EP2761604B1 - Method for examining the production quality of an optical security feature of a valuable document - Google Patents

Description

The present invention relates to a method for checking the manufacturing quality of an optical security feature in or on a section of a value document on the basis of pixel data of an image of the section, a method for checking an optical security feature of a value document and a device for checking an optical security feature of a value document.

In this context, documents of value are understood to be card-shaped and preferably sheet-shaped objects which, for example, represent a monetary value or an authorization and should therefore not be able to be produced by unauthorized persons at will. They therefore have security features that are not easy to produce, in particular to be copied, whose presence is an indication of authenticity, i.e. production by an authorized body. Important examples of such documents of value are identification documents, chip cards, coupons, vouchers, checks and, in particular, bank notes.

Of particular interest are optical security features, which in the context of the present invention are understood to be security features of a value document which show characteristic optical properties when interacting with optical radiation, i.e. electromagnetic radiation in the infrared, ultraviolet or visible spectral range. The optical properties can in particular be remission and / or transmission and / or luminescence properties.

Certain types of security features, also referred to below as human features, are intended to be able to be checked for authenticity without technical aids. Examples of such security features are in particular so-called OVD features, among which im The following security features are understood, which show viewing angle-dependent visual effects or whose optical properties, for example the color, depend on the viewing angle. Such security features can convey a different image impression to a viewer from different viewing angles and, for example, show a different color or brightness impression and / or a different graphic motif depending on the viewing angle. Such modern human traits, however, are not easy to produce. It can therefore happen that value documents are produced with such human characteristics that are ultimately not sufficiently suitable for checking without technical aids. Similar problems can also arise with other optical security features that are difficult to manufacture.

In DE 10 2009 058 850 A1 a method for checking a watermark introduced into a carrier is described. A carrier containing the watermark is illuminated. An image of the carrier is captured as a transmitted light gray value image. A watermark area to be checked within the transmitted light gray value image is defined. A first smoothing filter is applied to the watermark area in order to obtain a first smoothed transmitted light gray value image of the watermark area. A difference image is determined from the watermark area and the first smoothed transmitted light gray value image of the watermark area. A first threshold is defined. The number of pixels of the difference image whose gray value is smaller than the first threshold value is determined. A second threshold is defined. The determined number of pixels is compared with the second threshold value. A first signal is output if the determined number of pixels is less than the second threshold value or a second signal is output, if the determined number of pixels is greater than the second threshold value.

In WO 2004/008380 A1 Methods and systems for identifying banknotes are provided in a two-step process. During training, a set of discriminators is developed using a training set of banknotes representative of banknotes of different issuers and denominations. During an operational phase, a scanned image of a bank note to be identified is correlated or compared with various members of the set of discriminators. The results of the correlations and comparisons are fed to a decision module which either generates an identification code for the bank note or reports an unknown bank note. Images of the banknotes are taken with a spatial resolution of only 10 points per inch. At this resolution, the discrimination tables are reduced to masks and the discrimination process is quickly completed using simple logical or integer arithmetic operations.

In US 2005/0100204 A1 are methods and apparatus for authenticating various substrates including paper-based substrates such as banknotes. Techniques for using security features to generate security codes are disclosed. The security codes are decrypted with a device which has a color recognition subsystem which allows the authenticity of the substrate with the security feature to be verified.

In EP 1 990 779 A2 describes a security device for the identification or authentication of goods. It includes a stochastic Pattern which comprises structures with an average lateral structure size d and is arranged in such a way that an image of at least part of the safety device when treated by 2D Fourier transformation and calculation of a corresponding power spectral density can lead to a peak in a spatial frequency range that is in this range has a position correlated with d and a size distribution value w which, when inverted, correlates with a size distribution of the structures. According to the invention, the value w is less than 2 / d, so that when a coherent light beam is directed onto at least part of the structures, an annular scattering speckle pattern is formed, on the basis of which d and w can be calculated in order to identify or Implement authentication of the device.

The present invention is therefore based on the object of specifying methods for checking the manufacturing quality of optical OVD security features of value documents, which allow a quick and precise checking of the manufacturing quality, as well as creating means for carrying out the method.

The object is achieved firstly by a method for checking, preferably computer-aided, checking the manufacturing quality of a specified optical security feature, preferably OVD security feature, in or on a specified section of a document of value on the basis of pixel data from pixels of a spatially resolved image of the specified section, which are respectively assigned to locations in or on the section and reproduce optical properties of the document of value at the locations. The method checks whether a first number of those pixels or a first proportion of those pixels in the pixels of the image, their pixel data according to a first criterion specified for the security feature within a first reference range specified for the security feature for the pixel data, exceeds a first minimum hit value specified for the security feature, and whether a scatter of the pixel data of those pixels that are within the first reference range according to the first criterion exceeds a first minimum scatter specified for the security feature, and depending on the result of the check Quality signal is formed which only represents an indication of sufficient manufacturing quality if, according to the first criterion, the first number or the first proportion exceed the first minimum hit value and the spread exceeds the first minimum spread, and / or which represents an indication of a manufacturing defect, if the first number or the first proportion does not exceed the first minimum hit value and the spread does not exceed the first minimum spread.

Secondly, the object is achieved by a method for checking the manufacturing quality of a given optical security feature in or on a given section of a value document, in which, in order to capture an image of the given section, the value document is illuminated with optical radiation from an optical radiation source and radiation emanating from the value document is also illuminated a detection device is detected, depending on the detected radiation, pixel data of pixels of the image, which are respectively assigned to locations in or on the section and reproduce optical properties of the document of value at the locations, are formed and in which a method according to one of the preceding claims is carried out in which the formed pixel data are used as the pixel data.

In the case of printed security features, the production quality is preferably understood to mean the print quality. The indication of the adequate manufacturing quality is then an indication of an adequate one Print quality, the indication of the manufacturing defect, an indication of a printing error.

In the case of the method, pixel data of pixels of an image of the predetermined section of a value document are used, in or on which the security feature is formed in the case of a genuine value document. The position and shape of the section can therefore be based on the position of the security feature on a real value document or the shape of the security feature. The section can in particular be specified for a specific type of document of value to be checked, in the case of bank notes in particular a currency and denomination or denomination of the bank notes, and the specified security feature to be checked. The section can be given, for example, by the area of the security feature or only a predetermined part of the area occupied by the security feature. The image can in particular be a partial image of an overall image of the entire document of value.

The pixel data of a respective pixel reproduce optical properties at a location assigned to the respective pixel in the section of the value document. The pixel data for a respective pixel can generally have several components which represent different optical properties.

Two sub-tests are used to check the security feature: On the one hand, it is checked whether the pixel data lie within the first reference area that is specified for the security feature. For this purpose, the predefined first criterion for the pixel data is used, by means of which the position of the pixel data in relation to the first reference area can be determined. This is used to check whether the optical properties of the examined Section of the value document lie within predetermined limits that are predetermined for the security feature. On the other hand, it is checked whether the scatter of the pixel data within the first reference area exceeds the first minimum scatter minimum value specified for the security feature. This means that a check is made as to whether the pixel data in the first reference area are concentrated only in a part of the first reference area or rather are distributed more widely in this area.

The quality signal is then generated as a function of the result of the test. In the case of a data signal, for example by its shape or its level, this reproduces its content, in particular, or shows whether the test has indicated an indication of adequate manufacturing quality and / or whether the check has indicated an indication of a manufacturing defect. The quality signal is preferably formed for each test, ie independently of the result of the test; then there is either an indication of adequate manufacturing quality or an indication of a manufacturing defect. In particular, it is an indication of adequate manufacturing quality only if the first number or the first portion exceeds the first minimum hit value and the scatter exceeds the first minimum scatter. The quality signal can be used to store an indication of sufficient manufacturing quality or an indication of a manufacturing defect in a storage device. The quality notice can be used in an optional further check of the manufacturing quality of the security feature or the check of the manufacturing quality of the entire document of value solely as a criterion for a manufacturing defect, so that the security feature or document of value when there is a reference to a manufacturing defect or if there is no reference to a Sufficient manufacturing quality is classified as defective. It is especially when testing Documents of value with a total of at least two different security features, but it is also possible for the quality signal to be combined in an overall criterion with other quality signals which represent the manufacturing quality of other features of the document of value; then the quality notice is only used as a necessary condition for an adequate manufacturing quality.

Although the number of pixels in the image need only be greater than 5, it is preferably greater than 48, so that the proportion or the number of pixels in the first reference area and their scatter therein are also meaningful.

This enables the testing of optical security features that are characterized by a scattering of optical properties within a predetermined range, which are characteristic of the security feature and are not easy to forge, for example by copying with a color copier or printing with a laser printer. In particular, the method can be used to check OVD security features.

According to a preferred embodiment, the security feature can be a so-called OVD security feature, which can be obtained by printing with a printing ink with pigments whose reflectance properties are influenced by the direction of incidence of optical radiation on a particular pigment particle. Such printing inks are also referred to as “optically variable inks”, hereinafter also referred to as “optically variable printing inks”. A security feature with optically variable printing inks is also understood to mean, in particular, a security feature that is printed with a printing ink that contains pigments, the color of which depends on the direction the lighting and the direction of detection or observation depends.

According to another embodiment, the security feature can be a surface structure embodied in the value document, in particular an embossed structure, with a print embodied on certain flanks of the surface structure or embossed structure, which has an optically variable effect. In the context of the present invention, an optically variable effect is understood to mean an effect in which predetermined optical properties of a structure or a security feature depend on the direction from which this or this is viewed and / or the direction from which the structure or the Security feature for viewing is illuminated, depend; in particular, the optical properties can be colors. Such surface structures in the form of embossed structures are in the applications WO 97/17211 A1 , WO 02/20280 A1 , WO 2004/022355 A2 , WO 2006/018232 A1 described by the applicant. The surface structure, preferably an embossed structure, preferably has curved or angled embossed structural elements in the section which result in a distribution of the optical properties that is difficult to falsify.

In the first method, the test is carried out using a suitable device, preferably computer-aided; In the context of the present invention, “computer-aided testing” is understood to mean any testing with a computer. In the context of the invention, a computer is generally understood to mean a data processing device which processes the pixel data. In particular, for this purpose the data processing device can be an FPGA, a microcontroller or microprocessor, in particular also a DSP, or a combination of these components include or have only one of these components. It can furthermore comprise a memory in which a program is stored, the first method according to the invention being executed when it is executed on the computer.

The invention therefore also relates to a computer program with program code means in order to carry out the first method according to the invention when the program is executed on a computer.

The invention also relates to a computer program product with program code means which are stored on a computer-readable data carrier in order to carry out the first method according to the invention when the computer program product is executed on a computer.

The invention also relates to a test device for testing a predetermined security feature of a document of value by means of the method according to the invention with an optical sensor for capturing an image with pixels, the pixel data of which are assigned to locations in or on the section and reproduce optical properties of the document of value at the locations , a memory for storing a computer program according to the invention and a computer for executing the computer program with images captured by the sensor.

In principle, it may be sufficient to only carry out the specified partial examinations. Preferably, however, it is additionally checked whether a second number of those pixels or a second proportion of those pixels in the pixels of the image, their pixel data according to a second criterion predetermined for the security feature, within a predetermined one for the security feature second reference range, exceeds a predetermined second minimum hit value for the security feature. The quality signal can then be formed in such a way that it only represents an indication of sufficient manufacturing quality if the second number or the second proportion also exceeds the second minimum hit value, and / or that it represents an indication of a manufacturing error if the second Number or the second proportion does not exceed the second minimum hit value. This variant offers the advantage that a more differentiated check of the security feature is possible.

In a preferred development, it can be checked whether a scatter of the pixel data of those pixels which, according to the second criterion, lie within the second reference area exceeds a second minimum scatter specified for the security feature. The quality signal can then be formed in such a way that it only represents an indication of adequate manufacturing quality if the scatter of the pixel data in the second reference area also exceeds the second minimum scatter, and / or that it represents an indication of a manufacturing error if the scatter of the pixel data in the second reference area does not exceed the second minimum scatter. This embodiment allows, in particular, the testing of security features which have at least two different characteristically scattering optical properties.

In principle, the pixel data can reproduce any optical properties and, for this purpose, have a corresponding number of components for each location that represent the optical properties. Although the number of components is not limited in principle, it is preferably less than six, but is at least two.

In a first embodiment, the pixel data for one pixel or one location each have components that reproduce reflectance or transmission properties in at least two, preferably three different wavelength ranges, preferably within the visible spectral range, or at least two, preferably three colors. For this purpose, the illumination with optical radiation and the detection of radiation can take place in such a way that the pixel data for one pixel or one location each have the components mentioned. In the case of a representation of colors, preferably at least two, better still three, color components are used, although color representations in higher-dimensional color spaces are also possible. In particular, in one variant, the pixel data need not have any other components apart from color components in a three-dimensional color space. This allows the test to be carried out quickly.

In a second embodiment, the pixel data for one pixel or one location each have components that reflect reflectance and / or transmission properties in at least two, preferably at least three different wavelength ranges within the visible spectral range or at least two, preferably at least three colors and reflectance and / or represent transmission properties in a further wavelength range at least partially outside the visible spectral range, preferably in the infrared spectral range. For this purpose, the illumination with optical radiation and the detection of radiation can take place in such a way that the pixel data for one pixel or one location each have the components mentioned. The use of such pixel data allows in particular an examination of security features which are also characterized by characteristic properties in the non-visible optical spectral range. In the case of a representation of colors, the at least two or better three color components are preferably used here as well. In particular, in one variant, the pixel data need not have any further components apart from color components in a two- or three-dimensional color space and a component for the optical properties in the non-visible spectral range. This allows the test to be carried out quickly.

In these two embodiments, if the pixel data include color data or color components, color values in any color space can in principle be used as color data. For example, an RGB or HSI color space can be used as the color space. Preferably, however, those pixel data that represent properties in the visible spectral range or color values are transformed into a device-independent color space, preferably a Lab or Luv color space, particularly preferably a CIE Lab or CIE Luv color space, before testing, if they do not already exist in such a color space, or pixel data in a device-independent color space, preferably a Lab or Luv color space, are used as pixel data that represent properties in the visible spectral range or color values. On the one hand, this offers the advantage that a particularly simple adaptation of the method to different sensors, by means of which the pixel data are recorded, is made possible; on the other hand, the first and the second criterion can be determined more easily.

The first and possibly the second reference area and the first or second criterion, by means of which it is checked whether pixel data lie within the respective reference area, can be dependent on one another. In particular, the reference range can be given implicitly by the respective criterion.

The first and / or, if used, the second criterion for determining whether pixel data lie within the first and / or, if used, second reference area can provide, for example, that the reference area is also n-dimensional for pixel data with n components and accordingly the pixel data of a pixel lie in the reference area if the point given by the n components lies in the reference area. Here, n is a natural number greater than 1. The first and / or, if used, the second criterion for determining whether pixel data lie within the first and / or, if used, second reference area can, for example, also provide that pixel data in a reference area if only at least two predefined components of the available components lie within a correspondingly low-dimensional reference area.

In particular, when using pixel data that reproduce colors, a region that extends at least in one plane of a color space or lies in a plane of the color space that runs parallel to two axes of the color space, the different colors, can preferably be used as the first reference region correspond. The area can therefore be given by an area in the plane, ie extend only in the plane, or at least be three-dimensional and intersect the plane, the section in the plane being an area. The area of the area in the plane is finite and greater than 0. In particular, when using a Lab or Luv color space, the plane can be the ab or uv plane. This embodiment allows the testing of security features which show a color shift effect dependent on the viewing angle, preferably security features with optically variable printing inks.

Alternatively or additionally, in the event that the pixel data also reproduce at least one optical property outside the visible spectrum, a region can be used as the first or second reference region which extends at least in a plane that is parallel to an axis that is a luminance or Corresponds to brightness in one or the color space, and an axis which corresponds to a brightness or intensity in the further wavelength range at least partially outside of the visible spectral range runs. The term "extends" is understood here analogously to the term "extends" in the previous paragraph. Luminance or brightness is understood to mean the L component when using a Lab or Luv color space, for example.

To check whether the number of pixels or the proportion of pixels in a respective reference area exceeds the minimum hit value, a score can be determined, for example, which reproduces the number of those pixels in the image or the proportion of those pixels in the image that are after the security feature predetermined criterion lie in at least one predetermined reference range for the security feature for the pixel data. The hit rate can be given by the proportion or the number or a monotonic function of the proportion or the number in the range of the expected values of the proportion or the number. In particular, for a given resolution of the image, the proportion will be proportional to the number. Which of the alternatives is used depends, among other things, on the dimension of the reference area determined by the security feature and the type of test.

In principle, any quantities that reflect the scatter in the respective reference range can be used to characterize the scatter.

To check whether the respective spread of the pixel data within the respective reference area is greater than the respective minimum spread, a respective degree of spread can preferably be determined, which represents a spread of the pixel data in the respective reference area or predetermined components of the pixel data in the respective reference area. Particularly preferably, only those components of the pixel data are used to determine the scatter which are also used to check whether pixel data are in the respective reference area. The degree of dispersion therefore indicates whether the pixel data or components are concentrated in a part of the reference area or rather distributed more widely in this area. The respective minimum scatter can then be determined as a function of the respective degree of scatter.

For example, a function of the pixel data to be used for the determination or at least one of the components of this pixel data, which supplies a single numerical value, can be used as the degree of dispersion. In this case, the respective minimum scatter can be given by a respective minimum scatter value: The scatter exceeds the minimum scatter if the value of the function exceeds the respective minimum scatter value. The spread then exceeds the minimum spread.

However, a function of the pixel data to be used for the determination or at least one of the components of this pixel data, which has at least two components, can also be used as the degree of dispersion. These can represent, for example, scattering of the pixel data in at least two, preferably mutually orthogonal, directions in the color space in which the pixel data or color subspace in which the relevant components of the pixel data are located. The minimum scatter can then be determined by a corresponding number of threshold values or minimum scatter values be given. To check whether the respective scatter of the pixel data within the respective reference area is greater than the respective minimum scatter, scatter values can then be used for at least two, preferably mutually orthogonal, directions in the color space in which the pixel data, or color subspace in which the relevant components of the pixel data are to be determined. Each of the determined scatter values can then be compared with a corresponding threshold value.

For example, a variance and / or a covariance of the pixel data or components of the pixel data located in the first or second reference area or a monotonic function of the variance or covariance can be used as a function for the first and / or second variance or first and / or second variance be used.

However, it is also possible that a scatter of the projection of the pixel data or pixel data components in the reference area onto a predetermined direction of the reference area is used as the scatter. In this case, for example, the variance of this projected data can be used as a measure of dispersion. The direction in the reference area is preferably specified as the direction along which the greatest scatter is to be expected for genuine documents of value. This direction can be determined by examining real value documents as a reference. If the reference area has the shape of an ellipse or an ellipsoid, for example, the direction of the longest main axis of the ellipse or of the ellipsoid can be used as the direction.

A quality criterion can then be checked which shows whether, on the one hand, the first number represented by the first hit measure or the first portion represented by the first hit measure is for the security feature predetermined first minimum hit value and, on the other hand, the scatter represented by the first degree of scatter exceeds a first minimum scatter predetermined for the security feature, for example given by at least one minimum scatter value. This minimum value and the minimum scatter can be determined, for example, by measurements on specified genuine value documents of sufficient quality. The quality criterion can be formulated differently depending on the type of dimensions. If a measure is a monotonously increasing function of the proportion or the number or the spread, it can be checked, for example, whether the measure exceeds the corresponding minimum value. If, on the other hand, a measure is a monotonically falling function of the proportion or the number or the scatter, it can be checked, for example, whether the measure falls below a limit value corresponding to the minimum value. If, for example, the reciprocal value of the first number is used as the first hit rate, the quality criterion is met if the hit rate falls below a reciprocal of the minimum value which would have to be exceeded if the number were used as the hit rate.

When checking whether the second minimum hit value or the second minimum scatter, for example at least a second minimum scatter value, has been exceeded, the procedure can be analogous. The quality signal is then formed in such a way that it additionally reflects whether the second number represented by the second measure of hits or the second portion represented by the second measure of hits has a predetermined second minimum hit value and, if used, the scatter represented by the second measure of dispersion a predetermined second Exceed the minimum spread. The quality signal can then be formed in such a way that it additionally only represents the indication of sufficient manufacturing quality if the second number or the second component is additionally the second Minimum hit value and, if used, the spread exceed the second minimum spread, for example given by at least one second minimum spread value, and / or that it is an indication of a manufacturing error if the second number or the second proportion does not exceed the second minimum hit value and / or the second variation falls below the second minimum variation.

The invention also relates to a test device for testing a predetermined security feature, preferably an OVD security feature, a document of value by means of the method according to the invention with an optical sensor for capturing an image with pixels, the pixel data of which are assigned to locations in or on the section and optical Reproduce properties of the document of value at the locations, a memory for storing a computer program according to the invention and a computer for executing the computer program with images captured by the sensor.

The method according to the invention has the advantage that no complex optical sensors are necessary to acquire the pixel data. For example, a spatially resolving sensor for capturing a color image, particularly preferably additionally for capturing an image in the non-visible, optical spectral range, can be used to capture the image or the pixel data. The value document can preferably be transported past an illumination source which emits optical radiation which strikes the value document as at least one beam of rays converging with respect to a plane of convergence. A bundle of optical radiation that is convergent with respect to a plane of convergence is understood to mean a bundle of rays whose rays project a convergent bundle of rays onto the plane referred to as the plane of convergence results. The plane of convergence can preferably run parallel to the transport direction and orthogonal to the plane of the document of value. Particularly preferably, the lighting device generates a lighting strip on the document of value extending transversely to the transport direction, the optical radiation projected geometrically in a plane transverse to the transport direction and orthogonally onto a plane of the document of value not falling parallel onto the document of value.

The value document can also be illuminated by a bundle of optical radiation convergent with respect to a convergence plane from only one direction of illumination, and the radiation emanating from a respective illuminated location can only be detected from one direction of detection. The direction of illumination is understood to mean the direction obtained by averaging over all rays of the bundle. The direction of illumination and / or the direction of detection and / or the plane of convergence preferably enclose an angle of less than 5 ° with a normal to a plane of the document of value. This is especially true when checking OVD security features with optically variable printing inks. To check security features that have an embossed structure with a pressure formed on certain flanks of the embossed structure, it can be preferred that the direction of illumination and / or the direction of detection with a normal to a plane of the value document at an angle between 0 °, preferably 5 °, and 15 °.

The elements which, in the case of OVD security features with optically variable printing inks or security features which have a surface structure, preferably an embossed structure with a print formed on certain flanks of the embossed structure, cause the optical properties to be scattered, are generally very small. Nevertheless, the spread is good To be able to capture, the resolution of the image in the method is preferably better than 0.4 mm × 0.4 mm, particularly preferably better than 0.3 mm × 0.3 mm.

Fig. 1

eine schematische Darstellung einer Wertdokumentbearbeitungsvorrichtung,

Fig. 2a und b

schematische Darstellungen eines optischen Sensors der Wertdokumentbearbeitungsvorrichtung in Fig. 1 quer zu einer Transportrichtung, in der Wertdokumente transportiert werden, und von oben auf eine Transportebene, in der Wertdokumente transportiert werden,

Fig. 3

eine schematische Darstellung eines Beispiels für ein zu untersuchendes Wertdokument in Form einer Banknote,

Fig. 4

eine schematische Darstellung eines Beispiels für ein zu prüfendes optisches Sicherheitsmerkmal des Wertdokuments in Fig. 3

Fig. 5

ein vereinfachtes Ablaufdiagramm für eine erste Ausführungsform eines Verfahrens zum Prüfen eines optischen Sicherheitsmerkmals in oder auf einem Abschnitt eines Wertdokuments, das in der Wertdokumentbearbeitungsvorrichtung in Fig. 1 mit dem Sensor in Fig. 2a und 2b durchgeführt werden kann,

Fig. 6

eine schematische Darstellung von Verteilungen von Pixeldaten in einer R-B-Ebene und einer G-IR-Ebene für das Sicherheitsmerkmal in Fig. 4,

Fig. 7

ein vereinfachtes Ablaufdiagramm für eine zweite Ausführungsform eines Verfahrens zum Prüfen eines optischen Sicherheitsmerkmals in oder auf einem Abschnitt eines Wertdokuments,

Fig. 8

ein vereinfachtes Ablaufdiagramm für eine dritte Ausführungsform eines Verfahrens zum Prüfen eines optischen Sicherheitsmerkmals in oder auf einem Abschnitt eines Wertdokuments,

Fig. 9

eine schematische Darstellung von Verteilungen von Pixeldaten in einer H-S-Ebene und einer I-IR-Ebene für das Sicherheitsmerkmal in Fig. 4,

Fig. 10

ein vereinfachtes Ablaufdiagramm für eine weitere Ausführungsform eines Verfahrens zum Prüfen eines optischen Sicherheitsmerkmals in oder auf einem Abschnitt eines Wertdokuments,

Fig. 11

ein vereinfachtes Ablaufdiagramm für eine weitere Ausführungsform eines Verfahrens zum Prüfen eines optischen Sicherheitsmerkmals in oder auf einem Abschnitt eines Wertdokuments, und

Fig. 12

eine schematische Darstellung von Verteilungen von Pixeldaten in einer a-b-Ebene und einer L-IR-Ebene für das Sicherheitsmerkmal in Fig. 4.

The invention is explained further below by way of example with reference to the drawings. Show it:

Fig. 1

a schematic representation of a value document processing device,

Figures 2a and b

schematic representations of an optical sensor of the value document processing device in FIG Fig. 1 transversely to a transport direction in which value documents are transported and from above onto a transport level in which value documents are transported,

Fig. 3

a schematic representation of an example of a value document to be examined in the form of a bank note,

Fig. 4

a schematic representation of an example of an optical security feature to be checked of the value document in FIG Fig. 3

Fig. 5

a simplified flowchart for a first embodiment of a method for checking an optical security feature in or on a section of a document of value that is in the document of value processing device in FIG Fig. 1 with the sensor in Figures 2a and 2b can be carried out,

Fig. 6

a schematic representation of distributions of pixel data in an RB plane and a G-IR plane for the security feature in Fig. 4 ,

Fig. 7

a simplified flowchart for a second embodiment of a method for checking an optical security feature in or on a section of a value document,

Fig. 8

a simplified flowchart for a third embodiment of a method for checking an optical security feature in or on a section of a value document,

Fig. 9

a schematic representation of distributions of pixel data in an HS level and an I-IR level for the security feature in Fig. 4 ,

Fig. 10

a simplified flowchart for a further embodiment of a method for checking an optical security feature in or on a section of a value document,

Fig. 11

a simplified flowchart for a further embodiment of a method for checking an optical security feature in or on a section of a value document, and

Fig. 12

a schematic representation of distributions of pixel data in an ab plane and an L-IR plane for the security feature in Fig. 4 .

A device 10 for quality checking and sorting documents of value, in the example banknotes, in Fig. 1 serves, inter alia, to check the manufacturing quality of documents of value 12 in the form of banknotes and for sorting depending on the result of the inspection of the manufacturing quality. The device 10 has an input compartment 14 for inputting documents of value 12 to be processed, a separator 16 that can access documents of value 12 in the input compartment 14, a transport device 18 that transports documents of value along a transport path 22 and a switch 20 at a junction of the transport path 22, after the switch 20 at the end of one of the two transport path branches an output compartment 26 and at the end of the other of the two transport path branches a banknote shredder 28. Along the transport path 22 given by the transport device 18 is in front of the switch 20 and After the singler 16, a sensor arrangement 24 is arranged, which serves to detect properties of individually supplied documents of value 12 and to form sensor signals which reproduce the properties. A control device 30 is connected at least to the sensor arrangement 24 and the switch 20 via signal connections and is used to evaluate sensor signals from the sensor arrangement 24, in particular to check the manufacturing quality of documents of value detected by the sensor arrangement 24, and to control at least the switch 20 as a function of the Result of the evaluation of the sensor signals.

For this purpose, the sensor arrangement 24 comprises at least one sensor; In this embodiment, only one optical sensor 32 is provided for spatially resolved detection of color properties and IR properties, which detects optical radiation remitted by the value document. In other exemplary embodiments, at least one further sensor, e.g. for another property, can be provided.

While a document of value is being transported past, the sensor 32 records an overall image of the document of value in four spectral ranges accordingly the three color channels red, green and blue and in the infrared spectral range (IR channel), which is represented by corresponding sensor signals.

From the analog and / or digital sensor signals of the sensor 32, the control device 30 determines pixel data of pixels of the overall image during a sensor signal evaluation which are relevant for checking the banknotes with regard to their manufacturing quality. For this purpose, the control device 30 has an evaluation device 31 which, in the example, is integrated into the control device 30, but in other exemplary embodiments can also be part of the sensor arrangement 24, preferably the sensor 32.

In addition to a corresponding interface for the sensor 32, the control device 30 has a processor 34 and a memory 36 connected to the processor 34 in which at least one computer program with program code is stored Evaluates sensor signals, in particular for checking the manufacturing quality of a checked document of value, and thereby executes, inter alia, a method described below using the sensor signals or the pixel data. In a second function, the processor controls the device or, according to the evaluation, the transport device 18. The evaluation device 31 therefore forms a computer within the meaning of the present invention. The control device 30 also has a data interface 37.

During operation, the evaluation device 31, more precisely the processor 34 therein, can use a predetermined criterion for the manufacturing quality after determining pixel data Check the value document in which at least some of the recorded properties and reference data are included.

Depending on the ascertained manufacturing quality, the control device 30, in particular the processor 34 therein, controls the transport device 18, more precisely the gate 20, in such a way that the checked document of value is transported to the output compartment 26 for storage in the output compartment 26 or for destruction to the bank note destruction device 28 in accordance with its determined manufacturing quality becomes.

The device 10 also has a user interface 35 which is connected to the control device via a signal connection and by means of which control device 30 can acquire control commands from a user which the user inputs via the user interface 35. In the example, a touch-sensitive display device or a touchscreen is provided as the user interface 35, which is controlled by the control device 30 to display predetermined information, and its signals that indicate the operation by a user, i.e. H. here touches of a user, represent, detected.

To check the production quality of freshly printed documents of value 12, ie after their production but before issuing by a central bank, the type, ie the currency and denomination, of the documents of value to be processed is first recorded by means of the user interface 35 and stored in the control device 30. The possible types of value documents are specified. Thereafter, documents of value 12 inserted as a stack in the input compartment 14 are separated by the separator 16 and fed individually to the transport device 18, which feeds the separated documents of value 12 to the sensor arrangement 24. This captures optical Properties of the value documents 12, in the example the color image with an additional IR channel, with sensor signals being formed which reproduce the corresponding properties of the value document. The control device 30 detects the sensor signals, determines a production quality of the respective document of value as a function of these and, depending on the result, controls the gate 20 so that the examined documents of value are fed to the output compartment 26 or to the bank note destruction device 28 according to their determined production quality. When a value document is fed to the bank note destruction device 28, it is destroyed directly.

The sensor 32 is designed to capture images for three colors and IR radiation. In the example, it is designed as a line sensor which, while a document of value is being transported past the sensor 32, comprises a sequence of line images which result in an image of the document of value in a direction transverse to the direction of the line, ie in the direction of transport. In the present example, it includes Figures 2a and 2b Shown schematically only in an extremely simplified manner, an illumination device 38 for illuminating a strip running transversely to the transport direction T in a transport plane E (in Figure 2b parallel to the plane of the drawing) for the document of value 12 or in a plane of the document of value 12 with convergent, white light and IR radiation during the transport of the document of value over its entire extent transversely to the transport direction T. The sensor 32 also includes one of the lighting device 38 emitted bundle of rays arranged detection device 40, which shadows part of the radiation of the lighting device 38.

In order to enable a direction of illumination B and a direction of detection D orthogonal to a plane of the document of value, the illumination device has 38 via several radiation sources 39 for visible light and IR radiation arranged linearly transversely to the transport direction T, as well as two deflection elements 41 for bundling the radiation onto a strip in a transport plane for the value document 12 or on the value document 12, ie to generate an illumination strip. As in Fig. 2a As can be seen, the lighting device 38 generates a projected onto an orthogonal to the transport plane E (in Fig. 2a the plane of the drawing) and the plane of convergence, which runs parallel to the direction of transport T, is a convergent beam. The emitted bundle of rays is initially divided by the detection device 40 into two sub-bundles, which are brought together again by the deflection devices 41 to form a convergent bundle of rays. The maximum opening angle α between a perpendicular to the transport plane or the detection direction D and the outermost beam of the bundle in the plane is at most 40 °, preferably at most 30 °. In contrast, in a plane orthogonal to the transport direction T, the rays are not strongly bundled; rather, the radiation is diffuse. The direction of illumination B results as the mean over the directions of all rays of the bundle and, because of the symmetrical course of the partial bundles, is essentially parallel to the detection direction D.

In the example, four line cameras 42, 42 ', 42 ", 42'"'with red, green, blue and IR filters arranged in the beam path in front of them for the detection of red, green or blue or IR components of the optical radiation of the lighting device 38 remitted by the document of value. Each of the line cameras has a respective detector line with photodetection elements arranged in lines, in front of which the filter is arranged that corresponds to the color component of the remitted optical to be detected by the respective line camera Radiation corresponds. The sensor 32 can also include further optical elements, in particular for imaging or focusing, which are not shown here. The detector rows of photodetection elements are arranged parallel to one another. The sensor 32 is therefore constructed and arranged in such a way that the value document is illuminated with optical radiation from a direction B orthogonal to the plane of the value document or parallel to a normal to the transport plane in which the value document is transported and emanating from the value document 12 , remitted optical radiation is detected from a direction D orthogonal to the plane of the document of value or parallel to the direction of illumination.

To capture a color image of a document of value 12, it is transported past the sensor 32 in transport direction T at constant speed, with the line cameras 42, 42 ', 42 "and 42'" 'recording intensity data resolved in terms of location and color or spectral range at constant time intervals The intensity data represent pixel data which describe the properties of pixels 44 of a line image which reproduces the line-shaped area of the document of value 12 detected by the sensor 32. By placing the line images together according to the chronological order of the detection, ie corresponding assignment of the pixel data then an overall image of the document of value is obtained with pixels to which pixel data are assigned, which reproduce or represent optical properties of the document of value, namely color values for red, green, blue and the IR remission.

An image captured by the sensor 32 is therefore composed of pixels arranged in a rectangular matrix and is described by the pixel data. In the illustration of the image of a document of value 12 in Fig. 3 For the sake of clarity, only some of the pixels 44 are shown which are also shown greatly enlarged. In the exemplary embodiment, the resolution of the sensor 32 is at least so great that a pixel corresponds to an area of at most 0.3 mm × 0.3 mm on the value document. _{Each of the pixels is assigned color values r i} , g _i , b _i and IR _i for red, green and blue and IR remission as pixel data in addition to a number or number i, which reflects the position in the image. It is assumed that the signal processing device 44, after calibration, can generate and generate RGB color values from detection signals of the detector lines 42, 42 ', 42 "and 42"'. For easier representation, the property data can be converted into a vector V given by the components (i, r _i , g _i , b _i , IR _i ) _i = 1, N, where N is the number of pixels.

To check the value document, in the example, among other things, an optical security feature 46 is checked, which in this example is given by the value indication “100” in OVI print. If a viewer tilts the document of value in a suitable direction, he recognizes a change in the color of the print or the indication of value.

The actual security feature 46 is located in a section 48 of the document of value, which is shown in Fig. 4 and Fig. 5 is indicated by hatching. In Fig. 5 the pixels are in a higher resolution than in Fig. 4 shown, but do not represent real conditions due to the schematic representation.

To check the documents of value, a program is stored in the memory 36 in a section serving as part of the evaluation device 31 and thus in this example in the control device 30, which when executed by the evaluation device 31, ie here the processor 34, the following Carries out steps of a method for checking the manufacturing quality of a specified security feature of value documents.

In step S10, the evaluation device 31 uses the sensor 32 to acquire an overall image of the document of value to be checked, the type of which, i.e. the currency and denomination, is known after the input by the user described above and is stored in the control device 30.

In this example, the sensor 32 detects overall images of the documents of value, more precisely pixel or image data representing the overall images, in the example full-area images with three color channels, namely red, green and blue (RGB channels) and an IR reflectance value; the type of pixel data has already been described above. The pixel data thus indicate optical properties of the value document as a function of the location on the value document. The pixel data are transmitted to the evaluation device 31 and recorded by it. Depending on the type of sensor, preprocessing of the acquired data in the sensor 32 or the evaluation device 31 can also be carried out in this step, in which the image data is transformed, in particular filtered, for example to compensate for background noise.

Then, in step S12, the processor 34 or the evaluation device 31 determines, depending on the type of the value document, the position of the section of the value document in which the optical security feature must be found in the case of a genuine value document. For this purpose, the position of the edges of the document of value can first be recognized, in relation to which the position of the security feature can be given. The section or the image of the section is in Fig. 4 marked by hatching. For this purpose, the evaluation device 31 determines one of the for the section corresponding to the security feature predetermined evaluation area 50 or ROI (region of interest) in the image, which results from the known position of the security feature on genuine value documents of the specified type relative to the outlines of the value documents and an outline of the value document determined in the image. For this purpose, the evaluation device 31 can in particular use the results of the search or detection of edges of the document of value in the overall image in order to then position the ROI in the overall image as a function of the position of the edges in the overall image, ie to select corresponding pixel data

From the overall image, the processor 34 then determines in step S16 the pixel data of the pixels of the overall image which correspond to locations in this section; this corresponds to a determination of an image with the security element.

In steps S18 to S24, the evaluation device 31 then carries out steps for the actual checking of the security feature.

In the present example, two reference areas in which pixel data should be located are used to check the security feature. The first reference range lies in the RB level of the RGB color space (cf. Fig. 6 (a) ), the second in a plane that is spanned by the G color values and the IR reflectance axis (cf. Fig. 6 (b) ).

In the present example, the reference areas and the parameters for the criteria have been determined before the method is carried out by using the pixel data as reference documents for a predetermined set of other freshly printed documents of value of the type with sufficient print quality for those pixels that are also used in the test. The mean values of the RB components or G-IR components and their variances and covariances are then determined for this pixel data to determine the respective reference area and the respective criterion according to which pixel data lie within the respective reference area, assuming a normal distribution. The first reference range and the first criterion are then given by determining the Mahalanobis distance in the RB plane for the pixel data of a pixel relevant to the first criterion, the R and B components, and checking whether the Mahalanobis is -Distance is smaller than a predetermined first maximum distance value. The parameters for calculating the Mahalanobis distance depend in a known manner on the previously determined mean values, variances and covariances. Accordingly, the maximum distance value was determined on the basis of the reference documents. Analogously, the second reference range and the second criterion are given in that for pixel data of a pixel, here the G and IR components, the Mahalanobis distance in the G-IR plane, which is dependent on the corresponding mean values, variances and covariances, is determined and checked whether the Mahalanobis distance is smaller than a predetermined second maximum distance value that was determined for the reference value documents. In the present example, the proportion itself is used as the hit measure for the proportion of the pixel data that lie within the respective reference area. Therefore, a minimum hit value is defined for each of the reference areas, which must be exceeded by the hit size, in this case the portion of the pixel data in the respective reference area and which is characteristic of a security feature with sufficient manufacturing quality or a value document with such a security feature. Such a minimum hit value can be determined by examining the reference value documents.

In other exemplary embodiments, instead of the Mahalanobis distance, its square can be used in the case of a maximum square distance value.

In the present exemplary embodiment, the scatter of the pixel data that lie within the first reference range is also determined and compared with a minimum scatter value that represents the minimum scatter. The total variance, i.e. the sum of the variances of the R and B components, is used as the variance or variance measure. In order to determine the minimum dispersion value, the total variance, i.e. the sum of the variances of the R and B components, is determined as the first degree of dispersion for each of the reference value documents for the pixel data within the first reference area. From the distribution of the total variances determined, a mean dispersion value is then determined as a minimum dispersion value which must be exceeded by a first degree of dispersion determined for a security feature to be checked so that the manufacturing quality of the security feature can be considered sufficient. With this definition, the results for the scatter in the case of value documents whose security feature does not have an adequate manufacturing quality can also be used, if such exist.

To check the security feature, the evaluation device 31 therefore determines in step S18 which proportion of the pixel data for pixels corresponding to locations in the section 48 are within the first reference area by calculating the Mahalanobis distance in the RB plane for each pixel and using is compared to the maximum distance value. If the Mahalanobis distance is less than or equal to the maximum distance value, the pixel data are in the first reference area, otherwise outside. After determining the Proportion, the proportion is compared with the specified first minimum hit value.

In step S20, the evaluation device 31 or the processor 34 checks whether a first scatter of the pixel data that lie within the first reference area is greater than a predetermined minimum scatter, in this example given by a first minimum scatter value. This sum is compared with the specified first minimum dispersion value.

In step S22, the evaluation device 31 or the processor 34 then determines, in accordance with step S24, the proportion of that pixel data of the pixels used to check the security feature, ie the pixels in the section 48 that lie within the second reference area, by using for the pixel data of a respective one of the It is checked in each pixel whether the Mahalanobis distance in the G-IR plane is smaller than the corresponding second maximum distance value. If the proportion is determined, the processor 34 checks whether it exceeds the corresponding second minimum hit value.

In step S24 the evaluation device 31 or the processor 34 forms a quality signal as a function of the tests in steps S18 to S22, which, for example by its level or its shape, gives an indication of sufficient manufacturing quality, ie whether the security feature is genuine is viewed or not. A corresponding value is stored in the memory 36 with the quality signal. The quality signal is formed in such a way that it only provides an indication of sufficient manufacturing quality if the first number or the first portion exceeds the first minimum hit value, the first scatter exceeds the first minimum scatter value and the second portion exceeds the second minimum hit value.

A basis of the procedures in Figure 5 is in Fig. 6 illustrated. The distributions of pixel data of pixels corresponding to an OVI area in the RB color plane and the G-IR plane are shown there for a bank note. What can be seen is a typical scattering of the pixel data for the OVI element, which lies within an elliptical curve that represents a curve of equal Mahalanobis distances. If a normal copier color were used to falsify the security feature, pixel data could perhaps result which had the same mean value in the RB plane, but not the characteristic dispersion. The same applies in the example to the pixel data in the G-IR plane.

A second embodiment in Fig. 7 differs from the first exemplary embodiment in that the evaluation device 31 carries out, as an additional step S28, a check as to whether the scatter of the pixel data within the second reference area exceeds a second minimum scatter value specified for the security feature. The second minimum dispersion value was previously determined analogously to the first minimum dispersion value. The total variance in the G-IR plane is used here as the degree of dispersion, ie the sum of the variances of the G components and the IR components of those pixel data that lie in the second reference range. The second minimum dispersion value can be determined analogously to the first exemplary embodiment.

On the other hand, the evaluation device 31 executes step S26 'instead of step S26. This differs from step S26 solely in that the quality signal is formed in such a way that it only provides an indication of adequate manufacturing quality if, in addition to the conditions in the first exemplary embodiment, there is also the scattering of the pixel data exceeds the predefined second dispersion minimum value within the second reference range. This leads to a further increased accuracy of the test in the case of optical security features, which also have a typical scatter in the G-IR properties.

Further exemplary embodiments differ from the first exemplary embodiments in that a step S18 is provided in which a transformation of the color components into another color space, in the example the HSI color space, is provided. Fig. 8 shows a corresponding variant of the first embodiment, Fig. 9 a Fig. 6 corresponding representation.

Steps S20 to S26 are adapted to the other color space; in particular, the reference ranges and the corresponding criteria are adapted accordingly. For them, therefore, in Fig. 8 the same reference numerals are used as in the first exemplary embodiment. The chroma (hue) H, the saturation S and the intensity I are now used as pixel data in the HSI color space. Method steps S20 to S26 correspond formally to those of the corresponding steps of the first exemplary embodiment, with a and b being replaced by H and S and the reference areas, for example, correspondingly Fig. 9 can be chosen.

An exemplary embodiment for the HSI color space corresponding to the second exemplary embodiment results analogously.

Further embodiments in the Figures 10 to 12 differ from the previous exemplary embodiments in that, on the one hand, the signal processing device 44 of the sensor generates color values after calibration from detection signals of the detector lines 42, 42 ', 42 "and 42"' can and generated, which can be used in good approximation as color coordinates in the standardized CIE XYZ color space. On the other hand, a step S18 'is provided after step S16 of the method, in which the pixel data are transformed into a device-independent color space, in the example another CIE color space, so that the following steps can be carried out in a corresponding manner, in particular by specifying the Reference ranges and the criteria are adapted.

In the basically optional but advantageous step S18, the computer 34 transforms at least the pixel data for the section into a device-independent color space, in the example the CIE Lab color space. In the example, all pixel data of the overall image are transformed. In other exemplary embodiments, this step can also be carried out together with one of the preceding steps.

The pixel data in the CIE-Lab color space are then used for the following process steps. These steps are identified in the figures by the use of a "T" instead of an "S", but do not differ from the steps described above except for the use of corresponding adapted reference areas and criteria for the pixel data being in the respective reference area Embodiments.

To check the security feature, two reference areas are used in which pixel data should be located. The first reference area lies in the ab plane of the CIE-Lab color space (see Fig. 13 (a)), the second in a plane that is spanned by the luminance axis of the CIE-Lab color values and the IR reflectance axis ( see Fig. 13 (b)). In Figs. 13 (a) and 13 (b), for a bill, the distributions of pixel data of pixels corresponding to an OVI area are in the ab color plane and the L-IR plane shown. What can be seen is a typical scattering of the pixel data for the OVI element, which lies within an elliptical curve that represents a curve of equal Mahalanobis distances. If a normal copier color were used to falsify the security feature, pixel data could perhaps result which had the same mean value in the ab plane, but not the characteristic spread. The same applies in the example to the pixel data in the L-IR plane.

The reference areas and the parameters for the criteria have been determined before the method is carried out in that, for a given set of other freshly printed documents of value of the relevant type as reference documents, the pixel data for those pixels are recorded which are also used in the check. The mean values of the ab components or L-IR components and their variances and covariances are then determined for this pixel data to determine the respective reference area and the respective criterion according to which pixel data lie within the respective reference area, assuming a normal distribution. The first reference range and the first criterion are then given by determining the Mahalanobis distance in the ab plane for the pixel data of a pixel relevant to the first criterion, the a and b components, and checking whether the Mahalanobis distance is is smaller than a predetermined first maximum distance value. The parameters for calculating the Mahalanobis distance depend in a known manner on the previously determined mean values, variances and covariances. Accordingly, the maximum distance value is determined on the basis of the reference documents. Analogously, the second reference range and the second criterion are given in that for pixel data of a pixel, here the L and IR components, the Mahalanobis distance in the L-IR plane, which is dependent on the corresponding mean values, variances and covariances, is determined and checked becomes, whether the Mahalanobis distance is less than a predetermined second maximum distance value that was determined for the reference value documents. In the present example, the proportion itself is used as the hit measure for the proportion of the pixel data that lie within the respective reference area. Therefore, a minimum hit value is defined for each of the reference areas, which must be exceeded by the hit size, in this case the portion of the pixel data in the respective reference area and which is characteristic of a security feature with sufficient manufacturing quality or a value document with such a security feature. Such a minimum hit value can be determined by examining the reference value documents.

In the embodiment in Fig. 10 the scatter of the pixel data that lie within the first reference range is additionally determined and compared with a minimum scatter value. The total variance, ie the sum of the variances of the a and b components, is used as the scatter or degree of scatter. To determine the minimum value for dispersion, the total variance, ie the sum of the variances of the a and b components, is determined as the first degree of dispersion for each of the reference value documents for the pixel data within the first reference area. From the distribution of the total variances determined, a mean dispersion value is then determined as a minimum dispersion value which must be exceeded by a first degree of dispersion determined for a security feature to be checked so that the manufacturing quality of the security feature can be considered sufficient.

To check the security feature, the evaluation device 31 determines in step T20 which portion of the pixel data for pixels that correspond to locations in the section 48 lie within the first reference area by for each pixel the Mahalanobis distance in the ab plane is calculated and compared with the maximum distance value. If the Mahalanobis distance is less than or equal to the maximum distance value, the pixel data are in the first reference area, otherwise outside. After determining the proportion, the proportion is compared with the specified first minimum hit value.

In step T22, the evaluation device 31 or the processor 34 checks whether a first scatter of the pixel data that lie within the first reference area is greater than a predefined minimum scatter value. This sum is compared with the specified first minimum scatter value.

In step T24, the evaluation device 31 or the processor 34 then determines, in accordance with step S24, the proportion of that pixel data of the pixels used to check the security feature, ie the pixels in the section 48 that lie within the second reference area, by using for the pixel data of a respective one of the It is checked in each pixel whether the Mahalanobis distance in the L-IR plane is smaller than the corresponding second maximum distance value. If the proportion is determined, the processor 34 checks whether it exceeds the corresponding second minimum hit value.

In step T26 the evaluation device 31 or the processor 34 forms a quality signal as a function of the tests in steps T24 to T28, as in the first exemplary embodiment.

Another embodiment in Fig. 11 differs from the first embodiment in that the evaluation device 31 carries out, as an additional step T28, a check as to whether the scatter of the pixel data within the second reference area exceeds a second minimum scatter value specified for the security feature. Of the The second minimum dispersion value was previously established in a manner analogous to the first minimum dispersion value. The total variance in the L-IR plane is used here as the degree of dispersion, ie the sum of the variances of the L components and the IR components of those pixel data that lie in the second reference range. The second minimum dispersion value can be determined analogously to the first exemplary embodiment.

On the other hand, the evaluation device 31 executes step T26 'instead of step T26. Analogous to the third exemplary embodiment, this differs from step T26 solely in that the quality signal is formed in such a way that it only provides an indication of adequate manufacturing quality if, in addition to the conditions in the first exemplary embodiment, the scatter of the pixel data within the second reference area exceeds the predetermined second minimum dispersion value. This leads to a further increased accuracy of the test in the case of optical security features, which also have a typical scatter in the L-IR properties.

Further exemplary embodiments can differ from the exemplary embodiments described above in that in step S16 the section is only a rectangle in a center of the security feature, but not the smallest rectangle surrounding the security feature.

In still further exemplary embodiments, pixel data are used which only reproduce colors. The second criterion and the second reference range can then be given in that the L component must lie in a predetermined value range so that the pixel data lie within the second reference range.

Still further exemplary embodiments differ from the exemplary embodiments described in that an embossed structure is used as an optical security feature with a print formed on certain flanks of the embossed structure, which has an optically variable effect. Such embossed structures are in the applications WO 97/17211 A1 , WO 02/20280 A1 , WO 2004/022355 A2 , WO 2006/018232 A1 described by the applicant.

Still further exemplary embodiments differ from the exemplary embodiments described only in that a sensor such as the one used is used as the sensor WO 96/36021 A1 is described, the content of which is incorporated into the description by reference.

Other exemplary embodiments differ from the exemplary embodiments described, in which the HSI or the CIE Lab color space is used, in that only the first reference range is used, so that steps S28 and T28 can be omitted and steps S26 and T26, respectively are changed accordingly, so that the quality signal is only formed when the number of pixel data in the first reference area exceeds the minimum proportion and the spread of the pixel data within the first reference area exceeds the first minimum spread.

Still further exemplary embodiments differ from those described above in that no IR component is present. The second reference area is then one-dimensional and the second criterion is adapted accordingly.

Other exemplary embodiments differ from the exemplary embodiments described up to now in that the entry of the value document type by a user is omitted, and instead of after step S10 a step S11 is carried out in which the type is automatically determined. More precisely, the evaluation device 31 or: the processor 34 determines in this step S12 the type, ie the currency and the denomination, of a document of value to be checked as a function of the pixel data detected by the sensor 32. Different types are given. If possible, one of the predefined types can then be assigned to the value document. In the example, value documents are to be checked, the format of which depends on the type. The evaluation device 31 can therefore first carry out a search or recognition of edges of the bank note in the image. From the recognized margins, it can determine the format of the value document, the denomination or denomination and thus the type from the set of predefined possible value document types.

Still further exemplary embodiments differ from the preceding exemplary embodiments in that two scatter in two mutually orthogonal directions in the corresponding color space are used as the degree of scatter. The directions are given by the eigenvectors of the variance matrix of the pixel data or pixel data components for the security feature of the reference documents in the respective reference areas. The variance of the projection of the pixel data onto the one eigenvector and the variance of the projection of the pixel data onto the other eigenvector are then used as the scatter. A threshold value is then specified for each of the directions, which threshold value can be determined in each case by evaluating pixel data for the reference documents in a manner analogous to the first exemplary embodiment. The threshold values represent the minimum scatter. The scatter exceeds the minimum scatter if the variance for one of the directions is greater than the threshold value assigned to the respective direction.

In further exemplary embodiments, the evaluation device can be integrated into the sensor.

Other exemplary embodiments can differ from the preceding exemplary embodiments in that, instead of a line camera, a camera with an array of detection elements arranged in a matrix is provided.

In still further exemplary embodiments, sensor sections spaced apart from one another in the transport direction are provided in order to detect at least different components of the pixel data. For example, two parts could be provided, one of which includes lighting and a camera for detecting optical properties in the visible spectral range and the other lighting and camera for detecting optical properties in the non-visible spectral range, in particular the IR range. In this case, during the evaluation, the captured images, in the example two, must first be brought into congruence or positioned one on top of the other so that the necessary number of components is available for a location.

Claims (24)

1. A method for checking the production quality, preferably the printing quality, of a prescribed optical security feature (46) in or on a prescribed portion (48) of a value document (12) on the basis of pixel data of pixels (44) of an image of the prescribed portion which are respectively associated with places in or on the portion and render optical properties of the value document (12) at the places, wherein
   it is checked whether a first number of those pixels (44), or a first share of those pixels (44) in the pixels of the image, whose pixel data, according to a first prescribed criterion, lie within a first reference region prescribed for the security feature (46) exceeds a first minimum hit value prescribed for the security feature,
   and whether a first scatter of the pixel data of those pixels (44) lying within the first reference region for the pixel data according to the first criterion exceeds a first minimum scatter prescribed for the security feature,
   and there is formed in dependence on the result of the check a quality signal which represents an indication of a sufficient production quality only when the first number or first share exceeds the first minimum hit value, and the scatter the first minimum scatter, and/or which represents an indication of a production fault, when the first number or first share does not exceed the first minimum hit value, and the scatter the first minimum scatter.
2. The method according to claim 1, wherein it is additionally checked whether a second number of those pixels (44), or a second share of those pixels (44) in the pixels of the image, whose pixel data, according to a second criterion, lie within a second reference region prescribed for the security feature exceeds a second minimum hit value prescribed for the security feature, and the quality signal is so formed that it represents the indication of a sufficient production quality only when additionally the second number or second share exceeds the second minimum hit value, and/or that it represents an indication of a production fault when the second number or second share does not exceed the second minimum hit value, and
   it is preferably checked whether a second scatter of the pixel data of those pixels (44) lying within the second reference region according to the second criterion exceeds a second minimum scatter prescribed for the security feature, and the quality signal is so formed that it represents the indication of a sufficient production quality only when additionally the scatter of the pixel data in the second reference region exceeds the second minimum scatter and/or that it represents an indication of a production fault when the scatter of the pixel data in the second reference region does not exceed the second minimum scatter.
3. The method according to claim 1 or 2, wherein the pixel data for a respective pixel (44) or place have components that render remission or transmission properties in at least two, preferably at least three, different wavelength ranges, preferably within the visible spectral region, or colors.
4. The method according to claim 1 or claim 2, wherein the pixel data for a respective place have components that represent remission and/or transmission properties in at least two, preferably three, different wavelength ranges within the visible spectral region, or colors, and remission and/or transmission properties in a further wavelength range at least partly outside the visible spectral region, preferably in the infrared spectral region.
5. The method according to claim 3 or claim 4, wherein those pixel data representing properties in the visible spectral range or color values are transformed, before checking, into a device-independent color space, preferably a Lab or Luv color space, or there are employed, as pixel data representing properties in the visible spectral range or color values, pixel data in a device-independent color space, preferably a Lab or Luv color space.
6. The method according to any of claims 3 to 5, wherein there is employed as the first reference region a region extending at least in a plane which extends parallel to two axes of a color space which correspond to different colors.
7. The method according to claim 2 or one of claims 3 to 6 and claim 2,
   wherein there is employed as the first or second reference region a region extending at least in a plane which extends parallel to an axis corresponding to a luminance or brightness, and an axis corresponding to a brightness in the further wavelength range at least partly outside the visible spectral region.
8. The method according to any of the preceding claims, wherein there is employed as the first and/or second scatter a variance and/or a covariance of the pixel data lying in the first or second reference region, or components of the pixel data or a monotonic function of the variance or covariance.
9. The method according to any of the preceding claims, wherein there are employed edge image pixel data of pixels of an edge image portion which are respectively associated with places within a prescribed edge region along at least a part of an edge of the portion, preferably within a prescribed distance from an edge of the portion, there is ascertained from the edge pixel data a local condition value rendering the condition of the value document in the portion, and the local condition value is employed upon the checking of the first and/or second share or first and/or second number and/or the first and/or second scatter.
10. The method according to claim 9, wherein pixel data are corrected before checking.
11. The method according to claim 9 or 10, wherein the first criterion and/or the first reference region and/or the second criterion and/or the second reference region are changed or prescribed in dependence on the local condition value.
12. The method according to any of the preceding claims, wherein the security feature is an OVD security feature with an optically variable printing ink.
13. The method according to any of claims 1 to 11, wherein the security feature is a surface structure, preferably an embossed structure, which has an optically variable effect.
14. The method according to claim 13, wherein the embossed structure has bent or angled embossed structure elements.
15. A method for checking the production quality, preferably the printing quality, of a prescribed optical security feature in or on a prescribed portion of a value document (12), wherein, for capturing an image of the prescribed portion (48), the value document (12) is illuminated with optical radiation of an optical radiation source (39), and radiation emanating from the value document (12) is captured, there are formed, in dependence on the captured radiation, pixel data of pixels of the image which are respectively associated with places in or on the portion and render optical properties of the value document (12) at the places, and
    wherein a method according to any of the preceding claims is carried out, wherein there are employed as pixel data said formed pixel data.
16. The method according to claim 15, wherein the illuminating with optical radiation and the capturing of radiation are so effected that the pixel data for a respective pixel (44) or place have components that render remission or transmission properties in at least two, preferably three, different wavelength ranges, preferably within the visible spectral region, or at least two, preferably three, colors.
17. The method according to claim 15 or claim 16, wherein the illuminating with optical radiation and the capturing of radiation are so effected that the pixel data for a respective pixel or place have components that represent remission and/or transmission properties in at least two, preferably at least three, different wavelength ranges within the visible spectral region or at least two, preferably three, colors, and remission and/or transmission properties in a further wavelength range at least partly outside the visible spectral region, preferably in the infrared spectral region.
18. The method according to any of claims 15 to 17, wherein the value document (12) is transported past an illumination source (38) and illuminated thereby with a convergent bundle of optical radiation only from one illumination direction, and the radiation emanating from a respectively illuminated place is captured only from one capture direction, and wherein the illumination direction and/or the capture direction preferably enclose with a normal on a plane of the value document an angle smaller than 5 degrees.
19. The method according to any of claims 15 to 18, wherein upon the capture of the radiation emanating from the value document, there are formed edge image pixel data which are respectively associated with places within a prescribed distance from an edge of the portion and render optical properties of the value document at the places.
20. A computer program with program code means for carrying out the method according to any of claims 1 to 14 when the program is executed on a computer.
21. A computer program product with program code means which are stored on a computer-readable data carrier for carrying out the method according to any of claims 1 to 14 when the computer program product is executed on a computer.
22. A method for checking the quality of freshly printed value documents (12) which have a prescribed optical security feature in or on a prescribed portion of the value document, wherein for the value documents there is carried out a method according to any of claims 15 to 19 and
    when the quality signal for one of the value documents (12) represents no indication of a sufficient production quality, the one value document is destroyed.
23. The method according to claim 22, wherein for a value document (12), for which the quality signal for one of the value documents (12) represents no indication of a sufficient production quality, the pixel data and/or data ascertained upon the check are so stored in a storage device, that they can also be accessed after the end of the check of the value documents (12).
24. A checking device for checking the production quality of a prescribed security feature of a value document by means of a method according to any of claims 15 to 19, having an optical sensor (24) for capturing an image with pixels (44) whose pixel data are respectively associated with places in or on the portion (48) and render optical properties of the value document at the places, a memory (36) in which a computer program according to claim 20 is stored, and a computer (34) for executing the computer program with images captured by the sensor.

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