ImageIO: Add member functions to get pixel component type traits, remove MapPixelType specializations #5421
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type:Enhancement
Directly initialized `MapPixelType::CType` to its intended value in the primary template definition of `MapPixelType`, and removed its specializations. Removed `IMAGEIOBASE_TYPEMAP`, following C++ Core Guidelines, May 8, 2025, "Don’t use macros for program text manipulation", https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#es30-dont-use-macros-for-program-text-manipulation
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type:Enhancement
Added three static member functions to ImageIOBase:
IsComponentTypeFloatingPoint(IOComponentEnum)
IsComponentTypeUnsigned(IOComponentEnum)
GetNumberOfBitsOfComponentType(IOComponentEnum)
Eases estimating whether a component type is floating point, whether the type
is unsigned, and estimating its number of bits, respectively.
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Jun 27, 2025
Follow-up to pull request InsightSoftwareConsortium#5421 commit b209c1a "STYLE: Remove template specializations of `ImageIOBase::MapPixelType`" Note that `MeshIOBase::MapComponentType` supports `long double` as pixel component type, whereas `ImageIOBase::MapPixelType` does not. Moreover, `MeshIOBase::MapComponentType` unconditionally maps `char` to `CHAR`, whereas `ImageIOBase::MapPixelType` maps `char` to either `CHAR` or `UCHAR`, depending on the signedness of `char`.
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`ImageIOBase::GetComponentTypeTraits` incorrectly assumed that the plain `char` type is always mapped to `IOComponentEnum::CHAR`. However, that isn't the case when the default `char` type is an unsigned type (as can be specified by GCC option `-funsigned-char` and MSVC option `/J`). This bug was introduced with pull request InsightSoftwareConsortium#5421 commit 3604e0c "ENH: Ease getting type traits of pixel components from ImageIO" (merged to the master branch on June 23, 2025). The bug caused incorrect return values from the following function calls: ImageIOBase::GetNumberOfBitsOfComponentType(IOComponentEnum::INT8); ImageIOBase::GetNumberOfBitsOfComponentType(IOComponentEnum::CHAR); ImageIOBase::GetComponentTypeFromTypeTraits(false, false, 0); ImageIOBase::GetComponentTypeFromTypeTraits(false, false, 8); As was observed from the static_assert failures in "itkImageIOBaseTest.cxx", when using the compiler option that makes the default `char` unsigned.
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Jul 11, 2025
`ImageIOBase::GetComponentTypeTraits` incorrectly assumed that the plain `char` type is always mapped to `IOComponentEnum::CHAR`. However, that isn't the case when the default `char` type is an unsigned type (as can be specified by GCC option `-funsigned-char` and MSVC option `/J`). This bug was introduced with pull request #5421 commit 3604e0c "ENH: Ease getting type traits of pixel components from ImageIO" (merged to the master branch on June 23, 2025). The bug caused incorrect return values from the following function calls: ImageIOBase::GetNumberOfBitsOfComponentType(IOComponentEnum::INT8); ImageIOBase::GetNumberOfBitsOfComponentType(IOComponentEnum::CHAR); ImageIOBase::GetComponentTypeFromTypeTraits(false, false, 0); ImageIOBase::GetComponentTypeFromTypeTraits(false, false, 8); As was observed from the static_assert failures in "itkImageIOBaseTest.cxx", when using the compiler option that makes the default `char` unsigned.
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Added three static member functions to ImageIOBase:
Eases estimating whether a component type is floating point, whether the type is unsigned, and estimating its number of bits, respectively.
Removed the template specializations of
MapPixelType<TPixel>, to avoid GCC compile errors sayingerror: specialization of 'itk::ImageIOBase::MapPixelType' after instantiation. Presented as "STYLE" commit, as it would originally just be a nicety 😃