裁切图片，

- (void)webImageManager:(SDWebImageManager *)imageManager didFinishWithImage:(UIImage *)image

{

    CGSize targetSize = CGSizeMake(image.size.width*4/sqrt(5.0f),

                                   image.size.width*2/sqrt(5.0f));

    UIGraphicsBeginImageContext(targetSize);

    [image drawInRect:CGRectMake(image.size.width*(1/sqrt(5.0f)*2-1),

                                 image.size.width*(1/sqrt(5.0f)-1),

                                 image.size.width*2,

                                 image.size.height*2)];

    image = UIGraphicsGetImageFromCurrentImageContext();

    UIImage *blurredImage = [self blurryImage: image withBlurLevel: 0.1];

    [self.bgImageView setImage:blurredImage];

    [selfsetNeedsLayout];

}