VTKPNGWriter打印出黑色图像？

Question

我正在使用ITK进行一些图像处理，然后使用VTK将结果以.png格式输出，但输出的图片总是黑色的。

目前，我正在使用itk::Image转换为vtk::vtkImageData，使用itk::ImagetoVTKImageFilter（在我的代码中被定义为ITKtoVTKFilterType）。

ITKtoVTKFilterType::Pointer itk2vtkGray = ITKtoVTKFilterType::New();
itk2vtkGray->SetInput(grayBinary);  //grayBinary is of type itk::Image<unsigned short, 2>
itk2vtkGray->Update();

vtkSmartPointer<vtkImageData> grayVTK = vtkSmartPointer<vtkImageData>::New();
grayVTK->SetExtent(extent);
grayVTK->SetSpacing(m_spacing);
grayVTK->SetScalarTypeToUnsignedShort();
grayVTK->SetNumberOfScalarComponents(1);
grayVTK->AllocateScalars();
grayVTK->DeepCopy(static_cast<vtkImageData*>(itk2vtkGray->GetOutput()));
//grayVTK = itk2vtkGray->GetOutput();

我已经通过以下代码确认我的VTK ImageData包含值为255或0的数据。

int *dims = grayVTK->GetDimensions();

std::cout << "Dims: " << " x: " << dims[0] << " y: " << dims[1] << " z: " << dims[2] << std::endl;
std::cout << "Number of points: " << grayVTK->GetNumberOfPoints() << std::endl;
std::cout << "Number of cells: " << grayVTK->GetNumberOfCells() << std::endl;

for (int y = 0; y < dims[1]; y++)
{        
     for (int x = 0; x < dims[0]; x++)
     {
         unsigned short *pixel = static_cast<unsigned short*>(grayVTK->GetScalarPointer(x,y,0));
         std::cout << "PIXEL LOC/VAL "<< y*dims[0] + x << " " << pixel[0] <<std::endl;
     }
     std::cout << std::endl;
 }

我接着进行 ImageCast 操作，以确保数据类型为 unsignedShort。

vtkSmartPointer<vtkImageCast> cast2 = vtkSmartPointer<vtkImageCast>::New();
cast2->SetInput(grayVTK);
cast2->SetOutputScalarTypeToUnsignedShort();
cast2->ClampOverflowOn();
cast2->Update();

最后，我使用vtkPNGwriter输出.png文件。请注意，我尝试输出实际的vtkImageData以及ImageCastFilter的输出。

vtkSmartPointer<vtkPNGWriter> writer =
vtkSmartPointer<vtkPNGWriter>::New();
writer->SetFileName(filename.toStdString().c_str());
writer->SetInputConnection(cast2->GetOutputPort());
//writer->SetInput(grayVTK); I have tried to method as well but to no success
writer->Write();

然而，.png输出总是黑色的。有谁知道我做错了什么。

- user1084113

---

也许问题出在其中一个库或者你的VTK构建上了？如果你编译并运行这个例子 - http://www.vtk.org/Wiki/VTK/Examples/Cxx/IO/WritePNG，它是否按预期工作？ - Ilya Kobelevskiy

为什么不使用itkImageFileWriter来写PNG呢？ - David Doria

Answer 1

供日后参考，许多PNG阅读器不能显示16位数据。因此，我在最后进行的无符号短整型强制转换应该改为字符。

vtkSmartPointer<vtkImageCast> cast2 = vtkSmartPointer<vtkImageCast>::New();
cast2->SetInput(grayVTK);
cast2->SetOutputScalarTypeToChar();
cast2->ClampOverflowOn();
cast2->Update();

- user1084113