ITK to VTK Filter not working.

Algorithms
1

My code here is trying to read in an image as an itk image, turn it into a vtk image, flip it across the y axis, and show it. However, the display only shows black. (pixel values of 0). Why could this be? Here is the code:

#include <vtkSmartPointer.h>
#include <vtkImageFlip.h>
#include <vtkImageViewer2.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>

#include <itkImage.h>
#include <itkImageFileReader.h>
#include <itkImageToVTKImageFilter.h>

#include

int main() {
// Define the image type
typedef itk::Image<unsigned int, 3> ImageType;

// Read the ITK image
typedef itk::ImageFileReader<ImageType> ReaderType;
ReaderType::Pointer reader = ReaderType::New();
reader->SetFileName("C:\\Users\\satya\\Documents\\CLionProjects\\TreeTrack\\805338_TOF_B_exp.nii"); // Update the path to your image file

try {
    reader->Update();
} catch (itk::ExceptionObject & error) {
    std::cerr << "Error reading the image: " << error << std::endl;
    return EXIT_FAILURE;
}

// Convert ITK image to VTK image
typedef itk::ImageToVTKImageFilter<ImageType> ITKToVTKFilterType;
ITKToVTKFilterType::Pointer itkToVtkFilter = ITKToVTKFilterType::New();
itkToVtkFilter->SetInput(reader->GetOutput());

try {
    itkToVtkFilter->Update();
} catch (itk::ExceptionObject & error) {
    std::cerr << "Error converting ITK image to VTK image: " << error << std::endl;
    return EXIT_FAILURE;
}

// Flip the image along the y-axis
vtkSmartPointer<vtkImageFlip> imageFlip = vtkSmartPointer<vtkImageFlip>::New();
imageFlip->SetInputData(itkToVtkFilter->GetOutput());
imageFlip->SetFilteredAxis(1); // Flip along the y-axis
imageFlip->SetFlipAboutOrigin(true);
imageFlip->Update();

// Visualize the flipped image
vtkSmartPointer<vtkImageViewer2> viewer = vtkSmartPointer<vtkImageViewer2>::New();
viewer->SetInputData(imageFlip->GetOutput());
viewer->Render();

vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
viewer->GetRenderWindow()->SetInteractor(renderWindowInteractor);
viewer->Render();
renderWindowInteractor->Start();

return EXIT_SUCCESS;

}

Additionally, the whole thing works when I manually convert it into vtk instead of using the filter using this code:

#include <vtkSmartPointer.h>
#include <vtkImageFlip.h>
#include <vtkImageViewer2.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <itkImageRegionConstIterator.h>
#include <itkImage.h>
#include <itkImageFileReader.h>
#include <itkImageToVTKImageFilter.h>

#include

int main() {
// Define the image type
typedef itk::Image<unsigned int, 3> ImageType;

// Read the ITK image
typedef itk::ImageFileReader<ImageType> ReaderType;
ReaderType::Pointer reader = ReaderType::New();
reader->SetFileName("C:\\Users\\satya\\Documents\\CLionProjects\\TreeTrack\\805338_TOF_B_exp.nii"); // Update the path to your image file

try {
    reader->Update();
} catch (itk::ExceptionObject & error) {
    std::cerr << "Error reading the image: " << error << std::endl;
    return EXIT_FAILURE;
}

// Create an ITK iterator for the image
typedef itk::ImageRegionConstIterator<ImageType> IteratorType;
IteratorType it(reader->GetOutput(), reader->GetOutput()->GetLargestPossibleRegion());

// Manual conversion from ITK image to VTK image
vtkSmartPointer<vtkImageData> vtkImage = vtkSmartPointer<vtkImageData>::New();

// Set dimensions and spacing
vtkImage->SetDimensions(reader->GetOutput()->GetLargestPossibleRegion().GetSize()[0],
                        reader->GetOutput()->GetLargestPossibleRegion().GetSize()[1],
                        reader->GetOutput()->GetLargestPossibleRegion().GetSize()[2]);

// Allocate memory
vtkImage->AllocateScalars(VTK_UNSIGNED_INT, 1);

// Copy pixel values from ITK image to VTK image
for (it.GoToBegin(); !it.IsAtEnd(); ++it) {
    itk::Index<3> itkIndex = it.GetIndex();
    double value = it.Get(); // Get pixel value from ITK image
    //std::cout << "value: " << value;
    vtkImage->SetScalarComponentFromDouble(itkIndex[0], itkIndex[1], itkIndex[2], 0, value);
    //std::cout << "vtkvalue: " << vtkImage->GetScalarComponentAsFloat(itkIndex[0], itkIndex[1], itkIndex[2], 0) << std::endl;
}

// Flip the image along the y-axis
vtkSmartPointer<vtkImageFlip> imageFlip = vtkSmartPointer<vtkImageFlip>::New();
imageFlip->SetInputData(vtkImage);
imageFlip->SetFilteredAxis(1); // Flip along the y-axis
imageFlip->SetFlipAboutOrigin(true);
imageFlip->Update();

// Visualize the flipped image
vtkSmartPointer<vtkImageViewer2> viewer = vtkSmartPointer<vtkImageViewer2>::New();
viewer->SetInputData(imageFlip->GetOutput());
viewer->Render();

vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
viewer->GetRenderWindow()->SetInteractor(renderWindowInteractor);
viewer->Render();
renderWindowInteractor->Start();

return EXIT_SUCCESS;

}