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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 itkLinearInterpolateImageFunction_hxx
#define itkLinearInterpolateImageFunction_hxx
#include "itkConceptChecking.h"
#include "itkMath.h"
#include <algorithm> // For min and max.
namespace itk
{
template <typename TInputImage, typename TCoordRep>
auto
LinearInterpolateImageFunction<TInputImage, TCoordRep>::EvaluateUnoptimized(const ContinuousIndexType & index) const
-> OutputType
{
// Avoid the smartpointer de-reference in the loop for
// "return m_InputImage.GetPointer()"
const TInputImage * const inputImagePtr = this->GetInputImage();
// Compute base index = closest index below point
// Compute distance from point to base index
IndexType baseIndex;
InternalComputationType distance[ImageDimension];
for (unsigned int dim = 0; dim < ImageDimension; ++dim)
{
baseIndex[dim] = Math::Floor<IndexValueType>(index[dim]);
distance[dim] = index[dim] - static_cast<InternalComputationType>(baseIndex[dim]);
}
// The iInterpolated value is the weighted sum of each of the surrounding
// neighbors. The weight for each neighbor is the fraction overlap
// of the neighbor pixel with respect to a pixel centered on point.
// When RealType is VariableLengthVector, 'value' will be resized properly
// below when it's assigned again.
Concept::Detail::UniqueType<typename NumericTraits<RealType>::ScalarRealType>();
RealType value;
// Initialize variable "value" with overloaded function so that
// in the case of variable length vectors the "value" is initialized
// to all zeros of length equal to the InputImagePtr first pixel length.
this->MakeZeroInitializer(inputImagePtr, value);
Concept::Detail::UniqueType<typename NumericTraits<InputPixelType>::ScalarRealType>();
// Number of neighbors used in the interpolation
constexpr unsigned long numberOfNeighbors = 1 << TInputImage::ImageDimension;
for (unsigned int counter = 0; counter < numberOfNeighbors; ++counter)
{
InternalComputationType overlap = 1.0; // Fraction overlap
unsigned int upper = counter; // Each bit indicates upper/lower neighbour
IndexType neighIndex(baseIndex);
// Get neighbor index and overlap fraction
for (unsigned int dim = 0; dim < ImageDimension; ++dim)
{
if (upper & 1)
{
++(neighIndex[dim]);
// Take care of the case where the pixel is just
// in the outer upper boundary of the image grid.
neighIndex[dim] = std::min(neighIndex[dim], this->m_EndIndex[dim]);
overlap *= distance[dim];
}
else
{
// Take care of the case where the pixel is just
// in the outer lower boundary of the image grid.
neighIndex[dim] = std::max(neighIndex[dim], this->m_StartIndex[dim]);
overlap *= 1.0 - distance[dim];
}
upper >>= 1;
}
value += static_cast<RealType>(inputImagePtr->GetPixel(neighIndex)) * overlap;
}
return (static_cast<OutputType>(value));
}
template <typename TInputImage, typename TCoordRep>
void
LinearInterpolateImageFunction<TInputImage, TCoordRep>::PrintSelf(std::ostream & os, Indent indent) const
{
this->Superclass::PrintSelf(os, indent);
}
} // end namespace itk
#endif
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