裁剪image

- (UIImage *)cutImageWithSourceImage:(UIImage *)sourceImage size:(CGSize)targetSize{

UIGraphicsBeginImageContext(targetSize);

CGRect targetRect = CGRectZero;

//裁剪后的image的原点位置
targetRect.origin = CGPointZero;

//裁剪后的image的宽度
targetRect.size.width  = sourceImage.size.width;

//裁剪后的image的长度
targetRect.size.height = sourceImage.size.height-20;

//裁剪图片
[sourceImage drawInRect:targetRect];

UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}