code: public static void hessianBorder(GrayF32 integral, int skip , int size ,
  									 GrayF32 intensity)
  	{
  		final int w = intensity.width;
  		final int h = intensity.height;
  
  		// get convolution kernels for the second order derivatives
  		IntegralKernel kerXX = DerivativeIntegralImage.kernelDerivXX(size,null);
  		IntegralKernel kerYY = DerivativeIntegralImage.kernelDerivYY(size,null);
  		IntegralKernel kerXY = DerivativeIntegralImage.kernelDerivXY(size,null);
  
  		int radiusFeature = size/2;
  		final int borderOrig = radiusFeature+ 1 + (skip-(radiusFeature+1)%skip);
  		final int border = borderOrig/skip;
  
  		float norm = 1.0f/(size*size);
  
  		BoofConcurrency.loopFor(0, h, y -> {
  			int yy = y * skip;
  			for (int x = 0; x < border; x++) {
  				int xx = x * skip;
  				computeHessian(integral, intensity, kerXX, kerYY, kerXY, norm, y, yy, x, xx);
  			}
  			for (int x = w - border; x < w; x++) {
  				int xx = x * skip;
  				computeHessian(integral, intensity, kerXX, kerYY, kerXY, norm, y, yy, x, xx);
  			}
  		});
  
  		BoofConcurrency.loopFor(border, w-border, x -> {
  			int xx = x*skip;
  
  			for( int y = 0; y < border; y++ ) {
  				int yy = y*skip;
  				computeHessian(integral, intensity, kerXX, kerYY, kerXY, norm, y, yy, x, xx);
  			}
  			for( int y = h-border; y < h; y++ ) {
  				int yy = y*skip;
  				computeHessian(integral, intensity, kerXX, kerYY, kerXY, norm, y, yy, x, xx);
  			}
  		});
  	}
docs: Only computes the fast hessian along the border using a brute force approach