Merge pull request InsightSoftwareConsortium#5730 from N-Dekker/Use-std-array-for-HessianRecursiveGaussianImageFilter-m_SmoothingFilters

RecursiveGaussian filters: Use `std::array` for m_SmoothingFilters, remove GaussianFiltersArray alias

Author: thewtex

Modules/Core/Common/include/itkPrintHelper.h

@@ -19,6 +19,7 @@
 #ifndef itkPrintHelper_h
 #define itkPrintHelper_h
 
+#include <array>
 #include <iostream>
 #include <iterator>
 #include <list>
@@ -66,6 +67,22 @@ operator<<(std::ostream & os, const std::list<T> & l)
   return os << l.back() << ']';
 }
 
+template <typename T, size_t VLength>
+std::ostream &
+operator<<(std::ostream & os, [[maybe_unused]] const std::array<T, VLength> & container)
+{
+  if constexpr (VLength == 0)
+  {
+    return os << "()";
+  }
+  else
+  {
+    os << '(';
+    std::copy(container.cbegin(), std::prev(container.cend()), std::ostream_iterator<T>(os, ", "));
+    return os << container.back() << ')';
+  }
+}
+
 // Stream insertion operator for C-style arrays, excluding character arrays (strings)
 template <typename T, size_t VLength, typename = std::enable_if_t<!std::is_same_v<T, char>>>
 std::ostream &

Modules/Filtering/ImageFeature/include/itkHessianRecursiveGaussianImageFilter.h

@@ -23,6 +23,7 @@
 #include "itkImage.h"
 #include "itkSymmetricSecondRankTensor.h"
 #include "itkPixelTraits.h"
+#include <array>
 
 namespace itk
 {
@@ -92,7 +93,11 @@ class ITK_TEMPLATE_EXPORT HessianRecursiveGaussianImageFilter : public ImageToIm
 
   /**  Pointer to a gaussian filter.  */
   using GaussianFilterPointer = typename GaussianFilterType::Pointer;
-  using GaussianFiltersArray = std::vector<GaussianFilterPointer>;
+
+#ifndef ITK_FUTURE_LEGACY_REMOVE
+  using GaussianFiltersArray [[deprecated("This type alias is deprecated from ITK 6!")]] =
+    std::vector<GaussianFilterPointer>;
+#endif
 
   /**  Pointer to a derivative filter.  */
   using DerivativeFilterAPointer = typename DerivativeFilterAType::Pointer;
@@ -154,10 +159,10 @@ class ITK_TEMPLATE_EXPORT HessianRecursiveGaussianImageFilter : public ImageToIm
   EnlargeOutputRequestedRegion(DataObject * output) override;
 
 private:
-  GaussianFiltersArray      m_SmoothingFilters{};
-  DerivativeFilterAPointer  m_DerivativeFilterA{};
-  DerivativeFilterBPointer  m_DerivativeFilterB{};
-  OutputImageAdaptorPointer m_ImageAdaptor{};
+  std::array<GaussianFilterPointer, NumberOfSmoothingFilters> m_SmoothingFilters{};
+  DerivativeFilterAPointer                                    m_DerivativeFilterA{};
+  DerivativeFilterBPointer                                    m_DerivativeFilterB{};
+  OutputImageAdaptorPointer                                   m_ImageAdaptor{};
 
   /** Normalize the image across scale space */
   bool m_NormalizeAcrossScale{};

Modules/Filtering/ImageFeature/include/itkHessianRecursiveGaussianImageFilter.hxx

@@ -20,6 +20,7 @@
 
 #include "itkImageRegionIteratorWithIndex.h"
 #include "itkProgressAccumulator.h"
+#include <algorithm> // For generate.
 
 namespace itk
 {
@@ -31,15 +32,14 @@ HessianRecursiveGaussianImageFilter<TInputImage, TOutputImage>::HessianRecursive
   // note: this is not constant to suppress a warning
   const unsigned int numberOfSmoothingFilters = NumberOfSmoothingFilters;
 
-  for (unsigned int i = 0; i < numberOfSmoothingFilters; ++i)
-  {
+  std::generate(m_SmoothingFilters.begin(), m_SmoothingFilters.end(), [this] {
     const GaussianFilterPointer filter = GaussianFilterType::New();
     filter->SetOrder(GaussianOrderEnum::ZeroOrder);
     filter->SetNormalizeAcrossScale(m_NormalizeAcrossScale);
     filter->InPlaceOn();
     filter->ReleaseDataFlagOn();
-    m_SmoothingFilters.push_back(filter);
-  }
+    return filter;
+  });
 
   m_DerivativeFilterA = DerivativeFilterAType::New();
   m_DerivativeFilterB = DerivativeFilterBType::New();

Modules/Filtering/ImageGradient/include/itkGradientRecursiveGaussianImageFilter.h

@@ -26,7 +26,7 @@
 #include "itkProgressAccumulator.h"
 #include "itkImageRegionIterator.h"
 #include "itkVectorImage.h"
-#include <vector>
+#include <array>
 
 namespace itk
 {
@@ -246,9 +246,9 @@ class ITK_TEMPLATE_EXPORT GradientRecursiveGaussianImageFilter : public ImageToI
   }
 
 
-  std::vector<GaussianFilterPointer> m_SmoothingFilters{};
-  DerivativeFilterPointer            m_DerivativeFilter{};
-  OutputImageAdaptorPointer          m_ImageAdaptor{};
+  std::array<GaussianFilterPointer, ImageDimension - 1> m_SmoothingFilters{};
+  DerivativeFilterPointer                               m_DerivativeFilter{};
+  OutputImageAdaptorPointer                             m_ImageAdaptor{};
 
   /** Normalize the image across scale space */
   bool m_NormalizeAcrossScale{};

Modules/Filtering/ImageGradient/include/itkGradientRecursiveGaussianImageFilter.hxx

@@ -22,6 +22,7 @@
 #include "itkImageRegionIterator.h"
 #include "itkImageRegionConstIterator.h"
 #include "itkPrintHelper.h"
+#include <algorithm> // For generate.
 
 namespace itk
 {
@@ -34,16 +35,14 @@ GradientRecursiveGaussianImageFilter<TInputImage, TOutputImage>::GradientRecursi
   const unsigned int imageDimensionMinus1 = ImageDimension - 1;
   if constexpr (ImageDimension > 1)
   {
-    m_SmoothingFilters.resize(imageDimensionMinus1);
-
-    for (unsigned int i = 0; i != imageDimensionMinus1; ++i)
-    {
-      m_SmoothingFilters[i] = GaussianFilterType::New();
-      m_SmoothingFilters[i]->SetOrder(GaussianOrderEnum::ZeroOrder);
-      m_SmoothingFilters[i]->SetNormalizeAcrossScale(m_NormalizeAcrossScale);
-      m_SmoothingFilters[i]->InPlaceOn();
-      m_SmoothingFilters[i]->ReleaseDataFlagOn();
-    }
+    std::generate(m_SmoothingFilters.begin(), m_SmoothingFilters.end(), [this] {
+      const GaussianFilterPointer filter = GaussianFilterType::New();
+      filter->SetOrder(GaussianOrderEnum::ZeroOrder);
+      filter->SetNormalizeAcrossScale(m_NormalizeAcrossScale);
+      filter->InPlaceOn();
+      filter->ReleaseDataFlagOn();
+      return filter;
+    });
   }
 
   m_DerivativeFilter = DerivativeFilterType::New();