NeighborhoodIterators3.cxxΒΆ
Example source code (NeighborhoodIterators3.cxx):
#include "otbImage.h"
#include "otbImageFileReader.h"
#include "otbImageFileWriter.h"
#include "itkUnaryFunctorImageFilter.h"
#include "itkRescaleIntensityImageFilter.h"
#include "itkConstNeighborhoodIterator.h"
#include "itkImageRegionIterator.h"
// This example illustrates a technique for improving the efficiency of
// neighborhood calculations by eliminating unnecessary bounds checking. As
// described in Section~\ref{sec:NeighborhoodIterators}, the neighborhood
// iterator automatically enables or disables bounds checking based on the
// iteration region in which it is initialized. By splitting our image into
// boundary and non-boundary regions, and then processing each region using a
// different neighborhood iterator, the algorithm will only perform
// bounds-checking on those pixels for which it is actually required. This
// trick can provide a significant speedup for simple algorithms such as our
// Sobel edge detection, where iteration speed is a critical.
//
// Splitting the image into the necessary regions is an easy task when you use
// the \doxygen{itk}{ImageBoundaryFacesCalculator}. The face
// calculator is so named because it returns a list of the ``faces'' of the ND
// dataset. Faces are those regions whose pixels all lie within a distance $d$
// from the boundary, where $d$ is the radius of the neighborhood stencil used
// for the numerical calculations. In other words, faces are those regions
// where a neighborhood iterator of radius $d$ will always overlap the boundary
// of the image. The face calculator also returns the single \emph{inner}
// region, in which out-of-bounds values are never required and bounds checking
// is not necessary.
//
// The face calculator object is defined in \code{itkNeighborhoodAlgorithm.h}.
// We include this file in addition to those from the previous two examples.
#include "itkSobelOperator.h"
#include "itkNeighborhoodInnerProduct.h"
#include "itkNeighborhoodAlgorithm.h"
int main(int argc, char* argv[])
{
if (argc < 4)
{
std::cerr << "Missing parameters. " << std::endl;
std::cerr << "Usage: " << std::endl;
std::cerr << argv[0] << " inputImageFile outputImageFile direction" << std::endl;
return -1;
}
using PixelType = float;
using ImageType = otb::Image<PixelType, 2>;
using ReaderType = otb::ImageFileReader<ImageType>;
using NeighborhoodIteratorType = itk::ConstNeighborhoodIterator<ImageType>;
using IteratorType = itk::ImageRegionIterator<ImageType>;
ReaderType::Pointer reader = ReaderType::New();
reader->SetFileName(argv[1]);
try
{
reader->Update();
}
catch (itk::ExceptionObject& err)
{
std::cout << "ExceptionObject caught !" << std::endl;
std::cout << err << std::endl;
return -1;
}
ImageType::Pointer output = ImageType::New();
output->SetRegions(reader->GetOutput()->GetRequestedRegion());
output->Allocate();
itk::SobelOperator<PixelType, 2> sobelOperator;
sobelOperator.SetDirection(::atoi(argv[3]));
sobelOperator.CreateDirectional();
itk::NeighborhoodInnerProduct<ImageType> innerProduct;
// First we load the input image and create the output image and inner product
// function as in the previous examples. The image iterators will be created
// in a later step. Next we create a face calculator object. An empty list is
// created to hold the regions that will later on be returned by the face
// calculator.
using FaceCalculatorType = itk::NeighborhoodAlgorithm::ImageBoundaryFacesCalculator<ImageType>;
FaceCalculatorType faceCalculator;
FaceCalculatorType::FaceListType faceList;
// The face calculator function is invoked by passing it an image pointer, an
// image region, and a neighborhood radius. The image pointer is the same
// image used to initialize the neighborhood iterator, and the image region is
// the region that the algorithm is going to process. The radius is the radius
// of the iterator.
//
// Notice that in this case the image region is given as the region of the
// \emph{output} image and the image pointer is given as that of the
// \emph{input} image. This is important if the input and output images differ
// in size, i.e. the input image is larger than the output image. ITK
// and OTB image
// filters, for example, operate on data from the input image but only generate
// results in the \code{RequestedRegion} of the output image, which may be
// smaller than the full extent of the input.
faceList = faceCalculator(reader->GetOutput(), output->GetRequestedRegion(), sobelOperator.GetRadius());
// The face calculator has returned a list of $2N+1$ regions. The first element
// in the list is always the inner region, which may or may not be important
// depending on the application. For our purposes it does not matter because
// all regions are processed the same way. We use an iterator to traverse the
// list of faces.
FaceCalculatorType::FaceListType::iterator fit;
// We now rewrite the main loop of the previous example so that each region in the
// list is processed by a separate iterator. The iterators \code{it} and
// \code{out} are reinitialized over each region in turn. Bounds checking is
// automatically enabled for those regions that require it, and disabled for
// the region that does not.
IteratorType out;
NeighborhoodIteratorType it;
for (fit = faceList.begin(); fit != faceList.end(); ++fit)
{
it = NeighborhoodIteratorType(sobelOperator.GetRadius(), reader->GetOutput(), *fit);
out = IteratorType(output, *fit);
for (it.GoToBegin(), out.GoToBegin(); !it.IsAtEnd(); ++it, ++out)
{
out.Set(innerProduct(it, sobelOperator));
}
}
// The output is written as before. Results for this example are the same as
// the previous example. You may not notice the speedup except on larger
// images. When moving to 3D and higher dimensions, the effects are greater
// because the volume to surface area ratio is usually larger. In other
// words, as the number of interior pixels increases relative to the number of
// face pixels, there is a corresponding increase in efficiency from disabling
// bounds checking on interior pixels.
using WritePixelType = unsigned char;
using WriteImageType = otb::Image<WritePixelType, 2>;
using WriterType = otb::ImageFileWriter<WriteImageType>;
using RescaleFilterType = itk::RescaleIntensityImageFilter<ImageType, WriteImageType>;
RescaleFilterType::Pointer rescaler = RescaleFilterType::New();
rescaler->SetOutputMinimum(0);
rescaler->SetOutputMaximum(255);
rescaler->SetInput(output);
WriterType::Pointer writer = WriterType::New();
writer->SetFileName(argv[2]);
writer->SetInput(rescaler->GetOutput());
try
{
writer->Update();
}
catch (itk::ExceptionObject& err)
{
std::cout << "ExceptionObject caught !" << std::endl;
std::cout << err << std::endl;
return -1;
}
return EXIT_SUCCESS;
}