text: /*=========================================================================
   *
   *  Copyright NumFOCUS
   *
   *  Licensed under the Apache License, Version 2.0 (the "License");
   *  you may not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *         https://www.apache.org/licenses/LICENSE-2.0.txt
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS,
   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   *
   *=========================================================================*/
  
  #include "itkMath.h"
  #include "itkSqrtImageFilter.h"
  #include "itkSqrtImageAdaptor.h"
  #include "itkSubtractImageFilter.h"
  #include "itkTestingMacros.h"
  
  
  int
  itkSqrtImageFilterAndAdaptorTest(int, char *[])
  {
  
    // Define the dimension of the images
    constexpr unsigned int ImageDimension = 3;
  
    // Declare the pixel types of the images
    using PixelType = float;
  
    // Declare the types of the images
    using InputImageType = itk::Image<PixelType, ImageDimension>;
    using OutputImageType = itk::Image<PixelType, ImageDimension>;
  
    // Declare appropriate Iterator types for each image
    using InputIteratorType = itk::ImageRegionIteratorWithIndex<InputImageType>;
    using OutputIteratorType = itk::ImageRegionIteratorWithIndex<OutputImageType>;
  
    // Declare the type of the index to access images
    using IndexType = itk::Index<ImageDimension>;
  
    // Declare the type of the size
    using SizeType = itk::Size<ImageDimension>;
  
    // Declare the type of the Region
    using RegionType = itk::ImageRegion<ImageDimension>;
  
    // Create the input image
    auto inputImage = InputImageType::New();
  
    // Define its size, and start index
    SizeType size;
    size[0] = 2;
    size[1] = 2;
    size[2] = 2;
  
    IndexType start;
    start[0] = 0;
    start[1] = 0;
    start[2] = 0;
  
    RegionType region;
    region.SetIndex(start);
    region.SetSize(size);
  
    // Initialize the input image
    inputImage->SetRegions(region);
    inputImage->Allocate();
  
    // Create one iterator for the input image (this is a light object)
    InputIteratorType it(inputImage, inputImage->GetBufferedRegion());
  
    // Initialize the content of the input image
    const double value = itk::Math::pi / 6.0;
    it.GoToBegin();
    while (!it.IsAtEnd())
    {
      it.Set(value);
      ++it;
    }
  
    // Declare the type for the Sqrt filter
    using FilterType = itk::SqrtImageFilter<InputImageType, OutputImageType>;
  
    // Create the filter
    auto filter = FilterType::New();
  
    ITK_EXERCISE_BASIC_OBJECT_METHODS(filter, SqrtImageFilter, UnaryGeneratorImageFilter);
  
    // Set the input image
    filter->SetInput(inputImage);
  
  
    // Execute the filter
    filter->Update();
  
    // Get the filter output
    OutputImageType::Pointer outputImage = filter->GetOutput();
  
    // Create an iterator for going through the image output
    OutputIteratorType ot(outputImage, outputImage->GetRequestedRegion());
  
    // Check the content of the result image
    const OutputImageType::PixelType epsilon = 1e-6;
    ot.GoToBegin();
    it.GoToBegin();
    while (!ot.IsAtEnd())
    {
      const InputImageType::PixelType  input = it.Get();
      const OutputImageType::PixelType output = ot.Get();
      const OutputImageType::PixelType sqroot = std::sqrt(input);
      if (!itk::Math::FloatAlmostEqual(sqroot, output, 10, epsilon))
      {
        std::cerr.precision(static_cast<int>(itk::Math::abs(std::log10(epsilon))));
        std::cerr << "Error " << std::endl;
        std::cerr << " sqrt( " << input << ") = " << sqroot << std::endl;
        std::cerr << " differs from " << output;
        std::cerr << " by more than " << epsilon << std::endl;
        return EXIT_FAILURE;
      }
      ++ot;
      ++it;
    }
  
    //
    // Test the itk::SqrtImageAdaptor
    //
  
    using AdaptorType = itk::SqrtImageAdaptor<InputImageType, OutputImageType::PixelType>;
  
    auto sqrtAdaptor = AdaptorType::New();
  
    ITK_EXERCISE_BASIC_OBJECT_METHODS(sqrtAdaptor, SqrtImageAdaptor, ImageAdaptor);
  
    sqrtAdaptor->SetImage(inputImage);
  
    using DiffFilterType = itk::SubtractImageFilter<OutputImageType, AdaptorType, OutputImageType>;
  
    auto diffFilter = DiffFilterType::New();
  
    diffFilter->SetInput1(outputImage);
    diffFilter->SetInput2(sqrtAdaptor);
  
    diffFilter->Update();
  
    // Get the filter output
    OutputImageType::Pointer diffImage = diffFilter->GetOutput();
  
    // Check the content of the diff image
    //
  
    // Create an iterator for going through the image output
    OutputIteratorType dt(diffImage, diffImage->GetRequestedRegion());
  
    dt.GoToBegin();
    while (!dt.IsAtEnd())
    {
      const OutputImageType::PixelType diff = dt.Get();
      if (itk::Math::abs(diff) > epsilon)
      {
        std::cerr << "Error comparing results with Adaptors" << std::endl;
        std::cerr << " difference = " << diff << std::endl;
        std::cerr << " differs from 0 ";
        std::cerr << " by more than " << epsilon << std::endl;
        return EXIT_FAILURE;
      }
      ++dt;
    }
  
    return EXIT_SUCCESS;
  }
  