I want to know the width and height of image, but CGSize always returns 0.

```
let img : UIImage = UIImage.init(named: "icon_ear")!
NSLog("img w : %d, h : %d", img.size.width, img.size.height)
//img w : 0, h : 0 `      

```

and 

```
let cs = CGSize(width: 100, height: 100)
NSLog("cs w : %d, h : %d", cs.width, cs.height)
//cs w : 0, h : 0

```

What is wrong?