code: private void declareDerivativeImages(ImageGradient<T, D> gradient, ImageHessian<D> hessian, Class<D> derivType) {
  		if( gradient != null || hessian != null ) {
  			derivX = GeneralizedImageOps.createSingleBand(derivType, 1, 1);
  			derivY = GeneralizedImageOps.createSingleBand(derivType,1,1);
  		}
  		if( hessian != null ) {
  			derivXX = GeneralizedImageOps.createSingleBand(derivType,1,1);
  			derivYY = GeneralizedImageOps.createSingleBand(derivType,1,1);
  			derivXY = GeneralizedImageOps.createSingleBand(derivType,1,1);
  		}
  	}
docs: Declare storage for image derivatives as needed