EnhanceEdges
VTKEx/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)
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¶
EnhanceEdges.cxx
#include <vector>
#include <vtkCamera.h>
#include <vtkDataArray.h>
#include <vtkImageActor.h>
#include <vtkImageCast.h>
#include <vtkImageData.h>
#include <vtkImageLaplacian.h>
#include <vtkImageMapToWindowLevelColors.h>
#include <vtkImageMapper3D.h>
#include <vtkImageMathematics.h>
#include <vtkImageProperty.h>
#include <vtkImageReader2.h>
#include <vtkImageReader2Factory.h>
#include <vtkImageThreshold.h>
#include <vtkInteractorStyleImage.h>
#include <vtkPointData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>
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
auto readerFactory = vtkSmartPointer<vtkImageReader2Factory>::New();
vtkSmartPointer<vtkImageReader2> reader;
reader.TakeReference(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;
// Better to use this value.
auto middleSlice = 22;
// Work with triple images
auto cast = vtkSmartPointer<vtkImageCast>::New();
cast->SetInputConnection(reader->GetOutputPort());
cast->SetOutputScalarTypeToDouble();
cast->Update();
auto laplacian = vtkSmartPointer<vtkImageLaplacian>::New();
laplacian->SetInputConnection(cast->GetOutputPort());
laplacian->SetDimensionality(3);
auto 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
auto originalColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New();
originalColor->SetWindow(colorWindow);
originalColor->SetLevel(colorLevel);
originalColor->SetInputConnection(reader->GetOutputPort());
auto 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);
auto laplacianColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New();
laplacianColor->SetWindow(1000);
laplacianColor->SetLevel(0);
laplacianColor->SetInputConnection(laplacian->GetOutputPort());
auto laplacianActor = vtkSmartPointer<vtkImageActor>::New();
laplacianActor->GetMapper()->SetInputConnection(
laplacianColor->GetOutputPort());
laplacianActor->GetProperty()->SetInterpolationTypeToNearest();
laplacianActor->SetDisplayExtent(originalActor->GetDisplayExtent());
auto enhancedColor = vtkSmartPointer<vtkImageMapToWindowLevelColors>::New();
enhancedColor->SetWindow(colorWindow);
enhancedColor->SetLevel(colorLevel);
enhancedColor->SetInputConnection(enhance->GetOutputPort());
auto enhancedActor = vtkSmartPointer<vtkImageActor>::New();
enhancedActor->GetMapper()->SetInputConnection(
enhancedColor->GetOutputPort());
enhancedActor->GetProperty()->SetInterpolationTypeToNearest();
enhancedActor->SetDisplayExtent(originalActor->GetDisplayExtent());
// Setup renderers
auto originalRenderer = vtkSmartPointer<vtkRenderer>::New();
originalRenderer->AddActor(originalActor);
auto laplacianRenderer = vtkSmartPointer<vtkRenderer>::New();
laplacianRenderer->AddActor(laplacianActor);
auto 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;
auto 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]);
}
}
auto renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
auto 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
vtkvtkCommonCore
vtkvtkCommonDataModel
vtkvtkIOImage
vtkvtkImagingColor
vtkvtkImagingCore
vtkvtkImagingGeneral
vtkvtkImagingMath
vtkvtkInteractionStyle
vtkvtkRenderingContextOpenGL2
vtkvtkRenderingCore
vtkvtkRenderingFreeType
vtkvtkRenderingGL2PSOpenGL2
vtkvtkRenderingOpenGL2 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.