Hybrid image segmentation using watersheds and fast region merging

Kostas Haris*, Serafim N. Efstratiadis, Nicos Maglaveras, Aggelos K. Katsaggelos

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

624 Scopus citations


A hybrid multidimensional image segmentation algorithm is proposed, which combines edge and region-based techniques through the morphological algorithm of watersheds. An edge-preserving statistical noise reduction approach is used as a preprocessing stage in order to compute an accurate estimate of the image gradient. Then, an initial partitioning of the image into primitive regions is produced by applying the watershed transform on the image gradient magnitude. This initial segmentation is the input to a computationally efficient hierarchical (bottom-up) region merging process that produces the final segmentation. The latter process uses the region adjacency graph (RAG) representation of the image regions. At each step, the most similar pair of regions is determined (minimum cost RAG edge), the regions are merged and the RAG is updated. Traditionally, the above is implemented by storing all RAG edges in a priority queue. We propose a significantly faster algorithm, which additionally maintains the so-called nearest neighbor graph, due to which the priority queue size and processing time are drastically reduced. The final segmentation provides, due to the RAG, one-pixel wide, closed, and accurately localized contours/surfaces. Experimental results obtained with two-dimensional/three-dimensional (2-D/3-D) magnetic resonance images are presented.

Original languageEnglish (US)
Pages (from-to)1684-1699
Number of pages16
JournalIEEE Transactions on Image Processing
Issue number12
StatePublished - 1998


  • Image segmentation
  • Nearest neighbor region merging
  • Noise reduction
  • Watershed transform

ASJC Scopus subject areas

  • Software
  • Computer Graphics and Computer-Aided Design


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