# 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).

Other Languages

See (Python)

Question

### 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 <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;
}

int scalarRange[2];
scalarRange[0] =
scalarRange[1] =
std::cout << "Range: " << scalarRange[0] << ", " << scalarRange[1]
<< std::endl;
// int middleSlice = (reader->GetOutput()->GetExtent()[5] -
//    2;

// Better to use this value.
auto middleSlice = 22;

// Work with triple images
auto cast = vtkSmartPointer<vtkImageCast>::New();
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);

auto originalActor = vtkSmartPointer<vtkImageActor>::New();
originalActor->GetMapper()->SetInputConnection(
originalColor->GetOutputPort());
originalActor->GetProperty()->SetInterpolationTypeToNearest();
originalActor->SetDisplayExtent(
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();
auto laplacianRenderer = vtkSmartPointer<vtkRenderer>::New();
auto enhancedRenderer = vtkSmartPointer<vtkRenderer>::New();

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);
}
}

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
vtkCommonCore
vtkCommonDataModel
vtkIOImage
vtkImagingColor
vtkImagingCore
vtkImagingGeneral
vtkImagingMath
vtkInteractionStyle
vtkRenderingContextOpenGL2
vtkRenderingCore
vtkRenderingFreeType
vtkRenderingGL2PSOpenGL2
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
target_link_libraries(EnhanceEdges PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS EnhanceEdges MODULES${VTK_LIBRARIES}
)
endif ()


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.