ImageMagnitude

Description¶

There are two ways to convert images to greyscale: * vtkImageLuminance uses the [luminance equation](http://www.wikipedia.org/wiki/Luma_(video) for properly weighting the R, G, and B components; * vtkImageMagnitude does a simple sum-of-squares computation of the components (i.e. the Euclidean norm -- not the quadratic mean, and is meant for vector data.

For an example of usage of the vtkImageLuminance filter, see ImageLuminance.

Question

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

Code¶

ImageMagnitude.cxx

#include <vtkImageActor.h>
#include <vtkImageCanvasSource2D.h>
#include <vtkImageMagnitude.h>
#include <vtkImageMapper3D.h>
#include <vtkInteractorStyleImage.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

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

  // Create an image of a rectangle.
  vtkNew<vtkImageCanvasSource2D> source;
  source->SetScalarTypeToUnsignedChar();
  source->SetNumberOfScalarComponents(3);
  source->SetExtent(0, 200, 0, 200, 0, 0);

  // Clear the image.
  source->SetDrawColor(0, 0, 0);
  source->FillBox(0, 200, 0, 200);

  // Draw a red box.
  source->SetDrawColor(255, 0, 0);
  source->FillBox(100, 120, 100, 120);
  source->Update();

  vtkNew<vtkImageMagnitude> magnitudeFilter;
  magnitudeFilter->SetInputConnection(source->GetOutputPort());
  magnitudeFilter->Update();

  // Create actors.
  vtkNew<vtkImageActor> originalActor;
  originalActor->GetMapper()->SetInputConnection(source->GetOutputPort());

  vtkNew<vtkImageActor> magnitudeActor;
  magnitudeActor->GetMapper()->SetInputConnection(
      magnitudeFilter->GetOutputPort());

  // Define viewport ranges.
  // (xmin, ymin, xmax, ymax)
  double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
  double magnitudeViewport[4] = {0.5, 0.0, 1.0, 1.0};

  // Setup renderers.
  vtkNew<vtkRenderer> originalRenderer;
  originalRenderer->SetViewport(originalViewport);
  originalRenderer->AddActor(originalActor);
  originalRenderer->ResetCamera();
  originalRenderer->SetBackground(
      colors->GetColor3d("CornflowerBlue").GetData());

  vtkNew<vtkRenderer> magnitudeRenderer;
  magnitudeRenderer->SetViewport(magnitudeViewport);
  magnitudeRenderer->AddActor(magnitudeActor);
  magnitudeRenderer->ResetCamera();
  magnitudeRenderer->SetBackground(.4, .5, .7);
  magnitudeRenderer->SetBackground(colors->GetColor3d("SteelBlue").GetData());

  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->SetSize(600, 300);
  renderWindow->AddRenderer(originalRenderer);
  renderWindow->AddRenderer(magnitudeRenderer);
  renderWindow->SetWindowName("ImageMagnitude");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  vtkNew<vtkInteractorStyleImage> style;

  renderWindowInteractor->SetInteractorStyle(style);

  renderWindowInteractor->SetRenderWindow(renderWindow);
  renderWindow->Render();
  renderWindowInteractor->Initialize();

  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ImageMagnitude)

find_package(VTK COMPONENTS 
  CommonColor
  CommonCore
  ImagingMath
  ImagingSources
  InteractionStyle
  RenderingContextOpenGL2
  RenderingCore
  RenderingFreeType
  RenderingGL2PSOpenGL2
  RenderingOpenGL2
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "ImageMagnitude: 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(ImageMagnitude MACOSX_BUNDLE ImageMagnitude.cxx )
  target_link_libraries(ImageMagnitude PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS ImageMagnitude
  MODULES ${VTK_LIBRARIES}
)

Download and Build ImageMagnitude¶

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

cd ImageMagnitude/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:

./ImageMagnitude

WINDOWS USERS

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