What is the difference between sparse and dense optical flow?

Question

Lots of resources say that there are two types optical flow algorithms. And Lucas-Kanade is a sparse technique, but I can\'t find the meanings of sparse and dense? Can some one

Answer 1

Sparse optical flow gives you the flow vectors of some "interesting features" within the image.

Dense optical flow attempts to give you the flow all over the image - up to a flow vector per pixel.