Patent ID: 9317988
Filing Date: 2016-04-19
CPC Classification: G07D,H04N

Claim Text:
1. A method for generating a security bi-level image used to form one of the inks in a banknote, the method comprising the steps of: receiving an original bi-level image; obtaining a security pattern, said security pattern being obtained in the spatial domain by the inverse Fourier transform of the combination in the frequency domain between a two-dimensional phase component and a two-dimensional sweep, said two-dimensional sweep being a circularly symmetric, two-dimensional pattern created by sweeping a self-similar, one-dimensional function along a 360-degree arc, such that said security pattern being detectable from the maximum value of the cross-correlation of said one-dimensional function with the Fourier transform of one line of said banknote; determining a distance map of the original bi-level image; generating a merged image by linearly interpolating at least a part of said distance map with said security pattern; and thresholding the merged image to obtain the security bi-level image.