This is just a try to simulate the effect you can see in cnn and kickstarter app. When scroll down the scroll view, the bouncing will cause the header image to zoom.

But current version is only perfect in iPhone5, which is fast enoungh. In iPhone4 and Simulator, when you scroll fast to make it bounce, the UI update is not able to keep up with the speed of your scroll. I am still thinking about the solution.

A demo video: http://youtu.be/IkNuo1y1HC0