使图片与背景融为一体

    // 获取显示图片
    UIImage *showImage = [UIImage imageNamed:@"6"];
    
    // 获取遮罩图片
    UIImage *maskImage = [UIImage imageNamed:@"mask"];
    
    // 显示的图片
    UIImageView *imageView =         [[UIImageView alloc] initWithFrame:(CGRect){CGPointZero, showImage.size}];
    imageView.image        = showImage;
    imageView.center       = self.view.center;
    [self.view addSubview:imageView];
    
    // 带透明像素PNG图片
    UIImage *png = [maskImage blurImageWithRadius:20];

    // 将透明像素PNG图片转换为遮罩用mask
    CALayer *maskLayer = [CALayer layer];
    maskLayer.contents = (__bridge id)(png.CGImage);
    maskLayer.frame    = (CGRect){CGPointZero, showImage.size};
    
    // 使用遮罩mask
    CALayer *showLayer = [CALayer layer];
    showLayer.frame    = (CGRect){CGPointZero, showImage.size};
    showLayer.mask     = maskLayer;
    showLayer.backgroundColor = [showImage averageColor].CGColor; // 取图片平均颜色
    showLayer.position = self.view.center;
    
    // 设置背景色
    self.view.backgroundColor = [showImage averageColor];         // 取图片平均颜色
    [self.view.layer addSublayer:showLayer];