Fast Optical Flow Using Dense Inverse Search

Most recent works in optical flow extraction focus on the accuracy and neglect the time complexity. However, in real-life visual applications, such as tracking, activity detection and recognition, the time complexity is critical. We propose a solution with very low time complexity and competitive accuracy for the computation of dense optical flow. It consists of three parts: (1) inverse search for patch correspondences; (2) dense displacement field creation through patch aggregation along multiple scales; (3) variational refinement. At the core of our Dense Inverse Search-based method (DIS) is the efficient search of correspondences inspired by the inverse compositional image alignment proposed by Baker and Matthews (2001, 2004). DIS is competitive on standard optical flow benchmarks. DIS runs at 300 Hz up to 600 Hz on a single CPU core (1024x436 resolution. 42Hz/46 Hz when including preprocessing: disk access, image re-scaling, gradient computation. More details in Sect. 3.1.), reaching the temporal resolution of human's biological vision system. It is order(s) of magnitude faster than state-of-the-art methods in the same range of accuracy, making DIS ideal for real-time applications.