EP3050032B1 - Method of testing valubale documents of polymer material which has a transparent window and means to perform the method - Google Patents

Description

The present invention relates to a method for checking a document of value with a polymer substrate and at least one see-through window as well as means for carrying out the method.

In this context, documents of value are understood to be sheet-like 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 features that are not easy to produce, in particular to be copied, the presence of which is an indication of authenticity, i.e. production by an authorized body. Important examples of such documents of value are coupons, vouchers, checks and, in particular, bank notes.

The invention relates to the checking of a certain type of documents of value, namely those with a polymer substrate and at least one see-through window.

The documents of value have a polymer substrate, which is understood to mean that they have at least one polymer layer which at least partially serves as a carrier. They are preferably polymer banknotes.

Documents of value with such polymer substrates usually have on the surface of the polymer substrate one or preferably a plurality of cover layers which are opaque in the visible wavelength range and are applied over a large area; often the top layer or the top layers are printed on. With this or these, an appearance similar to a paper value document is to be achieved, among other things. The top layer also serves as, among other things Carrier for printing inks with which the value document is printed. However, the value document only needs to have an opacity in the visible wavelength range, as is customary with paper value documents. In particular, the value document with the cover layers can still be very weakly translucent.

The documents of value to be checked or checked within the scope of the invention also have a see-through window, which in the following is understood to be an area of the document of value that is transparent or translucent and not opaque, flat for optical radiation in a predetermined wavelength range, preferably the visible spectrum Has applied top layer. As far as the transparency or translucency is given, the see-through window can be printed over the whole area with a transparent or translucent printing ink or also printed with any other printing inks or a material used to form the cover layer in halftone printing.

The see-through window can have any shape and is delimited by at least one flat area formed by the one or more cover layers.

A problem of such documents of value is that they can lose printing ink or parts of the opaque, two-dimensional cover layer at individual points in the course of use or circulation. For example, the printing ink or the opaque layer can flake off at these points. Such a deviation from a new document of value caused by the loss of the opaque layer and / or the printing ink possibly located thereon is referred to in the context of the present invention as print erosion.

Such passages are errors in the document of value and, under certain circumstances, reduce its usability or fitness for circulation. It would therefore be desirable to be able to check documents of value for such print jobs. Checking is not easy, however, as there can be significant fluctuations between different print batches.

In WO 2013/091856 A1 describes a method for checking a value document of a predetermined value document type with a window that has a film area, in which spatially resolved measured values for an ultrasonic transmission of the value document are determined, and in which, using the measured values, it is checked whether for a predetermined number of locations In a given test area the ultrasound transmission according to a given criterion is greater than a given minimum ultrasound transmission which is characteristic of a given section of at least one value document of the given value document type lying outside the test area.

The present invention is therefore based on the object of creating a method for checking a document of value with a polymer substrate and a see-through window, by means of which the cover layer can be checked for the presence of print erosion, as well as providing means for carrying out the method.

The object is achieved by a method for checking a document of value with a polymer substrate and at least one see-through window, in which a digital transmission image of the document of value is recorded, the transmission image comprising pixels, in which an edge brightness value is determined for the brightness of an edge of the at least one see-through window in the transmission image using the edge brightness value a threshold value for the detection of a printing defect is determined, which is smaller than the edge brightness value, but is greater than the minimum brightness in the transmission image, and pixels of the transmission image are searched that are in at least one predetermined section of the transmission image and outside of the at least one see-through window and whose edge lie and which have a brightness that is above the threshold value.

The object is further achieved by a device for checking a document of value with a polymer substrate and at least one see-through window, with an evaluation device which is designed for this purpose to carry out the method according to the invention. In particular, the evaluation device can be designed to capture a digital transmission image of the document of value, the transmission image comprising pixels to determine an edge brightness value for the brightness of an edge of the at least one see-through window in the transmission image, using the edge brightness value to assign a threshold value for the detection of a printing error determine which is smaller than the edge brightness value, but greater than the minimum brightness in the transmission image, and to search for pixels of the transmission image which lie in at least one predetermined section of the transmission image and outside the at least one see-through window and its edge and which have a brightness, which is above the threshold. The method according to the invention can in particular be carried out by means of the device according to the invention.

To carry out the method, the device has the evaluation device. This can have a data processing device, which can have, for example, a computer or at least one processor and / or at least one FPGA, for processing the transmission image. The evaluation device can have a memory in which a computer program is stored so that the evaluation device, preferably the data processing device, executes the method according to the invention when the computer program is executed.

The object is therefore also achieved by a computer program for execution by means of a data processing device, which has program code, when the data processing device executes a method according to the invention when it is executed.

The object is further achieved by a physical data carrier which can be read by means of a data processing device and on which a computer program according to the invention is stored.

In the method, transmission images of the stated documents of value are used to identify print jobs in the stated documents of value. The transmission images can be transmission images in a predetermined wavelength range of the visible spectrum, for example in the green range. The transmission images are preferably transmission images in the infrared wavelength range, i.e. IR transmission images; the process then works particularly effectively. If the brightness of pixels in the transmission image that are outside the see-through window and its edge exceeds the threshold value, this is an indication of the presence of print removal. However, the threshold value is difficult to set for a large number of documents of value.

It has now been found that a see-through window in the transmission image has an edge with a particularly high intensity or brightness probably caused by scattering, which is suitable for determining the threshold value, so that fluctuations between different print batches no longer play such a major role. The edge is understood to mean an area delimiting the see-through window in the transmission image, which area can be one or more pixels wide.

In the method, the digital transmission image is first recorded, which comprises pixels, the properties of which are described by pixel data. The transmission image describes, spatially resolved, the intensity detected during a transmission examination with visible light or preferably during a transmission examination with IR or infrared radiation. In particular The pixel data can include a value for a brightness which corresponds to the intensity of the detected transmission radiation.

In principle, it is sufficient for the digital image to only be captured, for example corresponding pixel data to be read or received. For this purpose, the device, preferably the evaluation device, can have a suitable interface via which the digital image can be captured.

In the method, however, the transmission image is preferably recorded by means of an optical transmission sensor. For this purpose, the device preferably also has an optical transmission sensor for capturing a digital transmission image of the document of value, which is coupled to the evaluation device via a signal connection; the evaluation device is then designed to capture an image of the transmission sensor as a digital image. The transmission sensor can be, for example, a transmission sensor for capturing a transmission image in the visible wavelength range. The optical transmission sensor preferably comprises or is an optical transmission sensor for capturing a digital infrared transmission image of the document of value. The transmission sensor can in particular have a source for optical radiation in a specified visible wavelength range or infrared wavelength range and a receiver for optical radiation that has passed through the document of value in the specified visible wavelength range or infrared wavelength range.

Furthermore, in the method, the edge brightness value for the brightness of an edge of the at least one see-through window is determined.

The edge brightness value can be determined differently depending on the embodiment of the method and depending on the value document type of the value document. The value document type is given at least by the type of value document, for example a check or bank note. In the case of bank notes, the value document type is also given by the currency, the denomination or denomination and optionally the issue and / or the position in the transport path.

According to a first alternative, a maximum of the brightness of the pixels of the entire transmission image of the document of value is determined as the edge brightness value. In the device, the evaluation device is then preferably designed to determine, as the edge brightness value, a maximum of the brightness of the pixels of the entire transmission image of the document of value. This embodiment is particularly advantageous if the value document of the given value document type has a lower transmission in the wavelength range used, for example in the visible wavelength range or a lower infrared transmission in all areas except the edge of the see-through window. In particular, the edge brightness value can be determined very quickly, brightness maxima over columns or lines of the transmission image are available anyway. The exact position of the see-through window does not then need to be determined.

According to a second alternative, an area of the transmission image showing the at least one see-through window with its edge can be determined, and the maximum brightness value of at least two of the pixels of at least the edge of the image of the see-through window can be used as the edge brightness value. But it is also possible that the maximum of the brightnesses of the area of the transmission image is determined and used as Edge brightness value is used. The evaluation device of the device can then preferably be designed to determine an area of the transmission image showing the at least one see-through window with its edge, and to use the maximum of the brightnesses of at least two of the pixels of at least the edge of at least the edge of the see-through window as the edge brightness value, or it can be designed to determine the maximum brightness of the area of the image and to use it as the edge brightness value. The shape and size of the area and optionally also the position of the area on the value document can preferably be predetermined for a respective value document type and in particular be selected so that it encloses the see-through window and its edge in the transmission image or an edge area of suitable width around the see-through window. To determine the area, the value document type of the value document can then be determined beforehand. The edge brightness values determined in this way have proven to be particularly favorable for determining the threshold value.

If the value document has several see-through windows, preferably the mean value or particularly preferably the maximum of the edge brightness values of the several see-through windows can be used as the edge brightness value. The evaluation device can then be designed accordingly.

The edge brightness value is used to determine the threshold value. The threshold value is smaller than the determined edge brightness value, but greater than the minimum brightness in the transmission image. The threshold value is preferably determined in such a way that it is greater than a mean value over the brightnesses of the pixels in at least one predetermined part of the transmission image or a mean value over the brightnesses of the pixels in the transmission image of the entire document of value is. The evaluation device of the device is then preferably designed to determine the threshold value so that it is greater than a mean value over the brightnesses of the pixels in at least one predetermined part of the transmission image or an average value over the brightnesses of the pixels in the transmission image of the entire document of value. This results in a more reliable detection of print removals. This is the case in particular in the preferred embodiment of the method in which the predetermined part of the transmission image does not show the see-through window and the edge of the see-through window.

When searching for pixels that are located in at least one predetermined section of the transmission image and outside the see-through window and its edge and that have a brightness that is above the threshold value, pixels with brightnesses above the threshold value are determined or found, these locations are set up the document of value with a print removal. The predetermined section can preferably include the entire document of value without a predetermined area which contains the see-through window and its edge. If the value document has a plurality of see-through windows, the predefined section can preferably comprise the entire value document without predefined areas which each contain a see-through window and its respective edge. The area or areas are particularly preferably selected such that their area is in each case not, or at most 10%, greater than the area of the see-through window and its edge.

Preferably, pixels found during the search are used which are located within the specified section of the transmission image and outside the see-through window and its edge and which have a brightness which is above the threshold value is identified as a deviation pixel. The evaluation device can then be designed to identify pixels found during the search which are within the specified section of the transmission image and outside the see-through window and its edge and which have a brightness that is above the threshold value as deviation pixels. This can simplify the further investigation of possible print jobs. The identification can take place, for example, by storing corresponding data or by shifting the pixel data describing the pixels to other memory areas.

Depending on the result of the search, at least one signal can then be generated and / or at least one datum can be stored which represents the result of the search.

In principle, it can suffice to only check whether pixels have been found in the specified section whose brightness exceeds the threshold value. It is preferably determined how many pixels were found during the search. In the device, the evaluation device can then preferably be designed to determine how many pixels were found during the search. A corresponding value can then preferably be stored.

Furthermore, a local distribution of the pixels found during the search can preferably be determined, ie those pixels of the transmission image which are in the specified section and outside the see-through window and its edge and whose brightness is above the threshold value. The evaluation device of the device can then preferably be designed to determine a local distribution of the pixels found during the search, ie those pixels of the transmission image, which lie in the specified section and whose brightness is above the threshold value. Particularly preferably, for example, when determining the local distribution of the pixels found during the search, sets of deviation pixels can be determined in which two of the pixels of the same set are adjacent in each case. In the device, the evaluation device can then particularly preferably be designed to determine sets of deviation pixels when determining the local distribution of the pixels found during the search, in which two of the pixels of the same set are adjacent in the transmission image. In this case, pixels that are adjacent in the transmission image are preferably understood to mean pixels which are directly or next adjacent in the transmission image, that is to say have a minimal distance from one another. However, it is also possible for pixels that are adjacent in the transmission image to be understood as pixels that are next or next but one neighbors. The number of quantities and, for each of the quantities, the number of pixels therein and / or the area corresponding to the pixels can then be determined.

It is further preferred that a status value for the value document is determined as a function of the result of the search, preferably as a function of the determined number and / or the determined local distribution of the pixels found during the search. The evaluation device of the device can then preferably be designed to determine a status value for the value document as a function of the result of the search, preferably as a function of the determined number and / or the determined local distribution of the pixels found during the search. The status value can preferably represent an indication of the presence of a pressure removal and can be stored. The pixels found during the search are again those of the pixels of the transmission image that are in the specified section and outside of the at least a see-through window and its edge and the brightness of which is above the threshold value. The aforementioned number of sets and the maximum number of pixels of the sets can particularly preferably be used when determining the state value. This allows a particularly good statement about the significance of the damage to the document of value or its fitness for circulation, ie suitability for further use in the money cycle. When determining the status value, results of other tests of the value document can also be used.

The invention also relates to a device for processing documents of value with a feed device for feeding documents of value, an output device for receiving processed, i.e. H. sorted documents of value, and a transport device for transporting separated documents of value from the feed device to the output device. The device further comprises a device according to the invention for checking the transported documents of value.

Fig. 1

eine schematische Ansicht einer Wertdokumentbearbeitungsvorrichtung in Form einer Banknotensortiervorrichtung,

Fig. 2

eine schematische Darstellung eines Infrarot-Transmissionsbildes eines Wertdokuments mit einem Polymersubstrat und wenigstens einem Durchsichtsfenster, das mit der Vorrichtung in Fig. 1 für ein Wertdokument erfassbar ist,

Fig. 3

eine schematische Ansicht eines Schnitts durch das dem Transmissionsbild in Fig. 2 zugrundeliegende Wertdokument entlang der Linie A-A',

Fig. 4

ein vereinfachtes Ablaufdiagramm einer ersten Ausführungsform eines mittels der Vorrichtung in Fig. 1 durchführbaren Verfahrens zum Prüfen eines Wertdokuments mit einem Durchsichtsfenster, und

Fig. 5

eine schematische Darstellung der Lage von Abweichungspixeln in dem Bild in Fig. 2.

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

Fig. 1

a schematic view of a value document processing device in the form of a bank note sorting device,

Fig. 2

a schematic representation of an infrared transmission image of a document of value with a polymer substrate and at least one see-through window which is connected to the device in FIG Fig. 1 can be recorded for a value document,

Fig. 3

a schematic view of a section through the transmission image in FIG Fig. 2 underlying document of value along the line A-A ',

Fig. 4

a simplified flow chart of a first embodiment of a device by means of FIG Fig. 1 feasible method for checking a value document with a see-through window, and

Fig. 5

a schematic representation of the location of deviation pixels in the image in FIG Fig. 2 .

A value document processing device 10 in Fig. 1 , in the example a device for processing documents of value 12 in the form of banknotes, is designed for sorting documents of value as a function of the detection of the authenticity and the status of processed documents of value. The components of the device described below are arranged in a housing of the device (not shown) or held on this, unless they are designated as external.

The device has a feed device 14 for feeding documents of value, an output device 16 for receiving processed, i. H. sorted documents of value, and a transport device 18 for transporting separated documents of value from the feed device 14 to the output device 16.

In the example, the feed device 14 comprises an input compartment 20 for a stack of value documents and a separator 22 for separating documents of value from the stack of value documents in the input compartment 20 and for feeding the separated documents of value to the transport device 18.

In the example, the output device 16 has three output sections 24, 25 and 26 into which processed value documents can be sorted according to the result of the processing. In the example, each of the sections comprises a stacking compartment and a stacking wheel, not shown, by means of which supplied documents of value can be stored in the stacking compartment. In other exemplary embodiments, one of the output sections can be replaced by a device for destroying bank notes.

The transport device 18 has at least two, in the example three branches 28, 29 and 30, at the ends of which one of the output sections 24 or 25 or 26 is arranged, and at the branches via switches 32 and 34 which can be controlled by actuating signals Documents of value can be fed to branches 28 to 30 and thus to output sections 24 to 26 as a function of control signals.

A sensor device 38 is arranged on a transport path 36 defined by the transport device 18 between the feed device 14, more precisely the separator 22 in the example, and the first switch 32 in the transport direction after the separator 22, which measures and measures physical properties of the value documents during the transport of value documents past forms sensor signals reproducing the measurement results. In this example, the sensor device 38 has three sensors, namely an optical remission sensor 40 which detects a remission color image and a remission IR image of the value document, an optical transmission sensor 42 which detects a transmission color image and a transmission IR image of the value document, and a transmission ultrasonic sensor 44 which, as an ultrasonic property, detects or measures the ultrasonic transmission of the value document in a spatially resolved manner and, for the sake of simplicity, is only referred to as an ultrasonic sensor in the following. The ones formed by the sensors Sensor signals correspond to measurement data or raw data from the sensors which, depending on the sensor, may have already been subjected to a correction, for example as a function of calibration data and / or noise properties.

The value document processing device 10 has an input / output device 46 for the acquisition and display of operating data. In the example, the input / output device 46 is implemented by a touch-sensitive display device (“touch screen”). In other exemplary embodiments, it can for example comprise a keyboard and a display device, for example an LCD display.

A control and evaluation device 48 is connected to the sensor device 38, the input / output device 46 and the transport device 18, in particular the switches 32 and 34, via signal connections.

The control and evaluation device 48 forms a data processing device and, in addition to corresponding data interfaces (not shown in the figures) for the sensor device 38 or its sensors, has a processor 50 and a memory 52 connected to the processor 50 in which at least one computer program with program code is stored . When the computer program is executed, the control and evaluation device 48 or the processor 50 evaluates the signals or measured values of the sensor device 38 and controls the device in accordance with the properties of the value documents. Thus, in its function as an evaluation device, it can evaluate the sensor signals, in particular to determine an authenticity class and / or a condition class of a processed document of value; in its function as a control device, it can control the transport device 18 according to the evaluation, and optionally save the measurement data. In other exemplary embodiments, an evaluation device which is separate from the control device and which is connected via interfaces to the sensors of the sensor device 38 on the one hand and the control device on the other hand can also be provided. The evaluation device is then designed to evaluate the sensor signals and supplies the respective result to the control device which controls the transport device. The evaluation processes described below can then be carried out by the evaluation device alone.

The control and evaluation device 48 also controls the input / output device 46, inter alia for displaying operating data, and uses this to record operating data that correspond to inputs by an operator.

During operation, documents of value are separated from the feed device and transported past or through the sensor device 38. The sensor device 38 detects or measures physical properties of the document of value transported past it or through it and forms sensor signals or measurement data which describe the measurement values for the physical properties. The control and evaluation device 48 classifies the value document into one of predetermined authenticity and / or status classes as a function of the sensor signals from the sensor device 38 for a value document and on the classification parameters stored in the evaluation device and controls the transport device 18, in this case more precisely the Assign 32 or 34 in such a way that the value document is output in an output section of the output device 16 that is assigned to the class in accordance with its class determined during the classification. The assignment to one of the specified authenticity classes or the classification takes place depending on at least one predetermined authenticity criterion.

For the checking of documents of value, which is described in more detail below, infrared transmission images captured by the transmission sensor 42 are used in particular. The transmission sensor 42 has an illumination section, by means of which a predetermined detection area of the transport path can be illuminated with optical radiation in the visible and in a predetermined infrared wavelength range. On the opposite side of the transport path 18, the transmission sensor 42 has a detection device for spatially resolved detection of a color image in the wavelength range of visible light and an infrared transmission image in the predetermined infrared wavelength range.

The transmission sensor 42 is designed as a line sensor which, during the transport of the document of value through the sensor, successively detects transmission line images of strips of the document of value running transversely to the direction of transport of the document of value. The detection device accordingly comprises rows of detectors. The transmission sensor 42 combines the captured line images to form digital transmission images which include pixels, the properties of which are described by pixel data. In particular, it captures a digital infrared transmission image of the document of value forming pixel data describing the pixels of the image and transmits this to the evaluation device 48. The pixel data for a pixel particularly describe a brightness that describes the intensity for the pixel received by the detection device.

In the exemplary embodiment described below, value documents of predetermined value document types are checked, have a polymer substrate and a see-through window. An example of such a value document of one of these predetermined value document types and its infrared transmission image is shown in FIG Figures 3 and 2 respectively. Fig. 2 shows schematically the infrared transmission image of the document of value 54, Fig. 3 a schematic sectional view along the line AA 'in Fig. 2 .

The value document 54 has a sheet-shaped transparent polymer substrate 56 as a carrier, which has cover layers 58 applied flatly on both surfaces, which have an opacity comparable to or greater than the opacity of banknote paper, at least in the visible wavelength range. These cover layers are shown hatched in the figures. Printed on this layer with a suitable printing ink is a print image 59, which is shown in FIG Fig. 2 is only indicated schematically.

The value document 54 also has a see-through window 60. The see-through window 60 is formed, inter alia, in that there is no flat cover layer in its area. The cover layers 58 thus extend over the entire document of value with the exception of the see-through window 60. In the present example there is also an imprint 62 with a transparent printing ink, which is shown in FIG Fig. 2 is shown dotted. Furthermore, the imprint comprises cover layer material applied by raster printing, which in the example in FIG Fig. 2 forms a triangle.

In an infrared transmission image recorded with the transmission sensor 42, which is shown in FIG Fig. 2 is shown schematically, an edge 64 is shown in addition to the elements mentioned, which surrounds the see-through window 60. This edge 64 is characterized by a particularly high receiving intensity or brightness, which is probably due to scattered radiation, since it corresponds to an edge area around the see-through window which still has a flat cover layer. The thickness of this cover layer, or, if a plurality of cover layers arranged one above the other are used, their number, can differ from the thickness or number in the other regions of the document of value 54.

Fig. 2 further shows two areas 68 which correspond to print removal, ie areas in which the cover layers 58, optionally with an imprint, have been rubbed off or flaked off.

A first exemplary embodiment of a method for checking a document of value with a polymer substrate and at least one see-through window, in particular for the presence of at least one print removal, is at least partially shown in FIG Fig. 4 roughly outlined in the form of a flow chart. To carry out the method, a computer program is stored in the control and evaluation device 48, more precisely its memory 52, and when it is executed, the control and evaluation device 48, more precisely the processor 50, executes the first embodiment of the method.

In step S10, a digital infrared transmission image of a document of value transported by the transmission sensor 42 is first recorded by means of the transmission sensor 42. As described above, the transmission sensor 42 detects optical radiation emanating from the value document, in particular in the predetermined infrared wavelength range, and forms measurement signals representing the corresponding detected intensities. Formed from these pixel data for pixels of a digital infrared image is a document of value which the control and evaluation device 48 detects.

In step S12, the control and evaluation device 48 determines its value document type and position using a color image of the value document recorded by means of the remission sensor 40. The currency and the denomination of the value document are determined as the value document type, as the position one of the four possible orientations of the value document in the transport path, which can be obtained by rotating the value document about axes parallel and transverse to the transport direction.

In step S14, the control and evaluation device 48 determines, as a function of the determined type of value document and the position of the value document, an area or see-through window area 66 predetermined for the type of value document and the position (cf. Fig. 2 ) for the see-through window 60 in the captured infrared transmission image. This area is selected such that the see-through window 60 and its edge 64, taking into account possible fluctuations in its manufacture, lie within the area 66 with a predetermined certainty, but its size is as small as possible under this condition. In particular, it shows the see-through window 60 with its edge 64.

In step S16, the control and evaluation device 48 determines an edge brightness value of the edge 64 of the see-through window 60. In the present exemplary embodiment, the control and evaluation device 48 determines the maximum brightness of the pixels in the area 66 of the infrared transmission image and stores the maximum as the edge brightness value.

In step S18, the control and evaluation device 48 calculates an average value of the brightnesses in a predetermined part of the transmission image. In the present example, this part is the entire transmission image with the exception of the area 66 or without the area 66.

In step S20, the control and evaluation device 48 then determines a threshold value for the detection of print removal which is smaller than the edge brightness value but greater than the minimum brightness in the transmission image. For value documents of the value document type present here, due to the design, the brightnesses in the area 66 are always above the minimum brightness in the rest of the transmission image, provided there are no print marks. More precisely, the control and evaluation device 48 therefore defines the threshold value in such a way that it is greater than the mean value determined in step S18. In this example, the threshold value is a weighted mean value from the edge brightness value and the mean value, the weighting factor being specified for the value document type. This can be determined, for example, by examining specified reference value documents of the specified value document type with print jobs.

In step S22, the control and evaluation device 48 searches for pixels which are located in at least one predetermined section of the transmission image and outside the at least one see-through window and its edge and which have a brightness that is above the threshold value. The entire transmission image with the exception of the area 66, which was used to determine the edge brightness value, is used here as the predetermined section.

During this search, the control and evaluation device 48 marks the pixels found whose brightness exceeds the threshold value as deviation pixels. In this example, identifiers of the pixels that represent the location are stored for marking purposes.

In step S24, the control and evaluation device 48 determines on the one hand the number of deviation pixels determined in step S22 and stores a corresponding value. On the other hand, it determines a local distribution of the pixels found in step S22. To do this, it determines sets of deviation pixels in which two of the pixels of the same set are adjacent. For this purpose, among other things, methods known as "blob labeling" algorithms can be used. In this exemplary embodiment, adjacent pixels are pixels with a minimal distance from one another. The pixels of the quantities determined in this way each form contiguous areas in the transmission image, i.e. a path leads from each pixel of a respective set to every other pixel of the respective set via neighboring pixels. Each of these quantities can thus represent a pressure removal. The control and evaluation device 48 then calculates the number of quantities thus found and the number of pixels, d. H. Deviation pixels, in these quantities. The number of quantities and the numbers of pixels are stored.

Fig. 5 shows schematically pixels of the transmission image in FIG Fig. 2 . Pixels that were not recognized as deviation pixels are shown as white-filled squares and deviation pixels as black-filled squares. It is easy to see that two sets 70 and 70 'of contiguous deviation pixels were recognized, each having a different number of pixels. These quantities correspond exactly to the areas 68 with print removals.

In step S26, the control and evaluation device 48 then determines a status value as a function of the determined number of deviation pixels, the number of determined quantities and the number of pixels in the quantities, which indicates whether the document of value can still be reused or not. is fit or not. For this purpose, the control and evaluation device 48 can compare the number of deviation pixels with a permissible maximum number and the number of quantities in relation to the number of deviation pixels determined in total with a predetermined limit value. In some exemplary embodiments, this status value can represent whether or not there is at least one pressure removal.

Depending on the determined state value, the control and evaluation device 48 can then, as described above, control the transport device 18. In other exemplary embodiments, state values determined using the remission sensor and using the ultrasonic sensor can also be taken into account during activation.

A second exemplary embodiment differs from the previous exemplary embodiment only in that step S16 is replaced by a step S16 '. The control and evaluation device 48 or the computer program therein is then changed accordingly. All other steps and components are unchanged.

Step S16 'differs from step S16 in that the maximum brightness of the pixels of the entire transmission image is determined as the edge brightness value. This makes use of the fact that the design of the value documents of the specified value document type does not provide for any areas in which the transmission is greater than that of the edge 64.

A third exemplary embodiment differs from the first exemplary embodiment only in that step 16 is replaced by a step S16 ″. The control and evaluation device 48 or the computer program it is then changed accordingly. All other steps and components are unchanged.

Step S16 ″ differs from step S16 only in that the area 66 is replaced by a strip-shaped area 66 ′ extending transversely to the transport direction of the value document in the transmission image from one edge of the value document to the opposite edge of the value document. This area 66 'is further selected so that the see-through window 60 and its edge 64, taking into account possible fluctuations in its manufacture, lie within the area 66' with a predetermined certainty, but its size is as small as possible under this condition its edge 64.

Yet another exemplary embodiment differs from the first exemplary embodiment solely in that step S16 is replaced by a step S16 "'. The control and evaluation device 48 or the computer program therein is then changed accordingly. All other steps and components are unchanged.

Step S16 "'differs from step S16 in that the mean value of the brightnesses of at least two of the pixels of at least the edge is used as the edge brightness value. More precisely, a number N, for example 10 or 20, is specified and the N largest Brightnesses are determined in area 66, which, according to the design of the value documents of the specified value document type, corresponds to the N greatest brightnesses of the edge 64. The mean value over the N greatest brightnesses is now used as the edge brightness value.

Yet another exemplary embodiment differs from the first exemplary embodiment in that, in step S16, the pixels in the edge 64 are first determined and then the maximum brightness of only the determined pixels of the edge is used as the edge brightness value.

Further exemplary embodiments can differ from the exemplary embodiments described above in that value documents of a value document type are checked which have at least two see-through windows, but are structured analogously to the value documents described above.

Step S14 is then modified in such a way that for each of the at least two see-through windows a see-through window area which corresponds to area 66 of the first exemplary embodiment is determined.

To determine the edge brightness, an edge brightness value for the respective see-through window can now be determined for all see-through windows, analogously to the previous exemplary embodiments. One of the edge brightness values, the maximum of the edge brightness values determined for the individual see-through windows, or an average value of the edge brightness values determined for the individual see-through windows can then be used as the edge brightness value. The following steps then differ from the steps of the previously described embodiments in that, to determine the mean value of the brightnesses and to search for deviation pixels, areas of the document of value or parts of the transmission image are used that do not include or include any of the see-through windows and none of the edges of the see-through windows . show.

Further exemplary embodiments differ from the exemplary embodiments described above in that, instead of the infrared transmission images, transmission images in a predetermined visible wavelength range are used. The transmission color image detected by the transmission sensor 42, more precisely its green image, can preferably be used.

Claims (14)

1. A method for checking a value document (12) having a polymer substrate and at least one see-through window (60), in which

   a digital transmission image of the value document (12) is captured, the transmission image comprising pixels,

   in the image an edge brightness value for the brightness of an edge (64) of the at least one see-through window (60) is ascertained,

   using the edge brightness value, a threshold value for the recognition of a print removal is ascertained which is smaller than the edge brightness value but greater than the minimal brightness in the image, and

   pixels are searched which lie in at least one specified portion of the image and outside the at least one see-through window (60) and its edge and have a brightness which lies above the threshold value.
2. The method according to claim 1, in which the digital transmission image is a digital infrared transmission image.
3. The method according to claim 1 or 2, in which as an edge brightness value the maximum of the brightnesses of the pixels of the whole transmission image is ascertained.
4. The method according to claim 1 or 2, in which a region of the image showing the see-through window (60) with its edge (64) is ascertained, and as an edge brightness value the mean value or the maximum of the brightnesses of at least two of the pixels of at least the edge of the image of the see-through window (60) is employed, or the maximum of the brightnesses of the region of the image is ascertained and employed as an edge brightness value.
5. The method according to any of the preceding claims, in which the threshold value is ascertained such that it is greater than a mean value over the brightnesses of the pixels in at least one specified part of the image or the pixels of the image of the whole value document.
6. The method according to claim 4, in which the specified part of the image does not show the edge (64) of the see-through window (60) and the see-through window (60).
7. The method according to any of the preceding claims, in which it is ascertained how many pixels were found upon the search.
8. The method according to claim 6, in which a local distribution of the pixels found upon the search whose brightness lies above the threshold value is ascertained.
9. The method according to any of the preceding claims, in which in dependence on the result of the search, preferably in dependence on the number and/or the local distribution of the pixels found upon the search a state value for the value document is ascertained.
10. An apparatus for checking a value document (12) having a polymer substrate and a see-through window (60), with
    an evaluation device (48) which is configured for executing a method according to any of claims 1 to 9.
11. The apparatus according to claim 10, which further has an optical transmission sensor (42) for capturing a digital transmission image of the value document (12) which is coupled to the evaluation device (48), and in which the evaluation device (48) is configured to capture an image of the transmission sensor as a digital image.
12. The apparatus according to claim 11, in which the optical transmission sensor (42) comprises an optical transmission sensor (42) for capturing a digital transmission image of the value document.
13. A computer program for execution by means of a data processing device, which has program code, upon the execution of which the data processing device of an apparatus according to claims 10 to 12 has a method according to any of claims 1 to 9 executed.
14. A data carrier which is readable by means of a data processing device and on which a computer program according to claim 13 is stored.

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