Method for a banknote detector device, and a banknote detector device

Method in a banknote detector device for an automatic teller machine, to be used to differentiate non-accepted banknotes from accepted banknotes, the device comprises a banknote image sensor to receive and scan at least one face of an input banknote and to store a banknote image (BI) of each scanned face in a storage in dependence of said scanning, said banknote image comprises image data in the form of a number of pixels;

• and a reference banknote image (RBI) storage where one reference banknote image (RBI), being processed from a predetermined number of banknote images from accepted street-quality banknotes, is stored for each face of each relevant banknote, the banknote detector device further comprises an IR image sensor that is arranged to scan an input banknote and to store an IR-image of said banknote in said storage such that the IR-image being linked to the corresponding banknote image, wherein said method comprises:
• A) an alignment step where one side of the banknote image is aligned in relation to the respective side of the RBI by use of said IR-image, and that the banknote size is determined,
• B) a banknote face classification step where the face and orientation of the banknote image are determined,
• C) a printed pattern positioning step where the printed pattern of the banknote image (BI) is determined in order to exactly position the BI printed pattern in relation to the printed pattern of a reference banknote image (RBI),
• D) a comparison step where, for at least one face of the banknote, the BI and RBI, being in exact pattern position in relation to each other, are compared pixel per pixel according to a predefined comparison procedure resulting in that the input banknote is classified as accepted or non-accepted,
• wherein in step C, two predefined limited regions of the BI are identified, one horizontal region X having a preset width and running along the longer side of the banknote and one vertical region Y having a preset width and running along the shorter side of the banknote, a line-pattern is created by calculating the mean values of all pixels in one vertical row in the horizontal region X and then aligning all mean values, resulting in a horizontal data-area line Sx representing the whole region X, and the same procedure is performed for the vertical region Y resulting in a vertical data-area line Sy representing the whole region Y, wherein Sx and Sy are compared to line-patterns of the RBI obtained in the same way and that said line-patterns are adjusted in relation to each other such that differences between corresponding pixel positions are minimized and the BI and RBI are then adjusted accordingly in relation to each other.