Relevant Modelling Comparison of Geometric Distortions in Watermarking Systems

摘要

A challenging aspect in the development of robust watermarking algorithms is the ability to withstand complex geometric distortion of the media. A few existing techniques are known to deal with such transformations up to a certain level. Traditionally, the measure of the degradation caused by an attack on an image only addressed the pixel value modification. However, a degradation consequent to the geometric distortion of an image cannot be measured with traditional criteria. Therefore the evaluation and comparison of the robustness to desynchronization of different watermarking schemes was not possible. In this paper, we present an innovative method to measure the distortion introduced by complex geometric deformations of an image. The distortion measure is expressed in term of how closely the applied transform can be approximated by a simpler transform model (e.g. RST transform, affine transform). The scheme relies on the local least square estimation of the parameters of the reference transform model. Eventually, we illustrate the proposed measure by presenting some results for different complex image distortions.