minkowski_sub1 ( Region, StructElement : RegionMinkSub : Iterations : )

Erode a region.

minkowski_sub1 computes the Minkowski subtraction of the input regions with a structuring element. By applying minkowski_sub1 to a region, its boundary is smoothed. In the process, the area of the region is reduced. Furthermore, connected regions may be split. Such regions, however, remain logically one region. The Minkowski subtraction is a set-theoretic region operation. It uses the intersection operation.

Let M (StructElement) and R (Region) be two regions, where M is the ``structuring element'' and R is the region to be precessed. Furthermore, let m be a point in M. Then the displacement vector v(m) = (dx,dy) is defined as the difference of the center of gravity of M and the vector v(m). Let t(v(m))(R) denote the translation of a region R by a vector v(m). Then

                              __
                             /  \
      minkowski_sub1(R,M) := |  | t    (R)
                             |  |  v(m)
                            m in M

For each point m in M a translation of the region R is performed. The intersection of all these translations is the Minkowski subtraction of R with M. minkowski_sub1 is similar to the operator erosion1, the difference being that in erosion1 the structuring element is mirrored at the origin. The position of StructElement is meaningless, since the displacement vectors are determined with respect to the center of gravity of M.

The parameter Iterations determines the number of iterations which are to be performed with the structuring element. The result of iteration n-1 is used as input for iteration n. From the above definition it follows that the maximum region is generated in case of an empty structuring element.

Structuring elements (StructElement) can be generated with operators such as circle, rectangle1, rectangle2, ellipse, draw_region, store_polygon, store_coord, etc.


Parameters

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

StructElement (input_object)
region -> object
Structuring element.

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

Iterations (input_control)
integer -> integer
Number of iterations.
Default value: 1
Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 30, 40, 50
Range of values: 1 <= Iterations
Minimum increment: 1
Recommended increment: 1


Complexity

Let F1 be the area of the input region, and F2 be the area of the structuring element. The the runtime complexity for one region is:

    O(sqrt(F1) * sqrt(F2) * Iterations) .


Result

minkowski_sub1 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__, connection, union1, watersheds, class_ndim1__, circle, ellipse, rectangle1, rectangle2, draw_region, store_coord, struct_elements, store_filled_polygon


Possible Successors

reduce_domain, select_shape, area_center, connection


Alternatives

minkowski_sub2, erosion1


See also

transpose



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