code: static public GrayF32 nonMaxSuppressionCrude4(GrayF32 intensity , GrayS32 derivX , GrayS32 derivY, GrayF32 output )
  	{
  		InputSanityCheck.checkSameShape(intensity,derivX,derivY);
  		output = InputSanityCheck.checkDeclare(intensity,output);
  
  		if(BoofConcurrency.USE_CONCURRENT ) {
  			ImplEdgeNonMaxSuppressionCrude_MT.inner4(intensity, derivX, derivY, output);
  			ImplEdgeNonMaxSuppressionCrude_MT.border4(intensity, derivX, derivY, output);
  		} else {
  			ImplEdgeNonMaxSuppressionCrude.inner4(intensity, derivX, derivY, output);
  			ImplEdgeNonMaxSuppressionCrude.border4(intensity, derivX, derivY, output);
  		}
  
  		return output;
  	}
docs: <p>
  Sets edge intensities to zero if the pixel has an intensity which is less than any of
  the two adjacent pixels.  Pixel adjacency is determined based upon the sign of the image gradient.  Less precise
  than other methods, but faster.
  </p>
  
  @param intensity Edge intensities. Not modified.
  @param derivX Image derivative along x-axis.
  @param derivY Image derivative along y-axis.
  @param output Filtered intensity. If null a new image will be declared and returned. Modified.
  @return Filtered edge intensity.