ImageRegionIterator.cxx¶

Example usage:

./ImageRegionIterator Input/QB_Suburb.png Output/ImageRegionIteratorOutput.png 10 10 110 140


Example source code (ImageRegionIterator.cxx):

// \index{Iterators!speed}
// The \doxygen{itk}{ImageRegionIterator} is optimized for
// iteration speed and is the first choice for iterative, pixel-wise operations
// when location in the image is not
// important. ImageRegionIterator is the least specialized of the ITK
// image iterator classes.  It implements all of the methods described in the
// preceding section.
//
// The following example illustrates the use of
// \doxygen{itk}{ImageRegionConstIterator} and ImageRegionIterator.
// Most of the code constructs introduced apply to other ITK iterators as
// well. This simple application crops a subregion from an image by copying
// its pixel values into to a second, smaller image.
//
// \index{Iterators!and image regions}
// \index{itk::ImageRegionIterator!example of using|(}
// We begin by including the appropriate header files.

#include "otbImage.h"
#include "itkImageRegionIterator.h"
#include "otbImageFileWriter.h"

int main(int argc, char* argv[])
{
// Verify the number of parameters on the command line.
if (argc < 7)
{
std::cerr << "Missing parameters. " << std::endl;
std::cerr << "Usage: " << std::endl;
std::cerr << argv[0] << " inputImageFile outputImageFile startX startY sizeX sizeY" << std::endl;
return -1;
}

// Next we define a pixel type and corresponding image type. ITK iterator
// classes expect the image type as their template parameter.

const unsigned int Dimension = 2;

using PixelType = unsigned char;
using ImageType = otb::Image<PixelType, Dimension>;

using ConstIteratorType = itk::ImageRegionConstIterator<ImageType>;
using IteratorType      = itk::ImageRegionIterator<ImageType>;

using WriterType = otb::ImageFileWriter<ImageType>;

// Information about the subregion to copy is read from the command line. The
// subregion is defined by an \doxygen{itk}{ImageRegion} object, with a starting
// grid index and a size (Section~\ref{sec:ImageSection}).

ImageType::RegionType inputRegion;

ImageType::RegionType::IndexType inputStart;
ImageType::RegionType::SizeType  size;

inputStart[0] = ::atoi(argv[3]);
inputStart[1] = ::atoi(argv[4]);

size[0] = ::atoi(argv[5]);
size[1] = ::atoi(argv[6]);

inputRegion.SetSize(size);
inputRegion.SetIndex(inputStart);

// The destination region in the output image is defined using the input region
// size, but a different start index.  The starting index for the destination
// region is the corner of the newly generated image.

ImageType::RegionType outputRegion;

ImageType::RegionType::IndexType outputStart;

outputStart[0] = 0;
outputStart[1] = 0;

outputRegion.SetSize(size);
outputRegion.SetIndex(outputStart);

try
{
}
catch (itk::ExceptionObject& err)
{
std::cerr << "ExceptionObject caught !" << std::endl;
std::cerr << err << std::endl;
return -1;
}

// Check that the region is contained within the input image.
{
std::cerr << "Error" << std::endl;
std::cerr << "The region " << inputRegion << "is not contained within the input image region " << reader->GetOutput()->GetRequestedRegion() << std::endl;
return -1;
}

// After reading the input image and checking that the desired subregion is,
// in fact, contained in the input, we allocate an output image.  It is
// fundamental to set valid values to some of the basic image information
// during the copying process.
// In particular, the starting index of the output region
// is now filled up with zero values and the coordinates of the physical
// origin are computed as a shift from the origin of the input image. This is
// quite important since it will allow us to later
// register the extracted region against the original image.

ImageType::Pointer outputImage = ImageType::New();
outputImage->SetRegions(outputRegion);
double                        outputOrigin[Dimension];

for (unsigned int i = 0; i < Dimension; ++i)
{
outputOrigin[i] = inputOrigin[i] + spacing[i] * inputStart[i];
}

outputImage->SetSignedSpacing(spacing);
outputImage->SetOrigin(outputOrigin);
outputImage->Allocate();

// \index{Iterators!construction of} \index{Iterators!and image regions}
// The necessary images and region definitions are now in place.  All that is
// left to do is to create the iterators and perform the copy.  Note that image
// iterators are not accessed via smart pointers so they are light-weight
// objects that are instantiated on the stack.  Also notice how the input and
// output iterators are defined over the \emph{same corresponding region}.  Though the
// images are different sizes, they both contain the same target subregion.

IteratorType      outputIt(outputImage, outputRegion);

for (inputIt.GoToBegin(), outputIt.GoToBegin(); !inputIt.IsAtEnd(); ++inputIt, ++outputIt)
{
outputIt.Set(inputIt.Get());
}

// \index{Iterators!image dimensionality}
//  The \code{for} loop above is a common
// construct in ITK/OTB.  The beauty of these four lines of code is that they are
// equally valid for one, two, three, or even ten dimensional data, and no
// knowledge of the size of the image is necessary.  Consider the ugly
// alternative of ten nested \code{for} loops for traversing an image.

WriterType::Pointer writer = WriterType::New();
writer->SetFileName(argv[2]);
writer->SetInput(outputImage);

try
{
writer->Update();
}
catch (itk::ExceptionObject& err)
{
std::cerr << "ExceptionObject caught !" << std::endl;
std::cerr << err << std::endl;
return -1;
}

// Let's run this example on the image \code{QB\_Suburb.png} found
// in \code{Examples/Data}.  The command line arguments specify the
// input and output file names, then the $x$, $y$ origin and the $x$, $y$ size
// of the cropped subregion.
//
// \small
// \begin{verbatim}
// ImageRegionIterator QB_Suburb.png ImageRegionIteratorOutput.png 20 70 210 140
// \end{verbatim}
// \normalsize
//
// The output is the cropped subregion shown in
// Figure~\ref{fig:ImageRegionIteratorOutput}.
//
// \begin{figure}
// \centering
// \includegraphics[width=0.4\textwidth]{QB_Suburb.eps}
// \includegraphics[width=0.3\textwidth]{ImageRegionIteratorOutput.eps}
// \itkcaption[Copying an image subregion using ImageRegionIterator]{Cropping a
// region from an image.  The original image is shown at left.  The image on
// the right is the result of applying the ImageRegionIterator example code.}
// \protect\label{fig:ImageRegionIteratorOutput}
// \end{figure}
//
// \index{itk::ImageRegionIterator!example of using|)}

return EXIT_SUCCESS;
}