dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold (Operator)

Name

dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold — Threshold operator for signed images.

Signature

dual_threshold(Image : RegionCrossings : MinSize, MinGray, Threshold : )

dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold segments the input image into a region with gray values >= Threshold (“positive” regions) and a region with gray values <= -Threshold (“negative” regions). “Positive” or “negative” regions having a size of less than MinSizeMinSizeMinSizeMinSizeminSize are suppressed, as well as regions whose maximum gray value is less than MinGrayMinGrayMinGrayMinGrayminGray in absolute value.

The segmentation performed is not complete, i.e., the “positive” and “negative” regions together do not necessarily cover the entire image: Areas with a gray value between -ThresholdThresholdThresholdThresholdthreshold and ThresholdThresholdThresholdThresholdthreshold, -MinGrayMinGrayMinGrayMinGrayminGray and MinGrayMinGrayMinGrayMinGrayminGray, respectively, are not taken into account.

dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold is usually called after applying a Laplace operator (laplacelaplacelaplaceLaplaceLaplace, laplace_of_gausslaplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGauss, derivate_gaussderivate_gaussderivate_gaussDerivateGaussDerivateGauss or diff_of_gaussdiff_of_gaussdiff_of_gaussDiffOfGaussDiffOfGauss) to an image or with the difference of two images (sub_imagesub_imagesub_imageSubImageSubImage).

The zero crossings of a Laplace image correspond to edges in an image, and are the separating regions of the “positive” and “negative” regions in the Laplace image. They can be determined by calling dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold with ThresholdThresholdThresholdThresholdthreshold = 1 and then creating the complement regions with complementcomplementcomplementComplementComplement. The parameter MinGrayMinGrayMinGrayMinGrayminGray determines the noise invariance, while MinSizeMinSizeMinSizeMinSizeminSize determines the resolution of the edge detection.

Using byte images, only the positive part of the operator is applied. Therefore dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold behaves like a standard threshold operator (thresholdthresholdthresholdThresholdThreshold) with successive connectionconnectionconnectionConnectionConnection and select_grayselect_grayselect_graySelectGraySelectGray.

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 / int1 / int2 / int4 / real)

Input image.

RegionCrossingsRegionCrossingsRegionCrossingsRegionCrossingsregionCrossings (output_object) region-array → object

Positive and negative regions.

MinSizeMinSizeMinSizeMinSizeminSize (input_control) integer → (integer)

Regions smaller than MinSize are suppressed.

Default value: 20

Suggested values: 0, 10, 20, 50, 100, 200, 500, 1000

Typical range of values: 0 ≤ MinSize MinSize MinSize MinSize minSize ≤ 10000 (lin)

Minimum increment: 1

Recommended increment: 10

MinGrayMinGrayMinGrayMinGrayminGray (input_control) real → (real)

Regions whose maximum absolute gray value is smaller than MinGray are suppressed.

Default value: 5.0

Suggested values: 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 9.0, 11.0, 15.0, 20.0

Typical range of values: 0.001 ≤ MinGray MinGray MinGray MinGray minGray ≤ 10000.0 (lin)

Minimum increment: 1.0

Recommended increment: 10.0

Restriction: MinGray > 0

ThresholdThresholdThresholdThresholdthreshold (input_control) real → (real)

Regions that have a gray value smaller than Threshold (or larger than -Threshold) are suppressed.

Default value: 2.0

Suggested values: 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 9.0, 11.0, 15.0, 20.0

Typical range of values: 0.001 ≤ Threshold Threshold Threshold Threshold threshold ≤ 10000.0 (lin)

Minimum increment: 1.0

Recommended increment: 10.0

Restriction: (Threshold >= 1) && (Threshold <= MinGray)

Example (HDevelop)

* Edge detection with the Laplace operator (and edge thinning)
diff_of_gauss(Image,Laplace,2.0,1.6)
* find "`positive"' and "`negative"' regions:
dual_threshold(Laplace,Region,20,2,1)
* The zero runnings are the complement to these image section:
complement(Region,ZeroCrossings)

* Simulation of dual_threshold
dual_threshold(Laplace,Result,MinS,MinG,Threshold)
threshold(Laplace,Tmp1,Threshold,999999)
connection(Tmp1,Tmp2)
select_shape(Tmp2,Tmp3,'area','and',MinS,999999)
select_gray(Laplace,Tmp3,Tmp4,'max','and',MinG,999999)
threshold(Laplace,Tmp5,-999999,-Threshold)
connection(Tmp5,Tmp6)
select_shape(Tmp6,Tmp7,'area','and',MinS,999999)
select_gray(Laplace,Tmp7,Tmp8,'min','and',-999999,-MinG)
concat_obj(Tmp4,Tmp8,Result)

Example (C)

/* Edge detection with the Laplace operator (and edge thinning) */
diff_of_gauss(Image,&Laplace,2.0,1.6) ;
/* find "`positive"' and "`negative"' regions: */
dual_threshold(Laplace,&Region,20,2,1) ;
/*The zero runnings are the complement to these image section: */
complement(Region,ZeroCrossings) ;

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 != 2)
  {
    cout << "Usage : " << argv[0] << " 'image' " << endl;
    return (-1);
  }

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

  HRegionArray region,
               nulldg;

  image.Display (win);

  laplace = image.DiffOfGauss (2.0, 1.6);
  region  = laplace.DualThreshold (20, 2, 1);
  nulldg  = region.Complement ();

  laplace.Display (win);     win.Click ();
  region.Display (win);      win.Click ();
  nulldg.Display (win);      win.Click ();

  return (0);
}

Example (HDevelop)

* Edge detection with the Laplace operator (and edge thinning)
diff_of_gauss(Image,Laplace,2.0,1.6)
* find "`positive"' and "`negative"' regions:
dual_threshold(Laplace,Region,20,2,1)
* The zero runnings are the complement to these image section:
complement(Region,ZeroCrossings)

* Simulation of dual_threshold
dual_threshold(Laplace,Result,MinS,MinG,Threshold)
threshold(Laplace,Tmp1,Threshold,999999)
connection(Tmp1,Tmp2)
select_shape(Tmp2,Tmp3,'area','and',MinS,999999)
select_gray(Laplace,Tmp3,Tmp4,'max','and',MinG,999999)
threshold(Laplace,Tmp5,-999999,-Threshold)
connection(Tmp5,Tmp6)
select_shape(Tmp6,Tmp7,'area','and',MinS,999999)
select_gray(Laplace,Tmp7,Tmp8,'min','and',-999999,-MinG)
concat_obj(Tmp4,Tmp8,Result)

Example (HDevelop)

* Edge detection with the Laplace operator (and edge thinning)
diff_of_gauss(Image,Laplace,2.0,1.6)
* find "`positive"' and "`negative"' regions:
dual_threshold(Laplace,Region,20,2,1)
* The zero runnings are the complement to these image section:
complement(Region,ZeroCrossings)

* Simulation of dual_threshold
dual_threshold(Laplace,Result,MinS,MinG,Threshold)
threshold(Laplace,Tmp1,Threshold,999999)
connection(Tmp1,Tmp2)
select_shape(Tmp2,Tmp3,'area','and',MinS,999999)
select_gray(Laplace,Tmp3,Tmp4,'max','and',MinG,999999)
threshold(Laplace,Tmp5,-999999,-Threshold)
connection(Tmp5,Tmp6)
select_shape(Tmp6,Tmp7,'area','and',MinS,999999)
select_gray(Laplace,Tmp7,Tmp8,'min','and',-999999,-MinG)
concat_obj(Tmp4,Tmp8,Result)

Result

dual_thresholddual_thresholddual_thresholdDualThresholdDualThreshold 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.