Data Carrier Security via Fourier Transform Hidden Image
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Solution Overview
Problem
Existing methods for securing documents against counterfeiting, such as those using visible and invisible protection means, face challenges including the ease of mimicking certain effects, alignment issues with translucent features, and the increasing availability of luminescent inks.
Innovation Solution
The method involves generating an initial random picture, subjecting it to two-dimensional Fourier transformation to create a matrix of spatial frequencies, modifying these frequencies to hide a hidden picture, and then applying inverse Fourier transformation and automatic thresholding to produce a final picture with a hidden image that is difficult to reproduce.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional protection means such as translucent features with patterns are used, then visual verification is enabled, but alignment precision deteriorates causing unrecognizable pictures when misaligned
Solution Approach 1:
The patent replaces the mechanical/optical alignment system with a frequency domain analysis system. Instead of relying on precise physical alignment of translucent patterns, the solution uses Fourier transformation to convert spatial patterns into frequency patterns, where the hidden picture emerges through spectral analysis rather than physical alignment. This substitution eliminates the alignment precision requirement while maintaining visual verification capability.
Solution Approach 2:
The patent transforms the verification problem from spatial domain to frequency domain. By applying Fourier transformation, the hidden picture is encoded in the frequency spectrum rather than in spatial arrangement. This dimensional change allows verification through frequency analysis instead of spatial alignment, resolving the contradiction between ease of verification and manufacturing precision requirements.
2Ease of operation
If visible protection means are used, then verification is simplified, but counterfeiting ease increases
Solution Approach 1:
The patent introduces Fourier transformation as an intermediary step between the visible pattern and the hidden information. The visible protection pattern serves as a carrier that, when transformed through Fourier analysis, reveals the hidden picture. This intermediary process maintains verification simplicity while preventing counterfeiting, as the hidden picture cannot be extracted without performing the specific frequency transformation.
Solution Approach 2:
The patent changes the parameter space from spatial coordinates to frequency coordinates. The visible pattern remains unchanged in space, but its interpretation changes when viewed in the frequency domain. This parameter transformation allows the same visible pattern to serve both as a aesthetic element and as an encoded message, simplifying verification while increasing security against counterfeiting.
3Reliability
If complex protection means with multiple layers are used, then security level improves, but device complexity increases
Solution Approach 1:
The patent merges the visible protection pattern and the hidden security picture into a single integrated structure. Rather than using separate layers for visible features and hidden features, the solution encodes both functions within one pattern that serves dual purposes. The same printed pattern provides both aesthetic verification and encoded security information when transformed, reducing structural complexity while maintaining high security level.
Data Source
Figure 1a~1b
Figure 1c~2a
Figure 2b~2c
AI summary
The invention relates to a method for securing a data carrier, which is characterized in that in the step (101) of generating a random picture being the final picture, firstly, one defines the size of the random picture in pixels. In the step (102), one generates a hidden picture that is to be hidden in the final picture. The generated random picture, being in the form of a matrix of pixels, where every pixel has a given color, is subjected (103) to two-dimensional Fourier transformation, in this way generating a matrix of the spatial frequencies of the initial picture. Every pixel of the frequency space is modified (104) according to the pixel values of the hidden picture so that when the hidden picture pixels are of a first color, one modifies no frequency space, and when the hidden picture pixels are of a second color, one brightens the pixels of the hidden picture, whereas each of the intermediate tones of the grayscale increases the frequency of the signal in the frequency space according to a predefined function. The modified picture of the frequencies is subjected (105) to the inverse Fourier transformation generating, again, the initial picture but modified by the hidden picture. The generated picture is subjected (106) to a thresholding process that is based on comparing the characteristic features of every pixel against a predefined brightness index or the given color coverage index. The obtained matrix with the hidden picture after the thresholding is used for generating the final picture, where every pixel of the matrix is replaced with sub-pictures, wherein pixels of different colors are substituted by different sub-pictures or the same sub-pictures but differently arranged or the same sub-pictures but of different areas. The final picture is subjected to clipping (107) and replacing (108) steps, and it is applied on (109) a data carrier.