Operator Reference
expand_region (Operator)
expand_region — Fill gaps between regions or split overlapping regions.
Signature
expand_region(Regions, ForbiddenArea : RegionExpanded : Iterations, Mode : )
Description
expand_region closes gaps between the input regions, which
resulted from the suppression of small regions in a segmentation
operator, for example, (mode 'image'), or to separate
overlapping regions (mode 'region'). Both uses result from the
expansion of regions. The operator works by adding or removing a
one pixel wide “strip” to a region.
The expansion takes place only in regions that are designated as
not “forbidden” (parameter ForbiddenArea). The number
of iterations is determined by the parameter Iterations.
By passing 'maximal', expand_region iterates until
convergence, i.e., until no more changes occur. By passing 0 for
this parameter, all non-overlapping regions are returned. The two
modes of operation ('image' and 'region') are
different in the following ways:
- 'image'
The input regions are expanded iteratively until they touch another region or the image border. In this case, the image border is defined to be the rectangle ranging from (0,0) to (row_max,col_max). Here, (row_max,col_max) corresponds to the lower right corner of the smallest surrounding rectangle of all input regions (i.e., of all regions that are passed in
RegionsandForbiddenArea). Becauseexpand_regionprocesses all regions simultaneously, gaps between regions are distributed evenly to all regions. Overlapping regions are split by distributing the area of overlap evenly to both regions.- 'region'
No expansion of the input regions is performed. Instead, only overlapping regions are split by distributing the area of overlap evenly to the respective regions. Because the intersection with the original region is computed after the shrinking operation gaps in the output regions may result, i.e., the segmentation is not complete. This can be prevented by calling
expand_regiona second time with the complement of the original regions as “forbidden area.”
Execution Information
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Processed without parallelization.
Parameters
Regions (input_object) region(-array) → object
Regions for which the gaps are to be closed, or which are to be separated.
ForbiddenArea (input_object) region → object
Regions in which no expansion takes place.
RegionExpanded (output_object) region(-array) → object
Expanded or separated regions.
Iterations (input_control) integer → (integer / string)
Number of iterations.
Default: 'maximal'
Suggested values: 'maximal', 0, 1, 2, 3, 5, 7, 10, 15, 20, 30, 50, 70, 100, 200
Value range:
0
≤
Iterations
≤
1000 (lin)
Minimum increment: 1
Recommended increment: 1
Mode (input_control) string → (string)
Expansion mode.
Default: 'image'
List of values: 'image', 'region'
Example (HDevelop)
read_image(Image,'clip') threshold(Image,Dark,0,150) connection(Dark,ConnectedRegions) gen_circle (Circle, 400, 400, 200.5) expand_region (ConnectedRegions, Circle, RegionExpanded, 'maximal', 'image') dev_display (RegionExpanded)
Result
expand_region always returns the value 2 (
H_MSG_TRUE)
. The behavior in
case of empty input (no regions given) can be set via
set_system('no_object_result',<Result>),
the behavior in case of an empty input region via
set_system('empty_region_result',<Result>),
and the behavior in case of an empty result region via
set_system('store_empty_region',<'true'/'false'>).
If necessary, an exception is raised.
Possible Predecessors
pouring,
threshold,
dyn_threshold,
regiongrowing
Alternatives
See also
expand_gray,
interjacent,
skeleton
Module
Foundation