class DistortPixel extends PixelTransform{
  int getPixel(int i, int j){
     double alpha = i*1.0/width;
     double beta = j*1.0/height;
     i = (int) Math.round( alpha * alpha  * i );
     j = (int) Math.round( (1-(1-beta) *(1- beta)
                             + alpha * alpha )  * j /2 );
     return image.getRGB( i, j );
} }