JP2012205220A - Gradation conversion controller, image processing device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease possibility of generating jaggies on a contour part of a region and moire caused by two line groups.SOLUTION: In a binarization processor 25 of an image processing device, an image divider 31 divides multi-valued image data into unit images; an edge determination part 32 determines whether each unit image is an edge image including an edge of an object; a secondary color determination part 33 determines whether the color of the object in the edge image is a secondary color and whether an angle between two screens to the secondary color is within a specified range; an angle detector 34 detects an angle of the contour line of the object in the edge image; an edge screen determination part 35 selects the two screens to the secondary color after converting one of the two screens to a mirror image when the angles of the contour line and two screens are within specified ranges; and a screen processor 37 outputs binary image data by applying screen-processing on the object with the selected screen.

Description

  The present invention relates to a gradation conversion control device, an image processing device, and a program.

Analyzes the font of characters in the image data and determines that jaggies occur when the line segment angle of the font falls below the screen angle of the line screen and the threshold value. When it is determined that jaggies will eventually occur based on the count results for each occurrence of jaggies in the image data, for example, the output paper direction is rotated by 90 degrees. An image output apparatus that prevents the occurrence of jaggies by rotating the line screen angle by 90 degrees is known (see, for example, Patent Document 1).
Based on the drawing information indicated by the image data, the contour of the halftone object is extracted as an edge, and the density value in the vicinity of the extracted edge among the density values in the halftone object is corrected so as to increase the density value. Then, the corrected image data is converted into halftone dot image data composed of a halftone dot image based on the image data corrected using halftone dots formed by a plurality of pixels, An image output system that controls to output a halftone image on an image recording medium based on halftone image data is also known (see, for example, Patent Document 2).
The normal line dither method is applied to the matrix that does not include the outline of the drawing object, and the maximum value of each color density is calculated for the matrix that includes the outline of the drawing object. There is also known a color image processing apparatus that applies pseudo gradation processing different from that for a matrix that does not include an outline to the matrix (for example, see Patent Document 3).
The contour of graphic data, which is graphic information represented by numerical data in high gradation image data, is extracted, and a line dither pattern having a predetermined screen angle is applied to other regions other than the contour region of the graphic data. In order to prevent the occurrence of contour jaggies, image processing that performs gradation conversion by applying a pseudo multi-gradation method different from the line dither pattern having the predetermined screen angle to the contour area of the graphic data An apparatus is also known (see, for example, Patent Document 4).
It is detected whether the target pixel in the input multi-valued image data is an edge pixel located at an edge or a non-edge pixel. When the target pixel is an edge pixel, screen processing is performed on the target pixel, and N A gradation output value is determined, and when the target pixel is a non-edge pixel, a target value of the target pixel is calculated by performing a first filter process having a preset visual characteristic on a region including the target pixel. An image processing apparatus that corrects the value of a target pixel so as to approach a target value, determines an output value of N gradations, and outputs the determined output value is also known (see, for example, Patent Document 5).

JP 2009-111815 A JP 2006-014135 A JP 2004-221695 A JP 2004-040499 A Japanese Unexamined Patent Publication No. 2009-100288

  An object of the present invention is to reduce the possibility of jaggies occurring in the contour portion of a region, and to reduce the possibility of moire due to two line groups.

The invention according to claim 1 is an acquisition means for acquiring an image including a region of K (K ≧ 2) order color composed of a single color expressed by N (N ≧ 3) gradations, and the K order color The directions of two line groups predetermined for each of the two monochrome colors as information for expressing two of the K monochrome colors constituting the image with M (2 ≦ M <N) gradations However, when the determination unit determines whether both are within the specific range, and the determination unit determines that the directions of the two line groups are both within the specific range, the two Information for expressing one of the single colors in M gradations is determined as a line group determined in advance for the single color, and the other single color of the two single colors is determined in M gradations. Information for expressing in the direction of the direction in the other range that does not overlap with the specific range of the region The first partial region adjacent to the first partial region is determined as a first line group determined in advance with respect to the other single color, and the first partial region adjacent to the contour line in the direction within the specific range of the region. A gradation conversion control device comprising: a determining unit that determines a second line group in which the direction of the first line group is changed to a direction within the other range for the second partial region; It is.
The invention according to claim 2 is characterized in that the determining means uses, as the second line group, a line group obtained by mirror-image-transforming the first line group with reference to a predetermined axis. Item 2. The gradation conversion control device according to Item 1.
The invention according to claim 3 is such that one of the specific range and the other range is sandwiched between a right direction and an upward direction in the image, and the other is a left direction and an upward direction in the image. The gradation conversion control device according to claim 2, wherein the predetermined axis is a vertical axis in the image.
According to a fourth aspect of the present invention, the determining means determines which one of the two single colors is the one single color and which is the other single color, in the image, the one single color and the other single color. 4. The gradation conversion control device according to claim 1, wherein the gradation conversion control device is determined according to an occupied area.
According to a fifth aspect of the present invention, the determining means determines which of the two single colors is the one single color and which is the other single color, with respect to the light and dark difference between the one single color and the other single color. 4. The gradation conversion control device according to claim 1, wherein the gradation conversion control device is determined according to an influence degree.
According to a sixth aspect of the present invention, the determining unit is configured to display information for expressing the other single color in M gradations adjacent to the first partial region and the second partial region of the region. 6. The gradation according to claim 1, wherein the third partial region to be determined is determined as a halftone dot corresponding to the first line group and the second line group. It is a conversion control device.
According to the seventh aspect of the present invention, the direction of the contour line is based on the appearance frequency of the direction from one pixel to another pixel constituting the contour line in the partial image including the contour line of the region of the image. The gradation conversion control device according to claim 1, further comprising a detecting unit that detects the image.
According to an eighth aspect of the present invention, an image including an area of a K (K ≧ 2) order color composed of a single color expressed with N (N ≧ 3) gradations is provided with a plurality of predetermined sizes. Dividing means for dividing the image into partial images, and each of the two single colors as information for expressing two of the K single colors constituting the K-order color with M (2 ≦ M <N) gradations. A determination unit that determines whether or not the directions of two predetermined line groups are both within a specific range, and a specific part including a contour line of the region of the plurality of partial images Detecting means for detecting the direction of the contour line in the image; and the contour detected by the detecting means when both directions of the two line groups are determined to be within the specific range by the determining means. The specific part when the direction of the line is within the specific range; For an image, one single color of the two single colors is converted to M gradation using a line group predetermined for the one single color, and the other single color of the two single colors is Conversion means for converting to M gradations using a line group in which the direction of a predetermined line group for the other single color is changed to a direction in another range that does not overlap with the specific range. An image processing apparatus characterized by the above.
According to a ninth aspect of the present invention, there is provided a computer having a function of acquiring an image including an area of a K (K ≧ 2) order color composed of a single color expressed by N (N ≧ 3) gradations, and the K Two line groups predetermined for each of the two single colors as information for expressing two of the K single colors constituting the next color with M (2 ≦ M <N) gradations A function for determining whether or not the directions of the two lines are within a specific range, and when the directions of the two line groups are both within the specific range, Information for expressing one single color with M gradation is determined for a line group predetermined for the one single color, and the other single color of the two single colors is expressed with M gradation. Information adjacent to a contour line in a direction in another range that does not overlap with the specific range in the region. The first partial region is determined as the first line group determined in advance for the other single color, and the second portion adjacent to the contour line in the direction within the specific range in the region. The area is a program for realizing the function of determining the second line group in which the direction of the first line group is changed to the direction in the other range.

According to the first aspect of the present invention, it is possible to reduce the possibility that jaggy will occur in the contour portion of the region, and to reduce the possibility that moire occurs due to the two line groups.
According to the second aspect of the present invention, a line group in which the direction of the predetermined line group is changed can be easily created as compared with the case where the present configuration is not provided.
According to the third aspect of the present invention, a line group in which the direction of a predetermined line group is changed can be created by simple calculation as compared with the case where the present configuration is not provided.
According to the fourth aspect of the present invention, the possibility of jaggies occurring in the contour portion of the region is reduced while the influence on the appearance of the image is suppressed, and the possibility that moire is generated by the two line groups is also reduced. be able to.
According to the fifth aspect of the present invention, it is possible to reduce the possibility of jaggies occurring in the contour portion of the region while reducing the influence on the appearance of the image, and also reduce the possibility of occurrence of moire due to the two line groups. be able to.
According to the sixth aspect of the present invention, the possibility that an interference fringe is generated at the boundary between two line groups can be reduced as compared with the case where the present configuration is not provided.
According to the seventh aspect of the present invention, it is possible to determine a direction suitable as the direction of the contour line even when the contour line of the region is complicated as compared with the case where this configuration is not provided.
According to the invention of claim 8, it is possible to reduce the possibility that jaggy will occur in the contour portion of the region, and to reduce the possibility that moire will occur due to the two line groups.
According to the ninth aspect of the present invention, it is possible to reduce the possibility that jaggy will occur in the contour portion of the region, and to reduce the possibility that moire occurs due to the two line groups.

It is the figure which showed the example of a structure of the computer system with which embodiment of this invention is applied. It is the figure shown about selection of a screen. It is the figure shown about the difference in the image produced by the difference in selection of a screen. It is the figure shown about the streak which arises in the boundary of two screens which are a mirror image relationship, and its avoidance method. It is the block diagram which showed the function structural example of the binarization process part in the 1st Embodiment of this invention. It is the figure which showed the outline | summary of operation | movement of the angle detection part in the binarization process part in embodiment of this invention. It is the figure which showed the outline | summary of operation | movement of the angle detection part in the binarization process part in embodiment of this invention. It is the flowchart which showed the operation example of the binarization process part in the 1st Embodiment of this invention. It is the flowchart which showed the operation example of the binarization process part in the 1st Embodiment of this invention. It is the block diagram which showed the function structural example of the binarization process part in the 2nd Embodiment of this invention. It is the flowchart which showed the operation example of the binarization process part in the 2nd Embodiment of this invention. It is the figure which showed the hardware structural example of the computer which can implement | achieve embodiment of this invention.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 shows a configuration example of a computer system to which this embodiment is applied.
As shown in the figure, this computer system includes a host device 10, an image processing device 20, and an image forming device 40.

The host device 10 is a device that supplies image data that is the basis of an image formed on a recording medium such as paper, and includes at least an application program (hereinafter simply referred to as “application”) 11 and a printer driver 12. Here, the host device 10 is realized by, for example, a PC (Personal Computer).
The application 11 is document processing software, spreadsheet software, or the like, and outputs a command for requesting printing of the created data to the printer driver 12.
The printer driver 12 receives this command and converts it into a PDL (Page Description Language) which is a printer drawing command.

  The image processing device 20 is a device that performs image processing on image data supplied from the host device 10, and includes a PDL interpretation unit 21, a drawing unit 22, a rendering unit 23, a gamma correction unit 24, and binarization. And a processing unit 25. Here, the image processing apparatus 20 is realized inside a printer, for example.

When a PDL is sent from the host device 10, the PDL interpretation unit 21 interprets the PDL.
The drawing unit 22 converts a color signal (RGB in the figure) designated by PDL into a color signal (CYMK) of the image forming apparatus 40. At that time, drawing is performed with an intermediate code corresponding to the resolution of the image forming apparatus 40.
The rendering unit 23 renders the intermediate code drawn by the drawing unit 22 into raster image data.

The gamma correction unit 24 performs gamma correction on the C, M, Y, and K color signals.
The binarization processing unit 25 performs screen processing on each color signal (multi-valued image data) after the gamma correction by the gamma correction unit 24 using a dither pattern (screen), and the screen-processed color signal (binary) Image data) is output to the image forming apparatus 40.

  The image forming apparatus 40 is an apparatus that forms an image on a recording medium such as paper using toner corresponding to each color signal after binarization processing.

Incidentally, in the image subjected to the binarization processing in the binarization processing unit 25 of FIG. 1, there is a mismatch between the edge angle of the object in the image and the screen angle used in the binarization processing. In this case, specifically, when these angles are close, jaggy may occur.
Therefore, in this embodiment, jaggy is improved by image processing so that a high-quality image can be output. Specifically, the screen angle is selected so that no mismatch occurs between the edge angle of the object and the screen angle, and screen processing is performed using the selected screen.

FIG. 2 is a diagram showing selection of such a screen.
In the present embodiment, screen processing is performed using a first screen that is a line screen (line group) and a second screen that has a mirror image relationship with the first screen with respect to the Y axis. In the figure, a solid line 51 indicates the direction of the first screen, and the angle θ ₁ satisfies 0 ≦ θ ₁ ≦ 90 °. The solid line 52 indicates the direction of the second screen. Since the second screen is a mirror image of the first screen, the angle θ ₂ is represented by θ ₂ = 180 ° −θ ₁ .
On the other hand, a unit image 53 of a pixel × b pixel is extracted from the input image, and a dominant angle (hereinafter referred to as “dominant angle”) θ ₀ of the edge of the object to be screened in this unit image is obtained. . Based on the dominant angle θ ₀ , a suitable one of the first screen and the second screen is selected, and screen processing is performed using the selected screen. Specifically, the second screen is selected when 0 ≦ θ ₀ ≦ 90 °, and the first screen is selected when 90 ° ≦ θ ₀ ≦ 180 °. In the figure, the broken line 54 indicates the direction of the dominant angle θ ₀ , and 90 ° ≦ θ ₀ ≦ 180 °, so the first screen is selected.

FIG. 3 shows an image subjected to screen processing using the first screen and an image subjected to screen processing using the second screen when the dominant angle θ ₀ satisfies 90 ° ≦ θ ₀ ≦ 180 °. It is a figure which compares.
(A) is an example of an image when the second screen is used. Jaggy is noticeable because the angle of the object's edge and the angle of the screen do not match, that is, these angles are close.
(B) is an example of an image when the first screen is used. The jaggies are minor because the angle of the object edge and the screen angle are aligned, i.e., these angles are not close.

[First Embodiment]
Thus, in the present embodiment, a screen corresponding to the dominant angle θ ₀ in the unit image is selected from the first screen and the second screen that are in a mirror image relationship with each other, and this selected screen is used. Added screen processing.
However, if only one of the first screen and the second screen is selected, interference fringes (streaks) are generated at the boundary between the first screen and the second screen.
FIG. 4 is a diagram showing the occurrence of such streaks and a workaround for them.
(A) shows a state in which when a first screen and a second screen, which are mirror images of each other, are adjacent to each other, these screens interfere with each other and appear as vertical stripes.
In order to avoid such a state, the unit image adjacent to both the first screen and the second screen has, for example, the same angle and the same number of lines as the first screen and the second screen, as shown in (b). It is conceivable to apply a third screen which is a dot screen (halftone dot). Since the third screen has two angle components, that is, the angle of the first screen and the angle of the second screen, the streak as shown in (a) hardly occurs in this case.

FIG. 5 is a block diagram showing the configuration of the binarization processing unit 25 that performs such screen processing.
As illustrated, the binarization processing unit 25 includes an image dividing unit 31, an edge determination unit 32, an angle detection unit 34, an edge screen determination unit 35, a non-edge screen determination unit 36, and a screen processing unit 37. With.

The image dividing unit 31 divides the input multi-value image data (for example, image data of 256 gradations) into a unit image of a pixel × b pixel. In the present embodiment, an image dividing unit 31 is provided as an example of an acquisition unit that acquires an image. Further, a unit image is used as an example of a partial image, and an image dividing unit 31 is provided as an example of a dividing unit that divides an image into a plurality of partial images.
The edge determination unit 32 determines whether each unit image obtained by the division by the image dividing unit 31 is an image including an object edge (hereinafter referred to as “edge image”) or an image not including an object edge (hereinafter referred to as “edge image”). Or “non-edge image”).
The angle detection unit 34 detects the dominant angle θ ₀ in the unit image determined as the edge image by the edge determination unit 32. A method for detecting the dominant angle θ ₀ will be described later. In the present embodiment, an angle detection unit 34 is provided as an example of a detection unit that detects the direction of the contour line.

The edge screen determination unit 35 determines a screen (hereinafter referred to as “edge screen”) to be used in the edge image based on the dominant angle θ ₀ detected by the angle detection unit 34. Specifically, the second screen is selected if 0 ≦ θ ₀ ≦ 90 °, and the first screen is selected if 90 ° ≦ θ ₀ ≦ 180 °. In this embodiment, a range of 0 to 90 ° is used as an example of the specific range, and a range of 90 ° to 180 ° is used as an example of the other range, and the first in the direction within the specific range is used. The first screen is used as an example of a line group, and the second screen is used as an example of a second line group in a direction within another range. In the present embodiment, the edge screen determination unit 35 is provided as an example of a determination unit that determines information for expressing a single color in M gradations for a partial region adjacent to the contour line.

  The non-edge screen determination unit 36 determines a screen (hereinafter referred to as “non-edge screen”) to be used in the non-edge image based on the information on the edge screen determined by the edge screen determination unit 35. In the present embodiment, determination for determining information for expressing a single color with M gradations for a partial region in which the first line group is used and a partial region adjacent to the partial region in which the second line group is used. As an example of the means, a non-edge screen determination unit 36 is provided.

  The screen processing unit 37 performs screen processing on the input multi-valued image data based on the edge screen determined by the edge screen determination unit 35 and the non-edge screen determined by the non-edge screen determination unit 36. In the present embodiment, a screen processing unit 37 is provided as an example of conversion means for converting a single color into M gradations.

Here, a method for detecting the dominant angle θ ₀ will be specifically described.
In the present embodiment, the angle with the highest appearance frequency among the angles of the edges in the unit image is defined as the dominant angle θ ₀ .
FIG. 6 shows an example in which only one angle appears as an edge angle in the unit image.
(A) shows each pixel (pixel) in the unit image as a pixel representing an edge as “1” and a pixel not representing an edge as “0”.
First, as shown in (b), the appearance frequency of an angle from each pixel representing an edge to an adjacent pixel is examined.
(C) is a histogram showing the frequency of angle appearance. In this example, since 45 ° has the highest appearance frequency, the dominant angle θ ₀ in the unit image is 45 °.

FIG. 7 shows an example in which a plurality of angles appear as edge angles in the unit image.
(A) shows each pixel (pixel) in the unit image as a pixel representing an edge as “1” and a pixel not representing an edge as “0”.
First, as shown in (b), the appearance frequency of an angle from each pixel representing an edge to an adjacent pixel is examined.
(C) is a histogram showing the frequency of angle appearance. In this example, 0 °, 45 °, and 135 ° appear. Of these, 135 ° has the highest appearance frequency, so the dominant angle θ ₀ in the unit image is 135 °.

Next, the operation of the binarization processing unit 25 in the first embodiment will be described.
FIG. 8 is a flowchart showing an operation example of a part other than the non-edge screen determination unit 36 and the screen processing unit 37 in the binarization processing unit 25.
As shown in the figure, first, the image dividing unit 31 divides the input multi-value image data into P unit images (step 301). Here, the number p is assigned to the P unit images. It is assumed that a unit image including each pixel in the unit image can be specified by the number p by assigning a number p according to the position of the unit image in the multivalued image data. Then, the P unit images obtained by the division by the image dividing unit 31 are transferred to and held by the edge determination unit 32.

Next, the edge determination unit 32 substitutes 1 for the number p of the unit image (step 302). Then, the p-th unit image is taken out and it is determined whether or not the unit image is an edge image (step 303). Here, it is preferable to determine whether the unit image is an edge image using a known edge detection method.
When it is determined that the unit image is an edge image, the unit image and its number p are passed to the angle detection unit 34, and the angle detection unit 34 detects the dominant angle θ ₀ in the p-th unit image ( Step 304). Here, the dominant angle θ ₀ may be detected by the method described with reference to FIGS.
Then, the dominant angle θ ₀ and the unit image number p are transmitted to the edge screen determination unit 35, and the edge screen determination unit 35 determines whether the dominant angle θ ₀ satisfies 0 ≦ θ ₀ ≦ 90 °. (Step 305).

If the dominant angle θ ₀ satisfies 0 ≦ θ ₀ ≦ 90 °, the edge screen determination unit 35 selects the second screen as the screen used in the screen processing of the p-th unit image (step 306).

On the other hand, if the dominant angle θ ₀ does not satisfy 0 ≦ θ ₀ ≦ 90 °, the edge screen determination unit 35 selects the first screen as the screen used in the screen processing of the p-th unit image (step 307). .

  Whether the first screen or the second screen is selected as the screen used in the screen processing of the p-th unit image is correlated with the unit image number p by the edge screen determining unit 35 as screen selection information. Shall be retained.

  On the other hand, when it is determined in step 303 that the p-th unit image is a non-edge image, the edge determination unit 32 adds tag information indicating that the unit image is a non-edge image (step 308). .

  Thereafter, the edge determination unit 32 determines whether or not the number p of unit images has reached the number P of unit images (step 309). If p has not reached P, 1 is added to p (step 310), and the process returns to step 303. If p has reached P, the process ends.

FIG. 9 is a flowchart illustrating an operation example of the non-edge screen determination unit 36 in the binarization processing unit 25.
As shown in the figure, first, the non-edge screen determination unit 36 extracts Q non-edge images to which tag information is added from the P unit images held by the edge determination unit 32 (step 321). At this time, the number p as a unit image of the non-edge image is also taken out.
Next, the non-edge screen determination unit 36 substitutes 1 for the number q of the non-edge image (step 322). Then, the q-th non-edge image is extracted, and it is determined whether or not the non-edge image is adjacent to both the edge image with the first screen selected and the edge image with the second screen selected (step 323). ). Note that this determination is based on the number p as the unit image of the q-th non-edge image to obtain the number p ₁ , p ₂ ,... By checking whether there are both the first screen and the second screen among the screens associated with the unit image numbers p ₁ , p ₂ ,... Good.

  When it is determined that the q-th non-edge image is adjacent to both the edge image for which the first screen is selected and the edge image for which the second screen is selected, the non-edge screen determination unit 36 selects the first edge image. A third screen which is a dot screen having the same angle and the same number of lines as the first screen and the second screen is used as the screen for the screen processing of the q-th non-edge image so that no streak occurs at the boundary between the screen and the second screen A screen is selected (step 324).

On the other hand, when it is determined that the qth non-edge image is not adjacent to both the edge image from which the first screen is selected and the edge image from which the second screen is selected, the non-edge screen determination unit 36 determines whether the qth non-edge image is adjacent to the selected edge image for the second screen (step 325). Note that this determination is based on the number p as the unit image of the q-th non-edge image to obtain the number p ₁ , p ₂ ,... This may be done by checking whether there is a second screen among the screens associated with the unit image numbers p ₁ , p ₂ ,. If it is determined that the q-th non-edge image is not adjacent to the selected edge image of the second screen, no streaking occurs even if the first screen is selected. The first screen is selected (step 326). In addition, when it is determined that the q-th non-edge image is adjacent to the selected edge image of the second screen, a streak occurs when the first screen is selected. The second screen is selected (step 327).
Note that which of the first screen, the second screen, and the third screen is selected as the screen used in the screen processing of the qth non-edge image is associated with the number p as the unit image of the non-edge image, It is assumed that the non-edge screen determination unit 36 holds the screen selection information.

  Thereafter, the non-edge screen determination unit 36 determines whether the number q of the non-edge images has reached the number Q of non-edge images (step 328). If q has not reached Q, 1 is added to q (step 329), and the process returns to step 323. If q has reached Q, the process is terminated.

  Finally, the screen processing unit 37 performs screen processing on the input multi-value image data. Specifically, first, it is determined whether each pixel included in the multi-valued image data is subject to screen processing, that is, whether the color of each pixel is halftone. Next, for a pixel determined to be subject to screen processing, a unit image including the pixel is specified based on the unit image number. Then, by referring to the screen selection information for the specified unit image among the screen selection information held by the edge screen determination unit 35 or the non-edge screen determination unit 36, the first screen, the second screen, the third screen Any one of the screens is selected, and screen processing is performed for the pixel using the selected screen.

[Second Embodiment]
In the first embodiment, the monochromatic screen processing is mainly described. In the second embodiment, the screen processing for secondary colors or more is described.
For example, in the case of a YMCK four-color printer, in order to avoid moire, the screen angle of two of the four colors is set in the range of 0 to 90 °, and the screen angle of the remaining two of the four colors is set to 90 ° to It is often set in the range of 180 °. That is, the four screen angles are set so that the difference between the screen angles becomes large.
Here, the angle of the Y color and C color screens is set to an angle in the range of 0 to 90 °, and such a screen is referred to as an “acute angle screen”. Further, the angle of the M color screen and the K color screen is set to an angle within a range of 90 ° to 180 °, and such a screen is referred to as an “obtuse angle screen”.

  Under such conditions, first, screen processing for tertiary colors or more will be considered. In the case of a tertiary color or more, the angle of at least one single color screen constituting the color is an advantageous angle with respect to the object (an angle having a large difference from the angle of the edge of the object). In this case, it is preferable to use a screen predetermined for each single color as it is. Alternatively, if only one screen angle is advantageous for the object, the angle of one of the remaining screens may be advantageous for the object. Suppose that a predetermined screen for each single color is used as it is.

Next, consider secondary color screen processing. In the case of a secondary color, if both of the two monochrome screens that make up the color are acute or obtuse screens, moire occurs when both the angles of the two monochrome screens are set to an advantageous angle with respect to the object. Therefore, only the angle of one monochrome screen is set as an advantageous angle with respect to the object.
At that time, it is effective to set the angle of the monochrome screen having the larger coverage in the input multi-value image data of the two monochrome colors as an advantageous angle. In other words, it may be determined according to the area occupied by each single color in the image which one of the single color screens has an advantageous angle.
Alternatively, an angle of a single-color screen that easily obtains contrast between the two single colors may be set as an advantageous angle. As described above, if the Y and C screens are acute-angle screens, the angle of the C-color screen is an advantageous angle, and if the M- and K-color screens are obtuse screens, The angle may be an advantageous angle. In other words, which single-color screen angle is to be an advantageous angle may be determined in accordance with the degree of influence on the contrast of each single color.

FIG. 10 is a block diagram showing the configuration of the binarization processing unit 25 that performs such screen processing.
As illustrated, the binarization processing unit 25 includes an image dividing unit 31, an edge determination unit 32, a secondary color determination unit 33, an angle detection unit 34, an edge screen determination unit 35, and a non-edge screen determination. A unit 36 and a screen processing unit 37.

Since the image division unit 31, the edge determination unit 32, the angle detection unit 34, the edge screen determination unit 35, the non-edge screen determination unit 36, and the screen processing unit 37 have already been described in the first embodiment, description will be given here. Omitted.
The secondary color determination unit 33 determines whether the color of the unit image determined as the edge image by the edge determination unit 32 is a single color, a secondary color, a tertiary color or more, and a secondary color. In some cases, it is determined whether an acute screen or an obtuse screen is used. In the present embodiment, the secondary color determination unit 33 is provided as an example of a determination unit that determines whether the directions of the two line groups are both within a specific range.

Next, the operation of the binarization processing unit 25 in the second embodiment will be described.
FIG. 11 is a flowchart showing an example of the operation of the binarization processing unit 25 other than the non-edge screen determination unit 36 and the screen processing unit 37.
As shown in the figure, first, the image dividing unit 31 divides the inputted multi-value image data into P unit images (step 351). Here, the number p is assigned to the P unit images. It is assumed that a unit image including each pixel in the unit image can be specified by the number p by assigning a number p according to the position of the unit image in the multivalued image data. Then, the P unit images obtained by the division by the image dividing unit 31 are transferred to and held by the edge determination unit 32.

Next, the edge determination unit 32 substitutes 1 for the number p of the unit image (step 352). Then, the p-th unit image is taken out and it is determined whether or not the unit image is an edge image (step 353). Here, it is preferable to determine whether the unit image is an edge image using a known edge detection method.
When it is determined that the unit image is an edge image, the unit image and its number p are passed to the secondary color determination unit 33, and the secondary color determination unit 33 determines that the color of the p-th unit image is the secondary color. It is determined whether the following is true (step 354). In this operation example, it is assumed that one object part is included in the unit image and that the object part is filled with one color. Therefore, the “unit image color” here is a color that fills the object portion.
If it is determined that the color of the p-th unit image is equal to or less than the secondary color, then the secondary color determination unit 33 determines whether the color of the p-th unit image is a single color (primary color). Determination is made (step 355). If the color of the p-th unit image is a single color, the process proceeds to step 357 as it is. On the other hand, if the color of the p-th unit image is not a single color, that is, if it is a secondary color, the secondary color determination unit 33 determines that the two single-color screens constituting the secondary color are both acute angle screens, It is determined whether both are obtuse angle screens (step 356).

If it is determined in step 355 that the color of the p-th unit image is a single color, or if it is determined in step 356 that the two single-color screens are both acute angle screens or both are obtuse angle screens, the unit image And the number p is passed to the angle detector 34, and the angle detector 34 detects the dominant angle θ ₀ in the p-th unit image (step 357). Here, the dominant angle θ ₀ may be detected by the method described with reference to FIGS.
Then, the dominant angle θ ₀ and the unit image number p are transmitted to the edge screen determination unit 35, and the edge screen determination unit 35 determines whether the dominant angle θ ₀ satisfies 0 ≦ θ ₀ ≦ 90 °. (Step 358).

If the dominant angle θ ₀ satisfies 0 ≦ θ ₀ ≦ 90 °, the edge screen determination unit 35 selects the second screen as the screen used in the screen processing of the p-th unit image (step 359). Specifically, when the color of the p-th unit image is a single color, if the screen predetermined for the single color is an acute angle screen, a screen having a mirror image relationship with the screen is selected as the second screen. If the predetermined screen for the single color is an obtuse angle screen, the screen is selected as it is as the second screen. Further, when the color of the p-th unit image is a secondary color, if two screens predetermined for the two single colors constituting the secondary color are acute angle screens, one of the two screens and a mirror image are displayed. If the screen having the relationship is selected as the second screen and the two screens predetermined for the two single colors constituting the secondary color are obtuse angles, one of the two screens is set as the second screen. select. However, at this time, the other of the two screens is selected as it is.

On the other hand, if the dominant angle θ ₀ does not satisfy 0 ≦ θ ₀ ≦ 90 °, the edge screen determination unit 35 selects the first screen as the screen used in the screen processing of the p-th unit image (step 360). . Specifically, when the color of the p-th unit image is a single color, if the screen predetermined for the single color is an acute angle screen, the screen is selected as the first screen as it is, If the predetermined screen is an obtuse angle screen, a screen having a mirror image relationship with the screen is selected as the first screen. Further, when the color of the p-th unit image is a secondary color, if two screens predetermined for the two single colors constituting the secondary color are acute angle screens, one of the two screens is changed to the first color. If two screens selected as one screen and the two predetermined colors constituting the secondary color are obtuse angle screens, a screen having a mirror image relationship with one of the two screens is used as the first screen. select. However, at this time, the other of the two screens is selected as it is.

  Note that whether the first screen or the second screen is selected as the screen used in the screen processing of the p-th unit image is associated with the unit image number p for each color, and is selected as an edge screen as screen selection information. It is assumed that the determination unit 35 holds it.

  If it is determined in step 354 that the color of the p-th unit image is not a secondary color or less, that is, a tertiary color or more, or in step 356, two single-color screens are both acute angle screens or both Neither is an obtuse angle screen, that is, if it is determined that one of the two monochrome screens is an acute angle screen and the other is an obtuse angle screen, the unit image and its number p are passed to the edge screen determination unit 35. Then, the edge screen determination unit 35 selects a predetermined screen as it is as a screen used for the screen processing of the p-th unit image (step 361).

  On the other hand, when it is determined in step 353 that the p-th unit image is a non-edge image, the edge determination unit 32 adds tag information indicating that the unit image is a non-edge image (step 362). .

  Thereafter, the edge determination unit 32 determines whether or not the number p of unit images has reached the number P of unit images (step 363). If p has not reached P, 1 is added to p (step 364), and the process returns to step 353. If p has reached P, the process is terminated.

  Next, the non-edge screen determination unit 36 operates. Since this is substantially the same as that described with reference to the flowchart of FIG. 9 in the first embodiment, detailed description thereof is omitted. However, in the first embodiment, the color is not considered, whereas in the second embodiment, the process shown in the flowchart of FIG. 9 is executed for each color. In this case, the first screen means an acute angle screen among the screens selected for each single color, and the second screen means an obtuse angle screen among the screens selected for each single color. The screen selection information is also held in the non-edge screen determination unit 36 in association with not only the unit image number p but also the color.

  Finally, the screen processing unit 37 performs screen processing on the input multi-value image data. Specifically, first, it is determined whether each pixel included in the multi-valued image data is an object of screen processing, that is, whether any single color constituting the color of each pixel is halftone. Next, for a pixel determined to be subject to screen processing, a unit image including the pixel is specified based on the unit image number. The screen selection information held by the edge screen determination unit 35 or the non-edge screen determination unit 36 is referred to by the screen selection information for the specified unit image and its single color, thereby the first screen, the second screen, Any one of the third screens is selected, and screen processing is performed on the single color at the pixel using the selected screen.

In the present embodiment, the description has been made on the assumption that multi-value image data (for example, 256 gradations) is converted into binary image data, but the present invention is not limited to this. N (N ≧ 3) gradation image data may be premised on conversion to M (2 ≦ M <N) gradation image data.
In the present embodiment, the case where the present invention is applied to the screen processing for an object has been described. However, the present invention can also be applied to the screen processing for a specific color area of image data. In this sense, an object is an example of a region in an image.
Furthermore, in the present embodiment, the angle of the first screen is set in the range of 0 to 90 ° and the angle of the second screen is set in the range of 90 ° to 180 °, but this is not restrictive. The angle of the first screen and the angle of the second screen may be set in any two ranges that do not overlap each other.
Furthermore, in the present embodiment, the second screen is a mirror image converted from the first screen with respect to the Y axis. However, the reference for mirror image conversion is not limited to the Y axis, but may be another predetermined axis. Further, the angle of the second screen may be obtained by rotationally transforming the angle of the first screen, instead of obtaining the angle of the first screen by mirror image transformation.

Incidentally, the image processing apparatus 20 in the present embodiment may be realized in a printer, but can also be realized in a general-purpose computer such as a PC.
Hereinafter, the hardware configuration of such a general-purpose computer as the computer 90 will be described.

FIG. 12 is a diagram illustrating a hardware configuration of the computer 90.
As shown in the figure, the computer 90 includes a CPU (Central Processing Unit) 91 as a calculation means, a main memory 92 as a storage means, and a magnetic disk device (HDD: Hard Disk Drive) 93. Here, the CPU 91 executes various types of software such as an OS (Operating System) and applications to realize the above-described functions. The main memory 92 is a storage area for storing various software and data used for execution thereof, and the magnetic disk device 93 is a storage area for storing input data for various software, output data from various software, and the like. .
Further, the computer 90 includes a communication I / F 94 for performing communication with the outside, a display mechanism 95 including a video memory and a display, and an input device 96 such as a keyboard and a mouse.

  The program for realizing the present embodiment can be provided not only by communication means but also by storing it in a recording medium such as a CD-ROM.

DESCRIPTION OF SYMBOLS 10 ... Host apparatus, 20 ... Image processing apparatus, 21 ... PDL interpretation part, 22 ... Drawing part, 23 ... Rendering part, 24 ... Gamma correction part, 25 ... Binarization processing part, 31 ... Image division part, 32 ... Edge Determining unit, 33 ... secondary color determining unit, 34 ... angle detecting unit, 35 ... edge screen determining unit, 36 ... non-edge screen determining unit, 37 ... screen processing unit, 40 ... image forming apparatus

Claims (9)

Obtaining means for obtaining an image including a region of a K (K ≧ 2) order color composed of a single color expressed by N (N ≧ 3) gradations;
As information for expressing two of the K single colors constituting the K-order color with M (2 ≦ M <N) gradations, two predetermined colors for each of the two single colors are used. Determining means for determining whether or not the direction of the line group is within a specific range;
Information for expressing one of the two single colors in M gradations when the determination unit determines that the directions of the two line groups are both within the specific range, A line group determined in advance for the one single color is determined, and information for expressing another single color of the two single colors in M gradations overlaps with the specific range in the region. The first partial region adjacent to the contour line in the direction within the other range is determined as the first line group predetermined for the other single color, and the specific range of the region is determined. The second partial region adjacent to the contour line in the inner direction includes a determining unit that determines the second line group in which the direction of the first line group is changed to the direction in the other range. A gradation conversion control device characterized by that.   2. The gradation conversion control according to claim 1, wherein the determining unit uses, as the second line group, a line group obtained by mirror-image-converting the first line group with a predetermined axis as a reference. apparatus. One of the specific range and the other range is a range sandwiched between the right direction and the upper direction in the image, and the other is a range sandwiched between the left direction and the upper direction in the image,
The gradation conversion control apparatus according to claim 2, wherein the predetermined axis is a vertical axis in the image.   The determining means determines which of the two single colors is the one single color and which is the other single color according to the area occupied by the one single color and the other single color in the image. The gradation conversion control device according to any one of claims 1 to 3, wherein   The determining means determines which of the two single colors is the one single color and which is the other single color according to the degree of influence on the contrast between the one single color and the other single color. The gradation conversion control device according to any one of claims 1 to 3, wherein   The determining means provides information for expressing the other single color in M gradations, and for the third partial region adjacent to the first partial region and the second partial region of the region, 6. The gradation conversion control device according to claim 1, wherein halftone dots corresponding to the first line group and the second line group are determined.   The image processing apparatus further includes detection means for detecting the direction of the contour line based on the appearance frequency of the direction from one pixel constituting the contour line to another pixel in the partial image including the contour line of the region of the image. The gradation conversion control apparatus according to any one of claims 1 to 6, wherein A dividing unit that divides an image including an area of a K (K ≧ 2) order color constituted by a single color expressed by N (N ≧ 3) gradations into a plurality of partial images having a predetermined size;
As information for expressing two of the K single colors constituting the K-order color with M (2 ≦ M <N) gradations, two predetermined colors for each of the two single colors are used. Determining means for determining whether or not the direction of the line group is within a specific range;
Detecting means for detecting a direction of the contour line in a specific partial image including the contour line of the region of the plurality of partial images;
When it is determined by the determining means that the directions of the two line groups are both within the specific range, and the direction of the contour line detected by the detecting means is within the specific range, For the specific partial image, one single color of the two single colors is converted to M gradation using a line group predetermined for the single single color, and the other of the two single colors is converted. Conversion means for converting the single color of the second color into M gradations using a line group in which the direction of a predetermined line group with respect to the other single color is changed to a direction within another range that does not overlap with the specific range; An image processing apparatus comprising: On the computer,
A function of acquiring an image including an area of a K (K ≧ 2) order color composed of a single color expressed by N (N ≧ 3) gradations;
As information for expressing two of the K single colors constituting the K-order color with M (2 ≦ M <N) gradations, two predetermined colors for each of the two single colors are used. A function for determining whether the direction of each line group is within a specific range;
When it is determined that the directions of the two line groups are both within the specific range, information for expressing one single color of the two single colors with M gradations is displayed. Is determined to be a predetermined line group, and information for expressing the other single color of the two single colors in M gradations is another range that does not overlap the specific range of the region. The first partial region adjacent to the contour line in the inner direction is determined as the first line group determined in advance for the other single color, and the direction in the specific range of the region is determined. A program for realizing a function of determining a second line group in which the direction of the first line group is changed to a direction within the other range for the second partial region adjacent to the contour line.

Images