截取图片中指定区域大小部分

- (UIImage *)cutImageFromImage:(UIImage *)image inRect:(CGRect)rect{

//屏幕的缩放比 (非Retain屏为1，Retain屏为2）

    CGFloat s = [UIScreen mainScreen].scale;

    //根据缩放比转化rect

    CGRect transRect = CGRectMake(rect.origin.x*s, rect.origin.y*s, rect.size.width*s, rect.size.height*s);

    //创建像素位图

    CGImageRef newImageRef = CGImageCreateWithImageInRect([image CGImage], transRect);

    //得到最终图片

    UIImage *newImage = [UIImage imageWithCGImage:newImageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];

    //手动释放，否者会内存泄露

    CGImageRelease(newImageRef);

    return newImage;

}