Saturated Dynamic System Of Research In Digital Watermarking Scheme

The process of digital watermark embedded in a host figure can be viewed as communication systems.Watermark information is the input,and the image DCT domain is viewed as background noise.For detecting watermark,the non-linear system is equivalent to a detector,and the watermark embedding algorithm is based on nonlinear characteristics of nonlinear detector.This thesis focuses on the dynamical saturating system and its application to the watermark detection.Binary watermark is arranged in the order of a zig-zag sequence, and then modulated as one-dimensional pulse amplitude modulated signal.Particularly,a half inter-symbol interval delay can be set at any time in this modulated signal.This delay makes the linear systems,such as matched filter,difficult to extract the watermark information,thereby increases the ability of anti-conspiracy attack.Then,a suitable range of DCT coefficients is disordered as background noise.The watermarking signal is added to these disordered DCT coefficients,yielding the embedding DCT coefficients.The watermark can be extracted by nonlinear saturating detectors without prior knowledge of the original image and watermark,i.e.blind watermark detection.Interestingly,a higher match between the original watermark character and the extracted one can be further achieved by a parallel array of nonlinear detectors via the mechanism of array stochastic resonance.Robustness of the proposed watermarking scheme is shown in the presence of noise,filtering,cropping,and compression.Finally,the dynamical saturating detector is compared with the classical bistable detector in detecting the watermarking signal.