HALCON Reference Manual 10.0.2

Name

thresholdthresholdthresholdThresholdThreshold — Segment an image using global threshold.

Signature

threshold(Image : Region : MinGray, MaxGray : )

Description

thresholdthresholdthresholdThresholdThreshold selects the pixels from the input image whose gray values g fulfill the following condition:

             MinGray <= g <=  MaxGray .

All points of an image fulfilling the condition are returned as one region. If more than one gray value interval is passed (tuples for MinGrayMinGrayMinGrayMinGrayminGray and MaxGrayMaxGrayMaxGrayMaxGraymaxGray), one separate region is returned for each interval.

Attention

For input images of an integer type, floating point values in MinGrayMinGrayMinGrayMinGrayminGray and MaxGrayMaxGrayMaxGrayMaxGraymaxGray are truncated.

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

ImageImageImageImageimage (input_object) image(-array) → object (byte / direction / cyclic / int1 / int2 / uint2 / int4 / int8 / real / vector_field)

Input image.

RegionRegionRegionRegionregion (output_object) region(-array) → object

Segmented region.

MinGrayMinGrayMinGrayMinGrayminGray (input_control) number(-array) → (real / integer)

Lower threshold for the gray values.

Default value: 128.0

Suggested values: 0.0, 10.0, 30.0, 64.0, 128.0, 200.0, 220.0, 255.0

MaxGrayMaxGrayMaxGrayMaxGraymaxGray (input_control) number(-array) → (real / integer)

Upper threshold for the gray values.

Default value: 255.0

Suggested values: 0.0, 10.0, 30.0, 64.0, 128.0, 200.0, 220.0, 255.0

Restriction: MaxGray >= MinGray

Example (HDevelop)

read_image(Image,'fabrik')
sobel_dir(Image,EdgeAmp,EdgeDir,'sum_abs',3)
threshold(EdgeAmp,Seg,50,255)
skeleton(Seg,Rand)
connection(Rand,Lines)
select_shape(Lines,Edges,'area','and',10,1000000)

Example (C)

read_image(&Image,"fabrik");
sobel_amp(Image,&EdgeAmp,"sum_abs",3);
threshold(EdgeAmp,&Seg,50.0,255.0);
skeleton(Seg,&Rand);
connection(Rand,&Lines);
select_shape(Lines,&Edges,"area","and",10.0,1000000.0);

Example (C++)

#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 != 4)
  {
    cout << "Usage : " << argv[0] << " 'image' MinGray MaxGray" << endl;
    return (-1);
  }

  HImage   image (argv[1]),
           Sobel;
  HWindow  win;

  image.Display (win);

  int MinGray = atoi (argv[2]);
  int MaxGray = atoi (argv[3]);

  Sobel = image.SobelAmp ("sum_abs", 3);

  HRegionArray rand  = ((image >= MinGray) & (image <= MaxGray)).Skeleton();
  HRegionArray lines = rand.Connection();
  HRegionArray edges = lines.SelectShape("area", "and", 10.0, 10000000.0);

  edges.Display (win);
  win.Click ();

  return (0);
}

Example (HDevelop)

read_image(Image,'fabrik')
sobel_dir(Image,EdgeAmp,EdgeDir,'sum_abs',3)
threshold(EdgeAmp,Seg,50,255)
skeleton(Seg,Rand)
connection(Rand,Lines)
select_shape(Lines,Edges,'area','and',10,1000000)

Example (HDevelop)

read_image(Image,'fabrik')
sobel_dir(Image,EdgeAmp,EdgeDir,'sum_abs',3)
threshold(EdgeAmp,Seg,50,255)
skeleton(Seg,Rand)
connection(Rand,Lines)
select_shape(Lines,Edges,'area','and',10,1000000)

Complexity

Let A be the area of the input region. Then the runtime complexity is O(A).

Result

thresholdthresholdthresholdThresholdThreshold returns 2 (H_MSG_TRUE) if all parameters are correct. The behavior with respect to the input images and output regions can be determined by setting the values of the flags 'no_object_result'"no_object_result""no_object_result""no_object_result""no_object_result", 'empty_region_result'"empty_region_result""empty_region_result""empty_region_result""empty_region_result", and 'store_empty_region'"store_empty_region""store_empty_region""store_empty_region""store_empty_region" with set_systemset_systemset_systemSetSystemSetSystem. If necessary, an exception is raised.