Make 3D SobelOperator consistent with 2D, add UseLegacyCoefficients, add ND support #5718
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -19,7 +19,10 @@ | |
| #define itkSobelOperator_hxx | ||
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| #include "itkIndexRange.h" | ||
| #include "itkIntTypes.h" // For size_t. | ||
| #include "itkMath.h" | ||
| #include "itkObject.h" | ||
| #include <array> | ||
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| namespace itk | ||
| { | ||
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@@ -60,32 +63,85 @@ template <typename TPixel, unsigned int VDimension, typename TAllocator> | |
| auto | ||
| SobelOperator<TPixel, VDimension, TAllocator>::GenerateCoefficients() -> CoefficientVector | ||
| { | ||
| if (const unsigned int direction{ this->GetDirection() }; direction < VDimension) | ||
| { | ||
| if constexpr (VDimension == 3) | ||
| { | ||
| if (m_UseLegacyCoefficients) | ||
| { | ||
| switch (direction) | ||
| { | ||
| case 0: | ||
| return { -1, 0, 1, -3, 0, 3, -1, 0, 1, -3, 0, 3, -6, 0, 6, -3, 0, 3, -1, 0, 1, -3, 0, 3, -1, 0, 1 }; | ||
| case 1: | ||
| return { -1, -3, -1, 0, 0, 0, 1, 3, 1, -3, -6, -3, 0, 0, 0, 3, 6, 3, -1, -3, -1, 0, 0, 0, 1, 3, 1 }; | ||
| case 2: | ||
| return { -1, -3, -1, -3, -6, -3, -1, -3, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 1, 3, 6, 3, 1, 3, 1 }; | ||
| } | ||
| } | ||
| } | ||
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| // Create N-dimensional Sobel kernels (one per axis). | ||
| // Each kernel is size 3^N, stored in row-major order with the last dimension varying fastest. | ||
| // Standard Sobel definition: derivative = [-1, 0, 1], smoothing = [1, 2, 1]. | ||
| // Kernel for axis a is: K_a(x) = d[x_a] * Product_{i != a} s[x_i], with x_i being element of {-1,0,1}. | ||
| static constexpr auto sobelKernels = [] { | ||
| constexpr int derivative[3] = { -1, 0, 1 }; | ||
| constexpr int smoothing[3] = { 1, 2, 1 }; | ||
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| constexpr size_t total = Math::UnsignedPower(3, VDimension); | ||
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| // Allocate one kernel per axis | ||
| std::array<std::array<int, total>, VDimension> kernels{}; | ||
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| // Iterate over all N-D indices in {0,1,2}^N (mapping to {-1,0,1}) | ||
| for (size_t linear = 0; linear < total; ++linear) | ||
| { | ||
| // Convert linear index -> base-3 digits (idx[0..N-1]) | ||
| const auto idx = [linear] { | ||
| std::array<int, VDimension> result{}; | ||
| size_t temp = linear; | ||
| for (size_t i = 0; i < VDimension; ++i) | ||
| { | ||
| result[VDimension - 1 - i] = static_cast<int>(temp % 3); | ||
| temp /= 3; | ||
| } | ||
| return result; | ||
| }(); | ||
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| // For each axis, compute Sobel value at this point | ||
| for (size_t axis = 0; axis < VDimension; ++axis) | ||
| { | ||
| int val = derivative[idx[axis]]; | ||
| if (val == 0) | ||
| { // derivative center => whole product is 0 | ||
| kernels[axis][linear] = 0; | ||
| } | ||
| else | ||
| { | ||
| for (size_t i = 0; i < VDimension; ++i) | ||
| { | ||
| if (i != axis) | ||
| { | ||
| val *= smoothing[idx[i]]; | ||
| } | ||
| } | ||
| kernels[axis][linear] = val; | ||
| } | ||
| } | ||
| } | ||
| return kernels; | ||
| }(); | ||
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| // Note: It appears that `sobelKernels` is in the reverse order! | ||
| const auto & kernel = sobelKernels[VDimension - 1 - direction]; | ||
| return CoefficientVector(kernel.cbegin(), kernel.cend()); | ||
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Comment on lines
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There was a problem hiding this comment. Why not simply |
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| } | ||
| else | ||
| { | ||
| itkExceptionMacro("The direction value (" << direction << ") should be less than the dimensionality (" << VDimension | ||
| << ")."); | ||
| } | ||
| } | ||
| } // namespace itk | ||
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Note that
itkSetMacro(UseLegacyCoefficients, bool)does not compile, becauseitk::SobelOperatoris not derived fromitk::Object, and it does not supportthis->Modified().The macro (itkSetMacro) would make it
SetUseLegacyCoefficients(bool _arg)instead. But I thinkUseLegacyCoefficients(const bool useLegacyCoefficients)is more readable. OK?What about the other member function,
IsUsingLegacyCoefficients()? Is that clear enough?