EP0710574A2 - Method of generating a security design by electronic means - Google Patents

Abstract

The grid of parallel lines is generated with the aid of computer graphics giving a specific ratio of the line width (lo) to the periodicity (do). The background thus created is then varied by respacing in accordance with a modulation function having preselected parameters. Finally the line width is adjusted so that its ratio to the interline spacing reverts to the original value. The initially straight lines may also become curved and a pseudo-relief image may be created by erasure of those parts of the lines which lie within its contours.

Description

The present invention relates to a generation method using electronic means of a drawing of security intended to be printed on securities, including bank notes and fiduciary papers, composed of multiple lines, as well as a plate printing and value paper bearing at least a drawing generated by the implementation of the method.

In order to make it difficult, if not impossible, reproduction of securities, in particular banknotes of banks, fiduciary papers, shares, stamps post, etc. we are trying to integrate security elements. Thus, it has been proposed to have recourse separately or in combination, different means, namely: use a special watermarked paper, incorporated into the paper of a metallic or other security element, creation of designs whose counterfeiting is extremely costly making the expected gain of a such counterfeiting, use of colors and shades of color difficult to reproduce, etc.

Technological progress concerning photocopiers and scanners is such that many of these means don't are more than enough to thwart bad intentions counterfeiters. Since the appearance of photocopiers high-performance color, the focus has been by the manufacturers of such securities on creation moiré areas during digital copying, for example by a color photocopier of a document. These moirés alter the original image and give an indication that it is a copy.  

Moire appear when parallel lines or not spaced by a distance of the magnitude of the point are aligned perpendicularly to one of the machine's sampling axes. The reading of information is disturbed and the original image is altered, we especially encounter non-uniform changes in hues and colors. The appearance of such moiré patterns is difficult to predict because it depends on the features and settings of the device used for reproduction.

In EP-A-0204 552, a safety drawing is described comprising areas formed by non-parallel lines, whose width and / or distance vary.

In EP-A-0353 974, safety zones are described on securities comprising areas formed of parallel lines and parts of which are altered as to the width and / or the shape of the line for form latent images or not.

The choice of particular security drawings allows cause the appearance of moiré. The purpose of this invention is to provide a method for generating moiré drawings when copied digital. The invention therefore provides a method of generation of designs based on multiple lines.

a) on génère un fond uniforme constitué de lignes droites parallèles de sorte que la distance entre les axes médians longitudinaux des deux lignes consécutives que l'on désigne par l'espacement d₀ entre deux lignes soit constant et que la largeur l₀ des traits de lignes soit également constante, déterminant ainsi un rapport constant r₀ = l₀/d₀,

b) on modifie le fond en modulant l'espacement d₀ entre les lignes selon une fonction de modulation dont les paramètres sont choisis préalablement,

c) on modifie la largeur des traits de lignes de sorte que le rapport de la largeur l_n du trait d'une ligne sur son espacement d_n à la ligne suivante soit égal au rapport constant l_n/d_n = r₀.

The method according to the invention is characterized in that the following steps are carried out:

a) a uniform background is created consisting of parallel straight lines so that the distance between the longitudinal median axes of the two consecutive lines designated by the spacing d₀ between two lines is constant and the width l₀ of the line strokes is also constant, thus determining a constant ratio r₀ = l₀ / d₀,

b) the background is modified by modulating the spacing d₀ between the lines according to a modulation function whose parameters are chosen beforehand,

c) the width of the line strokes is modified so that the ratio of the width l _n of the line stroke of a line over its spacing d _n to the next line is equal to the constant ratio l _n / d _n = r₀.

The advantages of the method according to the invention are on the one hand, that changes in the distribution lines can be set according to the photocopiers or scanners against which one wishes to be protect and, on the other hand, that these modifications do not alter not the visual aspect, with the naked eye, original of the image thanks to the fact that the ratio between the width of a line on the spacing between two lines consecutive remains constant.

The securities which will be produced subsequently incorporating such designs may be provided with more than one safety drawings corresponding to parameters different so for a document we can protect ourselves against several machines of different types.

An important advantage of the invention is the fact that it allows you to create security drawings including geometric or artistic images while so far safety drawings of this type do not include no geometric or artistic images.  

Different variations for creating designs are proposed, so we can just transform straight lines to lines of another shape, for example of sinusoids, concentric circles, curved lines closed or not, etc. in every situation the line width of each line remaining equal to the value obtained in step c of the method.

According to another variant, the lines of the bottom can be turned from a certain angle α partially or totally or we can turn according to this angle only the line segments at inside a contour delimiting an image.

According to another alternative embodiment and with the aim of form an image, said lines are cut out, so interrupted inside the delimiting contour the image.

According to another variant of execution and still in the purpose of forming an image in addition to the background created by said lines, the lines are modulated by the form (outline) of an image and we create a relief effect by known means, in particular by breaking the continuity lines.

According to another alternative embodiment, with the aim of create a geometric image, the width of the lines is modified according to the density of the gray of the image original geometric.

Finally, according to a variant, the line segments do not not contributing to the formation of an image retain their width and spacing respecting the defined r₀ ratio in step c of the method.  

According to another alternative embodiment and with the aim of create an artistic image, the width of the lines is modified according to the original digital image obtained by a scanner.

The present invention also relates to a plate with at least one drawing generated according to one of claims 1 to 8 intended for printing of a security paper.

The invention also relates to a security paper comprising at least one safety drawing generated according to one of claims 1 to 8.

The invention will be described in more detail using the appended drawing showing different variant embodiments.

The method will now be described using the drawings attached.

In Figure 1, we have presented, in enlargement, two lines whose width is l₀ and the distance between the longitudinal median axes is equal to d₀.

Figures 2 to 4 show the modification of a network of regular lines according to a variant of the invention.

Figures 5 to 5 show the modification of a network lines according to another variant of the invention.  

The couples of drawings 8, 9; 10, 11; 12, 13; 14, 15; and 16, 17 represent the modification of the first drawing of the couple towards the second according to other variants of the invention.

In Figure 2, we have shown a set of lines straight parallels, the spacing between two lines consecutive is constant and equal to d₀, the width of the line along a line is equal to l₀ and the ratio r₀ = l₀ / d₀ is constant.

We then proceed to a modulation of the spacing between two lines so that the space between two consecutive lines t _{n + 1} is equal to d _n = d₀ + (n. Δ.), Δ being a parameter of linear modulation of the spacing. By applying this rule, we obtain a network of lines according to Figure 3.

Subsequently, to comply with the condition that the ratio of the width of a line over the spacing of one line to the next line is equal to the value of the constant support r₀, the width of the lines l _n is modified so that l _n = l₀ + (n. λ) that the ratio l _n / d _n is always equal to r₀, λ being a modulation parameter of the line width. In this case we obtain a network of lines having the form of FIG. 4, the visual appearance of which (with the naked eye) for widths and spacings less than those represented in the appended drawings is similar to that of FIG. 1 .

With a background like the one in figure 4, some copiers or scanners will not be able to eliminate the effect moire. It is obvious that parameters such as l₀ as well as δ and λ can be modified according to   machine characteristics. The interest is that diversity spacing between lines and widths lines give the naked eye a uniform appearance of the picture but it is impossible to avoid the formation moiré during reproduction even when modifying the characteristics of the reproduction machine within a range of values. The settings of the modulation of the spacing and width are chosen according to the reproduction machine (s) that we want to fight.

Another modulation variant is presented in FIGS. 5 to 7, FIG. 5 being identical to FIG. 2. In FIG. 6, the spacing is modulated according to the following rule d _n = d₀ + δ (1 + sin (2 Π n /NOT)). In this case N is the modulation period. We thus obtain a background where the spacing between two consecutive lines does not vary linearly as in Figure 2, but sinusoidally. Always in order to respect the condition of the constant ratio between the line width and the spacing, the line width and the line width are also modified and this is done according to the following rule: l _n = l₀ + λ x (1 + sin 2Π n / n). In this case we get Figure 7.

Another modification step after obtaining the figure 7 is to modify the shape of the lines while respecting the width of the lines obtained for example in the figure 4 or 7. Thus, starting from FIG. 8 which is identical to figure 7 we can get the figure 9 which is formed of lines forming waves or sinusoids. Similarly, with reference to Figures 10 and 11 where FIG. 10 is identical to FIG. 7, one can transform these lines into concentric closed curves respecting the width of the lines in the figure   10. The form of this transformation of lines straight in closed curves is not limited and it depends on the desired result.

Another execution, always starting from a figure 12 which is identical to figure 7 is to turn the lines with an angle for example of 45 ° and thereafter create the outline of an image (in this case a winged horse) by creating a relief effect or medal in breaking straight lines.

Always starting from a figure like that of the figure 7 shown here as figure 14, we can change the width of the lines according to the density of the gray of the original geometric image.

Finally, another way to proceed and create an image artistic is, starting from a network of lines along FIG. 16 which is identical to that of FIG. 7, we modify the width of the lines according to the image artistic which has been previously numbered via a scanner.

For line segments not contributing to the image formation, we could keep the report r₀.

The invention also relates to a printing plate. provided with at least one safety drawing created according to one described methods as well as a security paper provided at least one such drawing.

These safety drawings can be printed by any which technical process, for example offset, intaglio, etc.  

It is obvious that we proposed different executions regarding generating a drawing, but it's also possible inside a drawing to use many of these possibilities, for example we could rotate only 45 ° part of an image or create a complex design with several possibilities mentioned above.

Claims (10)

Method for generating, using electronic means, a security design intended to be printed on securities, in particular bank notes and fiduciary papers, composed of multiple lines, characterized in that the procedure is as follows: following steps : a) a uniform background is created consisting of parallel straight lines so that the distance between the longitudinal median axes of the two consecutive lines designated by the spacing d₀ between two lines is constant and the width l₀ of the line strokes is also constant, thus determining a constant ratio r₀ = l₀ / d₀. b) the background is modified by modulating the spacing d₀ between the lines according to a modulation function whose parameters are chosen beforehand, c) the width of the line strokes is modified so that the ratio of the width ln of the line stroke of a line over its spacing d _n to the next line is equal to the constant ratio l _n / d _n = r₀. Method according to claim 1, characterized by the fact that said straight lines are transformed in lines of different shape, the width of the line of each line being equal to the width obtained at step C of claim 1. Method according to one of claims 1 or 2, characterized by the fact that at least part of said lines are rotated by an angle α.   Method according to one of claims 1 to 3, characterized by the fact that in order to form a image, said lines are cut inside contours delimiting said image. Method according to one of claims 1 to 4, characterized by the fact that in order to form an image in relief, said lines are modulated by the shape of the image and transformed to create a relief effect. Method according to one of claims 1 to 5, characterized by the fact that in order to form an image geometric, the width of the lines is changed along of each line according to the density of the gray of the original geometric image. Method according to one of claims 1 to 4, characterized by the fact that in order to create an image artistic, the width of the lines is changed along of each line according to the original digital image scanned. Method according to one of claims 4 to 7, characterized by the fact that the line segments do not not contributing to the formation of the image present a width and spacing respecting the ratio r₀. Printing plate for printing securities, characterized by the fact that it is provided at least one safety drawing generated by the method according to one of claims 1 to 8. Value paper, characterized in that it is provided with at least one safety drawing generated according to the method of one of claims 1 to 8.