thinning

thinning_seq ( Region : RegionThin : GolayElement, Iterations : )

Remove the result of a hit-or-miss operation from a region (sequential).

thinning_seq calculates the sequential thinning of the input regions with a structuring element from the Golay alphabet (GolayElement). To do so, thinning_seq calls the operator thinning_golay with all possible rotations of the structuring element Iterations times. If Iterations is chosen large enough, the operator calculates the skeleton of a region if the structuring elements 'l' or 'm' are used. For the element 'c' the background and foreground are exchanged in order to have an effect on the interior boundary of a region. If a very large value or 'maximal' is passed for Iterations the iteration stops if no more changes occur. The following structuring elements are available:

  'l'
     Skeleton, similar to skeleton.  This structuring element is
     also used in morph_skiz.
  'm'
     A skeleton with many ``hairs'' and multiple (parallel)
     branches.
  'd'
     A skeleton without multiple branches, but with many gaps,
     similar to morph_skeleton.
  'c'
     Uniform erosion of the region.
  'e'
     One pixel wide lines are shortened.  This structuring element
     is also used in morph_skiz.
  'i'
     Isolated points are removed.  (Only Iterations = 1 is useful.)
  'f'
     Y-junctions are eliminated.  (Only Iterations = 1 is useful.)
  'f2'
     One pixel long branches and corners are removed.  (Only
     Iterations = 1 is useful.)
  'h'
     A kind of inner boundary, which is however thicker than the
     result of boundary, is generated.  (Only Iterations = 1 is
     useful.)
  'k'
     Junction points are eliminated, but also new ones are
     generated.

The Golay elements, together with all possible rotations, are described with the operator golay_elements.

Parameters

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

`RegionThin` (output_object)	region(-array) `->` object
Result of the thinning operator.

`GolayElement` (input_control)	string `->` string
Structuring element from the Golay alphabet.
Default value: 'l'
List of values: 'l', 'm', 'd', 'c', 'e', 'i', 'f', 'f2', 'h', 'k'

`Iterations` (input_control)	integer `->` integer / string
Number of iterations. For 'f', 'f2', 'h' and 'i' the only useful value is 1.
Default value: 20
Suggested values: 'maximal', 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 70, 100, 150, 200
Typical range of values: `1 <= Iterations`
Minimum increment: 1
Recommended increment: 1

Complexity

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

      O(Iterations * 6 * sqrt(F)) .

Result

thinning_seq returns 2 (H_MSG_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.

Parallelization Information

thinning_seq is reentrant and automatically parallelized (on tuple level).

Possible Predecessors

threshold, regiongrowing, connection, union1, watersheds, class_ndim_norm, gen_circle, gen_ellipse, gen_rectangle1, gen_rectangle2, draw_region, gen_region_points, gen_struct_elements, gen_region_polygon_filled

Possible Successors

pruning, reduce_domain, select_shape, area_center, connection, complement

Alternatives

skeleton, morph_skiz, expand_region

Module

Foundation