code: @Override
  	public void process() {
  		locations.reset();
  		descriptions.reset();
  
  		// see if the cell array needs to grow for this image.  Recycle data when growing
  		growCellArray(derivX.width, derivX.height);
  
  		computeCellHistograms();
  
  		int cellRowMax = (cellRows - (cellsPerBlockY -1));
  		int cellColMax = (cellCols - (cellsPerBlockX -1));
  
  		for (int i = 0; i < cellRowMax; i += stepBlock) {
  			for (int j = 0; j < cellColMax; j += stepBlock) {
  				computeDescriptor(i,j);
  			}
  		}
  
  	}
docs: Computes the descriptor across the input image