ITK与VTK对象的互相转化

ITK的数据流采用如图1所示流水线(pipeline)作业方式。遵循此方式，所处理的数据来龙去脉清晰明了。在图1中，数据流左边的ImageFile代表待处理的图像文件，而右边ImageFile则代表处理后的图像文件。ImageFileReade:将存贮图像文件读人到内存，形成Image，再调用所希望处理的Fileter算法(比如滤波、分割、配准等具体算法)，将对读人的图像数据进行处理。最后，ImageFileWriter将处理的图像数据结果保存，或输人给图形显示系统(如VTK)，进行数据可视化。


VTK是C++语言开发的、公开源码的、面向对象的数据可视化软件开发包，并不单纯用于医学图像数据的可视化。VTK支持跨平台的编译，可以应用于Windows,Linux等系统。VTK支持包括数量、向量、张量、结构和测定体积等方法一系列可视化算法，VTK还支持包括建模。VTK的数据流同样采用流水线作业方式，如图2所示。


vtkSource为整个可视化流的开始，比如读取、生成数据等。vtkFilte对输入源数据进行各种处理，与ITK的Fileter类似。原始数据经过各种Filte:的处理后，再由vtkMappe:转换(或映射)成可供其它算法模块直接使用的数据形式，比如为几何数据。vtkActor类用来描述绘制场景中一个实体，即绘制场景的某个角色(Actor)。通过SetMapper()方法，可以将几何数据的属性传递给Actor，再由vtkRenderer类将处理后的数据结果显示出来。

由于ITK和VTK的数据流都是采用流水线作业形式，比较方便地利用类库本身提供的类型转换类来实现，如图3所示。通过ITKtoVTKImageFilter类操作将ITK和VTK的图像数据连接了起来，VTK负责图像数据的显示，而ITK负责图像的处理，其中VTK的Image Viewe:是一个很方便实现的图像显示类，它在内部管理着vtkImageWindow, vtkRenderer, vtkActor2D和vtkImageMapper等图象类，实现图像查看、显示和可视化功能。


**下面具体解释下ITK对象到VTK对象的两种转换方式：**

**第一种**方式是使用**itkImageToVTKImageFilter**类

通过例子来说明：

#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageToVTKImageFilter.h"

#include "vtkImageViewer.h"
#include "vtkRenderWindowInteractor.h"

int main( int argc, char **argv ) 
{
    typedef itk::Image< unsigned short, 2 >             ImageType;
    typedef itk::ImageFileReader<ImageType>          ReaderType;
    typedef itk::ImageToVTKImageFilter< ImageType> FilterType;

    ReaderType::Pointer reader = ReaderType::New();
    FilterType::Pointer connector = FilterType::New();
    reader->SetFileName( "d:\\1.png");
    connector->SetInput( reader->GetOutput() );

    vtkImageViewer * viewer = vtkImageViewer::New();

    vtkRenderWindowInteractor * renderWindowInteractor = vtkRenderWindowInteractor::New();

    viewer->SetupInteractor( renderWindowInteractor );
    viewer->SetInput( connector->GetOutput() );
    viewer->Render();
    viewer->SetColorWindow( 255 );
    viewer->SetColorLevel( 128 );
    renderWindowInteractor->Start();

    return 0;
}

**第二种**方式是使用**itkVTKImageExport **/ **vtkImageImport**和**vtkImageExport **/ **vtkImageImport**类

例子如下：

#include "itkCommand.h"
#include "itkImage.h"
#include "itkVTKImageExport.h"
#include "itkVTKImageImport.h"
#include "itkCurvatureFlowImageFilter.h"
#include "itkCastImageFilter.h"
#include "itkRGBPixel.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "vtkImageData.h"

#include "vtkImageImport.h"
#include "vtkImageExport.h"
#include "vtkImageActor.h"
#include "vtkRenderer.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkInteractorStyleImage.h" 
#include "itkPNGImageIO.h"
/**
* This will be setup as a callback for a progress event on an ITK
* filter.
*/
struct ProgressDisplay
{
    ProgressDisplay(itk::ProcessObject* process): m_Process(process) {}

    void Display()
    {
        float progress = m_Process->GetProgress()*100.0;
        std::cout << "Progress " << progress << " percent." << std::endl;
    }

    itk::ProcessObject::Pointer m_Process;
};

/**
* This function will connect the given itk::VTKImageExport filter to
* the given vtkImageImport filter.
*/
template <typename ITK_Exporter, typename VTK_Importer> void ConnectPipelines(ITK_Exporter exporter, VTK_Importer* importer) { importer->SetUpdateInformationCallback(exporter->GetUpdateInformationCallback()); importer->SetPipelineModifiedCallback(exporter->GetPipelineModifiedCallback()); importer->SetWholeExtentCallback(exporter->GetWholeExtentCallback()); importer->SetSpacingCallback(exporter->GetSpacingCallback()); importer->SetOriginCallback(exporter->GetOriginCallback()); importer->SetScalarTypeCallback(exporter->GetScalarTypeCallback()); importer->SetNumberOfComponentsCallback(exporter->GetNumberOfComponentsCallback()); importer->SetPropagateUpdateExtentCallback(exporter->GetPropagateUpdateExtentCallback()); importer->SetUpdateDataCallback(exporter->GetUpdateDataCallback()); importer->SetDataExtentCallback(exporter->GetDataExtentCallback()); importer->SetBufferPointerCallback(exporter->GetBufferPointerCallback()); importer->SetCallbackUserData(exporter->GetCallbackUserData()); } 
/**
* This function will connect the given vtkImageExport filter to
* the given itk::VTKImageImport filter.
*/
template <typename VTK_Exporter, typename ITK_Importer> void ConnectPipelines(VTK_Exporter* exporter, ITK_Importer importer) { importer->SetUpdateInformationCallback(exporter->GetUpdateInformationCallback()); importer->SetPipelineModifiedCallback(exporter->GetPipelineModifiedCallback()); importer->SetWholeExtentCallback(exporter->GetWholeExtentCallback()); importer->SetSpacingCallback(exporter->GetSpacingCallback()); importer->SetOriginCallback(exporter->GetOriginCallback()); importer->SetScalarTypeCallback(exporter->GetScalarTypeCallback()); importer->SetNumberOfComponentsCallback(exporter->GetNumberOfComponentsCallback()); importer->SetPropagateUpdateExtentCallback(exporter->GetPropagateUpdateExtentCallback()); importer->SetUpdateDataCallback(exporter->GetUpdateDataCallback()); importer->SetDataExtentCallback(exporter->GetDataExtentCallback()); importer->SetBufferPointerCallback(exporter->GetBufferPointerCallback()); importer->SetCallbackUserData(exporter->GetCallbackUserData()); }

/**
* This program implements an example connection between ITK and VTK
* pipelines.  The combined pipeline flows as follows:
*
* itkImageFileReader ==> itkVTKImageExport ==>
*    vtkImageImport ==> vtkImageActor
*
* The resulting vtkImageActor is displayed in a vtkRenderWindow.
* Whenever the VTK pipeline executes, information is propagated
* through the ITK pipeline.  If the ITK pipeline is out of date, it
* will re-execute and cause the VTK pipeline to update properly as
* well.
*/
int main(int argc, char * argv [] )
{  

    // Load a color image using ITK and display it with VTK

    try
    {
        typedef itk::RGBPixel< unsigned char > PixelType;
        typedef itk::Image< PixelType, 2 > ImageType;

        typedef itk::ImageFileReader< ImageType > ReaderType;

        ReaderType::Pointer reader  = ReaderType::New();
        reader->SetFileName("d:\\1.png");
        reader->Update();

 typedef itk::VTKImageExport< ImageType > ExportFilterType; ExportFilterType::Pointer itkExporter = ExportFilterType::New(); itkExporter->SetInput( reader->GetOutput() );

        // Create the vtkImageImport and connect it to the
        // itk::VTKImageExport instance.
        vtkImageImport* vtkImporter = vtkImageImport::New();  
        ConnectPipelines(itkExporter, vtkImporter);

        // Just for double checking export it from VTK back into ITK 
        // and save it into a file.
 typedef itk::VTKImageImport< ImageType > ImportFilterType; ImportFilterType::Pointer itkImporter = ImportFilterType::New(); vtkImageExport* vtkExporter = vtkImageExport::New(); ConnectPipelines(vtkExporter, itkImporter);
 vtkExporter->SetInput( vtkImporter->GetOutput() );

        typedef itk::ImageFileWriter< ImageType > WriterType;
        WriterType::Pointer itkWriter = WriterType::New();
        itkWriter->SetInput( itkImporter->GetOutput() );

        const char * filename = "d:\\2.png";
        std::cout << "Writing file " << filename << std::endl;
        itkWriter->SetFileName( filename );

        itkWriter->Update();

        //------------------------------------------------------------------------
        // VTK pipeline.
        //------------------------------------------------------------------------

        // Create a vtkImageActor to help render the image.  Connect it to
        // the vtkImporter instance.
        vtkImageActor* actor = vtkImageActor::New();
        actor->SetInput(vtkImporter->GetOutput());

        vtkInteractorStyleImage * interactorStyle = vtkInteractorStyleImage::New();

        // Create a renderer, render window, and render window interactor to
        // display the results.
        vtkRenderer* renderer = vtkRenderer::New();
        vtkRenderWindow* renWin = vtkRenderWindow::New();
        vtkRenderWindowInteractor* iren = vtkRenderWindowInteractor::New();

        renWin->SetSize(500, 500);
        renWin->AddRenderer(renderer);
        iren->SetRenderWindow(renWin);
        iren->SetInteractorStyle( interactorStyle );

        // Add the vtkImageActor to the renderer for display.
        renderer->AddActor(actor);
        renderer->SetBackground(0.4392, 0.5020, 0.5647);

        // Bring up the render window and begin interaction.
        renWin->Render();
        iren->Start();

        // Release all VTK components
        actor->Delete();
        interactorStyle->Delete(); 
        vtkImporter->Delete();
        vtkExporter->Delete();
        renWin->Delete();
        renderer->Delete();
        iren->Delete();

    }
    catch( itk::ExceptionObject & e )
    {
        std::cerr << "Exception catched !! " << e << std::endl;
    }

    return 0;
}

【参考来源】：http://image.szpt.edu.cn/cn/Article_content.asp?id=311