//下面是sdk中UIImage.h头文件中的内容 UIKIT_EXTERN NSData *UIImagePNGRepresentation(UIImage *image); // return image as PNG. May return nil if image has no CGImageRef or invalid bitmap format UIKIT_EXTERN NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality); // return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compression is 0(most)..1(least)