Corresponding author.Wei Wei was born in 1979. He is a Ph.D. can- didate in School of computer Science, North- western Polytechnical University. His re- search interests are pattern recognition, com- puter vision and image processing. E-mail: weiwin 1979 @ hotmail.com Yanning Zhang was born in 1967. She is a Professor in School of Computer Science, Northwestern Polytechnical University. Her research interests are image processing, pat- tern recognition, computer vision and intelli- gent information processing. Chunna Tian was born in 1980. She is an asso- ciate professor in School of Electronic and En- gineering, Xidian University. Her research in- terests are pattern recognition and intelligent in- formation processing.