# ImageMagnitude

VTKExamples/Cxx/Images/ImageMagnitude

### Description¶

There are two ways to convert images to greyscale: * vtkImageLuminance uses the luminance equation 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

### Code¶

ImageMagnitude.cxx

#include <vtkSmartPointer.h>
#include <vtkImageData.h>
#include <vtkImageMapper3D.h>
#include <vtkImageCanvasSource2D.h>
#include <vtkImageMagnitude.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkImageActor.h>

int main(int, char *[])
{
// Create an image of a rectangle
vtkSmartPointer<vtkImageCanvasSource2D> source =
vtkSmartPointer<vtkImageCanvasSource2D>::New();
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();

vtkSmartPointer<vtkImageMagnitude> magnitudeFilter =
vtkSmartPointer<vtkImageMagnitude>::New();
magnitudeFilter->SetInputConnection(source->GetOutputPort());
magnitudeFilter->Update();

// Create actors
vtkSmartPointer<vtkImageActor> originalActor =
vtkSmartPointer<vtkImageActor>::New();
originalActor->GetMapper()->SetInputConnection(
source->GetOutputPort());

vtkSmartPointer<vtkImageActor> magnitudeActor =
vtkSmartPointer<vtkImageActor>::New();
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
vtkSmartPointer<vtkRenderer> originalRenderer =
vtkSmartPointer<vtkRenderer>::New();
originalRenderer->SetViewport(originalViewport);
originalRenderer->ResetCamera();
originalRenderer->SetBackground(.4, .5, .6);

vtkSmartPointer<vtkRenderer> magnitudeRenderer =
vtkSmartPointer<vtkRenderer>::New();
magnitudeRenderer->SetViewport(magnitudeViewport);
magnitudeRenderer->ResetCamera();
magnitudeRenderer->SetBackground(.4, .5, .7);

vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->SetSize(600, 300);

vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
vtkSmartPointer<vtkInteractorStyleImage> style =
vtkSmartPointer<vtkInteractorStyleImage>::New();

renderWindowInteractor->SetInteractorStyle(style);

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

renderWindowInteractor->Start();

return EXIT_SUCCESS;
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ImageMagnitude)

find_package(VTK COMPONENTS
vtkCommonCore
vtkCommonDataModel
vtkImagingMath
vtkImagingSources
vtkInteractionStyle
vtkRenderingContextOpenGL2
vtkRenderingCore
vtkRenderingFreeType
vtkRenderingGL2PSOpenGL2
vtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
message("Skipping ImageMagnitude: ${VTK_NOT_FOUND_MESSAGE}") return () endif() message (STATUS "VTK_VERSION:${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
# old system
include(${VTK_USE_FILE}) add_executable(ImageMagnitude MACOSX_BUNDLE ImageMagnitude.cxx ) target_link_libraries(ImageMagnitude PRIVATE${VTK_LIBRARIES})
else ()
# include all components
target_link_libraries(ImageMagnitude PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS ImageMagnitude MODULES${VTK_LIBRARIES}
)
endif ()


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.