dot color edge in the image whose distance from the edge is equal to or less than a predetermined value. Point color edges other than pixels adjacent to pixels;

The dot allocating unit allocates dots other than the largest dot among the dots of the plurality of sizes to the edge adjacent pixels of the dot color when the image is printed.

In this image processing device, since dot color edge adjacent pixels are detected from the pixels constituting the image data, dots other than the largest dot among dots of a plurality of sizes are assigned to the dot color edge adjacent pixels during image printing, so better Bleeding or thickening in the edge portion is effectively suppressed, and the printing quality is further improved.

[Application Example 4] is the image processing device described in Application Example 3,

The multiple sizes are more than 3 types of sizes;

When the image is printed, the dot size of the dot-color edge adjacent pixels is larger than the dot size of the dot-color edge pixels when the image is printed.

In this image processing device, bleeding or thickening of the edge portion can be more suppressed, and the printing quality can be further improved.

[Application Example 5] is the image processing device described in Application Example 3,

The dot allocating unit includes a halftone processing unit for specifying a dot formation state for pixels excluding the dot color edge pixel and the dot color edge adjacent pixel among the pixels constituting the image data by halftone processing.

In this image processing apparatus, since the dot formation state is determined by halftone processing for pixels other than the dot-color edge pixel and the dot-color edge-adjacent pixel, it is possible to calculate the total amount per unit area of the printing medium except for the edge-adjacent portion. The amount of ink is limited, which can suppress the bleeding of the color and improve the printing quality.

[Application Example 6] is the image processing device described in Application Example 1,

The image is an image composed of only one of white and the color of dots used for printing the image.

In this image processing device, when an image is printed using only one of white and the color of dots used for image printing, the print quality can be improved.

[Application Example 7] is the image processing device described in Application Example 1,

The image is an image composed of only one of black and the color of dots used for printing the image.

In this image processing device, when an image is printed using only one of black and dot colors used for image printing, the print quality can be improved.

[Application example 8] is the image processing device described in Application example 1,

The dots of the plurality of sizes are formed by the plurality of ink ejection amounts.

In this image processing device, it is possible to improve the print quality when printing is performed using dots of a plurality of sizes formed by a plurality of ejection amounts of ink.

[Application example 9] is the image processing device described in Application example 1,

The dots of the plurality of sizes are formed by a plurality of ink ejection times.

In this image processing device, it is possible to improve the printing quality when printing with dots of multiple sizes formed by multiple times of ink ejection.

[Application example 10] is the image processing device described in Application example 1,

The edge detection unit detects the dot color edge pixels from among pixels constituting the image data according to an RGB color space.

In this image processing device, since the dot color edge pixels are detected from the pixels constituting the image data based on the RGB color space, dots of the same size are allocated to the dot color edge pixels during image printing, so that jaggedness or lack of edges can be suppressed. , Improve printing quality.

In addition, the present invention can be realized in various forms, for example, it can be implemented as an image processing method and device, a dot formation state determination method and device, a dot data generation method and device, a print data generation method and device, a printing method and device, these methods or a computer program for device functions, a recording medium recording the computer program, or a data signal embodied in a carrier wave including the computer program.

Description of drawings

FIG. 1 is an explanatory diagram schematically showing the structure of a printing system in an embodiment of the present invention.

FIG. 2 is a flowchart showing the flow of determination processing of the dot formation state.

FIG. 3 is an explanatory view showing an example of an image to be printed after resolution conversion processing.

FIG. 4 is an explanatory diagram showing the configuration of the output buffer 32 .

FIG. 5 is an explanatory diagram showing a correspondence between the pixel position of the target image and the state of the output buffer 32 .

FIG. 6 is an explanatory diagram showing the correspondence between the pixel position of the target image and the state of the output buffer 32 .

FIG. 7 is an explanatory diagram showing a correspondence between the pixel position of the target image and the state of the output buffer 32 .

FIG. 8 is a flowchart showing the flow of a distance determination process from an edge.

FIG. 9 is an explanatory diagram showing the relationship between a pixel of interest, an adjacent pixel, and a pixel separated by two pixels.

FIG. 10 is an explanatory diagram showing an example of the dot formation state determined according to the present embodiment.

Symbol Description

10 applications

20 Printer driver

21 Resolution conversion processing unit

22 Edge detection department

23 Color conversion processing department

24 Halftone Processing Department

26 point distribution department

27 rasterizing processing unit

32 output buffer

40 Print object image

100 personal computers

110C PU

120 memory

130 Input and output interface part

200 printers

210 CPU

220 memory

230 Input and output interface part

240 unit control circuit

250 head unit

260 bracket units

270 Conveyor unit

1000 printing system

Detailed ways

Hereinafter, embodiments of the present invention will be described in the following order based on examples.

A embodiment:

B modification example:

A embodiment:

FIG. 1 is an explanatory diagram schematically showing the structure of a printing system in an embodiment of the present invention. The printing system 1000 in this embodiment includes a personal computer 100 as an image processing device, and a printer 200 connected to the personal computer 100 by wire or wirelessly.

The personal computer 100 includes: a CPU 110 for performing various processes or controls by executing programs, a memory 120 for storing programs or data/information, and an input/output interface (I/O) for exchanging data or information with external peripheral devices. F) Part 130. The memory 120 has an output buffer 32 used in a process of specifying a dot formation state to be described later. The personal computer 100 may further include an input device such as a keyboard or a pointing device, a display device such as a monitor, a recording/reproducing device such as a CD-ROM drive, and the like.

Programs such as the application program 10 and the printer driver 20 are installed in the personal computer 100 . The application program 10 or the printer driver 20 is executed by the CPU 110 under a predetermined operating system (not shown).

The application program 10 is, for example, a program for realizing an image editing function. The user can give an instruction to print the image edited by the application 10 through the user interface provided by the application 10 . When the application 10 receives a print instruction from the user, it outputs image data constituting a print target to the printer driver 20 . In addition, in this embodiment, image data is output as RGB data.

The printer driver 20 is a program for realizing a function of generating print data from image data output from the application program 10 . The printer driver 20 is distributed by being stored in various storage media (such as a computer-readable recording medium) such as a CD-ROM, or distributed via various communication means such as the Internet.

The printer driver 20 receives image data from the application program 10 , generates print data based on the image data, and outputs the generated print data to the printer 200 . Here, the print data is data in a format interpretable by the printer 200 and includes various command data and dot data. The command data is data for instructing the printer 200 to execute a specific operation. The dot data is data indicating the formation state of dots in pixels (printing pixels) constituting a printed image (printing image), specifically, indicating which color and size of dots (or not) are formed in each printing pixel. form point) data. Here, a "dot" refers to an area formed after ink ejected from the printer 200 lands on a printing medium.

As shown in FIG. 1 , the printer driver 20 includes a resolution conversion processing unit 21 , an edge detection unit 22 , a color conversion processing unit 23 , a halftone processing unit 24 , a dot allocation unit 26 , and a rasterization processing unit 27 . The color conversion processing unit 23 , the halftone processing unit 24 , and the dot allocating unit 26 correspond to the dot allocating unit in the present invention.

The resolution conversion processing unit 21 performs resolution conversion processing for converting the resolution ratio of the image data output from the application program 10 to match the printing resolution of the printer 200 .

The edge detection unit 22 determines whether or not each pixel constituting the image data is a black edge pixel, a black edge adjacent pixel, or a pixel that is neither a black edge pixel nor a black edge adjacent pixel (hereinafter referred to as a "normally processed pixel"). one. Here, the so-called black edge pixels in this embodiment are black pixels, which are pixels located at the black edge in the image. In addition, a pixel on a black edge is a pixel in which adjacent pixels adjacent to the pixel in at least one direction of up, down, left, right, upper right, lower right, upper left, and lower left are of a color other than black. In addition, in this embodiment, the black edge pixels are represented as having a distance of 1 from the black edge. In addition, the so-called black edge adjacent pixels are black pixels other than black edge pixels whose distance from the black edge is equal to or less than a predetermined value. In this embodiment, the predetermined value is set to 2. That is, the black edge adjacent pixels are black pixels other than the black edge pixels, and are pixels adjacent to the black edge pixels. In this embodiment, pixels adjacent to the black edge appear to have a distance of 2 from the black edge.

The color conversion processing unit 23 performs color conversion processing on a normal processing pixel (that is, a pixel that is not a black edge pixel or a black edge adjacent pixel) among the pixels constituting the image data. The printer 200 used in this embodiment is a printer that performs printing using inks of cyan (C), magenta (M), yellow (Y), and black (K). Therefore, the color conversion processing unit 23 converts the pixel value represented by the RGB value into the CMYK value for each target pixel.

The halftone processing unit 24 performs halftone processing based on the pixel value after the color conversion processing by the color conversion processing unit 23 , specifies the dot formation state in the printing pixel corresponding to the normal processing pixel, and records it in the output buffer 32 . In the present embodiment, the halftone processing section 24 performs halftone processing by dither matrix threshold value processing while setting a limit on the total amount of ink per unit area of the printing medium. In addition, the printer 200 used in this embodiment is capable of forming small-sized small dots (hereinafter also referred to as "S dots"), medium-sized mid-sized dots (hereinafter also referred to as "M dots"), and large-sized large dots. A dot printer for 3 types of dot sizes (hereinafter also referred to as "L dots"). Therefore, as the formation state of the dots in the printing pixels, for each ink color, there are a total of four selection branches: no dots are formed, S dots are formed, M dots are formed, and L dots are formed.

The dot allocating unit 26 allocates predetermined dots to printing pixels corresponding to black edge pixels and black edge adjacent pixels among pixels constituting the image data, thereby specifying dots among printing pixels corresponding to black edge pixels and black edge adjacent pixels. The resulting state is recorded in the output buffer 32 . The method of allocating points by the point allocating unit 26 will be described in detail later.

The rasterization processing unit 27 generates dot data based on the formation state of dots recorded in each printing pixel in the output buffer 32 , and sorts the dot data in the order to be transmitted to the printer 200 .

The printer 200 of this embodiment is an inkjet printer that forms ink dots on a printing medium to print an image. The printer 200 includes: a CPU 210 that executes overall control of the printer 200 or various processes by executing programs, a memory 220 that stores programs or data/information, and an input/output for exchanging data or information with an externally connected personal computer 100 The interface (I/F) part 230 controls the unit control circuit 240 of each unit, the head unit 250, the carriage unit 260, and the conveyance unit 270 according to the instruction|indication from CPU210.

The head unit 250 has a head (not shown) for ejecting ink onto the printing medium. The head has a plurality of nozzles, and ink is ejected intermittently from each nozzle. The head is mounted on a carriage (not shown), and when the carriage moves in a predetermined scanning direction (main scanning direction), the head also moves in the main scanning direction. By intermittently ejecting ink while the head is moving in the main scanning direction, dot lines (raster lines) in the main scanning direction are formed on the printing medium.

The carriage unit 260 is a driving device for reciprocating the carriage of the mounting head in the main scanning direction. In addition to the head, an ink cartridge for storing ink is detachably held on the carriage.

The transport unit 270 is a driving device for performing sub-scanning by transporting the printing medium to a printable position and transporting the printing medium by a predetermined transport amount in a predetermined transport direction during printing. The transport unit 270 is composed of, for example, a paper feed roller, a transport motor, transport rollers, drums, and paper discharge rollers (not shown).

When the user instructs image printing on the application 10 , a print command is issued from the application 10 to the printer driver 20 . Image data (RGB data) edited on the application program 10 is included in this print order.

In the printer driver 20 that has received the print command, the resolution conversion processing unit 21 converts the resolution of the image data included in the print command to match the print resolution. Next, the edge detection unit 22 determines whether or not each pixel constituting the image data is one of black edge pixels, black edge adjacent pixels, and normal processing pixels. For a pixel determined to be a normal processing pixel, the dot formation state is specified by the color conversion processing by the color conversion processing unit 23 and the halftone processing by the halftone processing unit 24 . For pixels determined to be black edge pixels and black edge adjacent pixels, the dot formation state is determined by the dot allocating unit 26 . The determined dot formation state is recorded in the output buffer 32 . The processing for specifying the formation state of dots will be described in detail later. The rasterization processing unit 270 generates dot data based on the formation state of dots recorded in each printing pixel in the output buffer 32, and at the same time, sorts the dot data in the order to be transmitted to the printer 200, and transfers the dot data containing dots through the input/output interface unit 130. The print data of the data is output to the printer 200 .

When the printer 200 receives print data from the personal computer 100, it executes print processing. First, CPU 210 receives print data from personal computer 100 via input/output interface unit 230 , and analyzes the contents of various commands included in the received print data. CPU 210 controls transport unit 270 through unit control circuit 240 based on the analysis result. Through this control, the transport unit 270 supplies the paper (print medium) to be printed into the printer 200 and positions the paper at the printing start position.

Next, CPU 210 controls cradle unit 260 through unit control circuit 240 . Through this control, the carriage unit 260 moves the carriage of the mounting head in the main scanning direction. Further, CPU 210 controls head unit 250 through unit control circuit 240 based on print data. Through this control, the head unit 250 intermittently ejects ink from the head moving in the main scanning direction according to the print data, and the ejected ink drops land on the paper to form dots on the paper. Further, the CPU 210 controls the conveyance unit 270 to convey the paper in the conveyance direction and move it relative to the head. Thus, the head can form dots at positions different from those previously formed. In this way, before data for printing is available, processes such as dot formation and transport are repeated, and an image composed of dots is printed on paper. After that, if the data for printing is gone, the printing process ends.

FIG. 2 is a flowchart showing the flow of determination processing of the dot formation state. The dot formation state specifying process is a process of specifying the dot formation state in each printing pixel based on the image data after the resolution conversion process, and recording it in the output buffer 32 .

In addition, FIG. 3 is an explanatory diagram showing an example of an image to be printed after resolution conversion processing. Next, an example of printing processing based on the print target image 40 shown in FIG. 3 will be described. The print target image 40 shown in FIG. 3 includes the line drawing A. As shown in FIG. Line image A is composed of 6 horizontal x 14 vertical black pixels. All the pixels in the portion of the image to be printed 40 other than the line drawing A are white pixels. That is, the print target image 40 is a monochrome image composed of only white and black which is one dot color. In addition, in FIG. 3 , x marks indicate a pixel of interest described later, and solid arrows indicate the trajectory of movement of the pixel of interest.

FIG. 4 is an explanatory diagram showing the configuration of the output buffer 32 (see FIG. 1 ). The output buffer 32 is configured to be able to record the dot formation state in printing pixels corresponding to each pixel of the printing target image 40 . A portion 32A shown in FIG. 4 is a portion corresponding to the line drawing A of the print target image 40 . In addition, the output buffer 32 is not necessarily configured to be able to record the dot formation state in the printing pixels corresponding to the pixels of the entire printing target image 40. ) unit, the output buffer 32 may be configured as long as it can record the dot formation state in the printing pixels corresponding to each pixel in the band.

In step S102 ( FIG. 2 ), the edge detection unit 22 ( FIG. 1 ) reads the image data subjected to resolution conversion processing by the resolution conversion processing unit 21 . In step S104 , the edge detection unit 22 sets the upper left pixel in the print target image 40 as the first pixel of interest. FIG. 5 to FIG. 7 are explanatory diagrams showing correspondence between the pixel position of the image of interest and the state of the output buffer 32 . 5 to 7 show the position of the pixel of interest (indicated by an X) in relation to the line drawing A (see FIG. 3 ) on the print target image 40, and the positions in the output buffer 32 are shown in the lower section. The state of the portion 32A (refer to FIG. 4 ) corresponding to the line diagram A. The symbol "S" in the figure indicates the dot formation state of "S dot formation". Similarly, the symbol "M" in the figure represents the dot formation state of "M dots are formed", and the symbol "L" represents the dot formation state of "L dots are formed". As time passes, the state (state a) at the left end of FIG. The state (state k) at the left end of FIG. 7 transitions to the state (state n) at the right end. State a shown in FIG. 5 represents a state when the upper left pixel in the print target image 40 is set as the first pixel of interest.

In step S106 ( FIG. 2 ), the edge detection unit 22 ( FIG. 1 ) determines whether or not the pixel of interest is a black pixel. Since all parts of the print target image 40 used in this embodiment other than the line drawing A are white, it is determined that the pixel of interest is not a black pixel in state a of FIG. 5 . When it is determined that the pixel of interest is not a black pixel (step S106: No), the color conversion processing unit 23 ( FIG. 1 ) performs color conversion processing, and the halftone processing unit 24 performs halftone processing (step S108 ). As a result of the halftone processing, the dot formation state of the printing pixel corresponding to the pixel of interest is determined as the state of "no dot formation".

Thereafter, in step S122 ( FIG. 2 ), the edge detection unit 22 determines whether or not the pixel of interest is a pixel at the right end of the print target image 40 . When it is determined that the pixel of interest is not the pixel at the right end of the print target image 40 (step S122: No), the edge detection unit 22 shifts the pixel of interest by one pixel to the right (step S124). Thereafter, the process returns to step S106. In state a of FIG. 5 , when the dot formation state of the printing pixel corresponding to the pixel of interest is specified, the pixel of interest is shifted to the right by 1 pixel (step S124 ). After that, in step S106, it is determined again that the pixel of interest is not a black pixel. Therefore, even in this state, the color conversion processing by the color conversion processing section 23 and the halftone processing by the halftone processing section 24 are executed (step S108), and the dot formation state of the printing pixel corresponding to the pixel of interest is determined as " Do not form a point" state. This process is repeated, and when the pixel of interest moves to the right end of the print target image 40 from state a in FIG. 5 , it is determined in step S122 that the pixel of interest is the right end. At this time, the edge detection unit 22 determines whether or not the pixel of interest is a pixel at the lower end of the image (step S126 ). When it is determined that the pixel of interest is not a pixel at the lower end of the image (step S126: No), the edge detection unit 22 moves the pixel of interest to the left end of the image one line below (step S128). Thereafter, the process returns to step S106.

The above process is repeated, and when the pixel of interest moves to the position shown in state b in FIG. 5 , it is determined in step S106 that the pixel of interest is a black pixel. At this time, the edge detection unit 22 executes a distance determination process from the edge (step S110 ). The distance determination process from the edge is a process of determining whether the distance of the pixel of interest from the black edge is one of "1", "2" and "greater than 2". That is, the distance determination process from the edge is a process of determining whether the pixel of interest is one of a black edge pixel, a black edge adjacent pixel, and a normal processing pixel.

FIG. 8 is a flowchart showing the flow of a distance determination process from an edge. In addition, FIG. 9 is an explanatory diagram showing the relationship between a pixel of interest, an adjacent pixel, and a pixel separated by two pixels. As shown in FIG. 9 , eight pixels (P1 to P8) adjacent to the pixel of interest P0 in each of the upper, lower, left, right, upper right, lower right, upper left, and lower left directions (P1 to P8) are referred to as adjacent pixels. In addition, the pixels ( P9 to P12 ) separated by 2 pixels from the pixel of interest P0 in each direction up, down, left, and right are referred to as 2-pixel separation pixels.

In step S202 ( FIG. 8 ), the edge detection unit 22 ( FIG. 1 ) determines whether or not there is a white pixel among pixels adjacent to the pixel of interest ( P1 to P8 in FIG. 9 ). When it is determined that there is a white pixel among the pixels adjacent to the pixel of interest (step S202: Yes), the distance from the black edge is set to 1 (step S204). This determination is because the pixel of interest is a black pixel and the adjacent pixel is a white pixel. A distance of 1 from the black edge means that the pixel of interest is a black edge pixel.

On the other hand, when it is determined that there is no white pixel in the adjacent pixels of the pixel of interest (step S202: No), the edge detection unit 22 determines whether the 2-pixel isolated pixel above the pixel of interest (P9 in FIG. 9 ) is a white pixel (step S206 ). When it is determined that the 2-pixel separation pixel above the pixel of interest is a white pixel (step S206: Yes), the edge detection unit 22 determines whether the adjacent pixel (P2 in FIG. 9 ) above the pixel of interest is a black pixel (step S208). When it is determined that the adjacent pixel above the pixel of interest is a black pixel (step S208: Yes), the distance from the black edge is set to 2 (step S210). Such determination is because the pixel of interest and the adjacent pixel above are black pixels, and the 2-pixel isolation pixel above is white pixel. A distance of 2 from the black edge means that the pixel of interest is a black edge neighbor. When it is determined that the adjacent pixel above the pixel of interest is not a black pixel (step S208: Yes), the process proceeds to step S212.

Next, similar to the determination of whether the upper pixel is a pixel adjacent to the black edge in steps S206 and S208 above, the determination of whether the pixel of interest is a pixel adjacent to the black edge is performed for the left, right, and lower sides, respectively. That is, in steps S212 and S214, the 2-pixel isolated pixel (P10 in FIG. 9 ) to the left of the pixel of interest is a white pixel (step S212: Yes), and the adjacent pixel to the left of the pixel of interest (P4 in FIG. 9 ) When it is a black pixel (step S214: yes), set the distance from the black edge to be 2 (that is, the attention pixel is a black edge adjacent pixel) (step 210). And, in steps S216 and S218, the 2 on the right side of the attention pixel The pixel isolation pixel (P11 of Fig. 9) is a white pixel (step S216: Yes), and when the adjacent pixel (P5 of Fig. 9 ) on the right side of the attention pixel is a black pixel (Step S218: Yes), the distance from the black edge is also set The distance is 2 (that is, the pixel of interest is a pixel adjacent to the black edge) (step S210). In addition, in steps S220 and S222, the 2-pixel isolated pixel below the pixel of interest (P12 in FIG. 9 ) is a white pixel (step S220: Yes), and the adjacent pixel below the pixel of interest (P7 in FIG. 9 ) is a black pixel (step S222: Yes), the distance from the black edge is also set to be 2 (that is, the pixel of interest is a pixel adjacent to the black edge) (step S210).

For one of top, left, right, and bottom, when it is determined that the pixel of interest is not a pixel adjacent to the black edge, the distance from the black edge is also set to be greater than 2 (step S224). A distance from the black edge greater than 2 means that the pixel of interest is a normally processed pixel.

When it is determined that the distance from the black edge is 1 (step S112: YES) by the distance determination process from the edge (step S110 of FIG. 2 ) shown in FIG. point (step S114). Since it is determined that the distance from the black edge is 1 (that is, the pixel of interest is a black edge pixel) when the pixel of interest is located at the position shown in state b of FIG. In the area of , record the formation status of the dot "form S dot". Thereafter, moving the pixel of interest and determining the dot formation state based on the determination result of the pixel of interest are repeated, and the state of the output buffer 32 transitions as shown in state c and state d in FIG. 5 .

When the pixel of interest moves to the position shown in state e in FIG. 5 , it is determined that the distance from the black edge is 2 in the edge distance determination process (step S110 in FIG. 2 ) (step S116: YES). At this time, the dot assignment unit 26 ( FIG. 1 ) assigns M dots to the pixel of interest, and records the dot formation state of "M dots formed" in the area corresponding to the pixel of interest in the output buffer 32 (step S118). Afterwards, the movement of the pixel of interest and the determination of the dot formation state based on the method according to the determination result of the pixel of interest are repeated, and the state of the output buffer 32 is as shown in state f, state g, state h, and state i of FIG. 6 migrate.

When the pixel of interest moves to the position shown in state j in FIG. 6 , it is determined that the distance from the black edge is greater than 2 in the edge distance determination process (step S110 in FIG. 2 ). That is, it is determined that the distance from the black border is neither 1 nor 2 (steps S112 and S116: NO). At this time, the pixel of interest becomes a normal processing pixel, and the color conversion processing of the color conversion processing 23 and the halftone processing of the halftone processing unit 24 are performed (step S120 ). When, for example, S dots are assigned to the pixel of interest as a result of halftone processing, the dot formation state of "S dots formed" is recorded in the area corresponding to the pixel of interest in the output buffer 32 (see state j in FIG. 6 ). Afterwards, the movement of the pixel of interest and the determination of the dot formation state based on the method according to the determination result of the pixel of interest are repeated, and the state of the output buffer 32 is as shown in state k, state 1, state m, and state n of FIG. 7 migrate. After state n, if the pixel of interest moves to the lower right end of the print target image 40 ( FIG. 3 ), it is determined in step S126 of FIG. 2 that the pixel of interest is the lower end of the image, and the process ends.

By the dot formation state determination processing described above, the dot formation state of the printing pixels corresponding to the line pattern A portion of the print target image 40 (see FIG. 3 ) is determined as shown in state n of FIG. 7 . In this state, when the printer 200 prints an image, S dots are formed in the printing pixels corresponding to the black edge pixels, and M dots are formed in the printing pixels corresponding to the black edge pixels. Also, the dot formation state of the printing pixels corresponding to the normal processing pixels whose distance from the black edge is greater than 2 is determined by normal halftone processing.

FIG. 10 is an explanatory diagram showing an example of the dot formation state determined according to the present embodiment. In FIG. 10( a ), it shows the dot formation state when printing a line pattern with a width W1 corresponding to 7 pixels of printing pixels, and in FIG. The state of dot formation on line graphs. The symbol "S" in FIG. 10 indicates the dot formation state of "S dot formation". Similarly, the symbol "M" represents the dot formation state of "M dots are formed", and the symbol "L" represents the dot formation state of "L dots are formed". In this embodiment, since dots of the same size (S dots in this embodiment) are assigned to all printing pixels corresponding to black edge pixels, jagged edges or lack of edges in the printed image are suppressed, and the printing quality is improved. . And, as shown in FIG. 10 (b), since when printing a thinner width line pattern, dots are allocated to the printing pixels corresponding to all the black edge pixels, and dots will not be missing. Printing quality is also improved for line drawings with a wider width.

Also, in this embodiment, since dots (in this embodiment, S dots) other than the largest dot (L dot) among dots of a plurality of sizes used for printing are allocated to the printing pixels corresponding to the black edge pixels, Therefore, bleeding or thickening in the edge portion is suppressed, and the print quality is further improved. In addition, in this embodiment, since a dot other than a dot (L dot) of the largest size among dots of a plurality of sizes used for printing is also assigned to a printing pixel corresponding to a pixel adjacent to the black edge (M dot in this embodiment) ), so bleeding or thickening in the edge portion is better suppressed, and the print quality is further improved. In addition, in this embodiment, since a dot larger in size than a dot (S dot in this embodiment) assigned to a printed pixel corresponding to a black edge pixel is assigned to a pixel adjacent to the black edge (this embodiment M point in the example), so bleeding or thickening in the edge portion is better suppressed, and the printing quality is further improved.

B: Variation

In addition, this invention is not limited to the said Example or embodiment, It can implement in various forms in the range which does not deviate from the summary, For example, the following modification is possible.

Modification 1 of B1:

In the above-described embodiment, dots of the smallest size, that is, S dots, are assigned to printed pixels corresponding to black edge pixels, but if dots of the same size are assigned to all printed pixels corresponding to black edge pixels, then M dots or L point. When M dots (or L dots) are allocated to all the printing pixels corresponding to the black edge pixels, jaggedness or lack of edge in the printed image is suppressed and dot loss does not occur, so the print quality is improved. In addition, it is more preferable to assign dots (S dots or M dots) other than the largest size dots (S dots or M dots) to printed pixels corresponding to black edge pixels, since bleeding or thickening in the edge portion is suppressed.

In addition, in the above-mentioned embodiment, M dots are assigned to the printing pixels corresponding to the pixels adjacent to the black edge, but it is only necessary to assign dots other than the largest size dot (L dot) to the printing pixels corresponding to the pixels adjacent to the black edge, for example , S points can be allocated to all the printing pixels corresponding to the pixels adjacent to the black edge, or M points can be allocated to a part of the printing pixels corresponding to the pixels adjacent to the black edge, and S points can be allocated to the remaining part.

In addition, in the above-mentioned embodiment, each pixel constituting the image data is discriminated into three types: black edge pixel, black edge adjacent pixel, and normal processing pixel, but it may be discriminated into two types: black edge pixel and normal processing pixel. In this case, it is also possible to assign S dots to all the printing pixels corresponding to the black edge pixels by determining the dot formation state by the color conversion processing and the halftone processing for the printing pixels corresponding to the normal processing pixels. Even so, jaggedness or chipping of the edge in the printed image is suppressed, and dot chipping does not occur, and bleeding or thickening of the edge portion is suppressed, so the print quality is also improved. Alternatively, at this time, M dots (or L dots) may be allocated to all printing pixels corresponding to black edge pixels. Even so, since jaggedness or chipping of edges in the printed image is suppressed, and dot chipping does not occur, the print quality is also improved. In addition, each pixel constituting the image data is discriminated into three types of black edge pixels, black edge adjacent pixels, and normal processing pixels, and if a dot other than the maximum size dot (L dot) is allocated to the printing pixel corresponding to the black edge adjacent pixel, Then, it is more preferable because bleeding or thickening in the edge portion is suppressed well.

B2 modification 2:

In the above-mentioned embodiment, the process of determining the dot formation state for improving the print quality in the vicinity of black edges has been described for an image composed only of white and black, but the present invention is also applicable to images composed of only white This is a process of determining the dot formation state for improving the print quality while the edge of the dot color is adjacent to an image composed of one dot color (for example, cyan, magenta, and yellow) used for image printing. That is, for each pixel constituting the image data, an edge pixel or an edge adjacent pixel of the color of the dot is detected, and a printed pixel corresponding to the detected edge pixel or edge adjacent pixel is assigned a predetermined dot instead of the normal halftone process. , the printing quality can be improved in the same way as in the above-mentioned embodiment.

In addition, the present invention is also applicable when the color of the printing medium is other than white. That is, the present invention can also be applied to an image composed of only the color of the printing medium (for example, black) and one of the dot colors used for image printing (for example, cyan, magenta, and yellow), and the dot color The determination processing of the dot formation state for improving the print quality near the edge.

Modification 3 of B3:

In the above-described embodiment, the same method is used to determine the dot formation state in the entire image to be printed 40, but it is also possible to only include characters or line drawings (symbols, figures, curves, etc.) in the image to be printed 40 The text area is used as an object, and the dot formation state is determined by using the method of the above-mentioned embodiment. In this case, for example, the text region can be detected based on the RGB values of the image data, and the text region can also be detected based on the brightness value of the pixel.

Modification 4 of B4:

In the above embodiments, the image data is RGB data, but the image data is not necessarily RGB data. In addition, in the above-mentioned embodiment, the printer 200 prints by using inks of 4 colors of CMYK to form dots of three types of sizes for printing, but the printer 200 may print by using inks of other colors than CMYK, or by forming 2 dots. Dots of different types (or more than 4 types) are used for printing.

In addition, in the above-described embodiment, the formation of dots of a plurality of sizes by the printer 200 can be realized by varying the ejection amount of ink according to the size of the dots to be formed. For example, as a waveform of a drive signal for controlling ink ejection, a waveform of ink ejecting amounts corresponding to dots of a plurality of sizes is prepared, and by ejecting ink using a waveform corresponding to the size of a formed dot, a dot of a desired size is formed. point. Alternatively, it is also possible to form dots of a desired size by providing nozzles having different ink ejection amounts on the head and ejecting ink from nozzles corresponding to the size of the dots to be formed. In addition, it is also possible to form dots of a plurality of sizes by varying the number of times ink is ejected according to the size of the dots to be formed. In addition, the ink can also be pressurized to continuously eject the liquid column of the ink. Using the principle that if the liquid column is heated by a heater, the liquid column will be separated into dots, and the timing of the heating pulse can be changed to realize the formation of multiple sizes. point.

In addition, in the above-mentioned embodiment, the color conversion processing unit 23 performs color conversion on a normal processing pixel (a pixel that is neither a black edge pixel nor a pixel adjacent to a black edge pixel), but the color conversion processing unit 23 may perform normal processing. Color conversion of pixels other than pixels. For example, the color conversion processing unit 23 may perform color conversion from RGB data to CMYK data for all pixels. In this case, the edge detection unit 22 may perform edge determination using CMYK data.

In addition, in the above-mentioned embodiment, the image data output from the application program 10 is RGB data, but the image data may be data of other colorimetric systems such as CMYK data. When the image data is data in another colorimetric system such as CMYK data, the edge detection unit 22 may use the data in another colorimetric system to perform edge determination.

Modification 5 of B5:

In the above-described embodiments, the image processing device is configured as the personal computer 100 , but the present invention can also be applied to an image processing device other than the personal computer 100 that performs image processing for specifying the dot formation state. For example, the image processing device may also be configured as the printer 200 .

Furthermore, in the above-described embodiments, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware.

Modification 6 of B6:

In the above-mentioned embodiments, a printer in which the head for ejecting ink onto the printing medium moves in the main scanning direction is taken as an example, but it can also be applied to a linear head printer in which a plurality of heads are arranged in line in the main scanning direction and the heads do not move. .

Furthermore, in the above-mentioned embodiment, the head has a plurality of nozzles, but the head may have only one nozzle.

In addition, in the above-mentioned embodiment, the personal computer 100 has the output buffer 32 , and the data indicating the formation state of the determined dots is recorded in the output buffer 32 , but the personal computer 100 does not necessarily have the output buffer 32 . Regardless of the presence or absence of the output buffer 32 , a streaming configuration may be adopted in which the data indicating the formation state of certain dots is not recorded in the output buffer 32 but flows into the printer 200 .

Furthermore, in the above-mentioned embodiments, an example using paper as a printing medium was described, but the present invention is also applicable to printing on various printing media other than paper such as paper, cloth, film, and circuit board.

In addition, the order of selecting pixels of interest in the above-described embodiments can be changed arbitrarily.

Claims (11)

1. An image processing device for determining, based on image data representing an image composed of a plurality of pixels, a dot formation state when the image is printed with dots of a plurality of sizes, comprising: an edge detection unit that detects, from pixels constituting the image data, a pixel of a dot color used for printing of the image, that is, a dot color edge pixel positioned at an edge in the image; and The dot allocation unit allocates dots of the same size to the dot color edge pixels when the image is printed. 2. The image processing device according to claim 1, characterized in that: The dots of the same size are dots other than the dot of the largest size among the dots of the plurality of sizes. 3. The image processing device according to claim 1 or 2, characterized in that: The edge detection unit detects, from among pixels constituting the image data, a pixel of a dot color used for printing the image, that is, an edge pixel of the dot color in the image whose distance from an edge is equal to or less than a predetermined value. Points other than color edge adjacent pixels; The dot allocating unit allocates dots other than the largest dot among the dots of the plurality of sizes to the edge adjacent pixels of the dot color when the image is printed. 4. The image processing device according to claim 3, characterized in that: The multiple sizes are more than 3 types of sizes; When the image is printed, the dot size for the dot-color edge adjacent pixels is larger than the dot size for the dot-color edge pixels when the image is printed. 5. The image processing device according to claim 3, characterized in that: The dot allocating unit includes a halftone processing unit for specifying a dot formation state for pixels other than the dot color edge pixel and the dot color edge adjacent pixel among the pixels constituting the image data by halftone processing. . 6. The image processing device according to claim 1, characterized in that: The image is an image composed of only one of white and the color of dots used for printing the image. 7. The image processing device according to claim 1, characterized in that: The image is an image composed of only one of black and the color of dots used for printing the image. 8. The image processing device according to claim 1, characterized in that: The dots of the plurality of sizes are formed by the plurality of ink ejection amounts. 9. The image processing device according to claim 1, characterized in that: The dots of the plurality of sizes are formed by a plurality of ink ejection times. 10. The image processing device according to claim 1, characterized in that: The edge detection unit detects the dot color edge pixels from among the pixels constituting the image data based on the RGB color space. 11. An image processing method for determining, based on image data representing an image composed of a plurality of pixels, a dot formation state when the image is printed using dots of a plurality of sizes, comprising: A step of detecting, from pixels constituting the image data, a pixel of a dot color used for printing of the image, that is, a dot color edge pixel positioned at an edge in the image; and A step of allocating dots of the same size to the dot color edge pixels at the time of image printing.

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