code: public static <I extends ImageGray<I>, O extends ImageGray<O>>
  	void hessian(O[] derivX, O[] derivY , ImageHessian<O> hessian , O[] derivXX, O[] derivYY , O[] derivXY )
  	{
  		for( int i = 0; i < derivX.length; i++ ) {
  			hessian.process(derivX[i],derivY[i],derivXX[i],derivYY[i],derivXY[i]);
  		}
  	}
docs: <p>
  Computes the hessian (2nd order derivative) for each image the pyramid.
  </p>
  
  @param derivX (Input) Pyramid where x-derivative is stored.
  @param derivY (Input) Pyramid where y-derivative is stored.
  @param hessian (Input) Computes hessian from gradient
  @param derivXX (Output) Second derivative XX
  @param derivYY (Output) Second derivative YY
  @param derivXY (Output) Second derivative XY