Banknote Security Pattern Generation Using Circular Symmetry
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Solution Overview
Problem
Existing methods for authenticating security documents, such as banknotes, require significant computational power and memory, making them unsuitable for devices with low processing capabilities like printers, scanners, and digital cameras, and struggle with authentication when only a partial document surface is available or when documents undergo geometrical transformations.
Innovation Solution
A method generating a circularly symmetric 2D security pattern using a self-similar 1D signal, which can be embedded into halftone images, allowing detection with minimal processing power and preserving essential characteristics, enabling authentication even with partial document surfaces and geometrical transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital signal processing methods are used for security feature detection, then detection accuracy is improved, but computational power and memory requirements increase significantly
Solution Approach 1:
The security feature is segmented into two distinct levels: a visible first level integrated into the document design that provides immediate authentication, and an invisible second level that offers enhanced security. This segmentation allows low-capability devices to use the simple visible features while high-capability devices can access the more complex invisible features, thus resolving the contradiction between detection accuracy and computational requirements.
Solution Approach 2:
The invention transitions from traditional 2D security patterns to a 3D multi-level security structure by adding the invisible second level that overlays the visible first level. This dimensional expansion enables detection methods to operate at different complexity levels, allowing simple visual inspection for basic authentication and complex signal processing only when needed, thereby reducing overall computational requirements while maintaining detection accuracy.
2Reliability
If invisible security features are used, then resistance against counterfeiting is improved, but detector implementation becomes more complex requiring high computational power
Solution Approach 1:
The security system is divided into visible and invisible components, each serving different authentication needs. The visible first level provides immediate authentication that can be verified by any device, while the invisible second level provides enhanced counterfeiting resistance that requires more sophisticated detection. This segmentation allows detectors to implement only the necessary level of complexity for their specific application.
Solution Approach 2:
The visible first level acts as an intermediary between the document and the detector, providing a simplified interface for authentication. For low-capability devices, the visible features serve as the primary authentication mechanism, mediating the interaction without requiring complex processing. High-capability devices can bypass this intermediary and directly access the invisible second level when enhanced security is needed.
3Ease of operation
If visible security features are used, then ease of detection is improved, but resistance against counterfeiting deteriorates
Solution Approach 1:
The security features are segmented into visible and invisible levels, each with different detection ease and security properties. The visible first level maintains ease of detection for immediate authentication, while the invisible second level provides enhanced resistance against counterfeiting. This segmentation allows the system to offer both ease of operation and high reliability depending on the authentication context.
4Measurement precision
If authentication requires access to large digitized area of the document, then detection accuracy is improved, but authentication becomes impossible when only partial document surface is available
Solution Approach 1:
The security pattern is segmented into local features distributed throughout the document. The visible first level consists of numerous small, independently detectable elements that can be authenticated in partial views. This segmentation enables authentication accuracy to be maintained even when only a portion of the document is available, as the local features provide sufficient information for verification without requiring access to the entire document surface.
Data Source
AI summary
The present invention proposes a method for generating a security bi-level image used to form one of the inks of a banknote, said image comprising an original bi-level image and 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 the Fourier transform of an auxiliary image 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 as 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, said method comprising the step of: —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, —thresholding the merged image to obtain the security bi-level image, —applying the security bi-level image on a support.