ENH: Ingest ITKGenericLabelInterpolator into Modules/Filtering

Modules/Filtering/GenericLabelInterpolator/CMakeLists.txt

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+itk_module_impl()

Modules/Filtering/GenericLabelInterpolator/README.md

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+# GenericLabelInterpolator
+
+In-tree ITK module providing a generic interpolator for multi-label
+images.  `itk::LabelImageGenericInterpolateImageFunction` interpolates
+each label independently with any ordinary image interpolator and
+returns, at each query point, the label whose interpolated value is
+highest.  Generalizes the Gaussian-only behavior of
+`itk::LabelImageGaussianInterpolateImageFunction`.
+
+## Origin
+
+Ingested from the standalone remote module
+[**InsightSoftwareConsortium/ITKGenericLabelInterpolator**](https://github.com/InsightSoftwareConsortium/ITKGenericLabelInterpolator)
+on 2026-04-25, at upstream commit
+[`081575cd`](https://github.com/InsightSoftwareConsortium/ITKGenericLabelInterpolator/commit/081575cdcc26b1a542d4c90feaf9250df5e104d9).
+The upstream repository will be archived read-only after this PR
+merges; it remains reachable at the URL above.
+
+## What lives here
+
+Per the v3 ingestion strategy (see
+`Utilities/Maintenance/RemoteModuleIngest/INGESTION_STRATEGY.md`), only
+paths matching the narrow whitelist (code, headers, tests, wrapping,
+module CMake) crossed the merge boundary:
+
+- `include/` — public C++ headers.
+- `test/` — CTest drivers and content-link stubs.
+- `wrapping/` — Python wrapping descriptors.
+- `CMakeLists.txt`, `itk-module.cmake` — build + module descriptors.
+
+Every surviving commit preserves original authorship; `git blame`
+walks across the merge boundary to upstream authors back to 2014.
+
+## What was intentionally left upstream
+
+Everything outside the whitelist stays in the archived upstream repo.
+If you need any of it, clone
+<https://github.com/InsightSoftwareConsortium/ITKGenericLabelInterpolator>.
+
+| Content in upstream | Why it did not ingest |
+|---|---|
+| `examples/` | Per-module `examples/` are routed to top-level [`Examples/`](https://github.com/InsightSoftwareConsortium/ITK/tree/main/Examples) via a separate follow-up PR. |
+| `README.rst` | Algorithm citations + background are folded into the Doxygen on the filter headers and the module DESCRIPTION. |
+| `.github/`, `azure-pipelines.yml`, `Dockerfile` | Standalone-build CI scaffolding; not useful in-tree. |
+| `CTestConfig.cmake`, `pyproject.toml`, `LICENSE`, `.clang-format` | Packaging / CI / style scaffolding superseded by ITK root. |
+
+## Long-form documentation
+
+- **Algorithm description** — see the Doxygen on
+  `itkLabelImageGenericInterpolateImageFunction`, plus the embedded
+  citation:
+
+  > Schaerer, J., Roche, F., Belaroussi, B.
+  > *A generic interpolator for multi-label images*.
+  > The Insight Journal, January–December 2014.
+  > <https://hdl.handle.net/10380/3506>
+
+- **Standalone build + usage examples** — see the archived upstream at
+  <https://github.com/InsightSoftwareConsortium/ITKGenericLabelInterpolator>.
+
+## Content-link status
+
+The 2 baseline / input content-links under `test/Baseline/` and
+`test/Input/` are already in `.cid` (IPFS Content Identifier) form;
+no `.md5` → `.cid` normalization is required for this module.

Modules/Filtering/GenericLabelInterpolator/include/itkLabelImageGenericInterpolateImageFunction.h

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+/*=========================================================================
+ *
+ *  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.
+ *
+ *=========================================================================*/
+#ifndef itkLabelImageGenericInterpolateImageFunction_h
+#define itkLabelImageGenericInterpolateImageFunction_h
+
+#include <itkInterpolateImageFunction.h>
+#include "itkLabelSelectionImageAdaptor.h"
+#include <vector>
+#include <set>
+
+namespace itk
+{
+
+/** \class LabelImageGenericInterpolateImageFunction
+ * \brief Interpolation function for multi-label images that implicitly interpolates each
+ * unique value in the image corresponding to each label set element and returns the
+ * corresponding label set element with the largest weight.
+ *
+ * This filter is an alternative to nearest neighbor interpolation for multi-label
+ * images. It can use almost any underlying interpolator.
+ * * \ingroup ITKImageFunction
+ * * \ingroup GenericLabelInterpolator
+ */
+
+template <typename TInputImage,
+          template <typename TInterpInputImage, typename TCoordRep> class TInterpolator,
+          typename TCoordRep = double>
+class ITK_EXPORT LabelImageGenericInterpolateImageFunction : public InterpolateImageFunction<TInputImage, TCoordRep>
+{
+public:
+  ITK_DISALLOW_COPY_AND_MOVE(LabelImageGenericInterpolateImageFunction);
+
+  /** Standard class type alias. */
+  using Self = LabelImageGenericInterpolateImageFunction;
+  using Superclass = InterpolateImageFunction<TInputImage, TCoordRep>;
+  using Pointer = SmartPointer<Self>;
+  using ConstPointer = SmartPointer<const Self>;
+  using InputPixelType = typename TInputImage::PixelType;
+
+  /** Run-time type information (and related methods). */
+  itkOverrideGetNameOfClassMacro(LabelImageGenericInterpolateImageFunction);
+
+  /** Method for creation through the object factory. */
+  itkNewMacro(Self);
+
+  /** ImageDimension constant */
+  static constexpr unsigned int ImageDimension = TInputImage::ImageDimension;
+
+  /** OutputType type alias support. */
+  using OutputType = typename Superclass::OutputType;
+
+  /** InputImageType type alias support. */
+  using InputImageType = typename Superclass::InputImageType;
+
+  /** RealType type alias support. */
+  using RealType = typename Superclass::RealType;
+
+  /** Index type alias support. */
+  using IndexType = typename Superclass::IndexType;
+
+  /** Size type alias support. */
+  using SizeType = typename Superclass::SizeType;
+
+  /** ContinuousIndex type alias support. */
+  using ContinuousIndexType = typename Superclass::ContinuousIndexType;
+
+  using LabelSelectionAdaptorType = LabelSelectionImageAdaptor<TInputImage, double>;
+
+  // The interpolator used for individual binary masks corresponding to each label
+  using InternalInterpolatorType = TInterpolator<LabelSelectionAdaptorType, TCoordRep>;
+
+  /**
+   * Evaluate at the given index
+   */
+  OutputType
+  EvaluateAtContinuousIndex(const ContinuousIndexType & cindex) const override
+  {
+    return this->EvaluateAtContinuousIndex(cindex, nullptr);
+  }
+
+  void
+  SetInputImage(const TInputImage * image) override;
+
+  /** Get the radius required for interpolation.
+   *
+   * This defines the number of surrounding pixels required to interpolate at
+   * a given point.
+   */
+  SizeType
+  GetRadius() const override
+  {
+    return SizeType::Filled(1);
+  }
+
+protected:
+  LabelImageGenericInterpolateImageFunction() = default;
+  ~LabelImageGenericInterpolateImageFunction() override = default;
+
+  std::vector<typename InternalInterpolatorType::Pointer>  m_InternalInterpolators;
+  std::vector<typename LabelSelectionAdaptorType::Pointer> m_LabelSelectionAdaptors;
+  using LabelSetType = std::set<typename TInputImage::PixelType>;
+  LabelSetType m_Labels;
+
+private:
+  /**
+   * Evaluate function value at the given index
+   */
+  virtual OutputType
+  EvaluateAtContinuousIndex(const ContinuousIndexType &, OutputType *) const;
+};
+
+} // end namespace itk
+
+#ifndef ITK_MANUAL_INSTANTIATION
+#  include "itkLabelImageGenericInterpolateImageFunction.hxx"
+#endif
+
+#endif

Modules/Filtering/GenericLabelInterpolator/include/itkLabelImageGenericInterpolateImageFunction.hxx

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+/*=========================================================================
+ *
+ *  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.
+ *
+ *=========================================================================*/
+#ifndef itkLabelImageGenericInterpolateImageFunction_hxx
+#define itkLabelImageGenericInterpolateImageFunction_hxx
+
+#include <itkImageRegionConstIterator.h>
+
+namespace itk
+{
+
+template <typename TInputImage,
+          template <typename TInterpInputImage, typename TCoordRep> class TInterpolator,
+          typename TCoordRep>
+void
+LabelImageGenericInterpolateImageFunction<TInputImage, TInterpolator, TCoordRep>::SetInputImage(
+  const TInputImage * image)
+{
+  /* We have one adaptor and one interpolator per label to keep the class thread-safe:
+   * changing the adaptor's accepted value wouldn't work when called from a multi-threaded filter */
+  using IteratorType = itk::ImageRegionConstIterator<TInputImage>;
+  if (image)
+  {
+    m_Labels.clear();
+    IteratorType it(image, image->GetLargestPossibleRegion());
+    for (it.GoToBegin(); !it.IsAtEnd(); ++it)
+    {
+      m_Labels.insert(it.Get());
+    }
+    m_InternalInterpolators.clear();
+    m_LabelSelectionAdaptors.clear();
+    for (auto i = m_Labels.begin(); i != m_Labels.end(); ++i)
+    {
+      typename LabelSelectionAdaptorType::Pointer adapt = LabelSelectionAdaptorType::New();
+      // This adaptor doesn't implement Set() so this should be safe
+      adapt->SetImage(const_cast<TInputImage *>(image));
+      adapt->SetAcceptedValue(*i);
+      m_LabelSelectionAdaptors.push_back(adapt);
+      typename InternalInterpolatorType::Pointer interp = InternalInterpolatorType::New();
+      interp->SetInputImage(adapt);
+      m_InternalInterpolators.push_back(interp);
+    }
+  }
+  Superclass::SetInputImage(image);
+}
+
+template <typename TInputImage,
+          template <typename TInterpInputImage, typename TCoordRep> class TInterpolator,
+          typename TCoordRep>
+typename LabelImageGenericInterpolateImageFunction<TInputImage, TInterpolator, TCoordRep>::OutputType
+LabelImageGenericInterpolateImageFunction<TInputImage, TInterpolator, TCoordRep>::EvaluateAtContinuousIndex(
+  const ContinuousIndexType & cindex,
+  OutputType *                itkNotUsed(grad)) const
+{
+  /* Interpolate the binary mask corresponding to each label and return the label
+   * with the highest value */
+  double         value = 0;
+  InputPixelType best_label = itk::NumericTraits<InputPixelType>::ZeroValue();
+  int            i = 0;
+  for (auto it = m_Labels.begin(); it != m_Labels.end(); ++it)
+  {
+    double tmp = m_InternalInterpolators[i]->EvaluateAtContinuousIndex(cindex);
+    if (tmp > value)
+    {
+      value = tmp;
+      best_label = (*it);
+    }
+    ++i;
+  }
+  return best_label;
+}
+
+} // namespace itk
+
+#endif

Modules/Filtering/GenericLabelInterpolator/include/itkLabelSelectionImageAdaptor.h

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+/*=========================================================================
+ *
+ *  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.
+ *
+ *=========================================================================*/
+#ifndef itkLabelSelectionImageAdaptor_h
+#define itkLabelSelectionImageAdaptor_h
+
+#include "itkLabelSelectionPixelAccessor.h"
+
+namespace itk
+{
+/** \class LabelSelectionImageAdaptor
+ * \brief Presents a label image as a binary image of one label
+ *
+ * Additional casting is performed according to the input and output image
+ * types following C++ default casting rules.
+ *
+ * \ingroup ImageAdaptors
+ * \ingroup ITKImageAdaptors
+ * \ingroup GenericLabelInterpolator
+ */
+template <class TImage, class TOutputPixelType>
+class ITK_EXPORT LabelSelectionImageAdaptor
+  : public ImageAdaptor<TImage, Accessor::LabelSelectionPixelAccessor<typename TImage::PixelType, TOutputPixelType>>
+{
+public:
+  ITK_DISALLOW_COPY_AND_MOVE(LabelSelectionImageAdaptor);
+
+  /** Standard class type alias. */
+  using Self = LabelSelectionImageAdaptor;
+  using Superclass =
+    ImageAdaptor<TImage, Accessor::LabelSelectionPixelAccessor<typename TImage::PixelType, TOutputPixelType>>;
+
+  using Pointer = SmartPointer<Self>;
+  using ConstPointer = SmartPointer<const Self>;
+
+  /** Method for creation through the object factory. */
+  itkNewMacro(Self);
+
+  /** Run-time type information (and related methods). */
+  itkOverrideGetNameOfClassMacro(LabelSelectionImageAdaptor);
+
+  void
+  SetAcceptedValue(typename TImage::PixelType value)
+  {
+    this->GetPixelAccessor().SetAcceptedValue(value);
+  }
+
+protected:
+  LabelSelectionImageAdaptor() = default;
+  ~LabelSelectionImageAdaptor() override = default;
+};
+} // end namespace itk
+
+#endif