code: protected void updateCurrent(ImagePyramid<I> image) {
  		this.currentImage = image;
  		for( int i = 0; i < image.getNumLayers(); i++ ) {
  			gradient.process(image.getLayer(i), currentDerivX[i], currentDerivY[i]);
  		}
  	}
docs: Computes the gradient and changes the reference to the current pyramid