Full-spectrum image coding for security document marking

Hans Oltmans

doi:10.1117/12.525402

3 June 2004 Full-spectrum image coding for security document marking

Hans Oltmans

Proceedings Volume 5310, Optical Security and Counterfeit Deterrence Techniques V; (2004) https://doi.org/10.1117/12.525402
Event: Electronic Imaging 2004, 2004, San Jose, California, United States

Abstract

A method of providing a digital image with a unique, machine readable, code image is presented. It is called "Full Spectrum," because the method uses Fourier transform techniques to embed the code in a wide range of spatial frequencies. The changes made to the original image by the encoding process are meaningless to the observer, and, by proper choice of the embedding parameters and the resolution (reproduction size) of the marked image, they can be made totally imperceptible. Full Spectrum has some intrinsic advantages for application to printed security structures in a document authentication/-identification environment. Using its mathematical properties, the method is shown to be invariant to shifting and cropping, which enables the code image to be reconstructed from a recording of the document with arbitrary position and size. Techniques to deal with possible rotation and scaling of the recorded image with respect to the (printed) original are elaborated. Finally, a general method is developed to match the reconstructed code image to the reference image (expected code image). Experiments show that the code image can survive various graphical transfer processes, such as halftone screening, printing and digitising. An actual document containing a printed Full Spectrum structure is demonstrated, the Security ID.

Citation Download Citation

Hans Oltmans "Full-spectrum image coding for security document marking", Proc. SPIE 5310, Optical Security and Counterfeit Deterrence Techniques V, (3 June 2004); https://doi.org/10.1117/12.525402

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KEYWORDS

Image compression

Fourier transforms

Image processing

Image resolution

Digital imaging

Modulation

Information security

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