Note: Descriptions are shown in the official language in which they were submitted.
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
Title: Substrates for printing
Field of Invention
This invention concerns substrates, primarily papers and in particular to a
method of
modifying the substrate to make it suitable for use in printing security
documents.
Background to the invention
It is known to scan a printed document and convert the image into digital data
for feeding
into a computer. A copy of the original document can be printed out using the
digital
image data using a laser jet or inkjet printer, and in this situation, the
imaging device
(usually a scanner), computer and printer, acts like a copier. The stored data
can be
edited or manipulated using graphics software so that the final print can be a
very accurate
reproduction of the original. Furthermore, the data can be transmitted for
e;;ample via the
Internet or by modem and telephone line to a remote location, or
stor:°d for future use on
a disk or other memory device, and this technology can be used to counterfeit
security
documen~s such as cheques, banknotes, identity documents and the like.
Prior art
Methods are known for modifying substrates so that genuine substrates can be
identified
and distinguished from counterfeit substrates. Typically these methods include
marking
the genuine substrate with materials which fluoresce under ultra-violet, or
which only emit
light at some special region of the visible spectrum, or involve the addition
of special
material such as magnetic materials or infra-red absorbing pigments, or the
inclusion of
large scale water marking in pictorial or bar code form on or in the
substrate. All these
methods require either a gross alteration of the substrate (as in watermarking
methods) or
the inclusion of special materials usually requiring special detectors to
determine if the
substrate of any document is genuine. Such methods tend to be expensive, the
effects are
X8-12-2600' CA 02357727 2001-07-05 GB 000000129
C569.011B
2
usually readi).y visible to the naked eye, and it is not impossibly to modify
paper anal other
substrates io a similar manner, so as to confuse a verification process.
rt is one object of the present invention to provide a special substrate on
which security
documents can be printed, having features which will not be reproduced by a
photocopier
but which can be detected using a computer err other data processor based
image systczn.
l:Iowevez, the featuzes will not normally be reproduced by a copier or primer
supplied with
image data signals obtained from an unprotected such system, as it can be
arranged that if
rt~~e coniputcr system oz copier detects the said features it can therefore
refuse to process
the image.
According to the present iuvez~doz~ a substrate on which a security document
is to be
printed comprises a plurality of identification features in the surface
thereof, which when
illuminated and imaged by scanning produce data signals in the output of a
photoelectric
device Sj~y~rac a 'ce j in ha ; '
(1) the contrast between said identil'xcatiozt features and the remainder of
the substrate
surface is such that image data signals corresponding to said features are
substantially
indistinguishable from image data signals r~l~tuxg to the remainder of the
substrate surface
andJor from background noise signals in the output of the photoelectric
device, and are
thereby indistinguishable by cyc; and
(2) said features repeat at intervals over at least some of the surface area
of the substrate,
whereby upon validation the time or position signals relating to each feature
will bear at
least one fixed relationship to signals relating to other of said features,
whereby a
computing device supplied with the image data signals can be programmed to
identify
whether feature signals bearing the said at least one fixed relationship are
present ire the
data, to assist in identifying floe imaged document.
AMENDED SHEET
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
3
The features may be repeated at regular intervals.
Each of the physical features may be similar in character to each of the other
features in
the said surface.
Documents of the same type may be printed on substrate bearing similar
features having
a similar fixed relationship over the surface of the substrate. Thus for
example bank notes
of one denomination may be printed on a substrate having surface features of a
particular
type and one or more particular spacings.
The spacing may be selected so as to be constant in one direction only or
varied according
to a special, known pattern.
A similar or different regular spacing may be selected for features in another
direction
bearing a particular spacial relationship relative to the first said
direction, for example
perpendicular to the said first direction.
In a preferred ~-xample the features are arranged in a 2D matrix in the
substrate surface.
The existence of such features in a substrate surface constitutes a primary
encoding of the
substrate allowing substrates to be distinguished from substrates not
containing said
features, or to be distinguished one from another depending on the choice of
features.
Secondary encoding of a substrate may be achieved by introducing a variation
into the
matrix such as by omitting features from particular positions in such a
regular matrix.
Thus for example every fourth feature along each third line may be omitted.
Preferably security documents are encoded using both primary and secondary
encodings.
In addition or alternatively secondary encoding may be provided if the matrix
is formed
from features having two distinctive characteristic and, instead of omitting
features at
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
4
specific positions within the matrix, features of one type are located at one
set of positions
in the matrix, and features of the other type are located at other positions
in the matrix.
Thus in a simple example one set of features may be generally circular in
shape, whereas
interspersed features producing a secondary encoding may have a different
readily
distinguishable shape such as rectangular or triangular.
Since the encoding of a substrate can be achieved by selecting the spacing
between
features or selecting features having a specific characteristic such as shape
which can be
identified in image data signals relating thereto, and/or by the substitution
of features
having a first characteristic at selected points in a regularly occurring
matrix of such
features by other features having a second different characteristic, and/or
the omission of
features at particular points in a matrix, there is an almost infinite number
of possible
combinations and permutations available to encode security document
substrates.
Therefore not only does the invention permit a reliable method for
identification of
security documents, so as to readily detect forgeries which are not printed on
an
appropriate substrate, but each individual type of security document such as
banknotes of
different denominations, cheques originating from different banks, passports
issued by
different offices, and the like, if desired can be uniquely identified by a
particular primary
and/or secondary encoding selected for the substrate on which they are to be
printed.
Image analysis techniques for identifying the presence of regularly occurring
patterns
and/or drop-outs within regularly occurring patterns and/or shapes) or other
visibly
distinguishable features of detectable features in an image, are readily
available and
known, and by using high speed processors such as DSPs and the like, image
data can be
checked and verified or otherwise, virtually instantaneously as documents are
scanned.
Preferably a physical feature is selected for encoding the surface of a
substrate to provide
a primary encoding, which will not appear in the electrostatic image of a
photocopier.
This ensures that attempts to reproduce the original by photocopying will
merely produce
a copy containing the printed content of the document unless the substrate
onto which it
is copied contains the correct physical encoding in the surface thereof.
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
More preferably, if a secondary encoding is present, any variation in the
primary encoding
which constitutes the secondary encoding is even less capable of being
distinguished by
the naked eye or picked up by a photosensitive device as used in a
photocopier.
Preferably the physical feature encoding is in the form of a repeat pattern.
As the identification features are such that the appearance of the security
document (for
example a bank note) is not affected or disturbed aesthetically, since in the
case of
banknotes, the introduction of new notes provided on substrate according to
the invention
is permissable alongside existing banknotes printed on unencoded substrate,
since if the
general appearance of the documents is unchanged to the naked eye, old but
nevertheless
authentic notes which do not contain the physical feature encoding on the
substrate surface
provided by the invention, will appear similar to banknotes printed on encoded
substrate.
Examples of physical feature encoding of a substrate as aforesaid comprise,
embossing
with inkless intaglio or embossing the surface by calendaring during
manufacture of the
substrate.
Two or more different encoding techniques may be combined in any substrate.
The invention also lies in impressing in the surface of a substrate onto which
a security
document is to be printed indentations and/or grooves in accordance with a
first pattern
which contains encoded therein a second pattern, to enable a security document
printed
on such a substrate to be identified by subjecting image data signals obtained
from
scanning the document to an appropriate mathematical algorithm to determine
whether the
second pattern can be found in image data signals relating to the first
pattern.
A pattern may be encoded to produce multiple iterations of a code on the
substrate.
The encoded pattern may not extend over the whole of the surface of the
substrate forming
each document but only over selected areas which align with particular printed
areas of
the substrate, and according to another aspect of the invention, the printed
areas are
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
6
selected so as to enhance the detection of the substrate surface variation
during scanning
and conversion of the image into image data signals.
Redundancy created by multiple iterations can be used to advantage since the
large number
of similar iterations enhances the detectability of the code by increasing the
effective signal
to noise ratio. This in combination with the selection of particular regions
of the printed
areas of the final document in which to locate the iterations, facilitates the
detection by a
data processor of the presence of an otherwise substantially invisible pattern
in the data
signals derived from the scanning.
For a document identification system to work, the encoding of the documents
must be
capable of being read for example by optically scanning the documents and
generating
image data signals which can be handled by a computer, or by using a
specialist imaging
and image analysing apparatus performing this function.
The invention also lies in a security document substrate adapted to be
identifiable as such
by having detectable surface features therein features to enable
identification as aforesaid.
The invention also lies in a security document when printed on a substrate as
aforesaid.
A primary application of the invention lies in treating the surface of a
substrate as
aforesaid for use in the production of security documents so as to inhibit or
degrade the
reproduction of such security documents using a scanning process which
converts the
image into image data signals for controlling a printing process, in which a
second control
is introduced if surface encoding is detected by subjecting the image data
signals to an
appropriate algorithm, which second control serves to downgrade or inhibit the
printing
process so as to prevent the reproduction of the original document, or of a
good quality
reproduction thereof.
A second application of the invention lies in a document verification method
by scanning
the document and converting the optical information into electrical signals
using a
photosensitive device and in which for recognition purposes, a data processor
is
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
7
programmed to look for one or more surface encoding, information in the
electrical signals
which if detected in image data obtained from imaging and scanning the
document, will
generate a confirmation signal, validating the document, and vice versa.
The invention thus also provides a computer based document scanning device
which can
be used to validate a document by checking that one or more patterns of one or
more
particular features are present in the document.
Thus for example bank note authentication devices can be provided at
relatively low cost
to be associated with tills in shops; banks and post offices, so that at
transaction points
bank notes tendered by the public can be verified before they are accepted.
In the case of a currency note, it may be of further interest to determine
what
denomination it is, and if more than one originating organisation is involved,
it may also
be advantageous to determine which organisation issued the note. Computer
based
document checking facilities of this type can be used as note accepters, can
be used in note
exchangers, and can be used to enable blind persons to discover what bank
notes they have
in their possession.
Description of different encoding techniques
The surface treatment of a substrate in accordance with the invention includes
any
technique which results in lighter and darker regions to be visible in the
surface of a
treated sheet of substrate when illuminated for scanning.
Either or both primary and secondary encodings may be in the form of repeat
pattern
which are distinguishable under appropriate illumination to provide detectable
content in
digital signals obtained by scanning.
(1) Embossing
In a first technique embodying the invention, the substrate may be embossed
during its
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
8
manufacture. Thus it is customary in paper or sheet plastics manufacture to
make the
material smooth enough for printing by passing it through a high pressure nip
between two
steel rollers, a process known as calendaring. By forming one or both of these
rollers
with indentations, a paper or plastics substrate forced therebetween, will be
formed with
an embossing pattern corresponding to the indentations. By suitably encoding
the
embossed features, the substrate will be encoded as required by the invention,
and can
be detected by suitable illumination and convened into digital data signals by
a scanner
for analysis by a data processor.
(2) Surface treatment of lacquered papers
Where a paper or plastics substrate material has mixed therewith a resin or
lacquer or
other material to provide a smooth surface for printing, an encoded structure
can be
formed in the surface such that the actual surface of the substrate is
sufficiently smooth
to accept printing ink to enable a security document to be printed thereon,
but at the same
time contains a fine pattern of less smooth regions, which may be less
receptive of
printing ink.
(3) Impre ng anon
The surface may also be modified by a technique in which selected regions of a
substrate
describe a repeat pattern by being impregnated with a fluid such as a resin,
or lacquer,
such that the optical absorbtion or reflectance characteristics or optical
density of the
substrate is altered sufficiently as between impregnated and non-impregnated
areas as to
be discernable under incident light as during scanning for digitising.
(4) Laser treatment
The surface of the substrate can be etched by a laser beam, so as to produce
cavities or
grooves in the surface to be printed (or awaiting printing). This technique
lends itself to
the production of very fine patterns in the surface of the substrate and since
a laser beam
can be modulated very accurately can be used to introduce depth modulation in
any such
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
9
grooves or cavities as well as or instead of edge or thickness of spacing
modulation.
(5) Watermarking
Watermarks alter the thickness and/or texture of a substrate, which variations
and/or can
be rendered visible under incident light and can be used to form primary
and/or secondary
encoding of the invention. They may be formed in two ways.
In the Fourdrinier paper making method, the wet paper is embossed using an
embossing
roller as it is being formed, thereby impacting a mark in the paper
corresponding to the
embossing. By forming the embossing in a suitable repeat pattern which extends
over the
area of the web, so the paper can be encoded with the watermark pattern.
A second technique for forming a watermark uses the so-called cylinder-mould
method.
In this method the watermark is formed by a cylindrical wire mesh on which is
impressed
"mouldings" in the form of images. During manufacture of the paper, fibres
build up to
a greater or lesser extent on the mesh moundings and where the thickness of
the paper is
greater, this gives a darker effect when viewed in transmission than do
regions which are
thinner and therefore which appear lighter when viewed in transmission.
However where
either types of watermark is just visible in incident light this can be used
to provide the
background coding required by the invention.
In accordance with the invention either watermarking technique may be employed
to apply
a pattern in the surface of a substrate especially a paper substrate, which is
virtually
imperceptible to the naked eye, but which will appear as a low contrast
pattern when
subjected to incident light as where a document is arranged for scanning and
digitising.
The techniques so far described provide a surface encoded substrate which
subsequently
can be printed to form a security document. However some of the encoding
techniques,
eg embossing, may be applied after some or all of the printing of the document
has
occurred.
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
For example embossing may be applied after a title, or other text, or personal
data for
example in the case of an ID document has been printed onto a plain substrate,
and a
surface encoding formed as a post-printing step.
Encoding by embossing can be achieved whilst printing at least some regions of
a
document. Thus the surface encoding may be imparted to the document by so-
called
"blind" intaglio printing, or intaglio printing with colourless ink. In such a
method an
image is printed using a plate containing engraved areas, some of which are
filled with ink
and some of which are left empty in the case of blind intaglio printing. The
engraved
plate, inked as appropriate, is pressed under high pressure against the
substrate so as to
cause the ink to transfer to the substrate. The substrate can become embossed
with the
engraved image, under the pressure applied, with parts of the substrate
surface being
printed, and others merely embossed.
Description of Drawings
In the accompanying drawings:-
Figure 1 shows a banknote substrate physically formed with barcode features in
practice
not discernable to the naked eye;
Figure 2 shows a banknote image printed over the substrate;
Figure 3 is a flow chart of the process for embossing the barcode features on
the substrate;
Figures 4 and 5 show images of the banknote revealed by a computer code
extraction
routine; and
Figure 6 is a flow chart of one possible detection routine.
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
11
Description of Embodiment
Production
The process for physically forming in this case embossing, identification
features on a
banknote (or other security document) substrate will be clear from Figure 3
without further
description.
The resulting substrate is shown in Figure 1, except that in practice the
identification
features, in this case a repetitive barcode pattern, would be invisible to the
naked eye.
The banknote is conventionally printed over the substrate and the result is
shown in Figure
4.
Since in practice the identification features are invisible to the naked eye,
they are not
aesthetically disturbing and do not affect the freedom of design of the
banknote image.
It is to be noted that the banknote design may be printed either before or
after the
identification features physically formed in this case by embossing (Figure
3).
Detection
There are various ways that computer based equipment can detect the aforesaid
identification features and two such methods are described hereinafter.
The encoded document when scanned into a computer, is converted to a digital
format.
This typically means that the image is analysed into red, green and blue
channels for each
picture element or pixel. The colour of the picture element is assigned a
value in each of
these channels on a scale from 0 to 255 (8 bits) typically such that a full
intensity is
assigned to the value 255 and 'no colour' the value 0. Thus, bright white will
be
represented by all three channels having the value 255 and black by a zero
intensity having
the value 0.
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
12
When a real image, such as that of the printed banknote is scanned into the
system, most
of the pixel values will lie in a central region between, say, 230 for the
paper background
and 40 for the darkest print. The pixels relating to the embossed encoding
will be affected
by the shadowing from the embossing caused by the lighting in the detection
device. They
will generally be within a band close to the paper background values.
Assume, for example, that the embossing is shallow so that the shadows are
weak and
mainly within a band of 20 grey scale values relative to that of the paper
background.
It is a simple matter for a computer program to reset all values between a
value just below
that of the paper (in this example, 228) and the bottom of the values relating
to the
encoding band (in this example say, 210) to a value of 10, or even zero (near
black) and
to reset all other values between 210 and 0 in this example to 230 (in other
words the
same colour as the paper background).
This procedure has the effect of eliminating all the printed design features
but not the
encoding and those very weak features associated with the design, which are
usually very
few in number since they cannot be easily seen and would not therefore be
included in the
design for aesthetic reasons. The embossed encoding itself would by this
procedure now
be rendered black (see Figure 5) so that it can be read by a program
especially designed
to recognise the coding. As a simple sample, if the coding were a series of
Alphanumeric
characters such as letters and numbers, an optical character recognition
program could be
used to read the data and determine if it was likely to be a known code.
Alternatively,
more sophisticated image detection techniques could be used, especially if the
coding were
of a more complex type such as that used in digital watermarking for example.
In some
cases, it may be preferred in order to show the encoding only (Figure 6).
Alternatively, the embossed encoding could be extracted using a contrast
enhancement
routine such as is commonly known as ' equalisation' . This is shown in Figure
7. This
type of routine sets the maximum value of the pixels in each channel to 255
and the
minimum value to 0 and then attempts to smoothly redistribute the intervening
pixel values
between the two. This has the effect of increasing the difference between the
pixel values
CA 02357727 2001-07-05
WO 00/45344 PCT/GB00/00129
13
close to the paper background and thus those relating to the code so that they
are easier
to recognise in an image recognition program or routine. This method has the
disadvantage that other design features unrelated to the code are still
present and need to
be disregarded by the recognition routine.
However, more sophisticated routines, can be used which recognise complex
encoding
patterns such as those used for high-level codes in complex images and
patterns.
