Abstract. We describe the implementation of a 2D optical flow algorithm published in the European Conference on Computer Vision (ECCV 2004) by Brox et al. [1] (best paper award) and a qualitative and quantitative evaluation of it for a number of synthetic and real image sequences. Their optical flow method combines three assumptions: a brightness constancy assumption, a gradient constancy assumption and a spatio-temporal smoothness constraint. A numerical scheme based on fixed point iterations is used. Their method uses a coarse-to-fine warping strategy to measure larger optical flow vectors. We have investigated the algorithm in detail and our evaluation of the method demonstrates that it produces very accurate optical flow fields from only 2 input images.