ImageStencil

VTKEx/Cxx/Images/ImageStencil

Description

This example creates a red image and a green image. It creates a mask that is half on and half off. It then combines the images according to the mask using an ImageStencil.

Seealso

ImageTransparency and Transparency

Question

If you have a simple question about this example contact us at VTKExProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

Code

ImageStencil.cxx

#include <vtkImageData.h>
#include <vtkImageMapper3D.h>
#include <vtkImageStencil.h>
#include <vtkImageStencilData.h>
#include <vtkImageToImageStencil.h>
#include <vtkPointData.h>
#include <vtkSmartPointer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkImageActor.h>

namespace
{
void CreateColorImage(vtkImageData*, unsigned int channel);
void CreateMask(vtkImageData*);
}

int main(int, char *[])
{
  vtkSmartPointer<vtkImageData> image1 = vtkSmartPointer<vtkImageData>::New();
  CreateColorImage(image1, 0); // Create a red image

  vtkSmartPointer<vtkImageData> image2 = vtkSmartPointer<vtkImageData>::New();
  CreateColorImage(image2, 1); // Create a green image

  vtkSmartPointer<vtkImageData> mask = vtkSmartPointer<vtkImageData>::New();
  CreateMask(mask);

  //vtkSmartPointer<vtkImageStencilData> stencilData = vtkSmartPointer<vtkImageStencilData>::New();
  vtkSmartPointer<vtkImageToImageStencil> imageToImageStencil = vtkSmartPointer<vtkImageToImageStencil>::New();
  imageToImageStencil->SetInputData(mask);
  imageToImageStencil->ThresholdByUpper(122);

  vtkSmartPointer<vtkImageStencil> stencil = vtkSmartPointer<vtkImageStencil>::New();
  stencil->SetInputConnection(2, imageToImageStencil->GetOutputPort());
  stencil->ReverseStencilOn();
  stencil->SetBackgroundInputData(image2);
  stencil->SetInputData(image1);
  stencil->Update();

  // Create an actor
  vtkSmartPointer<vtkImageActor> actor = vtkSmartPointer<vtkImageActor>::New();
  actor->GetMapper()->SetInputConnection(stencil->GetOutputPort());

  // Setup renderer
  vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
  renderer->AddActor(actor);
  renderer->ResetCamera();

  // Setup render window
  vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);

  // Setup render window interactor
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  vtkSmartPointer<vtkInteractorStyleImage> style =
    vtkSmartPointer<vtkInteractorStyleImage>::New();

  renderWindowInteractor->SetInteractorStyle(style);

  // Render and start interaction
  renderWindowInteractor->SetRenderWindow(renderWindow);

  renderWindow->Render();;
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}


namespace
{
void CreateColorImage(vtkImageData* image, const unsigned int channel)
{
  unsigned int dim = 20;

  image->SetDimensions(dim, dim, 1);
  image->AllocateScalars(VTK_UNSIGNED_CHAR,3);

  for(unsigned int x = 0; x < dim; x++)
  {
    for(unsigned int y = 0; y < dim; y++)
    {
      unsigned char* pixel = static_cast<unsigned char*>(image->GetScalarPointer(x,y,0));
      pixel[0] = 0;
      pixel[1] = 0;
      pixel[2] = 0;

      pixel[channel] = 255;
    }
  }

  image->Modified();
}

void CreateMask(vtkImageData* image)
{
  unsigned int dim = 20;

  image->SetDimensions(dim, dim, 1);
  image->AllocateScalars(VTK_UNSIGNED_CHAR, 1);

  for(unsigned int x = 0; x < dim; x++)
  {
    for(unsigned int y = 0; y < dim; y++)
    {
      unsigned char* pixel = static_cast<unsigned char*>(image->GetScalarPointer(x,y,0));
      if(x < dim/2)
      {
        pixel[0] = 0;
      }
      else
      {
        pixel[0] = 255;
      }
    }
  }

  image->Modified();
}
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ImageStencil)

find_package(VTK COMPONENTS 
  vtkvtkCommonCore
  vtkvtkCommonDataModel
  vtkvtkImagingCore
  vtkvtkImagingStencil
  vtkvtkInteractionStyle
  vtkvtkRenderingContextOpenGL2
  vtkvtkRenderingCore
  vtkvtkRenderingFreeType
  vtkvtkRenderingGL2PSOpenGL2
  vtkvtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
  message("Skipping ImageStencil: ${VTK_NOT_FOUND_MESSAGE}")
  return ()
endif()
message (STATUS "VTK_VERSION: ${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
  # old system
  include(${VTK_USE_FILE})
  add_executable(ImageStencil MACOSX_BUNDLE ImageStencil.cxx )
  target_link_libraries(ImageStencil PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(ImageStencil MACOSX_BUNDLE ImageStencil.cxx )
  target_link_libraries(ImageStencil PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS ImageStencil
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build ImageStencil

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

cd ImageStencil/build

If VTK is installed:

cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

make

and run it:

./ImageStencil

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.