EP0597056A1 - Method for the marking of documents - Google Patents

Method for the marking of documents

Info

Publication number
EP0597056A1
EP0597056A1 EP19930909744 EP93909744A EP0597056A1 EP 0597056 A1 EP0597056 A1 EP 0597056A1 EP 19930909744 EP19930909744 EP 19930909744 EP 93909744 A EP93909744 A EP 93909744A EP 0597056 A1 EP0597056 A1 EP 0597056A1
Authority
EP
European Patent Office
Prior art keywords
original
image
marking
fourier transform
mark
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19930909744
Other languages
German (de)
French (fr)
Inventor
Joseph BIGÜN
Benoít DUC
Murat Kunt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ecole Polytechnique Federale de Lausanne (EPFL)
Ecole Polytechnique, Palaiseau
Original Assignee
Ecole Polytechnique Federale de Lausanne (EPFL)
Ecole Polytechnique, Palaiseau
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to CH173292 priority Critical
Priority to CH1732/92 priority
Application filed by Ecole Polytechnique Federale de Lausanne (EPFL), Ecole Polytechnique, Palaiseau filed Critical Ecole Polytechnique Federale de Lausanne (EPFL)
Priority to PCT/CH1993/000135 priority patent/WO1993025038A1/en
Publication of EP0597056A1 publication Critical patent/EP0597056A1/en
Application status is Withdrawn legal-status Critical

Links

Classifications

    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03GELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G21/00Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
    • G03G21/04Preventing copies being made of an original
    • G03G21/043Preventing copies being made of an original by using an original which is not reproducible or only reproducible with a different appearence, e.g. originals with a photochromic layer or a colour background
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838Preventing unauthorised reproduction
    • H04N1/00883Auto-copy-preventive originals, i.e. originals that are designed not to allow faithful reproduction
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/32Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device
    • H04N2201/3201Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N2201/3269Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs
    • H04N2201/327Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs which are undetectable to the naked eye, e.g. embedded codes

Abstract

On incorpore une marque sur l'original lors de l'élaboration dudit original, de façon que cette marque soit invisible sur l'original mais apparaisse sur la copie de l'original effectuée à l'aide d'une photocopieuse. a mark is incorporated on the original during the development of that original, so that the mark is invisible on the original but appears on the copy of the original made using a photocopier. On incorpore la marque en mélangeant d'une façon additive l'image originale à protéger et l'image de marquage à camoufler dans l'original en modulant l'une ou l'autre des images ou par une manipulation de transformées de Fourier. the mark is incorporated by mixing an additive way to protect the original image and the marking image to camouflage in the original modulating either images or by manipulation of Fourier transforms.

Description

A method of marking documents

The present invention relates to a document marking method intended to avoid confusion with the original copies.

Historically, it has faced the need to reproduce documents and there is not so long, many documents were established with several printed copies using carbon paper. The appearance on the photocopier market has upset the data of this problem since it became possible to reduce repro¬ a finished document with virtually the same quality as 1Original.

While with the first black copiers / white on the market could be distinguished without difficulty an original from a copy, because a part of the copy quality and also the quality of the paper used for photocopying, technical development has allowed to reproduce materials on virtually any paper with a near-perfect quality.

However, in terms of black / white photocopiers, it was still possible to distinguish the original from the copy when the original was in color.

However, the introduction of copiers to reproduce colors scored again a technically significant progress. In the beginning, as was the case for copiers black / white, you had to use very special papers for color reproduction. Cepen¬ ing today the latter technique allows the use of paper media of any sort. It has become extremely difficult to distinguish an original from a copy of good quality, since firstly the designs and colors are reproduced with high fidelity and the other the same kind of paper can not be a criterion distinguish between an original and a copy.

Technicians and users are obviously welcome this new quality in the graphic reproduction industry. However, the same technical quality is dange¬ reuse when its operation is used in an illegal or improper purpose.

One thinks of course first bank notes that can be reproduced in color on the paper présen¬ as a grain that can obviously be confused with the original grain paper money. Falsification of documents by photocopying however still key to a much wider field of documents. Just think of all security papers and all documents that qualify for the issuance of a benefit in any form whatsoever.

Thus, it was observed an increasing number of attempts of falsification, the more difficult to detect that the technique of reproduction was making progress.

As a consequence of this evolution, the relatively complex nature of graphic paper values, which was the main guarantor of their originality assumes more or practically since this function becomes easy to everyone to reproduce, to he does little aside their scruples.

But not to change the fundamentals of trade, there is an extremely strong interest in power, despite the existence of the most sophisticated photocopiers, to continue to use reliable original documents without permanently ulterior motives for their original character or not.

The object of the present invention is precisely to provide a method the application of which enables to distinguish without fail a photocopy of an original, even when copying is performed by a copying machine of the most sophisticated type.

To this end, the invention relates to a method for marking documents in which a mark is incorporated on the original document during the preparation of said original document by digitally combining information on this mark with the information relating to the image proté- ger, so that this brand is invisible on the original document but appears on the copy of the original document made using a photocopier, scanning the original document is performed with no échantillon¬ swimming at least twice finer than the photocopieu- is.

Other important features of the invention are defined in the claims subordinate to claim 1.

The method of the present invention occurs at the information that needs to go on the document by digitally combining camouflage information and the information of the image to protect before printing the document without changing the procedure print, contraire¬ ment to processes that have been proposed to date, which generally use different ways to print the original infor¬ tion, or by a mixture of different colors, to mark the document. or by carrying out the marking by photographic printing.

This method allows incorporation of information on the original mar¬ quage, this information being invisible on the original and. appearing only after photoco- pie. It relies on the fact that the copies obtained with photocopiers, even the most modern, have a definition of lower paper (typically 2-fold) than the originals that are printed. It is of course likely that technical photocopiers continue to progress in order to further refine the definition of the document. It will then be enough to print the originals that you want to protect with greater definition yet.

two-dimensional sampling theorem

The luminance of a document (grayscale or black and white) can be represented by a two-dimensional analog function x '(u, v). For color images, information is represented by three functions of the same type for the primary colors red, green and blue. When such a document is scanned by the scanning system of a photocopier or other equipment, or that these functions are sampled in space with a very fine pitch which should normally be selected according to the two-dimensional sampling theorem (see M. Kunt, "Digital signal Processing", electricity Treaty, EPFL, Vol. XX, 402p.). Given the difficulties of appli¬ quer this theorem in practice, the sampling is usually chosen small enough that the document digitally reconstituted does not present a list pointil¬ effect to the eye of the observer. Common photocopiers use a sample between 300 and 600 dots per inch, that is to say the points of the order of 0.042 mm to 0.085 mm in width. It is this that allows them to have a good quality reproduction. The sampling theorem states that any pattern in the original whose fineness is less than twice these values ​​can not be correctly represented.

X is - = (f, g), the Fourier transform of the function x * (u, v).. The sampling of the function x "- (u, v) causes the periodic repetition of the Fourier transform Xa (f, g) in both directions, with periods equal to the inver¬ is double periods of spatial sampling, referred δu and .DELTA.V. If the original document contains components at frequencies greater than l / 2δu and / or l / 2δv, repeated versions of the function X * (f, g) are overlapped and a recovery effect takes place. This recovery is behind the figures of Moiré is observed on some copied documents.

The invention is based on the recovery and implies that the original must have a definition at least two times better than photocopiers.

The following description, given by way of example, refers to the drawing in which:

Figures la to illustrate the various stages of 1'échantillonage;

2 shows the four quadrants of the discrete Fourier transform of the marking image;

Figure 3 illustrates the arrangement of the Fourier transforms, so as to place the marking image in the high frequencies;

Figure 4 is a block diagram of a first variant of the marking method of the original image in the spatial domain;

Figure 5 is a block diagram of a second variant of the original image labeling method in the spatial domain;

Figure 6 is a block diagram of a third variant of the marking method of the original image in the spatial domain;

Figure 7 is a block diagram of a first variant of the original image labeling method in the frequency domain; 8 illustrates the distribution of the quadrants of the Fourier transform for carrying out the method according to a second variant in the frequency domain;

Figure 9 is a block diagram of the second variant of the marking method of the original image in the frequency domain; and

Figure 10 is a block diagram of a third variant of the marking method of the original image in the frequency domain.

Figure 1 shows the various stages of the échantil¬ bration. Figure la is a representation of the β function representing the luminance of an image. Figure lb is a representation of the sampling function. The re figu¬ illustrates the multiplication functions represented on the first two figures. Figure ld shows the Fourier transform of the original image and the figure shows the Fourier transform after sampling.

Marking Images

The process of the invention is precisely to introduce in the original document, in its development, one or more marker images whose components will be placed at frequencies higher than those of the pious photoco¬, so that this or these marking images are invisible on the original, but they appear on photocopies. The user is free to choose the image marking it wishes to appear on the photocopy. Such an image can for example be that of a text that says "This is a copy" or "This is a fake bill." The marking image may be any image grayscale "or color. This image is scanned during the preparation of the original document with a comparable sample not that of photocopiers. The two-dimensional discrete Fourier tranformée is calculated and shown also in digital form. Figure 2 shows all four quadrants 1 to 4 in the discrete Fourier transform of the marking image.

Preparation of the original document

The original document in picture form must be scanned with a pitch in any case twice finer than the best photocopier. Factor 2 is not critical. Any value greater than necessary.

The document protection by the introduction of the invisible marking image on the original can be carried out according to two equivalent methods, the spatial frequency method and the method. Will be described below, for example, three variations for each one.

1. The spatial method

According to a first variant of the spatial method, this is to calculate a new function y (k, l) where k and 1 represent the indices of the discrete points after numérisa¬ tion, by adding the scanned document image origi¬ unprotected final initial x (k, l) Image marking z (k, l) multiplied by cosine and sine functions judiciously chosen to place the marking image in the high frequencies, as illustrated in the field of Fourier in Figure 3. in the case of one-dimensional signals of radio communication, this operation is known as amplitude modulation name. The exact form of this operation is:

y (kj) = x (k, l) + z (JfcJ) ( "w [π (- - + - * -)] + C * M [Λ (- * --- * -)])" δδuu δδvv δδuu δδvv tt (1)

where δu and .DELTA.V are the sampling periods along the two axes of the original image. A block of this variant of the process scheme is shown in Figure 4. In this first embodiment, the indicia image does not overwrite the original image, but just superimposed thereto.

In a second variant of the spatial method, it is possible to replace the original image with the marking image of an almost complete manner. In this second variant, it is to hide a version of the original high frequency so that, after copying, only the marking image appears. To this end, we subtract the modulated version of the original. The corresponding relationship for the calculation is:

y (k_l) ≈ x (k, l) + [z (Jt,) - x (k_m {cos [π (-k- + - * -)] + aw [π0 ~ * - * -)])

\ Δu .DELTA.V δu .DELTA.V I (2)

A block diagram of this process variant is shown in Figure 5.

According to a third variant of the method space, located between the two previous alternatives, it is possible to weight the original image with respect to the marking image. In this third variant, it is also to hide a weighted version of the original image in the high frequencies, so that after photocopying, one can assay the appearance of the marking image. For this, we subtract the modulated and weighted version of the original. The corresponding relationship for the calculation is:

y (k, l) = x (k, l) + [z (k, T) - ax (k, I)] lcos [π (- + -L)] + cos [π {^ - - * - )]] m

\ Δu .DELTA.V δu .DELTA.V I w where α is a weighting factor. If α = 0 we again the first variant above, while if α = l, it falls on the second alternative above.

Depending on the size that one wishes to give to the marking image, it can also introduce a multiplication factor β before the function z (k, l) in equation (3). A block of this variant of the process scheme is repré¬ sented in Figure 6. It is of course possible to achieve, without diffi¬ culty and without departing from the scope of the present invention, many other variants of the method in which incor¬ pore a mark on the original by mixing an additive manner to protect the original image and the marking image to camouflage in the original by modulating the two images.

2. The frequency method

In a first variant of the frequency method, simply divide the quadrants of the Fourier transform of the image marking in Figure 2, in accordance with the locations indicated in Figure 3 (parts rasterized) and summing the corresponding values the Fourier transform of the unprotected original image. It then suffices to take the inverse Fourier transform of the resulting image to obtain the protected image. A block diagram of the process according to this variant is represented in Figure 7.

In a second variant of the frequency method, we returned quadrants 1 to 4 of the Fourier transform of the marking image of FIG 2 in accordance with the locations shown in Figure 8, by subtracting their corresponding quadrants lo, 2o, 3 and 4 of the Fourier transformed itself of the original image (halftone portions). Must then add the values ​​corresponding to the Fourier transform of the unprotected original image. He finally just take the Fourier transform of this is inver¬ resulting image for the protected image. A block diagram of the method according to this second variant of the frequency method is shown in Figure 9.

According to a third variant of the method frequented tial we replied quadrants of the Fourier transform of the marking image of FIG 2 in accordance with the locations indicated in Figure 8 by subtracting quadrants, weighted by α, corresponding the tranfor- Mee Fourier the original image (halftone portions). The α factor is the same as that of the equation (3). Must then add the values ​​corresponding to the trans¬ formed Fourier unprotected original image. He finally just take the Fourier transform is reversed from this resultant image for the protected image. A block diagram of the method according to this third variant of the frequency method is shown in Figure 10.

As in the case of the spatial method, it is of course possible to achieve without difficulty and without departing from the scope of the present invention, many other variants of the method in which a mark is incorporated on the original by mixing a additively origi¬ the final image to be protected and the marking image to camouflage in the original by manipulation of Fourier transforms.

Claims

claims
1. A method of marking documents, characterized in that a mark is incorporated on the original document during the preparation of said original document by digitally combining information on this mark with the information regarding the image protect, so that this brand is invisible on the original document but appears on the copy of the original document made using a photocopier, scanning the original document is performed with a sampling interval at least twice end than the photocopier.
2. Method according to claim 1, characterized in that the mark is incorporated by mixing an additive way to protect the original image and the marking image to camouflage in the original modulating one or other images.
3. A method according to one of claims 1 or 2, characterized in that it incorporates the mark on the original by mixing an additive way the original image and the image of marking, by summing the samples two frames after pre-multiplication the marking image according to formula (1).
4. Method according to one of claims 1 or 2, characterized in that it incorporates the mark on the original by mixing an additive way the original image and the image of marking, by summing the samples two frames after pre-multiplication the marking image and the original image according to formula (2).
5. Method according to one of claims 1 or 2, characterized in that it incorporates the mark on the original by mixing an additive way the original image and the image of marking, by summing the samples two frames after pre-multiplication the marking image and the original image according to formula (3).
6. The method of claim 1; characterized in that it incorporates the mark on the original by mixing an additive way to protect the original image and the marking image to camouflage in the original by manipulation of Fourier transforms.
7. The method of claim 6, characterized in that the mark on the original is incorporated by introducing the marking image in the field of the Fourier transform, by placing the Fourier transform of the marking image the ends of the Fourier transform of the original image (Figure 3).
8. The method of claim 6, characterized in that the mark on the original is incorporated by introducing the marking image in the field of the Fourier transform, by placing the Fourier transform of the marking image the ends of the Fourier transform of the original image, and subtracting the corresponding quadrants of the Fourier transform of the original image (Figure 8).
9. The method of claim 6, characterized ςn that is incorporated the mark on the original by introducing the marking image in the field of the Fourier transform, by placing the Fourier transform of the marking image the ends of the Fourier transform of the original image, and subtracting a weighted manner the corresponding quadrants of the Fourier transform of the original image (Figure 8).
10. Method according to one of the preceding claims, characterized in 'that the user can freely select image marking it desired to introduce into the original image.
EP19930909744 1992-05-29 1993-05-26 Method for the marking of documents Withdrawn EP0597056A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CH173292 1992-05-29
CH1732/92 1992-05-29
PCT/CH1993/000135 WO1993025038A1 (en) 1992-05-29 1993-05-26 Method for the marking of documents

Publications (1)

Publication Number Publication Date
EP0597056A1 true EP0597056A1 (en) 1994-05-18

Family

ID=4217304

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19930909744 Withdrawn EP0597056A1 (en) 1992-05-29 1993-05-26 Method for the marking of documents

Country Status (5)

Country Link
US (1) US5524933A (en)
EP (1) EP0597056A1 (en)
JP (1) JPH06511611A (en)
CA (1) CA2114548A1 (en)
WO (1) WO1993025038A1 (en)

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WO1993025038A1 (en) 1993-12-09
JPH06511611A (en) 1994-12-22
CA2114548A1 (en) 1993-12-09
US5524933A (en) 1996-06-11

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