EnhanceEdges
VTKExamples/Cxx/ImageProcessing/EnhanceEdges
Description¶
High-pass filters can also be used to compress the range of an image. Since low frequencies account for much of the dynamic range of an image but carry little information, a high-pass filter can significantly decrease an image’s scalar range and emphasize hidden details. The Laplacian filter, which is a second derivative operation, is one implementation of a high-pass filter. It eliminates constant and low frequencies leaving only high-frequency edges. The output of the Laplacian can be subtracted from the original image to produce edge enhancement or sharpening of an image.
This example subtracts the Laplacian (middle) from the original image (left) resulting in edge enhancement or a sharpening operation (right).
Info
See this figure in Chapter 10 the VTK Textbook.
Other Languages
See (Python)
Code¶
EnhanceEdges.cxx
#include <vtkCamera.h> #include <vtkDataArray.h> #include <vtkImageActor.h> #include <vtkImageCast.h> #include <vtkImageData.h> #include <vtkImageLaplacian.h> #include <vtkImageMapper3D.h> #include <vtkImageMapToWindowLevelColors.h> #include <vtkImageMathematics.h> #include <vtkImageProperty.h> #include <vtkImageReader2.h> #include <vtkImageReader2Factory.h> #include <vtkImageThreshold.h> #include <vtkInteractorStyleImage.h> #include <vtkPointData.h> #include <vtkRenderer.h> #include <vtkRenderWindow.h> #include <vtkRenderWindowInteractor.h> #include <vtkSmartPointer.h> #include <vector> int main (int argc, char *argv[]) { // Verify input arguments if ( argc != 2 ) { std::cout << "Usage: " << argv[0] << " Filename" << std::endl; return EXIT_FAILURE; } // Read the image vtkSmartPointer<vtkImageReader2Factory> readerFactory = vtkSmartPointer<vtkImageReader2Factory>::New(); vtkSmartPointer<vtkImageReader2> reader = readerFactory->CreateImageReader2(argv[1]); reader->SetFileName(argv[1]); reader->Update(); int scalarRange[2]; scalarRange[0] = reader->GetOutput()->GetPointData()->GetScalars()->GetRange()[0]; scalarRange[1] = reader->GetOutput()->GetPointData()->GetScalars()->GetRange()[1]; std::cout << "Range: " << scalarRange[0] << ", " << scalarRange[1] << std::endl; int middleSlice = (reader->GetOutput()->GetExtent()[5] - reader->GetOutput()->GetExtent()[4]) / 2; middleSlice = 22; // Work with triple images vtkSmartPointer<vtkImageCast> cast = vtkSmartPointer<vtkImageCast>::New(); cast->SetInputConnection(reader->GetOutputPort()); cast->SetOutputScalarTypeToDouble(); cast->Update(); vtkSmartPointer<vtkImageLaplacian> laplacian = vtkSmartPointer<vtkImageLaplacian>::New(); laplacian->SetInputConnection(cast->GetOutputPort()); laplacian->SetDimensionality(3); vtkSmartPointer<vtkImageMathematics> enhance = vtkSmartPointer<vtkImageMathematics>::New(); enhance->SetInputConnection(0, cast->GetOutputPort()); enhance->SetInputConnection(1, laplacian->GetOutputPort()); enhance->SetOperationToSubtract(); int colorWindow = (scalarRange[1] - scalarRange[0]); int colorLevel = colorWindow / 2; // Map the image through the lookup table vtkSmartPointer<vtkImageMapToWindowLevelColors> originalColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New(); originalColor->SetWindow(colorWindow); originalColor->SetLevel(colorLevel); originalColor->SetInputConnection(reader->GetOutputPort()); vtkSmartPointer<vtkImageActor> originalActor = vtkSmartPointer<vtkImageActor>::New(); originalActor->GetMapper()->SetInputConnection(originalColor->GetOutputPort()); originalActor->GetProperty()->SetInterpolationTypeToNearest(); originalActor->SetDisplayExtent( reader->GetDataExtent()[0], reader->GetDataExtent()[1], reader->GetDataExtent()[2], reader->GetDataExtent()[3], middleSlice, middleSlice); vtkSmartPointer<vtkImageMapToWindowLevelColors> laplacianColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New(); laplacianColor->SetWindow(1000); laplacianColor->SetLevel(0); laplacianColor->SetInputConnection(laplacian->GetOutputPort()); vtkSmartPointer<vtkImageActor> laplacianActor = vtkSmartPointer<vtkImageActor>::New(); laplacianActor->GetMapper()->SetInputConnection(laplacianColor->GetOutputPort()); laplacianActor->GetProperty()->SetInterpolationTypeToNearest(); laplacianActor->SetDisplayExtent(originalActor->GetDisplayExtent()); vtkSmartPointer<vtkImageMapToWindowLevelColors> enhancedColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New(); enhancedColor->SetWindow(colorWindow); enhancedColor->SetLevel(colorLevel); enhancedColor->SetInputConnection(enhance->GetOutputPort()); vtkSmartPointer<vtkImageActor> enhancedActor = vtkSmartPointer<vtkImageActor>::New(); enhancedActor->GetMapper()->SetInputConnection(enhancedColor->GetOutputPort()); enhancedActor->GetProperty()->SetInterpolationTypeToNearest(); enhancedActor->SetDisplayExtent(originalActor->GetDisplayExtent()); // Setup renderers vtkSmartPointer<vtkRenderer> originalRenderer = vtkSmartPointer<vtkRenderer>::New(); originalRenderer->AddActor(originalActor); vtkSmartPointer<vtkRenderer> laplacianRenderer = vtkSmartPointer<vtkRenderer>::New(); laplacianRenderer->AddActor(laplacianActor); vtkSmartPointer<vtkRenderer> enhancedRenderer = vtkSmartPointer<vtkRenderer>::New(); enhancedRenderer->AddActor(enhancedActor); std::vector<vtkSmartPointer<vtkRenderer> > renderers; renderers.push_back(originalRenderer); renderers.push_back(laplacianRenderer); renderers.push_back(enhancedRenderer); // Setup viewports for the renderers int rendererSize = 400; unsigned int xGridDimensions = 3; unsigned int yGridDimensions = 1; vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New(); renderWindow->SetSize( rendererSize * xGridDimensions, rendererSize * yGridDimensions); for (int row = 0; row < static_cast<int>(yGridDimensions); row++) { for (int col = 0; col < static_cast<int>(xGridDimensions); col++) { int index = row * xGridDimensions + col; // (xmin, ymin, xmax, ymax) double viewport[4] = { static_cast<double>(col) / xGridDimensions, static_cast<double>(yGridDimensions - (row + 1)) / yGridDimensions, static_cast<double>(col + 1) / xGridDimensions, static_cast<double>(yGridDimensions - row) / yGridDimensions}; renderers[index]->SetViewport(viewport); renderWindow->AddRenderer(renderers[index]); } } vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New(); vtkSmartPointer<vtkInteractorStyleImage> style = vtkSmartPointer<vtkInteractorStyleImage>::New(); renderWindowInteractor->SetInteractorStyle(style); renderWindowInteractor->SetRenderWindow(renderWindow); // Renderers share one camera renderWindow->Render(); renderers[0]->GetActiveCamera()->Dolly(1.5); renderers[0]->ResetCameraClippingRange(); for (size_t r = 1; r < renderers.size(); ++r) { renderers[r]->SetActiveCamera(renderers[0]->GetActiveCamera()); } renderWindowInteractor->Initialize(); renderWindowInteractor->Start(); return EXIT_SUCCESS; }
CMakeLists.txt¶
cmake_minimum_required(VERSION 3.3 FATAL_ERROR) project(EnhanceEdges) find_package(VTK COMPONENTS vtkCommonCore vtkCommonDataModel vtkIOImage vtkImagingColor vtkImagingCore vtkImagingGeneral vtkImagingMath vtkInteractionStyle vtkRenderingCore vtkRenderingFreeType vtkRenderingOpenGL2 QUIET) if (NOT VTK_FOUND) message("Skipping EnhanceEdges: ${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(EnhanceEdges MACOSX_BUNDLE EnhanceEdges.cxx ) target_link_libraries(EnhanceEdges PRIVATE ${VTK_LIBRARIES}) else () # include all components add_executable(EnhanceEdges MACOSX_BUNDLE EnhanceEdges.cxx ) target_link_libraries(EnhanceEdges PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS EnhanceEdges MODULES ${VTK_LIBRARIES} ) endif ()
Download and Build EnhanceEdges¶
Click here to download EnhanceEdges and its CMakeLists.txt file. Once the tarball EnhanceEdges.tar has been downloaded and extracted,
cd EnhanceEdges/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:
./EnhanceEdges
WINDOWS USERS
Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.