Method and software for creating halftone dot images

Abstract

To provide a creation method and creation software of a dot image that has a complicated dot shape required for a security printed matter and that is not dependent on the variation in the output resolution and screen line number.SOLUTION: There are provided a creation method and creation software of a dot image that has a complicated dot shape required for a security printed matter and that is not dependent on the variation in the output resolution and screen line number by the steps of: reading a gray-scale image; performing processing of re-sampling according to the output resolution; reading a unit constituted by a vector object group; creating a rendering image; performing optimization processing; and performing halftone screening processing.SELECTED DRAWING: Figure 20

Description

[Technical Field]

[0001] The present invention relates to a method and software for creating halftone dot images in the field of security printed matter, such as banknotes, passports, securities, certificates, and important documents, which require prevention of counterfeiting and alteration. [Background technology]

[0002] It is important to prevent counterfeiting and alteration in security printed materials such as banknotes, passports, securities, certificates, and important documents. In such printed materials, counterfeiting and alteration are prevented by using thin lines to form the printed surface.

[0003] Typical techniques using thin lines include background patterns and colored patterns. These are geometric figures made up of a collection of curved lines, and these geometric figures not only prevent counterfeiting and alteration, but also add design to the printed surface.

[0004] However, these geometric patterns are not suitable for expressing continuous gradations (density varying from 0% to 100%) like a photograph, for example. Therefore, when applying continuous gradation patterns to the above-mentioned security prints, gradation images are added to areas other than the geometric shapes.

[0005] To create a gradation image, it is necessary to create a halftone image from continuous tones. Halftone conversion is the process of converting a gradation image [1] into a halftone image [2], as shown in Figure 1, and the gradation is expressed by the size of the halftone dots in the halftone image [2].

[0006] As a method for creating a halftone dot image [2], for example, Non-Patent Document 1 describes a technique called halftone screening. This technique uses a threshold array (hereinafter referred to as a critical array [3]) as shown in Figure 2. This critical array [3] is a collection of elements [5] each having a threshold value [4] written as an 8-bit value (0 to 255) in decimal or hexadecimal notation, and determines the shape of the halftone dot.

[0007] Moreover, the gradation image [1] is a collection of pixels [6] as shown in Figure 3. Each pixel [6] has pixel value information written as an 8-bit value (0 to 255) in decimal or hexadecimal notation.

[0008] To convert such a gradation image [1] into halftone dots, for example, as shown in Figure 4, the pixel values ​​of the gradation image [1] are compared with the threshold value [4] of the critical array [3], and if the value obtained by inverting the gradation of the pixel value (255 - pixel value) is equal to or less than the threshold value [4], the pixel is converted to black, and otherwise converted to white. As a result, halftone screening is the process of matching (or approximating) the density per unit area of ​​the gradation image [1] (from 0% to 100%) with the area ratio per unit area of ​​the halftone dot image [2] (from 0% to 100%).

[0009] The concept of resolution exists in grayscale images [1]. Resolution is expressed in units of "dpi," which is the number of pixels arranged within 1 inch, as shown in Figure 5.

[0010] Halftone screening also involves the concept of screen ruling. As shown in Figure 6, screen ruling is expressed in units of "Lpi" and represents the number of halftone dots [7] arranged in one inch. For example, as shown in Figure 7, the reproducibility of motifs differs depending on whether the screen ruling is "low," "medium," or "high," and generally, the higher the screen ruling, the higher the resolution.

[0011] In halftone screening, the number of elements [5] in the critical array [3] is determined by the relationship between resolution and screen ruling. The number of elements [5] in a single direction in the critical array [3] is calculated using the following formula (1).

[0012]

number

[0013] There are roughly two ways to define the threshold value [4] for the element [5] of this critical array [3]. The first is an arithmetic definition method, which is classified as Type 1 in Non-Patent Document 1. The second is a descriptive definition method, which is classified as Type 3 in Non-Patent Document 1.

[0014] The former, Type 1, is a method in which the z value for each x and y coordinate is calculated using a three-dimensional function and then converted into a threshold value [4], as shown in Figure 8. To change the halftone dot shape, the three-dimensional function can be changed, as shown in Figure 10.

[0015] The latter, Type 3, is a method for defining the threshold value [4] by describing an 8-bit value (0 to 255), as shown in FIG.

[0016] Halftone screening is performed according to the critical array [3] defined in this way and the method for creating the halftone image [2] described above. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Patent No. 3855013 [Patent Document 2] Patent No. 6651198 [Non-patent literature]

[0018] [Non-Patent Document 1] PostScript "Reference Manual (2nd Edition)" (1991) Summary of the Invention [Problem to be solved by the invention]

[0019] In the aforementioned Type 1, the threshold is determined from the z value calculated using a three-dimensional function. Therefore, in order to create the complex halftone dot shapes required for security prints, it is necessary to calculate a complex three-dimensional function, which makes it difficult to create the desired halftone dot shapes.

[0020] Therefore, the applicant has filed patent applications for a screen creation method, creation device, and creation software as a means of creating the complex halftone dot shapes required for security prints (for example, Patent Documents 1 and 2). This creation method involves providing elements that involve changes in image area calculated from a three-dimensional function within a single or multiple divided areas in units that are contained in cells that make up the halftone dot shape and have the same movement but are arranged in different directions.

[0021] However, because it uses a three-dimensional function like the aforementioned Type 1, the halftone dot shape is limited to the range that can be expressed by a three-dimensional function, which makes it difficult to create halftone dot shapes with designs such as symbol marks.

[0022] Furthermore, in the aforementioned Type 3, after determining the number of elements [5] in the critical array [3] according to the output resolution and screen ruling, a threshold value [4] is written for each element [5], and the threshold value [4] is fixed. As shown in the aforementioned [Equation 1], if the output resolution is changed after the number of elements [5] in the critical array [3] has been fixed, the screen ruling will also change. Because the output resolution depends on the performance of the output device, there was an issue in that the screen ruling value would change to an unintended value when the output device was changed.

[0023] Furthermore, if the reproducibility, i.e., the screen ruling, is changed to match the motif of the gradation image [1], the number of elements [5] in the critical array [3] changes, which poses the problem of having to rewrite all thresholds [4].

[0024] In view of the above-mentioned problems, the present invention provides a method for creating a halftone image [2] that has the complex halftone dot shapes required for security prints and is not affected by variations in output resolution or screen line frequency. [Means for solving the problem]

[0025] The present invention is a method for creating a halftone image for expressing gradation in a printed matter, comprising the steps of: creating a unit for arranging a vector object formed by a Bezier curve or a spline curve, which is vector data; arranging the vector object in the unit; forming a vector object group by at least one of the steps of i) setting a gradation attribute to the vector object, or ii) setting a rasterization attribute to the vector object, or iii) arranging an arbitrary number of new vector objects and setting a blend attribute to an arbitrary number of vector objects; and, if necessary, adding a vector object group, repeating the steps of: saving the unit created by repeating the steps of reading the unit; and determining an output resolution and a screen resolution from the unit. a step of converting the rendering image to a critical array for halftone screening; a step of reading a gradation image to be subjected to halftone screening; a step of resampling the gradation image according to the output resolution to create a resampled image; a step of performing halftone screening on the resampled image using the critical array to create a halftone image; and a step of saving the halftone image, wherein the gradation attribute (i), the rasterization attribute (ii), and the blend attribute (iii) of the vector object group have a gradation difference of 1 or more and 255 or less in 8-bit values, and the arbitrary number of vector objects (iii) are vector objects having different densities and sizes.

[0026] The present invention also provides a method for creating a halftone image for expressing gradation in a printed matter, characterized in that a rendering image is divided into two, four, or eight parts, one of which is designated as a main part and the other parts are designated as sub-parts, and the main part is arranged in such a way that it is iv) inverted in point symmetry, or v) inverted in line symmetry, or vi) rotated clockwise / counterclockwise relative to the sub-parts.

[0027] The present invention also provides a method for creating a halftone image for expressing gradation in a printed matter, characterized by inverting the gradation of a rendering image, or by expanding and arranging a main region relative to a sub-region while inverting the gradation.

[0028] This is a method for creating halftone images for expressing gradation in printed materials, characterized in that a group of four adjacent 2x2 pixels in a rendering image is divided into groups, and each group overlaps with an adjacent group by one pixel.The average value of the 8-bit values ​​of the pixels in the group is calculated, and this average value is used as one pixel.While maintaining the order of the average values ​​in the rendering image, the x and y axes are displaced diagonally at a 45-degree angle, and the rendering image is reconstructed.

[0029] The present invention also provides a method for creating halftone images for expressing gradation in printed matter, characterized in that the rendered image is divided into four quadrants while maintaining the rectangular proportions of the rendered image, with the upper left region being region A, the upper right region being region B, the lower left region being region C, and the lower right region being region D; vii) the rendered image is expanded to 2n x m pixels and the top row is arranged in the order of region B, region C, region D, and region A from left to right, and the bottom row of the expanded rendered image is arranged in the order of region D, region A, region B, and region C from left to right; or viii) the left column of the rendered image is expanded to n x 2m pixels and the left column is arranged in the order of region C, region D, region B, and region A from top to bottom, and the right column of the expanded rendered image is arranged in the order of region D, region A, region C, and region B from top to bottom.

[0030] The present invention also provides software for creating halftone images for expressing gradation in printed matter, the software including a step of creating a unit for arranging vector objects formed by vector data, such as Bezier curves or spline curves, a step of arranging the vector objects in the unit, a step of forming a vector object group by at least one of the steps of i) setting a gradation attribute to the vector object, or ii) setting a rasterization attribute to the vector object, or iii) arranging an arbitrary number of new vector objects and setting a blend attribute to the arbitrary number of said vector objects, and a step of adding a vector object group as necessary, a step of saving the unit created by repeating the steps, a step of reading the unit, and a step of determining an output resolution and a spline attribute from the unit. This software is for creating halftone images to express gradation in printed matter, and is characterized in that it comprises the steps of: creating a rendering image of n x m pixels (n and m are integers) according to the clean line frequency; converting the rendering image into a critical array for halftone screening; reading a gradation image to be halftone screened; creating a resampled image by resampling the gradation image according to the output resolution; creating a halftone image by halftone screening the resampled image using the critical array; and saving the halftone image, wherein the gradation attribute of i) the vector object group, the rasterization attribute of ii) and the blend attribute of iii) have a gradation difference of 1 or more and 255 or less in 8-bit values; and the arbitrary number of vector objects of iii) are vector objects with different densities and sizes.

[0031] The present invention also provides software for creating halftone images to express gradation in printed matter, characterized in that a rendering image is divided into two, four, or eight parts, one of which is designated as a main part and the other parts are designated as sub-parts, and the main part is arranged in such a way that it is iv) inverted in point symmetry, or v) inverted in line symmetry, or vi) rotated clockwise / counterclockwise relative to the sub-parts.

[0032] The present invention also provides software for creating halftone images for expressing gradation in printed matter, characterized by inverting the gradation of a rendering image, or expanding and arranging a main region relative to a sub-region while inverting the gradation.

[0033] The present invention also provides software for creating halftone images for expressing gradation in printed materials, which is characterized by dividing a group of pixels consisting of four adjacent 2x2 pixels into groups for a rendering image, each group overlapping with an adjacent group by one pixel, calculating the average value of the 8-bit values ​​of the pixels included in the group, using the average value as one pixel, and permuting the x and y axes at a 45-degree angle while maintaining the order of the average values ​​of the rendering image, and reconstructing the rendering image.

[0034] The present invention also provides software for creating halftone images to express gradation in printed matter, characterized in that the rendered image is divided into four quadrants that maintain the rectangular ratio of the rendered image, with the upper left region being region A, the upper right region being region B, the lower left region being region C, and the lower right region being region D; vii) the rendered image is expanded to 2n x m pixels and the top row is arranged in the order of region B, region C, region D, and region A from left to right, and the bottom row of the expanded rendered image is arranged in the order of region D, region A, region B, and region C from left to right; or viii) the left column of the rendered image is expanded to n x 2m pixels and the left column is arranged in the order of region C, region D, region B, and region A from top to bottom, and the right column of the expanded rendered image is arranged in the order of region D, region A, region C, and region B from top to bottom. [Effects of the Invention]

[0035] By using the method for creating a halftone dot image of the present invention, it is possible to create a halftone dot image that is not affected by fluctuations in output resolution or screen ruling and has the complex halftone dot shapes required for security prints. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 10 is a diagram showing an example of converting a gradation image into a halftone image. [Figure 2] Diagram showing examples of critical arrays, elements, and thresholds [Figure 3] A diagram showing the relationship between a grayscale image and pixels [Figure 4] A diagram showing an example of halftone dot generation using a critical array for a gradation image with a specific density value. [Figure 5] Diagram showing the concept of resolution (dpi) [Figure 6] Diagram showing the concept of screen ruling (Lpi) [Figure 7] Diagram showing motif reproducibility depending on screen ruling [Figure 8] An example of creating a critical array using the Type 1 method. [Figure 9] An example of creating a critical array using the Type 3 method. [Figure 10] An example of creating a critical array using the Type 1 method, expressed as a three-dimensional function diagram. [Figure 11] FIG. 1 is a diagram showing a vector object according to an embodiment of the present invention. [Figure 12] FIG. 1 is a diagram showing a group of vector objects according to an embodiment of the present invention. [Figure 13] 1 is a diagram showing a unit according to an embodiment of the present invention; [Figure 14] FIG. 1 shows rendering in an embodiment of the present invention. [Figure 15] FIG. 1 is a diagram showing a rendering image according to an embodiment of the present invention; [Figure 16] FIG. 1 is a flowchart showing a method for creating a unit according to an embodiment of the present invention. [Figure 17]FIG. 10 is a diagram showing an example in which a gradation attribute is added to a vector object according to an embodiment of the present invention. [Figure 18] FIG. 10 is a diagram showing an example in which a rasterization attribute is added to a vector object according to an embodiment of the present invention. [Figure 19] FIG. 10 is a diagram showing an example in which a blend attribute is set between vector objects according to an embodiment of the present invention. [Figure 20] FIG. 1 is a flowchart showing a method for creating a halftone image according to an embodiment of the present invention. [Figure 21] FIG. 1 is a diagram showing a halftone dot image according to an embodiment of the present invention; [Figure 22] FIG. 1 is a flowchart showing an optimization process according to an embodiment of the present invention. [Figure 23] FIG. 10 shows an example of optimization processing performed in the embodiment of the present invention and its histogram. [Figure 24] FIG. 1 is a flowchart showing halftone screening according to an embodiment of the present invention. [Figure 25] FIG. 10 is a diagram showing an example in which a part of a rendering image is set as a main region and expanded to a sub-region while being rotated according to an embodiment of the present invention. [Figure 26] FIG. 10 is a diagram showing an example in which a part of a rendering image is set as a main region and expanded to a sub-region while being rotated and having its tone inverted, according to an embodiment of the present invention. [Figure 27] FIG. 1 is a diagram showing a halftone dot image according to an embodiment of the present invention; [Figure 28] FIG. 1 is a flowchart showing the process of development, tone reversal, and reconstruction according to an embodiment of the present invention. [Figure 29] FIG. 10 is a diagram showing an example of pixel groups and average values ​​according to an embodiment of the present invention. [Figure 30] FIG. 10 is a diagram showing an example of an image reconstructed using an average value according to an embodiment of the present invention. [Figure 31] FIG. 10 is a diagram showing an example of avoiding variations in screen ruling in an embodiment of the present invention. [Figure 32] FIG. 1 is a diagram showing a halftone dot image according to an embodiment of the present invention; [Figure 33]FIG. 1 is a flowchart showing the development, tone reversal, reconstruction, and extension processes according to an embodiment of the present invention. [Figure 34] FIG. 1 is a diagram showing a division of a rendering image according to an embodiment of the present invention. [Figure 35] FIG. 10 is a diagram showing a rendering image that has undergone extension processing according to an embodiment of the present invention. [Figure 36] FIG. 1 is a diagram showing a halftone dot image according to an embodiment of the present invention; [Figure 37] FIG. 10 is a diagram showing a rendering image that has undergone extension processing according to an embodiment of the present invention. [Figure 38] FIG. 1 is a diagram showing a halftone dot image according to an embodiment of the present invention; [Figure 39] FIG. 1 is a diagram showing an example of a halftone image according to each embodiment of the present invention; [Figure 40] FIG. 10 is a diagram showing the difference between halftone dot images and continuous tone halftone dots for each embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] The form for implementing the present invention will be described with reference to the drawings, but the present invention is not limited to the form for implementing the present invention described below, and various other embodiments are included as long as they are within the scope of the technical idea described in the claims.

[0038] (Embodiment 1) (unit) In the first embodiment of the present invention, for example, as shown in Fig. 11, a critical array [3] is created using a rectangular unit [9] having a vector object [8] described later. Note that in the first embodiment, the shape of the unit [9] is described as a square (M = N, M and N are integers), but the unit [9] may also be a rectangle where M ≠ N, as long as it has a shape that can fill the plane without gaps.

[0039] (vector object) A vector object [8] is a shape such as a circle, ellipse, or polygon drawn using vector data (for example, a Bezier curve or a spline curve), as shown in Figure 11. A group of multiple vector objects [8] is called a vector object group

[10] , as shown in Figure 12. When viewed from above, this vector object group

[10] becomes a unit [9] as shown in Figure 13.

[0040] (rendering) Rendering is the process of pixelating a unit [9] containing a group of vector objects

[10] to create a rendered image

[11] , as shown in Figure 14. This rendered image

[11] is composed of a collection of pixels [6], as shown in Figure 15. The number of elements [5] in the critical array [3] required for halftone screening and the threshold value [4] are determined from these pixels [6]. Each pixel [6] has a pixel value

[12] , which is an 8-bit value (0 to 255) written in decimal or hexadecimal.

[0041] (How to create a unit) Figure 16 shows a flowchart of the method for creating unit [9].

[0042] Create a unit [9] as S1-01. The size of the unit [9] is a rectangle of M x N (M and N are integers), and for example, M and N use the unit system of "mm".

[0043] As S1-02, vector object [8] is placed in unit [9]. If unit [9] does not contain vector object [8], halftone dots [7] that represent gradation cannot be created, and therefore gradation image [1] cannot be converted into halftone dot image [2]. Therefore, it is necessary to place vector object [8] so that at least a portion of it is included in unit [9].

[0044] In step S1-03, as shown in FIG. 17, a gradation attribute

[13] is set for the vector object [8]. The gradation attribute

[13] is used to impart continuous gradation (gradation) to the vector object [8]. This gradation attribute

[13] must have a gradation difference of 1 to 255 in 8-bit values. If there is no gradation difference, gradation cannot be imparted, making it difficult to express the desired halftone dot image. When converting the halftone image [1] to the halftone dot image [2], the size of each halftone dot [7] is determined based on the gradation difference.

[0045] S1-04 performs the same process as S1-02.

[0046] In step S1-05, as shown in FIG. 18, a rasterization attribute

[14] is set for the vector object [8]. The rasterization attribute

[14] is used to pixelate the vector object [8] and add gradation. This rasterization attribute

[14] must have a gradation difference of 1 to 255 in 8-bit values. If there is no gradation difference, the rasterization attribute cannot be added, making it difficult to express the desired halftone dot image. When converting the gradation image [1] to the halftone dot image [2], the size of each gradation of the halftone dot [7] is determined based on the gradation difference.

[0047] S1-06 performs the same process as S1-02.

[0048] In S1-07, a vector object [8] is placed that is a different size from the vector object [8] placed in S1-06. Note that the shape of the vector object [8] may be similar. Furthermore, the vector object [8] placed in S1-06 and the vector object [8] placed in S1-07 must have densities that differ by at least 1 in 8-bit values. If there is no difference in tone, the blend attribute described below cannot be applied, making it difficult to express the desired halftone dot image. When converting the halftone image [1] to the halftone dot image [2], the size of each tone of the halftone dot [7] is determined based on the difference in tone.

[0049] In step S1-08, another vector object [8] may be added. If an additional object is added, the process returns to the step immediately before step S1-07.

[0050] In step S1-09, as shown in FIG. 19, a blend attribute (15) is assigned to multiple vector objects (8(a), 8(b)) arranged in a matrix. The blend attribute (15) interpolates multiple vector objects (8(c)) that are evenly distributed with varying shapes and densities between vector object A (8(a)) and vector object B (8(b)), for example. The blend attribute (15) requires a gradation difference of 1 to 255 in 8-bit values. If the gradation difference is not present, the blend attribute cannot be assigned, making it difficult to achieve the desired halftone image. When converting halftone image (1) to halftone image (2), the size of each halftone dot (7) is determined based on the gradation difference.

[0051] In step S1-10, another vector object [8] may be added to the unit created in step S1-03, S1-05, or S1-09. If an additional vector object is added, the process returns to immediately after step S1-01.

[0052] In order to create a unit, it is necessary to set at least one of the following attributes for the vector object [8]: gradation attribute setting (S1-03), rasterization attribute setting (S1-05), and blend attribute setting (S1-09).

[0053] As S1-11, a unit [9] containing a vector object group

[10] consisting of a vector object [8] is stored.

[0054] (How to create a halftone image) FIG. 20 shows a flowchart of the method for creating halftone image [2].

[0055] As S2-01, the gradation image [1] is read. If the pixel group of the gradation image [1] is not an 8-bit value (0 to 255), it is converted to an 8-bit value (0 to 255). Here, a known method for converting to an 8-bit value may be used, such as continuing to divide by 256 until an 8-bit value is obtained.

[0056] In step S2-02, the gradation image [1] loaded in step S2-01 is resampled according to the output resolution. Note that resampling is a technique widely used in image processing, and is a calculation process (for example, the bilinear method or bicubic method) that increases or decreases the number of pixels in the gradation image [1].

[0057] As S2-03, the unit [9] created using the method for creating the unit [9] shown in S1-01 to S1-11 above is read.

[0058] In step S2-04, the unit [9] loaded in step S2-03 is subjected to the rendering process described above to create a rendered image

[11] . The number of pixels in this rendered image

[11] is determined by the output resolution and screen ruling. The number of vertical pixels (m) and horizontal pixels (n) of the rendered image

[11] (see Figure 15) are calculated using the following equation (2).

[0059]

number

[0060] In S2-05, the rendering image

[11] created in S2-04 is subjected to optimization processing, which will be described later.

[0061] In S2-06, the critical array [3] created by performing optimization processing on the rendering image

[11] in S2-05 is used to perform halftone screening processing, which will be described later, on the gradation image [1] that has been resampled in S2-02.

[0062] In step S2-07, the halftone dot image [2] created by executing the halftone screening process in step S2-06 is saved. The halftone dot image [2] created in this way has a form such as that shown in FIG.

[0063] (optimization) Figure 22 shows a flowchart of the process of optimizing the rendering image

[11] and converting it to the critical array [3]. Optimization means converting the pixel values ​​of the rendering image

[11] to values ​​that are optimal for the threshold value [4] of the critical array [3].

[0064] In S3-01, the total number of pixels [6] is calculated from the number of vertical and horizontal pixels of the rendering image

[11] .

[0065] In step S3-02, the number of pixels for each pixel value

[12] of the rendering image

[11] is tallied. The tallied result will be, for example, in the form shown in Table 1 below.

[0066] [Table 1]

[0067] S3-03 defines a cumulative array a(i) (0≦i≦255). This cumulative array a(i) is a one-dimensional array in computer programming.

[0068] As S3-04, substitute "0" into the cumulative array a(0). By setting the value of the cumulative array a(0) to 0, it is possible to prevent the occurrence of always black portions when converting the grayscale image [1] into a halftone image [2].

[0069] As S3-05, execute the processing of Loop 1. Loop 1 is an iterative process that starts from i = 1, adds 1 to i until i = 255. After the end of Loop 1, proceed to S3-07.

[0070] As S3-06, execute [Equation 3] shown below to store the cumulative number of pixels in each index (i) of the cumulative array a(i). After the end of Loop 1, the cumulative array a(i) will be in a form such as Table 2 shown below.

[0071]

Equation

[0072]

Table 2

[0073] As S3-07, define the threshold array b(n,m). This threshold array b(n,m) is a two-dimensional array in computer programming and is composed of elements of n×m (n and m are integers). Note that n and m are the same numbers as n and m of the rendering image

[11] created in S2-04.

[0074] As S3-08, define the variable y to execute the processing of Loop 2. Loop 2 is an iterative process that starts from y = 0 and adds 1 to y while y < m.

[0075] As S3-09, define the variable x to execute the processing of Loop 3. Loop 3 is an iterative process that starts from x = 0 and adds 1 to x while x < n. After the end of Loop 3, return to Loop 2.

[0076] As S3-10, execute [Equation 4] shown below and store the 8-bit value (from 0 to 255) calculated by [Equation 4] in the critical array b(x, y). Note that the decimal part values generated in this arithmetic processing are rounded to integer values.

[0077]

Equation

[0078] Through the above optimization processing, the rendering image

[11] with a histogram (image density distribution diagram) as shown in Fig. 23(a) is converted into a critical array [3] with a histogram as shown in Fig. 23(b).

[0079] (Halftone Screening) Fig. 24 shows a flowchart diagram of halftone screening.

[0080] As S4-01, as shown in Fig. 24, substitute the number of horizontal pixels of the tone image [1] for which resampling processing was executed in S2-02 into the variable h. Also, as shown in Fig. 24, substitute the number of vertical pixels of the tone image [1] for which resampling processing was executed in S2-02 into the variable v.

[0081] As S4-02, create a dot image (h, v). This dot image [2] is a two-dimensional array in computer programming.

[0082] As S4-03, define the variable y to execute the processing of Loop 1. Loop 1 starts from y = 0 and is an iterative process of adding 1 to y while y < v.

[0083] As S4-04, define the variable x to execute the processing of Loop 2. Loop 2 starts from x = 0 and is an iterative process of adding 1 to x while x < h. After the end of Loop 2, return to Loop 1.

[0084] As S4-05, the remainder obtained by dividing x by the number (n) of horizontal elements [5] in the critical array [3] is assigned to the variable dx as shown in Figure 24. As shown in Figure 24, the remainder obtained by dividing y by the number (m) of vertical elements [5] in the critical array [3] is assigned to the variable dy.

[0085] In S4-06, a process is performed in which the pixel value

[12] of the gradation image [1] (x, y) resampled in S2-02 is compared with the value (255 - threshold [4]) obtained by inverting the threshold [4] of the critical array b (dx, dy) described above. This process is a conditional branch in computer programming, which returns "true" if the former is smaller than the latter, and "false" otherwise.

[0086] In S4-07, "1" is assigned to the halftone image (x, y).

[0087] In S4-08, "0" is assigned to the halftone image (x, y).

[0088] By the above halftone screening process, a halftone dot image [2] as shown in FIG. 21 is generated.

[0089] (Embodiment 2) Next, we will explain embodiment 2. In embodiment 2, the rendering image

[11] is expanded, or the expansion and tone inversion process is added between S2-04 and S2-05 in embodiment 1, thereby adding complexity to the halftone dot shape.

[0090] In the second embodiment, an explanation will be given using a simplified diagram of the rendering image

[11] (hereinafter referred to as "simplified diagram [11']") as shown in Figure 25. The simplified diagram [11'] is divided into two, four, or eight parts, and one of the parts is designated as the main region

[16] , and the parts other than the main region

[16] are designated as sub-regions

[17] .

[0091] Figures 25(a), 25(b), 25(c) and 25(d) are examples of the expansion of the main region

[16] into the sub-region

[17] when the simplified diagram [11'] is divided into two. Figures 25(a) and 25(c) show the state in which the main region

[16] is expanded into the sub-region

[17] point-symmetrically, while Figures 25(b) and 25(d) show the state in which the main region

[16] is expanded into the sub-region

[17] line-symmetrically.

[0092] Furthermore, Figures 25(e), 25(f), 25(g), 25(h), 25(i) and 25(j) are examples of the main region

[16] being expanded into sub-regions

[17] when the simplified diagram [11'] is divided into four. Figures 25(e) and 25(h) show the state in which the main region

[16] is rotated 90 degrees clockwise into the sub-region

[17] and expanded clockwise, or the state in which the main region

[16] is rotated 90 degrees counterclockwise into the sub-region

[17] and expanded clockwise, or the state in which the main region

[16] is rotated 90 degrees counterclockwise into the sub-region

[17] and expanded clockwise, or the state in which the main region

[16] is rotated 90 degrees clockwise into the sub-region

[17] and expanded counterclockwise, and Figures 25(g) and Figure 25(j) shows the state in which the primary region

[16] is linearly expanded into the secondary region

[17] in either a clockwise or counterclockwise direction, and Figure 25(i) shows the state in which the primary region

[16] is rotated 90 degrees clockwise, expanded clockwise, then linearly expanded clockwise, and then rotated 90 degrees clockwise again and expanded clockwise, or the state in which the primary region is expanded counterclockwise in a line symmetry, then rotated 90 degrees counterclockwise, expanded counterclockwise, and then linearly expanded counterclockwise again.

[0093] Furthermore, Figures 25(k) and 25(l) are examples of expanding the main region

[16] into sub-regions

[17] when the simplified diagram [11'] is divided into eight parts. Figure 25(k) shows the state in which the main region

[16] is expanded into the sub-regions

[17] alternately in a clockwise direction with line symmetry, point symmetry, and line symmetry, or in a counterclockwise direction with point symmetry, line symmetry, and point symmetry, and Figure 25(l) shows the state in which the main region

[16] is expanded into the sub-regions

[17] alternately in a clockwise or counterclockwise direction with line symmetry.

[0094] The expansion of the main region

[16] into the sub-regions

[17] may all be performed using the same regularity, or may be performed using different regularities.

[0095] Next, we will explain the case where the process of inverting the gradation is added during development. Simplified diagram 2 [11''] shown in Figure 26 is the state in which the gradation of simplified diagram [11'] is inverted without being divided.

[0096] Furthermore, Figures 26(a), 26(b), 26(c), and 26(d) are developments similar to those of Figures 25(a), 25(b), 25(c), and 25(d) described above, with the addition of gradation inversion processing.

[0097] Similarly, Figures 26(e), 26(f), 26(g), 26(h), 26(i) and 26(j) are developments similar to those of Figures 25(e), 25(f), 25(g), 25(h), 25(i) and 25(j) described above, with the addition of gradation inversion processing.

[0098] Similarly, FIGS. 26(k) and 26(l) are the same developments as those in FIGS. 25(k) and 25(l) described above, to which gradation inversion processing has been added.

[0099] 27 is an example of a halftone dot image [2] created using embodiment 2. By creating a halftone dot image [2] using embodiment 2, it is possible to create a halftone dot image [2] with different dot shape characteristics compared to embodiment 1, even if the original rendering image

[11] is the same.

[0100] (Embodiment 3) Next, we will explain embodiment 3. In embodiment 3, as shown in Fig. 28, EX-3 is added between S2-04 and S2-05 in embodiment 1 as a process for reconstructing the rendering image

[11] . Note that the expansion and tone reversal process (EX-2) in embodiment 2 may be added before EX-3.

[0101] As shown in Figure 29, the rendered image

[11] is divided into groups

[18] of four adjacent 2x2 pixels, and the average value

[19] of the pixel values ​​contained in each group

[18] is calculated. Note that each group

[18] overlaps with its adjacent group

[18] by one pixel. This average value

[19] is used as one pixel to reconstruct the rendered image

[11] .

[0102] As shown in Figure 29, the average values ​​A [19(a)], average value B [19(b)], average value C [19(c)], average value D [19(d)], and average value E [19(e)] are lined up horizontally, but during reconstruction, they are arranged at a 45-degree angle to the x and y axes while maintaining the order of the average value

[19] , as shown in Figure 30. The arrangement of the average value A [19(a)], average value B [19(b)], average value C [19(c)], average value x [19(x)], and average value y [19(y)] after reconstruction is in the same order as the arrangement in the rendering image

[11] before reconstruction.

[0103] This reconstruction causes a change in the screen ruling, but as shown in Fig. 31, this can be avoided by creating the rendering image

[11] in advance by multiplying the number of pixels in both the vertical and horizontal directions by √2. Fig. 32 is an example of a halftone dot image [2] created using the third embodiment. By creating the halftone dot image [2] using the third embodiment, it is possible to create a halftone dot image [2] in which the halftone dot shape is rotated by 45 degrees compared to the second embodiment, even though the original rendering image

[11] is the same.

[0104] (Fourth embodiment) Next, we will explain embodiment 4. In embodiment 4, as shown in Fig. 33, EX-4 is added as an extension process between S2-04 and S2-05 in embodiment 1. Note that the expansion and gradation inversion process (EX-2) in embodiment 2 or the reconstruction process (EX-3) in embodiment 3 may be added before EX-4.

[0105] As shown in FIG. 34, the rendering image

[11] is divided into area A [11(a)], area B [11(b)], area C [11(c)], and area D [11(d)].

[0106] As shown in Figure 35(a), to create a rendering image

[11] expanded to 2n (the number of horizontal pixels n of the rendering image

[11] is doubled) x m pixels (n and m are integers), the areas are arranged in the following order from left to right in the top row, as shown in Figure 35(b): Area B [11(b)], Area C [11(c)], Area D [11(d)], Area A [11(a)], and from left to right in the bottom row, Area D [11(d)], Area A [11(a)], Area B [11(b)], Area C [11(c)]. Figure 36 is an example of a halftone dot image [2] created using the rendering image

[11] of Figure 35(a).

[0107] Similarly, to create a rendering image

[11] expanded to n x 2m pixels (n and m are integers), as shown in Figure 37(a), the pixels are arranged in the following order from top to bottom in the left column: Area C [11(c)], Area B [11(b)], Area D [11(d)], Area A [11(a)], and from top to bottom in the right column: Area D [11(d)], Area A [11(a)], Area C [11(c)], Area B [11(b)]. Figure 38 is an example of a halftone dot image [2] created using the rendering image

[11] of Figure 37(a). By creating a halftone dot image [2] using embodiment 4, it is possible to create a halftone dot image [2] that approximates a hexagonal arrangement, with the phase of the halftone dot shapes shifted by half the length, compared to embodiment 2, even though the original rendering image

[11] is the same. [Example]

[0108] An example of halftone dot image [2] is shown in Figure 39. Figure 39(a) shows the halftone dot image [2] created using the method of embodiment 1, Figure 39(b) shows the halftone dot image [2] created using the method of embodiment 3, and Figures 39(c) and 39(d) show the differences between halftone dot image [2] created using the method of embodiment 4.

[0109] Furthermore, an example of a gradation image [2] with a change in image area ratio from 0% to 100% is shown in Fig. 40. Fig. 40(a) shows the difference between a halftone image [2] created using the method of embodiment 1, Fig. 40(b) shows the difference between a halftone image [2] created using the method of embodiment 3, and Fig. 40(c) and Fig. 40(d) show the difference between a halftone image [2] created using the method of embodiment 4.

[0110] Although several embodiments and examples of the present invention have been described, these embodiments are presented as examples and are not intended to limit the technical scope of the invention. Furthermore, the embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the technical scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0111] 1-tone image 2 Halftone images 3 Critical Array 4 Threshold 5 Elements 6 pixels 7 Halftone Dots 8 Vector Objects 8(a) Vector Object A 8(b) Vector Object B 8(c) Multiple Vector Objects 9 units 10 Vector Objects 11 Rendered image 11' Simplified diagram 11'' Simplified diagram 2 11(a) Area A 11(b) Area B 11(c) Area C 11(d) Area D 12 pixel values 13 Gradient Attributes 14 Rasterization Attributes 15 Blending Attributes 16 Main area 17 Sub-area 18 groups 19 Average 19(a) Average A 19(b) Average B 19(c) Average C 19(d) Average value D 19(e) Average value E 19(x) Average x 19(y) Mean value y

Claims

1. A method for creating a halftone image for expressing gradation in a printed matter, comprising: A step of creating a unit for arranging a vector object formed by a Bezier curve or a spline curve, which is vector data; placing the vector object in the unit; i) setting a gradient attribute on the vector object, or ii) setting a rasterization attribute on the vector object; or iii) placing any number of new vector objects and setting blend attributes for the any number of said vector objects; forming a set of vector objects in at least one of the steps and further, if necessary, storing the units created by repeating the step of adding the vector objects. reading the unit; A step of generating a rendering image of n×m pixels (n and m are integers) according to an output resolution and a screen ruling from the unit; converting the rendered image to a critical alignment for halftone screening; reading a grayscale image to be subjected to halftone screening; resampling the gradient image in accordance with the output resolution to create a resampled image; performing the halftone screening on the resampled image using the critical array to generate the halftone image; storing the halftone image; the gradation attribute of the i), the rasterization attribute of the ii), and the blend attribute of the iii) of the vector object group have a gradation difference of 1 or more and 255 or less in 8-bit values; The arbitrary number of vector objects in iii) are vector objects having different densities and sizes. A method for creating halftone images to express gradation in printed materials.

2. The rendering image is divided into two, four, or eight regions, one of which is designated as a main region, and the other regions are designated as sub-regions; The main region is divided into the sub-regions. iv) Point symmetry inversion, or v) Inversion of axisymmetrical symmetry, or vi) Rotate clockwise / counterclockwise; 2. The method for creating a halftone image for expressing gradation in a printed matter according to claim 1, further comprising developing and arranging the halftone image.

3. Inverting the rendered image; or 3. The method for creating a halftone image for expressing gradation in a printed matter according to claim 2, wherein the main region is developed and arranged relative to the sub-region while inverting gradation.

4. In the rendering image, a pixel group consisting of four adjacent 2×2 pixels is divided into groups; The group overlaps with adjacent groups by one pixel, Calculating an average value of the 8-bit values ​​of the pixels included in the group; The average value is set to one pixel, while maintaining the order of the average values ​​of the rendering image, the x- and y-axes are displaced in a 45-degree diagonal direction; 4. The method for creating a halftone image for expressing gradation in a printed matter according to claim 1, further comprising the step of reconstructing the rendering image.

5. The rendering image is divided into four quadrants while maintaining the rectangular ratio of the rendering image, and the upper left region is defined as region A, the upper right region is defined as region B, the lower left region is defined as region C, and the lower right region is defined as region D. vii) The region B, the region C, the region D, and the region A are arranged in this order from left to right in the upper row of the rendering image expanded to 2n×m pixels, and the region D, the region A, the region B, and the region C are arranged in this order from left to right in the lower row of the expanded rendering image, or viii) The region C, the region D, the region B, and the region A are arranged in this order from top to bottom on the left column of the rendered image expanded to n×2m pixels, and the region D, the region A, the region C, and the region B are arranged in this order from top to bottom on the right column of the expanded rendered image.

5. The method for creating a halftone image for expressing gradation in a printed matter according to claim 1, further comprising:

6. Software for creating halftone images for expressing gradation in printed matter, A step of creating a unit for arranging a vector object formed by a Bezier curve or a spline curve, which is vector data; placing the vector object in the unit; i) setting a gradient attribute on the vector object, or ii) setting a rasterization attribute on the vector object; or iii) placing any number of new vector objects and setting blend attributes for the any number of said vector objects; forming a set of vector objects in at least one of the steps and further, if necessary, storing the units created by repeating the step of adding the vector objects. reading the unit; A step of generating a rendering image of n×m pixels (n and m are integers) according to an output resolution and a screen ruling from the unit; converting the rendered image to a critical alignment for halftone screening; reading a grayscale image to be subjected to halftone screening; resampling the gradient image in accordance with the output resolution to create a resampled image; performing the halftone screening on the resampled image using the critical array to generate the halftone image; storing the halftone image; the gradation attribute of the i), the rasterization attribute of the ii), and the blend attribute of the iii) of the vector object group have a gradation difference of 1 or more and 255 or less in 8-bit values; The arbitrary number of vector objects in iii) are vector objects having different densities and sizes. Software for creating halftone images to express gradation in printed materials.

7. The rendering image is divided into two, four, or eight regions, one of which is designated as a main region, and the other regions are designated as sub-regions; The main region is divided into the sub-regions. iv) Point symmetry inversion, or v) Inversion of axisymmetrical symmetry, or vi) Rotate clockwise / counterclockwise; 7. Software for creating a halftone image for expressing gradation in a printed matter according to claim 6, wherein the halftone image is developed and arranged.

8. Inverting the rendered image; or 8. Software for creating a halftone image for expressing gradation in a printed matter according to claim 7, characterized in that the main region is expanded and arranged relative to the sub-region while inverting gradation.

9. In the rendering image, a pixel group consisting of four adjacent 2×2 pixels is divided into groups; The group overlaps with adjacent groups by one pixel, Calculating an average value of the 8-bit values ​​of the pixels included in the group; The average value is set to one pixel, while maintaining the order of the average values ​​of the rendering image, the x- and y-axes are displaced in a 45-degree diagonal direction; 9. The software for creating a halftone image for expressing gradation in a printed matter according to claim 6, wherein the rendering image is reconstructed.

10. The rendering image is divided into four quadrants while maintaining the rectangular ratio of the rendering image, and the upper left region is defined as region A, the upper right region is defined as region B, the lower left region is defined as region C, and the lower right region is defined as region D. vii) The region B, the region C, the region D, and the region A are arranged in this order from left to right in the upper row of the rendering image expanded to 2n×m pixels, and the region D, the region A, the region B, and the region C are arranged in this order from left to right in the lower row of the expanded rendering image, or viii) The region C, the region D, the region B, and the region A are arranged in this order from top to bottom on the left column of the rendered image expanded to n×2m pixels, and the region D, the region A, the region C, and the region B are arranged in this order from top to bottom on the right column of the expanded rendered image.

10. Software for creating a halftone image for expressing gradation in a printed matter according to claim 5, wherein the software is configured to:

Images