Solved by ducha-aiki in post #3 
              
              
                NL is number of scale levels of the scale space, see SIFT paper, Figure 1 on the left. This mean to consequently blur the image more and more, which for linear filters is equivalent to resizing. 
If you just need a pyramid, which contains HW, H/2 W/2, H/4 W/4 and so on - use kornia.geometry.transfor…