We present an optical flow estimation approach that operates on the fullfour-dimensional cost volume. This direct approach shares the structuralbenefits of leading stereo matching pipelines, which are known to yield highaccuracy. To this day, such approaches have been considered impractical due tothe size of the cost volume. We show that the full four-dimensional cost volumecan be constructed in a fraction of a second due to its regularity. We thenexploit this regularity further by adapting semi-global matching to thefour-dimensional setting. This yields a pipeline that achieves significantlyhigher accuracy than state-of-the-art optical flow methods while being fasterthan most. Our approach outperforms all published general-purpose optical flowmethods on both Sintel and KITTI 2015 benchmarks.
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