Apply a Filter Only to a Specified Region of an Image#

Synopsis#

The key of using SetRequestedRegion to tell a filter to only operate on a specified ImageRegion is to call SetRequestedRegion on the filters GetOutput(). That is, to tell the DerivativeImageFilter to only operate on a small region, you must do

derivativeFilter->GetOutput()->SetRequestedRegion(smallRegion);
derivativeFilter->Update();

Results#

Code#

Python#

#!/usr/bin/env python

import itk

Dimension = 2
PixelType = itk.F
ImageType = itk.Image[PixelType, Dimension]

smallSize = itk.Size[Dimension]()
smallSize.Fill(10)

index = itk.Index[Dimension]()
index.Fill(0)

region = itk.ImageRegion[Dimension]()
region.SetIndex(index)
region.SetSize(smallSize)

bigSize = itk.Size[Dimension]()
bigSize.Fill(10)

RandomSourceType = itk.RandomImageSource[ImageType]
randomImageSource = RandomSourceType.New()
randomImageSource.SetNumberOfWorkUnits(1)  # to produce non-random results
randomImageSource.SetSize(bigSize)
randomImageSource.GetOutput().SetRequestedRegion(region)

print("Created random image.")

DerivativeImageFilterType = itk.DerivativeImageFilter[ImageType, ImageType]

derivativeFilter = DerivativeImageFilterType.New()
derivativeFilter.SetInput(randomImageSource.GetOutput())
derivativeFilter.SetDirection(0)  # "x" axis
derivativeFilter.GetOutput().SetRequestedRegion(region)
derivativeFilter.Update()

print("Computed derivative.")

C++#

#include "itkImage.h"
#include "itkRandomImageSource.h"
#include "itkDerivativeImageFilter.h"

int
main()
{
  constexpr unsigned int Dimension = 2;
  using PixelType = float;

  using ImageType = itk::Image<PixelType, Dimension>;

  ImageType::SizeType smallSize;
  smallSize.Fill(10);

  ImageType::IndexType index;
  index.Fill(0);

  ImageType::RegionType region(index, smallSize);

  ImageType::SizeType bigSize;
  bigSize.Fill(10000);

  using RandomSourceType = itk::RandomImageSource<ImageType>;
  auto randomImageSource = RandomSourceType::New();
  randomImageSource->SetNumberOfWorkUnits(1); // to produce non-random results
  randomImageSource->SetSize(bigSize);
  randomImageSource->GetOutput()->SetRequestedRegion(smallSize);

  std::cout << "Created random image." << std::endl;

  using DerivativeImageFilterType = itk::DerivativeImageFilter<ImageType, ImageType>;

  auto derivativeFilter = DerivativeImageFilterType::New();
  derivativeFilter->SetInput(randomImageSource->GetOutput());
  derivativeFilter->SetDirection(0); // "x" axis
  derivativeFilter->GetOutput()->SetRequestedRegion(smallSize);
  derivativeFilter->Update();

  std::cout << "Computed derivative." << std::endl;

  return EXIT_SUCCESS;
}

Classes demonstrated#

template<typename TPixel, unsigned int VImageDimension = 2> class Image : public itk::ImageBase<VImageDimension>

Templated n-dimensional image class.

Images are templated over a pixel type (modeling the dependent variables), and a dimension (number of independent variables). The container for the pixel data is the ImportImageContainer.

Within the pixel container, images are modelled as arrays, defined by a start index and a size.

The superclass of Image, ImageBase, defines the geometry of the image in terms of where the image sits in physical space, how the image is oriented in physical space, the size of a pixel, and the extent of the image itself. ImageBase provides the methods to convert between the index and physical space coordinate frames.

Pixels can be accessed directly using the SetPixel() and GetPixel() methods or can be accessed via iterators that define the region of the image they traverse.

The pixel type may be one of the native types; a Insight-defined class type such as Vector; or a user-defined type. Note that depending on the type of pixel that you use, the process objects (i.e., those filters processing data objects) may not operate on the image and/or pixel type. This becomes apparent at compile-time because operator overloading (for the pixel type) is not supported.

The data in an image is arranged in a 1D array as [][][][slice][row][col] with the column index varying most rapidly. The Index type reverses the order so that with Index[0] = col, Index[1] = row, Index[2] = slice, …

See

ImageBase

See

ImageContainerInterface

ITK Sphinx Examples: