Method and device for examining the optical state of value documents

Patent metadata

Field	Value
Publication number	US-9547949-B2
Application number	US-201113995372-A
Country	US
Kind code	B2
Filing date	Dec 20, 2011
Priority date	Dec 21, 2010
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

A method for examining the optical condition of a value document on the basis of a digital image of at least a specified region of the value document, the image comprising pixels, comprises searching the pixels of the digital image are searched for sets of error pixels which are respectively given in that the error pixels fulfill a specified deviation criterion for an impermissible deviation of at least one specified pixel property, and the distance of each error pixel of the respective set from at least one other error pixel of the same set does not exceed a specified distance that is greater than the distance of directly neighboring pixels of the digital image, and a number of sets found during the search and/or a value for at least one property of at least one of the sets found during the search is ascertained.

First claim

The invention claimed is:

1. A method for examining the optical condition of a value document on the basis of a digital image of at least a specified region of the value document, the digital image comprising pixels, said method comprising the steps:
searching pixels of the digital image for sets of error pixels, wherein the error pixels fulfill a specified deviation criterion for an impermissible deviation of at least one specified pixel property in order to determine pixels that lie outside a reference distribution for permissible pixel properties, and
a distance of each error pixel of the respective set from at least one other error pixel of the same set is smaller or equal to a specified distance that is greater than the distance of directly neighboring pixels of the digital image, and
ascertaining a number of sets found during the search and/or a value for at least one property of at least one of the sets found during the search.

2. The method according to claim 1 , wherein for searching for a set of error pixels, error pixels are associated with the set such that for an error pixel already associated with the set there is searched for a nearest error pixel that fulfills the deviation criterion and is not yet associated with the set and whose distance from the already associated pixel does not exceed the specified distance, and if the nearest error pixel is found, the nearest error pixel is associated with the set.

3. The method according to claim 2 , wherein during the search for a set, the search for the nearest error pixel and its associating are executed repeatedly, there being respectively employed as the error pixel already associated with the set the error pixel last associated with the set.

4. The method according to claim 3 , wherein for searching for the nearest error pixel, there is respectively searched for an error pixel in a search list of pixels which is determined at least by the error pixel last associated with the set and the specified distance or by the error pixel last associated with the set and a specified list.

5. The method according to claim 2 , wherein for searching for the nearest error pixel, until an error pixel is found, pixels are checked in an order that is obtainable by searching iteratively on a path from the last associated error pixel having the length of the specified distance in a given search direction starting out from the pixel nearest to the last associated error pixel on the straight line for further pixels on the straight line with increasing distances, and if no pixels are found, the search direction and the straight line are rotated in a specified search direction until a pixel lies on the rotated straight line and the search direction is chosen as the new given search direction.

6. The method according to claim 1 , wherein during the search for the sets, the pixels fulfilling the deviation criterion are first ascertained and thereafter the sets of error pixels are searched for only in said pixels.

7. The method according to claim 1 , wherein during the search for the sets, starting out from an error pixel of a set, pixels whose distance from the error pixel does not exceed the specified distance are examined as to whether they fulfill the deviation criterion.

8. The method according to claim 7 , wherein the deviation criterion depends on the distance between the error pixel and the checked pixel.

9. The method according to claim 1 , wherein for searching for a set of error pixels, there are first searched for groups of error pixels that respectively comprise error pixels that fulfill the deviation criterion and that are directly neighboring, wherein it is checked whether the distance of at least one error pixel of one of the groups from at least one error pixel of another of the groups whose error pixels are not yet associated with a set does not exceed the specified distance and, if this is the case, the error pixels of the two groups are associated with the same set.

10. The method according to claim 1 , wherein the number and/or the value is employed for ascertaining a value representing the optical condition.

11. The method according to claim 1 , wherein there is employed as a property of the set a function of the number of error pixels of the set and of the length of a line through the error pixels of the set which form the edge thereof.

12. A method for examining the optical condition of a value document comprising the steps:
capturing a first digital image of at least a specified region of the value document wherein, the first digital image comprises pixels, and
carrying out the method according to claim 1 with the first digital image.

13. An evaluation device configured to examine the optical condition of a value document on the basis of a digital image of at least a specified region of the value document, the digital image comprising pixels, wherein the evaluation apparatus has an interface for receiving a digital image of at least a specified region of the value document and is configured to carry out a method according to claim 1 on the basis of the digital image of at least a specified region of the value document that is received by the interface.

14. An apparatus for examining the optical condition of a value document, comprising:
an optical sensor configured to capture a digital image of at least a region of the value document, and
an evaluation device according to claim 13 whose interface is connected to the sensor via a signal connection, so that a digital image captured by the sensor is receivable by the evaluation device.

15. A non-transitory computer-readable data carrier comprising program code which when executed by a processor of a computer, the computer executes a method according to claim 1 .

16. A method for examining the optical condition of a value document on the basis of a digital image of at least a specified region of the value document, the digital image comprising pixels, said method comprising the steps:
searching pixels of the digital image for sets of error pixels, wherein the error pixels fulfill a specified deviation criterion for an impermissible deviation of at least one specified pixel property, and a distance of each error pixel of the respective set from at least one other error pixel of the same set does not exceed a specified distance that is greater than the distance of directly neighboring pixels of the digital image, and
ascertaining a number of sets found during the search and/or a value for at least one property of at least one of the sets found during the search,
wherein for searching for a set of error pixels, error pixels are associated with the set such that for an error pixel already associated with the set there is searched for a nearest error pixel that fulfills the deviation criterion and is not yet associated with the set and whose distance from the already associated pixel does not exceed the specified distance, and if the nearest error pixel is found, the nearest error pixel is associated with the set,
wherein during the search for a set, the search for the nearest error pixel and its associating are executed repeatedly, there being respectively employed as the error pixel already associated with the set the error pixel last associated with the set, and
wherein for searching for the nearest error pixel, there is respectively searched for an error pixel in a search list of pixels which is determined at least by the error pixel last associated with the set and the specified distance or by the error pixel last associated with the set and a specified list.

17. A metho

Assignees

• Holl Norbert
• Giesecke & Devrient Gmbh

Inventors

• Holl Norbert

Classifications

• G07D7/2008

  using pre-processing, e.g. de-blurring, averaging, normalisation or rotation · CPC title

• G07D7/124 Primary

  Physics · mapped topic

• G07D7/0066

  Physics · mapped topic

• G07D7/003 Primary

  using security elements (using digital security elements G07D7/004) · CPC title

• G07D7/0054

  involving markings the properties of which are altered from original properties · CPC title