Region growing in a island hierarchy

The segmentation itself operates in three phases:

  1. Coding
  2. Linking
  3. Splitting

 

Coding
In the coding phase homogenous color regions are detected in islands of level 0 and mapped in codeelements. A codeelement is a small data package which represents a color region in the image. A codeelement of level 0 contains all pixels which belong to one color homogenous region. These pixels are called sub pixels of the codeelement.

 

Linking
In the linking phase two homogenous color regions are merged together, if they are similar in color and overlap each other. This merging process takes exclusively place within islands. Only regions that are part of the same island may be merged together. If two codeelements have a common sub codeelement or a common sub pixel, the two regions represented by the codeelements, overlap each other. If further the two codeelements are similar in color they could be linked to a new codeelement. With preceding computation the algorithm produces a wood (Collection of trees). Each tree represents a entire color region in the image.

 

Splitting
In local region growing algorithms (e.g. region growing with single linkage strategy) two regions may be merged if they are connected via neighbored pixels with smoothly changing colors. The CSC solves this problem by using not only local color information but also global information. If two codeelements on any level has a common sub codeelement, that means the two color regions represented by the two codeelements are connected, and they are not similar in color, then the common sub region has to be divided upon both concerned regions. This task is realized by the splitting phase. In the splitting phase the algorithm tries to find a ideal parting line between both regions.