Biomedical subjects

Hsuan T Chang

Publications and source records attributed to Hsuan T Chang.

3 recordsLinked to original sources

PubMed2005

Image watermarking by use of digital holography embedded in the discrete-cosine-transform domain.

Digital holography techniques can be utilized to implement image watermarking schemes. In a previous method proposed by Takai and Mifune [Appl. Opt. 41,865 (2002)], a watermark image is transformed into a digital Fourier hologram, which then is directly superposed onto a content image to perform the embedding process. In the detection stage, the watermark is extracted based on the inverse Fourier transform and optical holography techniques. A method in which the hologram is superposed on the discrete-cosine-transform domain of the content image is proposed to significantly improve Takai and Mifune's method. The proposed method can greatly reduce the degradation on the superposed image, which is the major drawback in Takai and Mifune's method. Simulation results also demonstrate that the watermark can be successfully extracted under different kinds of attack.

Comment↗

PubMed2002

Design of cascaded phase keys for a hierarchical security system.

An image cryptosystem based on multiple phase-only masks is proposed. The proposed cryptosystem is a hierarchical security system that can use multiple phase keys to retrieve different amounts of data. In addition to the sequential order of the phase keys, the distance parameters among the phase keys are introduced to increase the system security. Even when an illegal user steals all the phase keys, the system cannot be broken without the correct sequential order and the distance parameters. However, the proposed system can verify the identities of the persons by the cascaded structure for the phase keys to generate different verification images. Simulation results are further demonstrated to verify the proposed method.

Journal Article↗

PubMed2002

Multiple-phase retrieval for optical security systems by use of random-phase encoding.

The technique of the multiple phase encoding for optical security and verification systems is presented in this paper. This technique is based on a 4-f optical correlator that is a common architecture for optical image encryption and verification systems. However, two or more phase masks are iteratively retrieved by use of the proposed multiple phases retrieval algorithm (MPRA) to obtain the target image. The convergent speed of the iteration process in the MPRA is significantly increased and the recovered image is much more similar to the target image than those in previous approaches. In addition, the quantization effects due to the finite resolution of the phase levels in practical implementation are discussed. The relationships between the number of phase masks and the quantized phase levels are also investigated. According to the simulation results, two and three phase masks are enough to design an efficient security verification system with 64 and 32 phase levels, respectively.

Journal Article↗