Hybrid phase unwrapping algorithm extended by a minimum-cost-matching strategy

摘要

A hybrid phase unwrapping algorithm has been proposed recently, which uses a window-based technique and two local phase unwrapping approaches to determine gradient information for each window. However, with this approach, in many practical applications, we encountered certain inconsistencies, e.g. caused by noise in the input phase map. In this paper, we present an improved window-based algorithm for unwrapping noisy phase maps. With pixel-based images, we can only obtain residues of charge one, but, with this new method, higher charges are possible. Eventually the total charge of positive and negative residues may be unequal. Therefore, we extend the set of residues by border residues until we obtain equal charges. We build connected components containing neighbours of residues using the breath-first-search method. Hereafter, we follow a minimum-cost graph-theory method determining the set of branch-cuts and computing the global minimum of the total cut-length. Every positive residue is associated to a corresponding negative residue. We connect these pairs by the path with the worst overlap error obtained by one of the local phase unwrapping approaches. Using this new method, we are able to reduce the rms-phase-error by factor 5, when comparing the results to the existing hybrid phase unwrapping algorithm.