Fill gaps between regions (depending on gray value or color) or split overlapping regions.

expand_gray closes gaps between the input regions, which resulted from the suppression of small regions in a segmentation operator, (mode 'image'), for example, or separates overlapping regions 'region'). Both uses result from the expansion of regions. The operator works by adding a one pixel wide ``strip'' to a region, in which the gray values or color are different from the gray values or color of neighboring pixles on the region's border by at most Threshold (in each channel). For images of type 'cyclic' (e.g., direction images), also points with a gray value difference of at least 255 - Threshold are added to the output region.

The expansion takes place only in regions, which are designated as not ``forbidden'' (parameter ForbiddenArea). The number of iterations is determined by the parameter Iterations. By passing 'maximal', expand_gray 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, or the expansion
          stops because of too high gray value differences.  Because
          expand_gray processes all regions simultaneously, gaps
          between regions are distributed evenly to all regions with
          a similar gray value.  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 regions having a matching gray
          value or color.

Because regions are only expanded into areas having a matching gray value or color, usually gaps will remain between the output regions, i.e., the segmentation is not complete.

#include  <iostream.h>
#include  "HalconCpp.h"

int main (int argc, char *argv[])
{
  HImage   image (argv[1]);
  HRegion  empty_region;
  HWindow  win;

  image.Display (win);

  HRegionArray seg = (image >= 100).Connection ();

  seg.Display (win);
  HRegionArray exp = seg.ExpandGray1 (image, empty_region,
                                      "maximal", "image", 32);
  win.SetDraw ("margin");
  win.SetColored (12);
  exp.Display (win);
  win.Click ();

  return (0);
}

expand_gray 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 handling is raised.

expand_gray is reentrant and processed without parallelization.

connection, regiongrowing, pouring, class_ndim_norm

select_shape

expand_gray_ref, expand_region

Region processing