Computer Vision Primer
Optical Flow Primer — Reading Velocity and Structure from Image Motion
Optical Flow is a vector field describing which direction each pixel in a sequence of images has moved. This article works through the brightness-constancy constraint, Lucas–Kanade and Horn–Schunck, pyramids, dense flow versus sparse feature tracking, learning-based methods such as RAFT, and camera motion, dynamic objects, and evaluation methodology, with the underlying math.