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Two-dimensional phase unwrapping is the problem of deducing unambiguous “phase” from values known only modulo 2π. Many authors agree that the objective of phase unwrapping should be to find a weighted minimum of the number of places where adjacent (discrete) phase values differ by more than π (called discontinuities). This NP-hard problem is of considerable practical interest, largely due to its importance in interpreting data acquired with synthetic aperture radar (SAR) interferometry. Consequently, many heuristic algorithms have been proposed. We present an efficient multi-level graph algorithm for the approximate solution of an equivalent problem—minimal residue cut in the dual graph.