EP2787490A1 - Method for testing printed articles - Google Patents

Abstract

The invention relates to a method for testing printed objects (1), in particular of printing units such as banknotes, wherein a) a digital image (2) is created by the respective object to be tested (1) and assigned to the respective object (1), b) the digital image (2) with respect to its resolution, in particular its color depth, the number of its color channels and its local resolution, is reduced and such a reduced digital image (3) created and the respective object (1) is assigned, characterized in that c) a comparison of the reduced digital image (3) with at least one reduced reference image (5) is carried out as part of a coarse examination, d) the reduced digital image (3) is recognized as belonging to a defect-free object (1) in the event of a match exceeding a predetermined first threshold value (S 1), and the examination of the respective object (1) is ended, e) the object is classified as potentially defective in the case of a match of the reduced digital image (3) with the reduced reference image (5) which does not exceed the first threshold value, f) in the event that an object (1) has been classified as potentially defective, the object is subjected to a fine test, using the digital image (2) assigned to it for the object (1) and including this digital image (2) with at least one Reference image (4) is compared, wherein the item (1) is classified in the case of a second threshold exceeding agreement as "error-free", otherwise as "faulty", g) that the objects to be examined (1) are transported before and / or during their picking up relative to the picking unit (11) performing the picking, in particular with a transporting device (22), preferably with a conveying device, h) that the objects (1) after their coarse examination with respect to the test result, in particular with a first switch (23a), separated, and the potentially erroneously recognized objects (1) are transferred to a buffer (24), and i) that the items (1) located in the temporary store (24) are fed to a second switch (23b) after the fine inspection has been carried out and separated according to their classification.

Description

The invention relates to a method for testing printed objects according to the preamble of claim 1. Furthermore, the invention relates to a device for testing printed objects according to the preamble of patent claim 10.

The invention is preferably used to test freshly printed or fed banknotes before dispensing. Of course, other objects, in particular printing units, can also be checked for conformity with a given reference object or with a reference printing unit.

A variety of different methods are known from the prior art, with which objects, in particular printing units, are compared with reference objects. In this case, a digital image is preferably created both from the respective printing unit to be tested and from the reference printing unit, and the two digital images thus created are compared with one another.

With modern recording methods it is easily possible to create a digital image with very high resolution for each of the objects to be tested. Although a check of this digital image based on a comparison with a reference image is possible in principle, it is time-consuming. In particular, it requires a tremendous computing power, as it were to examine printing units in real time after their production, if the digital image created by this printing unit is used in full resolution for the respective printing unit. A reduction in the resolution or the use of cameras with a lower resolution, conversely, that certain printing errors or low-quality printing units can not be detected at all. Even if the particular resolution used for the test is adjustable within certain limits, an optimal resolution, which allows both a resource-saving and a reliable test, can not be found. Thus, according to the state of the art, it is only possible to provide a test device with increased computing power.

Fig. 1 shows schematically the procedure of the prior art. In a production step, printing units 1 are created by a printing press 15. After production, the printing units 1 by means of a conveyor belt 12 through the Receiving area of a receiving unit 11 transported. The recording unit 11 creates a digital image 2 of the respective printing unit 1.

The digital image 2 is supplied to a computing unit 16. The arithmetic unit 16 optionally reduces the resolution of the digital image 2 of the printing unit 1, so that the arithmetic unit 16 can check the digital images 2 supplied to it at a speed which corresponds to the production rate or the clock rate of the objects 1. This avoids that the arithmetic unit 16 operates too slowly and an examination of the printing units in real time is not possible.

• " The Colour Image Processing Handbook", herausgegeben von S. J. Sangwine und R. E. N. Horne, veröffentlicht von Chapman & Hall, 1998, Seiten 8 bis 23, 66 bis 90 und 376 bis 384
• " Optical Pattern Recognition based on Color Vision Models" von M. S. Millán und M. Corbalán, erhalten am 2. Mai 1995, veröffentlicht von der Optical Society of America, 1995 , Optical Letters Vol. 20, Nr. 16, 15. August 1995, Seiten 1722 bis 1724
• " Opponent Color Space Motivated by Retinal Processing" von Silvio Borer et al, Verfahren des CGIV 2002 -- First European Conference on Color in Graphics, Imaging and Vision (CGIV), Poitiers, Frankreich, April 2002 .
• " Trichromatic opponent color classification" von E. J. Chichilnisky et al, erhalten am 4. März 1998, akzeptiert am 30. November 1998, veröffentlicht von Elsevier Science Ltd., 1999, 0042-6989/99/$ , Vision Research 39 (1999), Seiten 2444 bis 2458
• " Opponent Color Processing Based on Neural Models" von M. Bollmann et al, Advances in Structural and Syntactical Pattern Recognition, 6th International Workshop, SSPR '96, Leipzig, Deutschland, 20. bis 23. August 1996, Lecture Notes in Computer Science 1121 , herausgegeben von C. Goos et al (1996), J. Hartmanis und J. van Leeuwen
• DE 19744999 A1 der Heidelberger Druckmaschinen AG, veröffentlicht am 23. Juli 1998.

During the test, the respective digital image 2 is compared with a reference image 4, which has the same resolution in terms of number of pixels, color depth and number of image channels as the digital image 2. The reference image 4 corresponds to the expected digital image of a defect-free object 1. The specific nature of the comparison between digital image 2 and reference image 4 is not relevant to the present process. From general knowledge, a variety of methods for examining images are known. By way of example only, reference may be made to the following publications, with which differences between images and reference images can be determined:

• " The Color Image Processing Handbook, edited by SJ Sangwine and REN Horne, published by Chapman & Hall, 1998, pp. 8-23, 66-90, and 376-384
• " Optical Pattern Recognition based on Color Vision Models "by MS Millán and M. Corbalán, received on May 2, 1995, published by the Optical Society of America, 1995 . Optical Letters Vol. 20, No. 16, 15 August 1995, pages 1722 to 1724
• " Opponent Color Space Motivated by Retinal Processing "by Silvio Borer et al, CGIV 2002 method - First European Conference on Color in Graphics, Imaging and Vision (CGIV), Poitiers, France, April 2002 ,
• " Trichromatic opponent color classification "of EJ Chichilnisky et al., Issued March 4, 1998, accepted November 30, 1998, published by Elsevier Science Ltd., 1999, 0042-6989 / 99 / $ . Vision Research 39 (1999), pages 2444 to 2458
• " Opponent Color Processing Based on Neural Models "by M. Bollmann et al, Advances in Structural and Syntactic Pattern Recognition, 6th International Workshop, SSPR '96, Leipzig, Germany, August 20-23, 1996, Lecture Notes in Computer Science 1121 , edited by C. Goos et al (1996), J. Hartmanis and J. van Leeuwen
• DE 19744999 A1 Heidelberger Druckmaschinen AG, published on July 23, 1998.

As a result of such a comparison, a comparison result in the form of a comparison value is obtained. This comparison value is compared with a threshold, which indicates which comparison result is just considered to be tolerable. If the determined comparison result is worse than the threshold value, the digital image 2 and the object 1 from which the digital image originates are classified as defective; otherwise the digital image 2 and the object 1 assigned to it are classified as error-free.

Depending on the result of the classification by the arithmetic unit 16, the position of a switch 13 is switched, so that those objects 1b which have been identified as defective are rejected by the objects 1a identified as faultless. Faulty objects 1 b are destroyed or recycled or, if there are no serious defects, placed on the market as inadequate goods. In the present example, the articles 1a, 1b are stored and made available in separate containers 17a, 17b according to their classification via separate conveyor belts 12a, 12b downstream of the switch 13.

The aim of the invention is to provide a method which, on the one hand, permits a precise examination and, on the other hand, has a lower consumption of resources than the methods mentioned above.

The invention solves this problem in a method of the type mentioned above with the characterizing features of claim 1.

1. a) von dem jeweiligen zu prüfenden Gegenstand ein Digitalbild erstellt und dem jeweiligen Gegenstand zugeordnet wird,
2. b) das Digitalbild hinsichtlich seiner Auflösung, insbesondere seiner Farbtiefe, der Anzahl seiner Farbkanäle sowie seiner örtlichen Auflösung, reduziert wird und derart ein reduziertes Digitalbild erstellt und dem jeweiligen Gegenstand zugeordnet wird, vor, dass
3. c) im Rahmen einer Grobprüfung ein Vergleich des reduzierten Digitalbilds mit zumindest einem reduzierten Referenzbild durchgeführt wird,
4. d) das reduzierte Digitalbild im Falle einer einen vorgegebenen ersten Schwellenwert übersteigenden Übereinstimmung als übereinstimmend erkannt wird, wodurch der Gegenstand als fehlerfrei erkannt und die Überprüfung des Gegenstands beendet wird,
5. e) der Gegenstand im Falle einer den ersten Schwellenwert nicht übersteigenden Übereinstimmung des reduzierten Digitalbilds mit dem reduzierten Referenzbild als potentiell fehlerhaft eingestuft wird, und
6. f) für den Fall, dass ein Gegenstand als potentiell fehlerhaft eingestuft wurde, der Gegenstand einer Feinprüfung unterzogen wird, wobei für den Gegenstand das ihm jeweils zugeordnete Digitalbild herangezogen wird und dieses Digitalbild mit zumindest einem Referenzbild verglichen wird, wobei der Gegenstand im Falle einer einen zweiten Schwellenwert übersteigenden Übereinstimmung als "fehlerfrei" andernfalls als "fehlerhaft" klassifiziert wird.

The invention provides a method for testing printed objects, in particular printing units such as banknotes, wherein

1. a) a digital image is created by the respective object to be tested and assigned to the respective object,
2. b) the digital image is reduced in terms of its resolution, in particular its color depth, the number of its color channels and its local resolution, and is thus created a reduced digital image and associated with the respective object before
3. c) a comparison of the reduced digital image with at least one reduced reference image is performed as part of a coarse examination,
4. d) if the reduced digital image is detected as coincident in the case of a match exceeding a predetermined first threshold value, whereby the article is recognized as free of errors and the examination of the object is terminated,
5. e) the object is classified as potentially defective in the case of a match of the reduced digital image with the reduced reference image that does not exceed the first threshold value, and
6. (f) in the case where an object has been classified as potentially defective, subjecting the object to a fine test, using the digital image associated with the object and comparing that digital image with at least one reference image, the object in the case of a second match exceeding threshold as "error free" otherwise classified as "faulty".

This procedure has the significant advantage that a fine test is only required if the rough check previously carried out has not yielded a clear result. As a result, the effort associated with the fine inspection can be reduced to a small proportion of the objects, such as printing units.

• die zu untersuchenden Gegenstände vor und/oder während ihrer Aufnahme relativ zu der die Aufnahme durchführenden Aufnahmeeinheit, insbesondere mit einer Transportvorrichtung, vorzugsweise mit einem Förderband, befördert werden,
• die Gegenstände nach ihrer Grobprüfung hinsichtlich des Prüfungsergebnisses, insbesondere mit einer ersten Weiche, separiert und die als potentiell fehlerhaft erkannten Gegenstände in einen Zwischenspeicher überführt werden, und
• die im Zwischenspeicher befindlichen Gegenstände nach Durchführung der Feinprüfung einer zweiten Weiche zugeführt und entsprechend ihrer Klassifikation separiert werden.

A particularly simple integration into an automated production process or testing process, in particular printing process, can take place by

• the objects to be examined are conveyed before and / or during their picking up relative to the picking unit performing the picking, in particular with a transport device, preferably with a conveyor belt,
• the objects after their coarse examination with respect to the test result, in particular with a first turnout, separated and transferred as potentially defective detected objects in a cache, and
• the items in the buffer are fed after performing the fine test a second switch and separated according to their classification.

In order to avoid an unnecessary consumption of resources in the case of evidently defective objects, it can be provided that in the coarse examination objects whose assigned reduced digital images have a third threshold below the matching reduced reference image are recognized and classified as "in any case erroneous".

In order to eliminate such defective items quickly from the production or inspection, it can be provided that objects which are clearly detected as faulty in the coarse test, separated or discarded and not fed to the fine test, and / or only those items whose comparison no final assignment as faulty or error-free, the fine test to be supplied.

A simple and efficient implementation provides that the coarse test and the fine test respectively identical or different test algorithms are used, which are adapted to the respective resolution of the images to be compared.

In order to preclude premature classification of defective printing units as error-free, it can be provided that the first threshold value used for the coarse test for the distinction between error-free and potentially defective reduced digital images indicates a higher match than the second threshold used in the fine test.

In order to save computing time and storage requirements during the rough check, it can be provided that
In the creation of the reduced digital image and / or the reduced reference image, the resolution of the digital image and / or the reference image is reduced by reducing the local resolution of the respective image and / or by combining individual color channels, in particular by
the respective image is converted from color to black and white or grayscale and / or
by reducing the resolution depth of the individual color channels.

In order to make it possible to adapt the reduced digital image to the reduced reference image and to exclude transport-related effects such as rotations, fluttering, etc., it can be provided that the reduced digital images are fed to a piecewise affine transformation before the coarse examination and brought into coincidence with the reduced reference image.

In order to allow adaptation of the digital image to the reference image and to exclude transport-related effects such as rotations, flutter and moisture-related curvature of the object or printing unit during recording, it can be provided that the digital images before the fine test of a non-linear equalization, and possibly one before the fine test successive rotation, distortion or piecewise affine transformation supplied and gebacht with the reference image to cover.

In order to be able to make a concrete statement about the nature of the error that has occurred during production, in particular during printing, it can be provided that in the case of the Grobprüfung a subdivision of the class of detected as potentially defective objects in the manner of the potentially existing error made in several subclasses and assigned each detected as a faulty digital image in each case one or more of these subclasses. Through this information obtained in the course of the error classification, it is possible to avoid certain errors in the production of new objects, in particular in the printing of printing units, and to adapt parameters during production.

In order to achieve a uniform utilization of the coarse test and the fine test, it can be provided that always just as many objects are fine checked that the fine test is fully utilized, but not overloaded. For this purpose, during the coarse testing of a large number of objects, the first threshold value is set such that a certain proportion, in particular 3% to 10%, of the objects is recognized as potentially defective. Of course, this threshold must be constantly adapted.

The proportion 1 / n of objects which are fed to the fine test is calculated from this by how much longer the fine test for an article requires than the coarse test. Thus, n corresponds either directly to the ratio of the duration of the fine-testing procedure to the duration of the rough-checking procedure. Alternatively, it can also be provided for the same purpose that n corresponds to the ratio between the memory size of the digital image or the partial image to be tested and the memory size of the reduced digital image. By doing so, it can be avoided that the fine test is interrupted at a time during the examination procedure for lack of test jobs.

Alternatively, it can also be provided for the same purpose that during the sequential testing of a plurality of objects, the first threshold value is adjusted, in particular running, such that a proportion of 1 / n, in particular 3% to 10%, of the objects is "potentially defective where n is the ratio of the duration of the fine testing procedure to the duration of the coarse screening procedure.

• dass bei Feststellung eines "potentiell fehlerhaften", einem reduzierten Digitalbild zugeordneten Gegenstands , bei der Grobprüfung erkannt wird, an welcher Position und/oder in welchem Bereich des reduzierten Digitalbilds ein Fehler aufgetreten ist und diese Position und/oder dieser Bereich zwischengespeichert wird, und
• dass bei der Feinprüfung des dem Gegenstand zugeordneten Digitalbilds die Feinprüfung, insbesondere ausschließlich in den zwischengespeicherten Bereich oder an der zwischengespeicherten Position, vorgenommen wird, wobei insbesondere in Abhängigkeit von dem Bereich und/oder von der Position eine unterschiedliche Feinprüfung ausgeführt wird.

A further advantageous possibility for more rapid further processing, in which the fine test can fall back on findings made during the rough test, provides that

• that upon detection of a "potentially defective", a reduced digital image associated item, the coarse test is detected, at which position and / or in which area of the reduced digital image an error has occurred and this position and / or this area is temporarily stored, and
• that during the fine inspection of the digital image associated with the item, the fine check is carried out, in particular exclusively in the buffered area or at the buffered position, a different fine check being carried out, in particular depending on the area and / or position.

In order to avoid that objects of inferior quality are considered faultless, it can be provided that a minimum value of conformity is specified and objects whose conformity with the reduced reference image falls below this minimum value are in any case recognized as potentially defective.

In order to enable a further distribution of the utilization to a number of test stages running separately from each other, it can be provided that those objects that have been regarded as potentially defective in the course of the rough test are subjected to one or more sequential intermediate tests, in each case an intermediate classification is carried out and only such items are supplied to the respective subsequent intermediate test or the fine test, which were not clearly detected as "error-free" or "faulty".

It can be provided for the distribution of the workload over several computers, that the objects, in particular in the coarse test, are classified by potential error type, and each sequential intermediate test performs a separate error check for only one error type associated with it and thus the objects, if they the same type of fault how the current fine check has been assigned, is accordingly recognized as "faulty" or "error-free", otherwise it is sent to the respective next buffer.

In order to avoid that too many items are subjected to the fine test and there is thus a jam or an overflow in the buffer, individual objects in the buffer can be classified as defective and thus excluded from the fine test.

If at least one intermediate test is provided, it is also possible for individual items located in the intermediate storage to be fed to the subsequent intermediate or fine test in the event of overflow in one of the intermediate tests, without being checked by the current intermediate test

• dass im Rahmen der Grobprüfung Zwischenergebnisse ermittelt werden, insbesondere eine oder mehrere der folgenden Größen:
  1. a) die Ausrichtung und/oder Position des zu untersuchenden Gegenstands bei seiner Abbildung,
  2. b) die Ausrichtung und/oder Position des Abbilds des Gegenstands im jeweiligen reduzierten Digitalbild ,
  3. c) die Position und Ausrichtung einzelner Teilbereiche des Gegenstands , wie beispielsweise Sicherheitsfaden, Kinegramm, Passpunkte und Passstrecken im reduzierten Digitalbild ,
  4. d) die durchschnittliche Helligkeit und/oder eine durch Kalibrierung im Bezug auf das reduzierte Digitalbild gewonnene Farbgewichtung oder Farbtransformation,
  5. e) Korrekturfaktoren für die Entzerrung des Abbilds eines Gegenstands , der bei seiner Aufnahme aufgrund des Transports gebogen oder verzerrt wurde, sodass das Abbild des Gegenstands im Digitalbild oder im reduzierten Digitalbild verzerrt erscheint, und
• dass, sofern eine Feinprüfung des Gegenstands und/oder des für ihn erstellten Digitalbilds erforderlich wird, zumindest eines der erstellten Zwischenergebnisse bei der Feinprüfung zugrunde gelegt wird, wobei gegebenenfalls die betreffenden Größen auf Grundlage der Zwischenergebnisse verbessert oder verfeinert oder an das Digitalbild angepasst werden.

An advantageous, resource-saving embodiment of the invention provides

• that interim results are determined during the coarse examination, in particular one or more of the following variables:
  1. a) the orientation and / or position of the object to be examined in its imaging,
  2. b) the orientation and / or position of the image of the object in the respective reduced digital image,
  3. c) the position and orientation of individual parts of the object, such as security thread, kinegram, control points and pass distances in the reduced digital image,
  4. d) the average brightness and / or color weighting or color transformation obtained by calibration with respect to the reduced digital image;
  5. e) correction factors for the equalization of the image of an object that has been bent or distorted when it was taken due to the transport, so that the image of the object appears distorted in the digital image or in the reduced digital image, and
• if a fine test of the object and / or the digital image created for it is required, at least one of the intermediate results produced will be used for the fine test, where appropriate the respective quantities will be improved or refined on the basis of the intermediate results or adapted to the digital image.

By this measure, it is possible to make individual intermediate results, which are already absolutely necessary in the coarse test, usable for the fine test and in this way to allow a faster processing or a shortening of the time required for the fine test.

An advantageous division of the resources between coarse examination and fine examination provides that the potential presence of an error per se is detected by means of the coarse examination and, in the case of the fine inspection, a classification of the type of error and / or the severity of the error is additionally performed. Alternatively, an advantageous division also be made by means of the coarse test, a classification of the nature of the error is made, and in the fine test, the severity of the error is determined according to the degree of deviation of the digital image from the reference digital image.

By selecting one of the two measures, it is possible to shift an increased demand for resources from the rough test to the fine test or from the fine test to the rough test.

In order to avoid an overflow of the buffer, it can be provided that, when the buffer is overflowed, at least one object located in the buffer is classified as defective and / or discarded.

The invention solves the above object in a device of the type mentioned above with the characterizing features of claim 10.

1. a) eine Transporteinheit, insbesondere ein Förderband, zum Transport der Gegenstände,
2. b) eine Aufnahmeeinheit, deren Aufnahmebereich auf die auf der Transporteinheit befindlichen Gegenstände gerichtet ist und die für den Fall, dass sich ein Gegenstand in ihrem Aufnahmebereich befindet, ein Digitalbild erstellt,
3. c) eine der Aufnahmeeinheit nachgeschaltete Reduktionseinheit, der die erstellten Digitalbilder zugeführt werden und die das jeweilige Digitalbild hinsichtlich seiner Auflösung, insbesondere seiner Farbtiefe und/oder der Anzahl seiner Farbkanäle und/oder seiner örtlichen Auflösung, reduziert und derart ein reduziertes Digitalbild erstellt und dem jeweiligen Gegenstand zuordnet,
4. d) eine erste Recheneinheit zur Durchführung einer Grobprüfung der Gegenstände durch Vergleich des reduzierten Digitalbilds mit einem reduzierten Referenzbild und anschließender Grobklassifikation des Vergleichsergebnisses als "potentiell fehlerhaft" oder "fehlerfrei",
5. e) eine der Transporteinheit nachgeschaltete und von der ersten Recheneinheit gesteuerte erste Weiche zur Separation der Gegenstände gemäß ihrer Grobklassifikation,
6. f) eine zweite Recheneinheit zur Durchführung einer Feinprüfung der in der Grobprüfung als "potentiell fehlerhaft" klassifizierten Gegenstände durch Vergleich des dem jeweiligen Gegenstand zugeordneten Digitalbilds mit einem Referenzbild und anschließender Feinklassifikation des Vergleichsergebnisses als "fehlerhaft" oder "fehlerfrei", und
7. g) eine der ersten Weiche nachgeschaltete und von der zweiten Recheneinheit gesteuerte zweite Weiche zur Separation der als "potentiell fehlerhaft" Gegenstände gemäß ihrer Feinklassifikation.

In a device according to the invention for testing printed objects, in particular printing units such as banknotes, it is provided:

1. a) a transport unit, in particular a conveyor belt, for transporting the objects,
2. b) a receiving unit whose receiving area is directed towards the objects located on the transport unit and which creates a digital image in the event that an object is in its receiving area,
3. c) a reduction unit connected downstream of the recording unit to which the digital images produced are supplied and which reduces the respective digital image with respect to its resolution, in particular its color depth and / or the number of color channels and / or its local resolution, and thus creates a reduced digital image and the respective one Assigns an object,
4. d) a first arithmetic unit for performing a coarse examination of the objects by comparing the reduced digital image with a reduced reference image and then rough classification of the comparison result as "potentially defective" or "error-free",
5. e) a first switch downstream of the transport unit and controlled by the first computer unit for separating the items according to their rough classification,
6. f) a second arithmetic unit for performing a fine check of the objects classified as "potentially defective" in the coarse test by comparing the digital image associated with the respective object with a reference image and subsequent fine classification of the comparison result as "faulty" or "faultless", and
7. g) a second switch connected downstream of the first switch and controlled by the second computer unit for the purpose of separating the articles "potentially defective" according to their fine classification.

This will only require a fine check if the previous rough check has not produced a clear result. As a result, the effort associated with the fine test can be reduced to a small proportion of the objects or printing units.

• das reduzierte Digitalbild mit einem vorab vorgegebenen reduzierten Referenzbild vergleicht und einen der Übereinstimmung zwischen diesen reduzierten Bildern entsprechenden ersten Vergleichswert ermittelt,
• diesen ersten Vergleichswert mit einem vorgegebenen ersten Schwellenwert vergleicht,
• den Gegenstand als "fehlerfrei" klassifiziert, wenn der erste Vergleichswert eine höhere Übereinstimmung indiziert als der erste Schwellenwert,
• den Gegenstand andernfalls als "potentiell fehlerhaft" klassifiziert, und
• das so ermittelte Klassifikationsergebnis an ihrem Ausgang zur Verfügung hält.

In order to achieve an advantageous separation after the coarse testing, it can be provided that
the first arithmetic unit for rough checking and rough classification of a reduced digital image present at its input

• compares the reduced digital image with a predefined reduced reference image and determines a first comparison value corresponding to the correspondence between these reduced images,
• compares this first comparison value with a predetermined first threshold value,
• classifies the item as "error free" if the first comparison value indicates a higher match than the first threshold,
• otherwise classify the item as "potentially defective", and
• the result of the classification thus obtained is available at its exit.

For excreting articles of very poor quality, provision can be made for the first arithmetic unit to classify the object as "in any case erroneous" for coarse testing and rough classification of a reduced digital image present at its input if the first comparison value indicates a lower match than a predefined third threshold value.

• das Digitalbild mit einem vorab vorgegebenen Referenzbild vergleicht und einen der Übereinstimmung zwischen diesen Bildern entsprechenden zweiten Vergleichswert ermittelt,
• diesen zweiten Vergleichswert mit einem vorgegebenen zweiten Schwellenwert vergleicht,
• den Gegenstand als "fehlerfrei" klassifiziert, wenn der zweite Vergleichswert eine höhere Übereinstimmung indiziert als der zweite Schwellenwert,
• den Gegenstand andernfalls als " fehlerhaft" klassifiziert, und
• das so ermittelte Klassifikationsergebnis an ihrem Ausgang zur Verfügung hält.

In order to achieve an advantageous separation after the fine test, it can be provided that the second arithmetic unit for fine testing and fine classification of a present at its input digital image

• compares the digital image with a predetermined reference image and determines a second comparison value corresponding to the match between these images,
• compares this second comparison value with a predetermined second threshold value,
• classifies the item as "error free" if the second comparison value indicates a higher match than the second threshold,
• otherwise classify the item as "defective", and
• the result of the classification thus obtained is available at its exit.

• dass die erste Weiche einen Eingang und zumindest zwei Ausgänge aufweist,
• dass der Eingang der ersten Weiche der Transporteinheit nachgeschaltet ist,
• dass der erste Ausgang der ersten Weiche über eine zweite Transporteinrichtung zu einem Behälter für fehlerfreie Gegenstände führt, und
• dass der zweite Ausgang der ersten Weiche über eine dritte Transporteinrichtung zur zweiten Weiche führt,
• dass die erste Weiche Gegenstände von ihrem Eingang zu ihrem ersten Ausgang transportiert, wenn ihr das Grobklassifikationsergebnis "fehlerfrei" zugeführt ist, und
• dass die erste Weiche Gegenstände von ihrem Eingang zu ihrem zweiten Ausgang transportiert, wenn ihr das Grobklassifikationsergebnis "potentiell fehlerhaft" zugeführt ist.

A preferred arrangement of the first turnout provides

• that the first switch has an input and at least two outputs,
• that the input of the first turnout of the transport unit is connected downstream,
• that the first exit of the first turnout leads via a second transport means to a container for faultless articles, and
• the second exit of the first turnout leads to the second turnout via a third transport device,
• that the first switch transports items from their entrance to their first exit when the gross classification result is "error free", and
• that the first switch transports items from their entrance to their second exit when the gross classification result "potentially defective" is fed to them.

• dass die zweite Weiche einen Eingang und zumindest zwei Ausgänge aufweist,
• dass der Eingang der zweiten Weiche dem Ausgang der ersten Weiche für "potentiell fehlerhafte" Gegenstände nachgeschaltet ist,
• dass der erste Ausgang der zweiten Weiche über eine vierte Transporteinrichtung zu einem weiteren Behälter für fehlerfreie Gegenstände führt,
• dass der zweite Ausgang der zweiten Weiche über eine fünfte Transporteinrichtung zu einem weiteren Behälter für fehlerhafte Gegenstände führt,
• dass die zweite Weiche Gegenstände von ihrem Eingang zu ihrem ersten Ausgang transportiert, wenn ihr das Feinklassifikationsergebnis "fehlerfrei" zugeführt ist, und
• dass die zweite Weiche Gegenstände von ihrem Eingang zu ihrem zweiten Ausgang transportiert, wenn ihr das Feinklassifikationsergebnis " fehlerhaft" zugeführt ist.

A preferred arrangement of the second switch provides

• that the second switch has an input and at least two outputs,
• that the input of the second switch is connected downstream of the output of the first switch for "potentially defective" objects,
• that the first exit of the second switch leads via a fourth transport device to a further container for faultless articles,
• that the second exit of the second switch leads via a fifth transport device to a further container for defective articles,
• that the second switch transports items from their entrance to their first exit when the fine classification result is "error free", and
• the second diverter transports items from their entrance to their second exit when the fine classification result is "erroneous".

A preferred arrangement of the first switch provides that for the removal of objects with very poor quality, the first switch has a third output, which leads via a transport device provided for this purpose to a container for at least faulty items
and that the first diverter transports items from their entrance to their third exit if the gross classification result is "in any case erroneous".

• von der ersten Weiche ausgehende Gegenstände zwischenlagert und
• diese Gegenstände auf Anfrage der zweiten Recheneinheit, insbesondere nach der Durchführung der Feinprüfung des betreffenden Gegenstands, über die dritte Transporteinrichtung der zweiten Weiche zuführt.

In order to buffer the irregular occurrence of potentially defective objects and to avoid overloading of the second arithmetic unit, provision can be made for a, in particular FIFO, intermediate memory to be provided in the third transport device

• intermediately stored from the first turnout objects and
• these items on request of the second processing unit, in particular after the completion of the fine examination of the object in question, via the third transport means of the second switch supplies.

A simple and efficient implementation provides that for the coarse test and the fine test respectively programs with the same test algorithms are stored in the first arithmetic unit and the second arithmetic unit, which are adapted to the respective resolution of the digital images and reference images to be compared.

In order to rule out premature classification of faulty printing units as error-free, it can be provided that the first threshold used for the coarse test for the distinction between error-free and potentially erroneous pictures indicates a higher match than the second threshold used in the fine check.

• dass die erste Recheneinheit im Rahmen der Grobprüfung Zwischenergebnisse ermittelt werden, insbesondere ein oder mehrere der folgenden Größen:
  1. a) die Ausrichtung und/oder Position des zu untersuchenden Gegenstands bei seiner Abbildung,
  2. b) die Ausrichtung und/oder Position des Abbilds des Gegenstands im jeweiligen Digitalbild,
  3. c) die Position und Ausrichtung einzelner Teilbereiche des Gegenstands , wie beispielsweise Sicherheitsfaden, Kinegramm, Passpunkte und Passstrecken,
  4. d) die durchschnittliche Helligkeit und/oder eine durch Kalibrierung gewonnene Farbgewichtung oder Farbtransformation,
  5. e) Korrekturfaktoren für die Entzerrung des Abbilds eines Gegenstands , der bei seiner Aufnahme aufgrund des Transports gebogen oder verzerrt wurde, sodass das Abbild des Gegenstands im Digitalbild verzerrt erscheint,
• dass die erste Recheneinheit die Zwischenergebnisse für den Fall, dass die Grobprüfung den Gegenstand als "potentiell fehlerhaft" klassifiziert, an die zweite Recheneinheit weiterleitet, und
• dass die zweite Recheneinheit im Rahmen der Feinprüfung des Gegenstands und/oder des für ihn erstellten Digitalbilds , diese Zwischenergebnisse bei der Feinprüfung zugrunde legt und gegebenenfalls die betreffenden Größen auf Grundlage der Zwischenergebnisse verbessert oder verfeinert oder an das Digitalbild anpasst.

An advantageous, resource-saving embodiment of the invention provides

• that the first arithmetic unit in the course of the coarse test intermediate results are determined, in particular one or more of the following variables:
  1. a) the orientation and / or position of the object to be examined in its imaging,
  2. b) the orientation and / or position of the image of the object in the respective digital image,
  3. c) the position and orientation of individual parts of the object, such as security thread, kinegram, control points and pass distances,
  4. d) the average brightness and / or a color weighting or color transformation obtained by calibration,
  5. e) correction factors for the equalization of the image of an object that was bent or distorted when it was taken due to the transport, so that the image of the object appears distorted in the digital image,
• that the first arithmetic unit forwards the intermediate results to the second arithmetic unit in the event that the coarse test classifies the item as "potentially defective", and
• that the second arithmetic unit as part of the fine examination of the object and / or the digital image created for him, based on these intermediate results in the fine test and, where appropriate, improves or refines the relevant quantities based on the intermediate results or adapted to the digital image.

By this measure, it is possible to make individual intermediate results, which are already absolutely necessary in the coarse test, usable for the fine test and in this way to allow a faster processing or a shortening of the time required for the fine test.

A further alternative or additionally advantageous possibility for faster further processing, in which the fine check can fall back on findings made within the scope of the coarse test, provides that the first arithmetic unit additionally detects upon detection of a "potentially erroneous" reduced digital image assigned to an object, at which position and / or in which area of the reduced digital image an error has occurred and temporarily stores this position and / or this area and forwards them to the second arithmetic unit, and - that the second arithmetic unit in the fine examination of the digital image associated with the object, the fine test, in particular exclusively in the cached area or at the cached position, performs and, in particular depending on the operation and / or from the position a different fine test carried out.

Preferred embodiments of the invention and variants thereof are illustrated in more detail with reference to the following drawing figures.

Fig. 2 schematically shows a first embodiment of a test device according to the invention. Fig. 3 shows schematically the distribution of the quality of printing units and made by the coarse and fine check separation of the printing units based on the print quality.

In Fig. 2 a first embodiment of a test device according to the invention is shown. This testing device is preceded by a production unit 25, which creates the objects to be tested 1. Alternatively, it is also possible that the objects to be tested are located in a memory and are supplied to the respective test with a time delay.

The objects 1 are transported via a transport device 22, which in the present case is designed as a conveyor belt, and arrive on their transport through the receiving area 21 'of a receiving unit 21. The receiving unit 21 creates a digital image 2 from the respective object 1. A reduction unit 29 is created Basis of the digital image 2 a digital image reduced in its resolution 3.

The reduction of the resolution can be carried out according to different criteria, wherein only the reduction of the amount of data of the reduced digital image 3 with respect to the digital image 2 is required. In particular, a reduction of the resolution can be achieved by reducing the number of pixels. Alternatively or additionally, the number of image channels can also be reduced; for example, the reduced digital image 3 can be created by weighting the individual color values associated with a pixel and assigning them to the positionally corresponding pixel of the reduced digital image 3. It can also be provided that the color depth is reduced, i. that the discretization with which individual color values are resolved is coarsened. For example, a reduced digital image 3 can be created from a digital image 2 for which 16 bits are available per color channel and pixel, for which only 4 or 8 bits are available per color channel and pixel.

It is also possible to combine individual ways of reducing the resolution of the digital image 2 with each other, i. for example, to halve the number of pixel rows and pixel columns, and in addition to reduce the number of three 16-bit color channels to an 8-bit resolved black and white color channel. In this way a reduction of the image information by a factor of 24 is achieved.

The reduction of the resolution of the digital image 2 and the concomitant creation of the reduced digital image 3 is performed in the present embodiment of the reduction unit 29, which is the recording unit 21 downstream. The reduced digital image 3 is fed to a first computing unit 26a, which carries out a rough checking and rough classification of the object 1 or of the reduced digital image 3 that it has produced.

Alternatively, however, the digital image 2 can also be fed to the first arithmetic unit 26a, the reduction unit 29 being designed as part of the first arithmetic unit 26a, which generates the reduced digital image 3 on the basis of the digital image 2 supplied to it.

Furthermore, a reference image 4 is available for testing the object 1, which in terms of its resolution, its color depth and the channels used corresponds to the digital image 2 of a defect-free object 1 which is expected during the recording. This reference image 4 can be predetermined or created by taking a good object. Alternatively, the reference image 4 can also be determined by a statistical method, for example, by averaging or median formation, which creates values of digital images of several error-free reference objects.

Furthermore, it is also possible to set a minimum and a maximum tolerable color or brightness value for each pixel, or to specify a maximum permissible deviation value analogously for each pixel.

Based on the reference image 4, a reduced reference image 5 is created. The reduction of the image information of the reduced reference image 5 is carried out in the same way as in the creation of the reduced digital images 3 based on the captured digital images 2. The reduced reference image 5 is stored in the first processing unit 26a or otherwise kept available for retrieval.

Each reduced digital image 3 arriving at the first arithmetic unit 26a or created by the first arithmetic unit 26a is compared with the reduced reference image 5. For the comparison, the types of image comparison mentioned in connection with the prior art come into question. In particular, for comparison of a reduced digital image 3 with the reduced reference image 5, comparison methods can be used, as described in the cited documents. As a result of the comparison method in the coarse examination, a first comparison result V _{1 is obtained} in the form of a digital numerical value. This first comparison result V ₁ is compared with a first threshold value S ₁ . Indicates the first comparison result V ₁ a poorer match to the reduced digital image 3 with the reduced reference image 5 as a first threshold value S ₁ corresponding to the comparison result, so is the corresponding reduced digital image 3, and therefore also the article 1 from which the respective reduced digital image 3 comes , recognized as potentially defective and viewed. Otherwise, the article 1 is recognized as a defect-free article 1a and viewed.

In this particular embodiment of the invention also a third threshold S ₃ is still set, corresponding to a very bad comparison result. If the comparison result V ₁ obtained on the basis of the comparison of the reduced digital image 3 with the reduced reference image 5 indicates a worse match than the third threshold S ₃ , then the respective object 1 from which the reduced digital image 3 originates is referred to as a "faulty" object 1c viewed. Such a sorting out of at any case faulty objects 1c by the first arithmetic unit 26a merely constitutes a special development of the invention Relief of the still to be presented fine test and basically does not need to be provided.

In the manner described above, a rough classification into one of the classes "error-free" and "potentially defective" is made by the first arithmetic unit 26a for each of the items 1, the items optionally also being assigned to further classes, such as "in any case erroneous" can be. In addition, subclassifications such as "potential misprints of the species gradient" or "potential misprints of the type doctor blade" are also possible as subclasses of the class "potentially defective". These sub-classifications can be used to initiate feedback to the production unit 25, if present, and to carry out corresponding readjustments.

Depending on the classification by the first arithmetic unit 26a, a first diverter 23a is actuated by the latter. If the respective object 1 reaches the first switch 23a, the switch 23a is set depending on its classification, so that the object 1 reaches one of the transport units 22a, 22b, 22c assigned to the respective classes specified by the classification. The first switch 23a as well as the second switch 23b, shown later, each have a point setting unit which brings the respective switch 23a, 23b respectively into the position predetermined by the respective calculating unit 26a, 26b and permits separation of the supplied articles 1, 1b.

The first switch 23a has an input and at least two outputs. The input of the first switch 23a is connected downstream of the transport unit 22. The first exit of the first switch 23a leads via a second transport device 22a to a container 27a for faultless articles 1a. The second output of the first switch 23a leads via a third transport device 22b to the second switch 23b. The first switch 23a is, as already mentioned, controlled by the first computing unit 26a. The first diverter 23a transports items 1 from their entrance to their first exit when the gross classification result is fed "error-free". If the article 1 is classified as error-free, it is conveyed via a first transport unit 22a to a container 27a for defect-free articles 1a and held therein.

The first diverter 23a transports items 1 from their entrance to their second exit, when the gross classification result "potentially erroneous" is supplied to them. If the article 1 is classified as "potentially defective", it is conveyed via a second transport unit 22b to a buffer 24 for potentially defective articles 1b and kept available there. The buffer 24 has the task of buffering the irregular arrival of objects 1b classified as "potentially defective" and of making such objects 1b available on a regular basis, without there being any overloading of the second arithmetic unit 26b during the fine inspection of the articles 1b.

In this preferred embodiment of the invention, the first switch 23a has a third output and transports articles 1 from their input to their third output when the rough classification result is supplied to them "in any case erroneous". The objects 1c identified as "in any case defective" are, if the classification provided by the arithmetic unit 26a provides such a class, conveyed to a container 27c for in any case faulty objects 1c via a transport device 22c provided for this purpose and stored, possibly discarded or stored therein destroyed. As already mentioned, these devices, in particular a container 27c for in any case defective articles 1c as well as the transport device 22c leading to it, are not a mandatory component of the invention.

The first diverter 23a thus has a number of outputs corresponding to the number of classes provided by the classification of the first arithmetic unit 26a. Depending on the assignment of the respective object 1 to one of the classes, the position of the first switch 23a is selected accordingly, so that the respectively differently classified objects are separated according to their classification.

In order to obtain a clear association between the respective object 1 and the reduced digital image 3 and the determined first comparison result V ₁ and the classification during the control of the first switch 23a by the first computer 26a, at least the respective first comparison results V ₁ stored in a FIFO memory of the first arithmetic unit 26a. If an object 1 now arrives at the first switch 23a, the oldest value written to the FIFO memory is read out of it and the first switch 23a is set in accordance with this value. The value is then deleted from the FIFO memory.

As part of a fine test, the objects 1b classified as "potentially defective" are rechecked by a second arithmetic unit 26b. These potentially defective articles 1b are, as already mentioned, in one the second Output of the first switch 23b downstream buffer 24 is kept available.

Furthermore, the digital images 2 associated with the objects classified as potentially defective are transferred to the second arithmetic unit 26b and in this case according to the FIFO principle, i. in the order of their arrival, worked off. The order of execution of the fine examination of the digital images 2 corresponds to the order of the objects 1 b in the buffer.

Alternatively, it is also possible for the second arithmetic unit 26b to be supplied with the digital images 2 of all objects 1 to be tested. In this case, the arithmetic unit 26b discards the digital images 2 of the non-"potentially defective" classified articles 1a, 1c and processes only the digital images 2 of the articles 1b classified as "potentially defective".

The second arithmetic unit 26b carries out the fine classification on the basis of a comparison of the digital image 2 produced by the recording unit 21 with a reference image 4. For this purpose, a reference image 4 is provided, which corresponds to the expected digital image of a defect-free object 1 with regard to the resolution, the number of channels used and the color depth.

In the present embodiment of the invention, the second arithmetic unit 26b compares the digital image 2 of the subject 1 with the reference image 4 in the same way as the first arithmetic unit 26a compares the reduced digital image 3 with the reduced reference image 5. The only difference between the comparison process carried out on the first and the second arithmetic unit 26a, 26b is that the second arithmetic unit 26b determines a second comparison value V ₂ with the full image resolution. This second comparison value V ₂ is compared with a second threshold value S ₂ and a fine classification is carried out, with the respective object ₁ b being indicated as a "defective" object ₁ c in a comparison result V ₂ which indicates a worse match than the second threshold value S ₂ . otherwise it is classified as a "faultless" item 1a '.

Basically, comparison methods can be used for the coarse and the fine test, which differ only in terms of the resolution used.

However, it is particularly advantageous if several different test methods are available for the fine test, which are adapted to different types of errors. If a subclassification for potential error types is made in the rough check, depending on the subclassification in the course of the rough classification, a fine check specially tailored to the presumed error can be carried out. For example, if an item is considered "potentially defective" in the coarse classification, with a subclassification "potential misprints of the squeegee type" being made, the fine test may use a test method that specifically investigates the presence of squeegee strips. In addition, the rough classification can be added to the estimated position of the respective error and used as a parameter of fine classification.

If the fine classification of a potentially defective item 1b has ended, the items 1b are fed to the buffer 24 at the request of the second processor 26b to a second switch 23b, which is also controlled by the second processor 26b.

In the manner described above, the second arithmetic unit 26b carries out a fine classification for each of the items 1 into one of the classes "error-free" and "erroneous", wherein the items may optionally also be assigned to further classes. In addition, subclassifications such as "Color Error Fault Type Error" or "Squeegee Style Fault Type Error" are also possible as subclasses of the "Faulty" class. These sub-classifications can be used to initiate feedback to the production unit 25, if present, and to carry out corresponding readjustments.

According to the respective fine classification, the second switch 23b separates the articles 1b conveyed from the buffer 24 according to their classification into "defect-free" articles 1a 'and "defective" articles 1c' by guiding them to respective different transport units 28a, 28c.

In the present exemplary embodiment, the second switch 23b has one input and two outputs, it being additionally possible to provide a further output for each possible classification result of the fine classification. The input of the second switch 23b is connected downstream of the output of the first switch 23a for "potentially defective" articles 1 via the third transport unit 22b.

The first output of the second switch 23b leads via a fourth transport device 28a to a further container 27a 'for faultless articles 1 a'. The second output of the second switch 23b leads via a fifth transport device 28c to a further container 27c 'for defective articles 1c'. The second switch 23b transports items 1 from their entrance to their first exit when the fine classification result is supplied "error-free" by the second processing unit 26b. The second diverter 23b transports items 1 from their entrance to their second exit when the fine classification result is "erroneously" supplied from the second arithmetic unit 26b.

Articles 1a 'classified as such "free of defects" are transported via the fourth transport unit 28a to the further container 27a' for defect-free articles 1a 'and stored therein and made available. Articles 1c 'classified as "defective" in this way are transported via the fifth transport unit 28c to the container 27c' for defective articles 1c 'and stored therein and made available.

In order to obtain a clear association between the respective object 1b and the digital image 2 and the determined second comparison result V ₂ and the classification during the control of the second switch 23b by the second computing unit 26b, at least the respective second comparison results V ₂ in FIG another FIFO memory of the second arithmetic unit 26b stored. If an object 1b now arrives at the second switch 23b, the value written first to the further FIFO memory is read out of it and the second switch 23b is set in accordance with this value. The value is then deleted from the further FIFO memory.

In Fig. 3 schematically the setting of the first and the second threshold value S ₁ , S _{2 is} shown. Fig. 3 indicates on the ordinate the probability that an item 1 has a certain match with an ideal reference item. The abscissa shows the respective agreement, the comparison value V ₁ , V ₂ = 0 indicating an ideal match. The larger the respective comparison value V ₁ , V ₂ , the worse is the correspondence between the respective digital image ₂ , 3 and the associated reference image ₄ , 5.

The abscissa represents a threshold value T which corresponds to the quality that an object 1 may have in the worst case in order to be classified as error-free. Due to the examination of the coincidence of the respective digital image 2, 3 with the reference image 4, 5 by the first and second arithmetic unit 26a, 26b, the comparison value V ₂ determined by the second arithmetic unit 26b has a greater accuracy than that of the first Arithmetic unit 26a determined first comparison value V ₁ .

The inaccuracy with which the coarse test is affected is represented by the first interval I ₁ , whereby the qualitatively worst boundary, here the upper one, of this first interval I ₁ corresponds to the limit value T ₁ . This ensures that no item 1 is classified as error-free in the first classification, which has a lower quality than is indicated by the limit value T. For this purpose, the first threshold value S ₁ to a value S ₁ = T - set I _1/2, which is shifted by the respective half the interval width of the first interval _I1 with respect to the threshold T. For alternative measures of comparison, in which a high first comparison value V ₁ indicated good agreement, applies to S ₁ = T + I _1/2.

Similarly, the second threshold S ₂ used in the fine test is set to a value S ₂ = T - I _2/2 , which is shifted by the respective half-interval width of the first interval I ₂ relative to the threshold value T. For alternative comparison measures in which a high second comparison value V ₂ indicates a good match, S ₂ = T + I _2/2 applies accordingly. Since the fine test is much more accurate, the second interval I _{2 has} a smaller interval width than the first interval I ₁ . Due to the greater inaccuracy in the determination of the first comparison value V ₁ with respect to the determination of the second comparison value V _2, the second threshold value S ₂ closer to the limit value T than the first threshold S _1, thereby achieving a more accurate pass / fail statement to the fine examination ,

The width of the first interval I ₁ in this embodiment corresponds to the error spread of the comparison made during the coarse test. In this exemplary embodiment, the width of the second interval I ₂ corresponds to the lower error spread of the comparison made during the fine test compared to the rough test. In the present example, it was assumed that the intervals lie symmetrically about the respective threshold values S ₁ , S ₂ , S ₃ .

The obliquely shaded surface area under the curve indicates the maximum expected proportion of the objects to be tested in the course of the fine test. The closer the interval limits of the first interval I _{1 are} selected, the fewer items need to be subjected to the fine check, however, the more complex the coarse check will be.

If, according to the special embodiment of the invention presented at the beginning, a classification of the objects 1 into "error-free", "potentially defective" and "in any case erroneous" is carried out during the coarse test, then a third threshold value S ₃ can be selected as shown below. In order to avoid that reduced digital images 2, 3 of defect-free objects 1, which have been identified as potentially defective by the coarse examination or in which V ₁ > S ₁ , are discarded, the third threshold value S ₃ = T + I ₁ ' / 2 is set such that it is worse, here greater, than the limit value T by at least the interval width I ₁ '/ 2. For alternative comparison measures in which a high first comparison value V ₁ indicates a good match, S ₃ = T - I ₁ '/ 2. The width of the third interval I ₁ 'corresponds in this embodiment, the width of the first interval I _1, that is, the error diffusion of the comparison made in the rough examination. If, during the coarse examination, a classification is also carried out for any defective objects 1c, this proportion is reduced by the vertically hatched area under the curve. In order to avoid that error-free objects 1 are detected as "in any case faulty", the interval widths of the first and third intervals are defined as follows: I ₁ '≥ I ₁ .

Particularly advantageously, the following alternative adaptive procedure for creating a uniform utilization between the first arithmetic unit 26a and the second arithmetic unit 26b can be used. For example, if it is known that the fine test of a digital image 2 lasts about n times as long as the rough test of a reduced digital image 3, the first threshold S ₁ 'can alternatively be chosen so that on average every n-th reduced digital image 2 is potentially defective is recognized. For this purpose, the adaptive first threshold value S ₁ 'may be set in an interval between an optimum quality S _max and the first threshold value S ₁ . For the comparative measure used in which a low first comparison value V ₁ indicated good agreement, applies to S _{max <1} S '<S ₁ = T - I _1/2. For alternative comparison measurements, in which a high first comparison value V ₁ indicates a good agreement, applies to S _max> S ₁ '> S ₁ = T + I _1/2. Here S ₁ corresponds to a minimum value of agreement.

If too few reduced digital images 3 are identified or classified as potentially defective, the adaptive first threshold value S ₁ 'is adapted to a greater coincidence value within the predetermined interval so that more reduced digital images 3 are classified as potentially defective after this change. Conversely, if the number of reduced digital images 3 identified as potentially defective is too large, the adaptive first threshold value S ₁ 'is adapted so that less reduced digital images 3 are classified as potentially defective after this change.

In the present exemplary embodiment, the first threshold value S _{1 is} adaptively determined by specifying that only 4% of the digital images classified by the first arithmetic unit 26 a are classified as "potentially defective". If, as previously stated, the number of items 1b classified as "potentially defective" is about 4% of the total items 1 to be inspected, a real-time fine classification with the arithmetic unit 26b for each of the items 1b is about 25 times the time for fine inspection available.

In order to allow a particularly accurate comparison, in a particular embodiment of the invention, the reduced digital images 3 are supplied before the coarse examination of a piecewise affine transformation and brought into coincidence with the reduced reference image 5. Such a procedure is known from the prior art and is performed by the first computing unit 26a.

Likewise, to improve the comparison, the digital images 2 may be fed before the fine check of a non-linear equalization, and possibly a before or after rotation, distortion or piecewise affine transformation, and be covered with the reference image 4 to cover. This is likewise known from the prior art and is performed by the second arithmetic unit 26b.

Of course, it is also possible to perform several sequential intermediate tests between the rough test and the fine test. Items which have been considered potentially defective in the course of the rough examination will be successively subjected to the individual intermediate tests. Each of the intermediate tests is followed by an intermediate classification, with only items which are not clearly identified as "error-free" or "defective" being supplied to the respectively subsequent intermediate test or the fine test.

In the following, further improvements of the invention are shown, which can be used in combination with all embodiments shown according to the invention.

A first significant improvement of the invention is not immediately discard results that were determined in the context of the coarse test, but continue to use these results in the context of the fine test. In the coarse examination, it is typically necessary to determine measured variables which make a specific statement for a specific object or for the reduced digital image 3 created for the object. This can be a multitude of different intermediate and final results which, depending on the particular fine testing method used, would otherwise have to be determined separately as part of the fine test. In addition there would be the problem that these values would have to be determined on the basis of the much larger digital images 2, which, in contrast to the determination on the basis of the reduced digital images 3, would lead to a significantly increased need for resources. It is therefore advantageous to continue to use and, where appropriate, to refine these readings obtained during the rough test, even if these are based on a smaller and possibly less accurate database.

This can be used, for example, if the relative rotation of an object 1 to be examined, such as a banknote, for example, for the coarse examination of the reduced digital image 3 and for the fine examination of the digital image 2 is to be determined in relation to the image recording unit receiving it. Depending on the type of transport device 22, it may happen that the object 1 to be examined is rotated by a certain angle with respect to the image pickup unit receiving it, which results in the image of the object 1 also appearing twisted in the digital image 2 or in the reduced digital image 3 , In many coarse examination methods, it is therefore necessary to rotate the image of the object 1 in the reduced digital image 3 so that its outside edges are parallel, for example, to the edges of the reduced digital image 3. In this context, usually a rotation angle or a transformation is determined, which aligns the respective image of the object 1 in the reduced digital image 3. Such a detection has, depending on the size of the reduced digital image 3 a certain resource requirements. In the fine test, in which the full digital image 2 would have to be examined, depending on the nature of the digital image, especially at higher resolution, a higher therefore already alone Resource requirement, since more pixels would have to be considered for the determination of the rotation of the image of the object 1 in the digital image 2. If, however, the angle detected in the course of the coarse test is already known, then it can be stored together with the digital image 2 of the respective object 1 and passed to the fine test as an additional value next to the digital image 2 and further used by the fine test. In the fine test, on the one hand, the rotation of the image of the object 1 relative to the reduced digital image 3 detected in the course of the coarse examination can be used to correspondingly rotate the image of the object 1 in the digital image 2, so that this in the digital image 2, for example, parallel to the edges of the digital image 2 is aligned. On the other hand, the present approach could be improved to the extent that, especially at elevated resolution of the image, a more accurate detection is possible, which can be determined in an iterative process. In this case, the intermediate value determined from the coarse examination can form a starting point for the iterative method, so that the actual value for the rotation of the image of the object 1 in the digital image can be achieved with fewer iteration steps.

Even if the continued use of intermediate results from the coarse test for the fine test has been described above with reference to the rotation or the position of the image of the object 1 to be examined in the digital image 2 or in the reduced digital image 3, all interim results ascertained within the framework of the coarse examination can be used are relevant for the fine test procedure, are also used as a basis for the fine test and, if necessary, improved iteratively. In addition to the orientation of the image of the object 1 in the digital image 2 or in the reduced digital image 3, the position of the respective object 1 relative to the image recording unit or the position of the image of the object 1 in the digital image 2 or in the reduced digital image 3 can vary depending on the image , It is thus possible, as in the detection of the orientation, even in the detection of the position of the object to be examined 1, to continue to use the detected during the coarse examination position for the fine test.

It is of particular advantage in general that the reduced digital image 3 used for the coarse examination and the digital image 2 used for the fine inspection were created simultaneously by the image acquisition unit 21 and thus have the same origin.

Some methods for coarse or fine testing also determine the position of individual portions of the object 1 and the position of the images of these portions of the Article 1 in the digital image 2 or in the reduced digital image 3. Even in such a constellation, it may be advantageous during the coarse examination to continue to use the already determined area of the object 1 for the fine test. If the resolution of the reduced digital image 3 does not correspond to the resolution of the digital image 2, the position or the area corresponding to the image of the digital image 2 is changed to the reduced digital image 3. Typically, the position and possibly also the alignment of security threads, kinegrams, control points and pass distances, which were determined during the coarse examination, are used further in the fine test. In the case of these intermediate results, it is of course also possible to perform an additional iterative refinement of these values in the context of the fine test on the basis of the interim results determined in the course of the rough test.

Due to the rapid transport speed, it can happen, especially with very thin objects, such as printed paper or banknotes, that the objects flutter or be bent during locomotion due to aerodynamic effects. This can lead to the image of the object not being completely distortion-free, but due to the bending or the fluttering of the object, individual areas of the object appear to be of different sizes or possibly compressed or stretched in the digital image 2 or in the reduced digital image 3. If the basic appearance of an object 1 is known in principle, a transformation can be found on the basis of processes known from the prior art which correspondingly equalizes the distorted digital image 2 or the reduced digital image 3, so that in the digital image 2 or in the reduced digital image 3 after the distortion, an image of the object 1 is included, which reproduces it undistorted. If such an equalizing transformation is found during the coarse examination, this can in principle also be used in the context of the fine test. In the event that the resolution in the digital image 2 and the reduced digital image 3 is different, this transformation is adapted accordingly to the larger image area of the digital image 2. Once again, it is possible to use the equalization of the reduced digital image 3 as a starting point for an iterative improvement of an improved equalization for the digital image 2. As already mentioned, it is possible in this context to equalize the reduced digital image 3 by means of a piecewise affine transformation and to base this piecewise affine transformation on the calculation of a nonlinear transformation for equalizing the image on the digital image 2. Such a procedure is particularly special advantageous if the digital image 2 and the reduced digital image 3 are resolved differently.

In addition, as part of the rough examination, additional intermediate results can be obtained, which relate in particular to the brightness and color of the recorded object. In particular, if the illumination flickers or is of different brightness when the object 1 is being recorded, it may be advantageous to perform a color matching in advance and only then to perform the actual coarse examination, in which a comparison is made with the reduced reference digital image 5. In this case, a color transformation is obtained which is applied to all the pixels of the reduced digital image 3. By "color transformation" is meant, for example, the application of a color profile or a linear transformation of each individual color channel, including gain and offset. Since the reduced digital image 3 is created according to the invention from the digital image 2, also achieved by light flicker or different lighting influences on the created digital image 2 and on the resulting reduced digital image 3 are the same. Thus, in particular if the same color depths and the same color channels are used, the color transformation for the reduced digital image 3 can be used identically for the digital image 2. Otherwise, the color transformation suitable for the digital image 2 can be calculated from the color transformation created for the reduced digital image 3 and does not have to be completely redetermined.

If the same or similar steps that require similar color preprocessing are performed within the framework of coarse and fine inspection, the color transformation obtained during calibration of the reduced digital image 3, for example by calibration, can also be used in the examination of digital image 2 in the frame the fine test can be used.

Although only a few examples have been enumerated, it is generally possible to reuse intermediate results of the coarse test for the fine test. Results such as the position or the area in which an error has occurred can also be used in this way, which avoids a renewed localization of the error.

As already mentioned, it is possible to cascade the individual test steps together. In the embodiment of the invention shown below, a plurality of further fine checks is provided in addition to the coarse examination. For each fine exam, there is one exam step each comprising one Switch and a cache and a computing unit provided. The articles 1 marked or intended for the fine inspection during the coarse test are stored in a first intermediate store of the first fine-testing unit. This buffer is followed by a switch, which leads the respective object either in the fine test, the fine test is performed by a computing unit, or continues to the next fine inspection stage. Here, the object 1 is in turn passed to the buffer of this fine test stage; to this buffer in turn connects to a switch, etc.

One possible embodiment of these cascade-like checking steps is the following: In the rough checking, a classification is made of the potentially occurring error. Each of the exam levels is responsible for one of the errors found for the fine exam. For each item 1, which is fed to the fine test, the corresponding error class is stored along with the digital image 2 and fed to the fine test. If the item 1 is delivered to a check level associated with the same error class as it is, the switch of the relevant check level carries the item to the processing unit associated with the check level, which performs the fine check for that particular error class. If the object 1 of the fine test is sufficient, it is forwarded to the fault-free objects by another switch associated with the test stage, otherwise it is forwarded to the faulty objects.

In the event that the item 1 has been assigned a different error class than the fine test stage in which it is located, the object 1 is forwarded to the respective next fine test stage of the respective switch until it finally comes to the fine test stage, which puts him on those Checked for errors during the rough check.

In an alternative embodiment of the invention, the first fine inspection detects articles with very severe defects. The items with very serious errors are forwarded to a store for defective items, all other items 1 are forwarded to a next fine check stage, which detects items 1 with slightly less serious errors, etc. The smaller the deviation from the reference picture and the lower the error, the harder it is to discover these mistakes. It is therefore advantageous if each additional fine test has fewer and fewer items to check and therefore on the one hand has more time available and on the other hand also due to the previous tests more intermediate results.

In general, fault classification can be carried out both as part of the rough test and as part of the fine test. In addition, it is also possible to make a determination of the severity of the respective error within the scope of the fine test, possibly also in the context of the coarse test, whereby it is determined how much the respective digital image 2 differs from the reference digital image 4.

In print inspection, it is often common to distinguish between errors of different severity, e.g. There is a specification for very serious errors and these are called class A errors. Slightly lower errors are referred to as B errors, etc. Between the supplier, e.g. a printer, and the customer may be can not contain A errors, but some percent B errors and a few percent C errors.

The knowledge about the classification of errors according to their nature and / or their severity is therefore advantageous for a printing company. However, the application of the classification is usually computationally expensive. Nevertheless, the present invention enables this requirement of printing companies.

Claims (18)

Method for testing printed objects (1), in particular printing units such as banknotes, wherein a) a digital image (2) is created by the respective object to be tested (1) and assigned to the respective object (1), b) the digital image (2) with respect to its resolution, in particular its color depth, the number of its color channels and its local resolution, is reduced and such a reduced digital image (3) created and the respective object (1) is assigned, characterized in that c) a comparison of the reduced digital image (3) with at least one reduced reference image (5) is carried out as part of a coarse examination, d) the reduced digital image (3) is recognized as belonging to a defect-free object (1) in the event of a match exceeding a predetermined first threshold value (S ₁ ), and the examination of the respective object (1) is ended, e) the object is classified as potentially defective in the case of a match of the reduced digital image (3) with the reduced reference image (5) which does not exceed the first threshold value, f) in the event that an object (1) has been classified as potentially defective, the object is subjected to a fine test, using the digital image (2) assigned to it for the object (1) and including this digital image (2) with at least one Reference image (4) is compared, wherein the object (1) is classified as "error-free", otherwise as "faulty" in the case of a second threshold exceeding agreement, g) that the objects to be examined (1) are transported before and / or during their picking up relative to the picking unit (11) performing the picking, in particular with a transporting device (22), preferably with a conveying device, h) that the objects (1) after their coarse examination with respect to the test result, in particular with a first switch (23a), separated, and the potentially erroneously recognized objects (1) are transferred to a buffer (24), and i) that the objects (1) located in the temporary store (24) are fed to a second switch (23b) after the fine inspection has been carried out and separated according to their classification. Method according to claim 1, characterized in that a) in the coarse examination of the objects (1) whose associated reduced digital images (3) have a third threshold (S ₃ ) below matching with the reduced reference image (5) are recognized as "at least faulty" and classified, and in particular b) objects which were detected during the coarse test as "in any case faulty" or are clearly detected as "faulty", separated or rejected and not subjected to the fine test, and / or only those articles (1) whose comparison does not have a final classification as " in any case "faulty" or "error-free" allows the fine test to be supplied. Method according to one of the preceding claims, characterized in that a) identical or different test algorithms are used in the coarse test and the fine test, which are adapted to the respective resolution of the images to be compared (2, 3, 4, 5), and / or b) the first threshold value (S ₁ ) used for the coarse examination for the distinction between error-free and potentially defective reduced digital images (4) indicates a higher match than the second threshold (S ₂ ) used in the fine test, and / or c) in the creation of the reduced digital image (3) and / or the reduced reference image (5), the resolution of the digital image (2) and / or the reference image (4) is reduced by c1) the local resolution of the respective image is reduced and / or c2) individual color channels are combined, in particular by the respective image of color in black and white or gray scale is converted and / or c3) by reducing the resolution depth of the individual color channels, and / or d) that before the creation of the reduced digital image (3), a filter is applied to the digital image (2), in particular an edge filter or a smoothing filter. Method according to one of the preceding claims, characterized in that a) the reduced digital images (3) are fed before the coarse examination of a piecewise affine transformation and brought into coincidence with the reduced reference image (5), and / or b) the digital images (2) are fed before the fine test of a non-linear equalization, and / or a spin, distortion or piecewise affine transformation before the fine test and brought into coincidence with the reference image (4), and / or c) in the coarse test, subdividing the class of objects (1) identified as "potentially defective" into several subclasses in the manner of the potentially existing error and assigning each digital image (2) recognized as "defective" to one or more of these subclasses, in particular d) in the fine classification for the objects identified as "potentially defective" (1), depending on the respective subclass to which the item (1) has been assigned, a test method assigned to the respective subclass and adapted to the respective potentially existing error is carried out. Method according to one of the preceding claims, characterized - That upon detection of a "potentially defective", a reduced digital image (3) associated item (1) is detected in the coarse examination, at which position and / or in which area of the reduced digital image (3) an error has occurred and this position and / or this area is cached, and - That in the fine examination of the object (1) associated with the digital image (2), the fine test, in particular exclusively in the cached area or at the cached position, made, in particular, depending on the area and / or from the position of a different fine test is performed. Method according to one of the preceding claims, characterized in that in the case of the sequential checking of a multiplicity of objects, the first threshold value is set in such a way, in particular running, that a proportion of 1 / n, in particular 3% to 10%, of the objects is recognized as "potentially defective", - where n a) the ratio between the memory size of the digital image (2) and / or the partial image of the digital image (2) to be examined and the memory size of the reduced digital image (3), or b) the ratio of the duration of the fine-testing procedure to the duration of the rough-checking procedure equivalent. Method according to one of the preceding claims, characterized in that those objects (1) considered to be "potentially defective" during the coarse test are subjected to one or more sequential intermediate tests, in which preferably an intermediate classification is carried out in each case a) in the individual intermediate tests, only items (1) of the respectively subsequent intermediate test or the fine test are supplied, which were not clearly detected as "error-free" or "in any case faulty" and / or b) the items (1), in particular in the rough check, are classified according to potential error type, and each sequential intermediate check makes a separate error check for only one error type assigned to it and thus the items, if they have been assigned to the same type of error as the current fine check, accordingly is recognized as "faulty" or "error-free", otherwise it is sent to the respective next buffer and / or c) in the case of an overflow of the intermediate memory (24) or a data memory containing the not yet processed digital images (2), at least one object located in the intermediate memory (24) is classified as defective and / or discarded and / or the respectively subsequent intermediate test is supplied. Method according to one of the preceding claims, characterized - that interim results are determined in the coarse examination, in particular one or more of the following parameters: a) the orientation and / or position of the object to be examined (1) in its imaging, b) the orientation and / or position of the image of the object (1) in the respective reduced digital image (3), c) the position and orientation of individual portions of the object (1), such as security thread, kinegram, control points and pass distances in the reduced digital image (3), d) the average brightness and / or color weighting or color transformation obtained by calibration with respect to the reduced digital image (3); e) correction factors for the equalization of the image of an object (1) which has been bent or distorted when it was taken due to transport so that the image of the object (1) appears distorted in the digital image (2) or in the reduced digital image (3), and - that , where a detailed examination of the subject (1) and / or the digital image (2) made for it is required, at least one of the intermediate results produced shall be used for the purpose of the fine test, where appropriate on the basis of the interim results, the quantities concerned being improved or refined, or adapted to the digital image (2). Method according to one of the preceding claims, characterized that by means of the coarse test, the potential presence of an error per se is detected and in the fine test additionally a classification of the type of error and / or the severity of the error is made, and / or - That by means of the coarse examination, a classification of the nature of the error is made, and in the fine test, the severity of the error according to the degree of deviation of the digital image (2) from the reference digital image (4) is determined. Device for testing printed objects (1), in particular of printing units such as banknotes, for example a) a transport unit (22), in particular a conveyor belt, for transporting the objects (1), b) a receiving unit (21) whose receiving area (21 ') on the transport unit (22) located objects (1) is directed and in the event that an object (1) in its receiving area (21') is located , created a digital image (2), c) one of the receiving unit (21) downstream reduction unit (29) to which the created digital images (2) are supplied and the respective digital image (2) in terms of its resolution, in particular its color depth and / or the number of its color channels and / or its local Resolution, reduced and thus created a reduced digital image (3) and assigns the respective object (1), d) a first arithmetic unit (26a) for performing a coarse examination of the objects (1) by comparison of the reduced digital image (3) with a reduced reference image (5) and subsequent rough classification of the comparison result (V ₁ ) as "potentially defective" or "error-free" . e) a first switch (23a) connected downstream of the transport unit and controlled by the first computer unit (26a) for separating the articles (1) according to their rough classification, f) a second arithmetic unit (26b) for carrying out a fine test of the objects (1) classified as "potentially defective" by comparison of the digital image (2) associated with the respective object (1) with a reference image (4) and subsequent fine classification of Comparison result (V ₂ ) as "faulty" or "error-free", and g) a second switch (23b) connected downstream of the first switch and controlled by the second computer unit (26a) for separating the objects (1b) identified as "potentially defective" according to their fine classification. Apparatus according to claim 10, characterized in that a) the first arithmetic unit (26a) for rough checking and rough classification of a reduced digital image (3) present at its input comparing the reduced digital image (3) with a predefined reduced reference image (5) and determining a first comparison value (V ₁ ) corresponding to the correspondence between these reduced images (3, 5), comparing this first comparison value (V ₁ ) with a predetermined first threshold value (S ₁ ), the item (1) is classified as "error-free" if the first comparison value (V ₁ ) indicates a higher match than the first threshold value (S ₁ ), otherwise classify the item (1) as "potentially defective", and - the thus determined classification result is available at its output,
and or b) the first arithmetic unit (26a) for rough checking and rough classification of a reduced digital image (3) present at its input classifies the object (1) as "in any case erroneous" if the first comparison value (V ₁ ) indicates a lower match than a predetermined third one Threshold value (S ₃ ). Device according to one of claims 10 or 11, characterized in that the second arithmetic unit (26b) for fine checking and the fine classification of a present at its input digital image (2) comparing the digital image (2) with a predetermined reference image (4) and determining a second comparison value (V ₂ ) corresponding to the agreement between these images (2, 4), comparing this second comparison value (V ₂ ) with a predetermined second threshold value (S ₂ ), the item (1) is classified as "error-free" if the second comparison value (V ₂ ) indicates a higher match than the second threshold value (S ₂ ), - classify the item (1) otherwise as "defective", and - the thus determined classification result is available at its output. Device according to one of claims 10 to 12, characterized in that the first switch (23a) has an input and at least two outputs, - That the input of the first switch (23a) of the transport unit (22) is connected downstream, - That the first output of the first switch (23a) via a second transport means (22a) leads to a container (27a) for error-free articles (1 a), - That the second output of the first switch (23a) via a third transport means (22b) leads to the second switch (23b), - That the first switch (23a) transports items (1) from their entrance to their first exit, when the gross classification result is fed "error-free", and - That the first switch (23a) transports items (1) from their entrance to their second exit when the gross classification result "potentially defective" is supplied to them. Device according to one of claims 10 to 13, characterized in that the second switch (23b) has an input and at least two outputs, - That the input of the second switch (23b) is connected downstream of the output of the first switch (23a) for "potentially defective" objects (1), - That the first output of the second switch (23b) via a fourth transport means (28a) to another container (27a ') for error-free articles (1 a'), in that the second exit of the second switch (23b) leads via a fifth transport device (28c) to a further container (27c ') for defective articles (1c'), - That the second switch (23b) transports articles (1) from their entrance to their first exit, when the fine classification result is fed "error-free", and - That the second switch (23b) transports articles (1) from their entrance to their second exit, when the fine classification result is fed "incorrectly". Device according to one of claims 10 to 14, characterized - That the first switch (23a) has a third output, which leads via a transport device provided for this purpose (22c) to a container (27c) for in any case faulty objects and that the first switch (23a) objects (1) from its entrance to her transported third output, if the gross classification result "at any rate faulty" is fed and / or - That in the third transport means (22b) a, in particular FIFO, temporary storage (24) is provided, the - Intermediate from the first switch (23a) outgoing objects (1 b) and - On the request of the second processing unit (26b), in particular after the execution of the fine examination of the subject (1 b), these objects (1b) via the third transport means (22b) of the second switch (23b) supplies. Device according to one of claims 10 to 15, characterized in that a) for the coarse test and the fine test in each case programs with the same test algorithms in the first arithmetic unit (26 a) and the second arithmetic unit (26 b) are stored, the respective resolution of the digital images to be compared (2, 3) and reference images (4, 5 ), and / or b) the first threshold value (S ₁ ) used for the coarse examination for the distinction between error-free and potentially faulty images indicates a higher match than the second threshold value (S ₂ ) used in the fine test, and / or c) the first arithmetic unit (26a) performs a subclassification of the class "potentially defective" depending on the type of the assumed error and transmits the respectively determined subclass to the second arithmetic unit (26b), and the second arithmetic unit (26b) passes a fine test depending on the subclass communicated to it, it selects a fine check method adapted to the suspected error associated with the respective subclass. Device according to one of claims 10 to 16, characterized - that the first arithmetic unit (26a) are determined in the context of coarse testing intermediate results, in particular one or more of the following variables: a) the orientation and / or position of the object to be examined in its imaging, b) the orientation and / or position of the image of the object in the respective digital image, c) the position and orientation of individual parts of the object (1), such as security thread, kinegram, control points and pass distances, d) the average brightness and / or a color weighting or color transformation obtained by calibration, e) correction factors for the equalization of the image of an object (1) which has been bent or distorted when it was taken due to the transport, so that the image of the object (1) appears distorted in the digital image (2), - that the first arithmetic unit (26a) forwards the intermediate results to the second arithmetic unit (26b) in the event that the coarse test classifies the object (1) as "potentially defective", and - that the second arithmetic unit (26b), in the context of the fine examination of the object (1) and / or the digital image (2) created for it, bases these intermediate results on the fine test and if necessary improves or refines or determines the quantities concerned on the basis of the intermediate results the digital image (2) adapts. Device according to one of claims 10 to 17, characterized - That the first arithmetic unit (26a) additionally detects on detection of a "potentially defective" object (1) associated reduced digital image (3) at which position and / or in which area of the reduced digital image (3) an error has occurred and caches this position and / or this area and forwards them to the second arithmetic unit (26b), and - that the second arithmetic unit (26b) in the fine examination of the object (1) associated with the digital image (2), the fine test, in particular exclusively in the cached area or at the cached position, and performs, in particular in dependence on the operation and / or the position performs a different fine test.

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