WO2014029476A1

WO2014029476A1 - Method and apparatus for checking valuable documents

Info

Publication number: WO2014029476A1
Application number: PCT/EP2013/002441
Authority: WO
Inventors: Shanchuan Su
Original assignee: Giesecke & Devrient Gmbh
Priority date: 2012-08-24
Filing date: 2013-08-14
Publication date: 2014-02-27
Also published as: GB2518107B; GB201500503D0; DE102012016828A1; GB2518107A

Abstract

The invention describes a method for checking valuable documents, in particular also soiled valuable documents, for authenticity, having the steps of acquiring pixel data relating to pixels in an image of the valuable document, determining pixels in one or at least two predefined examination areas of the image and determining, for the examination areas, error pixels among the pixels in the particular examination area, wherein the pixel data relating to the error pixels are each outside a predefined pixel-dependent and/or location-dependent authenticity range, checking whether or not the error pixels in the examination area(s) correspond to soiling, for example staining, on the valuable document, and assigning an authenticity class from predefined authenticity classes to the valuable document on the basis of the checking result.

Description

Method and device for checking value documents

The present invention relates to a method for checking value documents, in particular soiled value documents, in particular authenticity, and means for carrying out the method. Under value documents are understood leaf-shaped objects that represent, for example, a monetary value or an authorization and not to be produced arbitrarily by unauthorized persons. They therefore have features or security features which are not easy to manufacture, in particular to be copied, the existence of which is an indication of the authenticity, i. the manufacture by an authorized agency. Important examples of such value documents are coupons, vouchers, checks and in particular banknotes.

Such value documents usually have a predefined print image in the visible wavelength range, and frequently such a print image is colored. Some value documents are additionally equipped with an IR print image, ie a print image which is recognizable in the infrared wavelength range. Such an IR print image does not have to match the visible print image, but may differ from it, depending on the type of value document.

Examinations of the printed image, in particular of the visible and / or, if present, of the IR printed image can give indications of the existence of a forged value document.

Such investigations are made difficult in value documents, in particular banknotes, but by contamination. Deviations in the printed image may be caused by counterfeiting or contamination. The soiling may be, for example, stains or marks. hung with a pen, such as a felt or pencil act. In the following, contamination which is not uniformly present on the value document and which does not occur during the production of the value document will lead to deviations in at least one printed image of the value document from a corresponding printed image specified for the value document type of the value document. In the context of the present invention, value document types are given by the fact that value documents of the same value document type have the same properties at least with respect to the print images, preferably also with respect to other features. In the case of documents of value in the form of banknotes, the types of value documents may be given, in particular, by the currency and the value of the banknote and, if appropriate, the issue of the banknote. The present invention is therefore based on the object of providing a method for examining documents of value, in particular contaminated documents of value, which permits the recognition of documents of forgery suspected of being forged, possibly also forged ones. Furthermore, means for carrying out the method should be provided.

The object is achieved by a method for checking value documents, in particular soiled value documents, for authenticity, with the steps: acquiring pixel data from pixels of an image of the value document, determining pixels in one or at least two predetermined examination regions of the image and for the or the at least two examination areas determining error pixels among the pixels in the examination area or a respective one of the at least two examination areas, the pixel data of the error pixels respectively outside a predetermined pixel- and / or location-dependent authenticity range, checking whether the error pixels in the examination area or areas of contamination, for example, a spot on the document of value or not, and assigning an authenticity class from predetermined authenticity classes to the value document in dependence on the Result of testing. Preferably, an authenticity signal is formed, which designates the assigned authenticity class, and / or a date is preferably stored which designates the assigned authenticity class. In this case, the method is carried out using an evaluation device which may have at least one processor, which may be programmed accordingly or which executes a corresponding program stored in the evaluation device for carrying out the method.

The object is further achieved by a device for checking documents of value, in particular soiled documents of value for authenticity, with an optical sensor for detecting an image of the document of value, wherein the image has pixels to which pixel data are assigned, and an evaluation device which is set up for this purpose to carry out a procedure according to the invention. In particular, the evaluation device is designed to detect pixel data of pixels of an image of the value document by means of the sensor, to determine pixels in one or at least two predetermined examination regions of the image and for the or the at least two examination regions among the pixels in the examination region or a To determine respective error pixels of the at least two examination areas, wherein the pixel data of the error pixels each lie outside a predetermined pixel- and / or location-dependent authenticity range, to check whether the error pixels in the investigation areas or areas of contamination, for example a spot, on correspond to the document of value or not, and to assign a value of authenticity class as a function of the result of the test ensue from the given authenticity classes. The device for testing, hereinafter also referred to as a test device, is thus designed in particular for the Durcriführung of the inventive method. Preferably, the evaluation device is designed to form an authenticity signal, which designates the assigned authenticity class, and / or preferably to store a datum designating the assigned authenticity class. The invention relates to the examination of value documents. In the test according to the invention, value documents can be assigned authenticity classes if these value documents have a predetermined value document type or one of a plurality of predetermined value document types.

It is provided to first capture pixel data of pixels of an image of the value document, which can be done by reading in via an interface and preferably by means of the optical sensor. The image can be an image in the visible wavelength range, for example a pure grayscale image or even a color image, the sensor of the test device is then designed to detect the corresponding image. Preferably, however, the image of the value document is an IR image of the value document. In the test device, the optical sensor is then preferably designed such that an IR image of the value document can be detected by means of the IR sensor. The image may then be an image in a predetermined wavelength range in the infrared wavelength range, which includes only intensity or brightness information in the wavelength range. Spectral properties are then irrelevant. In the usual way, the image is composed of pixels whose properties are described by the pixel data. The pixel data may include a different number of components depending on the type of image; For example, the pixel data for the pixels can each describe at least one color coordinate in a color space and / or a brightness. For a grayscale image in the visible wavelength range or an IR image, the pixel data may preferably describe a brightness of the pixels, in a color image the pixel data may be color coordinates for the pixels in a color space. The optical sensor of the test direction is designed to acquire corresponding images and to form corresponding pixel data, ie it may be a visible-range gray scale sensor, a color sensor operating in the visible range or a sensor operating in the IR range. In the captured image, pixels are now determined which lie in a predetermined examination area or at least two predetermined examination areas. In this case, the examination area or examination areas can be predetermined depending on the value document type and, depending on the value document type, preferably the orientation of the value document. The use of at least two examination areas has the advantage that a differentiated examination is possible, since the examination in the examination areas can be carried out depending on the respective examination area or the properties of the value document in the respective examination area. Under the orientation of the value document is understood in a rectangular value document one of the four possible layers that can be obtained by rotations of the value document about its longitudinal and transverse axes by 180 °. The examination area or the examination areas are preferably selected such that a good and reliable recognition of falsified or forgery-suspected value documents is obtained. The examination areas preferably each have an area of at least 4 mm ² . If only one examination area is used, its area is preferably more than 30% of the total area of the value document. If several examination areas are used, the total area thereof is preferably more than 30% of the total area of the value document.

For the examination area or the examination areas, error pixels are determined below the pixels in the respective examination area. For this purpose, a predetermined authenticity range, preferably specified for a respective value document type and / or a predetermined orientation of the value document, within which the pixel data must lie if the document of value is genuine or neither suspected of forgery, is used for the examination area or each of the at least two examination areas still to be regarded as fake. The authenticity range is preferably in each case location-dependent and / or pixel-dependent, ie for different pixels of the image or locations in the image or on the value document the authenticity range can be given differently or differently; however, the authenticity range or the authenticity ranges for certain different pixels can be the same, depending on the type of document of value. For example, in the case of one-dimensional pixel data, ie pixel data with only one component, the area of authenticity may be given by an interval whose boundaries may depend on the respective pixel or location. The size of the authenticity range can be determined, for example, by measurements on predefined value documents, preferably value documents of the value document type. Pixels whose pixel data will be outside the respective authenticity range are determined as error pixels. These pixels or their pixel data or references to them can be separates stored or only be marked as error pixels or pixel data of error pixels. The determination of pixels in the examination area (s) and the determination of the error pixels can be performed in any order and / or in one step. As a result, it is possible to obtain an error image of the examination area (s) that shows the pixels whose pixel data are outside the respective authenticity range.

It is then checked whether the detected error pixels in the examination area or the at least two examination areas correspond to a contamination, for example a spot, on the value document or not. For this purpose, at least one predefined contamination criterion can be used, by means of which it is determined when error pixels in the examination area or in the examination areas are classified as contaminants and when not. It can then be checked whether the detected error pixels in the or the at least two examination areas according to at least one contamination criterion of contamination, for example, a spot on the document of value or not. It thus represents a criterion for when defect pixels in the study area (s) are being searched by one of the students

Value document with a pollution, for example, at least one spot represent. The checking as to whether or not the detected error pixels in the examination area or examination areas correspond to soiling, in particular a spot, on the value document may comprise a plurality of different test sub-steps. The fouling criterion may then include subcriteria which, depending on the embodiment, must be fulfilled alternatively or cumulatively in order to detect the presence of fouling. The pollution criterion or a component criterion can in particular also be a criterion for the fact that the error pixels are not caused by contamination or correspond to contamination; in this case the pollution criterion or subcriterion would be met if the criterion is not met. The contamination criterion or subcriterion can also be predefined as a function of the examination area.

This approach makes use of the fact that, in many cases, forgery-induced error pixels have different properties and / or a different spatial distribution than due to contamination, in particular in the form of spots, caused error pixels.

Depending on the result of the check, one of at least two predefined authenticity classes is assigned to the respective value document or its image. For example, the authentication classes may include the classes "recognized as genuine" and "counterfeited", the classes "non-suspect" and "suspect", or the classes "recognized as genuine" and "suspect". Which authenticity classes are specified may depend on whether the result of the check of the value document is linked to the results of another authenticity check of the value document in order to obtain an overall classification.

In the method or the device, the class "forgery-suspect" can be assigned as an authenticity class, in particular, if the checking as to whether the error pixels in the examination region or the examination regions have revealed a contamination, for example a spot, on the document of value or not, that the error pixels do not correspond to contamination. But it is also possible, instead of the authenticity class "suspected of forgery" to assign the authenticity class "wrong", if this is provided.

It is then possible to form an authenticity signal, which designates or characterizes the result of the check, in particular the assignment to the authenticity class or the associated authenticity class, or it can be stored that the assignment to the authenticity class or the associated authenticity class Authenticity class designates or identifies. In the checking device, the evaluation device can be set up to form an authenticity signal which designates or characterizes the result of the check, in particular the assignment to the authenticity class or the associated authenticity class, or to store a date that matches the authenticity class or the assigned authenticity class designates or identifies. The authenticity signal can be stored or further processed directly.

In order to allow a good check for the presence of contaminants, it is preferred in the method that in the step of determining the error pixel or in the step of checking for the prevalence of contamination, ie, whether the error pixels in the examination area or the Fault pixels are divided into upper error pixels, their pixel data in a first direction out of the authenticity range Hegen, and lower error pixels whose pixel data in a second direction opposite to the first direction direction lie outside the area of authenticity. In the testing device, the evaluation device is then preferably designed such that, in the step of determining the error pixel or in the step of checking for the presence of contamination, ie, whether the error pixels in the or the The error pixel is divided into upper error pixels whose pixel data are in a first direction outside the authenticity range, and lower error pixels whose pixel data are in a second direction opposite to the first direction outside of the authenticity area. The division can be realized, for example, by assigning to the error pixels or their pixel data a corresponding identifier by means of which a distinction between upper and lower error pixels is possible, or upper error pixels and lower error pixels or their pixel data being stored separately from one another or in that lists are maintained for upper and lower error pixels in which references to the respective error pixels or pixel data of the respective error pixels are stored. Particularly preferably, in the method the authenticity range can be one-dimensional. The upper error pixels may then be error pixels whose pixel data are above the authenticity range, and the lower error pixel error pixels whose pixel data are below the authenticity range. The pixel data is then also one-dimensional. This embodiment is suitable, in particular, for IR images which have only brightness information whose pixels therefore have brightness values as pixel data.

The embodiments mentioned in the two preceding paragraphs have the advantage that a check for the presence of contamination can be made more differentiated than without such a division.

Preferably, in the method in the step of checking for the at least two examination regions, in each case during a first range test, it is checked whether the upper error pixels of at least one pollution, for example, at least one patch, and / or tested in each case in a second range check, if the lower error pixels correspond to at least one pollution. It can then be decided that the error pixels in the examination area (s) correspond to a contamination if at least a predetermined minimum number of area tests have revealed that the upper or lower error pixels in the respective examination area are at least one contamination, for example at least one spot , on which value document correspond. In particular, the predetermined minimum number may also be twice the number of examination areas, so that a presence of contamination is only recognized if all area checks have revealed this. In an alternative embodiment, it can be decided that error pixels in the or at least two examination areas do not correspond to at least one dirt, for example at least one patch, on the document of value if at least a predetermined minimum number of area tests have revealed that the upper or lower error pixels in the respective examination area do not correspond to at least one contamination, for example at least one spot, on the value document. The predetermined minimum number may be the same or different than in the first embodiment. In particular, the minimum number can be equal to 1.

The sequence of the range checks is arbitrary; for example, the second and then the first range check or first the second and then the first range check can be carried out for the examination area or the at least two examination areas. However, it is also possible to perform, for example, the second area checks for all examination areas and then validation for all areas of investigation. First and second range checks can also be reversed. Furthermore, it is also conceivable to execute them in parallel. The minimum counts may be selected depending on the value document types and a sensor used to capture the images and the desired selectivity of the test.

In particular, field examinations may include one or more of the examinations referred to below, alternatively or cumulatively. In these tests, an indication of the presence of contamination or an indication of the presence of any contamination may be detected. If only one of the tests is used, the indication of contamination is recognized as the presence of contamination. If several of the tests are used cumulatively, the presence of soiling in the respective examination area or the corresponding section of the value document can be detected if a given number of tests, preferably all the tests used, have given an indication of the presence of contamination. It is also possible to detect the presence of any contamination in the respective examination area or the corresponding section of the value document if at least one of the tests used or a specified number of tests used have given an indication of the presence of no contamination.

According to a first preferred option, in the method in the first range check for the examination area or one of the at least two examination areas, the number of upper error pixels in the respective examination area can be given a predetermined first Maximum value and / or compared in the second range examination for the examination area or one of the at least two examination areas, the number of lower error pixels with a predetermined second maximum value, and an indication of contamination in the respective examination area are recognized when the numbers of the respective Maximum value, or an indication of no contamination in the respective examination area is recognized on the document of value if the first and / or the second number exceeds the first or second maximum value. The maximum number is significantly smaller than the number of pixels in the respective examination area, preferably less than 80% of the number of pixels in the respective examination area. This test has the advantage that it is particularly easy to perform.

For the possibility described above, and in particular for the possibilities described below, it is advantageous for the method in determining or checking for the upper and lower error pixels to determine distances of the pixel data from the authenticity regions and to use the distances when checking the range criteria. This offers the advantage that in the case of print images with strong, print image-related variations of the pixel data, the deviations can be used more easily for the examination.

A second preferred option provides that during the first range check for the or one of the at least two examination areas, it is checked whether a distribution of the distances of the upper error pixels satisfies an upper distribution criterion prescribed for the respective examination area and / or a distribution in the second area examination the distances of the lower error pixels one for the respective sub- satisfies the lower distribution criterion for the presence of soiling. The upper and lower distribution criteria are predefined for the examination area or respectively the examination areas; the distribution criteria can furthermore be predetermined depending on the value document type and, depending on the value document type, the orientation. The distribution criteria may differ or preferably be the same. In addition, the distribution criteria for different study areas may be different or the same.

The distribution criterion can in principle be chosen arbitrarily. For example, a distribution function describing the frequency of occurrence of intervals may be predetermined and it may be checked whether the distribution of the distances satisfies the distribution function. In order to allow a quick but sufficiently accurate test, it is preferred that when checking the upper or lower distribution criterion, it is in each case checked whether the width of the distribution of the respective distances exceeds or falls below a predetermined upper or lower threshold value. Any suitable size, which is a measure of the width of the distribution, can be used below the width of the distribution, for example the half width (FWHM, "fill width at half maximum") or the variance or the variance coefficient (standard deviation / mean value). The upper and lower thresholds may be the same or different, depending on the value document type. Preferably, when the respective threshold value is exceeded, an indication of the presence of soiling is detected. The threshold values can be determined by analyzing value documents of the specified value document type. This embodiment is based on the observation that, in the case of counterfeiting, the deviations are production-related and therefore systematic, as a result of which, in particular in the case of IR images, for the Examination area should give a very narrow distribution of distances.

According to a third preferred possibility, in the method in the first range examination for the examination area or one of the at least two predetermined examination areas, a correlation of the upper error pixels in the examination area with a predetermined reference image of the examination area and / or in the second area examination for one of the predetermined examination areas a correlation of the lower error pixels in the examination area with a predetermined reference image of the examination area can be determined. The reference image may differ depending on the value document type. For example, the reference image may be an image of the same type as the image being scanned, so for a color image, the reference image may also be a color image, for an IR image an IR image. When using an IR image as the reference image, the printed image in the visible region is preferably used as the brightness image. The reference images can preferably be obtained by analyzing a plurality of genuine value documents of the respective value document type, for example as mean value. Here, the correlation is understood to mean a local or pixel-by-pixel correlation of the respective error pixels with the reference image or corresponding pixels of the reference image. The correlation of the pixel data or the distances of the respective error pixels with the pixel data of pixels of the reference image, which are arranged the same relative to each other as the error pixels, can be used. Preferably, a set of displacement vectors may be predetermined and the correlation may have the greatest correlation among the local or pixel-wise correlation of the pixel data or the distances of the error pixels with the pixel data of the corresponding pixels of the reference image or the corresponding pixels of the respective one of the predefined ones. Be shift vectors shifted reference image. This means that it is checked how the pixel data or distances of the error pixels are correlated with the pixel data of pixels of the reference image that correspond to the error pixels in their position, if necessary, except for a shift. Preferably, an indication of the presence of soiling is recognized in the first and second area checks if the correlations are smaller than the upper or lower maximum correlation values specified for the respective examination area. As a measure of the correlation, for example, a cross-correlation of the deviations or the pixel data of the error pixels with the pixel data of corresponding pixels of the reference image can be used. Preferably, a maximum cross correlation is obtained which is obtainable by specifying a set of displacement vectors and for which displacement vectors the largest cross-correlation between the deviations or the pixel data of the error pixels is determined with the pixel data of corresponding pixels of the reference image shifted by the respective displacement vector. Thus, an indication of the presence of contamination can then preferably be recognized if the correlation, preferably the cross-correlation or the maximum cross-correlation, is smaller than a first or second correlation threshold. The displacement vectors may be vectors on a given by the pixels of the detected image or the reference image grid whose length is preferably smaller than a predetermined maximum distance. Instead of the cross-correlation, an absolute or average quadratic error can also be used, with a small error corresponding to a high correlation.

If at least two of the possibilities for at least one of the examination areas are used cumulatively, the presence of a contamination is preferably recognized if either the tests for the upper fault pixels give an indication of the presence of contamination or the tests for the lower error pixels give an indication of contamination. Regardless of the previously described embodiments in which the distinction between upper and lower error pixels is used, in a preferred embodiment of the method it can be provided that in the step of checking whether the error pixels in the examination area or the at least two examination areas a contamination is detected, it is checked whether the number of error pixels is smaller than a predetermined threshold for the respective examination area, and if this, preferably for the or at least one of the examination areas, the case, a presence of contamination is detected or an indication is detected on the presence of pollution. The test can here indiscriminately include all error pixels in one of the examination areas. The threshold value can also be selected here as in the previously described embodiments.

The invention further provides a method for checking value documents, in particular contaminated documents of value, having a section with an IR-absorbing security feature, preferably a security thread, for authenticity, with the steps: detecting pixel data of pixels of an IR image of at least the section of the value document, determining gen- eral pixels among the pixels in the IR image of the section, wherein the pixel data of the authenticity pixels are above a minimum threshold, comparing the number of the authenticity pixels with a minimum number specified for the section, and assigning an authenticity class from given authenticity classes the value document depending on the result of comparing the number of authenticity pixel with the minimum number. The minimum threshold value is preferably chosen such that these pixel data, which correspond to only noise of the sensor used to acquire the IR image, are not recognized as authenticity pixels. The minimum number is preferably selected to correspond to the number of pixels in the portion of the value document that results in a true, fresh-print value document. For example, the minimum number may be greater than 85% of the number of pixels in the portion of the value document that results in a true, fresh-print value document. This procedure has the advantage that the exact position of the security feature need not be known, as long as it lies in the appropriate section to be selected.

The evaluation device of the test device can in principle be designed as desired, but preferably has a data processing device with at least one processor and a memory in which the program code is stored, in the execution of which the method according to the invention is carried out.

The subject of the present invention is therefore also a computer program for execution by means of a data processing device with a processor containing program code, in the execution of which the processor carries out the method according to the invention, in particular according to one or more of the previously described embodiments. Another object of the present invention is a computer-readable data carrier on which such a computer program is stored. The computer program is preferably stored on the disk not only volatile; this is therefore a non-volatile data storage or includes such. The test device according to the invention can preferably be used in devices for processing value documents, in particular soiled value documents. The subject matter of the present invention is therefore also a device for processing value documents, in particular soiled value documents, with a feed device for value documents to be processed, an output device for value documents which has at least two output sections for receiving processed value documents, a transport device for transporting separated documents Value documents from the feed device along a transport path to the output device, a test device according to the invention, in particular according to one or more of the previously described embodiments, which is arranged so that the transport path passes through the detection area, and a control device, which depends on an authenticity signal the checking device for a value document transported by the transport device controls the transport device in such a way that the value document changes into a value corresponding to the authenticity signal Output section of the at least two output sections is transported. Preferably, the device is designed to process value documents at a speed of more than 15 value documents / s.

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

1 is a schematic view of a value-document processing device, 2 shows a schematic illustration of a digital color image and an IR image of a value document,

3 is a flowchart for a first method of testing

Value documents by means of the device in Fig. 1,

4 shows a schematic illustration of authenticity areas and pixel data for the method in FIG. 3, FIG. 5 shows a flow chart for a step S18 of the method in FIG. 3,

FIGS. 6A, B are flowcharts for first and second range checks in FIG

Step S18 in Fig. 5, Fig. 7 is a flowchart for a second method for testing

Value documents by means of the device in Fig. 1,

FIG. 8 is a flowchart for a step S18 'of the method in FIG.

7,

FIGS. 9A, B are flowcharts for first and second range checks in FIG

Step S18 'in Fig. 8,

FIG. 10 distance distributions for an examination area of a genuine, soiled banknote (a) and for the same examination area of a counterfeit banknote (b), and FIG

Fig. 11 is a flow chart for another method for testing

Value documents by means of the device in FIG. 1. A device 10 for processing value documents 12, in the example a banknote processing device, in FIG. 1 is used inter alia for checking the authenticity of value documents 12 in the form of banknotes and for sorting the value documents as a function of the result of the authenticity check. The device 10 has a supply device 14 for the input or input of value documents 12 to be processed and a transport device 20 leading to an output device 18 for the occasional transport of value documents from the supply device 14 along a transport path 22 to the output device 18. The supply device 14 comprises in the example, an input tray 15 and a singler 16, which can access value documents 12 in the input tray 14 to singulate them. In the example, the transport device 20 transports isolated value documents 12 from the singler 16. The output device 18 serves to receive and output verified value documents and has at least two, in this example three, output areas 24, 24 'and 24 ", in the example stacked compartments for optional transport into the dispensing areas, the transport device 20 includes points arranged successively along the transport path 22, in the example two points 26 and 26 ', so that value documents can optionally be fed to one of the dispensing areas by actuation of the points 22 is arranged after the feeder 14, in the example in particular after the Vereinzeier 16, and in front of the switches 26 and 26 ', a sensor assembly 28 which serves for detecting characteristics of individually supplied value documents 12 and forming the sensor reproducing the characteristics of a sensor The sensor 30 is connected at least to the sensor arrangement 28 and the points 26 and 26 'via signal connections and serves for the evaluation of sensor signals of the sensor arrangement 28, in particular for Testing the authenticity of value documents, and for controlling at least the points 26 and 26 'as a function of the result of the evaluation of the sensor signals, ie in particular the results of the test for authenticity.

The sensor assembly 28 includes at least one sensor; In this embodiment, an optical sensor 32 for spatially resolved detection of color characteristics, i. H. a color image, and an optical sensor 33 for detecting IR characteristics, i. H. an IR image, provided that detects the remitted from the value document optical radiation in the visible wavelength range and in particular IR radiation in a predetermined wavelength range. The optical sensor 32 detects a digital color image of the value document in the three color channels red, green and blue during the transport before a value document, the optical sensor 33, a digital IR image in the infrared spectral range; the images are respectively represented or described by corresponding sensor signals or pixel data generated therefrom.

The digital images captured by the optical sensors 32 and 33 each include pixels whose characteristics are given by the pixel data representing color characteristics and IR characteristics, respectively.

To evaluate the sensor signals, the control device 30 has an evaluation device 34, which in the example is integrated into the control device 30, but in other exemplary embodiments can also be part of the sensor arrangement 28 itself.

The control device 30 has, in addition to corresponding interfaces 36 for the sensor device 28 and the sensors 32 and 33 for receiving the from this detected digital images via a connected to the interfaces 36 processor 38 and connected to the processor 38 memory 40 in which at least one computer program is stored with program code, in its execution, the processor 38 in a first function tion as part of the evaluation 34 evaluates the sensor signals, in particular for checking the authenticity of a detected value document, and thereby executes, inter alia, a method described below using the sensor signals or the pixel data. The evaluation device 34 also includes the interfaces 36. In a second function, the processor controls the device or, according to the evaluation, the transport device 20. The evaluation device 34 therefore forms a computer or a data processing device in the sense of the present invention.

In operation, the evaluation device 34 checks for each value document detected by the sensor arrangement 28 by means of the processor 38 on the basis of the digital images of the value document at least one predetermined criterion for the authenticity of the value document and determines one of predetermined authenticity classes for the value document.

Depending on the determined authenticity class, the control device 30, in particular the processor 38, controls the transport device 20, more precisely the switches, in such a way that the checked value document is transported for storage into corresponding output areas in accordance with its determined authenticity class. For example, the classes "counterfeit suspect" and "falsified" and "recognized as genuine" can be specified as authenticity classes; the authenticity class "recognized as genuine" can be assigned to those value documents which can not be assigned to either of the other two authenticity classes. Then the recognized as real value documents in the area 24, which are recognized as suspected counterfeit value documents in the area 24 'and those recognized as not genuine or falsified value documents in the area 24 "are issued , isolated as stack or individually inserted value documents 12 from the singler 16 and occasionally fed to the transport device 18, which feeds the singled value documents 12 to the sensor arrangement 28. This records optical properties of the value documents 12, in the example the color image and the IR image, The control device 30 acquires the sensor signals, determines the authenticity of the respective value document in dependence thereon and, depending on the result, controls the switches so that the examined ones are in the form of digital images Value documents be supplied to the output compartments according to their ascertained authenticity.

The optical sensor 32 is for acquiring images for three colors and color images, respectively, and the optical sensor 33 for images for IR radiation in a predetermined wavelength range for infrared radiation, i. H. IR images, formed in remission.

In the example, these sensors are each designed as line sensors which, during the transport of a value document past the sensors 32 and 33, respectively, detect a sequence of line images which produce a line image of the value document in a direction transverse to the direction of the line.

In the present example, the sensor 32 comprises a lighting device 42 shown only roughly schematically in FIG Transport direction T extending strip for the document of value 12 or in a plane of the value document 12 with convergent white light in the predetermined wavelength range during the transport of the value document over its entire length transverse to the transport direction T. Analogously, the sensor 33 in the present example, a in Fig. 1 only roughly schematically shown illumination device 43 for illuminating a transversely to the transport direction T extending strip for the document of value 12 or in a plane of the value document 12 with IR radiation in the predetermined wavelength range during the transport before the value document over its entire extent transverse to the transport direction In other embodiments, the sensors 32 and 33 may also include a common illumination device that outputs both white light and the desired IR radiation. Furthermore, the sensor 32 comprises a detection device 44 for detecting illumination radiation, which is remitted by an area of a value document illuminated by the illumination device 42. In the example, this detection device 44 has three line cameras (not shown in detail) with likewise red, green and blue filters arranged in the beam path for detecting red, green or blue portions of the optical radiation of the illumination device that is reflected from the value document 42. Analogously, the sensor 33 comprises a detection device 45 for detecting illumination radiation which is remitted by a region of a value document illuminated by the illumination device 43. In the example, this detection device 43 has a line scan camera (not shown in detail) with an IR filter of IR components of the optical radiation of the illumination device 45 remitted from the value document. Each of the line scan cameras has in each case one detector row with cell-shaped photodetection elements, in front of which the filter is arranged which corresponds to the color component or IR component of the remitted optical radiation to be detected by the respective line scan camera. The sensors 32 and 33 can also comprise further optical elements, in particular for imaging or focusing, which are not shown here. The detector lines of photodetection elements are arranged parallel to each other. Moreover, the sensors 32 and 33 in the figures include signal processing means, not shown, which generate corresponding digital images from the signals of the photodetection elements.

To capture a color image or an IR image of a value document 12, it is transported in the transport direction T at the sensors 32 and 33 at a constant speed, wherein at constant time intervals with the detection devices 44 and 45, in the example, the line scan camera intensity data for the four channels red, green, blue and IR spatially resolved to be detected. The intensity data or the color coordinates determined from these in a given color space or brightness values represent pixel data which describe the properties of pixels of a color or IR line image which correspond to the cell-shaped area of the image detected by the sensor 32 or sensor 33 Play the value document 12. By juxtaposing the line images in accordance with the time sequence of the acquisition, ie corresponding assignment of the pixel data, the digital color and IR images of the value document are then obtained with pixels to which pixel data are respectively assigned, the optical properties of the value document, namely color values for Red, green and blue and describe a brightness in the predetermined IR wavelength range or represent. A digital image captured by the sensor 32 and the sensor 33 is therefore composed of pixels arranged in a rectangular matrix and is described by the pixel data. The pixel data for the color image are color coordinates in a suitable color space, the pixel data for the IR image brightnesses or brightness values. The pixels are square in this embodiment, but may also have different side lengths. The length of a pixel is then the length of the longer side of the pixel.

For checking the value documents, a program with program code is stored in the memory 40 in a section serving as part of the evaluation device 34, and thus in this example in the control device 30, which program is executed by the evaluation device 34, i. Here, the processor 38, the steps of a method for checking value documents, in particular dirty value documents, performs authenticity, which are illustrated schematically in Fig. 3.

During the check, examination areas are defined for each orientation for a given value document type. In the present area, this is an IR print image area which has an IR print image in the case of genuine value documents of the specified value document type, and an IR-transparent print area which is transparent in the case of genuine value documents of the specified value document type in the IR range being examined. Furthermore, a security thread section is provided in which a security thread is present in the case of genuine value documents of the specified value document type. This section of the security thread, also referred to below as the special investigation area, is treated differently than the investigation areas. FIG. 2 shows, by way of example and schematically, a value document 12 with a colored print image 50 in the visible wavelength range and shown by solid lines and hatching dotted lines and dotted areas illustrated IR image 52, and - represented by dashed lines - an IR print image area 54, an IR-transparent printing area 56 and a security thread section 58 to a security thread 60. The security thread section is not used in the present first embodiment , Further, stain contamination 62 is shown in the IR print image area 54, which manifests itself in both the color image and the IR image.

For the described part of the procedure, which relates to the test on the basis of the IR image, the two authenticity classes "forgery-suspect" and "recognized as genuine" are used, whereby the authenticity class "recognized as genuine" is always assigned if the authenticity class is not "suspected of forgery" is assigned. First, in step S10, a digital IR image is detected by means of the optical sensor 33, and in this exemplary embodiment, by means of the optical sensor 32, a digital color image of a value document from the evaluation device 34 or the processor 38, each comprising pixels. In each case corresponding pixel data are recorded for the pixels.

The evaluation device 34 then determines in step S12 from the digital color image the value document type of the value document, in the case of banknotes thus for example the denomination or denomination and currency, and the orientation of the value document, for example front or back side of the banknote and upright orientation or not, and store corresponding values. Furthermore, the color image is no longer needed for the process to be described here, so that the further use of the color image will not be further described. In step S14, the evaluation device determines the pixels in the examination regions of the IR image specified for the value document type and the recognized orientation, and for these examination regions, among the pixels in the respective examination region error pixels. For this purpose, it checks, for each of the pixels in the respective examination region, whether the pixel data of the pixels lie within or outside a predetermined pixel- and / or location-dependent authenticity range. Pixels are recognized as error pixels if their pixel data is outside the predetermined pixel and / or location-dependent authenticity range. In the present example, all pixels can be run through in succession, the test being performed only for the pixels in the examination areas. However, in other exemplary embodiments it is also possible to determine for each of the examination areas a list of those pixels which lie within the respective examination area; then the test can then be performed for each of the examination areas using the respective list.

In the present example, the image is an IR image whose pixels have only brightness values as pixel data. The pixel data are only one-dimensional. Accordingly, the authenticity range for a respective pixel is also one dimensional only, in the present example an interval. The limits of the respective interval depend on the respective pixel of the image of the value document or the location on the value document. The intervals for the pixels of the examination areas can be obtained by capturing IR images for a given, preferably large, number of value documents of the specified value document type in the respective orientation and in fresh as well as used state, the IR images as well as possible to cover be brought and then from the distribution of the pixel data, in this example the brightness values, the limits of the respective interval are determined. The limits can be determined, for example, by statistical methods or by estimation. This results in two threshold images for the examination areas: an upper threshold image is given by the upper interval boundaries as pixel data and a lower threshold image by the lower interval boundaries as pixel data.

FIG. 4 shows by way of illustration a diagram in which brightnesses H are shown for pixel n along a straight line parallel to a longitudinal edge of a value document, for example the value document in FIG. 2. The lines OG and UG shown in solid lines for the sake of simplicity represent the upper and lower limits of the authenticity range for the pixels n. The authenticity range for a pixel lies between the lines UG and OG at a pixel corresponding to the n-axis the pixel corresponding point intersecting lines parallel to the H axis. By way of example, pixel data of a captured IR image are shown, which are represented by crosses. Some of the pixel data are within the authenticity range, i. H. between the upper and lower limits. The pixel data marked with o lie above the authenticity range, ie correspond to upper error pixels, the pixel data marked u are below the corresponding authenticity range and thus belong to lower error pixels.

In this embodiment, in the step of determining the error pixels for the examination areas, the error pixels are divided into upper error pixels whose pixel data are out of the authenticity range in a first direction and lower error pixels whose pixel data are in a second direction opposite to the first direction outside the authenticity area lie. Since the area of authenticity diminishes in this example sional and is an interval for a respective pixel, the upper error pixels are error pixels whose pixel data are above the authenticity range, in this case the upper interval limit, and the lower error pixel error pixels whose pixel data are below the authenticity range, in this case the lower interval limit , Hegen. During the check, the evaluation area 34 writes the pixels which it has detected as upper error pixels into a first list associated with the respective examination area and the pixels which it has recognized as lower error pixels into a second list assigned to the respective examination area. Specifically, by writing the pixels into the list, it can be understood, in particular, that corresponding pixel identifying data is written to the list. In other embodiments, however, it is also possible to assign identifiers to the pixels or pixel data which characterize a respective pixel as an upper or lower error pixel.

In the following step S16, the off-value means 34 checks if any error pixels have been detected. If this is not the case, the value document or its image is assigned the authenticity class "recognized as genuine" in a step S20.

If this is not the case, the evaluation device 34 checks in the following step S18 whether the error pixels in the examination areas correspond to a contamination, for example a patch, on the value document, or not. In the present exemplary embodiment, in the step of checking, the evaluation device 34 carries out for each of the examination regions a first range check S18A for the upper error pixels and a second range check S18B for the lower error pixels (see FIG. An area check is only carried out and considered in the sequence if corresponding upper or lower error pixels for the respective examination area were found. These area checks for the examination areas can be performed one after the other, nested or parallel.

The evaluation device 34 then determines that the upper or lower error pixels in the examination areas correspond to at least one contamination, for example at least one patch on the document of value, if a predetermined minimum number, in the example all area tests for the respective examination areas, indicate that the upper or lower error pixels lower error pixels in the respective examination area of at least one contamination, for example at least one spot, on the value document.

On the other hand, the evaluation device 34 recognizes that error pixels do not correspond to contamination if at least one of the area checks shows that the error pixels used in the respective area check do not correspond to soiling, for example at least one spot, on the value document.

In step S20, the evaluation device 34 assigns the security document "counterfeit-suspect" to the value document or image if an indication of no contamination has been detected, otherwise the authenticity class is assigned "recognized as genuine". In this step S20, the evaluation device 34 stores a corresponding value and forms a signal representing the assigned authenticity class.

These results for the authenticity classes are then linked in the following process steps, which are not described in more detail, with results of a color image based verification. These are in Fig. 3 as only Step S22 illustrated. Depending on the result of the test, the control device then controls the points. For example, a value document can be classified as "recognized as genuine" if all authenticity checks have yielded this authenticity class. In other cases, the authenticity class can be assigned "forgery-prone".

In the present embodiment, the evaluation device 34 compares for each of the examination areas as the area criterion in the first and second area tests, respectively, if the number of upper error pixels in the respective examination area determines a first maximum value specified for the respective examination area or the number of lower error pixels one for the exceed the given examination range given second maximum value. In the present exemplary embodiment, the upper and lower maximum values for a respective examination area are the same and equal to the smallest integer, which is greater than 90% of the number of all pixels in the respective examination area. The evaluation device 34 detects an indication of contamination in the examination area on the value document if the numbers of the error pixels, i. H. the number of upper error pixels and the lower error pixels, the respective maximum value fall below. These tests are symbolized in FIG. 6A or FIG. 6B by a block BlOa or BlOb.

A second embodiment in Fig. 7 differs from the previous embodiment in that the first and second area checks S18A and S18B are replaced by first and second area checks S18A 'and S18B' (see Fig. 8). For this purpose, step S14 is also replaced by a step S14 '. The other steps remain unchanged. Step S14 'differs from step S14 in that, in determining the error pixels for the upper and lower error pixels, distances of the pixel data from the authenticity regions are determined. For the upper error pixels, therefore, the difference between the pixel data and the upper range or interval limit is formed as the distance, and the difference from the lower range or interval limit and pixel data is formed and stored as the distance for the lower error pixels. This is illustrated in Fig. 4, in which the distance A ^{1 represents} the difference between the brightness, ie the pixel data and the upper limit, for an upper error pixel. Accordingly, the distance A "represents the difference between the lower limit and the brightness, ie the pixel data, for a lower error pixel.

The step S18 is replaced by a step S18 'shown roughly in FIG. 8, which differs from the step S18 in that instead of the range tests S18A and S18B with the range checks BlOa and BlOb for the examination areas, range checks S18A 'and S18B' with partial examinations B12a and B14a or B12b and B14b for the examination areas. When checking whether error pixels in the examination areas correspond to contamination, the evaluation unit 34 performs the partial checks B12a or B12b for the upper and lower error pixels of a respective examination area, whether a distribution of the distances of the upper error pixels according to a predefined for the respective examination area satisfies the upper distribution criterion and a distribution of the distances of the lower error pixels after a given for the particular study area lower distribution criterion for the presence of contamination or not. This is exemplified in FIG. In the two representations (a) and (b) histograms are shown which - in arbitrary units - show the frequency H of the distances found as a function of the distances A. Contaminated value documents (see Fig. 10 (a)) show a broad distribution since deviations due to contamination are not systematic. In the case of counterfeiting (see Fig. 10 (b)), on the other hand, the distances are much sharper, ie of smaller width, distributed, since the falsification-related deviations are very often systematic and in particular very similar. In the present exemplary embodiment, the evaluation device 34 (see block B12a or B12b in FIGS. 9A, 9B) checks in each case, when checking the upper or lower distribution criterion, whether the width of the distribution exceeds or exceeds a predetermined upper or lower threshold value below. As a measure of the width of the distribution, in the present embodiment, the variance coefficient, ie the standard deviation of the distances of the upper error pixels divided by the average of the distances of the upper error pixels and the standard deviation of the distances of the lower error pixels divided by the average of the distances of the lower error pixels , The threshold values are predetermined separately for each of the examination areas and can be determined by analyzing predefined value documents of the specified value document type, for example by estimation. The threshold values may in particular be greater than the corresponding variance coefficients of pressure-fresh value documents of the specified type.

When the respective threshold value is exceeded by the respectively determined width, in this case the distribution coefficient, an indication of the presence of soiling is recognized. Overall, in this range test, an indication of contamination is only recognized if the upper and lower coefficients of variance exceed the predetermined threshold. Furthermore, when checking whether error pixels in the examination areas or each of the examination areas correspond to contamination, the evaluation unit 34 carries out the partial tests B14a or B14b (see Figures 9A and 9B) for each of the examination areas in the area tests, whether a local correlation the upper error pixels in the respective examination region with a predetermined reference image of the examination region or a correlation of the lower error pixels in the examination region with a predetermined reference image of the examination region exceeds or does not exceed a predetermined upper or lower correlation maximum value for the region. Falling below is detected as an indication of the presence of contamination. In this embodiment image, a print image for value documents of the recognized value document type is used as the reference image, which can be obtained by averaging over a predetermined number of color print images of freshly printed value documents of the recognized value document type in the recognized orientation. With a high local correlation of the deviations with the reference image, one must assume systematic deviations, as typically occur in counterfeiting. However, stains are often randomly present on a document of value and show a non-uniform, often coincidental course, which then leads to deviations that do not correlate well with the reference image. In this embodiment, the correlation is determined for different displacement vectors on the grid of the pixels of the image, and the maximum correlation is used as a correlation. The displacement vectors v have a length smaller than a predetermined maximum length, in the case of play as a given factor M multiplied by the length of the pixels or the distance of nearest adjacent pixels from each other. In the example, the natural number M is 5. The correlation is represented by the maximum normalized cross-correlation between the distances of the error pixels and in their relative position to each other corresponding pixels of the reference image. Denote {i} or {j} the sets of upper and lower error pixels and Ai and A _j denote the deviations of the pixel data, ie brightnesses of the error pixels, the authenticity range boundaries at locations i and j in the IR image and Ri or R, the pixel data for a suitable color channel of the reference image, for example the red channel, for pixels at the locations i and j, respectively, can function as normalized cross-correlation as a function of the displacement vector v

for the correlation of the upper error pixels or the function

be used for the correlation of the lower error pixels.

Ri + v denotes the value for the pixel at the location that results by adding the vector v to the location of the error pixel i. The same applies to the lower error pixels. Only if the two partial examinations B12a and B14a or the two partial examinations B12b and B14b for a respective one of the examination areas show that indications of the presence of soiling have been detected, is S18A 'or S18B for the corresponding first or second area check 'recognized that the respective error pixels in the examination area correspond to at least one pollution.

It is then determined in step S18 'that the error pixels in the examination areas correspond to at least one contamination, if this was determined for the upper and lower error pixels in the area checks S18A' and S18B 'for all examination areas.

The assignment of the authenticity class in step S20 is carried out as in the first embodiment.

A third embodiment differs from the previous embodiment in that the first and second range checks S18A 'and S18B' are performed interleaved. In this case, the partial tests B12a, B14a, B12b, B14b are first carried out for each of the examination areas. It is determined for each of the examination areas, whether the error pixels in this at least one pollution or not. The evaluation device decides that the error pixels in the examination areas correspond to at least one contamination, if this has been determined for each of the examination areas.

A further exemplary embodiment differs from the preceding exemplary embodiments in that it is already decided in step S18 or step S18 'that error pixels do not correspond to contamination, if the first or second one of at least one of the examination regions Range check has shown that the upper and lower error pixels of this investigation area do not correspond to contamination, and then no further area checks are performed. Still further exemplary embodiments differ from the preceding exemplary embodiment or the second exemplary embodiment in that the first and second range tests have three partial tests, namely the tests BlOa or BlOb of the first exemplary embodiment and the partial tests B12a and B14a or B12b and B14b. The evaluation device 34 then determines, in step S18 ', that the first range check for the upper error pixels or the second range check for the lower error pixels results in the upper or lower error pixels in the respective examination area of at least one contamination, for example at least a patch corresponding to the document of value, if a predetermined minimum number, in the example two, of the partial checks for the respective area check result that the upper or lower error pixels in the respective examination area correspond to at least one contamination, for example at least one patch, on the value document.

Still other embodiments differ from the previous embodiments in that additionally the special investigation area is used for the test. Fig. 11 illustrates one of these embodiments, which corresponds to the first embodiment, but includes the examination of the special investigation area. Unless otherwise mentioned below, the steps correspond to the reference numerals of the first embodiment. Game the steps of the first embodiment and the explanations to these apply accordingly here.

As illustrated in Fig. 11, a step S14 "is executed instead of the step S14. The step S14 differs from the step S14 in that the evaluation means additionally determines, for the special investigation area among the pixels therein, authentication pixels whose pixel data are above a minimum threshold. In the case of the special investigation area which contains the security thread, the minimum threshold value defined is a minimum brightness value which corresponds to a transparent value document and can be selected, for example, as a function of the noise level of the sensor used. This can also be understood to mean that an interval is also defined here whose lower limit is zero and whose upper limit is the minimum value. To determine the authenticity pixels, the evaluation device 34 checks whether the pixel data of the pixels are above the minimum threshold value. If this is the case, the pixels are marked as authenticity pixels analogous to the error pixels.

In a manner corresponding to the test in the examination areas, the evaluation unit 34 performs a test for the special examination area. After the step S14 ", it compares the number of authenticity pixels with the minimum number specified for the section or special investigation area in a step S30. In the example, the minimum number is the integer greater than 95% of the number of pixels in the area Special investigation area or the corresponding section of the value document which results in a genuine, freshly printed value document. In step S32, it then assigns to the value document or image an authenticity class from the predefined authenticity classes as a function of the result of comparing the number of authenticity pixels with the minimum number. More precisely, the authenticity class is associated with "suspected counterfeiting" if the determined number of authenticity pixels is smaller than the minimum number. Otherwise, the authenticity class is assigned "recognized as true". As in step S20, the evaluation device 34 stores a corresponding value and in step S22 "forms a signal representing the assigned authenticity class, with the assigned authenticity class" only recognized as genuine "if both step S20 and step S32 have revealed this ..

Other exemplary embodiments differ from the preceding exemplary embodiments in that the range checks S18A or S18B are carried out for at least one of the examination regions and the range tests S18A ¹ or S18B 'for at least one other of the examination regions. Further exemplary embodiments differ from the preceding exemplary embodiments in that the reference image used is an IR image which can be obtained, for example, by averaging over a predetermined number of freshly printed genuine value documents in the recognized orientation.

Still other embodiments differ from the previous embodiments in that the IR image is not used but the color image. In the color space in which the pixel data is specified, then a direction is set. Instead of the IR data will be the projections of the pixel data attf used this direction. The areas of authenticity are then given in relation to this direction.

In yet further embodiments, instead of the normalized cross-correlation, the absolute or quadratic error may be used, with the highest correlation occurring with minimal error.

Other embodiments may differ from the previously described embodiment in that only one examination area is used.

Claims

P a n t a n s p r e c h e

1. A method for checking documents of value, in particular also soiled documents of value, on authenticity, with the steps

Capturing pixel data from pixels of an image of the value document,

Determining pixels in one or at least two predetermined examination areas of the image and for the or the at least two examination areas determining error pixels among the pixels in the or a respective one of the at least two examination areas, wherein the pixel data of the error pixels each outside a predetermined pixel and / or location-dependent authenticity range,

Checking whether or not the defect pixels in the examination areas correspond to contamination, for example a spot, on the document of value or not, and

Assign an authenticity class from predetermined authenticity classes to the value document as a function of the result of the checking.

The method of claim 1, wherein in the step of determining the error pixel or in the step of checking, the error pixels are divided into upper error pixels whose pixel data is out of the authenticity range in a first direction and lower error pixels whose pixel data in a second is to the first direction opposite direction lie outside the authenticity area.

3. The method of claim 2, wherein the authentication area is one-dimensional and the upper error pixels are error pixels whose pixel data are above the authenticity range, and the lower error pixels are error pixels whose pixel data are below the authenticity range.

4. The method of claim 2 or 3, wherein in the step of checking for the or the examination areas in each case at a first range check is checked whether the upper error pixels at least one pollution, for example, at least one patch, and / or in each case second area check is checked whether the lower error pixels correspond to at least one pollution, and

it is decided that the error pixels in the examination area (s) correspond to a contamination when at least a predetermined minimum number of area checks have revealed that the upper or lower error pixels in the respective examination area are at least contaminated, for example at least one spot Value document, or

It is decided that error pixels in the examination areas do not correspond to at least one contamination, for example at least one spot, on the value document if at least a predetermined minimum number of area checks have revealed that the upper or lower error pixels in the respective examination area do not at least one contamination, for example at least one patch, correspond to the document of value.

5. The method of claim 4, wherein in the first range check for the or one of the examination areas, the number of upper error pixels in the respective examination area with a predetermined first maximum value is compared and / or in the second range test for or one of Examination areas the number of lower error pixels is compared with a predetermined second maximum value, and an indication of contamination in the respective examination area is detected, if the numbers of the respective upper limit value, or an indication of no contamination on the value document in the respective examination area is detected if the first and / or the second number exceeds the first or second maximum value.

6. The method according to any one of claims 2 to 5, wherein when determining or checking for the upper and lower error pixels distances of the pixel data are determined by the authenticity areas.

7. The method according to claim 6, wherein in the first range check for the or one of the at least two examination areas it is checked whether a distribution of the distances of the upper error pixels satisfies an upper distribution criterion prescribed for the examination area and / or in the second range examination for or one of the at least two examination areas satisfies a distribution of the distances of the lower error pixels to a lower distribution criterion for the presence of contamination predetermined for the examination area.

Method according to Claim 7, in which, when checking the distribution criterion, it is in each case checked whether the width of the distribution exceeds or falls below a predetermined threshold value and, if the threshold value is exceeded, an indication of the presence of contamination is preferably detected.

Method according to one of claims 2 to 8, wherein in the first and second range test for the or one of the at least two predetermined examination areas, a correlation of the upper and lower error pixels in the examination area with a predetermined Reference image of the examination area is determined and preferably an indication of the presence of contamination is detected when the correlation of the upper and lower error pixels falls below a predetermined maximum correlation value.

10. The method of claim 1, wherein, in the step of checking whether the error pixels in the one or more examination regions correspond to a contamination, it is checked whether the number of error pixels is smaller than a threshold value specified for the respective examination region, and if this is the case, a presence of contamination is detected or an indication of the presence of contamination is detected.

11. The method according to any one of the preceding claims, wherein the image is an IR image of the value document.

12. A method for checking value documents, in particular soiled value documents, with section having an IR-absorbing security feature, preferably a security thread, on authenticity, with the steps

Capturing pixel data from pixels of an IR image of at least the portion of the value document,

Determining authenticity pixels among the pixels in the IR image of the section, wherein the pixel data of the authenticity pixels are above a minimum threshold value,

Comparing the number of authenticity pixels with a minimum number specified for the section, and

Assigning an authenticity class from predetermined authenticity classes to the value document as a function of the result of the comparison the number of authenticity pixels with the minimum number.

13. Device for checking documents of value, in particular soiled documents of value for authenticity, with

an optical sensor for capturing an image of the document of value, wherein the image has pixels to which pixel data are assigned, and an evaluation device which is adapted to carry out a method according to one of the preceding claims. 14. Apparatus for processing value documents, in particular also soiled value documents, with

a feeder for documents of value to be processed,

an output device for value documents, which has at least two output sections for receiving processed value documents, a transport device for transporting individual documents of value from the feed device along a transport path to the output device,

- A test device according to claim 13, which is arranged so that the transport path passes through the detection area, and

a control device which, in dependence on an authenticity signal of the checking device for a value document transported by the transport device, controls the transport device in such a way that the value document is transported into an output section of the at least two output sections corresponding to the authenticity signal.

15. Computer program for execution by means of a data processing device with a processor containing program code, in the execution of which the processor carries out the method according to one of claims 1 to 12.

16. Computer-readable data carrier on which a computer program according to claim 15 is stored.