code: void computeDescriptor(int row, int col) {
  		// set location to top-left pixel
  		locations.grow().set(col* pixelsPerCell,row* pixelsPerCell);
  
  		TupleDesc_F64 d = descriptions.grow();
  
  		int indexDesc = 0;
  		for (int i = 0; i < cellsPerBlockY; i++) {
  			for (int j = 0; j < cellsPerBlockX; j++) {
  				Cell c = cells[(row+i)*cellCols + (col+j)];
  
  				for (int k = 0; k < c.histogram.length; k++) {
  					d.value[indexDesc++] = c.histogram[k];
  				}
  			}
  		}
  
  		// Apply SIFT style L2-Hys normalization
  		DescribeSiftCommon.normalizeDescriptor(d,0.2);
  	}
docs: Compute the descriptor from the specified cells.  (row,col) to (row+w,col+w)
  @param row Lower extent of cell rows
  @param col Lower extent of cell columns