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WIP: Add StructuralSimilarityImageFilter
Salvaged from copilot session: https://github.com/InsightSoftwareConsortium/ITK/agents/pull/6031?session_id=100b799f-7c42-4c54-a76d-4b35dbe7ce91
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‎Modules/Filtering/ImageCompare/include/itkStructuralSimilarityImageFilter.h‎

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/*=========================================================================
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*
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* Copyright NumFOCUS
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0.txt
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*=========================================================================*/
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#ifndef itkStructuralSimilarityImageFilter_h
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#define itkStructuralSimilarityImageFilter_h
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#include "itkImageToImageFilter.h"
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#include "itkNumericTraits.h"
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#include "itkArray.h"
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namespace itk
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{
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/**
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* \class StructuralSimilarityImageFilter
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* \brief Computes the Structural Similarity Index Measure (SSIM) between two images.
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*
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* This filter computes the local SSIM map and an overall scalar SSIM value
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* between two input images. The SSIM is defined as:
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*
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* \f[
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* \text{SSIM}(x,y) = [l(x,y)]^{\alpha} \cdot [c(x,y)]^{\beta} \cdot [s(x,y)]^{\gamma}
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* \f]
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*
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* where
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* \f[
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* l(x,y) = \frac{2\mu_x\mu_y + C_1}{\mu_x^2 + \mu_y^2 + C_1}, \quad
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* c(x,y) = \frac{2\sigma_x\sigma_y + C_2}{\sigma_x^2 + \sigma_y^2 + C_2}, \quad
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* s(x,y) = \frac{\sigma_{xy} + C_3}{\sigma_x\sigma_y + C_3}
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* \f]
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*
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* with \f$C_1 = (K_1 L)^2\f$, \f$C_2 = (K_2 L)^2\f$, \f$C_3 = C_2 / 2\f$.
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* \f$L\f$ is the dynamic range (defaults to 255), and \f$K_1\f$ and \f$K_2\f$
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* are small stability constants (defaults 0.01 and 0.03 respectively).
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*
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* The exponents \f$\alpha\f$, \f$\beta\f$, and \f$\gamma\f$ control the
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* relative importance of luminance, contrast, and structure. With the default
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* values of 1.0 the formula simplifies to the standard SSIM:
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*
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* \f[
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* \text{SSIM}(x,y) = \frac{(2\mu_x\mu_y + C_1)(2\sigma_{xy} + C_2)}{(\mu_x^2 + \mu_y^2 + C_1)(\sigma_x^2 + \sigma_y^2 + C_2)}
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* \f]
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*
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* The output image contains the per-pixel SSIM map. The scalar mean SSIM
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* across all pixels can be retrieved with GetSSIM().
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*
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* The filter is N-dimensional and multi-threaded.
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*
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* \par Parameters
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* - Radius: neighborhood radius for local statistics (default: 1 in each dimension, giving a 3x3 window in 2D).
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* - LuminanceWeight (\f$\alpha\f$), ContrastWeight (\f$\beta\f$), StructureWeight (\f$\gamma\f$):
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* exponents for the three components (all default to 1.0).
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* - DynamicRange (\f$L\f$): range of pixel values (default: 255.0).
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* - K1, K2: stabilization constants (defaults: 0.01, 0.03).
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*
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* \sa SimilarityIndexImageFilter
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*
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* \ingroup ImageCompare
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* \ingroup ITKImageCompare
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*/
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template <typename TInputImage, typename TOutputImage = TInputImage>
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class ITK_TEMPLATE_EXPORT StructuralSimilarityImageFilter : public ImageToImageFilter<TInputImage, TOutputImage>
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{
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public:
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ITK_DISALLOW_COPY_AND_MOVE(StructuralSimilarityImageFilter);
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/** Standard class type aliases. */
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using Self = StructuralSimilarityImageFilter;
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using Superclass = ImageToImageFilter<TInputImage, TOutputImage>;
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using Pointer = SmartPointer<Self>;
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using ConstPointer = SmartPointer<const Self>;
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/** Method for creation through the object factory. */
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itkNewMacro(Self);
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/** \see LightObject::GetNameOfClass() */
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itkOverrideGetNameOfClassMacro(StructuralSimilarityImageFilter);
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/** Image type aliases. */
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using InputImageType = TInputImage;
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using OutputImageType = TOutputImage;
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using InputPixelType = typename InputImageType::PixelType;
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using OutputPixelType = typename OutputImageType::PixelType;
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using InputImageRegionType = typename InputImageType::RegionType;
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using OutputImageRegionType = typename OutputImageType::RegionType;
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using SizeType = typename InputImageType::SizeType;
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using IndexType = typename InputImageType::IndexType;
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static constexpr unsigned int ImageDimension = InputImageType::ImageDimension;
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/** Floating point type for computations. */
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using RealType = typename NumericTraits<InputPixelType>::RealType;
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/** Neighborhood radius type. */
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using RadiusType = SizeType;
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using RadiusValueType = typename RadiusType::SizeValueType;
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/** Set/Get the neighborhood radius for local statistics computation. */
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virtual void
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SetRadius(const RadiusType & radius);
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virtual void
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SetRadius(RadiusValueType radius);
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itkGetConstReferenceMacro(Radius, RadiusType);
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/** Set the first input image. */
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void
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SetInput1(const InputImageType * image)
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{
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this->SetInput(image);
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}
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/** Set the second input image. */
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void
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SetInput2(const InputImageType * image);
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/** Get the first input image. */
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const InputImageType *
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GetInput1() const
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{
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return this->GetInput(0);
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}
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/** Get the second input image. */
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const InputImageType *
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GetInput2() const;
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/** Set/Get the luminance exponent (alpha). Default: 1.0. */
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itkSetMacro(LuminanceWeight, RealType);
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itkGetConstMacro(LuminanceWeight, RealType);
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/** Set/Get the contrast exponent (beta). Default: 1.0. */
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itkSetMacro(ContrastWeight, RealType);
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itkGetConstMacro(ContrastWeight, RealType);
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/** Set/Get the structure exponent (gamma). Default: 1.0. */
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itkSetMacro(StructureWeight, RealType);
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itkGetConstMacro(StructureWeight, RealType);
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/** Set/Get the dynamic range L of the pixel values. Default: 255.0. */
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itkSetMacro(DynamicRange, RealType);
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itkGetConstMacro(DynamicRange, RealType);
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/** Set/Get the K1 stabilization constant. Default: 0.01. */
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itkSetMacro(K1, RealType);
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itkGetConstMacro(K1, RealType);
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/** Set/Get the K2 stabilization constant. Default: 0.03. */
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itkSetMacro(K2, RealType);
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itkGetConstMacro(K2, RealType);
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/** Get the computed mean SSIM value (available after Update()). */
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itkGetConstMacro(SSIM, RealType);
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itkConceptMacro(InputHasNumericTraitsCheck, (Concept::HasNumericTraits<InputPixelType>));
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protected:
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StructuralSimilarityImageFilter();
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~StructuralSimilarityImageFilter() override = default;
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void
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PrintSelf(std::ostream & os, Indent indent) const override;
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void
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GenerateInputRequestedRegion() override;
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void
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BeforeThreadedGenerateData() override;
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void
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AfterThreadedGenerateData() override;
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void
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DynamicThreadedGenerateData(const OutputImageRegionType & outputRegionForThread) override;
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private:
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RadiusType m_Radius{};
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RealType m_LuminanceWeight{ 1.0 };
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RealType m_ContrastWeight{ 1.0 };
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RealType m_StructureWeight{ 1.0 };
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RealType m_DynamicRange{ 255.0 };
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RealType m_K1{ 0.01 };
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RealType m_K2{ 0.03 };
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RealType m_SSIM{};
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/** Thread-local accumulators for computing the global mean SSIM. */
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std::mutex m_Mutex{};
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RealType m_AccumulatedSSIM{};
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SizeValueType m_PixelCount{};
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};
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} // end namespace itk
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#ifndef ITK_MANUAL_INSTANTIATION
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# include "itkStructuralSimilarityImageFilter.hxx"
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#endif
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#endif

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