auto_thresholdauto_thresholdauto_thresholdAutoThresholdAutoThreshold (Operator)

Name

auto_thresholdauto_thresholdauto_thresholdAutoThresholdAutoThreshold — Segment an image using thresholds determined from its histogram.

Signature

Description

auto_thresholdauto_thresholdauto_thresholdAutoThresholdAutoThreshold segments a single-channel image using multiple thresholding. First, the absolute histogram of the gray values is determined. Then, relevant minima are extracted from the histogram, which are used successively as parameters for a thresholding operation. The thresholds used for byte images are 0, 255, and all minima extracted from the histogram (after the histogram has been smoothed with a Gaussian filter with standard deviation SigmaSigmaSigmaSigmasigma). For each gray value interval one region is generated. Thus, the number of regions is the number of minima + 1. For uint2 images, the above procedure is used analogously. However, here the highest threshold is 65535. Furthermore, for uint2 images the value of SigmaSigmaSigmaSigmasigma (virtually) refers to a histogram with 256 values, although internally histograms with a higher resolution are used. This is done to facilitate switching between image types without having to change the parameter SigmaSigmaSigmaSigmasigma. For float images the thresholds are the minimum and maximum grayvalue in the image and all minima extracted from the histogram. Here, the scaling of the parameter SigmaSigmaSigmaSigmasigma refers to the original gray values of the image. The larger the value of SigmaSigmaSigmaSigmasigma is chosen, the fewer regions will be extracted. This operator is useful if the regions to be extracted exhibit similar gray values (homogeneous regions).

Parallelization

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on tuple level.
• Automatically parallelized on internal data level.

Parameters

read_image (Image, 'fabrik')
median_image (Image, Median, 'circle', 3, 'mirrored')
auto_threshold (Median, Seg, 2.0)
connection (Seg, Connected)

read_image(&Image,"fabrik");
median_image(Image,&Median,"circle",3,"mirrored");
auto_threshold(Median,&Seg,2.0);
connection(Seg,&Connected);
set_colored(WindowHandle,12);
disp_obj(Connected,WindowHandle);

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

int main (int argc, char *argv[])
{
  if (argc != 2)
  {
    cout << "Usage : " << argv[0] << " 'image' " << endl;
    return -1;
  }

  HImage       image(argv[1]);
  HImage       med;
  HWindow      w;

  w.SetDraw("margin");
  w.SetColored(12);

  image.Display (w);

  med = image.MedianImage("circle", 3, "mirrored");
  med.Display(w);

  HRegionArray reg = med.AutoThreshold(2.0);
  HRegionArray con = reg.Connection();

  cout << "Display image after AutoThreshold segmentation " << endl;
  con.Display(w);
  w.Click();

  return 0;
}

read_image (Image, 'fabrik')
median_image (Image, Median, 'circle', 3, 'mirrored')
auto_threshold (Median, Seg, 2.0)
connection (Seg, Connected)

read_image (Image, 'fabrik')
median_image (Image, Median, 'circle', 3, 'mirrored')
auto_threshold (Median, Seg, 2.0)
connection (Seg, Connected)

Possible Predecessors

anisotropic_diffusionanisotropic_diffusionanisotropic_diffusionAnisotropicDiffusionAnisotropicDiffusion, median_imagemedian_imagemedian_imageMedianImageMedianImage, illuminateilluminateilluminateIlluminateIlluminate

Possible Successors

connectionconnectionconnectionConnectionConnection, select_shapeselect_shapeselect_shapeSelectShapeSelectShape, select_grayselect_grayselect_graySelectGraySelectGray

Alternatives

bin_thresholdbin_thresholdbin_thresholdBinThresholdBinThreshold, char_thresholdchar_thresholdchar_thresholdCharThresholdCharThreshold

See also

gray_histogray_histogray_histoGrayHistoGrayHisto, gray_histo_absgray_histo_absgray_histo_absGrayHistoAbsGrayHistoAbs, histo_to_threshhisto_to_threshhisto_to_threshHistoToThreshHistoToThresh, smooth_funct_1d_gausssmooth_funct_1d_gausssmooth_funct_1d_gaussSmoothFunct1dGaussSmoothFunct1dGauss, thresholdthresholdthresholdThresholdThreshold

Module

Foundation