WIP: Add legacy Sobel option to GradientDifferenceImageToImageMetric

Modules/Registration/Common/include/itkGradientDifferenceImageToImageMetric.h

@@ -137,6 +137,22 @@ class ITK_TEMPLATE_EXPORT GradientDifferenceImageToImageMetric : public ImageToI
   itkSetMacro(DerivativeDelta, double);
   itkGetConstReferenceMacro(DerivativeDelta, double);
   /** @ITKEndGrouping */
+
+  /** Allows specifying whether or not the Sobel operators should use the legacy coordinate values, compatible with ITK
+   * <= 5.4.
+   * \sa SobelOperator::SetUseLegacyCoefficients */
+  void
+  UseLegacySobelOperatorCoordinates(const bool useLegacyCoefficients);
+
+  /** Tells whether or not the Sobel operators are using the legacy coordinate values, compatible with ITK <= 5.4.
+   * \sa SobelOperator::SetUseLegacyCoefficients */
+  bool
+  IsUsingLegacySobelOperatorCoordinates() const
+  {
+    // It is sufficient to just check the first operator, because this property is the same for all operators.
+    return m_FixedSobelOperators[0].IsUsingLegacyCoefficients();
+  }
+
 protected:
   GradientDifferenceImageToImageMetric();
   ~GradientDifferenceImageToImageMetric() override = default;

Modules/Registration/Common/include/itkGradientDifferenceImageToImageMetric.hxx

@@ -126,6 +126,27 @@ GradientDifferenceImageToImageMetric<TFixedImage, TMovingImage>::Initialize()
   }
 }
 
+
+template <typename TFixedImage, typename TMovingImage>
+void
+GradientDifferenceImageToImageMetric<TFixedImage, TMovingImage>::UseLegacySobelOperatorCoordinates(
+  const bool useLegacyCoefficients)
+{
+  if (useLegacyCoefficients != IsUsingLegacySobelOperatorCoordinates())
+  {
+    for (auto & sobelOperator : m_FixedSobelOperators)
+    {
+      sobelOperator.UseLegacyCoefficients(useLegacyCoefficients);
+    }
+    for (auto & sobelOperator : m_MovedSobelOperators)
+    {
+      sobelOperator.UseLegacyCoefficients(useLegacyCoefficients);
+    }
+    this->Modified();
+  }
+}
+
+
 template <typename TFixedImage, typename TMovingImage>
 void
 GradientDifferenceImageToImageMetric<TFixedImage, TMovingImage>::PrintSelf(std::ostream & os, Indent indent) const

Modules/Registration/Common/test/CMakeLists.txt

@@ -509,7 +509,11 @@ itk_add_test(
     1
 )
 
-set(ITKRegistrationGTests itkTransformInitializersGTest.cxx)
+set(
+  ITKRegistrationGTests
+  itkGradientDifferenceImageToImageMetricGTest.cxx
+  itkTransformInitializersGTest.cxx
+)
 creategoogletestdriver(ITKRegistration "${ITKRegistrationCommon-Test_LIBRARIES}" "${ITKRegistrationGTests}")
 
 if(BUILD_EXAMPLES)

Modules/Registration/Common/test/itkGradientDifferenceImageToImageMetricGTest.cxx

@@ -0,0 +1,37 @@
+/*=========================================================================
+ *
+ *  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.
+ *
+ *=========================================================================*/
+
+// First include the header file to be tested:
+#include "itkGradientDifferenceImageToImageMetric.h"
+#include "itkImage.h"
+#include <gtest/gtest.h>
+
+
+TEST(GradientDifferenceImageToImageMetric, UseLegacySobelOperatorCoordinates)
+{
+  using ImageType = itk::Image<float, 2>;
+  const auto metric = itk::GradientDifferenceImageToImageMetric<ImageType, ImageType>::New();
+
+  EXPECT_TRUE(metric->IsUsingLegacySobelOperatorCoordinates());
+
+  for (const bool useLegacyCoefficients : { false, true })
+  {
+    metric->UseLegacySobelOperatorCoordinates(useLegacyCoefficients);
+    EXPECT_EQ(metric->IsUsingLegacySobelOperatorCoordinates(), useLegacyCoefficients);
+  }
+}