ExtractComponents

Description¶

This example separates an image into the red channel, the green channel, and the blue channel using vtkImageExtractComponents.

Seealso

For the reverse operation, see CombiningRGBChannels.

Question

If you have a question about this example, please use the VTK Discourse Forum

Code¶

ExtractComponents.cxx

#include <vtkImageActor.h>
#include <vtkImageExtractComponents.h>
#include <vtkImageMapper3D.h>
#include <vtkImageReader2.h>
#include <vtkImageReader2Factory.h>
#include <vtkInteractorStyleImage.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>

int main(int argc, char* argv[])
{
  vtkNew<vtkNamedColors> colors;

  // Verify command line arguments.
  if (argc != 2)
  {
    std::cout << "Usage: " << argv[0] << " InputFilename e.g. Gourds2.jpg"
              << std::endl;
    return EXIT_FAILURE;
  }

  // Read the image.
  vtkNew<vtkImageReader2Factory> readerFactory;
  vtkSmartPointer<vtkImageReader2> reader;
  reader.TakeReference(readerFactory->CreateImageReader2(argv[1]));
  reader->SetFileName(argv[1]);
  reader->Update();

  vtkNew<vtkImageExtractComponents> extractRedFilter;
  extractRedFilter->SetInputConnection(reader->GetOutputPort());
  extractRedFilter->SetComponents(0);
  extractRedFilter->Update();

  vtkNew<vtkImageExtractComponents> extractGreenFilter;
  extractGreenFilter->SetInputConnection(reader->GetOutputPort());
  extractGreenFilter->SetComponents(1);
  extractGreenFilter->Update();

  vtkNew<vtkImageExtractComponents> extractBlueFilter;
  extractBlueFilter->SetInputConnection(reader->GetOutputPort());
  extractBlueFilter->SetComponents(2);
  extractBlueFilter->Update();

  // Create actors
  vtkNew<vtkImageActor> inputActor;
  inputActor->GetMapper()->SetInputConnection(reader->GetOutputPort());

  vtkNew<vtkImageActor> redActor;
  redActor->GetMapper()->SetInputConnection(extractRedFilter->GetOutputPort());

  vtkNew<vtkImageActor> greenActor;
  greenActor->GetMapper()->SetInputConnection(
      extractGreenFilter->GetOutputPort());

  vtkNew<vtkImageActor> blueActor;
  blueActor->GetMapper()->SetInputConnection(
      extractBlueFilter->GetOutputPort());

  // Define viewport ranges.
  // (xmin, ymin, xmax, ymax)
  double inputViewport[4] = {0.0, 0.0, 0.25, 1.0};
  double redViewport[4] = {0.25, 0.0, 0.5, 1.0};
  double greenViewport[4] = {0.5, 0.0, 0.75, 1.0};
  double blueViewport[4] = {0.75, 0.0, 1.0, 1.0};

  // Setup renderers
  vtkNew<vtkRenderer> inputRenderer;
  inputRenderer->SetViewport(inputViewport);
  inputRenderer->AddActor(inputActor);
  inputRenderer->ResetCamera();
  inputRenderer->SetBackground(colors->GetColor3d("Snow").GetData());

  vtkNew<vtkRenderer> redRenderer;
  redRenderer->SetViewport(redViewport);
  redRenderer->AddActor(redActor);
  redRenderer->ResetCamera();
  redRenderer->SetBackground(colors->GetColor3d("Tomato").GetData());

  vtkNew<vtkRenderer> greenRenderer;
  greenRenderer->SetViewport(greenViewport);
  greenRenderer->AddActor(greenActor);
  greenRenderer->ResetCamera();
  greenRenderer->SetBackground(colors->GetColor3d("Mint").GetData());

  vtkNew<vtkRenderer> blueRenderer;
  blueRenderer->SetViewport(blueViewport);
  blueRenderer->AddActor(blueActor);
  blueRenderer->ResetCamera();
  blueRenderer->SetBackground(colors->GetColor3d("Peacock").GetData());

  // Setup render window
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->SetSize(1000, 250);
  renderWindow->AddRenderer(inputRenderer);
  renderWindow->AddRenderer(redRenderer);
  renderWindow->AddRenderer(greenRenderer);
  renderWindow->AddRenderer(blueRenderer);
  renderWindow->SetWindowName("ExtractComponents");

  // Setup render window interactor.
  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  vtkNew<vtkInteractorStyleImage> style;

  renderWindowInteractor->SetInteractorStyle(style);

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

  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ExtractComponents)

find_package(VTK COMPONENTS 
  CommonColor
  CommonCore
  IOImage
  ImagingCore
  InteractionStyle
  RenderingContextOpenGL2
  RenderingCore
  RenderingFreeType
  RenderingGL2PSOpenGL2
  RenderingOpenGL2
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "ExtractComponents: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
add_executable(ExtractComponents MACOSX_BUNDLE ExtractComponents.cxx )
  target_link_libraries(ExtractComponents PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS ExtractComponents
  MODULES ${VTK_LIBRARIES}
)

Download and Build ExtractComponents¶

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

cd ExtractComponents/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:

./ExtractComponents

WINDOWS USERS

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