METHOD OF DETECTING FOREIGN IMAGES ON A BANKNOTE Russian patent published in 2019 - IPC G07D7/00 

FIELD: monitoring devices.

SUBSTANCE: invention relates to a method of detecting foreign images on a banknote. According to the method, a digital image of the banknote is obtained and its compliance with one of the predetermined types and orientations is determined. Using the shape and location of the controlled area on the surface of the banknote, corresponding to the given type and orientation of the banknotes, an evaluation image is formed by binarisation of the monitored zone. Individual binarization threshold value for each pixel of the monitored area is calculated based on a binarisation parameter map predefined for a predetermined type and orientation of banknotes, and is associated with elements of said card with a known functional relationship. One element of the binarisation parameter map determines a binarization threshold value for a group of at least two neighboring pixels, and the known functional relationship is established taking into account the statistical distribution of pixel brightness in the digital image of the banknote. Then, an evaluation criterion is used to determine an alien image detection criterion based on an analysis of black pixels in said evaluation image, and based on said criterion, a decision is made on the presence of an extraneous image in the controlled area of the digital image of the banknote. Elements of the map of the binarisation parameter are selected so as to increase corresponding individual binarization threshold values and provide an acceptable low level of probability of a false decision on the presence of an extraneous image when performing said sequence of actions for banknotes of a predetermined type and orientation, which obviously do not contain extraneous images.

EFFECT: high sensitivity of the method of detecting foreign images with reduced parasitic sensitivity to geometrical distortions of scanning.

13 cl, 13 dwg