ITK  5.2.0
Insight Toolkit
Examples/IO/ImageReadWrite.cxx
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* Licensed under the Apache License, Version 2.0 (the "License");
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// Software Guide : BeginLatex
//
// The classes responsible for reading and writing images are located at the
// beginning and end of the data processing pipeline. These classes are
// known as data sources (readers) and data sinks (writers).
// Generally speaking they are referred to as filters, although readers have
// no pipeline input and writers have no pipeline output.
//
// The reading of images is managed by the class \doxygen{ImageFileReader}
// while writing is performed by the class \doxygen{ImageFileWriter}. These
// two classes are independent of any particular file format. The actual low
// level task of reading and writing specific file formats is done behind
// the scenes by a family of classes of type \doxygen{ImageIO}.
//
// The first step for performing reading and writing is to include the
// following headers.
//
// \index{itk::ImageFileReader|textbf}
// \index{itk::ImageFileReader!header}
//
// \index{itk::ImageFileWriter|textbf}
// \index{itk::ImageFileWriter!header}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
// Software Guide : EndCodeSnippet
#include "itkImage.h"
int
main(int argc, char ** argv)
{
// Verify the number of parameters in the command line
if (argc < 3)
{
std::cerr << "Usage: " << std::endl;
std::cerr << argv[0] << " inputImageFile outputImageFile " << std::endl;
return EXIT_FAILURE;
}
// Software Guide : BeginLatex
//
// Then, as usual, a decision must be made about the type of pixel used to
// represent the image processed by the pipeline. Note that when reading
// and writing images, the pixel type of the image \textbf{is not
// necessarily} the same as the pixel type stored in the file. Your
// choice of the pixel type (and hence template parameter) should be
// driven mainly by two considerations:
//
// \begin{itemize}
// \item It should be possible to cast the pixel type in the file to
// the pixel type you select. This casting will be performed using the
// standard C-language rules, so you will have to make sure that the
// conversion does not result in information being lost.
// \item The pixel type in memory should be appropriate to the type of
// processing you intend to apply on the images.
// \end{itemize}
//
// A typical selection for medical images is illustrated in
// the following lines.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using PixelType = short;
constexpr unsigned int Dimension = 2;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Note that the dimension of the image in memory should match that of
// the image in the file. There are a couple of special cases in which this
// condition may be relaxed, but in general it is better to ensure that
// both dimensions match.
//
// We can now instantiate the types of the reader and writer. These two
// classes are parameterized over the image type.
//
// \index{itk::ImageFileReader!Instantiation}
// \index{itk::ImageFileWriter!Instantiation}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using ReaderType = itk::ImageFileReader<ImageType>;
using WriterType = itk::ImageFileWriter<ImageType>;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Then, we create one object of each type using the New() method and
// assign the result to a \doxygen{SmartPointer}.
//
// \index{itk::ImageFileReader!New()}
// \index{itk::ImageFileWriter!New()}
// \index{itk::ImageFileReader!SmartPointer}
// \index{itk::ImageFileWriter!SmartPointer}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
ReaderType::Pointer reader = ReaderType::New();
WriterType::Pointer writer = WriterType::New();
// Software Guide : EndCodeSnippet
// Here we recover the file names from the command line arguments
//
const char * inputFilename = argv[1];
const char * outputFilename = argv[2];
// Software Guide : BeginLatex
//
// The name of the file to be read or written is passed to the
// SetFileName() method.
//
// \index{itk::ImageFileReader!SetFileName()}
// \index{itk::ImageFileWriter!SetFileName()}
// \index{SetFileName()!itk::ImageFileReader}
// \index{SetFileName()!itk::ImageFileWriter}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
reader->SetFileName(inputFilename);
writer->SetFileName(outputFilename);
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// We can now connect these readers and writers to filters to create a
// pipeline. For example, we can create a short pipeline by passing
// the output of the reader directly to the input of the writer.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
writer->SetInput(reader->GetOutput());
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// At first glance this may look like a quite useless program, but it is
// actually implementing a powerful file format conversion tool! The
// execution of the pipeline is triggered by the invocation of the
// \code{Update()} methods in one of the final objects. In this case, the
// final data pipeline object is the writer. It is a wise practice of
// defensive programming to insert any \code{Update()} call inside a
// \code{try/catch} block in case exceptions are thrown during the
// execution of the pipeline.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
try
{
writer->Update();
}
catch (const itk::ExceptionObject & err)
{
std::cerr << "ExceptionObject caught !" << std::endl;
std::cerr << err << std::endl;
return EXIT_FAILURE;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Note that exceptions should only be caught by pieces of code that know
// what to do with them. In a typical application this \code{catch} block
// should probably reside in the GUI code. The action on the \code{catch}
// block could inform the user about the failure of the IO operation.
//
// The IO architecture of the toolkit makes it possible to avoid explicit
// specification of the file format used to read or write
// images.\footnote{In this example no file format is specified; this
// program can be used as a general file conversion utility.} The object
// factory mechanism enables the ImageFileReader and ImageFileWriter to
// determine (at run-time) which file format it is working
// with. Typically, file formats are chosen based on the filename
// extension, but the architecture supports arbitrarily complex processes
// to determine whether a file can be read or written. Alternatively, the
// user can specify the data file format by explicit instantiation and
// assignment of the appropriate \doxygen{ImageIO} subclass.
//
// For historical reasons and as a convenience to the user, the
// \doxygen{ImageFileWriter} also has a \code{Write()} method that is
// aliased to the \code{Update()} method. You can in principle use either
// of them but \code{Update()} is recommended since \code{Write()} may be
// deprecated in the future.
//
// Software Guide : EndLatex
return EXIT_SUCCESS;
}
itkImageFileReader.h
itkImage.h
itk::ImageFileReader
Data source that reads image data from a single file.
Definition: itkImageFileReader.h:75
itk::ImageFileWriter
Writes image data to a single file.
Definition: itkImageFileWriter.h:87
itkImageFileWriter.h
itk::Image
Templated n-dimensional image class.
Definition: itkImage.h:86
itk::GTest::TypedefsAndConstructors::Dimension2::Dimension
constexpr unsigned int Dimension
Definition: itkGTestTypedefsAndConstructors.h:44