The present application claims the priority based on Japanese Patent Applications No. 2008-5470 filed on Jan. 15, 2008, and No. 2008-268395 filed on Oct. 17, 2008, the disclosure of which is hereby incorporated by reference in its entirety.
1. Technical Field
The present invention relates to image processing adapted to afford enhanced print quality around edges in an image.
2. Description of Related Art
Ink-jet printers are one known class of printing device adapted for printing images through formation of dots on printing media of various kinds such as paper, cloth, or film. An ink-jet printer prints an image onto the printing medium by jetting ink of several colors, for example, cyan (C), magenta (M), yellow (Y), and black (K onto the printing medium to produce ink dots on the printing medium. Some ink-jet printers have the ability to form dots of several different sizes, for example, large dots (L dots), medium dots (M dots), and small dots (S dots).
During printing of an image by an ink-jet printer, it is typical to carry out a process (called halftone process) for determining a state of dot formation on each printing pixel on the basis of the image data that represents the image. Here, the determination as to the state of dot formation on each printing pixel refers to the determination as to what color and what size of dot to form (or whether to form no dot) at each printing pixel.
In certain instances, during the halftone process, limits are established as to the total quantity of ink deposited per unit of area of the printing medium so as to inhibit bleeding of colors. In such instances, there is a possibility, for example, that intermingled dots of differing size are formed on printing pixels that constitute the edge portions of text or line image in an image, or that dots are not to be formed on some of the printing pixels, thus posing a risk of diminished print quality due to jagged or missing sections at the edges.
This problem is not limited to printing of images by ink-jet printers, but is rather a problem common to instances where formation status of dots on printing pixels is determined in the course of printing of an image using dots.
An object of the present invention is to provide a technology making it possible to determine a state of dot formation on printing pixels in such a way as to enhance print quality.
In one aspect of the present invention, there is provided an image processing device for determining states of formation of dots, based on image data representing an image composed of a plurality of pixels, in printing the image utilizing the dots of a plurality of sizes. The image processing device comprises an edge detection unit and a dot assignment unit. The edge detection unit detects, from among the pixels making up the image data, dot color edge pixels that are pixels of dot color used to print the image and that are situated at an edge in the image. The dot assignment unit assigns dots of identical size to the dot color edge pixels during printing of the image.
According to this image processing device, dot color edge pixels are detected from the pixels that make up image data, and during printing of the image, dots of identical size are assigned to the dot color edge pixels, thereby reducing jagged or missing sections at the edges, and enhancing print quality.
The present invention can be realized in various aspects. For example, the present invention can be realized in aspects such as an image processing method and associated apparatus, a formation status of dots determination method and associated apparatus, a dot data generation method and associated apparatus, a printing data generation method and associated apparatus, a printing method and associated apparatus, a computer program that executes the functions of these methods and apparatuses, a recording medium on which such computer program is recorded, a computer program product that includes this recording medium, or a data signal encoded in a carrier wave that incorporates this computer program.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.
The embodiments of the present invention are described below in the indicated order:
The personal computer 100 includes a CPU 110 for carrying out various processes and controls through execution of programs; a memory 120 for storing programs and data/information; and an input/output interface (I/F) 130 for exchanging data and information with externally connected peripheral devices. The memory 120 has an output buffer 32 for use in a dot formation state determination process, discussed later. The personal computer 100 may additionally be provided with an input device such as a keyboard and/or pointing device; a display device such as a monitor; and a recording/playback device such as a CD-ROM drive.
Programs such as an application program 10 and a printer driver 20 are installed on the personal computer 100. The application program 10 and the printer driver 20 are executed on a prescribed operating system (not shown) by the CPU 110.
The application program 10 may be a program for carrying out picture editing, for example. Via a user interface provided by the application program 10, a user is able to enter an instruction to print images edited using the application program 10. When the application program 10 receives a print instruction from the user, the image data targeted for printing is output to the printer driver 20. In the present embodiment, image data is output as RGB data.
The printer driver 20 is a program for carrying out the function of generating print data on the basis of the image data output by the application program 10. The printer driver 20 may be distributed in a form stored on a CD-ROM or any of various other kinds of recording medium (computer-readable recording media); or may be downloaded through communication means such as the Internet.
The printer driver 20 receives image data from the application program 10, generates print data on the basis of the image data, and outputs the generated print data the printer 200. Here, the print data is data of a format that can be interpreted by the printer 200, and includes command data of various kinds, as well as dot data. Command data is data for the purpose of instructing the printer 200 to carry out specific operations. Dot data is data representing states of dot formation on pixels (printing pixels) that make up the image to be printed (print image); specifically, the data indicates what color and size of dot to form (or whether to form no dot) on each printing pixel. Here, a “dot” refers to a single area formed by ink jetted onto a printing medium by the printer 200.
As shown in
The resolution conversion process module 21 carries out a resolution conversion process to convert the resolution of the image data output by the application program 10, so as to match the print resolution of the printer 200.
For each pixel making up the image data, the edge detection module 22 determines whether the pixel is a black edge pixel; a black edge neighboring pixel; or neither a black edge pixel nor a black edge neighboring pixel (hereinafter termed a “normal processing pixel”). In the present embodiment, a black edge pixel refers to a pixel of black color located at black edges in the image. A pixel located at black edges refers to a pixel having an adjacent pixel of a color other than black situated adjacently thereto in at least one direction, i.e. above or below, or to the left, right, upper right, lower right, upper left, or lower left of the pixel. In the present embodiment, black edge pixels are represented as being a distance of “1” away from a black edge. A black edge neighboring pixel refers to a pixel that is also black in color but is not a black edge pixel, and that is situated a distance no more than a prescribed value away from a black edge. In the present embodiment, this prescribed value is set to “2.” That is, a black edge neighboring pixel is a pixel of black color that is not a black edge pixel, and that is situated adjacently to a black edge pixel. In the present embodiment, black edge neighboring pixels are represented as being a distance of “2” away from a black edge.
The color conversion process module 23 performs a color conversion process targeting a normal processing pixel (i.e. a pixel that is neither a black edge pixel nor a black edge neighboring pixel) in the image data. The printer 200 employed in the present embodiment is a printer that carries out printing using inks of the colors cyan (C), magenta (M), yellow (Y), and black (K). Accordingly, the color conversion process module 23 converts pixel values represented by RGB values to CMYK values for the target pixels.
The halftone process module 24 carries out a halftone process on the basis of the pixel values color-converted by the color conversion process module 23 to determine states of dot formation on printing pixels that correspond to normal processing pixels, which is then recorded to the output buffer 32. In the present embodiment, the halftone process module 24 carries out the halftone process through a threshold value process using a dither matrix, while limiting the total quantity of ink that is deposited per unit of area of the printing medium. The printer 200 employed in the present embodiment is a printer capable of forming dots of three different sizes, namely, small dots of small size (hereinafter also termed “S dots”), medium dots of medium size (hereinafter also termed “M dots”), and large dots of large size (hereinafter also termed “L dots”). Thus, for each ink color, there are four possible options for the state of dot formation on a printing pixel, namely: form no dot; form an S dot; form an M dot; or form an L dot.
The dot assignment module 26 assigns prescribed dots to the printing pixels that correspond to black edge pixels and black edge neighboring pixels among the pixels making up the image data to determine states of dot formation for the printing pixels that correspond to the black edge pixels and black edge neighboring pixels, which is then recorded to the output buffer 32. The method by which the dot assignment module 26 assigns dots is discussed in detail later.
The rasterizing process module 27 generates dot data on the basis of the states of dot formation of the printing pixels recorded in the output buffer 32, and sorts the dot data into a sequence for transfer to the printer 200.
The printer 200 of the present embodiment is an ink-jet printer that prints images by forming ink dots on a printing medium. The printer 200 includes a CPU 210 for carrying out overall control of the printer 200 and various processes through execution of programs; a memory 220 for storing programs and data/information; an input/output interface (I/F) 230 for exchanging data and information with the externally connected personal computer 100; a unit control circuit 240 for controlling units according to instructions from the CPU 210; a head unit 250; a carriage unit 260; and a feed unit 270.
The head unit 250 has a head (not shown) for jetting ink onto the printing medium. The head has a plurality of nozzles, and ink is jetted intermittently from the nozzles. The head rides on a carriage (not shown), and when the carriage moves in a prescribed scanning direction (main scanning direction), the head also moves in the main scanning direction. During the time that the head is moving in the main scanning direction, the head jets ink intermittently to produce dot lines (raster lines) along the main scanning direction on the printing medium.
The carriage unit 260 is a driving device for causing the carriage on which the head rides to undergo reciprocating movement in the main scanning direction. In addition to the head, detachable ink cartridges containing ink are retained on the carriage.
The feed unit 270 is a driving device adapted to feed the printing medium to a location at which printing can be done on the medium, and to sub-scan the printing medium by feeding the medium in prescribed increments in a prescribed feed direction during printing. The feed unit 270 may be composed, for example, of a paper pickup roller, a feed motor, a feed roller, a platen, and a paper discharge roller (not shown).
When the user issues an instruction to print an image via the application program 10, a print command is issued to the printer driver 20 by the application program 10. This print command includes image data (RGB data) that has been edited by the application program 10.
In the printer driver 20 that has received a print command, the resolution conversion process module 21 converts the resolution of the image data included in the print command so as to match the print resolution. Next, for each pixel making up the image data, the edge detection module 22 determines whether the pixel is a black edge pixel, a black edge neighboring pixel, or a normal processing pixel. For pixels determined to be normal processing pixels, states of dot formation are determined via the color conversion process by the color conversion process module 23 and the halftone process by the halftone process module 24. For pixels determined to be black edge pixels or black edge neighboring pixels, states of dot formation are determined by the dot assignment module 26. States of dot formation determined in this way are recorded in the output buffer 32. The process for determining states of dot formation is described in detail later. The rasterizing process module 27 then generates dot data on the basis of the states of dot formation of the printing pixels which have been recorded in the output buffer 32; sorts the dot data into a sequence for transfer to the printer 200; and outputs the print data (inclusive of the dot data) to the printer 200 via the input/output interface 130.
When the printer 200 receives the print data from the personal computer 100, the printer 200 executes the printing process. First, the CPU 210 receives the print data from the personal computer 100 via the input/output interface 230, and parses various commands included in the received print data. Based on the parsing outcome the CPU 210 controls the feed unit 270 via the unit control circuit 240. Through this control, the feed unit 270 supplies the paper to be printed (printing medium) into the printer 200, and positions the paper at the print start location.
Next, the CPU 210 controls the carriage unit 260 via the unit control circuit 240. Through this control, the carriage unit 260 moves the carriage having the head in the main scanning direction. The CPU 210 also controls the head unit 250 on the basis of the print data, via the unit control circuit 240. Through this control, the head unit 250 jets ink intermittently from the head on the basis of the print data as the head moves in the main scanning direction, to form dots on the paper through impact of the jetted ink drops against the paper. Further, the CPU 210 controls the feed unit 270 to advance the paper in the feed direction so as to move relative to the head. By so doing, the head can produce dots at different locations from those of dots formed previously. The processes of dot formation and advance are repeated until no data for printing remains, to print an image composed of dots onto the paper. Subsequently, if there is no additional data to be printed, the printing process terminates.
In Step S102 (
In Step S106 (
Subsequently, in Step S122 (
As this process is repeated and the pixel of interest now shifts to the location indicated by “state b” of
In Step S202 (
On the other hand, in the event of a determination that there are no white pixels among adjacent pixels of the pixel of interest (Step S202: No), the edge detection module 22 then determines whether the pixel two pixels away in the direction above the pixel of interest (P9 in
Subsequently, in the same manner as the determination made in the aforementioned Steps S206 and S208 in relation to the direction above the pixel of interest as to whether the pixel is a black pixel-neighboring pixel similar black pixel-neighboring pixel determinations are made in relation to the leftward direction, the rightward direction, and the direction below respectively. Specifically, in Steps S212 and 214, if the pixel two pixels away in the leftward direction from the pixel of interest (P10 of
If a determination that the pixel of interest is not a black pixel-neighboring pixel is made in relation to the direction above, the leftward direction, the rightward direction, and the direction below, a distance of greater than 2 from a black edge is posited. A distance of greater than 2 from a black edge means that the pixel of interest is a normal processing pixel.
If through the process for determining distance from the edge (Step S110 of
Once the pixel of interest has shifted to the location shown by “state e” in
Once the pixel of interest has shifted to the location shown by “state j” in
Through the state of dot formation determination process described above, the states of dot formation of printing pixels corresponding to the section of the line drawing A in the image for printing 40 (see
Furthermore, in the present embodiment, since printing pixels that correspond to black edge pixels are assigned dots different in size from the largest dots (L dots) among the several dot sizes used in printing (in the present embodiment, they are S dots), bleeding and thickening at the edge sections are reduced, and print quality is enhanced. Moreover, in the present embodiment, since printing pixels that correspond to black edge neighboring pixels are assigned dots different from the largest dots (L dots) among the several dot sizes used in printing (in the present embodiment, they are M dots), bleeding and thickening at edge sections are effectively reduced, and print quality is enhanced. Additionally, in the present embodiment, since printing pixels corresponding to black edge neighboring pixels are assigned dots larger in size than the dots assigned to printing pixels corresponding to black edge pixels (in the present embodiment, M dots versus S dots), bleeding and thickening at edge sections are effectively reduced, and print quality is enhanced.
The present invention is not limited to the embodiments and aspects described above. The present invention may be worked in various aspects within limits that involve no departure from the spirit of the-invention; for example, the following variations are possible.
In the preceding embodiment, dots of the smallest size (S dots) are assigned to printing pixels that correspond to black edge pixels, but it is also acceptable for printing pixels corresponding to black edge pixels to be assigned M dots or L dots, provided that the dots are all of identical size. Where M dots (or L dots) are assigned to all printing pixels corresponding to black edge pixels, jagged or missing sections at the edges in a printed image can be reduced, and missing dots can be eliminated, thus enhancing print quality. In preferred practice, dots of size other than the largest dot size (i.e. S dots or M dots) are assigned to printing pixels corresponding to black edge pixels, so as to limit bleeding and thickening in edge sections.
In the preceding embodiment, M dots are assigned to printing pixels that correspond to black edge neighboring pixels, but it is also acceptable for printing pixels corresponding to black edge neighboring pixels to be assigned dots of size other than the largest dots (L dots), for example, to assign S dots to all printing pixels corresponding to black edge neighboring pixels. Alternatively, M dots may be assigned to some of the printing pixels that correspond to black edge neighboring pixels, and S dots may be assigned to the remainder.
In the preceding embodiment, pixels making up image data are differentiated into three types, i.e. black edge pixels, black edge neighboring pixels, and normal processing pixels; however, pixels may instead be differentiated into two types, i.e. black edge pixels and normal processing pixels. In this case, for printing pixels that correspond to normal processing pixels, states of dot formation may be determined through the color conversion process and the halftone process, while printing pixels that correspond to black edge pixels may all be assigned S dots. With this approach as well, jagged or missing sections at the edges in a printed image can be reduced, missing dots can be eliminated, and bleeding or thickening in edge sections can be reduced, thus enhancing print quality. Alternatively, in this case M dots (or L dots) may be assigned to all printing pixels that correspond to black edge pixels. With this approach as well, jagged or missing sections at the edges in a printed image can be reduced and missing dots can be eliminated, thus enhancing print quality. In preferred practice, pixels making up image data are differentiated into the three types of black edge pixels, black edge neighboring pixels, and normal processing pixels; and printing pixels that correspond to black edge neighboring pixels are assigned dots of size other than the largest dots (L dots), so as to limit bleeding and thickening in edge sections.
In the preceding embodiment, the process of determining states of dot formation for the purpose of improving print quality in proximity to black edges is described in the context of an image composed of white and black only; however, the present invention may be implemented analogously in a process of determining states of dot formation for the purpose of improving print quality in proximity to edges of one dot color (e.g. cyan, magenta, or yellow) for an image composed exclusively of white and the dot color that is used to print the image. That is, for the pixels making up the image data, edge pixels and edge neighboring pixels of the dot color in question may be detected, and for the printing pixels that correspond to the detected edge pixels and edge neighboring pixels, prescribed dots may be assigned in place of the normal halftone process, thereby affording enhanced print quality comparable to the preceding embodiment.
The present invention is also applicable in instances where the color of the printing medium is a color other than white. That is, the present invention may be implemented analogously in a process of determining states of dot formation for the purpose of improving print quality in proximity to edges of one dot color (e.g. cyan, magenta, or yellow) for an image composed exclusively of the color of the printing medium (e.g. black) and the dot color that is used to print the image.
While in the preceding embodiment the process of determining states of dot formation is carried out by the same method throughout the entire image for printing 40, it is acceptable to instead carry out determination of states of dot formation by the method taught in the embodiment, exclusively for text areas that include text or line diagrams (symbols, graphics, graphs etc.) in the image for printing 40. In this case, text areas may be detected on the basis of the RGB values of the image data, or text areas may be detected on the basis of pixel luminance values, for example.
In the preceding embodiment, the image data is assumed to be RGB data, but it is not essential for the image data to be RGB data. In the embodiment, the printer 200 carries out printing by forming dots of three different sizes using inks of the four colors CMYK, but it is acceptable for the printer 200 to instead carry out printing using inks of colors other than CMYK, as well as to carry out printing by forming dots of two (or four or more) different sizes.
In the preceding embodiment, formation of dots of several different sizes by the printer 200 may be accomplished by varying the ejected ink quantity according to the size of the dot being formed. For example, waveforms adapted to produce ejection of ejected ink quantities that correspond to dots of several different sizes may be provided as waveforms for the drive signal that controls jetting of the ink; and the ink jetted using waveform corresponding to the size of the dots being formed, to produce dots of the desired size. Alternatively, the head may be provided with nozzles adapted to eject mutually different quantities of ink, and the ink then ejected from nozzles that correspond to the size of the dots being formed, to produce dots of the desired size. In another possible approach, formation of dots of several different sizes may be accomplished by varying the number of times of ink ejection according to the size of the dot being formed. In yet another possible approach, the ink may be ejected continuously as a column of fluid through pressurization of the ink, and utilizing the basic principle whereby the column of fluid separates into dots when the column of fluid is heated by a heater, dots of several different sizes may be formed by varying the heating pulse timing.
In the preceding embodiment, the color conversion process module 23 is constituted to perform color conversion on normal processing pixels (pixels that are neither black edge pixels nor black edge neighboring pixels); however, the color conversion process module 23 may also perform color conversion on pixels besides normal processing pixels. For example, it is acceptable for the color conversion process module 23 to perform color conversion from RGB data to Cry data on all pixels. In this case, the edge detection module 22 may use CMYK data to carry out edge determination.
In the embodiment, the image data output by the application program 10 is assumed to be RGB data, but the image data may instead consist of data of another color system such as CMYK data. Where the image data is data of another color system such as CMYK data, the edge detection module 22 may use the data of the other color system to carry out edge determination.
In the preceding embodiment, the image processing device is constituted by a personal computer 100; however, it is possible for the present invention to be implemented analogously in other image processing devices besides a personal computer 100, which are adapted to carry out image processing through determination of states of dot formation. For example, the image processing device may be constituted by the printer 200.
In the preceding embodiment, some of the arrangements implemented through hardware may be replaced by software, and conversely some of the arrangements implemented through software may be replaced by hardware.
While the preceding embodiment described an example of a printer in which the head for jetting ink onto the printing medium moves in the main scanning direction, the present invention may also be implemented in a line printer having a plurality of heads arrayed in the main scanning direction, with the heads being stationary.
Moreover, while in the preceding embodiment the head has a plurality of nozzles, the head may have a single nozzle only.
In the preceding embodiment, the personal computer 100 has an output buffer 32, and data representing the determined states of dot formation is recorded to the output buffer 32; however, it is not essential for the personal computer 100 to have an output buffer 32. Regardless of whether an output buffer 32 is provided, it is possible to employ a configuration of stream format whereby data representing the determined states of dot formation is streamed to the printer 200 without being recorded to an output buffer 32.
While the preceding embodiment described an example in which the printing medium is paper, the present invention may be implemented analogously for printing onto paper of various other types of printing media besides paper, such as cloth, film, or circuit boards.
The selection sequence of the pixel of interest in the preceding embodiment may be modified arbitrarily.
Number | Date | Country | Kind |
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2008-005470 | Jan 2008 | JP | national |
2008-268395 | Oct 2008 | JP | national |