# ICAExample.cxx¶

Example usage:

./ICAExample Input/wv2_cannes_8bands.tif \
Output/FastICAOutput.tif \
Output/InverseFastICAOutput.tif \
Output/FastICA-input-pretty.png \
Output/FastICA-output-pretty.png \
Output/FastICA-invoutput-pretty.png \
8 \
20 \
1.


Example source code (ICAExample.cxx):

#include "otbVectorImage.h"
#include "otbImageFileWriter.h"
#include "otbPrintableImageFilter.h"

// This example illustrates the use of the
// \doxygen{otb}{FastICAImageFilter}.
// This filter computes a Fast Independent Components Analysis transform.
//
// Like Principal Components Analysis, Independent Component Analysis
// \cite{jutten1991blind} computes a set of
// orthogonal linear combinations, but the criterion of Fast ICA is
// different: instead of maximizing variance, it tries to maximize
// statistical independence between components.
//
// In the Fast ICA algorithm \cite{hyvarinen1999fast},
// statistical independence is measured by evaluating non-Gaussianity
// of the components, and the maximization is done in an iterative way.

// The first step required to use this filter is to include its header file.

#include "otbFastICAImageFilter.h"

int main(int itkNotUsed(argc), char* argv[])
{
using PixelType                          = double;
const unsigned int Dimension             = 2;
const char*        inputFileName         = argv;
const char*        outputFilename        = argv;
const char*        outputInverseFilename = argv;
const unsigned int numberOfPrincipalComponentsRequired(atoi(argv));
const char*        inpretty      = argv;
const char*        outpretty     = argv;
const char*        invoutpretty  = argv;
unsigned int       numIterations = atoi(argv);
double             mu            = atof(argv);

// We start by defining the types for the images, the reader, and
// the writer. We choose to work with a \doxygen{otb}{VectorImage},
// since we will produce a multi-channel image (the independent
// components) from a multi-channel input image.

using ImageType  = otb::VectorImage<PixelType, Dimension>;
using WriterType = otb::ImageFileWriter<ImageType>;
// We instantiate now the image reader and we set the image file name.

// We define the type for the filter. It is templated over the input
// and the output image types and also the transformation direction. The
// internal structure of this filter is a filter-to-filter like structure.
// We can now the instantiate the filter.

using FastICAFilterType                  = otb::FastICAImageFilter<ImageType, ImageType, otb::Transform::FORWARD>;
FastICAFilterType::Pointer FastICAfilter = FastICAFilterType::New();

// We then set the number of independent
// components required as output. We can choose to get less ICs than
// the number of input bands.

FastICAfilter->SetNumberOfPrincipalComponentsRequired(numberOfPrincipalComponentsRequired);

// We set the number of iterations of the ICA algorithm.

FastICAfilter->SetNumberOfIterations(numIterations);

// We also set the $\mu$ parameter.

FastICAfilter->SetMu(mu);

// We now instantiate the writer and set the file name for the
// output image.

WriterType::Pointer writer = WriterType::New();
writer->SetFileName(outputFilename);
// We finally plug the pipeline and trigger the ICA computation with
// the method \code{Update()} of the writer.

writer->SetInput(FastICAfilter->GetOutput());

writer->Update();

// \doxygen{otb}{FastICAImageFilter} allows also to compute inverse
// transformation from ICA coefficients. In reverse mode, the
// covariance matrix or the transformation matrix
// (which may not be square) has to be given.

using InvFastICAFilterType              = otb::FastICAImageFilter<ImageType, ImageType, otb::Transform::INVERSE>;
InvFastICAFilterType::Pointer invFilter = InvFastICAFilterType::New();

invFilter->SetMeanValues(FastICAfilter->GetMeanValues());
invFilter->SetStdDevValues(FastICAfilter->GetStdDevValues());
invFilter->SetTransformationMatrix(FastICAfilter->GetTransformationMatrix());
invFilter->SetPCATransformationMatrix(FastICAfilter->GetPCATransformationMatrix());
invFilter->SetInput(FastICAfilter->GetOutput());

WriterType::Pointer invWriter = WriterType::New();
invWriter->SetFileName(outputInverseFilename);
invWriter->SetInput(invFilter->GetOutput());

invWriter->Update();

// Figure~\ref{fig:FastICA_FILTER} shows the result of applying forward
// and reverse FastICA transformation to a 8 bands Worldview2 image.
// \begin{figure}
// \center
// \includegraphics[width=0.32\textwidth]{FastICA-input-pretty.eps}
// \includegraphics[width=0.32\textwidth]{FastICA-output-pretty.eps}
// \includegraphics[width=0.32\textwidth]{FastICA-invoutput-pretty.eps}
// \itkcaption[PCA Filter (forward trasnformation)]{Result of applying the
// \doxygen{otb}{FastICAImageFilter} to an image. From left
// to right:
// original image, color composition with first three independent
// components and output of the
// inverse mode (the input RGB image).}
// \label{fig:FastICA_FILTER}
// \end{figure}

// This is for rendering in software guide
using PrintFilterType = otb::PrintableImageFilter<ImageType, ImageType>;
using VisuImageType   = PrintFilterType::OutputImageType;
using VisuWriterType  = otb::ImageFileWriter<VisuImageType>;

PrintFilterType::Pointer inputPrintFilter        = PrintFilterType::New();
PrintFilterType::Pointer outputPrintFilter       = PrintFilterType::New();
PrintFilterType::Pointer invertOutputPrintFilter = PrintFilterType::New();
VisuWriterType::Pointer  inputVisuWriter         = VisuWriterType::New();
VisuWriterType::Pointer  outputVisuWriter        = VisuWriterType::New();
VisuWriterType::Pointer  invertOutputVisuWriter  = VisuWriterType::New();

inputPrintFilter->SetChannel(5);
inputPrintFilter->SetChannel(3);
inputPrintFilter->SetChannel(2);
outputPrintFilter->SetInput(FastICAfilter->GetOutput());
outputPrintFilter->SetChannel(1);
outputPrintFilter->SetChannel(2);
outputPrintFilter->SetChannel(3);
invertOutputPrintFilter->SetInput(invFilter->GetOutput());
invertOutputPrintFilter->SetChannel(5);
invertOutputPrintFilter->SetChannel(3);
invertOutputPrintFilter->SetChannel(2);

inputVisuWriter->SetInput(inputPrintFilter->GetOutput());
outputVisuWriter->SetInput(outputPrintFilter->GetOutput());
invertOutputVisuWriter->SetInput(invertOutputPrintFilter->GetOutput());

inputVisuWriter->SetFileName(inpretty);
outputVisuWriter->SetFileName(outpretty);
invertOutputVisuWriter->SetFileName(invoutpretty);

inputVisuWriter->Update();
outputVisuWriter->Update();
invertOutputVisuWriter->Update();

return EXIT_SUCCESS;
}