CA2057479C - Support provided with a security element - Google Patents
Support provided with a security element Download PDFInfo
- Publication number
- CA2057479C CA2057479C CA002057479A CA2057479A CA2057479C CA 2057479 C CA2057479 C CA 2057479C CA 002057479 A CA002057479 A CA 002057479A CA 2057479 A CA2057479 A CA 2057479A CA 2057479 C CA2057479 C CA 2057479C
- Authority
- CA
- Canada
- Prior art keywords
- image
- security element
- gradation value
- visual system
- human visual
- 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.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/00838—Preventing unauthorised reproduction
- H04N1/00856—Preventive measures
- H04N1/00875—Inhibiting reproduction, e.g. by disabling reading or reproduction apparatus
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
- B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
- B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
- B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
- B42D25/29—Securities; Bank notes
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/00838—Preventing unauthorised reproduction
- H04N1/0084—Determining the necessity for prevention
- H04N1/00843—Determining the necessity for prevention based on recognising a copy prohibited original, e.g. a banknote
- H04N1/00846—Determining the necessity for prevention based on recognising a copy prohibited original, e.g. a banknote based on detection of a dedicated indication, e.g. marks or the like
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/00838—Preventing unauthorised reproduction
- H04N1/00856—Preventive measures
- H04N1/00859—Issuing an alarm or the like
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
- H04N2201/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
- H04N2201/3201—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
- H04N2201/3269—Display, 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
- H04N2201/327—Display, 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S283/00—Printed matter
- Y10S283/901—Concealed data
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S283/00—Printed matter
- Y10S283/902—Anti-photocopy
Abstract
A support provided with a machine-detectable security element, particularly a copying-security element. The security element comprises a first image perceptible to the human visual system, said first image incorporating a second image that is substantially imperceptible to the human visual system.
Description
2Q~'~~'~9 SOPPORT PROVIDED WITH A SECORITY ELEMENT
The invention relates to a support provided with a machine-detectable security element, particularly a copying-security element.
Now sophisticated copiers, such as colour copiers with a matrix laser scanner in particular, and graphic lay-out stati-ons are becoming available for an increasing public, large numbers of photocopies of an original can be produced in an inexpensive and rapid way, the photocopies being not at all or scarcely - distinguishable from the original.
In order to put an end to this technique of copying documents such as valuable documents, e.g. bank notes, or confidential documents, one thought of providing the support with a copy-ing-security element detectable by a copier, so that in the event of detection suitable measures can be taken. In this concept, the copying-security element is formed by an object that is detectable by the copier, e.g. a filament which is incorporated in the support during the manufacturing process of the support, or by a unique type of printing ink having particular optical features. Furthermore, the copier should be provided with suitable detection means.
The invention aims to provide a support with a security ele-ment without any special treatment of the support or the use of special printing inks being required for the provision of the security element.
- X0574.79 In accordance with one aspect of the present invention there is provided an image support carrying a first image perceptible to the human visual system, and a machine-detectable security element, particularly a copying-security element, said first image being composed of line segments arranged in a regular raster pattern, characterized in that line segments have different angular orientations in a plane of the support, said first image incorporates a second image that is substantially imperceptible to the human visual system, said second image being formed by the difference in angular orientation of the line segments, said angular orientation of the line segments being a function of a gradation value of the security element, said first and second images being perceptible to the human visual system after copying.
In accordance with another aspect of the present invention there is provided a method of producing a regular raster pattern for printing a first image perceptible to the human visual system on an image support, and a machine-detectable security element, particularly a copying-security element, said regular raster pattern consisting of raster picture elements each consisting of a line segment, said method being characterized in that line segments are given different angular orientations in a plane of the support, in that a second image is incorporated into the first image by forming said angular orientations of line segments as a function of a gradation value of the security element, said second image being substantially imperceptible to the human visual system, said first and second images being perceptible to the human visual system after copying.
A
- 2a - L057't79 Additional purposes, characteristics and advantages of the support according to the invention will become clear after the following description of a number of preferred embodiments of the support according to the invention, in which references are made to the accompanying drawings, in which:
Fig. la shows an enlargement of an image on a support that is obtained by raster printing techniques;
Fig. lb shows an enlargement of a copy of the image of fig. la;
Fig. 2a shows an enlargement of a substantially uniform image on a support according to the invention that is provided with a first embodiment of a copying-security element;
Fig. 2b shows a partial enlargement of fig. 2a;
Fig. 2c shows an enlargement of a copy of the image of fig. 2a;
Fig. 2d shows a partial enlargement of fig. 2c;
Fig. 3a shows an enlargement of an image on a support according to the invention, in said image the copying-security element of fig. 2a being superposed on the image of fig. la;
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Fig. 3b shows an enlargement of a copy of the image according to fig. 3a;
Fig. 4a shows an enlargement of the substantially uniform image on a support according to the invention which is provi-ded with a second embodiment of a copying-security element;
Fig. 4b shows a partial enlargement of fig. 4a;
Fig. 4c shows an enlargement of a copy of the image according to fig. 4a;
Fig. 4d shows a partial enlargement according to fig. 4c;
Fig. 5a shows an enlargement of an image on a support accor-ding to the invention, wherein the copying-security element of fig. 4a is superposed on the image of fig. la; and Fig. 5b shows an enlargement of a copy of the image according to fig. 5a.
In order to make the description as clear as possible, all images represented in the figures are shown on a larger scale.
Particularly the images according to figures 2b, 2d, 4b and 4d are represented at six times the full scale, the other images are represented at circa three times the full scale. Whenever a normal distance of assessment is given below, one should take this enlargement into consideration. Furthermore, when assessing the undermentioned visual effects one should realize that the figures accompanying the description are in fact copies, even if they are referred to in the text as originals, which have been obtained by copying the originals once or every so often.
The invention relates to a support provided with a machine-detectable security element, particularly a copying-security element.
Now sophisticated copiers, such as colour copiers with a matrix laser scanner in particular, and graphic lay-out stati-ons are becoming available for an increasing public, large numbers of photocopies of an original can be produced in an inexpensive and rapid way, the photocopies being not at all or scarcely - distinguishable from the original.
In order to put an end to this technique of copying documents such as valuable documents, e.g. bank notes, or confidential documents, one thought of providing the support with a copy-ing-security element detectable by a copier, so that in the event of detection suitable measures can be taken. In this concept, the copying-security element is formed by an object that is detectable by the copier, e.g. a filament which is incorporated in the support during the manufacturing process of the support, or by a unique type of printing ink having particular optical features. Furthermore, the copier should be provided with suitable detection means.
The invention aims to provide a support with a security ele-ment without any special treatment of the support or the use of special printing inks being required for the provision of the security element.
- X0574.79 In accordance with one aspect of the present invention there is provided an image support carrying a first image perceptible to the human visual system, and a machine-detectable security element, particularly a copying-security element, said first image being composed of line segments arranged in a regular raster pattern, characterized in that line segments have different angular orientations in a plane of the support, said first image incorporates a second image that is substantially imperceptible to the human visual system, said second image being formed by the difference in angular orientation of the line segments, said angular orientation of the line segments being a function of a gradation value of the security element, said first and second images being perceptible to the human visual system after copying.
In accordance with another aspect of the present invention there is provided a method of producing a regular raster pattern for printing a first image perceptible to the human visual system on an image support, and a machine-detectable security element, particularly a copying-security element, said regular raster pattern consisting of raster picture elements each consisting of a line segment, said method being characterized in that line segments are given different angular orientations in a plane of the support, in that a second image is incorporated into the first image by forming said angular orientations of line segments as a function of a gradation value of the security element, said second image being substantially imperceptible to the human visual system, said first and second images being perceptible to the human visual system after copying.
A
- 2a - L057't79 Additional purposes, characteristics and advantages of the support according to the invention will become clear after the following description of a number of preferred embodiments of the support according to the invention, in which references are made to the accompanying drawings, in which:
Fig. la shows an enlargement of an image on a support that is obtained by raster printing techniques;
Fig. lb shows an enlargement of a copy of the image of fig. la;
Fig. 2a shows an enlargement of a substantially uniform image on a support according to the invention that is provided with a first embodiment of a copying-security element;
Fig. 2b shows a partial enlargement of fig. 2a;
Fig. 2c shows an enlargement of a copy of the image of fig. 2a;
Fig. 2d shows a partial enlargement of fig. 2c;
Fig. 3a shows an enlargement of an image on a support according to the invention, in said image the copying-security element of fig. 2a being superposed on the image of fig. la;
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Fig. 3b shows an enlargement of a copy of the image according to fig. 3a;
Fig. 4a shows an enlargement of the substantially uniform image on a support according to the invention which is provi-ded with a second embodiment of a copying-security element;
Fig. 4b shows a partial enlargement of fig. 4a;
Fig. 4c shows an enlargement of a copy of the image according to fig. 4a;
Fig. 4d shows a partial enlargement according to fig. 4c;
Fig. 5a shows an enlargement of an image on a support accor-ding to the invention, wherein the copying-security element of fig. 4a is superposed on the image of fig. la; and Fig. 5b shows an enlargement of a copy of the image according to fig. 5a.
In order to make the description as clear as possible, all images represented in the figures are shown on a larger scale.
Particularly the images according to figures 2b, 2d, 4b and 4d are represented at six times the full scale, the other images are represented at circa three times the full scale. Whenever a normal distance of assessment is given below, one should take this enlargement into consideration. Furthermore, when assessing the undermentioned visual effects one should realize that the figures accompanying the description are in fact copies, even if they are referred to in the text as originals, which have been obtained by copying the originals once or every so often.
2 ~l 5'~ 4'~ 9 Fig. la shows an image applied onto a support, said image being composed of image elements divided according to a regu-lar raster pattern which consist of circular raster pixels, the surface of which, particularly the diameter, being modula-ted in a way that is common practice in techniques of printing with one or several colours by the use of one or more rasters.
The image is represented at circa three times the full scale.
The density of the raster pixels amounts to circa 100 dpi in reality, which corresponds to a distance of raster pixels of circa 250 ~cm. The support can be made of every material that is suitable for supporting an image perceptible to the human visual system, e.g. paper or synthetic materials.
In the event of a normal distance of assessment, the human visual system will be unable to discern any individual raster pixels, so that the image will be seen as a continuous halfto-ne image.
Fig. lb shows an enlargement of a copy of the image of fig.
la, said copy being obtained by means of a Cannon matrix laser copier having a resolution of 400 dpi and by laser scanning of the original in a matrix. As a result, the distance of the matrix grid of this copier is circa 60 ~,m. As the distance of the grid is smaller than that of the raster pixels, undersam-pling can be avoided, even when the standard model of the copier is provided with a digital filter operating on 3x3 submatrices.
Fig. 2a shows an enlargement of an image of a support accor-ding to the invention, percepted by the human eye as a uniform image at a normal distance of assessment, the image being composed of image elements formed by raster elements or raster "pixels" of a density of 100 dpi, each raster point being shaped as a line segment instead of a circular point as in fig. la. Fig. 2b shows a partial enlargement of fig. 2a. This deformation of circular raster pixels into linear ones will be imperceptible to the human visual system at a normal distance of assessment, due to the high density of the raster pixels.
In other words, a second image is incorporated in the uniform image in the form of a deformation of the image elements of the uniform image into line segments, said second image being imperceptible to the human eye at a normal distance of asses-sment. As the resolution of the copier is nevertheless of an adequate level, this copier will be able to distinguish circu-lar raster pixels from linear ones. Consequently, when this deformation of the raster pattern is detected by the copier, a blocking circuit being part of the copier or connected to it will prevent the copying of the image and/or give an alarm.
Corresponding to a density of raster pixels of 100 dpi is a distance of raster pixels of circa 250 Vim. The width of a line segment is 30 ~cm in this particular example. Such a width is feasible according to raster printing techniques that are currently avaible.
As is shown in fig. 2a, not only the deformation into line segments, in this case the deformation of all the raster pixels although that is not necessary, but also the degree of deformation of the raster pixels differs due to different angular orientations of the line segments in the plane of the support. In that case the angular orientation is a function of a gradation value of a picture corresponding to the mirror image of fig. la. Therefore, the function ~ for the raster point i is represented by:
- 6 - L0574.79 ~t = ~d~x~Y)- dmin~ ~+ ~p ~dmax - dmin) wherein d (x, y) is the gradation value of the picture at the point with the coordinates (x, y), dmin is the minimum gradation value, d",aX is the maximum gradation value, and ~o is an initial angle which equals n/2 in the example.
Therefore, ~i varies continuously within the range rz/2 to 3rr/2.
The copy of the image of fig. 2a, obtained by means of the copier, said copy being represented in fig. 2c, shows clearly that the copy's picture is perceptible indeed or at least considerably more perceptible to the human visual system at a normal distance of assessment. Fig 2d shows a partial enlargement of fig 2c. This visual effect can be explained on account of the fact that the current sophisticated copiers are provided with digital filter circuits such as sharpness-enhancing filters.
Furthermore, changes of colour seemed to occur in the copy, even when the original image was applied in black and white on the support. These changes of colour facilitate the perceptibility of the picture to the human visual system to a further degree.
In addition to that, the orientation of the raster pattern of the support with respect to the matrix of the copier appears to have relevance, e.g. to the angles 0°, 45° and 90°, as well as the mode in which the copier was set , a . g . normal mode or photo mode .
In this way, the support according to the invention is provided with a second image which is imperceptible at a normal '~ ~l 5'~ 4'~ 9 distance of assessment, yet which is perceptible in the copy in the form of a picture to the human visual system at a normal distance of assessment, when the copier allows produ-cing and supplying a copy, which can be the case, for example, when the copier is not provided with a copying-security ele-ment detection circuit and/or a blocking circuit. Therefore, without any additional appliances an original document can be distinguished from a copy. Besides, there are no special requirements with respect to the support and/or applied prin-ting ink. A major advantage is that the copier can be of the currently used type which is not provided with special detec-tion and blocking circuits.
Due to the fact that the deformation of the first image of the support according to the invention is not at all or scarcely perceptible, the second image can be superposed on an image that is modulated in the usual way, e.g. the image according to fig. la, the amplitude of which is modulated. As an exam-ple, reference is made to fig. 3a which shows an enlargement of an image on a support, the second image of fig. 2a being superposed on the image of fig. la. The modulation of the image perceptible to the human visual system is performed by modulating the width of the line segments similarly to the modulation of the diameter of the circular raster pixels in fig. la.
Fig. 3b shows an enlargement of a copy of the image of fig.
3a. At a normal distance of assessment the deformation of the original image is clearly perceptible, so that the mirror image of fig. la is also visible now - this time in negative.
In this case the minimum line width is only 30 ~,m. It is advantageous to select the non-modulated line width as small as possible, as the provision of an out-of-focus filter in the copier may even cause the total absence of the lightest parts from the copy, so that the copy and the original are visibly distinct.
- 8 - 20574.79 A major advantage of the security element according to the invention, in particular the picture concealed in the image whuch represents in this case the mirror image of fig. la, is that it extends over a considerable surface area of the perceptible image, in this case the entire surface. The effect of this is that the copying-security element is fully incorporated in the image of the support to be protected, and moreover, in such a way that the perceptibility of the first image does not - or only scarcely - decrease. The picture concealed in the image as a result of the deformation can also represent a code which is, for example, composed of alphanumeric symbols or a bar code. In that case the copier may be provided with appropriate reading circuits.
Fig. 4a shows an enlargement of a substantially uniform image on a support according to the invention, wherein a second embodiment of the copying-security element is provided which comprises a deformation of raster pixels into line segments which are orientated in accordance with the following function:
. - (d(x,y) - dgem) . 7t + 7t (2) 1 Id(x,y) - dgeml 4 4 wherein ~i is the angle of the image segment i with the horizontal, d(x,y) is the gradation value of the picture at the point with coordinates (x, y) , and deem is an average gradation value. Therefore, each line segment is inclined at an angle of 0 or rr/2, and the function ~ is a binary function. The average value dgem can, for example, equal half of the maximum gradation value of the original picture or which is the limit set by the printing process. Fig. 4b shows a partial enlargement of fig. 4a.
_.. ~~5'~4'?'9 _ g Fig. 4c shows an enlargement of a copy of the image on the support according to fig. 4a, wherein the copy clearly shows the deformation, even at a normal distance of assessment by the human visual system. Fig. 4d shows a partial enlargement of fig. 4c.
In a way similar to that of figures 3a and 3b, figures 5a and 5b show an enlargement of an image and its copy, respectively, wherein the image according to fig. 4a is superposed on the image according to fig. la.
It is noted that the examples with respect to the figures are only meant to illustrate a support provided with a security element according to the invention.
It will be obvious to the expert that many variations of the above-described embodiments of the support according to the invention are feasible within the scope of the invention.
Therefore, other deformations of the image element can be selected than the ones described, including a deformation comprising local translations of the image elements. The foregoing numerical values are only meant to be illustrative and may be adjusted to the specifications of the copiers. The invention also relates to supports provided with an image that is visually perceptible and that is obtained by means of so-called frequency modulation techniques.
The image is represented at circa three times the full scale.
The density of the raster pixels amounts to circa 100 dpi in reality, which corresponds to a distance of raster pixels of circa 250 ~cm. The support can be made of every material that is suitable for supporting an image perceptible to the human visual system, e.g. paper or synthetic materials.
In the event of a normal distance of assessment, the human visual system will be unable to discern any individual raster pixels, so that the image will be seen as a continuous halfto-ne image.
Fig. lb shows an enlargement of a copy of the image of fig.
la, said copy being obtained by means of a Cannon matrix laser copier having a resolution of 400 dpi and by laser scanning of the original in a matrix. As a result, the distance of the matrix grid of this copier is circa 60 ~,m. As the distance of the grid is smaller than that of the raster pixels, undersam-pling can be avoided, even when the standard model of the copier is provided with a digital filter operating on 3x3 submatrices.
Fig. 2a shows an enlargement of an image of a support accor-ding to the invention, percepted by the human eye as a uniform image at a normal distance of assessment, the image being composed of image elements formed by raster elements or raster "pixels" of a density of 100 dpi, each raster point being shaped as a line segment instead of a circular point as in fig. la. Fig. 2b shows a partial enlargement of fig. 2a. This deformation of circular raster pixels into linear ones will be imperceptible to the human visual system at a normal distance of assessment, due to the high density of the raster pixels.
In other words, a second image is incorporated in the uniform image in the form of a deformation of the image elements of the uniform image into line segments, said second image being imperceptible to the human eye at a normal distance of asses-sment. As the resolution of the copier is nevertheless of an adequate level, this copier will be able to distinguish circu-lar raster pixels from linear ones. Consequently, when this deformation of the raster pattern is detected by the copier, a blocking circuit being part of the copier or connected to it will prevent the copying of the image and/or give an alarm.
Corresponding to a density of raster pixels of 100 dpi is a distance of raster pixels of circa 250 Vim. The width of a line segment is 30 ~cm in this particular example. Such a width is feasible according to raster printing techniques that are currently avaible.
As is shown in fig. 2a, not only the deformation into line segments, in this case the deformation of all the raster pixels although that is not necessary, but also the degree of deformation of the raster pixels differs due to different angular orientations of the line segments in the plane of the support. In that case the angular orientation is a function of a gradation value of a picture corresponding to the mirror image of fig. la. Therefore, the function ~ for the raster point i is represented by:
- 6 - L0574.79 ~t = ~d~x~Y)- dmin~ ~+ ~p ~dmax - dmin) wherein d (x, y) is the gradation value of the picture at the point with the coordinates (x, y), dmin is the minimum gradation value, d",aX is the maximum gradation value, and ~o is an initial angle which equals n/2 in the example.
Therefore, ~i varies continuously within the range rz/2 to 3rr/2.
The copy of the image of fig. 2a, obtained by means of the copier, said copy being represented in fig. 2c, shows clearly that the copy's picture is perceptible indeed or at least considerably more perceptible to the human visual system at a normal distance of assessment. Fig 2d shows a partial enlargement of fig 2c. This visual effect can be explained on account of the fact that the current sophisticated copiers are provided with digital filter circuits such as sharpness-enhancing filters.
Furthermore, changes of colour seemed to occur in the copy, even when the original image was applied in black and white on the support. These changes of colour facilitate the perceptibility of the picture to the human visual system to a further degree.
In addition to that, the orientation of the raster pattern of the support with respect to the matrix of the copier appears to have relevance, e.g. to the angles 0°, 45° and 90°, as well as the mode in which the copier was set , a . g . normal mode or photo mode .
In this way, the support according to the invention is provided with a second image which is imperceptible at a normal '~ ~l 5'~ 4'~ 9 distance of assessment, yet which is perceptible in the copy in the form of a picture to the human visual system at a normal distance of assessment, when the copier allows produ-cing and supplying a copy, which can be the case, for example, when the copier is not provided with a copying-security ele-ment detection circuit and/or a blocking circuit. Therefore, without any additional appliances an original document can be distinguished from a copy. Besides, there are no special requirements with respect to the support and/or applied prin-ting ink. A major advantage is that the copier can be of the currently used type which is not provided with special detec-tion and blocking circuits.
Due to the fact that the deformation of the first image of the support according to the invention is not at all or scarcely perceptible, the second image can be superposed on an image that is modulated in the usual way, e.g. the image according to fig. la, the amplitude of which is modulated. As an exam-ple, reference is made to fig. 3a which shows an enlargement of an image on a support, the second image of fig. 2a being superposed on the image of fig. la. The modulation of the image perceptible to the human visual system is performed by modulating the width of the line segments similarly to the modulation of the diameter of the circular raster pixels in fig. la.
Fig. 3b shows an enlargement of a copy of the image of fig.
3a. At a normal distance of assessment the deformation of the original image is clearly perceptible, so that the mirror image of fig. la is also visible now - this time in negative.
In this case the minimum line width is only 30 ~,m. It is advantageous to select the non-modulated line width as small as possible, as the provision of an out-of-focus filter in the copier may even cause the total absence of the lightest parts from the copy, so that the copy and the original are visibly distinct.
- 8 - 20574.79 A major advantage of the security element according to the invention, in particular the picture concealed in the image whuch represents in this case the mirror image of fig. la, is that it extends over a considerable surface area of the perceptible image, in this case the entire surface. The effect of this is that the copying-security element is fully incorporated in the image of the support to be protected, and moreover, in such a way that the perceptibility of the first image does not - or only scarcely - decrease. The picture concealed in the image as a result of the deformation can also represent a code which is, for example, composed of alphanumeric symbols or a bar code. In that case the copier may be provided with appropriate reading circuits.
Fig. 4a shows an enlargement of a substantially uniform image on a support according to the invention, wherein a second embodiment of the copying-security element is provided which comprises a deformation of raster pixels into line segments which are orientated in accordance with the following function:
. - (d(x,y) - dgem) . 7t + 7t (2) 1 Id(x,y) - dgeml 4 4 wherein ~i is the angle of the image segment i with the horizontal, d(x,y) is the gradation value of the picture at the point with coordinates (x, y) , and deem is an average gradation value. Therefore, each line segment is inclined at an angle of 0 or rr/2, and the function ~ is a binary function. The average value dgem can, for example, equal half of the maximum gradation value of the original picture or which is the limit set by the printing process. Fig. 4b shows a partial enlargement of fig. 4a.
_.. ~~5'~4'?'9 _ g Fig. 4c shows an enlargement of a copy of the image on the support according to fig. 4a, wherein the copy clearly shows the deformation, even at a normal distance of assessment by the human visual system. Fig. 4d shows a partial enlargement of fig. 4c.
In a way similar to that of figures 3a and 3b, figures 5a and 5b show an enlargement of an image and its copy, respectively, wherein the image according to fig. 4a is superposed on the image according to fig. la.
It is noted that the examples with respect to the figures are only meant to illustrate a support provided with a security element according to the invention.
It will be obvious to the expert that many variations of the above-described embodiments of the support according to the invention are feasible within the scope of the invention.
Therefore, other deformations of the image element can be selected than the ones described, including a deformation comprising local translations of the image elements. The foregoing numerical values are only meant to be illustrative and may be adjusted to the specifications of the copiers. The invention also relates to supports provided with an image that is visually perceptible and that is obtained by means of so-called frequency modulation techniques.
Claims (6)
1. An image support carrying a first image perceptible to the human visual system, and a machine-detectable security element, particularly a copying-security element, said first image being composed of line segments arranged in a regular raster pattern, characterized in that line segments have different angular orientations in a plane of the support, said first image incorporates a second image that is substantially imperceptible to the human visual system, said second image being formed by the difference in angular orientation of the line segments, said angular orientation of the line segments being a function of a gradation value of the security element, said first and second images being perceptible to the human visual system after copying.
2. The image support according to claim 1, characterized in that the function of the gradation value is a continuous function of the gradation value of a security element forming an area identical to the area formed by the first image, said first image and said security element being perceptible to the human visual system after copying.
3. The image support according to claim 2, characterized in that said function is:
wherein .PHI.i is the angle formed by line segment i having coordinates (x, y) within the area of the raster pattern, d(x,y) is the gradation value of the security element at the point (x, y) within the area of the security element, d min is the minimum gradation value, d max is the maximum gradation value, and .PHI.0 is an initial angle.
wherein .PHI.i is the angle formed by line segment i having coordinates (x, y) within the area of the raster pattern, d(x,y) is the gradation value of the security element at the point (x, y) within the area of the security element, d min is the minimum gradation value, d max is the maximum gradation value, and .PHI.0 is an initial angle.
4. A method of producing a regular raster pattern for printing a first image perceptible to the human visual system on an image support, and a machine-detectable security element, particularly a copy-security element, said regular raster pattern consisting of raster picture elements each consisting of a line segment, said method being characterized in that line segments are given different angular orientations in a plane of the support, in that a second image is incorporated into the first image by forming said angular orientations of line segments as a function of a gradation value of the security element, said second image being substantially imperceptible to the human visual system, said first and second images being perceptible by the human visual system after copying.
5. The method according to claim 4, characterized in that as said function a continuous function of the gradation value of the security element forming an area identical to the area formed by the raster pattern is chosen, said first image and said security element being perceptible by the human visual system after copying.
6. The method according to claim 5, characterized in that said function is:
wherein .PHI.i is the angle formed by line segment i having coordinates (x, y) within the area of the raster pattern, d(x,y) is the gradation value of the security element at the point (x,y) within the area of the security element, d min is the minimum gradation value, d maX is the maximum gradation value, and .PHI.o is an initial angle.
wherein .PHI.i is the angle formed by line segment i having coordinates (x, y) within the area of the raster pattern, d(x,y) is the gradation value of the security element at the point (x,y) within the area of the security element, d min is the minimum gradation value, d maX is the maximum gradation value, and .PHI.o is an initial angle.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL9002740A NL192610C (en) | 1990-12-13 | 1990-12-13 | Image carrier and method for printing an image on an image carrier. |
NL9002740 | 1990-12-13 |
Publications (2)
Publication Number | Publication Date |
---|---|
CA2057479A1 CA2057479A1 (en) | 1992-06-14 |
CA2057479C true CA2057479C (en) | 2000-11-21 |
Family
ID=19858136
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002057479A Expired - Lifetime CA2057479C (en) | 1990-12-13 | 1991-12-12 | Support provided with a security element |
Country Status (12)
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US (1) | US5374976A (en) |
EP (1) | EP0490457B1 (en) |
JP (1) | JP3242684B2 (en) |
AT (1) | ATE136848T1 (en) |
CA (1) | CA2057479C (en) |
DE (1) | DE69118837T2 (en) |
DK (1) | DK0490457T3 (en) |
ES (1) | ES2089118T3 (en) |
GR (1) | GR3020558T3 (en) |
HK (1) | HK1006957A1 (en) |
IL (1) | IL100352A (en) |
NL (1) | NL192610C (en) |
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- 1990-12-13 NL NL9002740A patent/NL192610C/en not_active IP Right Cessation
-
1991
- 1991-12-11 DE DE69118837T patent/DE69118837T2/en not_active Expired - Lifetime
- 1991-12-11 AT AT91203279T patent/ATE136848T1/en not_active IP Right Cessation
- 1991-12-11 ES ES91203279T patent/ES2089118T3/en not_active Expired - Lifetime
- 1991-12-11 DK DK91203279.4T patent/DK0490457T3/en active
- 1991-12-11 EP EP91203279A patent/EP0490457B1/en not_active Expired - Lifetime
- 1991-12-12 IL IL10035291A patent/IL100352A/en not_active IP Right Cessation
- 1991-12-12 CA CA002057479A patent/CA2057479C/en not_active Expired - Lifetime
- 1991-12-13 JP JP35125491A patent/JP3242684B2/en not_active Expired - Fee Related
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1993
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1996
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1998
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JPH06152928A (en) | 1994-05-31 |
DK0490457T3 (en) | 1996-08-26 |
EP0490457B1 (en) | 1996-04-17 |
ATE136848T1 (en) | 1996-05-15 |
JP3242684B2 (en) | 2001-12-25 |
CA2057479A1 (en) | 1992-06-14 |
IL100352A (en) | 1994-02-27 |
ES2089118T3 (en) | 1996-10-01 |
NL9002740A (en) | 1992-07-01 |
IL100352A0 (en) | 1992-09-06 |
NL192610C (en) | 1997-11-04 |
DE69118837T2 (en) | 1996-12-12 |
US5374976A (en) | 1994-12-20 |
NL192610B (en) | 1997-07-01 |
HK1006957A1 (en) | 1999-03-26 |
DE69118837D1 (en) | 1996-05-23 |
EP0490457A1 (en) | 1992-06-17 |
GR3020558T3 (en) | 1996-10-31 |
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