Fast Approximate Energy Minimization via Graph Cuts

Yuri Boykov, Olga Veksler, Ramin Zabih

In International Conference on Computer Vision, 1999, to appear.

Abstract

In this paper we address the problem of minimizing a large class of energy functions that occur in early vision. The major restriction is that the energy function's smoothness term must only involve pairs of pixels. We propose two algorithms that use graph cuts to compute a local minimum even when very large moves are allowed. The first move we consider is an "ab"-swap: for a pair of labels "a", "b", this move exchanges the labels between an arbitrary set of pixels labeled "a" and another arbitrary set labeled "b". Our first algorithm generates a labeling such that there is no swap move that decreases the energy. The second move we consider is an "a"-expansion: for a label "a", this move assigns an arbitrary set of pixels the label "a". Our second algorithm, which requires the smoothness term to be a metric, generates a labeling such that there is no expansion move that decreases the energy. Moreover, this solution is within a known factor of the global minimum. We experimentally demonstrate the effectiveness of our approach on image restoration, stereo and motion.


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More details on "a"-expansion moves in case of the Potts model of interaction can be found in "A New Algorithm for Energy Minimization with Discontinuities" (ps file), in workshop on Energy Minimization Methods in Computer Vision and Pattern Recognition, England, 1999. This paper contains the proof that a local minimum found by the "a"-expansion algorithm is within the factor of 2 from the global minimum of the Potts energy.