ITK  5.4.0 Insight Toolkit
Examples/Iterators/NeighborhoodIterators6.cxx
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#include "itkImage.h"
// Software Guide : BeginLatex
//
// Some image processing routines do not need to visit every pixel in an
// image. Flood-fill and connected-component algorithms, for example, only
// visit pixels that are locally connected to one another. Algorithms
// such as these can be efficiently written using the random access
// capabilities of the neighborhood iterator.
//
// The following example finds local minima. Given a seed point, we can
// search the neighborhood of that point and pick the smallest value $m$.
// While $m$ is not at the center of our current neighborhood, we move in the
// direction of $m$ and repeat the analysis. Eventually we discover a local
// minimum and stop. This algorithm is made trivially simple in ND using an
// ITK neighborhood iterator.
//
// To illustrate the process, we create an image that descends everywhere to a
// single minimum: a positive distance transform to a point. The details of
// creating the distance transform are not relevant to the discussion of
// neighborhood iterators, but can be found in the source code of this
// example. Some noise has been added to the distance transform image for
//
// Software Guide : EndLatex
int
main(int argc, char ** argv)
{
if (argc < 4)
{
std::cerr << "Missing parameters. " << std::endl;
std::cerr << "Usage: " << std::endl;
std::cerr << argv[0] << " outputImageFile startX startY" << std::endl;
return EXIT_FAILURE;
}
using PixelType = float;
using ImageType = itk::Image<PixelType, 2>;
using NeighborhoodIteratorType = itk::NeighborhoodIterator<ImageType>;
using FastMarchingFilterType =
auto fastMarching = FastMarchingFilterType::New();
using NodeContainer = FastMarchingFilterType::NodeContainer;
using NodeType = FastMarchingFilterType::NodeType;
auto seeds = NodeContainer::New();
ImageType::IndexType seedPosition;
seedPosition[0] = 128;
seedPosition[1] = 128;
constexpr double initialDistance = 1.0;
NodeType node;
const double seedValue = -initialDistance;
ImageType::SizeType size = { { 256, 256 } };
node.SetValue(seedValue);
node.SetIndex(seedPosition);
seeds->Initialize();
seeds->InsertElement(0, node);
fastMarching->SetTrialPoints(seeds);
fastMarching->SetSpeedConstant(1.0);
noise->SetSize(size.m_InternalArray);
noise->SetMin(-.7);
noise->SetMax(.8);
try
{
fastMarching->SetOutputSize(size);
fastMarching->Update();
}
catch (const itk::ExceptionObject & excep)
{
std::cerr << "Exception caught !" << std::endl;
std::cerr << excep << std::endl;
return EXIT_FAILURE;
}
// Software Guide : BeginLatex
//
// The variable \code{input} is the pointer to the distance transform image.
// The local minimum algorithm is initialized with a seed point read from
// the command line.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
index[0] = std::stoi(argv[2]);
index[1] = std::stoi(argv[3]);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Next we create the neighborhood iterator and position it at the seed
// point.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
it.SetLocation(index);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Searching for the local minimum involves finding the minimum in the
// current neighborhood, then shifting the neighborhood in the direction of
// that minimum. The \code{for} loop below records the \doxygen{Offset} of
// the minimum neighborhood pixel. The neighborhood iterator is then moved
// using that offset. When a local minimum is detected, \code{flag} will
// remain false and the \code{while} loop will exit. Note that this code is
// valid for an image of any dimensionality.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
bool flag = true;
while (flag == true)
{
NeighborhoodIteratorType::OffsetType nextMove;
nextMove.Fill(0);
flag = false;
PixelType min = it.GetCenterPixel();
for (unsigned int i = 0; i < it.Size(); ++i)
{
if (it.GetPixel(i) < min)
{
min = it.GetPixel(i);
nextMove = it.GetOffset(i);
flag = true;
}
}
it.SetCenterPixel(255.0);
it += nextMove;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Figure~\ref{fig:NeighborhoodExample6} shows the results of the algorithm
// for several seed points. The white line is the path of the iterator from
// the seed point to the minimum in the center of the image. The effect of
// the additive noise is visible as the small perturbations in the paths.
//
// \begin{figure} \centering
// \includegraphics[width=0.3\textwidth]{NeighborhoodIterators6a}
// \includegraphics[width=0.3\textwidth]{NeighborhoodIterators6b}
// \includegraphics[width=0.3\textwidth]{NeighborhoodIterators6c}
// \itkcaption[Finding local minima]{Paths traversed by the neighborhood
// iterator from different seed points to the local minimum.
// The true minimum is at the center
// of the image. The path of the iterator is shown in white. The effect of
// noise in the image is seen as small perturbations in each path. }
// \protect\label{fig:NeighborhoodExample6} \end{figure}
//
// Software Guide : EndLatex
using WritePixelType = unsigned char;
using WriteImageType = itk::Image<WritePixelType, 2>;
using RescaleFilterType =
auto rescaler = RescaleFilterType::New();
rescaler->SetOutputMinimum(0);
rescaler->SetOutputMaximum(255);
rescaler->SetInput(input);
auto writer = WriterType::New();
writer->SetFileName(argv[1]);
writer->SetInput(rescaler->GetOutput());
try
{
writer->Update();
}
catch (const itk::ExceptionObject & err)
{
std::cerr << "ExceptionObject caught !" << std::endl;
std::cerr << err << std::endl;
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
Pointer
SmartPointer< Self > Pointer
itkNeighborhoodIterator.h
itk::GTest::TypedefsAndConstructors::Dimension2::SizeType
ImageBaseType::SizeType SizeType
Definition: itkGTestTypedefsAndConstructors.h:49
itkImage.h
itk::SmartPointer< Self >
itkFastMarchingImageFilter.h
itk::GTest::TypedefsAndConstructors::Dimension2::IndexType
ImageBaseType::IndexType IndexType
Definition: itkGTestTypedefsAndConstructors.h:50
itk::ImageFileWriter
Writes image data to a single file.
Definition: itkImageFileWriter.h:88
itk::FastMarchingImageFilter
Solve an Eikonal equation using Fast Marching.
Definition: itkFastMarchingImageFilter.h:136
itkRescaleIntensityImageFilter.h
itkImageFileWriter.h
itk::NeighborhoodIterator
Defines iteration of a local N-dimensional neighborhood of pixels across an itk::Image.
Definition: itkNeighborhoodIterator.h:212