docs: public static <T extends ImageGray<T>>
  	void gradient(T ii, double tl_x, double tl_y, double samplePeriod ,
  				  int regionSize, double kernelWidth,
  				  boolean useHaar, double[] derivX, double derivY[])
  	{
  		ImplSurfDescribeOps.naiveGradient(ii, tl_x, tl_y, samplePeriod , regionSize, kernelWidth, useHaar, derivX, derivY);
  	}