Optical flow Forward Warping


From papers related to optical flow & respective code, it’s clear how backward warping works e.g. say you have 2 images I1 and I2, using the forward flow map F12, backward warping BW(I2, F12) results in I1. I want to know how one could use such flow maps to get reproduce I2? so this I believe is forward warping.

I tried to follow the following thread: [Solved]How to do the interpolating of optical flow?
but no solution was posted from what I saw. Any help would be highly appreciated