用法
//第一步
_bgImageLayer = [CALayer layer];
_bgImageLayer.backgroundColor = [UIColor whiteColor].CGColor;
_bgImageLayer.frame = self.view.bounds;
[self.view.layer addSublayer:_bgImageLayer];
//第二步
UIImageView *imgv =[[UIImageView alloc]initWithFrame:self.view.bounds];
imgv.image = [UIImage imageNamed:@"IMG_2877.JPG"];
UIImage *img = [imgv.image blurredImageWithSize:CGSizeMake(100, 200)];
[CATransaction begin];
[CATransaction setAnimationDuration:1];
_bgImageLayer.contents = (id)img.CGImage;
```