Anybody got a clue?
There is a distance term where you determine how far you are from the center point (the cutoff
being in the effect or outside of the effect). That distance term is used to compute displacement as refraction.
You could either try "fading out" the effect of the filter near the edges by blending with the original image or you could apply an additional scale term to the distance term if you are near the edge to soften it.
Thanks for the answers!
Finaly I apply the Spherize filter with differents radius and amplitude to ease the boarder.
I know it's not the best but it works perfectly!!!