Graph cuts in computer vision: Difference between revisions

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In the [[Bayesian statistics|Bayesian]] statistical context of smoothing noisy (or corrupted) images, they showed how the [[MAP estimate|maximum a posteriori estimate]] of a [[binary image]] can be obtained ''exactly'' by maximizing the [[Flow network|flow]] through an associated image network, involving the introduction of a ''source'' and ''sink''. The problem was therefore shown to be efficiently solvable. Prior to this result, ''approximate'' techniques such as [[simulated annealing]] (as proposed by the [[Donald Geman|Geman brothers]]),<ref>D. Geman and S. Geman (1984), ''[http://www.dam.brown.edu/people/documents/stochasticrelaxation.pdf Stochastic relaxation, Gibbs distributions and the Bayesian restoration of images]'', IEEE Trans. Pattern Anal. Mach. Intell., '''6''', 721–741.</ref> or [[iterated conditional modes]] (a type of [[greedy algorithm]] suggested by [[Julian Besag]])<ref>J.E. Besag (1986), ''On the statistical analysis of dirty pictures (with discussion)'', [[Journal of the Royal Statistical Society]] Series B, '''48''', 259–302</ref> were used to solve such image smoothing problems.

Although the general [[Graph coloring|<math>k</math>-colour problem]] is NP completehard for <math>k > 2,</math> the approach of Greig, Porteous and Seheult<ref name="D.M. Greig, B.T 1989" /> has turned out<ref>Y. Boykov, O. Veksler and R. Zabih (1998), "[http://www.cs.cornell.edu/~rdz/Papers/BVZ-cvpr98.pdf Markov Random Fields with Efficient Approximations]", ''International Conference on Computer Vision and Pattern Recognition (CVPR)''.</ref><ref name="boykov2001fast">Y. Boykov, O. Veksler and R. Zabih (2001), "[http://www.cs.cornell.edu/~rdz/Papers/BVZ-pami01-final.pdf Fast approximate energy minimisation via graph cuts]", ''IEEE Transactions on Pattern Analysis and Machine Intelligence'', '''29''', 1222–1239.</ref> to have wide applicability in general computer vision problems. Greig, Porteous and Seheult's approaches are often applied iteratively to a sequence of binary problems, usually yielding near optimal solutions.

In 2011, C. Couprie ''et al''.<ref>Camille Couprie, Leo Grady, Laurent Najman and Hugues Talbot, "[http://leogrady.net/wp-content/uploads/2017/01/couprie2011power.pdf Power Watersheds: A Unifying Graph-Based Optimization Framework]”, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 33, No. 7, pp. 1384-1399, July 2011</ref> proposed a general image segmentation framework, called the "Power Watershed", that minimized a real-valued [[indicator function]] from [0,1] over a graph, constrained by user seeds (or unary terms) set to 0 or 1, in which the minimization of the indicator function over the graph is optimized with respect to an exponent <math>p</math>. When <math>p=1</math>, the Power Watershed is optimized by graph cuts, when <math>p=0</math> the Power Watershed is optimized by shortest paths, <math>p=2</math> is optimized by the [[random walker algorithm]] and <math>p=\infty</math> is optimized by the [[Watershed (image processing)|watershed]] algorithm. In this way, the Power Watershed may be viewed as a generalization of graph cuts that provides a straightforward connection with other energy optimization segmentation/clustering algorithms.