参考
① http://www.cnblogs.com/smileEvday/archive/2013/05/25/IOSImageEdit.html
② http://www.cocoachina.com/bbs/read.php?tid-77731-page-1.html
③ http://supershll.blog.163.com/blog/static/3707043620128492741525/
④ http://www.cnblogs.com/delonchen/archive/2011/08/03/iostransform.html
iOS - Core Graphics 之 Quartz2D
原文：http://www.cnblogs.com/loying/p/5189420.html