rounded imageView 's border is not smooth after setting image property
<pre><code>class PPAvatarCollectionCell: UICollectionViewCell {
    var imageView:UIImageView!

override init(frame: CGRect) {
    super.init(frame: frame)

    imageView = UIImageView(frame: CGRect(origin: CGPointMake(0, 0), size: CGSizeMake(frame.size.width, frame.size.height)))

    self.addSubview(imageView)

    imageView.contentMode = .ScaleAspectFill
    imageView.backgroundColor = UIColor.whiteColor()

    imageView.layer.borderColor = UIColor.greenColor().CGColor
    imageView.layer.borderWidth = 10
    imageView.image = UIImage(named: "demo")
    imageView.layer.cornerRadius = frame.size.width*0.5
    imageView.clipsToBounds = true

}
</code></pre>

<p>the border is smooth and great with above code 
but after  add    <code>imageView.image = UIImage(named: "demo")</code></p>

<p>the imageView's border is no longer smooth.
Why did this happen ?</p>

<p><a href="https://i.stack.imgur.com/MRN2E.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MRN2E.png" alt="smooth image"></a></p>

<p><a href="https://i.stack.imgur.com/7U3OI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7U3OI.png" alt="not smooth image"></a></p>

<hr>

<p>UPDATE:</p>

<p>Seems something wrong with layer.radius ,the border is smooth even with image property set on imageView after remove    <code>imageView.layer.cornerRadius = frame.size.width*0.5</code></p>

<p><a href="https://i.stack.imgur.com/Vfn6C.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Vfn6C.png" alt="enter image description here"></a></p>

<hr>

<p>UPDATE 2:
turn out to be something wrong with UICollectionViewCell , imageView is a part of UICollectionViewCell</p>

<hr>