erosion_circle (Operator)

Name

`erosion_circle` — Erode a region with a circular structuring element.

Signature

`erosion_circle(Region : RegionErosion : Radius : )`

Description

`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 reduced regions, smoothed region boundaries, and the regions smaller than the circular mask are eliminated. 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 a circle having a non-integer center of gravity which is rounded to the next integer.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Automatically parallelized on tuple level.

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

Typical range of values: ```0.5 ≤ Radius ≤ 511.5``` (lin)

Minimum increment: 1.0

Recommended increment: 1.0

Example (C++)

```#include "HIOStream.h"
#if !defined(USE_IOSTREAM_H)
using namespace std;
#endif
#include "HalconCpp.h"

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

HByteImage img("monkey");
HWindow    w;

HRegion      circ   = HRegion::GenCircle (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 complexity for one region is:

Result

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

Otherwise, an exception is raised.

Possible Predecessors

`threshold`, `regiongrowing`, `watersheds`, `class_ndim_norm`

Possible Successors

`connection`, `reduce_domain`, `select_shape`, `area_center`

Alternatives

`minkowski_sub1`

`gen_circle`, `dilation_circle`, `closing_circle`, `opening_circle`