JPH11268229A - Method for forming halftone screen and its printed matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a forgery, a falsification by incorporating a meaning in a symbol mark itself, and forming a continuous gradation image made of a halftone screen generated by a graphic form for obtaining a screen shape having a design property by a function. SOLUTION: A heart type screen shape is disposed in x- and y-coordinates of -1 to 1 of a cell C. An areal division of the coordinates and a shape H are represented by numeric formulae. A density change is generated by enlarging or contracting the shape, or the density change is conducted to form a shape by enlarging a plurality of shapes having no similar relationship at each area. The screen cell C is divided into four areas. A spot function is formed by a shape change of an illite to a shadow by using four circular formulae. This function is registered with a screen generator. An image is screen calculated by the generator to obtain a film. Thus, the image represented by a screen is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the printing field where it is necessary to prevent banknotes, passports, securities, cards, valuable printed materials, etc. from being forged and tampered with, and to require a design. is there.

[0002]

2. Description of the Related Art Counterfeiting and falsification prevention are important factors in printed matter such as securities such as banknotes, stock certificates and bonds, various certificates and important documents. Therefore, the printed surface of the printed matter is constituted by a very fine image which has room for taking countermeasures against forgery and alteration. Techniques for preventing counterfeiting and alteration with a fine image include a method using a fine line and a method using a fine component.

[0003] As a typical technique of the method using a thin wire,
There are a tint block, a color pattern, a relief pattern, and the like, and the pattern is basically configured by a set of curved lines with a fixed line width. These patterns take into account the design properties of the printed matter, etc., can be counterfeited and prevent counterfeiting, making it difficult to produce the same pattern in a forged product by complicating the pattern, Use colors that are difficult to reproduce with plate making equipment or copying machines,
The role as a countermeasure for preventing forgery is enhanced by generating a moiré for a scanning input / output of a copying machine and a scanner by forming a complicated music image line. In addition, the patterns are widely used worldwide in the design of securities prints and the like, and at the same time, have been used for a long time as prints having a monetary value, such as banknotes, stock certificates, and bonds,
Even today, it is generally an important design as a design that gives a sense of luxury. Therefore, in printed matter such as banknotes, stock certificates, bonds, and other securities, various certificates, and important documents, graphics composed of thin lines are indispensable in design.

As a typical technique of a method using a fine component, there is a method in which a fine component is used as a minute character. The countermeasures against forgery and alteration of small characters make it difficult to create the same pattern in forgery by making the pattern minute and complicated, and use colors that are difficult to be extracted by a photoengraving device or reproduced by a copying machine. The role of counterfeit prevention. Furthermore, by forming a large number of small characters on the printing surface, forgery,
A copy-forgery-inhibited pattern that is effective in preventing falsification can be formed, and at the same time, a large amount of text information that is essential for a printed product can be provided. In addition, since it is a method by which ordinary people can easily identify whether the text and the shape of the small characters are genuine by observing with a magnifying glass or the like during the market distribution process, the small characters are designed for design of securities prints and the like. At the same time, it has been widely used in the world, and it has been used for a long time as a pattern of printed matter with monetary value such as banknotes, stocks, bonds, etc. In printed materials such as banknotes, stock certificates, bonds, and other securities, various certificates, and important documents, minute characters are indispensable in design.

As a typical technique of a method using other fine structural elements, a group of single tone reproducing elements on a printed matter such as a halftone dot and a line, that is, a single image area There is a series of techniques commonly referred to as copy-protection streaks that use printed halftone dots with a percentage. That is, the latent image applied to the printed matter appears by copying by the copying machine. In a printed material suitable for preventing forgery by such a copying machine, for example, according to Japanese Patent Application Laid-Open No. 57-20395, characters composed of fine structural elements, for example, 85 lines and 30% halftone dots are displayed on the base paper surface. A latent image is printed using silver ink, and then a blank portion other than the latent image is printed with halftone dots of coarser or denser (for example, 150 lines 30%) than the latent image. There is a printed matter with a latent image suitable for preventing forgery by copying, which applies a printed pattern such as a color pattern or a ground pattern, and according to Japanese Patent Application Laid-Open No. 60-79991, a latent image is printed with halftone dots on the surface of paper, The background of the latent image at the same density as the line is printed at the same time, and the decorative pattern is overprinted on the upper surface of the latent image including the background with a thin transparent ink that cannot be reproduced by copying. Finish and copy the pattern There is a printed matter suitable for copy prevention, in which the background is reproduced and the latent image is not reproduced, and the density difference between the background and the latent image is obvious and it can be seen at a glance that it is a copy. According to Japanese Patent Application Laid-Open No. 60-87380, a latent image plate having a latent image consisting of halftone dots of 150 lines and 10% and having a background consisting of about 50% to 60 lines of 10% lines on a white ground surrounding the latent image is disclosed. Using the overprinting plate with a corrugated pattern consisting of parallel lines that form a moiré pattern when subjected to dark printing on the surface of the paper and interfere with the background lines, using a copier on the paper surface By applying a light-colored overprint that is not performed, a moiré pattern that distracts the naked eye is formed on the surface of the printed matter, making it difficult to identify the presence of the latent image. Only background plays Since the,
There is disclosed a camouflage method for preventing latent images in printed matter, in which a latent image is recognized separately from the background.

However, although the above-described method using the geometrical figure and the fine structural element is a print object for preventing forgery and alteration, the above-mentioned geometrical figure and the fine structural element have continuous gradation (image area ratio of 0). To 100% of the full range continuous tone). Therefore, in a security using the forgery prevention measure having the advanced image configuration as described above, when a continuous tone image is used, the forgery prevention measure must be used for an area other than that part.

[0007] On the other hand, for securities that use or use continuous tone frequently, such as stamps and stamps, or products whose printing area is smaller than that of banknotes or stock certificates, the aforementioned geometrical figures and fine constituent elements are used. Therefore, there is not enough room to provide the countermeasures, and it is not possible to provide sufficient counterfeit prevention measures.

In general, in order to apply a gradation image (full-range continuous gradation with an image area ratio of 0 to 100%) to a printed material using a fine component, a group of gradation reproduction elements called a screen is required. Halftone dots (continuous circle, ellipse,
Rhombus, square, line, cross, grain), line (scanning line)
The continuous tone is produced by the size of the image area such as. Naturally, when printing securities using ordinary printing means,
Since these objects can be easily created by the existing plate making technology or image processing technology, they cannot be implemented as countermeasures for forgery.

One of the countermeasures against forgery and alteration of stamps, stamps, etc., is a conventional gravure screen, which is a rare conventional counterpart in the printing industry, which is called a conventional gravure screen. This is to use a halftone dot shape formed only in gravure plate making. The reason is that most of the printed materials such as newspapers and magazines that are seen by ordinary people today are expressed in gradation using the size of halftone dots of circles, ellipses, and squares, whereas conventional gravure screens are This is because, although the diameters of the halftone dots are all equal, there is a unique halftone dot in which the density of each halftone dot changes. The difference between a general screen shape and a conventional gravure screen can be determined by enlarging and viewing with an auxiliary tool such as a magnifying glass. But,
This difference can be determined only by those who have knowledge of the printing technology, and not everyone can judge the authenticity.

The conventional gravure screen is merely a means for expressing a continuous tone of an image on a printed matter, and the image used in the conventional gravure screen is a set of aligned square halftone dots. That is, since there is a drawback that the forgery prevention function of the image pattern in the ground pattern, the color pattern, the relief pattern, etc. of the geometrical figures described above, and the fine characters of the fine constituent elements, etc. cannot be taken into account, in the case of highly public securities, There has been a demand for a method that can easily determine the authenticity by visual observation or observation with a simple auxiliary tool such as a magnifying glass.

Therefore, there is a need for a forgery prevention tone reproduction element and a group of tone reproduction elements which are geometrical figures taking into account the designability and which can express a continuous tone image composed of fine constituent elements. In other words, the shape of a unit tone reproduction element (hereinafter, screen shape) is a geometric figure having a counterfeiting prevention measure and a design property, while being a group of tone reproduction elements (hereinafter referred to as a screen) such as a halftone dot and a line. A forgery prevention screen is required.

As a technology for realizing a screen for preventing forgery, there is Special Rasters, a digital image processing technology commercialized by Barco Graphics. Special Rasters uses digital image processing technology to transform an arbitrary bitmap continuous tone image into an arbitrary shape figure formed by a draw curve (spline curve) based on the gray level.
The variable amount related to the deformation of the figure is controlled in accordance with the gray level of the original bitmap continuous tone image, and the draw curve of the figure and the line width of the straight line at the position opposite to the original bitmap continuous tone image and the shape of the figure are controlled. There is a method in which the size is changed and the continuity of the density of the original bitmap continuous tone image is given as an image element (image size, graphic size) of the graphic to the graphic. However, in order to accurately express full-scale continuous gradation, calculate the image area ratio of a figure in a unit area, and then, for example, if the gradation is 100 gradations, the image area ratio in a unit area for each gradation It is necessary to create a total of 100 figures having the following and assign the figure to each gradation. Further, in a product in which tone reproducibility is regarded as important, gradation adjustment in the plate making process is indispensable because the current printing technology includes many factors of tone variation. However, in this method, an image as completed digital data is already simulated by utilizing the visual illusion of a human due to the difference in the area ratio between a colored portion (image portion) and a non-colored portion (non-image portion). It reproduces the gradation in the original, and the information as the original continuous tone image is
It is held as gradation. For this reason, it is impossible to adjust the gradation of the completed image, and the necessity of the adjustment means that an inefficient process must be reversed.

[0013]

A halftone characterized in that a screen shape having a meaning or a design itself such as a trademark, a family crest, a symbol mark, and a character is generated by a graphic obtained by a function. It is a screen, which is applied as a continuous tone image consisting of a halftone screen that is not reproduced by a copying machine, etc., to banknotes, securities, etc., to prevent forgery and tampering, and also in the printing field where designability is required. Can be used. By comparing such a halftone screen with a machine reading means or the like, it is possible to automatically, quickly and accurately judge the authenticity.

[0014]

A halftone characterized in that a screen shape having a meaning or a design itself, such as a trademark, a family crest, a symbol mark, or a character, is generated by a graphic obtained by a function. The screen creation method, wherein the screen cells of the screen shape are divided into regions using xy coordinates, and the screen shape is a screen shape generated by a figure obtained by a function for each region; The halftone screen creation method described above, wherein the screen shape is a screen shape generated by a graphic obtained by a function including a mathematical expression, the screen cells are divided into regions with xy coordinates, and for each divided region, Before being characterized in that it is a screen shape generated by a figure obtained by a function consisting of a mathematical expression including coordinate transformation The halftone screen creation method described above, wherein the screen cell is divided into regions with xy coordinates, and each of the divided regions has a screen shape generated by a figure that is a point object or a line object. A halftone screen creation method, wherein a state in which a plurality of adjacent unit screen shapes are connected is a geometric pattern,
It becomes an intermediate product as a plate making screen made of film, using this plate making screen, a halftone screen characterized by obtaining a screen configuration according to the amount of transmitted light by an optical method, using a personal computer and image processing software, The halftone screen making method described above, characterized in that a screen shape is made, the copying machine cannot be used, thereby preventing forgery. An original film and a printed material thereof as described above, which can be made.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a grayscale image as digital data is output to a printing medium in an efficient manner, that is, when plate making is performed, generally, information necessary for plate making is included in an image and its arrangement information. , A page description language that is a kind of general-purpose computer language, for example, a postscript language can be used. This PostScript language and screen generation using the PostScript language are techniques belonging to Adobe Systems. The PostScript language and the screen generation by the PostScript language are widely disclosed technologies, and the detailed contents thereof can be easily obtained from a commercially available book, for example, a PostScript reference manual (ASCII).

In the screen generation method using the postscript language, a screen is generated as a repetitive pattern in which elements constituting a square screen called cells or screen cells are one unit. The screen is determined by defining two items (or three items) of the size of the cell and the screen shape to be generated in the cell (and the cell arrangement depending on the definition method).

In generating a screen using the PostScript language, a screen designer can define the screen shape in one of the following two ways.
That is, a method of defining a screen shape using a mathematical expression described in a postscript language called a spot function, and a method of defining a character string called a threshold critical array.

Of the above two methods, in the method of defining the screen shape using the spot function, the cell has its own, that is, the center of the square is the origin and the corners x and y are plus or minus one. Consider a coordinate system (FIG. 1). In this coordinate system, the center of each pixel of the cell is the x and y coordinates. In the output device, a cell (C, a square surrounded by a thick line in the drawing) is formed by pixels (Cp, all squares surrounded by a thin line in the drawing) of the output device.

A pixel is a minimum unit of output in an output device, that is, a pixel, and is also called a dot in the printing related field. For devices that output to media such as paper and film,
Typically, pixels are turned on and off, for example, inked (on) and not turned on (off), or unexposed (on) when a high contrast (ie, reproduces two colors, black and white) film is exposed (on). ).

The cells are formed by a plurality of pixels determined by a size of a pixel that can be generated by an output device, that is, an output resolution in an operation process for output.

In generating a screen, a spot function expresses the relationship between the position of a pixel, that is, the xy coordinate of the pixel, and the order z in which the pixels in the cell are turned on using a mathematical expression. If this spot function is represented using a general formula z = f (x, y), it is said that z, which is the order in which the pixels are turned on, must be greater than or equal to -1 and less than or equal to 1.

The larger the value of z, which is the value returned by the spot function, the higher the priority of the pixel on. That is, the number of pixels corresponding to the density of the image assigned to a certain cell is turned on in the descending order of z. For example, when 50% density is assigned to an arbitrary cell formed of 256 pixels, 127 pixels are turned on in order from the pixel having the largest z value.

The screen shape is determined by the equation used for the spot function. For example, z = 1-
If (x ^ 2 + y ^ 2) is used, a circular screen is formed.

In this technique, the information of the gradation and the information of the screen shape are independent from each other, and the density of the pixels is converted into the image area ratio of the screen, that is, the rasterization is performed on the printing medium. This is the output stage.

The anti-counterfeiting screen shape according to the present invention has a screen anti-counterfeiting effect, and is a shape which is only required to improve the reproducibility of gradation, which is required for conventional screens. Is different in purpose. The shape having a forgery prevention effect will be described below.

In the first embodiment, as a specific example related to the above, the shape itself is a reproducible form of a shape that has its own meaning, such as a trademark, a family crest, a symbol mark, or a character. As a second specific example, a traditional geometric design, for example, FIG. 2A to FIG. 2A is a design called a cloisonne or cloisonne bridge, and FIG. 2B is a weight connection or the like. Both are traditional Japanese designs, and can be found in kimonos, handicrafts, etc. These are just examples of useful designs.
The present invention is not limited to these examples. ｝ Or the reproduction of a geometric design similar to it, ｛For example, Fig. 3 (a) shows a pattern seen in a building in West Asia, etc. Fig. 3b shows a pattern seen in Ainu clothing, handicrafts, etc. Each was referenced. These are examples of designed designs, and the present invention is not limited to these examples. ｝ It must be a reproduction of the description, regardless of whether it is abstract or concrete.

Therefore, a general screen shape does not correspond to a screen shape usable as a forgery prevention screen. In other words, screen shapes that are generally focused only on gradation reproduction, such as circles, ellipses, diamonds, squares, lines, crosses, grain lines (including FM screens), and lines, can be used as forgery prevention screens. Can not.

Further, it is possible to reproduce continuous gradation (full-range continuous gradation with an image area ratio of 0 to 100%), which is a prerequisite of the screen. It is indispensable that the size and the image line thickness be distinguishable and printable.

As an embodiment of the present invention, a method for forming a forgery prevention screen could be implemented by a digital method. The following example describes a forgery prevention screen generated by a digital method.

The digital method of screen generation depends on the page description language used or the screen generation style used by the language. Further, even in the case of the same page description language and screen generation format, there are cases where a plurality of designation formats that can be used for the screen definition are prepared.

In the embodiment of the present invention, the parameters given by the postscript sethalftone operator (command) are a screen angle, a screen ruling, and a spot function (a function that defines a screen shape, sometimes called a dot function). ) Was used.

The shape of the screen introduced in the present embodiment is important, and the language, generation style, function, and any other screen definition method relating to the generation of the screen shape are not limited in the present invention.

Based on the above description, a forgery prevention screen obtained by a screen generation method using a spot function in the PostScript language will be described below with reference to the drawings.

FIG. 4 shows arbitrary patterns used in the present invention, but these are merely examples, and the present invention is not limited to these examples.

FIG. 5 is a flowchart showing a screen generation method using a spot function according to the present invention. FIG.
The flowchart of FIG. 5 will be described by taking the heart-shaped screen shape (H) shown as an example. First, the adopted shape (H) was arranged at the xy coordinates of -1 to 1 of the cell (C). FIG. 7 shows the arranged shape (H).

Next, the shape is calculated by dividing the coordinates into regions and using mathematical expressions.
(H) was reproduced. FIG. 8 is a schematic diagram showing an example of a shape change of a screen reproducing the shape (H) {(FIG. 8 (a) and FIG.
(b)}, in the present invention, the shape to be reproduced is the shape (H) as shown in FIG. 8 (a) in the process of the density change from the highlight of the screen to the shadow, that is, the change of the image area ratio. The density is changed by enlarging or reducing the shape, or as shown in FIG. 8B, a plurality of shapes not similar to the shape (H) are enlarged for each region to form (H). Whether to cause the concentration change is not particularly limited. In the present embodiment, description will be made hereinafter with reference to the screen shape of FIG. 8 (a) and 8 (b), enlarged views shown in circles are provided.

In this embodiment, as shown in FIG. 9, the screen cell (C) is arranged at coordinates in order to define the screen of FIG. 8B, and the screen cell (C) is divided into four areas, ie, C areas.
a, Cb, Cc, and Cd were used to create a spot function in which the change in shape from highlight to shadow was as shown in FIG. 8B using the equation of four circles. In this embodiment, the following equations are used, but the equations used for the spot function are not particularly limited as long as they satisfy the definition of screen generation.

First, a formula of a circle centered at (x, y) = (0.5, 0.5) is given in the Ca region by the following equation (1).

(Equation 1) Was used. Next, in the area of Cb, the equation of a circle centered on (x, y) = (− 0.5, 0.5) is given by Equation 2

(Equation 2) And the expression of a circle centered at (x, y) = (− 0.5, 0.5) in the area of Cc

(Equation 3) Was used. In the area of Cd, the equation of a circle centered on (x, y) = (0.5, 0.5) is given by Equation 4.

(Equation 4) The curly braces (for example, {(x-0.5) ^ 2 + (y-0.5) ^ 2}) in the above equation represent a circle equation, and the outer coefficient (4 or 1 / 2.25) represents the spot function. This is a coefficient required to satisfy the definition that "z must be -1 or more and 1 or less". The reason why the expression is z = 1-{...} is to make the slope of the curve z into a mountain shape so that the generated screen is generated from the center.

Equations (1) to (4) prepared in the preceding section are described using a postscript condition classification operator, an arithmetic operator and the like. An operator is a command in PostScript. Conditioning operator is, for example, x>
Arithmetic operators were used to describe addition, subtraction, multiplication and division, squares, etc.

Thus, a spot function F, which is a screen definition for generating the shape (H), was obtained. The function F for generating one shape is not always one. The spot function F was registered in a screen generator, that is, a raster image processor, which is a computer-centered device that converts the gradation of an image, which is a digital signal, into a defined image area ratio of a screen.

FIG. 10 is a digital image (I) to which the screen S defined by the function F is to be adapted. The image (I) is merely an example, and the present invention is not limited to this example. The image (I) is a black-and-white image, but the printing color is not limited to one black color. Similarly, the colors that make up the image are not limited to single colors, but multiplications of multiple colors, for example, multiplication of cyan, magenta, yellow, and black called process colors, or process colors called special colors such as red, blue, and metal colors The present invention is also possible with a combination of the colors. Further, when an image is multiplied by a plurality of colors, that is, when an image is reproduced by using a plurality of printing plates, the color to which the screen obtained in the present invention is applied, that is, the printing plate is not limited to a single color or a plurality. In this embodiment, the screen S is applied to the entire surface of the image (I).
The portion where the screen S obtained by the present invention is applied may be a part of an image, and a plurality of different screens S for each portion may be simultaneously applied to one color.

Using the screen generator, an image (I)
Was subjected to screen arithmetic processing, and the film was output by a film exposure device. Thus, a film output I ′ of the image (I) reproduced on the screen S was obtained. In this embodiment, a printing plate making film is used as an output medium of an image to which a screen is to be adapted. However, the output medium is different depending on a printing method to be used or a system configuration of a plate making process, and is not particularly limited in the present invention.

Using the above-mentioned film output product I ', printing was performed by a general offset plate making and printing method to obtain a printed product P. An enlarged photograph of the printed matter P is shown in the printed matter (P ′) of FIG. The printing system is not limited to the offset system as long as the screen shape can be clearly reproduced. Also, the printing substrate (paper or the like) is not limited as long as it can clearly reproduce the screen shape.

Next, in a second embodiment, a screen-shaped cell generated in the first embodiment is divided into a plurality of regions, and a complex screen shape is created using different mathematical expressions. As a result, a complicated screen shape could be obtained using a mathematical expression having a different form from that of the first embodiment.

In the second embodiment, the spot function is described using a mathematical expression including a coordinate transformation in the expression. The conversion of coordinates, that is, when expressed by a general mathematical formula,

(Equation 5) It is. Figure 14 shows a wavy line screen using trigonometric functions
(w), and to define the screen (w), first the equation g
(x, y) and h (x, y) respectively

(Equation 6) And number 7

(Equation 7) Was used to determine the hg coordinate, which is a new coordinate space, from the xy coordinates of the pixels contained in the cell (that is, Equations 6 and 7 were described by PostScript). Next, the number 8 representing a straight line (line) on the hg coordinate

(Equation 8) (Ie, Equation 8 is described by PostScript) to obtain a spot function that defines the screen (w).

In this embodiment, as the coordinate conversion, a cosine curve is used for the x-axis of the coordinate as shown in Expression 7, and a straight line (line) is used.
Is applied to Expression 8, but these are merely examples, and the mathematical formula used in the present invention is not particularly limited. The above equation 9 is described in the postscript language, and the wavy line screen
A spot function defining (w) can be obtained.

As a third embodiment, as a further development of the first and second embodiments, a cell is divided into a plurality of regions, and a more complicated structure is obtained by using a mathematical expression including coordinate transformation for each region. The shape could be defined. FIG. 15 shows the configuration of the spot function obtained by this embodiment. This will be described below using the screen shape (r) in FIG.

FIG. 17 arranges the cell (C ′) at coordinates to define the screen of FIG. 16 and defines the area of the screen cell (C ′).
It is divided into four areas by the xy coordinate axis. With respect to C'b, C'c, and C'd among the four divided regions of the cell (C '), the center of the cell (C') is the center of rotation, and 90 degrees clockwise. The coordinates were converted so that they could be rotated 180 and 270 degrees. For example, in the region C′b, an arrow in FIG.
(X, y) = (-1,1) which is a point rotated like (x ', y') =
Converted to (1,1). When this conversion or rotation is performed, the area
C'b, C'c, and C'd are collected into an area C'a. After the transformation, Equation 9 is an equation of an ellipse generated from the center of the cell.

(Equation 9) Is described by PostScript, and the screen shape (r)
We got a spot function that defines

In this embodiment, the coordinates are rotated by coordinate conversion to create a point-symmetric screen shape. However, if other coordinate conversion methods are used, a screen shape that is line-symmetric such as a left-right symmetric shape can be created. is there. Although the center of the cell is used as the center of symmetry, the center in point symmetry and the axis of symmetry in line symmetry are arbitrary, and are not particularly limited in the present invention.

[0050]

As a forgery experiment 1 of a printed matter provided with a forgery prevention screen, the printed matter (P) obtained in Example 1 was copied with a color copying machine to obtain a copied matter (P'1). An enlarged photograph of the copy (P'1) is shown in FIG. Printed matter (P) and copy matter (P '
Comparing 1) visually, the genuine printed matter (P)
Then, the screen shape (heart shape) that can be clearly seen is re-graded in the copy (P'1) by the gradation reproduction screen shape of the color copying machine. Therefore, FIG. 11 and FIG.
As shown in Fig. 12, the screen shape originally in the printed matter (P) cannot be identified at all, and this copied matter (P'1) can easily be counterfeit when observed with the naked eye or with an auxiliary tool such as a magnifying glass. Can be identified.

In a forgery experiment 2 of a printed matter provided with a forgery prevention screen, the printed matter (P) was
The printing surface was read at 4000 dpi with a prepress color flatbed scanner Topaz, the read image was RIP-processed using a Delta Workstation, and output as a film using the company's Imagesetter HerkullresPro. As the screen shape of the output film, a chain dot generally used was used. As for the screen ruling, since the screen ruling often used in general printed matter is 175 lpi, re-gradation was performed at a screen ruling of 175 lpi. The film was printed by a general offset plate making and printing technique to obtain a duplicate (P'2). Enlarged photo of copy (P'2)
See Figure 13. In a genuine printed matter (P), a clearly visible screen shape is re-graded by a chain dot screen shape in a duplicate (P'2).
Therefore, as shown in FIGS. 11 and 13, the original screen shape cannot be identified at all, and can be easily identified as a counterfeit when observed with the naked eye or an auxiliary tool such as a magnifying glass.

As described above, according to the present invention, trademarks, family crests,
A screen shape that has a meaning or a design in itself, such as symbol marks and characters, is truly useful as a halftone screen that can be generated by a figure obtained by a function, and it is reproduced on a copying machine etc. It is applied to banknotes and securities, etc. as a continuous tone image consisting of halftone screens that are not used, prevents forgery and tampering, and significantly expands the application field even in the printing field where designability is required Can be done. Further, by using such a halftone screen as an intermediate product produced as a film-made plate-making screen and using this plate-made screen, a screen configuration corresponding to the amount of transmitted light can be easily made by an optical method. It can create any screen shape using a relatively inexpensive personal computer and image processing software, and decodes a small area of a printed matter to which it is attached using a machine reading means or the like. As a result, the authenticity of the authenticity can be easily determined.

[Brief description of the drawings]

FIG. 1 is a diagram showing a coordinate system of an arbitrary cell (C).

FIG. 2 is a diagram showing an example of a traditional geometric design.

FIG. 3 is a diagram showing an example of a geometric design designed based on a traditional geometric design.

FIG. 4 is a diagram showing an arbitrary pattern used in the present invention.

FIG. 5 is a diagram showing a screen generation method using a spot function by a flowchart.

FIG. 6 is an example of a screen shape employed in the first embodiment, which is a heart-shaped mark.

FIG. 7 is a diagram in which adopted screen shapes (H) are arranged in a coordinate system of a cell (C).

FIG. 8 is a diagram schematically illustrating an example of a density change of a screen shape (H).

FIG. 9 arranges screen cells (C) at coordinates to define the screen of FIG. 8b, and four areas Ca, Cb, Cc, Cd
FIG.

FIG. 10 shows an image (I) having a spot function (F) for generating a shape (H).
Is an example of an image to which a screen S defined by the following is applied.

FIG. 11 Printed matter P obtained by using film output matter (I ′)
This is a printed matter (P ') of the enlarged photograph of FIG. The enlarged part is shown in FIG.
(e).

FIG. 12 is an enlarged photograph of a copy (P′1). The enlarged portion corresponds to (e) of FIG.

FIG. 13 is an enlarged photograph of a duplicate (P′2). The enlarged portion corresponds to (e) of FIG.

FIG. 14 is an example of a screen shape employed in the second embodiment, which is a wavy line.

FIG. 15 is a diagram illustrating the structure of a spot function obtained in Embodiment 3 in the order of arithmetic processing.

FIG. 16 shows a whirligig mark in an example of a screen shape adopted in the third embodiment.

FIG. 17 is a diagram in which cells (C ′) are arranged at coordinates to define the screen of FIG. 16 and divided into four regions C′a, C′b, C′c, and C′d.

FIG. 18 is a schematic diagram illustrating rotation of a region C′b due to coordinate conversion.

Claims (9)

[Claims] 1. A method for producing a halftone screen, wherein a screen shape having a meaning or a design such as a trademark, a family crest, a symbol mark, or a character itself is generated by a graphic obtained by a function. 2. The halftone screen creating method according to claim 1, wherein the screen cells of the screen shape are divided into regions using xy coordinates, and each of the regions has a screen shape generated by a figure obtained by a function. . 3. The halftone screen creating method according to claim 1, wherein a figure obtained by a function formed by a mathematical expression including coordinate transformation has a screen shape to be generated. 4. The screen cell is divided into regions by xy coordinates, and each of the divided regions has a screen shape generated by a graphic obtained by a function including a mathematical expression including coordinate transformation. 1. The method for producing a halftone screen according to 1. 5. The halftone screen according to claim 4, wherein the screen cell is divided into regions by xy coordinates, and each of the divided regions has a screen shape generated by a graphic that is a point object or a line object. Creation method. 6. A method for producing a halftone screen, wherein a state in which a plurality of adjacent unit screen shapes are connected is a geometric pattern. 7. A halftone screen, which becomes an intermediate product as a film-making screen and obtains a screen configuration corresponding to the amount of transmitted light by an optical technique using the screen. 8. The method for producing a halftone screen according to claim 1, wherein a screen shape is arbitrarily created using a personal computer and image processing software. 9. The copying machine according to claim 1, wherein the copying machine cannot be used, thereby preventing forgery, and the authenticity of the provided halftone screen in the narrow area can be discriminated by using a machine reading means or the like. Original film and its printed matter.