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| This example demonstrates how to write a filter which uses multiple threads.
| | {{warning|1=The media wiki content on this page is no longer maintained. The examples presented on the https://itk.org/Wiki/* pages likely require ITK version 4.13 or earlier releases. In many cases, the examples on this page no longer conform to the best practices for modern ITK versions.}} |
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| 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: | |
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| Thread 0 given region: ImageRegion (0xbf9e2d0c)
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| Dimension: 2
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| Index: [0, 0]
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| Size: [3, 1]
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| Thread 1 given region: ImageRegion (0xb74b62dc)
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| Dimension: 2
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| Index: [0, 1]
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| Size: [3, 1]
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| In the example, we set the corner (GetIndex()) of each region to the id of the thread that processed the region.
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| The output is (linearly output in raster order) thus: | |
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| 0
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| 100
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| 100
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| 1
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| 100
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| 100
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| ==MultiThreadedImageFilter.cxx==
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| <source lang="cpp">
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| #include "itkImage.h"
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| #include "itkImageFileReader.h"
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| #include "itkImageFileWriter.h"
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| #include "MultiThreadedImageFilter.h"
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| template <typename TImage>
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| static void CreateImage(TImage* const image);
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| template <typename TImage>
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| static void OutputImage(TImage* const image);
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| int main(int, char*[])
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| {
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| // Setup types
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| typedef itk::Image<int, 2> ImageType;
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| typedef itk::MultiThreadedImageFilter<ImageType> FilterType;
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| ImageType::Pointer image = ImageType::New();
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| CreateImage(image.GetPointer());
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| // Create and the filter
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| FilterType::Pointer filter = FilterType::New();
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| filter->SetInput(image);
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| // filter->SetNumberOfThreads(3); // There is no need to specify this, it is automatically determined
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| filter->Update();
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| std::cout << "Image after filter: " << std::endl;
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| OutputImage(image.GetPointer());
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| std::cout << "Output: " << std::endl;
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| OutputImage(filter->GetOutput());
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| return EXIT_SUCCESS;
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| }
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| template <typename TImage>
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| void CreateImage(TImage* const image)
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| {
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| // Create an image with 2 connected components
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| typename TImage::IndexType corner = {{0,0}};
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| // unsigned int NumRows = 200;
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| // unsigned int NumCols = 300;
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| unsigned int NumRows = 3;
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| unsigned int NumCols = 2;
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| typename TImage::SizeType size = {{NumRows, NumCols}};
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| typename TImage::RegionType region(corner, size);
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| image->SetRegions(region);
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| image->Allocate();
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| image->FillBuffer(0);
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| }
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| template <typename TImage>
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| void OutputImage(TImage* const image)
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| {
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| itk::ImageRegionConstIterator<TImage> imageIterator(image, image->GetLargestPossibleRegion());
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| while(!imageIterator.IsAtEnd())
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| {
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| std::cout << imageIterator.Get() << std::endl;
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| ++imageIterator;
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| }
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| }
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| </source>
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| ==MultiThreadedImageFilter.h==
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| <source lang="cpp">
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| #ifndef __itkImageFilter_h
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| #define __itkImageFilter_h
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| #include "itkImageToImageFilter.h"
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| namespace itk
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| {
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| template< class TImage>
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| class MultiThreadedImageFilter : public ImageToImageFilter< TImage, TImage >
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| {
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| public:
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| /** Standard class typedefs. */
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| typedef MultiThreadedImageFilter Self;
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| typedef ImageToImageFilter< TImage, TImage > Superclass;
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| typedef SmartPointer< Self > Pointer;
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| typedef typename Superclass::OutputImageRegionType OutputImageRegionType;
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| /** Method for creation through the object factory. */
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| itkNewMacro(Self);
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| /** Run-time type information (and related methods). */
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| itkTypeMacro(ImageFilter, ImageToImageFilter);
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| protected:
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| MultiThreadedImageFilter(){}
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| ~MultiThreadedImageFilter(){}
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| virtual void ThreadedGenerateData(const OutputImageRegionType &,
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| ThreadIdType);
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| private:
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| MultiThreadedImageFilter(const Self &); //purposely not implemented
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| void operator=(const Self &); //purposely not implemented
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| };
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| } //namespace ITK
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| #ifndef ITK_MANUAL_INSTANTIATION
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| #include "MultiThreadedImageFilter.hxx"
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| #endif
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| #endif // __itkMultiThreadedImageFilter_h
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| </source>
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| ==MultiThreadedImageFilter.hxx==
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| <source lang="cpp">
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| #ifndef __itkMultiThreadedImageFilter_hxx
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| #define __itkMultiThreadedImageFilter_hxx
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| #include "MultiThreadedImageFilter.h"
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| #include "itkObjectFactory.h"
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| #include "itkImageRegionIterator.h"
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| #include "itkImageRegionConstIterator.h"
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| namespace itk
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| {
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| template< class TImage>
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| void MultiThreadedImageFilter< TImage>
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| ::ThreadedGenerateData(const OutputImageRegionType & region, ThreadIdType threadId)
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| {
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| std::cout << "Thread " << threadId << " given region: " << region << std::endl;
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| typename TImage::ConstPointer input = this->GetInput();
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| typename TImage::Pointer output = this->GetOutput();
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| ImageAlgorithm::Copy(input.GetPointer(), output.GetPointer(), region,
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| region);
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| itk::Index<2> cornerPixel = region.GetIndex();
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| std::cout << "cornerPixel: " << cornerPixel << std::endl;
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| typename TImage::PixelType newValue = 3;
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| output->SetPixel( cornerPixel, newValue );
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| }
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| }// end namespace
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| #endif
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| </source>
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| {{ITKCMakeLists|{{SUBPAGENAME}}}}
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