A better scheme is proposed for image authentication and restoration based on standard deviation (STD) using two watermarks, one for detecting tampered regions and the other for retrieval. The main contribution of this work is a decrease of recovery watermark, which is compressed from three categories according to the STD values of every quantization discrete cosine transformation coefficients block. In addition, blocks corresponding to different categories are encoded to variable lengths and then encrypted based on the index of a chaotic sequence in an ascending order. At the same time, the authentication watermark uses a pixel-wise scheme obtained by random permutations and suitable exclusive OR operations among bitplanes of the host image. Experimental results show that the proposed scheme is not only secure but also detect any modification made to images and restore regions that have been modified.
An extensive model test program had been carried out to investigate the issues of ice loading on bridge pier model. This
paper investigated design principle of three kinds of FBG sensor modules, including FBG-based displacement sensor
module, FBG-based strain sensor module and FBG-based force sensor module. A series of calibration tests of all FBG
sensors had been made to detect the sensitivity of FBG sensor modules previously. There were 12 FBG-based sensors
applied to monitor the failure progress and to predict the cracking inside the bridge pier model. The results of the ice
loading tests proved that the FBG-based sensor had many advantages, characterized by its small size, high precision,
easier installation, water resistance and cold resistance, demonstrating promising potentials in cracking and failure
monitoring of bridge pier model.