New complexity bounds for image matching under rotation and scaling

  • Authors:
  • Christian Hundt;Maciej Likiewicz

  • Affiliations:
  • Institut für Informatik, Universität Rostock, Germany;Institut für Theoretische Informatik, Universität zu Lübeck, Germany

  • Venue:
  • Journal of Discrete Algorithms
  • Year:
  • 2011

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Abstract

Image matching under rotation is a computational problem to determine for two given images A and B a rotation of A that most accurately resembles B. The research in combinatorial pattern matching led to a series of improved algorithms which commonly solve this problem by a sophisticated search in the set of all rotations of A. This paper provides the lower bound @W(n^3) on the worst case cardinality of this set for images of size nxn and presents the first optimal algorithm of such kind, i.e., one that solves image matching under rotations in time O(n^3). Moreover, for image matching under compositions of rotation and scaling a new lower bound @W(n^6/logn) on the worst case cardinality of the set of rotated and scaled transformations of an nxn image is provided. This bound almost matches the upper bound O(n^6).