Multispectral.cxx

Example usage:

./Multispectral Input/qb_RoadExtract.tif Output/qb_blue.tif Output/qb_shiftscale.tif

Example source code (Multispectral.cxx):

//  First, we are going to use \doxygen{otb}{VectorImage} instead of the now
// traditional \doxygen{otb}{Image}. So we include the required header:


// We also include some other header which will be useful later. Note that we
// are still using the \doxygen{otb}{Image} in this example for some of the
// output.

#include "otbImageFileReader.h"
#include "otbImageFileWriter.h"
#include "otbMultiToMonoChannelExtractROI.h"
#include "itkShiftScaleImageFilter.h"
#include "otbPerBandVectorImageFilter.h"

int main(int argc, char* argv[])
{
  if (argc != 4)
  {
    std::cerr << "Usage: " << argv[0] << " <input_filename> <output_extract> <output_shifted_scaled>" << std::endl;
  }

  // We want to read a multispectral image so we declare the image type and the
  // reader. As we have done in the previous example we get the filename from
  // the command line.

  using PixelType       = unsigned short;
  using VectorImageType = otb::VectorImage<PixelType, 2>;

  using ReaderType           = otb::ImageFileReader<VectorImageType>;
  ReaderType::Pointer reader = ReaderType::New();

  reader->SetFileName(argv[1]);

  //  Sometime, you need to process only one spectral band of the image. To get
  // only one of the spectral band we use the
  // \doxygen{otb}{MultiToMonoChannelExtractROI}. The declaration is as usual:

  using ExtractChannelType                   = otb::MultiToMonoChannelExtractROI<PixelType, PixelType>;
  ExtractChannelType::Pointer extractChannel = ExtractChannelType::New();
  //  We need to pass the parameters to the filter for the extraction. This
  // filter also allow extracting only a spatial subset of the image. However,
  // we will extract the whole channel in this case.
  //
  // To do that, we need to pass the desired region using the
  // \code{SetExtractionRegion()} (method such as \code{SetStartX},
  // \code{SetSizeX} are also available). We get the region from the reader with
  // the \code{GetLargestPossibleRegion()} method. Before doing that we need to
  // read the metadata from the file: this is done by calling the
  // \code{UpdateOutputInformation()} on the reader's output. The difference with the
  // \code{Update()} is that the pixel array is not allocated (yet !) and reduce
  // the memory usage.

  reader->UpdateOutputInformation();
  extractChannel->SetExtractionRegion(reader->GetOutput()->GetLargestPossibleRegion());

  //  We chose the channel number to extract (starting from 1) and we plug the
  // pipeline.

  extractChannel->SetChannel(3);
  extractChannel->SetInput(reader->GetOutput());

  //  To output this image, we need a writer. As the output of the
  // \doxygen{otb}{MultiToMonoChannelExtractROI} is a \doxygen{otb}{Image}, we
  // need to template the writer with this type.

  using ImageType            = otb::Image<PixelType, 2>;
  using WriterType           = otb::ImageFileWriter<ImageType>;
  WriterType::Pointer writer = WriterType::New();

  writer->SetFileName(argv[2]);
  writer->SetInput(extractChannel->GetOutput());

  writer->Update();

  // After this, we have a one band image that we can process with most OTB
  // filters.
  //
  // In some situation, you may want to apply the same process to all bands of
  // the image. You don't have to extract each band and process them separately.
  // There is several situations:
  //
  // \begin{itemize}
  // \item the filter (or the combination of filters) you want to use are doing
  // operations that are well defined for \doxygen{itk}{VariableLengthVector}
  // (which is the pixel type), then you don't have to do anything special.
  // \item if this is not working, you can look for the equivalent filter
  // specially designed for vector images.
  // \item some of the filter you need to use applies operations undefined for
  // \doxygen{itk}{VariableLengthVector}, then you can use the
  // \doxygen{otb}{PerBandVectorImageFilter} specially designed for this
  // purpose.
  // \end{itemize}
  //
  // Let's see how this filter is working. We chose to apply the
  // \doxygen{itk}{ShiftScaleImageFilter} to each of the spectral band. We start
  // by declaring the filter on a normal \doxygen{otb}{Image}. Note that we
  // don't need to specify any input for this filter.

  using ShiftScaleType               = itk::ShiftScaleImageFilter<ImageType, ImageType>;
  ShiftScaleType::Pointer shiftScale = ShiftScaleType::New();
  shiftScale->SetScale(0.5);
  shiftScale->SetShift(10);

  // We declare the \doxygen{otb}{PerBandVectorImageFilter} which has three
  // template: the input image type, the output image type and the filter type
  // to apply to each band.
  //
  // The filter is selected using the \code{SetFilter()} method and the input
  // by the usual \code{SetInput()} method.

  using VectorFilterType                 = otb::PerBandVectorImageFilter<VectorImageType, VectorImageType, ShiftScaleType>;
  VectorFilterType::Pointer vectorFilter = VectorFilterType::New();
  vectorFilter->SetFilter(shiftScale);

  vectorFilter->SetInput(reader->GetOutput());

  // Now, we just have to save the image using a writer templated over an
  // \doxygen{otb}{VectorImage}:

  using VectorWriterType                 = otb::ImageFileWriter<VectorImageType>;
  VectorWriterType::Pointer writerVector = VectorWriterType::New();

  writerVector->SetFileName(argv[3]);
  writerVector->SetInput(vectorFilter->GetOutput());

  writerVector->Update();

  return EXIT_SUCCESS;
}