ITK/Examples/Developer/MultiThreadedImageFilter

This example demonstrates how to write a filter which uses multiple threads.

The image is automatically broken into pieces and the ThreadedGenerateData is called with each piece. For example with this 3x2 image and 2 threads, the filter is called with the following regions:

Thread 0 given region: ImageRegion (0xbf9e2d0c)

 Dimension: 2
 Index: [0, 0]
 Size: [3, 1]

Thread 1 given region: ImageRegion (0xb74b62dc)

 Dimension: 2
 Index: [0, 1]
 Size: [3, 1]

In the example, we set the corner (GetIndex()) of each region to the id of the thread that processed the region.

The output is (linearly output in raster order) thus:

0 100 100 1 100 100

MultiThreadedImageFilterExample.cxx

<source lang="cpp">

1. include "itkImage.h"
2. include "itkImageFileReader.h"
3. include "itkImageFileWriter.h"

1. include "MultiThreadedImageFilter.h"

template <typename TImage> static void CreateImage(TImage* const image);

template <typename TImage> static void OutputImage(TImage* const image);

int main(int, char*[]) {

 // Setup types
 typedef itk::Image<int, 2>   ImageType;
 typedef itk::MultiThreadedImageFilter<ImageType>  FilterType;

 ImageType::Pointer image = ImageType::New();
 CreateImage(image.GetPointer());

 // Create and the filter
 FilterType::Pointer filter = FilterType::New();
 filter->SetInput(image);
 // filter->SetNumberOfThreads(3); // There is no need to specify this, it is automatically determined
 filter->Update();

 std::cout << "Image after filter: " << std::endl;
 OutputImage(image.GetPointer());

 std::cout << "Output: " << std::endl;
 OutputImage(filter->GetOutput());

 return EXIT_SUCCESS;

}

template <typename TImage> void CreateImage(TImage* const image) {

 // Create an image with 2 connected components
 typename TImage::IndexType corner = Template:0,0;

// unsigned int NumRows = 200; // unsigned int NumCols = 300;

 unsigned int NumRows = 3;
 unsigned int NumCols = 2;
 typename TImage::SizeType size = Template:NumRows, NumCols;

 typename TImage::RegionType region(corner, size);

 image->SetRegions(region);
 image->Allocate();

 image->FillBuffer(0);

}

template <typename TImage> void OutputImage(TImage* const image) {

 itk::ImageRegionConstIterator<TImage> imageIterator(image, image->GetLargestPossibleRegion());

 while(!imageIterator.IsAtEnd())
   {
   std::cout << imageIterator.Get() << std::endl;

   ++imageIterator;
   }

}

</source>

MultiThreadedImageFilter.h

<source lang="cpp">

1. ifndef __itkImageFilter_h
2. define __itkImageFilter_h

1. include "itkImageToImageFilter.h"

namespace itk { template< class TImage> class MultiThreadedImageFilter : public ImageToImageFilter< TImage, TImage > { public:

 /** Standard class typedefs. */
 typedef MultiThreadedImageFilter             Self;
 typedef ImageToImageFilter< TImage, TImage > Superclass;
 typedef SmartPointer< Self >        Pointer;

 typedef typename Superclass::OutputImageRegionType OutputImageRegionType;

 /** Method for creation through the object factory. */
 itkNewMacro(Self);

 /** Run-time type information (and related methods). */
 itkTypeMacro(ImageFilter, ImageToImageFilter);

protected:

 MultiThreadedImageFilter(){}
 ~MultiThreadedImageFilter(){}

 virtual void ThreadedGenerateData(const OutputImageRegionType &,
                                   ThreadIdType);

private:

 MultiThreadedImageFilter(const Self &); //purposely not implemented
 void operator=(const Self &);  //purposely not implemented

}; } //namespace ITK

1. ifndef ITK_MANUAL_INSTANTIATION
2. include "MultiThreadedImageFilter.hxx"
3. endif

1. endif // __itkMultiThreadedImageFilter_h

</source>

MultiThreadedImageFilter.hxx

<source lang="cpp">

1. ifndef __itkMultiThreadedImageFilter_hxx
2. define __itkMultiThreadedImageFilter_hxx

1. include "MultiThreadedImageFilter.h"

1. include "itkObjectFactory.h"
2. include "itkImageRegionIterator.h"
3. include "itkImageRegionConstIterator.h"

namespace itk {

template< class TImage> void MultiThreadedImageFilter< TImage>

ThreadedGenerateData(const OutputImageRegionType & region, ThreadIdType threadId)

{

 std::cout << "Thread " << threadId << " given region: " << region << std::endl;

 typename TImage::ConstPointer input = this->GetInput();
 typename TImage::Pointer output = this->GetOutput();

 ImageAlgorithm::Copy(input.GetPointer(), output.GetPointer(), region,
                      region);

 itk::Index<2> cornerPixel = region.GetIndex();
 std::cout << "cornerPixel: " << cornerPixel << std::endl;
 typename TImage::PixelType newValue = 3;

 output->SetPixel( cornerPixel, newValue );

}

}// end namespace

1. endif

</source>

CMakeLists.txt

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

project(MultiThreadedImageFilter)

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

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

endif()

add_executable(MultiThreadedImageFilter MACOSX_BUNDLE MultiThreadedImageFilter.cxx)

if( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(MultiThreadedImageFilter ITKReview ${ITK_LIBRARIES})

else( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(MultiThreadedImageFilter ${ITK_LIBRARIES})

endif( "${ITK_VERSION_MAJOR}" LESS 4 )

</syntaxhighlight>

Download and Build MultiThreadedImageFilter

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

cd MultiThreadedImageFilter/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:

./MultiThreadedImageFilter

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.