DOVID Authentication via Illumination Distribution Feature Extraction
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Solution Overview
Problem
Existing methods for authenticating DOVID imprints on objects, such as banknotes, are labor-intensive and inefficient, requiring microscopic examination or point-by-point refraction pattern comparison, which is not suitable for rapid verification of large numbers of objects.
Innovation Solution
A method that extracts the illumination distribution function's eccentricity and orientation angle as characteristic features, using histogram comparison and Fourier transforms to determine the presence and correctness of DOVID imprints with a minimal number of images, allowing for easy verification using a simple setup and multicolor digital imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microscopic examination or point-by-point refraction pattern comparison is used to verify DOVID imprints, then measurement precision is improved, but productivity deteriorates due to time-consuming manual processes
Solution Approach 1:
The patent replaces manual microscopic examination and point-by-point refraction pattern comparison with an automated image processing system. The system captures images of the DOVID imprint under oblique illumination and uses computer algorithms to extract illumination distribution functions, calculate characteristic values, and perform histogram comparisons, thereby substituting mechanical manual operations with automated optical and computational processes.
Solution Approach 2:
The patent transforms the verification process by changing from direct visual or microscopic inspection to analyzing parameter-based representations. It extracts illumination distribution functions from images, calculates characteristic values (histograms of illumination intensity distributions), and compares these parameters mathematically. This parameter transformation enables rapid automated comparison while maintaining verification accuracy.
2Measurement precision
If complex verification equipment is used to accurately detect DOVID imprints, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary computational layer between the simple image capture device and the verification decision. Instead of requiring complex optical equipment, the system uses a standard image capture device to obtain images, then employs computer algorithms to extract illumination distribution functions and perform histogram comparisons. This intermediary processing layer enables accurate verification with simple hardware.
Solution Approach 2:
The patent creates a digital copy (image) of the DOVID imprint and performs all verification operations on this copy rather than directly manipulating or examining the physical object. The illumination distribution function and its histogram serve as digital representations that can be analyzed computationally, eliminating the need for complex physical measurement equipment.
3Measurement precision
If a large number of images are captured to ensure accurate verification, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent extracts the essential verification information from images by calculating illumination distribution functions and their characteristic histograms. Instead of analyzing multiple complete images, the system extracts these condensed statistical representations that capture the essential features of the DOVID imprint's light scattering properties, enabling verification with minimal imaging data.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables quick and accurate verification of DOVID imprints, invariant to rotation, with a small number of images, facilitating rapid authentication of objects by comparing feature images and histograms, thus improving efficiency and ease of implementation.
Implementation Method 1
a light source (31, 31b, ...) with different angles of incidence (φ, θ) illuminates an area (11) of the object (10) having a DOVID imprint (21)
Implementation Method 2
DOVIDs, short for 'Diffractive Optically Variable Image Device'
Data Source
Figure 1a~1b
Figure 2~3
Figure 4
AI summary
The invention relates to a method for comparing the surface of an object (10), in particular a banknote, a chip card or an identity card, comprising a DOVID area (11), with a reference object (20), also comprising a DOVID area (21), a) wherein the object (10) is recorded by an image acquisition unit (30) and digital images (32a, 32b, ...) of the same size are thus created, wherein each digital image (32a, 32b, ...) is created under illumination by a light source (31a, 31b, ...) with different angles of incidence (ϕ, θ), and a stack of images (39) comprising the individual digital images (32a, 32b, ...) is thus created, b) wherein a feature image (33) is created which has the same size as the created digital images (32a, 32b, ...), wherein for each pixel (34x, 34y, ...) of the feature image to be created Feature image (33) - each a lighting distribution function (36x, 36y, ...) is determined, which indicates how strongly the part of the DOVID area (11) depicted in the pixel (34x, 34y, ...) reflects light when illuminated at the respective angle of incidence (ϕ, θ), and - from the illumination distribution function (36x, 36y, ...) one or more characteristic features (37x, 37y, ... ) are extracted and assigned to the respective pixel (34x, 34y, ...) of the feature image (33), and c) wherein the feature image (33) is compared with a reference feature image (23) created from a reference object (20) according to the same criteria.