CONNECTED COMPONENTS EXTRACTION

Code

• hysteresis thresholding (see the page on edge detection)
• specification of the minimal size of the connected components to be retained
• choice of the connectivity (among 4, 8, 6, 10, 18, 26)
• specification of the maximal number of connected components to be retained (by specifying 1, only the largest connected component is retained)

Examples obtained with the code

Original binary image

• Labeling the connected components: a different grey level value (from 1 to the number of connected components) is given to each component. Here, there are 36 connected components.

  Counting the connected components
  %test-connexe-pnm ironbin.ppm ironcc.ppm -v

• Filtering the connected components by size: only the connected components with a size larger than the minimal size are retained . Here, there are 16 connected components of size larger or equal to 10.

  Selecting the connected components by size
  %test-connexe-pnm ironbin.ppm ironccsize=10.ppm -ms 10 -v

• Ordering the connected components by size: only the n largest connected are kept. Labels are given in the order of decreasing sizes (1 is the largest connected component, etc).

  Ordering the connected components by size
  %test-connexe-pnm ironbin.ppm ironccmax=n.ppm -ms n -v
  n=10	n=1