Region Segmentation

REGION MERGING


- a process of eliminating false boundaries and spurious regions by merging adjacent regions that belong to the same object.
- suitable for edge data segmentation.
- involve identifying each pixel in a raw image as a small region and then merging regions together systematically  to grow larger regions.

  ++ Algorithm for Region Merging ++
        1. Merging schemes begin with a partition satisfying condition (4) - using threshold
                                               
                                                       (4) P(Ri) = True

        2. Then proceed to fulfill condition (5) by gradually merging adjacent image regions.
                   
                                                       (5) P(Ri U Rj) = False

           a. Form initial regions in the image.
           b. Build a region adjacency graph (RAG).
           c. For each region do :-  consider its adjacent region and test to see if they are similar.
                                             -  for regions that are similar (P(Ri U Rj) = True), merge them and modify the      
                                                RAG
           d. Repeat step (c) until no regions are merged.

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REGION SPLITTING

 - a process of adding missing boundaries by splitting regions that contain parts of different objects.

 ++ Algorithm for Region Splitting ++

       1. Splitting schemes begin with a partition satisfying condition (5)

                                                     (5) P(Ri U Rj) = False

       2. Then, proceed to satisfy condition (4) by gradually splitting image regions.

                                                      (4) P(Ri) = True

             a.  If P(R) = False, split R into four quadrants.
             b. If P is false on any quadrant, subsplit.

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REGION SPLITTING AND MERGING

- A better result of region segmentation can be produced by integrating both region splitting and merging together.

- Takes partition that possibly not satisfies neither condition (4) nor (5) with the aim of producing a segmentation that satisfies both condition.

++ Algorithm for Region Splitting and Merging++

   1.  Split into four disjointed quadrants any region Ri where P(Ri) = False.

   2.  Merge any adjacent regions Rj and Rk for which P(Rj U Rk) = True.

   3.  Stop when no further merging or splitting is possible.

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REGION USING QUAD TREES
- Extension of pyramids for binary images.
- Three types of nodes (white,black,grey).
-White or black node no splitting.
- Gray node split into 4 sub-regions

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