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ImageMagnify

vtk-examples/Cxx/Images/ImageMagnify


Description

vtkImageMagnify increases the dimensions of an image by integral magnification factors. It also adjusts the spacing of the pixels so that the magnified image covers the same region as the original image. To stretch the image, the pixel spacing needs to be adjusted. This example uses vtkImageChangeInformation to modify the magnified image's spacing. The result is an image that has increased numbers of pixels and is stretched in the magnified directions.

Question

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

Code

ImageMagnify.cxx

#include <vtkImageActor.h>
#include <vtkImageChangeInformation.h>
#include <vtkImageData.h>
#include <vtkImageMagnify.h>
#include <vtkImageMapper3D.h>
#include <vtkInteractorStyleImage.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPNGReader.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

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

  // Handle the arguments
  if (argc < 2)
  {
    std::cout << "Required arguments: filename.png e.g. Gourds.png"
              << std::endl;
    return EXIT_FAILURE;
  }

  // Read the image
  vtkNew<vtkPNGReader> reader;
  reader->SetFileName(argv[1]);

  // Increase the dimensions of the image
  vtkNew<vtkImageMagnify> magnifyFilter;
  magnifyFilter->SetInputConnection(reader->GetOutputPort());
  magnifyFilter->SetMagnificationFactors(2, 1, 1);
  magnifyFilter->Update();

  // Adjust the spacing of the magnified image. This will stretch the
  // image
  vtkNew<vtkImageChangeInformation> changeFilter;
  changeFilter->SetInputConnection(magnifyFilter->GetOutputPort());
  changeFilter->SetSpacingScale(magnifyFilter->GetMagnificationFactors()[0],
                                magnifyFilter->GetMagnificationFactors()[1],
                                magnifyFilter->GetMagnificationFactors()[2]);

  vtkNew<vtkImageActor> originalActor;
  originalActor->GetMapper()->SetInputConnection(reader->GetOutputPort());

  vtkNew<vtkImageActor> magnifiedActor;
  magnifiedActor->GetMapper()->SetInputConnection(
      changeFilter->GetOutputPort());

  // Define viewport ranges
  // (xmin, ymin, xmax, ymax)
  double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
  double magnifiedViewport[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> magnifiedRenderer;
  magnifiedRenderer->SetViewport(magnifiedViewport);
  magnifiedRenderer->AddActor(magnifiedActor);
  magnifiedRenderer->ResetCamera();
  magnifiedRenderer->SetBackground(colors->GetColor3d("SteelBlue").GetData());

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

  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(ImageMagnify)

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

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

Download and Build ImageMagnify

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

cd ImageMagnify/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:

./ImageMagnify

WINDOWS USERS

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