JP2008294609A - Image output device, image output method, and image output program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image output device that deters unevenness (jaggedness) of segments from being conspicuous because the angle of the segment of a thin line of image data to be printed becomes closer to the angle (screen angle) of an array of stripes when halftones are represented using a dither method of the parallel line tint screen. <P>SOLUTION: The font of a character is adjusted and when the segment angle of the font becomes less than a screen angle of the parallel line tint screen and a threshold, it is determined that jaggedness is generated to generate an output image by rotating all parallel line tint screens of respective colors by 90°. The jaggedness is thereby prevented from being generated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  When a line screen is generated using a striped pattern to express gradation in an image output device, the angle of a thin line segment and the angle of arrangement of dots in the striped pattern of the line screen (screen The present invention relates to a technique for suppressing the concavity and convexity (jags) of the line segment from becoming conspicuous.

  In an image output apparatus such as an image forming apparatus or an image display apparatus, a method of expressing the color density of an output image using a line screen is generally used.

  In addition, a dither method that expresses shading by increasing or decreasing the number or size of points is known, but in particular, it generates multi-tone by generating a striped pattern and changing the number of stripes and the width of the stripes. Is expressed as a dither method using a line screen (FIG. 1; details will be described later).

  In general, in a color image forming apparatus, an image is formed using toners of four colors of C (cyan), M (magenta), Y (yellow), and K (black). Represent intermediate colors using the method. At this time, the intermediate gradation of the line screen is expressed for each toner color, and the intermediate color is expressed by superposing printing of the respective toner colors.

  In this case, a different angle (screen angle) is provided for each plane (toner output surface) as shown in FIG. 3 so that a moire pattern is not generated between the overlapping stripe patterns of different toners. For example, magenta color is set to 75 degrees, black is set to 45 degrees, cyan is set to 15 degrees, and yellow is set to 0 degrees so that the screen angles are different.

  However, when printing is performed by the dither method using this line screen, the angle of the line segment of the fine line and the angle of the dot formation in the dither method (screen angle) are close to each other, and the unevenness of the line segment ( There was a problem that Jagi was conspicuous.

  FIG. 1 (A) shows a case where the katakana “Le” character is displayed on a single-color line screen and the “le” bounce portion is close to the screen angle. FIG. 1B shows an example in which the angle of the “le” jumping portion is separated from the screen angle. In FIG. 1, the size of the pixel points is enlarged so that the state of the line screen can be clearly understood, but when viewing FIG. 1 away from the eyes, Compared with), it can be clearly seen that jaggies in which the unevenness of the outline of the character is conspicuous are generated.

  As a conventional technique for suppressing the jaggies phenomenon, in order to improve the image quality when the line is thin in the print data of characters and ruled lines, binary expression is made based on the line width detected by calculating the line width in dot units. There has been a method of selecting a dot pattern for performing (see Patent Document 1).

  However, this method takes time because the line width is calculated for each character. In addition, when the arrangement pattern is changed, in the case of color, the color of each character in the character string varies.

  In addition, in an image processing apparatus that displays multi-gradation using a line screen, the outline portion of each element of the output image adopts a pseudo multi-gradation method different from the line dither pattern, thereby causing a jaggy phenomenon. There was a method of suppressing (refer patent document 2).

  However, in this method, since different dither patterns are used for all the contour portions of the image, the calculation time becomes enormous, and there is a problem that the processing takes time as in Patent Document 1.

JP 09-186902 A JP 2004-40499 A

  The problem to be solved is that the processing time is reduced to reduce the noticeable unevenness (jagged edges) at the edges of fine lines and characters when the halftone screen is used for dithering in the image output device. It was a point that could not be performed efficiently without spending time.

  The image output device of the present invention extracts an angle of a line segment of the image data, an image conversion unit that converts the image data into a halftone output image using a line screen that forms pixel points in a striped pattern. An element angle extraction unit to be recorded, a jaggy determination unit that determines whether or not a jaggy occurs in the contour portion of the output image based on the angle of the line segment extracted by the element angle extraction unit, and the jail determination unit When it is determined that a jaggy occurs in the contour portion, the main feature is that it has a screen angle setting unit that rotates the screen angle of the line screen by 90 degrees in a direction to suppress the jaggy phenomenon.

  According to the image output method of the present invention, image data is converted into a halftone output image using a line screen that forms pixel points in a striped pattern, and the angles of line segments of the image data are extracted and recorded. , Based on the angle of the recorded line segment, it is determined whether or not a jaggy occurs in the contour portion of the output image, and when it is determined that a jaggy occurs in the contour portion, the direction of suppressing the jaggy phenomenon Further, the output image is generated by rotating the screen angle of the line screen by 90 degrees.

  An image output program according to the present invention is an image output program executed in a computer of an image output apparatus, wherein the computer converts the image data into a halftone output image using a line screen that forms pixel points in stripes. Based on the image conversion means for conversion, the element angle means for extracting and recording the angle of the line segment of the image data, and the recorded line segment angle, whether or not a jaggy occurs in the contour portion of the output image A screen angle setting for rotating the screen angle of the line screen by 90 degrees in a direction to suppress the jaggy phenomenon when the jaggy determination unit determines that a jaggy occurs in the contour portion. It is characterized by functioning as a means.

  The image output device of the present invention extracts an angle of a line segment of the image data, an image conversion unit that converts the image data into a halftone output image using a line screen that forms pixel points in a striped pattern. An element angle extraction unit to be recorded, a jaggy determination unit that determines whether or not a jaggy occurs in the contour portion of the output image based on the angle of the line segment extracted by the element angle extraction unit, and the jail determination unit When it is determined that a jaggy occurs in the contour portion, the most important feature is that it has a screen angle setting unit that rotates the screen angle of the line screen by 90 degrees in a direction to suppress the jaggy phenomenon. When expressing a halftone by a dithering method using a line screen, it becomes possible to suppress unevenness (jagged edges) that are conspicuously noticeable at the edge of a fine line or character without taking a long time for processing.

  According to the image output method of the present invention, image data is converted into a halftone output image using a line screen that forms pixel points in a striped pattern, and the angles of line segments of the image data are extracted and recorded. , Based on the angle of the recorded line segment, it is determined whether or not a jaggy occurs in the contour portion of the output image, and when it is determined that a jaggy occurs in the contour portion, the direction of suppressing the jaggy phenomenon In addition, the output image is generated by rotating the screen angle of the line screen by 90 degrees. Conspicuous irregularities (jags) can be suppressed without taking a long time for the treatment.

  An image output program according to the present invention is an image output program executed in a computer of an image output apparatus, wherein the computer converts the image data into a halftone output image using a line screen that forms pixel points in stripes. Based on the image conversion means for conversion, the element angle means for extracting and recording the angle of the line segment of the image data, and the recorded line segment angle, whether or not a jaggy occurs in the contour portion of the output image A screen angle setting for rotating the screen angle of the line screen by 90 degrees in a direction to suppress the jaggy phenomenon when the jaggy determination unit determines that a jaggy occurs in the contour portion. Because it functions as a means, when expressing halftones by dithering with a multi-line screen, fine lines and edge portions of characters It has become possible to suppress without applying long time treatment significantly noticeable irregularities (jaggies).

  In an image output device, when expressing halftones by dithering with a multi-line screen, it is possible to efficiently reduce irregularities (jags) that are conspicuously noticeable at the edges of fine lines and small characters without long-time processing. If it is determined that jaggies are generated based on the angle of the thin line or character line segment and the screen angle of the line screen, the occurrence of jaggies can be prevented by rotating the screen angle of the line screen by 90 degrees. It became possible to suppress.

  An image forming apparatus as an embodiment of the image output apparatus of the present invention will be described below.

[Rotation of dither table to suppress jaggy generation]
When expressing a neutral color with a striped pattern by dithering (dithering with a multi-line screen), an edge portion with an angle component close to the angle of the striped pattern (screen angle) or a small character with the same angle component ( In particular, unevenness (hereinafter referred to as jaggies) is particularly noticeable in the italic characters (the same edge portion), and lines and characters cannot be seen beautifully (FIG. 1A).

  In the present invention, when jaggies are generated in the data including characters, a dither table for calculation (2 describing the striped pattern is described) for generating a striped pattern set for each toner color. The table of dimensions; FIG. 2) is rotated 90 degrees to suppress the occurrence of jaggies. Hereinafter, the rotation of the dither table will be described with reference to FIG.

  2A and 2B are examples of an 8 × 8 two-dimensional matrix dither table. Depending on the color value (image density), dots are struck at the corresponding value positions. In FIG. 2, hatching is applied for the case of a density of 50% for easy understanding. Thereby, in FIG. 2A, a striped pattern is formed horizontally, indicating that the screen angle of the line screen is 0 degree. When the dither table is rotated 90 degrees clockwise, as shown in FIG. 2B, the stripe pattern becomes vertical, and it can be seen that the screen angle is 90 degrees.

  In the example of FIG. 2, the cases of 0 degree and 90 degrees are shown. However, the present invention is not limited to this, and an oblique direction (for example, a screen angle of 30 degrees) is naturally possible by the same method.

  In order to realize the method for suppressing jaggies by the rotation of the dither table, the angle data of the image elements of the image data is necessary. In the present invention, the angle of the line segment constituting the character with respect to the character data. Has the most frequently used angle as attribute information of the character data. If the font information is stored in the ROM of the printing apparatus, the angle information is obtained in advance by the font information management unit (element angle extraction unit) by analyzing the vector direction from the font data bitmap or outline. Later, it can be held on the ROM.

  It is possible to take a method of obtaining the most frequent angle data for each page by counting the same most frequently occurring angle data held by each font when it appears in the image data.

  In addition, when a bitmap is sent directly from the host, it is determined whether the italic is set for the character, and if the angle of the italic is used as the angle information of the character, the bitmap and outline are analyzed for high speed. Processing is possible.

  When the print data is character data, a jaggy determination unit (screen angle setting unit) is provided for determining whether or not a jaggy occurs based on the difference between the character color, the angle of the character attribute information, and the screen angle. When it is determined that the image is likely to occur, the drawing processing unit (screen angle setting unit) rotates all the dither tables existing at different angles for each plane by 90 degrees to prevent the jaggy from being noticeable.

[Judge determination method of Jagi determination unit]
Next, an example of the determination method of the jaggy determination unit (screen angle setting unit) will be described.

  First, each color value of the plane representing the color of the character (surface that is output for each toner color; cyan (C), magenta (M), yellow (Y), and black (K) is commonly used in laser printers) is halftone. It is determined whether it is (not solid).

  In the case of solid coating, since the jaggy caused by the striped pattern does not occur, normal processing is performed.

  When the plane is halftone, the screen angle of the plane having the largest color value (the toner color most used for character printing in the printed matter) is used to determine whether or not jaggies are likely to occur. When the difference between the screen angle and the character angle (the angle of the line segment most frequently used for a certain font or the italic angle used for the italic character) is below a certain threshold (for example, 30 degrees). It is determined that jaggies are likely to occur as shown in FIG.

  In this case, in the generation of the halftone pattern that becomes the character color, the occurrence of jaggies can be minimized by using a plane dither having a screen angle rotated 90 degrees from the originally set screen angle. Is possible.

  For example, when a character is a gray-scale Gray (with black toner) value and the angle of the character is close to 45 ° (for example, 50 degrees) and less than a threshold (30 degrees in the above example), Gray is expressed. Since the original screen angle of the black toner is 45 degrees (see FIG. 3), if the screen angle is used as it is, many jaggies are generated. Therefore, by using a dither pattern of 135 degrees obtained by rotating 45 degrees by 90 degrees as a screen angle used for generating a halftone that expresses a gray value, an angle of 85 degrees is obtained between the angle of the line segment and 50 degrees. Jagi is inconspicuous due to the gap.

  As described above, the occurrence of jaggies is predicted based on the angle information of the characters, and when jaggies occur, the screen angles determined for each toner color are rotated by 90 degrees for all colors to prevent the occurrence of jaggies. Suppress.

[Constitution]
FIG. 4 is a functional block diagram of the image forming apparatus according to the embodiment of the present invention.

  The image forming apparatus 100 includes a print data reception unit 101, a print data analysis unit 102, a drawing data processing unit 103, a memory management unit 104, a system control unit 105, a page rasterization processing unit 106 (image conversion unit), and an output unit 107. ing.

  The drawing data processing unit 103 includes a drawing environment management unit 103.1, a drawing processing unit 103.2 (screen angle setting unit), a font information management unit 103.3 (element angle extraction unit), and a jaggy determination unit 103.4. (Screen angle setting unit) and intermediate language creating unit 103.5 are provided with functional blocks.

  Each functional unit will be described below.

  The print data receiving unit 101 receives print data sent from a PC (Personal Computer).

  The print data analysis unit 102 analyzes the contents of the print data written in the page description language, and analyzes the data for conversion to an intermediate language (display list). Further, it is determined whether each element is character data, whether each plane (output surface for each toner color) is an output including an intermediate color, or the like.

  The drawing data processing unit 103 performs processing of drawing data for suppressing the occurrence of jaggies.

  The drawing environment management unit 103.1 manages setting information related to drawing such as an enlargement / reduction setting matrix and a currently effective color or dither.

  The drawing processing unit 103.2 (screen angle setting unit) processes a complicated figure into a simple drawing primitive after the print data analysis unit 102 analyzes the print data. Further, when the jaggy determination unit 103.4 described below determines that a jaggy occurs, the screen angles of all color line screens are set to rotate 90 degrees.

  The font information management unit 103.3 (element angle extraction unit) is used for character attribute information to be set (normal font information and the angle of a line segment most frequently used for a certain font or the italic character described above. Italic angle).

  The jaggy determination unit 103.4 (screen angle setting unit) determines whether or not a jaggy is likely to occur based on the color and character attribute information and the screen angle.

  The intermediate language creation unit 103.5 creates a display list (intermediate language) based on the information processed by the drawing processing unit 103.2.

  The memory management unit 104 manages the memory of the system.

  The system control unit 105 manages system common information and controls the system.

  The page rasterization processing unit 106 (image conversion unit) decodes the display list created by the intermediate language creation unit 103.5 and rasterizes one page. At this time, the page rasterization processing unit 106 converts to a halftone output image using a line screen generated by a dither method using a striped pattern.

  The output unit 107 includes a print engine that is a mechanism unit that performs printing, and actually performs printing on a recording medium (generally paper, other OHP paper, or the like).

  In the functional block diagram of FIG. 4, portions not related to the essence of the present invention, such as an image reading unit and a paper feed mechanism unit that are normally provided in the image forming apparatus, are omitted.

[flowchart]
The operation flow will be described with reference to the flowchart of FIG.

  S1: The print data receiving unit 101 receives print data.

  S2: The print data analysis unit 102 analyzes the print data.

  S3: As a result of the analysis in S2, the jaggy determination unit 103.4 determines whether the print data element is character data. If it is character data, the operation proceeds to S4. If it is not character data, the operation proceeds to S9.

  S4: The jaggy determination unit 103.4 determines whether all the planes (output surfaces for CMYK toner colors) are halftone. If it is halftone, the operation proceeds to S5. If it is not halftone, the operation proceeds to S9.

  S5: The drawing processing unit 103.2 selects a screen angle corresponding to the color of each plane.

  S6: The font information management unit 103.3 acquires angle information of each font acquired in advance.

  S7: The drawing processing unit 103.2 determines whether the difference between the font angle and the screen angle is equal to or less than a certain value. If it is below a certain value, the operation proceeds to S8. If it is not less than the predetermined value, the operation proceeds to S9.

  S8: The drawing processing unit 103.2 rotates the dither pattern plane by 90 degrees for all colors.

  S9: The intermediate language creation unit 103.5 creates a display list according to the dither pattern rotated 90 degrees in S8 or the default dither pattern (depending on the flow path).

  S10: The intermediate language creation unit 103.5 determines whether or not the creation of the display list (DL) for one page is finished after the processing of each element in one page is finished.

  A display list is generated by the series of operations described above. Thereafter, the page rasterization processing unit 106 decodes the display list created in S9 and creates rasterized data (output image) rasterized by the dither method. At this time, the page rasterization processing unit 106 converts to a halftone output image using a line screen generated by a dither method using a striped pattern. The page rasterization processing unit 106 transmits the rasterized data to the output unit 107, and the printing unit 107 prints the rasterized data and ends the process.

[Effect of Example]
The image forming apparatus according to the embodiment of the present invention enables the following.

  By having the angle of the font as attribute information, it is possible to determine at a high speed whether or not jaggies will occur (character reproducibility will deteriorate).

  When italic characters are set for a character, it is possible to determine the occurrence of jagging at a higher speed by using the angle of the italic as attribute information of the character angle.

  By rotating the dither pattern of all the planes that determines the font color, it is possible to reduce the jaggedness of the edge portion according to each character while keeping the color of the character string uniform, thereby improving the image quality. Further, even if the dither table is rotated 90 degrees, the subsequent processing time is not different from the case where the dither table is not rotated 90 degrees.

  Since the halftone patterns of all the planes are equally rotated by 90 degrees, there is no concern about the occurrence of moire patterns between the planes.

[Others]
In the flowchart of the above embodiment, the dither pattern is replaced only in the case of characters. However, even in the case of graphic data other than characters, the drawing processing unit obtains the frequent angle of the line segment and the same angle and the screen angle. A method of selecting a dither pattern may be taken so as not to be close.

  If there is an italic character, the process may be performed with the angle of the italic as the frequent angle.

  In this embodiment, the case where the image output apparatus is an image forming apparatus has been described. However, the image output apparatus may be a display device such as a display.

It is an enlarged view of the case where the jaggy phenomenon is noticeable due to the difference in rotation of the dither pattern (A) and the case where it is not noticeable (B). (Example 1) which is the figure (B) which rotated the table same as the dither table example (A) 90 degrees. It is a figure of arrangement | positioning of the rotation angle by the toner color of a normal dither pattern. 1 is a functional block diagram of an image forming apparatus according to an embodiment of the present invention (Embodiment 1). FIG. 1 is a flowchart of an image forming apparatus according to an embodiment of the present invention (Embodiment 1).

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Print data receiving part 102 Print data analysis part 103 Drawing data processing part 103.1 Drawing environment management part 103.2 Drawing processing part (screen angle setting part)
103.3 Font information management unit (element angle extraction unit)
103.4 Judge determination unit (screen angle setting unit)
103.5 Intermediate language creation unit 104 Memory management unit 105 System control unit 106 Page rasterization processing unit (image conversion unit)
107 Output unit

Claims (7)

An image conversion unit that converts image data into a halftone output image using a line screen that forms pixel points in a striped pattern;
An element angle extractor for extracting and recording the angle of the line segment of the image data;
A jump determination unit that determines whether or not a jump occurs in the contour portion of the output image, based on the angle of the line segment extracted by the element angle extraction unit;
And a screen angle setting unit that rotates the screen angle of the line screen by 90 degrees in a direction to suppress the jagging phenomenon when the jaggy determination unit determines that a jaggy occurs in the contour portion. Image output device. The image output apparatus according to claim 1,
The image output apparatus, wherein the screen angle setting unit determines that jaggies occur when the angle of the line segment extracted by the element angle extraction unit and the screen angle of the line screen are equal to or less than a threshold value. The image output apparatus according to claim 1 or 2,
The image output apparatus, wherein the element angle extraction unit extracts and records an angle of a line segment in a font of characters of the image data, or extracts and records an italic angle of an italic character. The image output device according to any one of claims 1 to 3,
The element angle extraction unit extracts and records an angle of a line segment for each color element of the image data,
The screen angle setting unit rotates all the angles of the line screen for each color element by 90 degrees. The image output device according to any one of claims 1 to 4,
The image output device, wherein the image conversion unit generates a line screen by a dither method using the striped pattern. Convert the image data into a halftone output image using a line screen that forms pixel points in stripes,
Extract and record the line segment angle of the image data,
Based on the angle of the recorded line segment, determine whether or not a jaggy occurs in the contour portion of the output image,
An image output method comprising: generating an output image by rotating the screen angle of the line screen by 90 degrees in a direction to suppress a jaggy phenomenon when it is determined that a jaggy occurs in the contour portion. An image output program executed in a computer of an image output device,
Image conversion means for converting the computer data into a halftone output image using a line screen that forms pixel points in a striped pattern;
Element angle extraction means for extracting and recording the angle of the line segment of the image data;
Judge determination means for determining whether or not a jaggy occurs in the contour portion of the output image based on the angle of the recorded line segment;
A screen angle setting means for rotating the screen angle of the line screen by 90 degrees in a direction to suppress the jaggy phenomenon when the jaggy determination means determines that a jaggy occurs in the contour portion;
Image output program to make it function.

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