中文摘要：

To whom correspondence should be addressed.Zhang Fan, He received his Ph. D degree in Computer Science from Beijing University of Technology, China, in 2005. Now, he is a postdoctoral researcher in College of Electronic ＆ Information Engineering, Tianjin University, China. His research interests include image processing, computer vision, pattern recognition and in-formation hiding. E-mail： zhangfan@vip.sohu.com