erosion_circle ( Region : RegionErosion : Radius : )

Erode a region with a circular structuring element.

erosion_circle applies a Minkowski subtraction with a circular structuring element to the input regions Region. Because the circular mask is symmetrical, this is identical to an erosion. The size of the circle used as structuring element is determined by Radius.

The operator results in the region being reduced, the smoothing of the region's boundaries, and the elimination of regions smaller than the circular mask. It is useful to select only values like 3.5, 5.5, etc. for Radius in order to avoid a translation of a region, because integer radii result in the circle having a non-integer center of gravity which is rounded to the next integer.


Parameters

Region (input_object)
region(-array) -> object
Regions to be eroded.

RegionErosion (output_object)
region(-array) -> object
Eroded regions.

Radius (input_control)
real -> real / integer
Radius of the circular structuring element.
Default value: 3.5
Suggested values: 1.5, 2.5, 3.5, 4.5, 5.5, 7.5, 9.5, 12.5, 15.5, 19.5, 25.5, 33.5, 45.5, 60.5, 110.5
Range of values: 0.5 <= Radius <= 511.5 (lin)
Minimum increment: 1.0
Recommended increment: 1.0


Example
#include  
#include  "HCPP.H"

main()
{
  cout << "Reproduction of 'erosion_circle ()" << endl;
  cout << "First = original image " << endl;
  cout << "Red   = after segmentation " << endl;
  cout << "Blue  = after erosion " << endl;

  HByteImage img("affe");
  HWindow    w;

  HRegion      circ   = HRegion::Circle (10, 10, 1.5);
  HRegionArray regs   = (img >= 128).Connection();
  HRegionArray minsub = regs.MinkowskiSub1 (circ, 1);

                        img.Display (w);      w.Click ();
  w.SetColor ("red");   regs.Display (w);     w.Click ();
  w.SetColor ("blue");  minsub.Display (w);   w.Click ();

  return(0);
}

Complexity

Let F1 be the area of an input region. Then the runtime for one region is:

       O(2 * Radius * sqrt(F1)) .


Result

erosion_circle returns TRUE if all parameters are correct. The behavior in case of empty or no input region can be set via:

  a) no region:    set_system(::'no_object_result',<RegionResult>:)
  b) empty region: set_system(::'empty_region_result',<RegionResult>:)
Otherwise, an exception is raised.


Possible Predecessors

threshold__, regiongrowing__, watersheds, class_ndim1__


Possible Successors

connection, reduce_domain, select_shape, area_center


Alternatives

minkowski_sub1


See also

circle, dilation_circle, closing_circle, opening_circle



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