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UM E-Theses Collection (澳門大學電子學位論文庫)

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Title

Reversible watermarking for digital images in spatial domain and encrypted domain

English Abstract

Due to widespread of internet, distribution and transmission of digital content through the internet becomes popular, and importance of digital watermarking in copyright protection, integrity control and authentication of the digital contents rises. Among existing digital watermarking, reversible digital watermarking attracts a lot of attention owing to its reversibility. However, conventional reversible watermarking methods are not robust against attacks like JPEG compression, a slight modification leads to failure in watermark retrieval and image recovery. Existing robust reversible watermarking methods usually have poor visual quality or unstable robustness and reversibility, implies that reversibility cannot be assured even in lossless channel. In addition, demands for reversible data hiding in encrypted images arise in recent years, yet the current methods usually have comparatively low hiding capacity. Hence, in this thesis, three reversible watermarking algorithms for different domains and situation are proposed, including a conventional reversible watermarking algorithm, the robust version of the algorithm and a version that is applied in encrypted images. In conventional reversible watermarking algorithm, an influential threshold is determined adaptively with adaptive thresholding to preserve good visual quality. Efficient location map encoding is also proposed to reduce location map size, which is a major constituent of overhead, so that more space is left for watermark embedding. For robust reversible watermarking method, adaptive bit plane manipulation is applied to hide watermark bits in bit planes that are lesser affected by attacks. Region iv filtering is also adopted to find blocks that result in low variance for watermark embedding to further increase its robustness. In reversible data hiding for encrypted images, a Burrows-Wheeler transform based image encryption method that suits conventional reversible watermarking is proposed. To maintain good visual quality in approximate images derived from direct decryption, variance-sorted blocks embedding is employed in the algorithm. Experimental results verify the influence of our contributions, and show that our methods have improved performances compared with state-of-the-art technologies. For the reversible image watermarking methods in both spatial domain and encrypted domain, higher embedding rate can be achieved, and better surviving bit rate, a robustness measure, is obtained in the robust reversible watermarking algorithm.

Issue date

2016

Author

Choi, Ka Cheng

Faculty

Faculty of Science and Technology

Degree

Ph.D.

Subject

Data encryption (Computer science)

Digital watermarking

Software Engineering -- Department of Computer and Information Science

Supervisor

Pun, Chi Man

Files In This Item

Full-text (Intranet)

Location
1/F Zone C
Library URL
991001903919706306