how to add Spherical Filter Effect (a fish eye) on UIImage in objective - C or in Realtime camera

Question

I want to add a fisheye filter effect on UIImage in iphone App. on googling i get the effect like spherical image effect with vignette image effect. I have completed vignette effect but can't implement Spherical Image effect. Can any one suggest how to implement this or i can implement fisheye in camera ?

Thanks