Hi, I don't know why the mask input is type "unsigned char". I think if it could be bool/bit, it could save a lot of memory, since we only need values 0 and 1 in a mask? Thank you! ___________________________________________________________ 雅虎邮箱传递新年祝福,个性贺卡送亲朋! http://cn.mail.yahoo.com/gc/index.html?entry=5&souce=mail_mailletter_tagline