JP5764892B2 - Printed material with invisible information superimposed - Google Patents

Description

  The present invention relates to a printing technique mainly applied to the field of anti-counterfeiting, and more particularly to a printed matter that can visualize a hidden image that is normally invisible by a simple method when used.

Various methods have been proposed as authenticity determination means for confirming the authenticity of an article, and various methods have been put into practical use even if they are limited to those using printing technology. Banknotes, etc. are typical ones that require authenticity determination, and anti-counterfeiting technologies that are put into them include those that use special ink, those that use visual effects such as fluorescent ink, and those that use fine patterns Wide range. In addition, by using a plurality of methods in combination, the effect (that is, forgery difficulty) is higher.
However, those using special techniques such as those described above are difficult to increase in cost and process load. In particular, in the printing field using printer technology called on-demand printing or plateless printing, forgery prevention technology that can be applied without using special materials or processes is strongly desired.
On the other hand, it is also an important factor to be able to confirm the authenticity, and in particular, the fact that it can be visually confirmed, that is, “understand” is very important in the industry that handles widely distributed goods and products. The The above-described fluorescent ink is an example in which the convenience of visual discrimination is advantageous, although ultraviolet light is required to visualize a hidden image.

  Further, there is a visual decryption type encryption technique as a technique excellent in information concealment while having the convenience of being “seeable”. This is to process the original image information into an image that cannot be visually recognized by dispersing it into a plurality of encrypted images (called shared images) composed of irregular patterns, and superimposing these shared images. Thus, the original image information is restored (that is, decoded) to a visible state. As described above, the visual decryption encryption technique uses a plurality of media on which the shared images are recorded in order to restore the original information from the plurality of shared images, but does not require any special equipment for the restoration, and the result is It is easy to understand just by looking.

For example, Patent Document 1 is a representative example of visual decryption encryption technology, and a technology related to the configuration and production of a recording medium that conceals information without using a concealment layer or the like using a visual decryption secret sharing method. Is disclosed.
Various methods have been proposed for the visual decryption secret sharing method, the shared image generation means, and the like, and the principle and generation method are described in detail in Non-Patent Document 1, which is a pioneering paper. .

JP 2001-118122 A

M.Naor and A.Shamir, "Visual Cryptography", Proc. Of Eurocrypt'94 May 1994

  As described above, since the visual decryption encryption technology generates a plurality of shared images from the original image (original image), a medium of the number of shared images is required for one original image. There is a convenience that can be restored by visual observation, and there is also an advantage that character numbers are transmitted instead of simple authenticity determination.

  FIG. 2 is a diagram showing a process of encryption and restoration using the visual decryption secret sharing method. As shown in FIG. 2, in the encryption process, the original image 10 is a share of an irregular pattern. It is decomposed into images. In the share image A (symbol 11) and the share image B (symbol 12) generated in this way, an irregular pattern is visually recognized alone, and significant information cannot be read.

  Thus, in the normal visual decoding secret sharing method, each pixel constituting the shared image is constituted by a set of white and black cells. Here, assuming that a shared image is created by printing or the like, a white cell refers to an area where nothing is applied, and a transparent object such as a film is an area that remains transparent. A black cell refers to a region to which a color material such as ink is applied, and is shown in black in FIG. 2, but the color material applied to the black cell is not limited to black and has a chromatic color. May be.

  In order to restore the original image from the shared image, the shared image A (symbol 11) and the shared image B (symbol 12) may be superimposed at a predetermined position. As a result, a pattern such as the restored image 13 appears, and as shown in FIG. 2, the irregular pattern is used as the background portion and the shape of the original image “T” (referred to as the “image portion” with respect to the background portion) is obtained. Can be read. This is because the background portion has an irregular pattern in which black and white are mixed, whereas the image line portion is filled with black, and therefore the image line portion appears due to the difference in shading.

  The present invention is normally visually indecipherable, and can be created by a general color printer using four-color toner while mounting secret information that can be visually confirmed by a simple method when used. It is an object to provide a printed matter on which invisible information is superimposed (hereinafter simply referred to as “printed matter”).

Superimposed print condition like invisible information of the present invention to solve the above problems, a plurality of share images the original image has been generated by encrypting the visual secret sharing scheme, a predetermined position of each of the sharing image The first secret image, which is one of the share images, and the second secret image, which is another share image, are printed at the predetermined position on the sheet. In the printed matter, image information is obtained by a color printing machine using yellow, red, indigo, and black color materials on the paper using a paper containing a fluorescent material that emits visible light when irradiated with ultraviolet light as the paper. a printed material formed, the image information, first secret image formed by the color material of the yellow, and the second formed by said any one of red or blue or black coloring material from the secret image Characterized in that that.

The printed matter of the present invention exhibits a high level of anti-counterfeiting effect due to the synergistic effect of the secret image using fluorescence and the secret image by the visual decoding type secret sharing method by using a sheet containing a fluorescent material. Since it can be created by a four-color printing machine or a color printer, it becomes easy to incorporate variable information into a secret image, and further exerts an effect of preventing forgery.

Schematic diagram of printed matter of the present invention The figure which shows the encryption pattern of the encryption recording medium Diagram showing the visual characteristics of color materials

FIG. 1 is a schematic diagram of a printed matter of the present invention. Here, together with the mode of the printed material 1 under normal observation conditions, the mode when the printed material 1 is generated and the mode when restoring the secret image (mode when reading) are also shown. Note that the normal observation condition refers to a state of observing under a light source made of visible light.
The printed matter 1 is formed by superimposing a monochrome image 6 and a share image A (reference numeral 11), which will be described in detail later, on a sheet of paper, and the monochrome image 6 includes an original image α corresponding to a first secret image. The shape information of (symbol 5) and the shape information of the original image β (symbol 14) corresponding to the second secret image are hidden in the shared image A (symbol 11). Moreover, the paper of the printed matter 1 contains a fluorescent material, and is configured to develop visible light when irradiated with ultraviolet light having a predetermined wavelength.

<About share image A>
Share image A (symbol 11) is one of a plurality of encryption patterns generated from the original image β (symbol 14) by the visual decryption secret sharing method.
FIG. 2 is a diagram showing the process of encryption and restoration by the visual decryption secret sharing method. As shown in FIG. 2, in the process of encryption, the original image β (reference numeral 14) is an irregular pattern. Is broken down into share images. In the share image A (symbol 11) and the share image B (symbol 12) generated in this way, an irregular pattern is visually recognized alone, and significant information cannot be read. In the example of FIG. 2, there are two share images, but the number of share images may be two or more.

  Thus, in the visual decryption secret sharing method, the shared image is configured by a set of white and black small areas (hereinafter referred to as cells). Here, assuming that a shared image is created by printing or the like, a white cell refers to an area where nothing is applied, and a transparent object such as a film is an area that remains transparent. A black cell refers to a region to which a color material such as ink is applied, and is shown in black in FIG. 2, but the color material applied to the black cell is not limited to black and has a chromatic color. May be.

<About monochromatic image 6>
The single color image 6 is an image obtained by printing the original image α (symbol 5) with a single color material. In the example of FIG. 1, the color material is applied to the background portion of “A” which is the shape information of the original image α (symbol 5). Is represented in the form of a letter, and the color material portion is shaded. In the printed matter 1 of the present invention, the color material forming the single color image 6 is a yellow color material so that the shape of “A” is not noticeable.

  A color material exhibiting a yellow hue used for general color printing has absorption in the vicinity of 400 to 500 nm, but this band corresponds to “blue” of the primary color of light, and the visual sensitivity of the human eye is comparable to other primary colors. However, since it is low, yellow placed on a white background has a characteristic that it is difficult to distinguish visually. The use of the yellow color material for the monochromatic image 6 utilizes this characteristic.

This will be described with reference to FIG. 3. A general yellow color material has a spectral reflection characteristic as shown in the reflection characteristic 31 of the yellow color material in FIG. It shows a characteristic that it is lower than the reflectance in the wavelength band. This characteristic becomes clearer when the ideal yellow reflection characteristic 32 is seen.
On the other hand, the visual sensitivity of the human eye has a characteristic in which the peak is around 550 nm with respect to the wavelength of light and attenuates before and after, as shown by the relative luminous sensitivity curve 33 in FIG. Since the relative sensitivity is low in the range of 500 nm, the discrimination ability for colors in this band is inferior.

Furthermore, in the printed matter 1, the share image A (reference numeral 11) composed of an irregular pattern is superimposed, and a blinding effect is exhibited by using a color material other than yellow for the share image A (reference numeral 11). The shape of “A” is invisible under normal observation conditions. In the printed matter 1 in FIG. 1, for convenience of explanation, the shape of “A” is expressed so as to be visible.

<Restoring secret images>
First, reproduction of the original image α (reference numeral 5) will be described with reference to FIG.
In the printed matter 1 under normal observation conditions, the monochromatic image 6 may be superimposed with the shared image A (symbol 11), and the shape of “A” cannot be read. As shown, the portion hidden by the yellow color material does not emit light, and the portion where the paper is exposed emits light, so that the shape of “A” can be clearly seen.

  Further, in order to restore the original image β (symbol 14), the share image A and the share image B may be overlapped. For example, for restoration in which the share image B (symbol 12) is formed by printing or the like on a sheet-like transparent film. If the medium is overlaid at a predetermined position on the printed material 1 on which the shared image A (reference numeral 11) is printed, a “T” shape as shown in the restored image 15 appears.

  Even if the monochrome image 6 is formed of a yellow color material and has a blinding effect due to the shared image A (reference numeral 11), a portion having the shape of “A” (this is called an image line portion) and a background portion The smaller the difference in density, the better. Therefore, the present inventor has obtained a condition under which the fluorescent image 8 is clearly observable under ultraviolet light and the fluorescent image 8 can be clearly observed. The background of the monochrome image 6 is formed of a yellow color material. The image area was formed with halftone dots using the same yellow coloring material, and good results were obtained when the halftone dots were 20 to 40% in area ratio.

  As described above, the printed matter of the present invention has a high level of anti-counterfeiting properties by having two types of hidden images together, and it is possible to determine authenticity by visual observation with simple means.

For the production of the printed matter 1, a printing method using a printing ink called process ink used for general color printing may be used, but an electrophotographic method or an ink jet method in which it is difficult to introduce a special color material can also be used. In particular, the electrophotographic method and the ink jet method based on the printer technology make it easy to create a printed material 1 using the original image α (reference numeral 5) and the original image β (reference numeral 14) as variable information. 8 and the restored image 15 can be changed variously.

The paper used for the printed material of the present invention includes a fluorescent material, but it is not necessarily a special paper. Some commonly used papers contain a fluorescent material and are applied to the printed material of the present invention. be able to.
According to the trial of the present inventor, when the printed matter 1 was made of paper called high-quality paper and irradiated with black light, the fluorescent image 8 was clearly visible.

1 Printed material 5 Original image α
6 Monochromatic image 8 Fluorescent image 10 Original image 11 Share image A
12 share image B
13 Restored image 14 Original image β
15 Restoration image 16 Ultraviolet light

Claims (1)

The plurality of share images generated by encrypting the original image by the visual decryption secret sharing method are images that can be restored by overlapping each share image at a predetermined position, and one of the share images In the printed matter in which the first secret image that is the second secret image and the second secret image that is another share image are printed at the predetermined position on the paper, the paper contains a fluorescent material that emits visible light by irradiation with ultraviolet light yellow with paper on the paper to, a printed matter of red, indigo, and the image information by a black color printing machine using the color material is formed, the image information is formed by the color material of the yellow that the first confidential image, and the red, blue, and black second superimposed print invisible information characterized by Rukoto such a secret image formed by any one of color material.

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