ITK/Examples/Morphology/ForegroundHasAccurateArea

Ball with mode off	Ball with mode on	Annulus with mode off	Annulus with mode on

When using the FlatStructuringElement, the "ball" and "annulus" structuring elements have an optional flag called "foregroundHasAccurateArea". Setting this flag to true will generate structuring elements with more accurate areas, which can be especially important when morphological operations are intended to remove or retain objects of particular sizes. This mode was introduced because the original ball and annulus structuring elements have a systematic bias in the radius of +0.5 voxels in each dimension relative to the analytic definition of the radius.

We recommend using this mode for more accurate structuring elements. However, this mode is turned off by default for backward compatibility.

Here is the output of the test in the code below: 2D ball of radius 5 with foregroundHasAccurateArea mode off: Expected foreground area: 78.5398 Computed foreground area: 97 Foreground area error: 23.5042%

Writing out image Ball_ModeOff.png 2D ball of radius 5 with foregroundHasAccurateArea mode on: Expected foreground area: 78.5398 Computed foreground area: 81 Foreground area error: 3.1324%

Writing out image Ball_ModeOn.png 2D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off: Expected foreground area: 50.2655 Computed foreground area: 60 Foreground area error: 19.3662%

Writing out image Annulus_ModeOff.png 2D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on: Expected foreground area: 50.2655 Computed foreground area: 52 Foreground area error: 3.45071%

Writing out image Annulus_ModeOn.png 3D ball of radius 5 with foregroundHasAccurateArea mode off: Expected foreground area: 523.599 Computed foreground area: 739 Foreground area error: 41.1386%

3D ball of radius 5 with foregroundHasAccurateArea mode on: Expected foreground area: 523.599 Computed foreground area: 515 Foreground area error: 1.64224%

3D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off: Expected foreground area: 410.501 Computed foreground area: 560 Foreground area error: 36.4185%

3D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on: Expected foreground area: 410.501 Computed foreground area: 392 Foreground area error: 4.50703%

4D ball of radius 5 with foregroundHasAccurateArea mode off: Expected foreground area: 3084.25 Computed foreground area: 4785 Foreground area error: 55.143%

4D ball of radius 5 with foregroundHasAccurateArea mode on: Expected foreground area: 3084.25 Computed foreground area: 2929 Foreground area error: 5.03368%

4D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off: Expected foreground area: 2684.53 Computed foreground area: 4024 Foreground area error: 49.8957%

4D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on: Expected foreground area: 2684.53 Computed foreground area: 2504 Foreground area error: 6.72491%

ForegroundHasAccurateArea.cxx

<source lang="cpp">

1. include "itkFlatStructuringElement.h"

// Helper function template< class SEType> bool ComputeAreaError(SEType k, unsigned int thickness = 0);

int main(int, char *[]) {

 int scalarRadius = 5;
 int scalarThickness = 2;
 bool foregroundHasAccurateArea = true;

 typedef itk::FlatStructuringElement< 2 > SE2Type;
 SE2Type::RadiusType r2;
 r2.Fill( scalarRadius );
 SE2Type k2;

 std::cout << "2D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k2 = SE2Type::Ball( r2 );
 ComputeAreaError(k2);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "2D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k2 = SE2Type::Ball(r2, foregroundHasAccurateArea);
 ComputeAreaError(k2);

 std::cout << "2D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k2 = SE2Type::Annulus(r2,scalarThickness,false);
 ComputeAreaError(k2,scalarThickness);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "2D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k2 = SE2Type::Annulus(r2,scalarThickness,false,foregroundHasAccurateArea);
 ComputeAreaError(k2,scalarThickness);

 typedef itk::FlatStructuringElement< 3 > SE3Type;
 SE3Type::RadiusType r3;
 r3.Fill( scalarRadius );
 SE3Type k3;

 std::cout << "3D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k3 = SE3Type::Ball( r3 );
 ComputeAreaError(k3);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "3D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k3 = SE3Type::Ball(r3, foregroundHasAccurateArea);
 ComputeAreaError(k3);

 std::cout << "3D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k3 = SE3Type::Annulus(r3,scalarThickness,false);
 ComputeAreaError(k3,scalarThickness);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "3D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k3 = SE3Type::Annulus(r3,scalarThickness,false,foregroundHasAccurateArea);
 ComputeAreaError(k3,scalarThickness);

 typedef itk::FlatStructuringElement< 4 > SE4Type;
 SE4Type::RadiusType r4;
 r4.Fill( scalarRadius );
 SE4Type k4;

 std::cout << "4D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k4 = SE4Type::Ball( r4 );
 ComputeAreaError(k4);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "4D ball of radius " << scalarRadius
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k4 = SE4Type::Ball(r4, foregroundHasAccurateArea);
 ComputeAreaError(k4);

 std::cout << "4D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode off:" << std::endl;
 k4 = SE4Type::Annulus(r4,scalarThickness,false);
 ComputeAreaError(k4,scalarThickness);

 // Test the foregroundHasAccurateArea mode.
 std::cout << "4D annulus of radius " << scalarRadius
 << " and thickness " <<  scalarThickness
 << " with foregroundHasAccurateArea mode on:" << std::endl;
 k4 = SE4Type::Annulus(r4,scalarThickness,false,foregroundHasAccurateArea);
 ComputeAreaError(k4,scalarThickness);

 return EXIT_SUCCESS;

}

template< class SEType > bool ComputeAreaError(SEType k, unsigned int thickness) {

 float expectedOuterForegroundArea = 1;
 float expectedInnerForegroundArea;
 if( thickness == 0 )
 {
   // Circle/Ellipse has no inner area to subract.
   expectedInnerForegroundArea = 0;
 }
 else
 {
   // Annulus does have inner area to subract.
   expectedInnerForegroundArea = 1;
 }
 if( SEType::NeighborhoodDimension == 2)
 {
   expectedOuterForegroundArea *= vnl_math::pi;
   expectedInnerForegroundArea *= vnl_math::pi;
 }
 else if( SEType::NeighborhoodDimension == 3 )
 {
   expectedOuterForegroundArea *= 4.0/3.0 * vnl_math::pi;
   expectedInnerForegroundArea *= 4.0/3.0 * vnl_math::pi;
 }
 else if ( SEType::NeighborhoodDimension == 4 )
 {
   expectedOuterForegroundArea *= 0.5 * vnl_math::pi * vnl_math::pi;
   expectedInnerForegroundArea *= 0.5 * vnl_math::pi * vnl_math::pi;
 }
 else
 {
   return EXIT_FAILURE;
 }
 for( unsigned int i = 0; i < SEType::NeighborhoodDimension; i++ )
 {
   expectedOuterForegroundArea *= k.GetRadius()[i];
   expectedInnerForegroundArea *= (k.GetRadius()[i] - thickness);
 }

 float expectedForegroundArea = expectedOuterForegroundArea - expectedInnerForegroundArea;

 // Show the neighborhood if it is 2D.
 typename SEType::Iterator SEIt;
 if( SEType::NeighborhoodDimension == 2 )
 {
   for( SEIt = k.Begin(); SEIt != k.End(); ++SEIt )
   {
     std::cout << *SEIt << "\t";
     if( (SEIt - k.Begin()+1) % k.GetSize()[0] == 0 )
     {
       std::cout << std::endl;
     }
   }
 }

 // Compute the area/volume.
 float computedForegroundArea = 0;
 for( SEIt = k.Begin(); SEIt != k.End(); ++SEIt )
 {
   if( *SEIt )
   {
     computedForegroundArea++;
   }
 }

 std::cout << "Expected foreground area: " << expectedForegroundArea << std::endl;
 std::cout << "Computed foreground area: " << computedForegroundArea << std::endl;
 std::cout << "Foreground area error: "
 << 100 * vnl_math_abs(expectedForegroundArea-computedForegroundArea)/expectedForegroundArea
 << "%" << "\n\n";
 
 return EXIT_FAILURE;

} </source>

CMakeLists.txt

<syntaxhighlight lang="cmake"> cmake_minimum_required(VERSION 3.9.5)

project(ForegroundHasAccurateArea)

find_package(ITK REQUIRED) include(${ITK_USE_FILE}) if (ITKVtkGlue_LOADED)

 find_package(VTK REQUIRED)
 include(${VTK_USE_FILE})

endif()

add_executable(ForegroundHasAccurateArea MACOSX_BUNDLE ForegroundHasAccurateArea.cxx)

if( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ForegroundHasAccurateArea ITKReview ${ITK_LIBRARIES})

else( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ForegroundHasAccurateArea ${ITK_LIBRARIES})

endif( "${ITK_VERSION_MAJOR}" LESS 4 )

</syntaxhighlight>

Download and Build ForegroundHasAccurateArea

Click here to download ForegroundHasAccurateArea and its CMakeLists.txt file. Once the tarball ForegroundHasAccurateArea.tar has been downloaded and extracted,

cd ForegroundHasAccurateArea/build

• If ITK is installed:

cmake ..

• If ITK is not installed but compiled on your system, you will need to specify the path to your ITK build:

cmake -DITK_DIR:PATH=/home/me/itk_build ..

Build the project:

make

and run it:

./ForegroundHasAccurateArea

WINDOWS USERS PLEASE NOTE: Be sure to add the ITK bin directory to your path. This will resolve the ITK dll's at run time.

Building All of the Examples

Many of the examples in the ITK Wiki Examples Collection require VTK. You can build all of the the examples by following these instructions. If you are a new VTK user, you may want to try the Superbuild which will build a proper ITK and VTK.

ItkVtkGlue

ITK >= 4

For examples that use QuickView (which depends on VTK), you must have built ITK with Module_ITKVtkGlue=ON.

ITK < 4

Some of the ITK Examples require VTK to display the images. If you download the entire ITK Wiki Examples Collection, the ItkVtkGlue directory will be included and configured. If you wish to just build a few examples, then you will need to download ItkVtkGlue and build it. When you run cmake it will ask you to specify the location of the ItkVtkGlue binary directory.